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	简介	R/W	具体说明
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
	SO_ERROR	Get and clear the pending socket error.	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(7)	TCP_NODELAY	Turn off Nagle's algorithm.
	TCP_MAXSEG	Limit MSS
	TCP_KEEPINTVL	Interval between keepalives
	TCP_USER_TIMEOUT	How long for loss retry before timeout		it specifies the maximum amount of time in milliseconds that transmitted data may remain unacknowledged, or buffered data may remain untransmitted (due to zero window size) before TCP will forcibly close the corresponding connection and return ETIMEDOUT to the application. 已经发送的包仍未被确认-未收到对应的ACK（发送数据后启动计时）或缓冲区内的数据仍未发送-对方缓冲已满（处于zero window size 启动计时）的最大时间。超时后连接被forcibly 关闭，返回错误码为ETIMEOUT

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