使用splice實現高效的代理服務器 - myd620－IT工程師數位筆記本

文章出處

很多網絡應用場景下，當原設備與目標設備無法直接建立連接時，這時就需要一臺代理服務器進行中轉。代理服務器只需要將來自源設備的報文原封不動的轉發給目標設備，而并不需要知道報文的具體內容。在這種情況下，服務器就沒必要將客戶端的報文讀出來。每讀取一次都需要從內核態到用戶態的一次拷貝，在流量密集型的應用中，這樣做顯然很消耗服務器性能。而splice就是為了解決這個問題，它實現了不同文件描述符之間的0拷貝操作。關于splice函數的描述如下：

ssize_t splice(int fd_in, loff_t* off_in,int fd_out, loff_t* off_out, size_t len, unsigned int flags);

fd_in參數是帶輸入的文件描述符

off_in表示從輸入數據流的何處開始讀取數據，如果fd_in是管道文件描述符，則必須設置為NULL，表示從0開始

fd_out/off_out 表示輸出的文件描述符與偏移

len表示要讀取的長度

flags 標志，常用的兩個標志SPLICE_F_NONBLOCK，表示非阻塞的splice操作，但要依賴于文件描述符本身的阻塞狀態；SPLICE_F_MORE表示給內核一個提示，后續splice調用將讀取更多數據

使用splice時，fd_in于fd_out必須至少有一個是管道文件描述符

下面給出一個demo，實現兩個客戶端之間的報文透傳

服務器代碼：

#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <assert.h>
#include <stdio.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>
#include <fcntl.h>
#include <stdlib.h>
#include <sys/epoll.h>
#include <pthread.h>

#define MAX_EVENT_NUMBER 1024
#define BUFFER_SIZE 10

int connfd[2] = {0};

int setnonblocking( int fd )
{
    int old_option = fcntl( fd, F_GETFL );
    int new_option = old_option | O_NONBLOCK;
    fcntl( fd, F_SETFL, new_option );
    return old_option;
}

void addfd( int epollfd, int fd, bool enable_et )
{
    epoll_event event;
    event.data.fd = fd;
    event.events = EPOLLIN;
    if( enable_et )
    {
        event.events |= EPOLLET;
    }
    epoll_ctl( epollfd, EPOLL_CTL_ADD, fd, &event );
    setnonblocking( fd );
}

void lt( epoll_event* events, int number, int epollfd, int listenfd )
{
    char buf[ BUFFER_SIZE ];
    for ( int i = 0; i < number; i++ )
    {
        int sockfd = events[i].data.fd;
        if ( sockfd == listenfd )
        {
            static int conntimes = 0;
            struct sockaddr_in client_address;
            socklen_t client_addrlength = sizeof( client_address );
            int fd = accept( listenfd, ( struct sockaddr* )&client_address, &client_addrlength );
            addfd( epollfd, fd, false );
            if(conntimes <= 1)
            {
                connfd[conntimes] = fd;
            }
            conntimes++;
            printf("new conn, %d\n",fd);
        }
        else if ( events[i].events & EPOLLIN  )
        {
            int pipefd[2];
            pipe(pipefd);
            if(sockfd == connfd[0])
            {
                splice(connfd[0], NULL, pipefd[1], NULL, 4096,SPLICE_F_MORE);
                splice(pipefd[0], NULL, connfd[1], NULL, 4096,SPLICE_F_MORE);
            }
            else if(sockfd == connfd[1])
            {
                splice(connfd[1], NULL, pipefd[1], NULL, 4096,SPLICE_F_MORE); 
                splice(pipefd[0], NULL, connfd[0], NULL, 4096,SPLICE_F_MORE); 
            }
            else
            {
                int recvlen =  read(sockfd,buf,BUFFER_SIZE-1);
                buf[recvlen] = 0;
                printf("recv buf : %s\n",buf);
            }
            close(pipefd[0]);
            close(pipefd[1]);
        }
        else
        {
            printf( "something else happened \n" );
        }
    }
}



int main( int argc, char* argv[] )
{
    if( argc <= 2 )
    {
        printf( "usage: %s ip_address port_number\n", basename( argv[0] ) );
        return 1;
    }
    const char* ip = argv[1];
    int port = atoi( argv[2] );

    int ret = 0;
    struct sockaddr_in address;
    bzero( &address, sizeof( address ) );
    address.sin_family = AF_INET;
    inet_pton( AF_INET, ip, &address.sin_addr );
    address.sin_port = htons( port );

    int listenfd = socket( PF_INET, SOCK_STREAM, 0 );
    assert( listenfd >= 0 );

    ret = bind( listenfd, ( struct sockaddr* )&address, sizeof( address ) );
    assert( ret != -1 );

    ret = listen( listenfd, 5 );
    assert( ret != -1 );

    epoll_event events[ MAX_EVENT_NUMBER ];
    int epollfd = epoll_create( 5 );
    assert( epollfd != -1 );
    addfd( epollfd, listenfd, true );

    while( 1 )
    {
        int ret = epoll_wait( epollfd, events, MAX_EVENT_NUMBER, -1 );
        if ( ret < 0 )
        {
            printf( "epoll failure\n" );
            break;
        }
        lt( events, ret, epollfd, listenfd );
    }
    close( listenfd );
    return 0;
}

客戶端代碼：

#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <assert.h>
#include <stdio.h>
#include <unistd.h>
#include <string.h>
#include <stdlib.h>
#include <poll.h>
#include <fcntl.h>


int connectserver(const char *ip, int port)
{
    int rcv_size = 0;
    size_t optlen = sizeof(int);
    struct sockaddr_in server_address;
    bzero( &server_address, sizeof( server_address ) );
    server_address.sin_family = AF_INET;
    inet_pton( AF_INET, ip, &server_address.sin_addr );
    server_address.sin_port = htons( port );
    int sockfd = socket( PF_INET, SOCK_STREAM, 0 );
    assert( sockfd >= 0 );
    if ( connect( sockfd, ( struct sockaddr* )&server_address, sizeof( server_address ) ) < 0 )
    {
        printf( "connection failed\n" );
        close( sockfd );
        return -1;
    }
    return sockfd;
}


int main( int argc, char* argv[] )
{
    if( argc <= 2 )
    {
        printf( "usage: %s ip_address port_number\n",  argv[0]  );
        return 1;
    }
    const char* ip = argv[1];
    int port = atoi( argv[2] );
    int pipefd[2];
    pipe(pipefd);
    int sockfd = connectserver(ip,port);
    assert(sockfd >= 0);
    fd_set readsets;
    FD_ZERO(&readsets);
    while(1)
    {
        FD_SET(STDIN_FILENO,&readsets);
        FD_SET(sockfd, &readsets);
        int ret = select(sockfd+1 , &readsets,NULL,NULL,NULL);
        assert(ret >= 0);
        if(FD_ISSET(STDIN_FILENO, &readsets))
        {
            splice(STDIN_FILENO, NULL, pipefd[1], NULL, 4096,SPLICE_F_MORE); 
            splice(pipefd[0], NULL, sockfd, NULL, 4096,SPLICE_F_MORE); 
        }
        else if(FD_ISSET(sockfd,&readsets))
        {
            splice(sockfd, NULL, pipefd[1], NULL, 4096,SPLICE_F_MORE); 
            splice(pipefd[0], NULL, STDOUT_FILENO, NULL, 4096,SPLICE_F_MORE); 
        }
    }
    close(pipefd[0]);
    close(pipefd[1]);
    close(sockfd);
    return 1;
}