Redis源码分析（二十一）--- anet网络通信的封装

           昨天非常轻松的分析完Redis的事件驱动模型之后，今天我来看看anet的代码，anet是Redis对于Client/Server的网络操作的一个小小封装。代码中对此文件的官方解释为:

/* anet.c -- Basic TCP socket stuff made a bit less boring
 * 基于简单的基本TCP的socket连接

int anetTcpConnect(char *err, char *addr, int port); /* TCP的默认连接 */
int anetTcpNonBlockConnect(char *err, char *addr, int port); /* TCP的非阻塞连接 */
int anetUnixConnect(char *err, char *path); /* anet的Unix方式的默认连接方式 */
int anetUnixNonBlockConnect(char *err, char *path); /* anet的Unix方式的非阻塞连接方式 */
int anetRead(int fd, char *buf, int count); /* anet网络读取文件到buffer中操作 */
int anetResolve(char *err, char *host, char *ipbuf, size_t ipbuf_len); /* 解析所有的东西 */
int anetResolveIP(char *err, char *host, char *ipbuf, size_t ipbuf_len); /* 单单解析IP的地址 */
int anetTcpServer(char *err, int port, char *bindaddr, int backlog);
int anetTcp6Server(char *err, int port, char *bindaddr, int backlog);
int anetUnixServer(char *err, char *path, mode_t perm, int backlog);
int anetTcpAccept(char *err, int serversock, char *ip, size_t ip_len, int *port);
int anetUnixAccept(char *err, int serversock);
int anetWrite(int fd, char *buf, int count); /* anet通过网络从buffer中写入文件操作 */
int anetNonBlock(char *err, int fd); /* anet设置非阻塞的方法 */
int anetEnableTcpNoDelay(char *err, int fd); /* 启用TCP没有延迟 */
int anetDisableTcpNoDelay(char *err, int fd); /* 禁用TCP连接没有延迟 */
int anetTcpKeepAlive(char *err, int fd); /* 设置TCP保持活跃连接状态。适用于所有系统 */
int anetPeerToString(int fd, char *ip, size_t ip_len, int *port);
int anetKeepAlive(char *err, int fd, int interval); /* 设置TCP连接一直存活，用来检测已经死去的结点，interval选项只适用于Linux下的系统 */
int anetSockName(int fd, char *ip, size_t ip_len, int *port);

/* anet设置非阻塞的方法 */
int anetNonBlock(char *err, int fd)
{
    int flags;

    /* Set the socket non-blocking.
     * Note that fcntl(2) for F_GETFL and F_SETFL can't be
     * interrupted by a signal. */
    if ((flags = fcntl(fd, F_GETFL)) == -1) {
        anetSetError(err, "fcntl(F_GETFL): %s", strerror(errno));
        return ANET_ERR;
    }
    //调用fcntl方法设置非阻塞方法
    if (fcntl(fd, F_SETFL, flags | O_NONBLOCK) == -1) {
        anetSetError(err, "fcntl(F_SETFL,O_NONBLOCK): %s", strerror(errno));
        return ANET_ERR;
    }
    return ANET_OK;
}

(1).能设置BLOCK连接还是NONE_BLOCKED方式的connect；

/* TCP的默认连接 */
int anetTcpConnect(char *err, char *addr, int port)
{
    return anetTcpGenericConnect(err,addr,port,ANET_CONNECT_NONE);
}

/* TCP的非阻塞连接 */
int anetTcpNonBlockConnect(char *err, char *addr, int port)
{
    return anetTcpGenericConnect(err,addr,port,ANET_CONNECT_NONBLOCK);
}

/* 设置TCP连接是否NODelay没有延迟 */
static int anetSetTcpNoDelay(char *err, int fd, int val)
{
    if (setsockopt(fd, IPPROTO_TCP, TCP_NODELAY, &val, sizeof(val)) == -1)
    {
        anetSetError(err, "setsockopt TCP_NODELAY: %s", strerror(errno));
        return ANET_ERR;
    }
    return ANET_OK;
}

/* 启用TCP没有延迟 */
int anetEnableTcpNoDelay(char *err, int fd)
{
    return anetSetTcpNoDelay(err, fd, 1);
}

/* 禁用TCP连接没有延迟 */
int anetDisableTcpNoDelay(char *err, int fd)
{
    return anetSetTcpNoDelay(err, fd, 0);
}

(3).对ip地址有ipv4和ipv6地址不同的处理方法。这个作者想得还是非常全面的。在对地址做resolve解析的时候就考虑到了这个问题:

/* anetGenericResolve() is called by anetResolve() and anetResolveIP() to
 * do the actual work. It resolves the hostname "host" and set the string
 * representation of the IP address into the buffer pointed by "ipbuf".
 *
 * If flags is set to ANET_IP_ONLY the function only resolves hostnames
 * that are actually already IPv4 or IPv6 addresses. This turns the function
 * into a validating / normalizing function. */
/* 解析的泛型方法，可以根据条件解析host主机名或IP地址 */
int anetGenericResolve(char *err, char *host, char *ipbuf, size_t ipbuf_len,
                       int flags)
{
    struct addrinfo hints, *info;
    int rv;

    memset(&hints,0,sizeof(hints));
    if (flags & ANET_IP_ONLY) hints.ai_flags = AI_NUMERICHOST;
    hints.ai_family = AF_UNSPEC;
    hints.ai_socktype = SOCK_STREAM;  /* specify socktype to avoid dups */

	//解析hostName
    if ((rv = getaddrinfo(host, NULL, &hints, &info)) != 0) {
        anetSetError(err, "%s", gai_strerror(rv));
        return ANET_ERR;
    }
    
    //根据类型解析ipV4的地址还是ipV6的地址
    if (info->ai_family == AF_INET) {
        struct sockaddr_in *sa = (struct sockaddr_in *)info->ai_addr;
        inet_ntop(AF_INET, &(sa->sin_addr), ipbuf, ipbuf_len);
    } else {
        struct sockaddr_in6 *sa = (struct sockaddr_in6 *)info->ai_addr;
        inet_ntop(AF_INET6, &(sa->sin6_addr), ipbuf, ipbuf_len);
    }

    freeaddrinfo(info);
    return ANET_OK;
}

/* socket连接操作 */
static int anetGenericAccept(char *err, int s, struct sockaddr *sa, socklen_t *len) {
    int fd;
    while(1) {
    	//通过while循环等待连接
        fd = accept(s,sa,len);
        if (fd == -1) {
            if (errno == EINTR)
                continue;
            else {
                anetSetError(err, "accept: %s", strerror(errno));
                return ANET_ERR;
            }
        }
        break;
    }
    return fd;
}