lwIP(V1.3.0) RAW API函数源码分析3----tcp_listen()函数

叁歲伎倆 2022-09-29 01:29 93阅读 0赞

在lwip-x.x.x/src/core/tcp.h中定义:

\#define tcp\_listen(pcb)tcp\_listen\_with\_backlog(pcb, TCP\_DEFAULT\_LISTEN\_BACKLOG)

所以, tcp\_listen(pcb) 和tcp\_listen\_with\_backlog(pcb, TCP\_DEFAULT\_LISTEN\_BACKLOG)是一回事. TCP\_DEFAULT\_LISTEN\_BACKLOG在opt.h中定义,默认值为0xFF,指明最大允许的可等待TCP监听链接个数.

位于: 位于:lwip-x.x.x/src/core/tcp.c

原型: struct tcp\_pcb \* tcp\_listen\_with\_backlog(struct tcp\_pcb \*pcb, u8\_t backlog)

功能: 使指定的连接开始进入监听状态

函数源码:

/\*\* \* Set the state of the connection to be LISTEN, which means that it \* is able to accept incoming connections. The protocol control block \* is reallocated in order to consume less memory. Setting the \* connection to LISTEN is an irreversible process. \*设置连接进入LISTEN状态,这意味着这个连接能够接受传入的连接,为了消耗更少的内存, 协议控制块会被重新分配.设置连接进入LISTEN状态是一个不可逆转的过程 \* @param pcb the original tcp\_pcb \* @param backlog the incoming connections queue limit传入连接的队列限制 \* @return tcp\_pcb used for listening, consumes less memory. \* \* @note The original tcp\_pcb is freed(原始的tcp\_pcb会被释放). This function therefore has to be \* called like this: \* tpcb = tcp\_listen(tpcb); \*/ struct tcp\_pcb \* tcp\_listen\_with\_backlog(struct tcp\_pcb \*pcb, u8\_t backlog) \{ struct tcp\_pcb\_listen \*lpcb; LWIP\_UNUSED\_ARG(backlog); // \#define LWIP\_UNUSED\_ARG(x) (void)x LWIP\_ERROR("tcp\_listen: pcb already connected", pcb->state == CLOSED, return NULL); /\* already listening? 是否应经处于监听?\*/ if (pcb->state == LISTEN) \{ return pcb; \} lpcb = memp\_malloc(MEMP\_TCP\_PCB\_LISTEN);//申请一块内存 if (lpcb == NULL) \{ return NULL; \} lpcb->callback\_arg = pcb->callback\_arg; lpcb->local\_port = pcb->local\_port; lpcb->state = LISTEN; //置监听标志位 lpcb->so\_options = pcb->so\_options; lpcb->so\_options |= SOF\_ACCEPTCONN; lpcb->ttl = pcb->ttl; lpcb->tos = pcb->tos; ip\_addr\_set(&lpcb->local\_ip, &pcb->local\_ip); TCP\_RMV(&tcp\_bound\_pcbs, pcb); memp\_free(MEMP\_TCP\_PCB, pcb); //释放原来的(原始的) PCB \#if LWIP\_CALLBACK\_API lpcb->accept = tcp\_accept\_null; //默认回调函数 \#endif /\* LWIP\_CALLBACK\_API \*/ \#if TCP\_LISTEN\_BACKLOG lpcb->accepts\_pending = 0; lpcb->backlog = (backlog ? backlog : 1); \#endif /\* TCP\_LISTEN\_BACKLOG \*/ TCP\_REG(&tcp\_listen\_pcbs.listen\_pcbs, lpcb); //将连接放入已监听队列 return (struct tcp\_pcb \*)lpcb; \}

分析:这个函数从原理上看也比较简单,首先是做一些必要的检查,判断原始pcb是否已经处于连接状态,如果没有则申请一块tcp\_pcb类型的内存,将原始的必要的pcb内容复制到新的pcb中,设置新的pcb状态为LISTEN,释放原始的pcb,并将新pcb连接放入已监听队列.