anet.c中实现了一些网络相关的设置操作，可以参考我的linux网络编程那篇文章。
这里使用的socket属性更多，帮我复习了tcp相关的知识。
我们先来看anet.h

#ifndef ANET_H
#define ANET_H
#include <sys/types.h>
#define ANET_OK 0
#define ANET_ERR -1
#define ANET_ERR_LEN 256
/* Flags used with certain functions. 某些函数使用的flag*/
#define ANET_NONE 0
#define ANET_IP_ONLY (1<<0)

int anetTcpConnect(char *err, char *addr, int port);
int anetTcpNonBlockConnect(char *err, char *addr, int port);
int anetTcpNonBlockBindConnect(char *err, char *addr, int port, char *source_addr);
int anetTcpNonBlockBestEffortBindConnect(char *err, char *addr, int port, char *source_addr);
int anetUnixConnect(char *err, char *path);
int anetUnixNonBlockConnect(char *err, char *path);
int anetRead(int fd, char *buf, int count);
int anetResolve(char *err, char *host, char *ipbuf, size_t ipbuf_len);
int anetResolveIP(char *err, char *host, char *ipbuf, size_t ipbuf_len);
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);
int anetNonBlock(char *err, int fd);
int anetBlock(char *err, int fd);
int anetEnableTcpNoDelay(char *err, int fd);

anet.c

#include "fmacros.h"//这个头文件包含了一些系统的宏定义
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/stat.h>
#include <sys/un.h>
#include <sys/time.h>
#include <netinet/in.h>
#include <netinet/tcp.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <fcntl.h>
#include <string.h>
#include <netdb.h>
#include <errno.h>
#include <stdarg.h>
#include <stdio.h>
#include "anet.h"
//anet设置错误
static void anetSetError(char *err, const char *fmt, ...)
{
    va_list ap;

    if (!err) return;
    va_start(ap, fmt);
    vsnprintf(err, ANET_ERR_LEN, fmt, ap);//将所有字符追加到err中
    va_end(ap);
}
//设置阻塞或者非阻塞
int anetSetBlock(char *err, int fd, int non_block) {
    int flags;

    /* Set the socket blocking (if non_block is zero) or non-blocking. Note that fcntl(2) for F_GETFL and F_SETFL can't be interrupted by a signal. 设置套接字阻塞或者非阻塞，fcntl不能被信号中断*/
    if ((flags = fcntl(fd, F_GETFL)) == -1) {
        anetSetError(err, "fcntl(F_GETFL): %s", strerror(errno));//如果获取fd的属性失败了，就返回错误
        return ANET_ERR;
    }

    if (non_block)
        flags |= O_NONBLOCK;
    else
        flags &= ~O_NONBLOCK;

    if (fcntl(fd, F_SETFL, flags) == -1) {//设置fd的属性为flag
        anetSetError(err, "fcntl(F_SETFL,O_NONBLOCK): %s", strerror(errno));
        return ANET_ERR;
    }
    return ANET_OK;
}
//设置文件描述符非阻塞
int anetNonBlock(char *err, int fd) {
    return anetSetBlock(err,fd,1);
}
//设置文件描述符阻塞
int anetBlock(char *err, int fd) {
    return anetSetBlock(err,fd,0);
}
/* Set TCP keep alive option to detect dead peers. The interval option is only used for Linux as we are using Linux-specific APIs to set the probe send time, interval, and count. 设置TCP保持活动选项来检测死等，interval选项用于linux，因为我们使用特定于linux的api来设置探针发送时间间隔和技术*/
int anetKeepAlive(char *err, int fd, int interval)
{
    int val = 1;

    if (setsockopt(fd, SOL_SOCKET, SO_KEEPALIVE, &val, sizeof(val)) == -1)//设置文件描述符保持生命
    {
        anetSetError(err, "setsockopt SO_KEEPALIVE: %s", strerror(errno));
        return ANET_ERR;
    }

#ifdef __linux__
    /* Default settings are more or less garbage, with the keepalive time set to 7200 by default on Linux. Modify settings to make the feature actually useful. 默认设置或多或少都是垃圾，默认情况下linux上保持活动时间为7200，修改设置以使该功能真正有用*/

    /* Send first probe after interval. 间隔后发送第一个探针*/
    val = interval;
    if (setsockopt(fd, IPPROTO_TCP, TCP_KEEPIDLE, &val, sizeof(val)) < 0) {//对一个连接进行有效性探测之前运行的最大非活跃时间间隔
        anetSetError(err, "setsockopt TCP_KEEPIDLE: %s\n", strerror(errno));
        return ANET_ERR;
    }

    /* Send next probes after the specified interval. Note that we set the delay as interval / 3, as we send three probes before detecting an error (see the next setsockopt call). 在指定间隔后发送下一个感测，我们将延迟设置为间隔/3，因为我们在检测到错误之前发送了三个探针*/
    val = interval/3;
    if (val == 0) val = 1;
    if (setsockopt(fd, IPPROTO_TCP, TCP_KEEPINTVL, &val, sizeof(val)) < 0) {//两个探测的时间间隔
        anetSetError(err, "setsockopt TCP_KEEPINTVL: %s\n", strerror(errno));
        return ANET_ERR;
    }

    /* Consider the socket in error state after three we send three ACK probes without getting a reply. 考虑到三个错误状态之后我们发送三个ack探测器没有得到答复*/
    val = 3;
    if (setsockopt(fd, IPPROTO_TCP, TCP_KEEPCNT, &val, sizeof(val)) < 0) {//关闭一个非活跃连接之前进行探测的最大次数
        anetSetError(err, "setsockopt TCP_KEEPCNT: %s\n", strerror(errno));
        return ANET_ERR;
    }
#else
    ((void) interval); /* Avoid unused var warning for non Linux systems. */
#endif

    return ANET_OK;
}
//设置tcp不延迟
static int anetSetTcpNoDelay(char *err, int fd, int val)
{
    if (setsockopt(fd, IPPROTO_TCP, TCP_NODELAY, &val, sizeof(val)) == -1)//禁止nagle算法，有需要发送的就立即发送
    {
        anetSetError(err, "setsockopt TCP_NODELAY: %s", strerror(errno));
        return ANET_ERR;
    }
    return ANET_OK;
}
//设置文件描述符不延迟
int anetEnableTcpNoDelay(char *err, int fd)
{
    return anetSetTcpNoDelay(err, fd, 1);
}
//设置文件描述符不启用nodelay
int anetDisableTcpNoDelay(char *err, int fd)
{
    return anetSetTcpNoDelay(err, fd, 0);
}
//改变发送缓冲区的大小
int anetSetSendBuffer(char *err, int fd, int buffsize)
{
    if (setsockopt(fd, SOL_SOCKET, SO_SNDBUF, &buffsize, sizeof(buffsize)) == -1)
    {
        anetSetError(err, "setsockopt SO_SNDBUF: %s", strerror(errno));
        return ANET_ERR;
    }
    return ANET_OK;
}
//设置连接保持声明周期/心跳
int anetTcpKeepAlive(char *err, int fd)
{
    int yes = 1;
    if (setsockopt(fd, SOL_SOCKET, SO_KEEPALIVE, &yes, sizeof(yes)) == -1) {
        anetSetError(err, "setsockopt SO_KEEPALIVE: %s", strerror(errno));
        return ANET_ERR;
    }
    return ANET_OK;
}
/* Set the socket send timeout (SO_SNDTIMEO socket option) to the specified number of milliseconds, or disable it if the 'ms' argument is zero. 将套接字发送超时设置为指定的ms，如果ms为0，则禁用*/
int anetSendTimeout(char *err, int fd, long long ms) {
    struct timeval tv;

    tv.tv_sec = ms/1000;
    tv.tv_usec = (ms%1000)*1000;
    if (setsockopt(fd, SOL_SOCKET, SO_SNDTIMEO, &tv, sizeof(tv)) == -1) {//设置发送超时时间
        anetSetError(err, "setsockopt SO_SNDTIMEO: %s", strerror(errno));
        return ANET_ERR;
    }
    return ANET_OK;
}
/* 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. 解析主机名，并将ip地址的字符串表示设置到ipbuf指向的缓冲区，付过flags设置为ANET_IP_ONLY，则该函数仅解析实际上已经是IPv4或IPv6的主机名，则将函数转换为验证/标准化函数*/
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 指定socktype以避免dups*/

    if ((rv = getaddrinfo(host, NULL, &hints, &info)) != 0) {
        anetSetError(err, "%s", gai_strerror(rv));//获取网络相关信息
        return ANET_ERR;
    }
    if (info->ai_family == AF_INET) {//ipv4
        struct sockaddr_in *sa = (struct sockaddr_in *)info->ai_addr;
        inet_ntop(AF_INET, &(sa->sin_addr), ipbuf, ipbuf_len);//将addr转换为ipbuf
    } 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;
}
//网络解析
int anetResolve(char *err, char *host, char *ipbuf, size_t ipbuf_len) {
    return anetGenericResolve(err,host,ipbuf,ipbuf_len,ANET_NONE);
}
//解析ip
int anetResolveIP(char *err, char *host, char *ipbuf, size_t ipbuf_len) {
    return anetGenericResolve(err,host,ipbuf,ipbuf_len,ANET_IP_ONLY);
}
//设置端口重用
static int anetSetReuseAddr(char *err, int fd) {
    int yes = 1;
    /* Make sure connection-intensive things like the redis benckmark will be able to close/open sockets a zillion of times 确保连接密集的东西，如redis基准将能够关闭/打开一百万次套接字*/
    if (setsockopt(fd, SOL_SOCKET, SO_REUSEADDR, &yes, sizeof(yes)) == -1) {//设置地址重用，SO_REUSEADDR可以让端口释放后立即就可以被再次使用
        anetSetError(err, "setsockopt SO_REUSEADDR: %s", strerror(errno));
        return ANET_ERR;
    }
    return ANET_OK;
}
//创建socket
static int anetCreateSocket(char *err, int domain) {
    int s;
    if ((s = socket(domain, SOCK_STREAM, 0)) == -1) {
        anetSetError(err, "creating socket: %s", strerror(errno));
        return ANET_ERR;
    }

    /* Make sure connection-intensive things like the redis benchmark will be able to close/open sockets a zillion of times 确保连接密集事件可以频繁的打开关闭socket*/
    if (anetSetReuseAddr(err,s) == ANET_ERR) {
        close(s);
        return ANET_ERR;
    }
    return s;
}

#define ANET_CONNECT_NONE 0
#define ANET_CONNECT_NONBLOCK 1
#define ANET_CONNECT_BE_BINDING 2 /* Best effort binding. */
static int anetTcpGenericConnect(char *err, char *addr, int port,
                                 char *source_addr, int flags)
{
    int s = ANET_ERR, rv;
    char portstr[6];  /* strlen("65535") + 1; 这里用字符串表示short端口号*/
    struct addrinfo hints, *servinfo, *bservinfo, *p, *b;

    snprintf(portstr,sizeof(portstr),"%d",port);
    memset(&hints,0,sizeof(hints));
    hints.ai_family = AF_UNSPEC;//表示函数返回的是适用于指定主机名和服务名且适合任何协议族的地址
    hints.ai_socktype = SOCK_STREAM;//tcp流连接

    if ((rv = getaddrinfo(addr,portstr,&hints,&servinfo)) != 0) {
        anetSetError(err, "%s", gai_strerror(rv));
        return ANET_ERR;
    }
    for (p = servinfo; p != NULL; p = p->ai_next) {
        /* 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.尝试创建套接字并连接它，如果我们在socket（）调用或者connect（）中失败，我们将重试servinfo中的下一个条目*/
        if ((s = socket(p->ai_family,p->ai_socktype,p->ai_protocol)) == -1)
            continue;
        if (anetSetReuseAddr(err,s) == ANET_ERR) goto error;
        if (flags & ANET_CONNECT_NONBLOCK && anetNonBlock(err,s) != ANET_OK)
            goto error;
        if (source_addr) {
            int bound = 0;
            /* Using getaddrinfo saves us from self-determining IPv4 vs IPv6 使用这个函数可以帮我们节省自行确定的ipv4 vs ipv6 */
            if ((rv = getaddrinfo(source_addr, NULL, &hints, &bservinfo)) != 0)
            {
                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) {//绑定ip
                    bound = 1;
                    break;
                }
            }
            freeaddrinfo(bservinfo);
            if (!bound) {
                anetSetError(err, "bind: %s", strerror(errno));
                goto error;
            }
        }
        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. 如果套接字是非阻塞的，connect会返回一个EINPROGRESS错误*/
            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. 如果我们结束了没有错误的for迭代，我们有一个连接的套接字，回到调用者*/
        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. 处理尽力而为的绑定：如果使用绑定地址，但无法创建套接字，请在没有绑定地址的情况下再次尝试*/
    if (s == ANET_ERR && source_addr && (flags & ANET_CONNECT_BE_BINDING)) {
        return anetTcpGenericConnect(err,addr,port,NULL,flags);
    } else {
        return s;
    }
}
//下面是tcp按照不同属性的连接调用
int anetTcpConnect(char *err, char *addr, int port)
{
    return anetTcpGenericConnect(err,addr,port,NULL,ANET_CONNECT_NONE);
}
int anetTcpNonBlockConnect(char *err, char *addr, int port)
{
    return anetTcpGenericConnect(err,addr,port,NULL,ANET_CONNECT_NONBLOCK);
}
int anetTcpNonBlockBindConnect(char *err, char *addr, int port,
                               char *source_addr)
{
    return anetTcpGenericConnect(err,addr,port,source_addr,
            ANET_CONNECT_NONBLOCK);
}
int anetTcpNonBlockBestEffortBindConnect(char *err, char *addr, int port,
                                         char *source_addr)
{
    return anetTcpGenericConnect(err,addr,port,source_addr,
            ANET_CONNECT_NONBLOCK|ANET_CONNECT_BE_BINDING);
}
//unix的通用连接
int anetUnixGenericConnect(char *err, char *path, int flags)
{
    int s;
    struct sockaddr_un sa;

    if ((s = anetCreateSocket(err,AF_LOCAL)) == ANET_ERR)
        return ANET_ERR;

    sa.sun_family = AF_LOCAL;
    strncpy(sa.sun_path,path,sizeof(sa.sun_path)-1);
    if (flags & ANET_CONNECT_NONBLOCK) {
        if (anetNonBlock(err,s) != ANET_OK)
            return ANET_ERR;
    }
    if (connect(s,(struct sockaddr*)&sa,sizeof(sa)) == -1) {
        if (errno == EINPROGRESS &&
            flags & ANET_CONNECT_NONBLOCK)
            return s;

        anetSetError(err, "connect: %s", strerror(errno));
        close(s);
        return ANET_ERR;
    }
    return s;
}
//下面是unix地址族的连接
int anetUnixConnect(char *err, char *path)
{
    return anetUnixGenericConnect(err,path,ANET_CONNECT_NONE);
}
int anetUnixNonBlockConnect(char *err, char *path)
{
    return anetUnixGenericConnect(err,path,ANET_CONNECT_NONBLOCK);
}
/* Like read(2) but make sure 'count' is read before to return (unless error or EOF condition is encountered) 读fd的方法，按照字节数读*/
int anetRead(int fd, char *buf, int count)
{
    ssize_t nread, totlen = 0;
    while(totlen != count) {
        nread = read(fd,buf,count-totlen);
        if (nread == 0) return totlen;
        if (nread == -1) return -1;
        totlen += nread;
        buf += nread;
    }
    return totlen;
}

/* Like write(2) but make sure 'count' is written before to return (unless error is encountered) 写fd方法，按照自写书写*/
int anetWrite(int fd, char *buf, int count)
{
    ssize_t nwritten, totlen = 0;
    while(totlen != count) {
        nwritten = write(fd,buf,count-totlen);
        if (nwritten == 0) return totlen;
        if (nwritten == -1) return -1;
        totlen += nwritten;
        buf += nwritten;
    }
    return totlen;
}
//listen方法,包含bind绑定和监听listen
static int anetListen(char *err, int s, struct sockaddr *sa, socklen_t len, int backlog) {
    if (bind(s,sa,len) == -1) {
        anetSetError(err, "bind: %s", strerror(errno));
        close(s);
        return ANET_ERR;
    }

    if (listen(s, backlog) == -1) {
        anetSetError(err, "listen: %s", strerror(errno));
        close(s);
        return ANET_ERR;
    }
    return ANET_OK;
}
//设置只支持ipv6
static int anetV6Only(char *err, int s) {
    int yes = 1;
    if (setsockopt(s,IPPROTO_IPV6,IPV6_V6ONLY,&yes,sizeof(yes)) == -1) {
        anetSetError(err, "setsockopt: %s", strerror(errno));
        close(s);
        return ANET_ERR;
    }
    return ANET_OK;
}
//创建tcp服务
static int _anetTcpServer(char *err, int port, char *bindaddr, int af, int backlog)
{
    int s = -1, rv;
    char _port[6];  /* strlen("65535") */
    struct addrinfo hints, *servinfo, *p;

    snprintf(_port,6,"%d",port);
    memset(&hints,0,sizeof(hints));
    hints.ai_family = af;
    hints.ai_socktype = SOCK_STREAM;
    hints.ai_flags = AI_PASSIVE;    /* No effect if bindaddr != NULL 如果绑定地址的话没有效果*/

    if ((rv = getaddrinfo(bindaddr,_port,&hints,&servinfo)) != 0) {
        anetSetError(err, "%s", gai_strerror(rv));
        return ANET_ERR;
    }
    for (p = servinfo; p != NULL; p = p->ai_next) {
        if ((s = socket(p->ai_family,p->ai_socktype,p->ai_protocol)) == -1)
            continue;

        if (af == AF_INET6 && anetV6Only(err,s) == ANET_ERR) goto error;
        if (anetSetReuseAddr(err,s) == ANET_ERR) goto error;
        if (anetListen(err,s,p->ai_addr,p->ai_addrlen,backlog) == ANET_ERR) goto error;
        goto end;
    }
    if (p == NULL) {
        anetSetError(err, "unable to bind socket, errno: %d", errno);
        goto error;
    }

error:
    if (s != -1) close(s);
    s = ANET_ERR;
end:
    freeaddrinfo(servinfo);
    return s;
}
//tcp服务的属性
int anetTcpServer(char *err, int port, char *bindaddr, int backlog)
{
    return _anetTcpServer(err, port, bindaddr, AF_INET, backlog);
}
int anetTcp6Server(char *err, int port, char *bindaddr, int backlog)
{
    return _anetTcpServer(err, port, bindaddr, AF_INET6, backlog);
}
//unixserver
int anetUnixServer(char *err, char *path, mode_t perm, int backlog)
{
    int s;
    struct sockaddr_un sa;

    if ((s = anetCreateSocket(err,AF_LOCAL)) == ANET_ERR)
        return ANET_ERR;

    memset(&sa,0,sizeof(sa));
    sa.sun_family = AF_LOCAL;
    strncpy(sa.sun_path,path,sizeof(sa.sun_path)-1);
    if (anetListen(err,s,(struct sockaddr*)&sa,sizeof(sa),backlog) == ANET_ERR)
        return ANET_ERR;
    if (perm)
        chmod(sa.sun_path, perm);
    return s;
}
//anet通用accept
static int anetGenericAccept(char *err, int s, struct sockaddr *sa, socklen_t *len) {
    int fd;
    while(1) {
        fd = accept(s,sa,len);
        if (fd == -1) {
            if (errno == EINTR)//是被信号打断的
                continue;
            else {
                anetSetError(err, "accept: %s", strerror(errno));
                return ANET_ERR;
            }
        }
        break;
    }
    return fd;
}
//tcpAccept
int anetTcpAccept(char *err, int s, char *ip, size_t ip_len, int *port) {
    int fd;
    struct sockaddr_storage sa;
    socklen_t salen = sizeof(sa);
    if ((fd = anetGenericAccept(err,s,(struct sockaddr*)&sa,&salen)) == -1)
        return ANET_ERR;

    if (sa.ss_family == AF_INET) {
        struct sockaddr_in *s = (struct sockaddr_in *)&sa;
        if (ip) inet_ntop(AF_INET,(void*)&(s->sin_addr),ip,ip_len);
        if (port) *port = ntohs(s->sin_port);
    } else {
        struct sockaddr_in6 *s = (struct sockaddr_in6 *)&sa;
        if (ip) inet_ntop(AF_INET6,(void*)&(s->sin6_addr),ip,ip_len);
        if (port) *port = ntohs(s->sin6_port);
    }
    return fd;
}
//unixAccept
int anetUnixAccept(char *err, int s) {
    int fd;
    struct sockaddr_un sa;
    socklen_t salen = sizeof(sa);
    if ((fd = anetGenericAccept(err,s,(struct sockaddr*)&sa,&salen)) == -1)
        return ANET_ERR;

    return fd;
}
//获取连接名称
int anetPeerToString(int fd, char *ip, size_t ip_len, int *port) {
    struct sockaddr_storage sa;
    socklen_t salen = sizeof(sa);

    if (getpeername(fd,(struct sockaddr*)&sa,&salen) == -1) goto error;
    if (ip_len == 0) goto error;

    if (sa.ss_family == AF_INET) {
        struct sockaddr_in *s = (struct sockaddr_in *)&sa;
        if (ip) inet_ntop(AF_INET,(void*)&(s->sin_addr),ip,ip_len);
        if (port) *port = ntohs(s->sin_port);
    } else if (sa.ss_family == AF_INET6) {
        struct sockaddr_in6 *s = (struct sockaddr_in6 *)&sa;
        if (ip) inet_ntop(AF_INET6,(void*)&(s->sin6_addr),ip,ip_len);
        if (port) *port = ntohs(s->sin6_port);
    } else if (sa.ss_family == AF_UNIX) {
        if (ip) strncpy(ip,"/unixsocket",ip_len);
        if (port) *port = 0;
    } else {
        goto error;
    }
    return 0;

error:
    if (ip) {
        if (ip_len >= 2) {
            ip[0] = '?';
            ip[1] = '\0';
        } else if (ip_len == 1) {
            ip[0] = '\0';
        }
    }
    if (port) *port = 0;
    return -1;
}

/* Format an IP,port pair into something easy to parse. If IP is IPv6 (matches for ":"), the ip is surrounded by []. IP and port are just separated by colons. This the standard to display addresses within Redis. 将ip，端口对格式化为易于解析的东西，如果ip是ipv6，则ip被[]保卫，ip和端口只用于冒号分开，这是在redis中显示地址的标准*/
int anetFormatAddr(char *buf, size_t buf_len, char *ip, int port) {
    return snprintf(buf,buf_len, strchr(ip,':') ?
           "[%s]:%d" : "%s:%d", ip, port);
}
/* Like anetFormatAddr() but extract ip and port from the socket's peer. 从套接字的同行提取ip和端口*/
int anetFormatPeer(int fd, char *buf, size_t buf_len) {
    char ip[INET6_ADDRSTRLEN];
    int port;

    anetPeerToString(fd,ip,sizeof(ip),&port);
    return anetFormatAddr(buf, buf_len, ip, port);
}
//获取连接名称
int anetSockName(int fd, char *ip, size_t ip_len, int *port) {
    struct sockaddr_storage sa;
    socklen_t salen = sizeof(sa);

    if (getsockname(fd,(struct sockaddr*)&sa,&salen) == -1) {
        if (port) *port = 0;
        ip[0] = '?';
        ip[1] = '\0';
        return -1;
    }
    if (sa.ss_family == AF_INET) {
        struct sockaddr_in *s = (struct sockaddr_in *)&sa;
        if (ip) inet_ntop(AF_INET,(void*)&(s->sin_addr),ip,ip_len);
        if (port) *port = ntohs(s->sin_port);
    } else {
        struct sockaddr_in6 *s = (struct sockaddr_in6 *)&sa;
        if (ip) inet_ntop(AF_INET6,(void*)&(s->sin6_addr),ip,ip_len);
        if (port) *port = ntohs(s->sin6_port);
    }
    return 0;
}
//按格式获取连接名称
int anetFormatSock(int fd, char *fmt, size_t fmt_len) {
    char ip[INET6_ADDRSTRLEN];
    int port;

    anetSockName(fd,ip,sizeof(ip),&port);
    return anetFormatAddr(fmt, fmt_len, ip, port);
}