popo

server-api-socket

Posted on Edited on

原型

create an endpoint for communication

创建一个套接字用于通信

函数原型
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
// domain
//      The  domain argument specifies a communication domain; this selects the proto‐col family which will be used for communication.
//      需要指定的通信协议族(protocol family)
//          AF_UNIX, AF_LOCAL
//              Local communication
//              UNIX 进程通信协议
//          AF_INET
//              IPv4 Internet protocols
//              Ipv4网络协议
//          AF_INET6
//              IPv6 Internet protocols
//              Ipv6 网络协议
//          AF_IPX
//              IPX - Novell protocols
//              IPX-Novell协议
//          AF_NETLINK
//              Kernel user interface device
//              核心用户接口装置
//          AF_X25
//              ITU-T X.25 / ISO-8208 protocol
//              X.25/ISO-8208 协议
//          AF_AX25
//              Amateur radio AX.25 protocol
//              业余无线AX.25协议
//          AF_ATMPVC
//              Access to raw ATM PVCs
//              存取原始ATM PVCs
//          AF_APPLETALK
//              Appletalk
//              appletalk（DDP）协议
//          AF_PACKET
//              Low level packet interface
//              初级封包接口
// type
//      指定socket类型,流式套接字SOCK_STREAM,数据报套接字SOCK_DGRAM,原始套接字SOCK_RAW
//          SOCK_STREAM
//              Provides sequenced, reliable, two-way,  connection-based  byte streams. An  out-of-band  data transmission mechanism may be supported.
//              提供双向连续且可信赖的数据流，即TCP。支持OOB 机制，在所有数据传送前必须使用connect()来建立连线状态。
//          SOCK_DGRAM
//              Supports datagrams (connectionless, unreliable messages  of  a fixed maximum length).
//              使用不连续不可信赖的数据包连接(udp)
//          SOCK_SEQPACKET
//              Provides  a sequenced, reliable, two-way connection-based data transmission path for datagrams of  fixed  maximum  length;  a consumer  is required to read an entire packet with each input system call.
//              提供连续可信赖的数据包连接
//          SOCK_RAW
//              Provides raw network protocol access.
//              提供原始网络协议存取
//          SOCK_RDM
//              Provides a reliable datagram layer  that  does  not  guarantee ordering.
//              提供可信赖的数据包连接
//          SOCK_PACKET
//              Obsolete   and  should  not  be  used  in  new  programs
//              提供和网络驱动程序直接通信。
//          SOCK_NONBLOCK
//              Set  the  O_NONBLOCK  file  status  flag  on the new open file description.  Using this flag saves extra calls to fcntl(2) to achieve the same result.
//              给描述符加上O_NONBLOCK标识，省去fcntl的操作
//          SOCK_CLOEXEC
//              Set  the  close-on-exec  (FD_CLOEXEC)  flag  on  the  new file descriptor.
//              给描述符加上FD_CLOEXEC标识
// protocol
//      The protocol specifies a particular protocol to be used with the socket.  Normally only a single protocol exists to support a particular socket type within a  given  protocol family, in which case protocol can be specified as 0.  How‐ever, it is possible that many protocols may exist, in which case a particular protocol must be specified in this manner.  The protocol number to use is spe‐cific to the “communication domain” in which communication is to  take  place; see  protocols(5).   See getprotoent(3) on how to map protocol name strings to protocol numbers.
//      该协议指定了与套接字一起使用的特定协议。 通常，只有一个协议支持给定协议族中的特定套接字类型，在这种情况下协议可以指定为0.但是，可能存在许多协议(如原始套接口)，在这种情况下必须指定特定协议。
//
// return:
//      On success, a file descriptor for the new socket is returned.  On error, -1 is returned, and errno is set appropriately.
//      成功返回一个文件描述符，失败返回-1，并设置errno的值
//
// error:
//      EACCES
//          Permission  to create a socket of the specified type and/or protocol is denied.
//          权限不足，无法建立type或protocol指定的协议
//      EAFNOSUPPORT
//          The implementation does not support the specified address family.
//          该实现不支持指定的地址族。
//      EINVAL
//          Unknown protocol, or protocol family not available.
//          Invalid flags in type.
//          参数domain/type/protocol不合法
//      EMFILE
//          Process file table overflow.
//          进程文件表溢出，无法再建立新的socket
//      ENFILE
//          The system limit on the total number of open files has been reached.
//          系统对打开文件总数的限制已经达到
//      ENOBUFS or ENOMEM
//          Insufficient memory is available.  The socket cannot be  created  until sufficient resources are freed.
//          内存不足
//      EPROTONOSUPPORT
//          The  protocol  type  or  the specified protocol is not supported within this domain.
//          参数domain指定的类型不支持参数type或protocol指定的协议
//
int socket(int domain, int type, int protocol);

AF_XXX与PF_XXX

AF_前缀代表地址族，PF_前缀代表协议族。历史上曾经有这样的想法；单个协议族可以支持多个地址族，PF_值用来创建套机接口，而AF_值用于套接口地址结构。但实际上，支持多个地址族的协议族从来就未出现过，而且头文件<sys/socket.h>中定义的PF_值总是与次协议的AF_值相对。尽管这种相等关系并不保证永远正确，若有人试图给已有的协议改变这种约定，则许多现存代码都将崩溃。为与现存代码保持一致，推荐使用AF_值

使用参考

支持一个客户端的回射服务器
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
#include<unistd.h>
#include<sys/types.h>
#include<sys/socket.h>
#include<netinet/in.h>
#include<arpa/inet.h>

#include<stdlib.h>
#include<stdio.h>
#include<errno.h>
#include<string.h>

#define ERR_EXIT(m)\
    do\
    {\
        perror(m); \
        exit(EXIT_FAILURE); \
    }while (0)

int main(void)
{
    int listenfd;
    /*if ((listenfd = socket(PF_INET, SOCK_STREAM, 0))<0)*/
    if ((listenfd = socket(PF_INET, SOCK_STREAM, IPPROTO_TCP)) < 0)
        ERR_EXIT("socket");

    struct sockaddr_in servaddr;
    memset(&servaddr, 0, sizeof(servaddr));
    servaddr.sin_family = AF_INET;
    servaddr.sin_port = htons(5188);
    // inet_aton("127.0.0.1", &servaddr.sin_addr);
    // servaddr.sin_addr.s_addr = htonl(INADDR_ANY);
    // servaddr.sin_addr.s_addr = inet_addr("127.0.0.1");
    inet_pton(AF_INET, "127.0.0.1", &servaddr.sin_addr);

    int on = 1;
    if(setsockopt(listenfd, SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)
        ERR_EXIT("SETSOCKOPT") ;

    if (bind(listenfd, (struct sockaddr*)&servaddr, sizeof(servaddr)) < 0)
        ERR_EXIT("BIND");

    if (listen(listenfd, SOMAXCONN) < 0)
        ERR_EXIT("LISTEN");

    struct sockaddr_in peeraddr;
    socklen_t peerlen = sizeof(peeraddr);
    int conn;
    if ((conn = accept(listenfd, (struct sockaddr*)&peeraddr, &peerlen)) < 0)
        ERR_EXIT("ACCEPT");

    char ip_addr[INET_ADDRSTRLEN] = {0};
    printf("ip=%s port=%d\n", inet_ntop(AF_INET, &peeraddr.sin_addr, ip_addr, INET_ADDRSTRLEN), ntohs(peeraddr.sin_port));

    char recvbuf[1024];
    while (1)
    {
        memset(recvbuf, 0, sizeof(recvbuf));
        int ret = read(conn, recvbuf, sizeof(recvbuf));
        fputs(recvbuf, stdout);
        write(conn, recvbuf, ret);
    }

    close(conn);
    close(listenfd) ;

    return 0;
}