前两天重装VPS的时候突然发现Shadowsocks支持[TCP Fast Open 特性],找了会资料才理解这个.

TCP Fast Open简称TFO,是谷歌为了加速网络传输速度和效率,其特性就是在三次握手的第一次握手时客户端发送(syn+TFO cookie)包;服务端收到后,如果其支持TFO则发出了(ack+syn+TFO cookie)回应包后,立即就开始发数据包,缩短了TTFB的时间;如果服务端不支持TFO,则会发送正常的(syn+ack)回应包,走正常的三次握手流程.

因此,使用TFO的特性需要两端都支持TFO.客户端侧需要Linux Kernel 3.6及以上版本;而服务端侧则是Linux Kernel 3.7及更高版本才支持.并且服务端侧需要设置内核的net.ipv4.tcp_fastopen参数为2或3.

net.ipv4.tcp_fastopen参数释义:

1 表示客户端请求开启.
2 表示服务端请求开启.
3 表示客户端与服务端请求同时开启.

服务端使用命令:

echo "net.ipv4.tcp_fastopen=3" >> /etc/sysctl.conf
sysctl -p

客户端使用命令:

echo "net.ipv4.tcp_fastopen=1" >> /etc/sysctl.conf
sysctl -p

服务端代码:

#include <string.h>
#include <sys/types.h> /* See NOTES */
#include <sys/socket.h>
#include <netinet/in.h>
int main(){
    int portno = 5060;
    socklen_t clilen;
    char buffer[256];
    struct sockaddr_in serv_addr, cli_addr;
    int cfd;
    int sfd = socket(AF_INET, SOCK_STREAM, 0);   // Create socket
    bzero((char *) &serv_addr, sizeof(serv_addr));
    serv_addr.sin_family = AF_INET;
    serv_addr.sin_addr.s_addr = INADDR_ANY;
    serv_addr.sin_port = htons(portno);
    bind(sfd, &serv_addr,sizeof(serv_addr));      // Bind to well known address
    int qlen = 5;                 // Value to be chosen by application
    int err = setsockopt(sfd, IPPROTO_TCP/*SOL_TCP*/, 23/*TCP_FASTOPEN*/, &qlen, sizeof(qlen));
    listen(sfd,1);                // Mark socket to receive connections
    cfd = accept(sfd, NULL, 0);   // Accept connection on new socket
    while(1){
        int len = read(cfd,buffer,256);
        if(len)
             printf("tcp fast open: %s\\n",buffer);
        else
             break;
        // read and write data on connected socket cfd
    }
    close(cfd);
}

客户端代码:
“`C
#include <sys/socket.h>
#include <netinet/in.h>
#include <netdb.h>
#include <errno.h>
int main(){
struct sockaddr_in serv_addr;
struct hostent *server;

char *data = "Hello, tcp fast open";
int data_len = strlen(data);

int sfd = socket(AF_INET, SOCK_STREAM, 0);
server = gethostbyname("localhost");

bzero((char *) &serv_addr, sizeof(serv_addr));
serv_addr.sin_family = AF_INET;
bcopy((char *)server->h_addr,
     (char *)&serv_addr.sin_addr.s_addr,
     server->h_length);
serv_addr.sin_port = htons(5060);
int len = sendto(sfd, data, data_len, 0x20000000/*MSG_FASTOPEN*/,
            (struct sockaddr *) &serv_addr, sizeof(serv_addr));
printf("error: %s\\n",strerror(errno));
close(sfd);
sleep(5);

}