React-native 热更新(2) 脚本增量更新 android部分

迈不过友情╰ 2022-05-31 07:56 222阅读 0赞

前一篇文章总结了脚本的更新和图片的增量更新

[《React-native 热更新(1) 脚本与图片更新+图片加载源码分析 android部分》][React-native _1_ _ android]

这篇文章总结脚本的增量更新

之前我们已经知道，脚本的变更主要是靠bundle文件。增量更新也就是比较bundle文件，生成补丁文件，通过补丁文件，可以得到最新的bundle文件。由于bundle文件就是文本，我们可以用google的google-diff-match-patch来进行比较并生成补丁。

总体思路为：

1、在打包apk的时候，把最初的asset中的bundle文件记录下来。

2、每次加入新功能的时候，通过react native bundle命令获得最新的bundle。也可以重新打包apk，在android\\app\\build\\intermediates\\assets\\release目录下也能获得最新的bundle文件。

3、通过google-diff-match-patch生成相应的补丁，将补丁和增量图片打包为压缩文件放在服务端

4、app下载补丁文件，和assets文件夹中的最初bundle文件进行合并，完成app的更新

注意：

1、在打断点debug或者使用react native的debug模式时，获得assets文件夹中的bundle文件为一开始创建工程时创建的bundle文件。

2、打包成apk以后，assets文件夹中的bundle文件已经不是debug时的bundle文件，而是打包时最新的bundle文件。它们分别存在这两个目录下

android\\app\\build\\intermediates\\assets\\release

android\\app\\build\\intermediates\\assets\\debug

这两点需要特别注意，不然会出现debug断点调试发现没问题，但是实际打包成apk后却更新异常。

服务端生成补丁文件代码示例

public static void createPatchFile(String resource, String target, String dest){	
    		
    		// 对比
    		diff_match_patch dmp = new diff_match_patch();		
    		LinkedList<Diff> diffs = dmp.diff_main(FileUtil.getStringFromFile(resource), FileUtil.getStringFromFile(target));       
    		
    		// 生成差异补丁包  
    		LinkedList<Patch> patches = dmp.patch_make(diffs);  
    		
    		// 解析补丁包     
    		String patchesStr = dmp.patch_toText(patches); 		
    		
    		try { 		
    			// 将补丁文件写入到某个位置
    			Files.write(Paths.get(dest), patchesStr.getBytes());
    		} catch (IOException e) {		 		
    		   	e.printStackTrace();	
    		}
        }

其中diff\_match\_partch可以直接在网上下载

/*
     * Diff Match and Patch
     *
     * Copyright 2006 Google Inc.
     * http://code.google.com/p/google-diff-match-patch/
     *
     * Licensed under the Apache License, Version 2.0 (the "License");
     * you may not use this file except in compliance with the License.
     * You may obtain a copy of the License at
     *
     *   http://www.apache.org/licenses/LICENSE-2.0
     *
     * Unless required by applicable law or agreed to in writing, software
     * distributed under the License is distributed on an "AS IS" BASIS,
     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     * See the License for the specific language governing permissions and
     * limitations under the License.
     */
    
    package com.xyt.util;
    
    import java.io.UnsupportedEncodingException;
    import java.net.URLEncoder;
    import java.net.URLDecoder;
    import java.util.ArrayList;
    import java.util.Arrays;
    import java.util.HashMap;
    import java.util.LinkedList;
    import java.util.List;
    import java.util.ListIterator;
    import java.util.Map;
    import java.util.Stack;
    import java.util.regex.Matcher;
    import java.util.regex.Pattern;
    
    /*
     * Functions for diff, match and patch.
     * Computes the difference between two texts to create a patch.
     * Applies the patch onto another text, allowing for errors.
     *
     * @author fraser@google.com (Neil Fraser)
     */
    
    /**
     * Class containing the diff, match and patch methods.
     * Also contains the behaviour settings.
     */
    public class diff_match_patch {
    
      // Defaults.
      // Set these on your diff_match_patch instance to override the defaults.
    
      /**
       * Number of seconds to map a diff before giving up (0 for infinity).
       */
      public float Diff_Timeout = 1.0f;
      /**
       * Cost of an empty edit operation in terms of edit characters.
       */
      public short Diff_EditCost = 4;
      /**
       * At what point is no match declared (0.0 = perfection, 1.0 = very loose).
       */
      public float Match_Threshold = 0.5f;
      /**
       * How far to search for a match (0 = exact location, 1000+ = broad match).
       * A match this many characters away from the expected location will add
       * 1.0 to the score (0.0 is a perfect match).
       */
      public int Match_Distance = 1000;
      /**
       * When deleting a large block of text (over ~64 characters), how close do
       * the contents have to be to match the expected contents. (0.0 = perfection,
       * 1.0 = very loose).  Note that Match_Threshold controls how closely the
       * end points of a delete need to match.
       */
      public float Patch_DeleteThreshold = 0.5f;
      /**
       * Chunk size for context length.
       */
      public short Patch_Margin = 4;
    
      /**
       * The number of bits in an int.
       */
      private short Match_MaxBits = 32;
    
      /**
       * Internal class for returning results from diff_linesToChars().
       * Other less paranoid languages just use a three-element array.
       */
      protected static class LinesToCharsResult {
        protected String chars1;
        protected String chars2;
        protected List<String> lineArray;
    
        protected LinesToCharsResult(String chars1, String chars2,
            List<String> lineArray) {
          this.chars1 = chars1;
          this.chars2 = chars2;
          this.lineArray = lineArray;
        }
      }
    
    
      //  DIFF FUNCTIONS
    
    
      /**
       * The data structure representing a diff is a Linked list of Diff objects:
       * {Diff(Operation.DELETE, "Hello"), Diff(Operation.INSERT, "Goodbye"),
       *  Diff(Operation.EQUAL, " world.")}
       * which means: delete "Hello", add "Goodbye" and keep " world."
       */
      public enum Operation {
        DELETE, INSERT, EQUAL
      }
    
      /**
       * Find the differences between two texts.
       * Run a faster, slightly less optimal diff.
       * This method allows the 'checklines' of diff_main() to be optional.
       * Most of the time checklines is wanted, so default to true.
       * @param text1 Old string to be diffed.
       * @param text2 New string to be diffed.
       * @return Linked List of Diff objects.
       */
      public LinkedList<Diff> diff_main(String text1, String text2) {
        return diff_main(text1, text2, true);
      }
    
      /**
       * Find the differences between two texts.
       * @param text1 Old string to be diffed.
       * @param text2 New string to be diffed.
       * @param checklines Speedup flag.  If false, then don't run a
       *     line-level diff first to identify the changed areas.
       *     If true, then run a faster slightly less optimal diff.
       * @return Linked List of Diff objects.
       */
      public LinkedList<Diff> diff_main(String text1, String text2,
                                        boolean checklines) {
        // Set a deadline by which time the diff must be complete.
        long deadline;
        if (Diff_Timeout <= 0) {
          deadline = Long.MAX_VALUE;
        } else {
          deadline = System.currentTimeMillis() + (long) (Diff_Timeout * 1000);
        }
        return diff_main(text1, text2, checklines, deadline);
      }
    
      /**
       * Find the differences between two texts.  Simplifies the problem by
       * stripping any common prefix or suffix off the texts before diffing.
       * @param text1 Old string to be diffed.
       * @param text2 New string to be diffed.
       * @param checklines Speedup flag.  If false, then don't run a
       *     line-level diff first to identify the changed areas.
       *     If true, then run a faster slightly less optimal diff.
       * @param deadline Time when the diff should be complete by.  Used
       *     internally for recursive calls.  Users should set DiffTimeout instead.
       * @return Linked List of Diff objects.
       */
      private LinkedList<Diff> diff_main(String text1, String text2,
                                         boolean checklines, long deadline) {
        // Check for null inputs.
        if (text1 == null || text2 == null) {
          throw new IllegalArgumentException("Null inputs. (diff_main)");
        }
    
        // Check for equality (speedup).
        LinkedList<Diff> diffs;
        if (text1.equals(text2)) {
          diffs = new LinkedList<Diff>();
          if (text1.length() != 0) {
            diffs.add(new Diff(Operation.EQUAL, text1));
          }
          return diffs;
        }
    
        // Trim off common prefix (speedup).
        int commonlength = diff_commonPrefix(text1, text2);
        String commonprefix = text1.substring(0, commonlength);
        text1 = text1.substring(commonlength);
        text2 = text2.substring(commonlength);
    
        // Trim off common suffix (speedup).
        commonlength = diff_commonSuffix(text1, text2);
        String commonsuffix = text1.substring(text1.length() - commonlength);
        text1 = text1.substring(0, text1.length() - commonlength);
        text2 = text2.substring(0, text2.length() - commonlength);
    
        // Compute the diff on the middle block.
        diffs = diff_compute(text1, text2, checklines, deadline);
    
        // Restore the prefix and suffix.
        if (commonprefix.length() != 0) {
          diffs.addFirst(new Diff(Operation.EQUAL, commonprefix));
        }
        if (commonsuffix.length() != 0) {
          diffs.addLast(new Diff(Operation.EQUAL, commonsuffix));
        }
    
        diff_cleanupMerge(diffs);
        return diffs;
      }
    
      /**
       * Find the differences between two texts.  Assumes that the texts do not
       * have any common prefix or suffix.
       * @param text1 Old string to be diffed.
       * @param text2 New string to be diffed.
       * @param checklines Speedup flag.  If false, then don't run a
       *     line-level diff first to identify the changed areas.
       *     If true, then run a faster slightly less optimal diff.
       * @param deadline Time when the diff should be complete by.
       * @return Linked List of Diff objects.
       */
      private LinkedList<Diff> diff_compute(String text1, String text2,
                                            boolean checklines, long deadline) {
        LinkedList<Diff> diffs = new LinkedList<Diff>();
    
        if (text1.length() == 0) {
          // Just add some text (speedup).
          diffs.add(new Diff(Operation.INSERT, text2));
          return diffs;
        }
    
        if (text2.length() == 0) {
          // Just delete some text (speedup).
          diffs.add(new Diff(Operation.DELETE, text1));
          return diffs;
        }
    
        String longtext = text1.length() > text2.length() ? text1 : text2;
        String shorttext = text1.length() > text2.length() ? text2 : text1;
        int i = longtext.indexOf(shorttext);
        if (i != -1) {
          // Shorter text is inside the longer text (speedup).
          Operation op = (text1.length() > text2.length()) ?
                         Operation.DELETE : Operation.INSERT;
          diffs.add(new Diff(op, longtext.substring(0, i)));
          diffs.add(new Diff(Operation.EQUAL, shorttext));
          diffs.add(new Diff(op, longtext.substring(i + shorttext.length())));
          return diffs;
        }
    
        if (shorttext.length() == 1) {
          // Single character string.
          // After the previous speedup, the character can't be an equality.
          diffs.add(new Diff(Operation.DELETE, text1));
          diffs.add(new Diff(Operation.INSERT, text2));
          return diffs;
        }
    
        // Check to see if the problem can be split in two.
        String[] hm = diff_halfMatch(text1, text2);
        if (hm != null) {
          // A half-match was found, sort out the return data.
          String text1_a = hm[0];
          String text1_b = hm[1];
          String text2_a = hm[2];
          String text2_b = hm[3];
          String mid_common = hm[4];
          // Send both pairs off for separate processing.
          LinkedList<Diff> diffs_a = diff_main(text1_a, text2_a,
                                               checklines, deadline);
          LinkedList<Diff> diffs_b = diff_main(text1_b, text2_b,
                                               checklines, deadline);
          // Merge the results.
          diffs = diffs_a;
          diffs.add(new Diff(Operation.EQUAL, mid_common));
          diffs.addAll(diffs_b);
          return diffs;
        }
    
        if (checklines && text1.length() > 100 && text2.length() > 100) {
          return diff_lineMode(text1, text2, deadline);
        }
    
        return diff_bisect(text1, text2, deadline);
      }
    
      /**
       * Do a quick line-level diff on both strings, then rediff the parts for
       * greater accuracy.
       * This speedup can produce non-minimal diffs.
       * @param text1 Old string to be diffed.
       * @param text2 New string to be diffed.
       * @param deadline Time when the diff should be complete by.
       * @return Linked List of Diff objects.
       */
      private LinkedList<Diff> diff_lineMode(String text1, String text2,
                                             long deadline) {
        // Scan the text on a line-by-line basis first.
        LinesToCharsResult b = diff_linesToChars(text1, text2);
        text1 = b.chars1;
        text2 = b.chars2;
        List<String> linearray = b.lineArray;
    
        LinkedList<Diff> diffs = diff_main(text1, text2, false, deadline);
    
        // Convert the diff back to original text.
        diff_charsToLines(diffs, linearray);
        // Eliminate freak matches (e.g. blank lines)
        diff_cleanupSemantic(diffs);
    
        // Rediff any replacement blocks, this time character-by-character.
        // Add a dummy entry at the end.
        diffs.add(new Diff(Operation.EQUAL, ""));
        int count_delete = 0;
        int count_insert = 0;
        String text_delete = "";
        String text_insert = "";
        ListIterator<Diff> pointer = diffs.listIterator();
        Diff thisDiff = pointer.next();
        while (thisDiff != null) {
          switch (thisDiff.operation) {
          case INSERT:
            count_insert++;
            text_insert += thisDiff.text;
            break;
          case DELETE:
            count_delete++;
            text_delete += thisDiff.text;
            break;
          case EQUAL:
            // Upon reaching an equality, check for prior redundancies.
            if (count_delete >= 1 && count_insert >= 1) {
              // Delete the offending records and add the merged ones.
              pointer.previous();
              for (int j = 0; j < count_delete + count_insert; j++) {
                pointer.previous();
                pointer.remove();
              }
              for (Diff newDiff : diff_main(text_delete, text_insert, false,
                  deadline)) {
                pointer.add(newDiff);
              }
            }
            count_insert = 0;
            count_delete = 0;
            text_delete = "";
            text_insert = "";
            break;
          }
          thisDiff = pointer.hasNext() ? pointer.next() : null;
        }
        diffs.removeLast();  // Remove the dummy entry at the end.
    
        return diffs;
      }
    
      /**
       * Find the 'middle snake' of a diff, split the problem in two
       * and return the recursively constructed diff.
       * See Myers 1986 paper: An O(ND) Difference Algorithm and Its Variations.
       * @param text1 Old string to be diffed.
       * @param text2 New string to be diffed.
       * @param deadline Time at which to bail if not yet complete.
       * @return LinkedList of Diff objects.
       */
      protected LinkedList<Diff> diff_bisect(String text1, String text2,
          long deadline) {
        // Cache the text lengths to prevent multiple calls.
        int text1_length = text1.length();
        int text2_length = text2.length();
        int max_d = (text1_length + text2_length + 1) / 2;
        int v_offset = max_d;
        int v_length = 2 * max_d;
        int[] v1 = new int[v_length];
        int[] v2 = new int[v_length];
        for (int x = 0; x < v_length; x++) {
          v1[x] = -1;
          v2[x] = -1;
        }
        v1[v_offset + 1] = 0;
        v2[v_offset + 1] = 0;
        int delta = text1_length - text2_length;
        // If the total number of characters is odd, then the front path will
        // collide with the reverse path.
        boolean front = (delta % 2 != 0);
        // Offsets for start and end of k loop.
        // Prevents mapping of space beyond the grid.
        int k1start = 0;
        int k1end = 0;
        int k2start = 0;
        int k2end = 0;
        for (int d = 0; d < max_d; d++) {
          // Bail out if deadline is reached.
          if (System.currentTimeMillis() > deadline) {
            break;
          }
    
          // Walk the front path one step.
          for (int k1 = -d + k1start; k1 <= d - k1end; k1 += 2) {
            int k1_offset = v_offset + k1;
            int x1;
            if (k1 == -d || (k1 != d && v1[k1_offset - 1] < v1[k1_offset + 1])) {
              x1 = v1[k1_offset + 1];
            } else {
              x1 = v1[k1_offset - 1] + 1;
            }
            int y1 = x1 - k1;
            while (x1 < text1_length && y1 < text2_length
                   && text1.charAt(x1) == text2.charAt(y1)) {
              x1++;
              y1++;
            }
            v1[k1_offset] = x1;
            if (x1 > text1_length) {
              // Ran off the right of the graph.
              k1end += 2;
            } else if (y1 > text2_length) {
              // Ran off the bottom of the graph.
              k1start += 2;
            } else if (front) {
              int k2_offset = v_offset + delta - k1;
              if (k2_offset >= 0 && k2_offset < v_length && v2[k2_offset] != -1) {
                // Mirror x2 onto top-left coordinate system.
                int x2 = text1_length - v2[k2_offset];
                if (x1 >= x2) {
                  // Overlap detected.
                  return diff_bisectSplit(text1, text2, x1, y1, deadline);
                }
              }
            }
          }
    
          // Walk the reverse path one step.
          for (int k2 = -d + k2start; k2 <= d - k2end; k2 += 2) {
            int k2_offset = v_offset + k2;
            int x2;
            if (k2 == -d || (k2 != d && v2[k2_offset - 1] < v2[k2_offset + 1])) {
              x2 = v2[k2_offset + 1];
            } else {
              x2 = v2[k2_offset - 1] + 1;
            }
            int y2 = x2 - k2;
            while (x2 < text1_length && y2 < text2_length
                   && text1.charAt(text1_length - x2 - 1)
                   == text2.charAt(text2_length - y2 - 1)) {
              x2++;
              y2++;
            }
            v2[k2_offset] = x2;
            if (x2 > text1_length) {
              // Ran off the left of the graph.
              k2end += 2;
            } else if (y2 > text2_length) {
              // Ran off the top of the graph.
              k2start += 2;
            } else if (!front) {
              int k1_offset = v_offset + delta - k2;
              if (k1_offset >= 0 && k1_offset < v_length && v1[k1_offset] != -1) {
                int x1 = v1[k1_offset];
                int y1 = v_offset + x1 - k1_offset;
                // Mirror x2 onto top-left coordinate system.
                x2 = text1_length - x2;
                if (x1 >= x2) {
                  // Overlap detected.
                  return diff_bisectSplit(text1, text2, x1, y1, deadline);
                }
              }
            }
          }
        }
        // Diff took too long and hit the deadline or
        // number of diffs equals number of characters, no commonality at all.
        LinkedList<Diff> diffs = new LinkedList<Diff>();
        diffs.add(new Diff(Operation.DELETE, text1));
        diffs.add(new Diff(Operation.INSERT, text2));
        return diffs;
      }
    
      /**
       * Given the location of the 'middle snake', split the diff in two parts
       * and recurse.
       * @param text1 Old string to be diffed.
       * @param text2 New string to be diffed.
       * @param x Index of split point in text1.
       * @param y Index of split point in text2.
       * @param deadline Time at which to bail if not yet complete.
       * @return LinkedList of Diff objects.
       */
      private LinkedList<Diff> diff_bisectSplit(String text1, String text2,
                                                int x, int y, long deadline) {
        String text1a = text1.substring(0, x);
        String text2a = text2.substring(0, y);
        String text1b = text1.substring(x);
        String text2b = text2.substring(y);
    
        // Compute both diffs serially.
        LinkedList<Diff> diffs = diff_main(text1a, text2a, false, deadline);
        LinkedList<Diff> diffsb = diff_main(text1b, text2b, false, deadline);
    
        diffs.addAll(diffsb);
        return diffs;
      }
    
      /**
       * Split two texts into a list of strings.  Reduce the texts to a string of
       * hashes where each Unicode character represents one line.
       * @param text1 First string.
       * @param text2 Second string.
       * @return An object containing the encoded text1, the encoded text2 and
       *     the List of unique strings.  The zeroth element of the List of
       *     unique strings is intentionally blank.
       */
      protected LinesToCharsResult diff_linesToChars(String text1, String text2) {
        List<String> lineArray = new ArrayList<String>();
        Map<String, Integer> lineHash = new HashMap<String, Integer>();
        // e.g. linearray[4] == "Hello\n"
        // e.g. linehash.get("Hello\n") == 4
    
        // "\x00" is a valid character, but various debuggers don't like it.
        // So we'll insert a junk entry to avoid generating a null character.
        lineArray.add("");
    
        String chars1 = diff_linesToCharsMunge(text1, lineArray, lineHash);
        String chars2 = diff_linesToCharsMunge(text2, lineArray, lineHash);
        return new LinesToCharsResult(chars1, chars2, lineArray);
      }
    
      /**
       * Split a text into a list of strings.  Reduce the texts to a string of
       * hashes where each Unicode character represents one line.
       * @param text String to encode.
       * @param lineArray List of unique strings.
       * @param lineHash Map of strings to indices.
       * @return Encoded string.
       */
      private String diff_linesToCharsMunge(String text, List<String> lineArray,
                                            Map<String, Integer> lineHash) {
        int lineStart = 0;
        int lineEnd = -1;
        String line;
        StringBuilder chars = new StringBuilder();
        // Walk the text, pulling out a substring for each line.
        // text.split('\n') would would temporarily double our memory footprint.
        // Modifying text would create many large strings to garbage collect.
        while (lineEnd < text.length() - 1) {
          lineEnd = text.indexOf('\n', lineStart);
          if (lineEnd == -1) {
            lineEnd = text.length() - 1;
          }
          line = text.substring(lineStart, lineEnd + 1);
          lineStart = lineEnd + 1;
    
          if (lineHash.containsKey(line)) {
            chars.append(String.valueOf((char) (int) lineHash.get(line)));
          } else {
            lineArray.add(line);
            lineHash.put(line, lineArray.size() - 1);
            chars.append(String.valueOf((char) (lineArray.size() - 1)));
          }
        }
        return chars.toString();
      }
    
      /**
       * Rehydrate the text in a diff from a string of line hashes to real lines of
       * text.
       * @param diffs LinkedList of Diff objects.
       * @param lineArray List of unique strings.
       */
      protected void diff_charsToLines(LinkedList<Diff> diffs,
                                      List<String> lineArray) {
        StringBuilder text;
        for (Diff diff : diffs) {
          text = new StringBuilder();
          for (int y = 0; y < diff.text.length(); y++) {
            text.append(lineArray.get(diff.text.charAt(y)));
          }
          diff.text = text.toString();
        }
      }
    
      /**
       * Determine the common prefix of two strings
       * @param text1 First string.
       * @param text2 Second string.
       * @return The number of characters common to the start of each string.
       */
      public int diff_commonPrefix(String text1, String text2) {
        // Performance analysis: http://neil.fraser.name/news/2007/10/09/
        int n = Math.min(text1.length(), text2.length());
        for (int i = 0; i < n; i++) {
          if (text1.charAt(i) != text2.charAt(i)) {
            return i;
          }
        }
        return n;
      }
    
      /**
       * Determine the common suffix of two strings
       * @param text1 First string.
       * @param text2 Second string.
       * @return The number of characters common to the end of each string.
       */
      public int diff_commonSuffix(String text1, String text2) {
        // Performance analysis: http://neil.fraser.name/news/2007/10/09/
        int text1_length = text1.length();
        int text2_length = text2.length();
        int n = Math.min(text1_length, text2_length);
        for (int i = 1; i <= n; i++) {
          if (text1.charAt(text1_length - i) != text2.charAt(text2_length - i)) {
            return i - 1;
          }
        }
        return n;
      }
    
      /**
       * Determine if the suffix of one string is the prefix of another.
       * @param text1 First string.
       * @param text2 Second string.
       * @return The number of characters common to the end of the first
       *     string and the start of the second string.
       */
      protected int diff_commonOverlap(String text1, String text2) {
        // Cache the text lengths to prevent multiple calls.
        int text1_length = text1.length();
        int text2_length = text2.length();
        // Eliminate the null case.
        if (text1_length == 0 || text2_length == 0) {
          return 0;
        }
        // Truncate the longer string.
        if (text1_length > text2_length) {
          text1 = text1.substring(text1_length - text2_length);
        } else if (text1_length < text2_length) {
          text2 = text2.substring(0, text1_length);
        }
        int text_length = Math.min(text1_length, text2_length);
        // Quick check for the worst case.
        if (text1.equals(text2)) {
          return text_length;
        }
    
        // Start by looking for a single character match
        // and increase length until no match is found.
        // Performance analysis: http://neil.fraser.name/news/2010/11/04/
        int best = 0;
        int length = 1;
        while (true) {
          String pattern = text1.substring(text_length - length);
          int found = text2.indexOf(pattern);
          if (found == -1) {
            return best;
          }
          length += found;
          if (found == 0 || text1.substring(text_length - length).equals(
              text2.substring(0, length))) {
            best = length;
            length++;
          }
        }
      }
    
      /**
       * Do the two texts share a substring which is at least half the length of
       * the longer text?
       * This speedup can produce non-minimal diffs.
       * @param text1 First string.
       * @param text2 Second string.
       * @return Five element String array, containing the prefix of text1, the
       *     suffix of text1, the prefix of text2, the suffix of text2 and the
       *     common middle.  Or null if there was no match.
       */
      protected String[] diff_halfMatch(String text1, String text2) {
        if (Diff_Timeout <= 0) {
          // Don't risk returning a non-optimal diff if we have unlimited time.
          return null;
        }
        String longtext = text1.length() > text2.length() ? text1 : text2;
        String shorttext = text1.length() > text2.length() ? text2 : text1;
        if (longtext.length() < 4 || shorttext.length() * 2 < longtext.length()) {
          return null;  // Pointless.
        }
    
        // First check if the second quarter is the seed for a half-match.
        String[] hm1 = diff_halfMatchI(longtext, shorttext,
                                       (longtext.length() + 3) / 4);
        // Check again based on the third quarter.
        String[] hm2 = diff_halfMatchI(longtext, shorttext,
                                       (longtext.length() + 1) / 2);
        String[] hm;
        if (hm1 == null && hm2 == null) {
          return null;
        } else if (hm2 == null) {
          hm = hm1;
        } else if (hm1 == null) {
          hm = hm2;
        } else {
          // Both matched.  Select the longest.
          hm = hm1[4].length() > hm2[4].length() ? hm1 : hm2;
        }
    
        // A half-match was found, sort out the return data.
        if (text1.length() > text2.length()) {
          return hm;
          //return new String[]{hm[0], hm[1], hm[2], hm[3], hm[4]};
        } else {
          return new String[]{hm[2], hm[3], hm[0], hm[1], hm[4]};
        }
      }
    
      /**
       * Does a substring of shorttext exist within longtext such that the
       * substring is at least half the length of longtext?
       * @param longtext Longer string.
       * @param shorttext Shorter string.
       * @param i Start index of quarter length substring within longtext.
       * @return Five element String array, containing the prefix of longtext, the
       *     suffix of longtext, the prefix of shorttext, the suffix of shorttext
       *     and the common middle.  Or null if there was no match.
       */
      private String[] diff_halfMatchI(String longtext, String shorttext, int i) {
        // Start with a 1/4 length substring at position i as a seed.
        String seed = longtext.substring(i, i + longtext.length() / 4);
        int j = -1;
        String best_common = "";
        String best_longtext_a = "", best_longtext_b = "";
        String best_shorttext_a = "", best_shorttext_b = "";
        while ((j = shorttext.indexOf(seed, j + 1)) != -1) {
          int prefixLength = diff_commonPrefix(longtext.substring(i),
                                               shorttext.substring(j));
          int suffixLength = diff_commonSuffix(longtext.substring(0, i),
                                               shorttext.substring(0, j));
          if (best_common.length() < suffixLength + prefixLength) {
            best_common = shorttext.substring(j - suffixLength, j)
                + shorttext.substring(j, j + prefixLength);
            best_longtext_a = longtext.substring(0, i - suffixLength);
            best_longtext_b = longtext.substring(i + prefixLength);
            best_shorttext_a = shorttext.substring(0, j - suffixLength);
            best_shorttext_b = shorttext.substring(j + prefixLength);
          }
        }
        if (best_common.length() * 2 >= longtext.length()) {
          return new String[]{best_longtext_a, best_longtext_b,
                              best_shorttext_a, best_shorttext_b, best_common};
        } else {
          return null;
        }
      }
    
      /**
       * Reduce the number of edits by eliminating semantically trivial equalities.
       * @param diffs LinkedList of Diff objects.
       */
      public void diff_cleanupSemantic(LinkedList<Diff> diffs) {
        if (diffs.isEmpty()) {
          return;
        }
        boolean changes = false;
        Stack<Diff> equalities = new Stack<Diff>();  // Stack of qualities.
        String lastequality = null; // Always equal to equalities.lastElement().text
        ListIterator<Diff> pointer = diffs.listIterator();
        // Number of characters that changed prior to the equality.
        int length_insertions1 = 0;
        int length_deletions1 = 0;
        // Number of characters that changed after the equality.
        int length_insertions2 = 0;
        int length_deletions2 = 0;
        Diff thisDiff = pointer.next();
        while (thisDiff != null) {
          if (thisDiff.operation == Operation.EQUAL) {
            // Equality found.
            equalities.push(thisDiff);
            length_insertions1 = length_insertions2;
            length_deletions1 = length_deletions2;
            length_insertions2 = 0;
            length_deletions2 = 0;
            lastequality = thisDiff.text;
          } else {
            // An insertion or deletion.
            if (thisDiff.operation == Operation.INSERT) {
              length_insertions2 += thisDiff.text.length();
            } else {
              length_deletions2 += thisDiff.text.length();
            }
            // Eliminate an equality that is smaller or equal to the edits on both
            // sides of it.
            if (lastequality != null && (lastequality.length()
                <= Math.max(length_insertions1, length_deletions1))
                && (lastequality.length()
                    <= Math.max(length_insertions2, length_deletions2))) {
              //System.out.println("Splitting: '" + lastequality + "'");
              // Walk back to offending equality.
              while (thisDiff != equalities.lastElement()) {
                thisDiff = pointer.previous();
              }
              pointer.next();
    
              // Replace equality with a delete.
              pointer.set(new Diff(Operation.DELETE, lastequality));
              // Insert a corresponding an insert.
              pointer.add(new Diff(Operation.INSERT, lastequality));
    
              equalities.pop();  // Throw away the equality we just deleted.
              if (!equalities.empty()) {
                // Throw away the previous equality (it needs to be reevaluated).
                equalities.pop();
              }
              if (equalities.empty()) {
                // There are no previous equalities, walk back to the start.
                while (pointer.hasPrevious()) {
                  pointer.previous();
                }
              } else {
                // There is a safe equality we can fall back to.
                thisDiff = equalities.lastElement();
                while (thisDiff != pointer.previous()) {
                  // Intentionally empty loop.
                }
              }
    
              length_insertions1 = 0;  // Reset the counters.
              length_insertions2 = 0;
              length_deletions1 = 0;
              length_deletions2 = 0;
              lastequality = null;
              changes = true;
            }
          }
          thisDiff = pointer.hasNext() ? pointer.next() : null;
        }
    
        // Normalize the diff.
        if (changes) {
          diff_cleanupMerge(diffs);
        }
        diff_cleanupSemanticLossless(diffs);
    
        // Find any overlaps between deletions and insertions.
        // e.g: <del>abcxxx</del><ins>xxxdef</ins>
        //   -> <del>abc</del>xxx<ins>def</ins>
        // e.g: <del>xxxabc</del><ins>defxxx</ins>
        //   -> <ins>def</ins>xxx<del>abc</del>
        // Only extract an overlap if it is as big as the edit ahead or behind it.
        pointer = diffs.listIterator();
        Diff prevDiff = null;
        thisDiff = null;
        if (pointer.hasNext()) {
          prevDiff = pointer.next();
          if (pointer.hasNext()) {
            thisDiff = pointer.next();
          }
        }
        while (thisDiff != null) {
          if (prevDiff.operation == Operation.DELETE &&
              thisDiff.operation == Operation.INSERT) {
            String deletion = prevDiff.text;
            String insertion = thisDiff.text;
            int overlap_length1 = this.diff_commonOverlap(deletion, insertion);
            int overlap_length2 = this.diff_commonOverlap(insertion, deletion);
            if (overlap_length1 >= overlap_length2) {
              if (overlap_length1 >= deletion.length() / 2.0 ||
                  overlap_length1 >= insertion.length() / 2.0) {
                // Overlap found. Insert an equality and trim the surrounding edits.
                pointer.previous();
                pointer.add(new Diff(Operation.EQUAL,
                                     insertion.substring(0, overlap_length1)));
                prevDiff.text =
                    deletion.substring(0, deletion.length() - overlap_length1);
                thisDiff.text = insertion.substring(overlap_length1);
                // pointer.add inserts the element before the cursor, so there is
                // no need to step past the new element.
              }
            } else {
              if (overlap_length2 >= deletion.length() / 2.0 ||
                  overlap_length2 >= insertion.length() / 2.0) {
                // Reverse overlap found.
                // Insert an equality and swap and trim the surrounding edits.
                pointer.previous();
                pointer.add(new Diff(Operation.EQUAL,
                                     deletion.substring(0, overlap_length2)));
                prevDiff.operation = Operation.INSERT;
                prevDiff.text =
                  insertion.substring(0, insertion.length() - overlap_length2);
                thisDiff.operation = Operation.DELETE;
                thisDiff.text = deletion.substring(overlap_length2);
                // pointer.add inserts the element before the cursor, so there is
                // no need to step past the new element.
              }
            }
            thisDiff = pointer.hasNext() ? pointer.next() : null;
          }
          prevDiff = thisDiff;
          thisDiff = pointer.hasNext() ? pointer.next() : null;
        }
      }
    
      /**
       * Look for single edits surrounded on both sides by equalities
       * which can be shifted sideways to align the edit to a word boundary.
       * e.g: The c<ins>at c</ins>ame. -> The <ins>cat </ins>came.
       * @param diffs LinkedList of Diff objects.
       */
      public void diff_cleanupSemanticLossless(LinkedList<Diff> diffs) {
        String equality1, edit, equality2;
        String commonString;
        int commonOffset;
        int score, bestScore;
        String bestEquality1, bestEdit, bestEquality2;
        // Create a new iterator at the start.
        ListIterator<Diff> pointer = diffs.listIterator();
        Diff prevDiff = pointer.hasNext() ? pointer.next() : null;
        Diff thisDiff = pointer.hasNext() ? pointer.next() : null;
        Diff nextDiff = pointer.hasNext() ? pointer.next() : null;
        // Intentionally ignore the first and last element (don't need checking).
        while (nextDiff != null) {
          if (prevDiff.operation == Operation.EQUAL &&
              nextDiff.operation == Operation.EQUAL) {
            // This is a single edit surrounded by equalities.
            equality1 = prevDiff.text;
            edit = thisDiff.text;
            equality2 = nextDiff.text;
    
            // First, shift the edit as far left as possible.
            commonOffset = diff_commonSuffix(equality1, edit);
            if (commonOffset != 0) {
              commonString = edit.substring(edit.length() - commonOffset);
              equality1 = equality1.substring(0, equality1.length() - commonOffset);
              edit = commonString + edit.substring(0, edit.length() - commonOffset);
              equality2 = commonString + equality2;
            }
    
            // Second, step character by character right, looking for the best fit.
            bestEquality1 = equality1;
            bestEdit = edit;
            bestEquality2 = equality2;
            bestScore = diff_cleanupSemanticScore(equality1, edit)
                + diff_cleanupSemanticScore(edit, equality2);
            while (edit.length() != 0 && equality2.length() != 0
                && edit.charAt(0) == equality2.charAt(0)) {
              equality1 += edit.charAt(0);
              edit = edit.substring(1) + equality2.charAt(0);
              equality2 = equality2.substring(1);
              score = diff_cleanupSemanticScore(equality1, edit)
                  + diff_cleanupSemanticScore(edit, equality2);
              // The >= encourages trailing rather than leading whitespace on edits.
              if (score >= bestScore) {
                bestScore = score;
                bestEquality1 = equality1;
                bestEdit = edit;
                bestEquality2 = equality2;
              }
            }
    
            if (!prevDiff.text.equals(bestEquality1)) {
              // We have an improvement, save it back to the diff.
              if (bestEquality1.length() != 0) {
                prevDiff.text = bestEquality1;
              } else {
                pointer.previous(); // Walk past nextDiff.
                pointer.previous(); // Walk past thisDiff.
                pointer.previous(); // Walk past prevDiff.
                pointer.remove(); // Delete prevDiff.
                pointer.next(); // Walk past thisDiff.
                pointer.next(); // Walk past nextDiff.
              }
              thisDiff.text = bestEdit;
              if (bestEquality2.length() != 0) {
                nextDiff.text = bestEquality2;
              } else {
                pointer.remove(); // Delete nextDiff.
                nextDiff = thisDiff;
                thisDiff = prevDiff;
              }
            }
          }
          prevDiff = thisDiff;
          thisDiff = nextDiff;
          nextDiff = pointer.hasNext() ? pointer.next() : null;
        }
      }
    
      /**
       * Given two strings, compute a score representing whether the internal
       * boundary falls on logical boundaries.
       * Scores range from 6 (best) to 0 (worst).
       * @param one First string.
       * @param two Second string.
       * @return The score.
       */
      private int diff_cleanupSemanticScore(String one, String two) {
        if (one.length() == 0 || two.length() == 0) {
          // Edges are the best.
          return 6;
        }
    
        // Each port of this function behaves slightly differently due to
        // subtle differences in each language's definition of things like
        // 'whitespace'.  Since this function's purpose is largely cosmetic,
        // the choice has been made to use each language's native features
        // rather than force total conformity.
        char char1 = one.charAt(one.length() - 1);
        char char2 = two.charAt(0);
        boolean nonAlphaNumeric1 = !Character.isLetterOrDigit(char1);
        boolean nonAlphaNumeric2 = !Character.isLetterOrDigit(char2);
        boolean whitespace1 = nonAlphaNumeric1 && Character.isWhitespace(char1);
        boolean whitespace2 = nonAlphaNumeric2 && Character.isWhitespace(char2);
        boolean lineBreak1 = whitespace1
            && Character.getType(char1) == Character.CONTROL;
        boolean lineBreak2 = whitespace2
            && Character.getType(char2) == Character.CONTROL;
        boolean blankLine1 = lineBreak1 && BLANKLINEEND.matcher(one).find();
        boolean blankLine2 = lineBreak2 && BLANKLINESTART.matcher(two).find();
    
        if (blankLine1 || blankLine2) {
          // Five points for blank lines.
          return 5;
        } else if (lineBreak1 || lineBreak2) {
          // Four points for line breaks.
          return 4;
        } else if (nonAlphaNumeric1 && !whitespace1 && whitespace2) {
          // Three points for end of sentences.
          return 3;
        } else if (whitespace1 || whitespace2) {
          // Two points for whitespace.
          return 2;
        } else if (nonAlphaNumeric1 || nonAlphaNumeric2) {
          // One point for non-alphanumeric.
          return 1;
        }
        return 0;
      }
    
      // Define some regex patterns for matching boundaries.
      private Pattern BLANKLINEEND
          = Pattern.compile("\\n\\r?\\n\\Z", Pattern.DOTALL);
      private Pattern BLANKLINESTART
          = Pattern.compile("\\A\\r?\\n\\r?\\n", Pattern.DOTALL);
    
      /**
       * Reduce the number of edits by eliminating operationally trivial equalities.
       * @param diffs LinkedList of Diff objects.
       */
      public void diff_cleanupEfficiency(LinkedList<Diff> diffs) {
        if (diffs.isEmpty()) {
          return;
        }
        boolean changes = false;
        Stack<Diff> equalities = new Stack<Diff>();  // Stack of equalities.
        String lastequality = null; // Always equal to equalities.lastElement().text
        ListIterator<Diff> pointer = diffs.listIterator();
        // Is there an insertion operation before the last equality.
        boolean pre_ins = false;
        // Is there a deletion operation before the last equality.
        boolean pre_del = false;
        // Is there an insertion operation after the last equality.
        boolean post_ins = false;
        // Is there a deletion operation after the last equality.
        boolean post_del = false;
        Diff thisDiff = pointer.next();
        Diff safeDiff = thisDiff;  // The last Diff that is known to be unsplitable.
        while (thisDiff != null) {
          if (thisDiff.operation == Operation.EQUAL) {
            // Equality found.
            if (thisDiff.text.length() < Diff_EditCost && (post_ins || post_del)) {
              // Candidate found.
              equalities.push(thisDiff);
              pre_ins = post_ins;
              pre_del = post_del;
              lastequality = thisDiff.text;
            } else {
              // Not a candidate, and can never become one.
              equalities.clear();
              lastequality = null;
              safeDiff = thisDiff;
            }
            post_ins = post_del = false;
          } else {
            // An insertion or deletion.
            if (thisDiff.operation == Operation.DELETE) {
              post_del = true;
            } else {
              post_ins = true;
            }
            /*
             * Five types to be split:
             * <ins>A</ins><del>B</del>XY<ins>C</ins><del>D</del>
             * <ins>A</ins>X<ins>C</ins><del>D</del>
             * <ins>A</ins><del>B</del>X<ins>C</ins>
             * <ins>A</del>X<ins>C</ins><del>D</del>
             * <ins>A</ins><del>B</del>X<del>C</del>
             */
            if (lastequality != null
                && ((pre_ins && pre_del && post_ins && post_del)
                    || ((lastequality.length() < Diff_EditCost / 2)
                        && ((pre_ins ? 1 : 0) + (pre_del ? 1 : 0)
                            + (post_ins ? 1 : 0) + (post_del ? 1 : 0)) == 3))) {
              //System.out.println("Splitting: '" + lastequality + "'");
              // Walk back to offending equality.
              while (thisDiff != equalities.lastElement()) {
                thisDiff = pointer.previous();
              }
              pointer.next();
    
              // Replace equality with a delete.
              pointer.set(new Diff(Operation.DELETE, lastequality));
              // Insert a corresponding an insert.
              pointer.add(thisDiff = new Diff(Operation.INSERT, lastequality));
    
              equalities.pop();  // Throw away the equality we just deleted.
              lastequality = null;
              if (pre_ins && pre_del) {
                // No changes made which could affect previous entry, keep going.
                post_ins = post_del = true;
                equalities.clear();
                safeDiff = thisDiff;
              } else {
                if (!equalities.empty()) {
                  // Throw away the previous equality (it needs to be reevaluated).
                  equalities.pop();
                }
                if (equalities.empty()) {
                  // There are no previous questionable equalities,
                  // walk back to the last known safe diff.
                  thisDiff = safeDiff;
                } else {
                  // There is an equality we can fall back to.
                  thisDiff = equalities.lastElement();
                }
                while (thisDiff != pointer.previous()) {
                  // Intentionally empty loop.
                }
                post_ins = post_del = false;
              }
    
              changes = true;
            }
          }
          thisDiff = pointer.hasNext() ? pointer.next() : null;
        }
    
        if (changes) {
          diff_cleanupMerge(diffs);
        }
      }
    
      /**
       * Reorder and merge like edit sections.  Merge equalities.
       * Any edit section can move as long as it doesn't cross an equality.
       * @param diffs LinkedList of Diff objects.
       */
      public void diff_cleanupMerge(LinkedList<Diff> diffs) {
        diffs.add(new Diff(Operation.EQUAL, ""));  // Add a dummy entry at the end.
        ListIterator<Diff> pointer = diffs.listIterator();
        int count_delete = 0;
        int count_insert = 0;
        String text_delete = "";
        String text_insert = "";
        Diff thisDiff = pointer.next();
        Diff prevEqual = null;
        int commonlength;
        while (thisDiff != null) {
          switch (thisDiff.operation) {
          case INSERT:
            count_insert++;
            text_insert += thisDiff.text;
            prevEqual = null;
            break;
          case DELETE:
            count_delete++;
            text_delete += thisDiff.text;
            prevEqual = null;
            break;
          case EQUAL:
            if (count_delete + count_insert > 1) {
              boolean both_types = count_delete != 0 && count_insert != 0;
              // Delete the offending records.
              pointer.previous();  // Reverse direction.
              while (count_delete-- > 0) {
                pointer.previous();
                pointer.remove();
              }
              while (count_insert-- > 0) {
                pointer.previous();
                pointer.remove();
              }
              if (both_types) {
                // Factor out any common prefixies.
                commonlength = diff_commonPrefix(text_insert, text_delete);
                if (commonlength != 0) {
                  if (pointer.hasPrevious()) {
                    thisDiff = pointer.previous();
                    assert thisDiff.operation == Operation.EQUAL
                           : "Previous diff should have been an equality.";
                    thisDiff.text += text_insert.substring(0, commonlength);
                    pointer.next();
                  } else {
                    pointer.add(new Diff(Operation.EQUAL,
                        text_insert.substring(0, commonlength)));
                  }
                  text_insert = text_insert.substring(commonlength);
                  text_delete = text_delete.substring(commonlength);
                }
                // Factor out any common suffixies.
                commonlength = diff_commonSuffix(text_insert, text_delete);
                if (commonlength != 0) {
                  thisDiff = pointer.next();
                  thisDiff.text = text_insert.substring(text_insert.length()
                      - commonlength) + thisDiff.text;
                  text_insert = text_insert.substring(0, text_insert.length()
                      - commonlength);
                  text_delete = text_delete.substring(0, text_delete.length()
                      - commonlength);
                  pointer.previous();
                }
              }
              // Insert the merged records.
              if (text_delete.length() != 0) {
                pointer.add(new Diff(Operation.DELETE, text_delete));
              }
              if (text_insert.length() != 0) {
                pointer.add(new Diff(Operation.INSERT, text_insert));
              }
              // Step forward to the equality.
              thisDiff = pointer.hasNext() ? pointer.next() : null;
            } else if (prevEqual != null) {
              // Merge this equality with the previous one.
              prevEqual.text += thisDiff.text;
              pointer.remove();
              thisDiff = pointer.previous();
              pointer.next();  // Forward direction
            }
            count_insert = 0;
            count_delete = 0;
            text_delete = "";
            text_insert = "";
            prevEqual = thisDiff;
            break;
          }
          thisDiff = pointer.hasNext() ? pointer.next() : null;
        }
        if (diffs.getLast().text.length() == 0) {
          diffs.removeLast();  // Remove the dummy entry at the end.
        }
    
        /*
         * Second pass: look for single edits surrounded on both sides by equalities
         * which can be shifted sideways to eliminate an equality.
         * e.g: A<ins>BA</ins>C -> <ins>AB</ins>AC
         */
        boolean changes = false;
        // Create a new iterator at the start.
        // (As opposed to walking the current one back.)
        pointer = diffs.listIterator();
        Diff prevDiff = pointer.hasNext() ? pointer.next() : null;
        thisDiff = pointer.hasNext() ? pointer.next() : null;
        Diff nextDiff = pointer.hasNext() ? pointer.next() : null;
        // Intentionally ignore the first and last element (don't need checking).
        while (nextDiff != null) {
          if (prevDiff.operation == Operation.EQUAL &&
              nextDiff.operation == Operation.EQUAL) {
            // This is a single edit surrounded by equalities.
            if (thisDiff.text.endsWith(prevDiff.text)) {
              // Shift the edit over the previous equality.
              thisDiff.text = prevDiff.text
                  + thisDiff.text.substring(0, thisDiff.text.length()
                                               - prevDiff.text.length());
              nextDiff.text = prevDiff.text + nextDiff.text;
              pointer.previous(); // Walk past nextDiff.
              pointer.previous(); // Walk past thisDiff.
              pointer.previous(); // Walk past prevDiff.
              pointer.remove(); // Delete prevDiff.
              pointer.next(); // Walk past thisDiff.
              thisDiff = pointer.next(); // Walk past nextDiff.
              nextDiff = pointer.hasNext() ? pointer.next() : null;
              changes = true;
            } else if (thisDiff.text.startsWith(nextDiff.text)) {
              // Shift the edit over the next equality.
              prevDiff.text += nextDiff.text;
              thisDiff.text = thisDiff.text.substring(nextDiff.text.length())
                  + nextDiff.text;
              pointer.remove(); // Delete nextDiff.
              nextDiff = pointer.hasNext() ? pointer.next() : null;
              changes = true;
            }
          }
          prevDiff = thisDiff;
          thisDiff = nextDiff;
          nextDiff = pointer.hasNext() ? pointer.next() : null;
        }
        // If shifts were made, the diff needs reordering and another shift sweep.
        if (changes) {
          diff_cleanupMerge(diffs);
        }
      }
    
      /**
       * loc is a location in text1, compute and return the equivalent location in
       * text2.
       * e.g. "The cat" vs "The big cat", 1->1, 5->8
       * @param diffs LinkedList of Diff objects.
       * @param loc Location within text1.
       * @return Location within text2.
       */
      public int diff_xIndex(LinkedList<Diff> diffs, int loc) {
        int chars1 = 0;
        int chars2 = 0;
        int last_chars1 = 0;
        int last_chars2 = 0;
        Diff lastDiff = null;
        for (Diff aDiff : diffs) {
          if (aDiff.operation != Operation.INSERT) {
            // Equality or deletion.
            chars1 += aDiff.text.length();
          }
          if (aDiff.operation != Operation.DELETE) {
            // Equality or insertion.
            chars2 += aDiff.text.length();
          }
          if (chars1 > loc) {
            // Overshot the location.
            lastDiff = aDiff;
            break;
          }
          last_chars1 = chars1;
          last_chars2 = chars2;
        }
        if (lastDiff != null && lastDiff.operation == Operation.DELETE) {
          // The location was deleted.
          return last_chars2;
        }
        // Add the remaining character length.
        return last_chars2 + (loc - last_chars1);
      }
    
      /**
       * Convert a Diff list into a pretty HTML report.
       * @param diffs LinkedList of Diff objects.
       * @return HTML representation.
       */
      public String diff_prettyHtml(LinkedList<Diff> diffs) {
        StringBuilder html = new StringBuilder();
        for (Diff aDiff : diffs) {
          String text = aDiff.text.replace("&", "&").replace("<", "<")
              .replace(">", ">").replace("\n", "¶<br>");
          switch (aDiff.operation) {
          case INSERT:
            html.append("<ins style=\"background:#e6ffe6;\">").append(text)
                .append("</ins>");
            break;
          case DELETE:
            html.append("<del style=\"background:#ffe6e6;\">").append(text)
                .append("</del>");
            break;
          case EQUAL:
            html.append("<span>").append(text).append("</span>");
            break;
          }
        }
        return html.toString();
      }
    
      /**
       * Compute and return the source text (all equalities and deletions).
       * @param diffs LinkedList of Diff objects.
       * @return Source text.
       */
      public String diff_text1(LinkedList<Diff> diffs) {
        StringBuilder text = new StringBuilder();
        for (Diff aDiff : diffs) {
          if (aDiff.operation != Operation.INSERT) {
            text.append(aDiff.text);
          }
        }
        return text.toString();
      }
    
      /**
       * Compute and return the destination text (all equalities and insertions).
       * @param diffs LinkedList of Diff objects.
       * @return Destination text.
       */
      public String diff_text2(LinkedList<Diff> diffs) {
        StringBuilder text = new StringBuilder();
        for (Diff aDiff : diffs) {
          if (aDiff.operation != Operation.DELETE) {
            text.append(aDiff.text);
          }
        }
        return text.toString();
      }
    
      /**
       * Compute the Levenshtein distance; the number of inserted, deleted or
       * substituted characters.
       * @param diffs LinkedList of Diff objects.
       * @return Number of changes.
       */
      public int diff_levenshtein(LinkedList<Diff> diffs) {
        int levenshtein = 0;
        int insertions = 0;
        int deletions = 0;
        for (Diff aDiff : diffs) {
          switch (aDiff.operation) {
          case INSERT:
            insertions += aDiff.text.length();
            break;
          case DELETE:
            deletions += aDiff.text.length();
            break;
          case EQUAL:
            // A deletion and an insertion is one substitution.
            levenshtein += Math.max(insertions, deletions);
            insertions = 0;
            deletions = 0;
            break;
          }
        }
        levenshtein += Math.max(insertions, deletions);
        return levenshtein;
      }
    
      /**
       * Crush the diff into an encoded string which describes the operations
       * required to transform text1 into text2.
       * E.g. =3\t-2\t+ing  -> Keep 3 chars, delete 2 chars, insert 'ing'.
       * Operations are tab-separated.  Inserted text is escaped using %xx notation.
       * @param diffs Array of Diff objects.
       * @return Delta text.
       */
      public String diff_toDelta(LinkedList<Diff> diffs) {
        StringBuilder text = new StringBuilder();
        for (Diff aDiff : diffs) {
          switch (aDiff.operation) {
          case INSERT:
            try {
              text.append("+").append(URLEncoder.encode(aDiff.text, "UTF-8")
                                                .replace('+', ' ')).append("\t");
            } catch (UnsupportedEncodingException e) {
              // Not likely on modern system.
              throw new Error("This system does not support UTF-8.", e);
            }
            break;
          case DELETE:
            text.append("-").append(aDiff.text.length()).append("\t");
            break;
          case EQUAL:
            text.append("=").append(aDiff.text.length()).append("\t");
            break;
          }
        }
        String delta = text.toString();
        if (delta.length() != 0) {
          // Strip off trailing tab character.
          delta = delta.substring(0, delta.length() - 1);
          delta = unescapeForEncodeUriCompatability(delta);
        }
        return delta;
      }
    
      /**
       * Given the original text1, and an encoded string which describes the
       * operations required to transform text1 into text2, compute the full diff.
       * @param text1 Source string for the diff.
       * @param delta Delta text.
       * @return Array of Diff objects or null if invalid.
       * @throws IllegalArgumentException If invalid input.
       */
      public LinkedList<Diff> diff_fromDelta(String text1, String delta)
          throws IllegalArgumentException {
        LinkedList<Diff> diffs = new LinkedList<Diff>();
        int pointer = 0;  // Cursor in text1
        String[] tokens = delta.split("\t");
        for (String token : tokens) {
          if (token.length() == 0) {
            // Blank tokens are ok (from a trailing \t).
            continue;
          }
          // Each token begins with a one character parameter which specifies the
          // operation of this token (delete, insert, equality).
          String param = token.substring(1);
          switch (token.charAt(0)) {
          case '+':
            // decode would change all "+" to " "
            param = param.replace("+", "%2B");
            try {
              param = URLDecoder.decode(param, "UTF-8");
            } catch (UnsupportedEncodingException e) {
              // Not likely on modern system.
              throw new Error("This system does not support UTF-8.", e);
            } catch (IllegalArgumentException e) {
              // Malformed URI sequence.
              throw new IllegalArgumentException(
                  "Illegal escape in diff_fromDelta: " + param, e);
            }
            diffs.add(new Diff(Operation.INSERT, param));
            break;
          case '-':
            // Fall through.
          case '=':
            int n;
            try {
              n = Integer.parseInt(param);
            } catch (NumberFormatException e) {
              throw new IllegalArgumentException(
                  "Invalid number in diff_fromDelta: " + param, e);
            }
            if (n < 0) {
              throw new IllegalArgumentException(
                  "Negative number in diff_fromDelta: " + param);
            }
            String text;
            try {
              text = text1.substring(pointer, pointer += n);
            } catch (StringIndexOutOfBoundsException e) {
              throw new IllegalArgumentException("Delta length (" + pointer
                  + ") larger than source text length (" + text1.length()
                  + ").", e);
            }
            if (token.charAt(0) == '=') {
              diffs.add(new Diff(Operation.EQUAL, text));
            } else {
              diffs.add(new Diff(Operation.DELETE, text));
            }
            break;
          default:
            // Anything else is an error.
            throw new IllegalArgumentException(
                "Invalid diff operation in diff_fromDelta: " + token.charAt(0));
          }
        }
        if (pointer != text1.length()) {
          throw new IllegalArgumentException("Delta length (" + pointer
              + ") smaller than source text length (" + text1.length() + ").");
        }
        return diffs;
      }
    
    
      //  MATCH FUNCTIONS
    
    
      /**
       * Locate the best instance of 'pattern' in 'text' near 'loc'.
       * Returns -1 if no match found.
       * @param text The text to search.
       * @param pattern The pattern to search for.
       * @param loc The location to search around.
       * @return Best match index or -1.
       */
      public int match_main(String text, String pattern, int loc) {
        // Check for null inputs.
        if (text == null || pattern == null) {
          throw new IllegalArgumentException("Null inputs. (match_main)");
        }
    
        loc = Math.max(0, Math.min(loc, text.length()));
        if (text.equals(pattern)) {
          // Shortcut (potentially not guaranteed by the algorithm)
          return 0;
        } else if (text.length() == 0) {
          // Nothing to match.
          return -1;
        } else if (loc + pattern.length() <= text.length()
            && text.substring(loc, loc + pattern.length()).equals(pattern)) {
          // Perfect match at the perfect spot!  (Includes case of null pattern)
          return loc;
        } else {
          // Do a fuzzy compare.
          return match_bitap(text, pattern, loc);
        }
      }
    
      /**
       * Locate the best instance of 'pattern' in 'text' near 'loc' using the
       * Bitap algorithm.  Returns -1 if no match found.
       * @param text The text to search.
       * @param pattern The pattern to search for.
       * @param loc The location to search around.
       * @return Best match index or -1.
       */
      protected int match_bitap(String text, String pattern, int loc) {
        assert (Match_MaxBits == 0 || pattern.length() <= Match_MaxBits)
            : "Pattern too long for this application.";
    
        // Initialise the alphabet.
        Map<Character, Integer> s = match_alphabet(pattern);
    
        // Highest score beyond which we give up.
        double score_threshold = Match_Threshold;
        // Is there a nearby exact match? (speedup)
        int best_loc = text.indexOf(pattern, loc);
        if (best_loc != -1) {
          score_threshold = Math.min(match_bitapScore(0, best_loc, loc, pattern),
              score_threshold);
          // What about in the other direction? (speedup)
          best_loc = text.lastIndexOf(pattern, loc + pattern.length());
          if (best_loc != -1) {
            score_threshold = Math.min(match_bitapScore(0, best_loc, loc, pattern),
                score_threshold);
          }
        }
    
        // Initialise the bit arrays.
        int matchmask = 1 << (pattern.length() - 1);
        best_loc = -1;
    
        int bin_min, bin_mid;
        int bin_max = pattern.length() + text.length();
        // Empty initialization added to appease Java compiler.
        int[] last_rd = new int[0];
        for (int d = 0; d < pattern.length(); d++) {
          // Scan for the best match; each iteration allows for one more error.
          // Run a binary search to determine how far from 'loc' we can stray at
          // this error level.
          bin_min = 0;
          bin_mid = bin_max;
          while (bin_min < bin_mid) {
            if (match_bitapScore(d, loc + bin_mid, loc, pattern)
                <= score_threshold) {
              bin_min = bin_mid;
            } else {
              bin_max = bin_mid;
            }
            bin_mid = (bin_max - bin_min) / 2 + bin_min;
          }
          // Use the result from this iteration as the maximum for the next.
          bin_max = bin_mid;
          int start = Math.max(1, loc - bin_mid + 1);
          int finish = Math.min(loc + bin_mid, text.length()) + pattern.length();
    
          int[] rd = new int[finish + 2];
          rd[finish + 1] = (1 << d) - 1;
          for (int j = finish; j >= start; j--) {
            int charMatch;
            if (text.length() <= j - 1 || !s.containsKey(text.charAt(j - 1))) {
              // Out of range.
              charMatch = 0;
            } else {
              charMatch = s.get(text.charAt(j - 1));
            }
            if (d == 0) {
              // First pass: exact match.
              rd[j] = ((rd[j + 1] << 1) | 1) & charMatch;
            } else {
              // Subsequent passes: fuzzy match.
              rd[j] = (((rd[j + 1] << 1) | 1) & charMatch)
                  | (((last_rd[j + 1] | last_rd[j]) << 1) | 1) | last_rd[j + 1];
            }
            if ((rd[j] & matchmask) != 0) {
              double score = match_bitapScore(d, j - 1, loc, pattern);
              // This match will almost certainly be better than any existing
              // match.  But check anyway.
              if (score <= score_threshold) {
                // Told you so.
                score_threshold = score;
                best_loc = j - 1;
                if (best_loc > loc) {
                  // When passing loc, don't exceed our current distance from loc.
                  start = Math.max(1, 2 * loc - best_loc);
                } else {
                  // Already passed loc, downhill from here on in.
                  break;
                }
              }
            }
          }
          if (match_bitapScore(d + 1, loc, loc, pattern) > score_threshold) {
            // No hope for a (better) match at greater error levels.
            break;
          }
          last_rd = rd;
        }
        return best_loc;
      }
    
      /**
       * Compute and return the score for a match with e errors and x location.
       * @param e Number of errors in match.
       * @param x Location of match.
       * @param loc Expected location of match.
       * @param pattern Pattern being sought.
       * @return Overall score for match (0.0 = good, 1.0 = bad).
       */
      private double match_bitapScore(int e, int x, int loc, String pattern) {
        float accuracy = (float) e / pattern.length();
        int proximity = Math.abs(loc - x);
        if (Match_Distance == 0) {
          // Dodge divide by zero error.
          return proximity == 0 ? accuracy : 1.0;
        }
        return accuracy + (proximity / (float) Match_Distance);
      }
    
      /**
       * Initialise the alphabet for the Bitap algorithm.
       * @param pattern The text to encode.
       * @return Hash of character locations.
       */
      protected Map<Character, Integer> match_alphabet(String pattern) {
        Map<Character, Integer> s = new HashMap<Character, Integer>();
        char[] char_pattern = pattern.toCharArray();
        for (char c : char_pattern) {
          s.put(c, 0);
        }
        int i = 0;
        for (char c : char_pattern) {
          s.put(c, s.get(c) | (1 << (pattern.length() - i - 1)));
          i++;
        }
        return s;
      }
    
    
      //  PATCH FUNCTIONS
    
    
      /**
       * Increase the context until it is unique,
       * but don't let the pattern expand beyond Match_MaxBits.
       * @param patch The patch to grow.
       * @param text Source text.
       */
      protected void patch_addContext(Patch patch, String text) {
        if (text.length() == 0) {
          return;
        }
        String pattern = text.substring(patch.start2, patch.start2 + patch.length1);
        int padding = 0;
    
        // Look for the first and last matches of pattern in text.  If two different
        // matches are found, increase the pattern length.
        while (text.indexOf(pattern) != text.lastIndexOf(pattern)
            && pattern.length() < Match_MaxBits - Patch_Margin - Patch_Margin) {
          padding += Patch_Margin;
          pattern = text.substring(Math.max(0, patch.start2 - padding),
              Math.min(text.length(), patch.start2 + patch.length1 + padding));
        }
        // Add one chunk for good luck.
        padding += Patch_Margin;
    
        // Add the prefix.
        String prefix = text.substring(Math.max(0, patch.start2 - padding),
            patch.start2);
        if (prefix.length() != 0) {
          patch.diffs.addFirst(new Diff(Operation.EQUAL, prefix));
        }
        // Add the suffix.
        String suffix = text.substring(patch.start2 + patch.length1,
            Math.min(text.length(), patch.start2 + patch.length1 + padding));
        if (suffix.length() != 0) {
          patch.diffs.addLast(new Diff(Operation.EQUAL, suffix));
        }
    
        // Roll back the start points.
        patch.start1 -= prefix.length();
        patch.start2 -= prefix.length();
        // Extend the lengths.
        patch.length1 += prefix.length() + suffix.length();
        patch.length2 += prefix.length() + suffix.length();
      }
    
      /**
       * Compute a list of patches to turn text1 into text2.
       * A set of diffs will be computed.
       * @param text1 Old text.
       * @param text2 New text.
       * @return LinkedList of Patch objects.
       */
      public LinkedList<Patch> patch_make(String text1, String text2) {
        if (text1 == null || text2 == null) {
          throw new IllegalArgumentException("Null inputs. (patch_make)");
        }
        // No diffs provided, compute our own.
        LinkedList<Diff> diffs = diff_main(text1, text2, true);
        if (diffs.size() > 2) {
          diff_cleanupSemantic(diffs);
          diff_cleanupEfficiency(diffs);
        }
        return patch_make(text1, diffs);
      }
    
      /**
       * Compute a list of patches to turn text1 into text2.
       * text1 will be derived from the provided diffs.
       * @param diffs Array of Diff objects for text1 to text2.
       * @return LinkedList of Patch objects.
       */
      public LinkedList<Patch> patch_make(LinkedList<Diff> diffs) {
        if (diffs == null) {
          throw new IllegalArgumentException("Null inputs. (patch_make)");
        }
        // No origin string provided, compute our own.
        String text1 = diff_text1(diffs);
        return patch_make(text1, diffs);
      }
    
      /**
       * Compute a list of patches to turn text1 into text2.
       * text2 is ignored, diffs are the delta between text1 and text2.
       * @param text1 Old text
       * @param text2 Ignored.
       * @param diffs Array of Diff objects for text1 to text2.
       * @return LinkedList of Patch objects.
       * @deprecated Prefer patch_make(String text1, LinkedList<Diff> diffs).
       */
      public LinkedList<Patch> patch_make(String text1, String text2,
          LinkedList<Diff> diffs) {
        return patch_make(text1, diffs);
      }
    
      /**
       * Compute a list of patches to turn text1 into text2.
       * text2 is not provided, diffs are the delta between text1 and text2.
       * @param text1 Old text.
       * @param diffs Array of Diff objects for text1 to text2.
       * @return LinkedList of Patch objects.
       */
      public LinkedList<Patch> patch_make(String text1, LinkedList<Diff> diffs) {
        if (text1 == null || diffs == null) {
          throw new IllegalArgumentException("Null inputs. (patch_make)");
        }
    
        LinkedList<Patch> patches = new LinkedList<Patch>();
        if (diffs.isEmpty()) {
          return patches;  // Get rid of the null case.
        }
        Patch patch = new Patch();
        int char_count1 = 0;  // Number of characters into the text1 string.
        int char_count2 = 0;  // Number of characters into the text2 string.
        // Start with text1 (prepatch_text) and apply the diffs until we arrive at
        // text2 (postpatch_text). We recreate the patches one by one to determine
        // context info.
        String prepatch_text = text1;
        String postpatch_text = text1;
        for (Diff aDiff : diffs) {
          if (patch.diffs.isEmpty() && aDiff.operation != Operation.EQUAL) {
            // A new patch starts here.
            patch.start1 = char_count1;
            patch.start2 = char_count2;
          }
    
          switch (aDiff.operation) {
          case INSERT:
            patch.diffs.add(aDiff);
            patch.length2 += aDiff.text.length();
            postpatch_text = postpatch_text.substring(0, char_count2)
                + aDiff.text + postpatch_text.substring(char_count2);
            break;
          case DELETE:
            patch.length1 += aDiff.text.length();
            patch.diffs.add(aDiff);
            postpatch_text = postpatch_text.substring(0, char_count2)
                + postpatch_text.substring(char_count2 + aDiff.text.length());
            break;
          case EQUAL:
            if (aDiff.text.length() <= 2 * Patch_Margin
                && !patch.diffs.isEmpty() && aDiff != diffs.getLast()) {
              // Small equality inside a patch.
              patch.diffs.add(aDiff);
              patch.length1 += aDiff.text.length();
              patch.length2 += aDiff.text.length();
            }
    
            if (aDiff.text.length() >= 2 * Patch_Margin) {
              // Time for a new patch.
              if (!patch.diffs.isEmpty()) {
                patch_addContext(patch, prepatch_text);
                patches.add(patch);
                patch = new Patch();
                // Unlike Unidiff, our patch lists have a rolling context.
                // http://code.google.com/p/google-diff-match-patch/wiki/Unidiff
                // Update prepatch text & pos to reflect the application of the
                // just completed patch.
                prepatch_text = postpatch_text;
                char_count1 = char_count2;
              }
            }
            break;
          }
    
          // Update the current character count.
          if (aDiff.operation != Operation.INSERT) {
            char_count1 += aDiff.text.length();
          }
          if (aDiff.operation != Operation.DELETE) {
            char_count2 += aDiff.text.length();
          }
        }
        // Pick up the leftover patch if not empty.
        if (!patch.diffs.isEmpty()) {
          patch_addContext(patch, prepatch_text);
          patches.add(patch);
        }
    
        return patches;
      }
    
      /**
       * Given an array of patches, return another array that is identical.
       * @param patches Array of Patch objects.
       * @return Array of Patch objects.
       */
      public LinkedList<Patch> patch_deepCopy(LinkedList<Patch> patches) {
        LinkedList<Patch> patchesCopy = new LinkedList<Patch>();
        for (Patch aPatch : patches) {
          Patch patchCopy = new Patch();
          for (Diff aDiff : aPatch.diffs) {
            Diff diffCopy = new Diff(aDiff.operation, aDiff.text);
            patchCopy.diffs.add(diffCopy);
          }
          patchCopy.start1 = aPatch.start1;
          patchCopy.start2 = aPatch.start2;
          patchCopy.length1 = aPatch.length1;
          patchCopy.length2 = aPatch.length2;
          patchesCopy.add(patchCopy);
        }
        return patchesCopy;
      }
    
      /**
       * Merge a set of patches onto the text.  Return a patched text, as well
       * as an array of true/false values indicating which patches were applied.
       * @param patches Array of Patch objects
       * @param text Old text.
       * @return Two element Object array, containing the new text and an array of
       *      boolean values.
       */
      public Object[] patch_apply(LinkedList<Patch> patches, String text) {
        if (patches.isEmpty()) {
          return new Object[]{text, new boolean[0]};
        }
    
        // Deep copy the patches so that no changes are made to originals.
        patches = patch_deepCopy(patches);
    
        String nullPadding = patch_addPadding(patches);
        text = nullPadding + text + nullPadding;
        patch_splitMax(patches);
    
        int x = 0;
        // delta keeps track of the offset between the expected and actual location
        // of the previous patch.  If there are patches expected at positions 10 and
        // 20, but the first patch was found at 12, delta is 2 and the second patch
        // has an effective expected position of 22.
        int delta = 0;
        boolean[] results = new boolean[patches.size()];
        for (Patch aPatch : patches) {
          int expected_loc = aPatch.start2 + delta;
          String text1 = diff_text1(aPatch.diffs);
          int start_loc;
          int end_loc = -1;
          if (text1.length() > this.Match_MaxBits) {
            // patch_splitMax will only provide an oversized pattern in the case of
            // a monster delete.
            start_loc = match_main(text,
                text1.substring(0, this.Match_MaxBits), expected_loc);
            if (start_loc != -1) {
              end_loc = match_main(text,
                  text1.substring(text1.length() - this.Match_MaxBits),
                  expected_loc + text1.length() - this.Match_MaxBits);
              if (end_loc == -1 || start_loc >= end_loc) {
                // Can't find valid trailing context.  Drop this patch.
                start_loc = -1;
              }
            }
          } else {
            start_loc = match_main(text, text1, expected_loc);
          }
          if (start_loc == -1) {
            // No match found.  :(
            results[x] = false;
            // Subtract the delta for this failed patch from subsequent patches.
            delta -= aPatch.length2 - aPatch.length1;
          } else {
            // Found a match.  :)
            results[x] = true;
            delta = start_loc - expected_loc;
            String text2;
            if (end_loc == -1) {
              text2 = text.substring(start_loc,
                  Math.min(start_loc + text1.length(), text.length()));
            } else {
              text2 = text.substring(start_loc,
                  Math.min(end_loc + this.Match_MaxBits, text.length()));
            }
            if (text1.equals(text2)) {
              // Perfect match, just shove the replacement text in.
              text = text.substring(0, start_loc) + diff_text2(aPatch.diffs)
                  + text.substring(start_loc + text1.length());
            } else {
              // Imperfect match.  Run a diff to get a framework of equivalent
              // indices.
              LinkedList<Diff> diffs = diff_main(text1, text2, false);
              if (text1.length() > this.Match_MaxBits
                  && diff_levenshtein(diffs) / (float) text1.length()
                  > this.Patch_DeleteThreshold) {
                // The end points match, but the content is unacceptably bad.
                results[x] = false;
              } else {
                diff_cleanupSemanticLossless(diffs);
                int index1 = 0;
                for (Diff aDiff : aPatch.diffs) {
                  if (aDiff.operation != Operation.EQUAL) {
                    int index2 = diff_xIndex(diffs, index1);
                    if (aDiff.operation == Operation.INSERT) {
                      // Insertion
                      text = text.substring(0, start_loc + index2) + aDiff.text
                          + text.substring(start_loc + index2);
                    } else if (aDiff.operation == Operation.DELETE) {
                      // Deletion
                      text = text.substring(0, start_loc + index2)
                          + text.substring(start_loc + diff_xIndex(diffs,
                          index1 + aDiff.text.length()));
                    }
                  }
                  if (aDiff.operation != Operation.DELETE) {
                    index1 += aDiff.text.length();
                  }
                }
              }
            }
          }
          x++;
        }
        // Strip the padding off.
        text = text.substring(nullPadding.length(), text.length()
            - nullPadding.length());
        return new Object[]{text, results};
      }
    
      /**
       * Add some padding on text start and end so that edges can match something.
       * Intended to be called only from within patch_apply.
       * @param patches Array of Patch objects.
       * @return The padding string added to each side.
       */
      public String patch_addPadding(LinkedList<Patch> patches) {
        short paddingLength = this.Patch_Margin;
        String nullPadding = "";
        for (short x = 1; x <= paddingLength; x++) {
          nullPadding += String.valueOf((char) x);
        }
    
        // Bump all the patches forward.
        for (Patch aPatch : patches) {
          aPatch.start1 += paddingLength;
          aPatch.start2 += paddingLength;
        }
    
        // Add some padding on start of first diff.
        Patch patch = patches.getFirst();
        LinkedList<Diff> diffs = patch.diffs;
        if (diffs.isEmpty() || diffs.getFirst().operation != Operation.EQUAL) {
          // Add nullPadding equality.
          diffs.addFirst(new Diff(Operation.EQUAL, nullPadding));
          patch.start1 -= paddingLength;  // Should be 0.
          patch.start2 -= paddingLength;  // Should be 0.
          patch.length1 += paddingLength;
          patch.length2 += paddingLength;
        } else if (paddingLength > diffs.getFirst().text.length()) {
          // Grow first equality.
          Diff firstDiff = diffs.getFirst();
          int extraLength = paddingLength - firstDiff.text.length();
          firstDiff.text = nullPadding.substring(firstDiff.text.length())
              + firstDiff.text;
          patch.start1 -= extraLength;
          patch.start2 -= extraLength;
          patch.length1 += extraLength;
          patch.length2 += extraLength;
        }
    
        // Add some padding on end of last diff.
        patch = patches.getLast();
        diffs = patch.diffs;
        if (diffs.isEmpty() || diffs.getLast().operation != Operation.EQUAL) {
          // Add nullPadding equality.
          diffs.addLast(new Diff(Operation.EQUAL, nullPadding));
          patch.length1 += paddingLength;
          patch.length2 += paddingLength;
        } else if (paddingLength > diffs.getLast().text.length()) {
          // Grow last equality.
          Diff lastDiff = diffs.getLast();
          int extraLength = paddingLength - lastDiff.text.length();
          lastDiff.text += nullPadding.substring(0, extraLength);
          patch.length1 += extraLength;
          patch.length2 += extraLength;
        }
    
        return nullPadding;
      }
    
      /**
       * Look through the patches and break up any which are longer than the
       * maximum limit of the match algorithm.
       * Intended to be called only from within patch_apply.
       * @param patches LinkedList of Patch objects.
       */
      public void patch_splitMax(LinkedList<Patch> patches) {
        short patch_size = Match_MaxBits;
        String precontext, postcontext;
        Patch patch;
        int start1, start2;
        boolean empty;
        Operation diff_type;
        String diff_text;
        ListIterator<Patch> pointer = patches.listIterator();
        Patch bigpatch = pointer.hasNext() ? pointer.next() : null;
        while (bigpatch != null) {
          if (bigpatch.length1 <= Match_MaxBits) {
            bigpatch = pointer.hasNext() ? pointer.next() : null;
            continue;
          }
          // Remove the big old patch.
          pointer.remove();
          start1 = bigpatch.start1;
          start2 = bigpatch.start2;
          precontext = "";
          while (!bigpatch.diffs.isEmpty()) {
            // Create one of several smaller patches.
            patch = new Patch();
            empty = true;
            patch.start1 = start1 - precontext.length();
            patch.start2 = start2 - precontext.length();
            if (precontext.length() != 0) {
              patch.length1 = patch.length2 = precontext.length();
              patch.diffs.add(new Diff(Operation.EQUAL, precontext));
            }
            while (!bigpatch.diffs.isEmpty()
                && patch.length1 < patch_size - Patch_Margin) {
              diff_type = bigpatch.diffs.getFirst().operation;
              diff_text = bigpatch.diffs.getFirst().text;
              if (diff_type == Operation.INSERT) {
                // Insertions are harmless.
                patch.length2 += diff_text.length();
                start2 += diff_text.length();
                patch.diffs.addLast(bigpatch.diffs.removeFirst());
                empty = false;
              } else if (diff_type == Operation.DELETE && patch.diffs.size() == 1
                  && patch.diffs.getFirst().operation == Operation.EQUAL
                  && diff_text.length() > 2 * patch_size) {
                // This is a large deletion.  Let it pass in one chunk.
                patch.length1 += diff_text.length();
                start1 += diff_text.length();
                empty = false;
                patch.diffs.add(new Diff(diff_type, diff_text));
                bigpatch.diffs.removeFirst();
              } else {
                // Deletion or equality.  Only take as much as we can stomach.
                diff_text = diff_text.substring(0, Math.min(diff_text.length(),
                    patch_size - patch.length1 - Patch_Margin));
                patch.length1 += diff_text.length();
                start1 += diff_text.length();
                if (diff_type == Operation.EQUAL) {
                  patch.length2 += diff_text.length();
                  start2 += diff_text.length();
                } else {
                  empty = false;
                }
                patch.diffs.add(new Diff(diff_type, diff_text));
                if (diff_text.equals(bigpatch.diffs.getFirst().text)) {
                  bigpatch.diffs.removeFirst();
                } else {
                  bigpatch.diffs.getFirst().text = bigpatch.diffs.getFirst().text
                      .substring(diff_text.length());
                }
              }
            }
            // Compute the head context for the next patch.
            precontext = diff_text2(patch.diffs);
            precontext = precontext.substring(Math.max(0, precontext.length()
                - Patch_Margin));
            // Append the end context for this patch.
            if (diff_text1(bigpatch.diffs).length() > Patch_Margin) {
              postcontext = diff_text1(bigpatch.diffs).substring(0, Patch_Margin);
            } else {
              postcontext = diff_text1(bigpatch.diffs);
            }
            if (postcontext.length() != 0) {
              patch.length1 += postcontext.length();
              patch.length2 += postcontext.length();
              if (!patch.diffs.isEmpty()
                  && patch.diffs.getLast().operation == Operation.EQUAL) {
                patch.diffs.getLast().text += postcontext;
              } else {
                patch.diffs.add(new Diff(Operation.EQUAL, postcontext));
              }
            }
            if (!empty) {
              pointer.add(patch);
            }
          }
          bigpatch = pointer.hasNext() ? pointer.next() : null;
        }
      }
    
      /**
       * Take a list of patches and return a textual representation.
       * @param patches List of Patch objects.
       * @return Text representation of patches.
       */
      public String patch_toText(List<Patch> patches) {
        StringBuilder text = new StringBuilder();
        for (Patch aPatch : patches) {
          text.append(aPatch);
        }
        return text.toString();
      }
    
      /**
       * Parse a textual representation of patches and return a List of Patch
       * objects.
       * @param textline Text representation of patches.
       * @return List of Patch objects.
       * @throws IllegalArgumentException If invalid input.
       */
      public List<Patch> patch_fromText(String textline)
          throws IllegalArgumentException {
        List<Patch> patches = new LinkedList<Patch>();
        if (textline.length() == 0) {
          return patches;
        }
        List<String> textList = Arrays.asList(textline.split("\n"));
        LinkedList<String> text = new LinkedList<String>(textList);
        Patch patch;
        Pattern patchHeader
            = Pattern.compile("^@@ -(\\d+),?(\\d*) \\+(\\d+),?(\\d*) @@$");
        Matcher m;
        char sign;
        String line;
        while (!text.isEmpty()) {
          m = patchHeader.matcher(text.getFirst());
          if (!m.matches()) {
            throw new IllegalArgumentException(
                "Invalid patch string: " + text.getFirst());
          }
          patch = new Patch();
          patches.add(patch);
          patch.start1 = Integer.parseInt(m.group(1));
          if (m.group(2).length() == 0) {
            patch.start1--;
            patch.length1 = 1;
          } else if (m.group(2).equals("0")) {
            patch.length1 = 0;
          } else {
            patch.start1--;
            patch.length1 = Integer.parseInt(m.group(2));
          }
    
          patch.start2 = Integer.parseInt(m.group(3));
          if (m.group(4).length() == 0) {
            patch.start2--;
            patch.length2 = 1;
          } else if (m.group(4).equals("0")) {
            patch.length2 = 0;
          } else {
            patch.start2--;
            patch.length2 = Integer.parseInt(m.group(4));
          }
          text.removeFirst();
    
          while (!text.isEmpty()) {
            try {
              sign = text.getFirst().charAt(0);
            } catch (IndexOutOfBoundsException e) {
              // Blank line?  Whatever.
              text.removeFirst();
              continue;
            }
            line = text.getFirst().substring(1);
            line = line.replace("+", "%2B");  // decode would change all "+" to " "
            try {
              line = URLDecoder.decode(line, "UTF-8");
            } catch (UnsupportedEncodingException e) {
              // Not likely on modern system.
              throw new Error("This system does not support UTF-8.", e);
            } catch (IllegalArgumentException e) {
              // Malformed URI sequence.
              throw new IllegalArgumentException(
                  "Illegal escape in patch_fromText: " + line, e);
            }
            if (sign == '-') {
              // Deletion.
              patch.diffs.add(new Diff(Operation.DELETE, line));
            } else if (sign == '+') {
              // Insertion.
              patch.diffs.add(new Diff(Operation.INSERT, line));
            } else if (sign == ' ') {
              // Minor equality.
              patch.diffs.add(new Diff(Operation.EQUAL, line));
            } else if (sign == '@') {
              // Start of next patch.
              break;
            } else {
              // WTF?
              throw new IllegalArgumentException(
                  "Invalid patch mode '" + sign + "' in: " + line);
            }
            text.removeFirst();
          }
        }
        return patches;
      }
    
    
      /**
       * Class representing one diff operation.
       */
      public static class Diff {
        /**
         * One of: INSERT, DELETE or EQUAL.
         */
        public Operation operation;
        /**
         * The text associated with this diff operation.
         */
        public String text;
    
        /**
         * Constructor.  Initializes the diff with the provided values.
         * @param operation One of INSERT, DELETE or EQUAL.
         * @param text The text being applied.
         */
        public Diff(Operation operation, String text) {
          // Construct a diff with the specified operation and text.
          this.operation = operation;
          this.text = text;
        }
    
        /**
         * Display a human-readable version of this Diff.
         * @return text version.
         */
        public String toString() {
          String prettyText = this.text.replace('\n', '\u00b6');
          return "Diff(" + this.operation + ",\"" + prettyText + "\")";
        }
    
        /**
         * Create a numeric hash value for a Diff.
         * This function is not used by DMP.
         * @return Hash value.
         */
        @Override
        public int hashCode() {
          final int prime = 31;
          int result = (operation == null) ? 0 : operation.hashCode();
          result += prime * ((text == null) ? 0 : text.hashCode());
          return result;
        }
    
        /**
         * Is this Diff equivalent to another Diff?
         * @param obj Another Diff to compare against.
         * @return true or false.
         */
        @Override
        public boolean equals(Object obj) {
          if (this == obj) {
            return true;
          }
          if (obj == null) {
            return false;
          }
          if (getClass() != obj.getClass()) {
            return false;
          }
          Diff other = (Diff) obj;
          if (operation != other.operation) {
            return false;
          }
          if (text == null) {
            if (other.text != null) {
              return false;
            }
          } else if (!text.equals(other.text)) {
            return false;
          }
          return true;
        }
      }
    
    
      /**
       * Class representing one patch operation.
       */
      public static class Patch {
        public LinkedList<Diff> diffs;
        public int start1;
        public int start2;
        public int length1;
        public int length2;
    
        /**
         * Constructor.  Initializes with an empty list of diffs.
         */
        public Patch() {
          this.diffs = new LinkedList<Diff>();
        }
    
        /**
         * Emmulate GNU diff's format.
         * Header: @@ -382,8 +481,9 @@
         * Indicies are printed as 1-based, not 0-based.
         * @return The GNU diff string.
         */
        public String toString() {
          String coords1, coords2;
          if (this.length1 == 0) {
            coords1 = this.start1 + ",0";
          } else if (this.length1 == 1) {
            coords1 = Integer.toString(this.start1 + 1);
          } else {
            coords1 = (this.start1 + 1) + "," + this.length1;
          }
          if (this.length2 == 0) {
            coords2 = this.start2 + ",0";
          } else if (this.length2 == 1) {
            coords2 = Integer.toString(this.start2 + 1);
          } else {
            coords2 = (this.start2 + 1) + "," + this.length2;
          }
          StringBuilder text = new StringBuilder();
          text.append("@@ -").append(coords1).append(" +").append(coords2)
              .append(" @@\n");
          // Escape the body of the patch with %xx notation.
          for (Diff aDiff : this.diffs) {
            switch (aDiff.operation) {
            case INSERT:
              text.append('+');
              break;
            case DELETE:
              text.append('-');
              break;
            case EQUAL:
              text.append(' ');
              break;
            }
            try {
              text.append(URLEncoder.encode(aDiff.text, "UTF-8").replace('+', ' '))
                  .append("\n");
            } catch (UnsupportedEncodingException e) {
              // Not likely on modern system.
              throw new Error("This system does not support UTF-8.", e);
            }
          }
          return unescapeForEncodeUriCompatability(text.toString());
        }
      }
    
      /**
       * Unescape selected chars for compatability with JavaScript's encodeURI.
       * In speed critical applications this could be dropped since the
       * receiving application will certainly decode these fine.
       * Note that this function is case-sensitive.  Thus "%3f" would not be
       * unescaped.  But this is ok because it is only called with the output of
       * URLEncoder.encode which returns uppercase hex.
       *
       * Example: "%3F" -> "?", "%24" -> "$", etc.
       *
       * @param str The string to escape.
       * @return The escaped string.
       */
      private static String unescapeForEncodeUriCompatability(String str) {
        return str.replace("%21", "!").replace("%7E", "~")
            .replace("%27", "'").replace("%28", "(").replace("%29", ")")
            .replace("%3B", ";").replace("%2F", "/").replace("%3F", "?")
            .replace("%3A", ":").replace("%40", "@").replace("%26", "&")
            .replace("%3D", "=").replace("%2B", "+").replace("%24", "$")
            .replace("%2C", ",").replace("%23", "#");
      }
    }

app端下载后，解压并将assets中的bundle文件和补丁进行合并

public static void handleZIP(final Context context) {
    	// 开启单独线程，解压，合并。
    	new Thread(new Runnable() {
    		@Override
    		public void run() {
    			// 解压到根目录
    			FileUtil.decompression(FileConstant.JS_PATCH_LOCAL_FOLDER);
    		   
    			// 合并
    			try {
    				mergePatAndAsset(context);
    			} catch (Exception e) {
    				e.printStackTrace();
    			}
    		   
    			// 删除ZIP压缩包
    			FileUtil.deleteFile(FileConstant.JS_PATCH_LOCAL_PATH);
    		}
    	}).start();
    }

private static void mergePatAndAsset(Context context) throws Exception{
    	// 1.解析Asset目录下的bundle文件
    	String assetsBundle = FileUtil.getJsBundleFromAssets(context);
    	// 2.解析bundle当前目录下.pat文件字符串
    	String patcheStr = FileUtil.getStringFromPat(FileConstant.JS_PATCH_LOCAL_FILE);
    
    	// 3.合并
    	merge(patcheStr,assetsBundle);
    	// 4.删除pat
    	FileUtil.deleteFile(FileConstant.JS_PATCH_LOCAL_FILE);
    }

public static String getJsBundleFromAssets(Context context) {
    
            String result = "";
            try {
                InputStream is = context.getAssets().open(JS_BUNDLE_LOCAL_FILE);
                int size = is.available();
                byte[] buffer = new byte[size];
                is.read(buffer);
                is.close();
                result = new String(buffer,"UTF-8");
    
            } catch (IOException e) {
                e.printStackTrace();
            }
            return result;
        }

public static String getStringFromPat(String patPath) {
    
            FileReader reader = null;
            String result = "";
            try {
                reader = new FileReader(patPath);
                int ch = reader.read();
                StringBuilder sb = new StringBuilder();
                while (ch != -1) {
                    sb.append((char)ch);
                    ch  = reader.read();
                }
                reader.close();
                result = sb.toString();
            } catch (FileNotFoundException e) {
                e.printStackTrace();
            } catch (IOException e) {
                e.printStackTrace();
            }
            return result;
        }

private static void merge(String patcheStr, String bundle) {
    	// 1.初始化 dmp
    	diff_match_patch dmp = new diff_match_patch();
    	// 2.转换pat
    	LinkedList<diff_match_patch.Patch> pathes = (LinkedList<diff_match_patch.Patch>) dmp.patch_fromText(patcheStr);
    	// 3.pat与bundle合并，生成新的bundle
    	Object[] bundleArray = dmp.patch_apply(pathes,bundle);
    	// 4.保存新的bundle文件
    	try {
    		Writer writer = new FileWriter(FileConstant.JS_BUNDLE_LOCAL_PATH);
    		String newBundle = (String) bundleArray[0];
    		writer.write(newBundle);
    		writer.close();
    	} catch (IOException e) {
    		e.printStackTrace();
    	}
    }

[React-native _1_ _ android]: http://mp.blog.csdn.net/postedit/79289441