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1、wordLWIP之SOCKET的实现 bluefish.blog.51cto./214870/158413Lwip协议栈的实现目的，无非是要上层用来实现app的socket编程。好，我们就从socket开始。为了兼容性，lwip的socket应该也是提供标准的socket接口函数，恩，没错，在srcincludelwipsocket.h文件中可以看到下面的宏定义：#if LWIP_PAT_SOCKETS#define accept(a,b,c) lwip_accept(a,b,c)#define bind(a,b,c) lwip_bind(a,b,c)#define shutdown(a,b)
2、 lwip_shutdown(a,b)#define closesocket(s) lwip_close(s)#define connect(a,b,c) lwip_connect(a,b,c)#define getsockname(a,b,c) lwip_getsockname(a,b,c)#define getpeername(a,b,c) lwip_getpeername(a,b,c)#define setsockopt(a,b,c,d,e) lwip_setsockopt(a,b,c,d,e)#define getsockopt(a,b,c,d,e) lwip_getsockopt(a
3、,b,c,d,e)#define listen(a,b) lwip_listen(a,b)#define recv(a,b,c,d) lwip_recv(a,b,c,d)#define recvfrom(a,b,c,d,e,f) lwip_recvfrom(a,b,c,d,e,f)#define send(a,b,c,d) lwip_send(a,b,c,d)#define sendto(a,b,c,d,e,f) lwip_sendto(a,b,c,d,e,f)#define socket(a,b,c) lwip_socket(a,b,c)#define select(a,b,c,d,e) l
4、wip_select(a,b,c,d,e)#define ioctlsocket(a,b,c) lwip_ioctl(a,b,c)#if LWIP_POSIX_SOCKETS_IO_NAMES#define read(a,b,c) lwip_read(a,b,c)#define write(a,b,c) lwip_write(a,b,c)#define close(s) lwip_close(s)先不说实际的实现函数，光看这些定义的宏，就是标准socket所必须有的接口。接着看这些实际的函数实现。这些函数实现在srcapisocket.c中。先看下承受连接的函数，这个是tcp的原型：int l
5、wip_accept(int s, struct sockaddr *addr, socklen_t *addrlen)可以看到这里的socket类型参数 s，实际上是个int型在这个函数中的第一个函数调用是sock = get_socket(s);这里的sock变量类型是lwip_socket，定义如下：/* Contains all internal pointers and states used for a socket */struct lwip_socket /* sockets currently are built on netconns, each socket has on
6、e netconn */ struct netconn *conn;/* data that was left from the previous read */ struct netbuf *lastdata; /* offset in the data that was left from the previous read */ u16_t lastoffset; /* number of times data was received, set by event_callback(), tested by the receive and select functions */ u16_
7、t rcvevent;/* number of times data was received, set by event_callback(), tested by select */ u16_t sendevent;/* socket flags (currently, only used for O_NONBLOCK) */ u16_t flags;/* last error that occurred on this socket */ int err;好，这个结构先不管它，接着看下get_socket函数的实现【也是在文件中】，在这里我们看到这样一条语句sock = &sockets
8、s;很明显，返回值也是这个sock，它是根据传进来的序列号在sockets数组中找到对应的元素并返回该元素的地址。好了，那么这个sockets数组是在哪里被赋值了这些元素的呢？进展到这里似乎应该从标准的socket编程的开始，也就是socket函数讲起，那我们就顺便看一下。它对应的实际实现是下面这个函数Int lwip_socket(int domain, int type, int protocol)【】这个函数根据不同的协议类型，也就是函数中的type参数，创建了一个netconn结构体的指针，接着就是用这个指针作为参数调用了alloc_socket函数，下面具体看下这个函数的实现stat
9、ic int alloc_socket(struct netconn *newconn) int i;/* Protect socket array */ sys_sem_wait(socksem); /* allocate a new socket identifier */ for (i = 0; i NUM_SOCKETS; +i) if (!socketsi.conn) socketsi.conn = newconn; socketsi.lastdata = NULL; socketsi.lastoffset = 0; socketsi.rcvevent = 0; socketsi.s
10、endevent = 1; /* TCP send buf is empty */ socketsi.flags = 0; socketsi.err = 0;sys_sem_signal(socksem); return i; sys_sem_signal(socksem);return -1;对了，就是这个时候对全局变量sockets数组的元素赋值的。既然都来到这里了，那就顺便看下netconn结构的情况吧。它的学名叫netconn descriptor/* A netconn descriptor */struct netconn /* type of the netconn (TCP,
11、UDP or RAW) */ enum netconn_type type; /* current state of the netconn */ enum netconn_state state; /* the lwIP internal protocol control block */ union struct ip_pcb *ip; struct tcp_pcb *tcp; struct udp_pcb *udp; struct raw_pcb *raw; pcb; /* the last error this netconn had */ err_t err; /* sem that
12、 is used to synchroneously execute functions in the core context */ sys_sem_t op_pleted; /* mbox where received packets are stored until they are fetched by the netconn application thread (can grow quite big) */ sys_mbox_t recvmbox; /* mbox where new connections are stored until processed by the app
13、lication thread */ sys_mbox_t acceptmbox; /* only used for socket layer */ int socket;#if LWIP_SO_RCVTIMEO /* timeout to wait for new data to be received (or connections to arrive for listening netconns) */ int recv_timeout;#endif /* LWIP_SO_RCVTIMEO */#if LWIP_SO_RCVBUF /* maximum amount of bytes q
14、ueued in recvmbox */ int recv_bufsize;#endif /* LWIP_SO_RCVBUF */ u16_t recv_avail; /* TCP: when data passed to netconn_write doesnt fit into the send buffer, this temporarily stores the message. */ struct api_msg_msg *write_msg; /* TCP: when data passed to netconn_write doesnt fit into the send buffer, this temporarily stores how much is already sent. */ int write_offset;#if LWIP_TCPIP_CORE_LOCKING /* TCP: when data passed to netconn_write doesnt fit into the send buffer, this temporarily stores whether
