9.1 套接字的多种可选项

mingStudent2025/11/29大约 3 分钟

9.1 套接字的多种可选项

可配置的选项

协议层	选项名	说明	R/W
SOL_SOCKET socket相关设置来源 `socket.h`	SO_DEBUG	Record debugging information.
	SO_ACCEPTCONN	Accept connections on socket.
	SO_REUSEADDR	Allow reuse of local addresses.
	SO_KEEPALIVE	Keep connections alive and send SIGPIPE when they die.
	SO_SNDBUF	Send buffer size.
	SO_RCVBUF	Receive buffer size.
	SO_TYPE	Compatible name for SO_STYLE.	R
IPPROTO_IP ip协议相关设置。来源 `in.h`	IP_TOS	int; IP type of service and precedence.
	IP_TTL	int; IP type of service and precedence.
	IP_MULTICAST_IF	in_addr; set/get IP multicast i/f
	IP_MULTICAST_TTL	unsigned char; set/get IP multicast ttl
	IP_MULTICAST_LOOP	bool; set/get IP multicast loopback
IPPROTO_TCP TCP 协议相关设置来源 `tcp.h`	TCP_NODELAY	Turn off Nagle's algorithm.
	TCP_MAXSEG	Limit MSS
	TCP_KEEPINTVL	Interval between keepalives

注：未说明R/W 的均为可读可写选项

get

       #include <sys/types.h>          /* See NOTES */
       #include <sys/socket.h>

       int getsockopt(int sockfd, int level, int optname,
                      void *optval, socklen_t *optlen);

参数	值	用途	说明
sockfd		socket file descriptor
level	SOL_SOCKET、IPPROTO_IP、IPPROTO_TCP		可配置选项按照协议分类，对于socket单独用SOL_SOCKET。
optname	SO_TYPE、IP_TTL	指定要配置的选项的名称
optval		identify a buffer in which the value for the requested option(s) are to be returned
optlen		a value-result argument, initially containing the size of the buffer pointed to by optval, and modified on return to indicate the actual size of the value returned.

	int tcp_sock, upd_sock;
    int sock_type;
    socklen_t optlen;

    tcp_sock = socket(PF_INET, SOCK_STREAM, 0);
    upd_sock = socket(PF_INET, SOCK_DGRAM, 0);

    printf("SOCK_STREAM: %d\n", SOCK_STREAM);
    printf("SOCK_DGRAM: %d\n", SOCK_DGRAM);

    int state;
    state = getsockopt(tcp_sock, SOL_SOCKET, SO_TYPE, &sock_type, &optlen);
    if(state == -1)
        unix_error("getsockopt error for TCP socket");
    else
        printf("TCP socket type: %d\n", sock_type);

效果：

SOCK_STREAM: 1
SOCK_DGRAM: 2
TCP socket type: 1
UDP socket type: 2

set

读写SO_SNBUF

实现：

    int sock = socket(PF_INET, SOCK_STREAM, 0);
    socklen_t buf_size;
    socklen_t optlen = sizeof(buf_size);

    int state;
    state = getsockopt(sock, SOL_SOCKET, SO_SNDBUF, &buf_size, &optlen);
    if(state == -1)
        unix_error("getsockopt error for TCP socket");
    else
        printf("TCP sock sendbuffer size : %d\n", buf_size);

    buf_size = 0;
    state = setsockopt(sock, SOL_SOCKET, SO_SNDBUF, &buf_size, optlen);
    //...

行号	功能	说明
13	设置sendbuffer 的大小为0	setsockopt 最后一个参数的类型是 `socklen_t optlen`，指示设置的参数的内存大小

效果：

TCP sock sendbuffer size : 16384
TCP sock sendbuffer size changed to : 4608

设置过后重新通过get获取sendbuffer 的大小，返回的结果和设置的值-0 不一致。

设置值	实际值
5000	10000
4609	9218
4607	9214
1000	4608