anetTcpGenericConnect 详解

/*
	参数释义：
		addr：传入服务器地址信息，其中内容将用于创建监听套接字
		source_addr：相当于客户端地址信息
		flags：这我还真没看明白。。。再最后一块儿，注释给出了，如果没猜错，应该是和仅打开监听套接字有关的
*/
static int anetTcpGenericConnect(char *err, const char *addr, int port,const char *source_addr, int flags)
{
    int s = ANET_ERR, rv;
    char portstr[6];  /* strlen("65535") + 1; */
    struct addrinfo hints, *servinfo, *bservinfo, *p, *b;

    snprintf(portstr,sizeof(portstr),"%d",port);
    memset(&hints,0,sizeof(hints));
    hints.ai_family = AF_UNSPEC;	//未指定
    hints.ai_socktype = SOCK_STREAM;//有序、可靠、面向连接的双向字节流

    if ((rv = getaddrinfo(addr,portstr,&hints,&servinfo)) != 0) {	//解析addr信息，存入 servinfo
    //不懂一定要看上面的工具包，写了一晚上呢
        anetSetError(err, "%s", gai_strerror(rv));	//这个不管它，报错函数而已
        return ANET_ERR;
    }
    for (p = servinfo; p != NULL; p = p->ai_next) {		//工具包里有说，给你一个addrinfo，它可能是一串
        /* Try to create the socket and to connect it.
         * If we fail in the socket() call, or on connect(), we retry with
         * the next entry in servinfo. */
        if ((s = socket(p->ai_family,p->ai_socktype,p->ai_protocol)) == -1)	//这里s成为了监听套接字
            continue;	//如果没打开，那就继续循环，无碍
        if (anetSetReuseAddr(err,s) == ANET_ERR) goto error;	//设置地址重用
        if (flags & ANET_CONNECT_NONBLOCK && anetNonBlock(err,s) != ANET_OK)	//设置非阻塞
            goto error;
        if (source_addr) {	//source_addr：传入参数
            int bound = 0;
            /* Using getaddrinfo saves us from self-determining IPv4 vs IPv6 */
            if ((rv = getaddrinfo(source_addr, NULL, &hints, &bservinfo)) != 0)	//内啥，不多说了啊
            {
                anetSetError(err, "%s", gai_strerror(rv));
                goto error;
            }
            for (b = bservinfo; b != NULL; b = b->ai_next) {
                if (bind(s,b->ai_addr,b->ai_addrlen) != -1) {
                    bound = 1;
                    break;
                }
            }
            freeaddrinfo(bservinfo);
            if (!bound) {
                anetSetError(err, "bind: %s", strerror(errno));
                goto error;
            }
        }	//for循环到这里结束
        if (connect(s,p->ai_addr,p->ai_addrlen) == -1) {
            /* If the socket is non-blocking, it is ok for connect() to
             * return an EINPROGRESS error here. */
            if (errno == EINPROGRESS && flags & ANET_CONNECT_NONBLOCK)
                goto end;
            close(s);
            s = ANET_ERR;
            continue;
        }

        /* If we ended an iteration of the for loop without errors, we
         * have a connected socket. Let's return to the caller. */
        goto end;
    }
    if (p == NULL)
        anetSetError(err, "creating socket: %s", strerror(errno));

error:
    if (s != ANET_ERR) {
        close(s);
        s = ANET_ERR;
    }

end:
    freeaddrinfo(servinfo);

    /* Handle best effort binding: if a binding address was used, but it is
     * not possible to create a socket, try again without a binding address. */
    if (s == ANET_ERR && source_addr && (flags & ANET_CONNECT_BE_BINDING)) {	
    //#define ANET_CONNECT_BE_BINDING 2 /* Best effort binding. */
        return anetTcpGenericConnect(err,addr,port,NULL,flags);
    } else {
        return s;
    }
}