1--Socket的多种可选项

Socket 拥有多种可选项，其可分为 SOL_SOCKET 层，IPPROTO_IP 层和IPPROTO_TCP 层等，一般通过 getsocketopt() 和 setsockopt() 函数进行获取和设置；

2--getsocketopt()

#include <sys/socket.h>
int getsockopt(int sock, int level, int optname, void* optval, socklen_t* optlen);
// 成功时返回 0，失败时返回 -1
// sock 用于查看选项 socket 的文件描述符
// level 表示要查看的可选项的协议层
// optname 表示要查看的可选项名
// optval 表示保存查看结果的缓冲地址值
// optlen 表示向第四个参数 optval 传递的缓冲大小，调用函数后，该变量中保存通过第四个参数返回的可选项信息的字节数

3--setsockopt()

#include <sys/socket.h>
int setsockopt(int sock, int level, int optname, const void* optval, socklen_t optlen);
// 成功时返回 0，失败时返回 -1
// sock 用于更改可选项 socket 的文件描述符
// level 表示要更改的可选项的协议层
// optname 表示要更改的可选项名
// optval 表示保存更改的选项信息的缓冲地址值
// optlen 表示向第四个参数 optval 传递的可选项信息的字节数

4--代码实例

① 基于 getsockopt() 函数，利用设置协议层为 SOL_SOCKET 和 SO_TYPE 可选项名来查看 SOCKET 的类型：

// gcc sock_type.c -o sock_type
// ./sock_type#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/socket.h>void error_handling(char *message){fputs(message, stderr);fputc('\n', stderr);exit(1);
}int main(int argc, char* argv[]){int tcp_sock, udp_sock;int sock_type;socklen_t optlen;int state;optlen = sizeof(sock_type);tcp_sock = socket(PF_INET, SOCK_STREAM, 0); // create tcp socketudp_sock = socket(PF_INET, SOCK_DGRAM, 0); // create udp socketprintf("SOCK_STREAM: %d \n", SOCK_STREAM);printf("SOCK_DGRAM: %d \n", SOCK_DGRAM);state = getsockopt(tcp_sock, SOL_SOCKET, SO_TYPE, (void*)&sock_type, &optlen);if(state){error_handling("getsockopt() error!");}printf("Socket type one: %d \n", sock_type);state = getsockopt(udp_sock, SOL_SOCKET, SO_TYPE, (void*)&sock_type, &optlen);if(state){error_handling("getsockopt() error!");}printf("Socket type two: %d \n", sock_type);}

② 通过可选项名为 SO_SNDBUF 和 SO_RCVBUF 来查看和设置 I/O 缓冲：

// gcc get_buf.c -o get_buf
// ./get_buf#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/socket.h>void error_handling(char *message){fputs(message, stderr);fputc('\n', stderr);exit(1);
}int main(int argc, char* argv[]){int sock;int snd_buf, rcv_buf, state;socklen_t len;sock = socket(PF_INET, SOCK_STREAM, 0);len = sizeof(snd_buf);state = getsockopt(sock, SOL_SOCKET, SO_SNDBUF, (void*)&snd_buf, &len);if(state){error_handling("getsockopt() error!"); }len = sizeof(rcv_buf);state = getsockopt(sock, SOL_SOCKET, SO_RCVBUF, (void*)&rcv_buf, &len);if(state){error_handling("getsockopt() error!"); }printf("Input buffer size: %d \n", rcv_buf);printf("Output buffer size: %d \n", snd_buf);return 0;    
}

// gcc set_buf.c -o set_buf
// ./set_buf#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/socket.h>void error_handling(char *message){fputs(message, stderr);fputc('\n', stderr);exit(1);
}int main(int argc, char* argv[]){int sock;int snd_buf = 1024*3, rcv_buf = 1024*3;int state;socklen_t len;sock = socket(PF_INET, SOCK_STREAM, 0);state = setsockopt(sock, SOL_SOCKET, SO_SNDBUF, (void*)&snd_buf, sizeof(snd_buf));if(state){error_handling("getsockopt() error!"); }state = setsockopt(sock, SOL_SOCKET, SO_RCVBUF, (void*)&rcv_buf, sizeof(rcv_buf));if(state){error_handling("getsockopt() error!"); }len = sizeof(snd_buf);state = getsockopt(sock, SOL_SOCKET, SO_SNDBUF, (void*)&snd_buf, &len);if(state){error_handling("getsockopt() error!"); }len = sizeof(rcv_buf);state = getsockopt(sock, SOL_SOCKET, SO_RCVBUF, (void*)&rcv_buf, &len);if(state){error_handling("getsockopt() error!"); }printf("Input buffer size: %d \n", rcv_buf);printf("Output buffer size: %d \n", snd_buf);return 0; 
}

③ 通过更改 SO_REUSEADDR 的状态来将处于 Time-wait 状态的 SOCKET 端口号重新分配给新的 SOCKET：

// gcc reuseadr_eserver.c -o reuseadr_eserver
// ./reuseadr_eserver 9190#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <arpa/inet.h>
#include <sys/socket.h>#define TRUE 1
#define FALSE 0void error_handling(char *message){fputs(message, stderr);fputc('\n', stderr);exit(1);
}int main(int argc, char *argv[]){int serv_sock, clnt_sock;char message[30];int option, str_len;socklen_t optlen, clnt_adr_sz;struct sockaddr_in serv_adr, clnt_adr;if(argc != 2){printf("Usage : %s <port>\n", argv[0]);exit(1);}serv_sock = socket(PF_INET, SOCK_STREAM, 0);if(serv_sock == -1){error_handling("socket() error");}// set SO_REUSEADDR optlen = sizeof(option);option = TRUE;setsockopt(serv_sock, SOL_SOCKET, SO_REUSEADDR, (void*)&option, optlen);memset(&serv_adr, 0, sizeof(serv_adr));serv_adr.sin_family = AF_INET;serv_adr.sin_addr.s_addr = htonl(INADDR_ANY);serv_adr.sin_port = htons(atoi(argv[1]));if(bind(serv_sock, (struct sockaddr*)&serv_adr, sizeof(serv_adr)) == -1){error_handling("bind() error");}if(listen(serv_sock, 5) == -1){error_handling("listen() error");}clnt_adr_sz = sizeof(clnt_adr);clnt_sock = accept(serv_sock, (struct sockaddr*)&clnt_adr, &clnt_adr_sz);while((str_len = read(clnt_sock, message, sizeof(message))) !=0){write(clnt_sock, message, str_len);write(1, message, str_len);}close(clnt_sock);close(serv_sock);return 0;
}