C language: explain in detail the two local communication methods based on TCP and UDP

One . Local communication (UNIX Domain socket )

1.1 Concept

socket It can also be used for local communication to create sockets using local protocols PF_UNIX( or PF_LOCAL) It is divided into streaming socket and user datagram socket , The difference is whether there is a connection or not, which is often used for front and back process communication .

The mechanism used

struct sockaddr_un {
    sa_family_t sun_family;               /* AF_UNIX */
    char        sun_path[108];            /*  Path and file name  */
};

1.2TCP Local communication process

The server ：

Create socket socket( )

Populate the server local information structure sockaddr_un

Bind the socket to the server local information structure bind( )

Set the socket to passive listening state listen( )

Block the connection request waiting for the client accept( )

communicate recv( )/send( ) or read( )/write( )

client ：

Create socket socket( )

Populate the server local information structure sockaddr_un

Send the connection request of the client connect( )

communicate send( )/recv( )

1.3 Code implementation

Code instructions ： This is a code for a cyclic response , To explain local communication

Server code
 

#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/un.h>
#include <string.h>
#include <unistd.h>
#include <stdlib.h>
#include <arpa/inet.h>

#define ERRLOG(errmsg) do{\
        printf("%s:%s:%d --", __FILE__, __func__, __LINE__);\
        perror(errmsg);\
        exit(-1);\
    }while(0)

int main(int argc, const char *argv[]){
    if(2 != argc){
        printf("Usage : %s <filename>\n", argv[0]);
        return -1;
    }

    // Create a streaming socket 
    int sockfd = socket(AF_UNIX, SOCK_STREAM, 0);
    if(-1 == sockfd){
        ERRLOG("socket error");
    }

    // Fill information local information structure 
    struct sockaddr_un serveraddr;
    memset(&serveraddr, 0, sizeof(serveraddr));
    serveraddr.sun_family = AF_UNIX;
    strcpy(serveraddr.sun_path, argv[1]);

    socklen_t serveraddr_len = sizeof(serveraddr);

    // binding 
    if(-1 == bind(sockfd, (struct sockaddr *)&serveraddr, serveraddr_len)){
        ERRLOG("bind error");
    }

    // monitor 
    if(-1 == listen(sockfd, 5)){
        ERRLOG("listen error");
    }

    // Define the structure to save the information of the other party 
    struct sockaddr_un clientaddr;
    memset(&clientaddr, 0, sizeof(clientaddr));
    socklen_t clientaddr_len = sizeof(clientaddr);

    int acceptfd = accept(sockfd, (struct sockaddr *)&clientaddr, &clientaddr_len);
    if(-1 == acceptfd){
        ERRLOG("accept error");
    }
    printf(" client [%s] Connect to the server \n", clientaddr.sun_path);

    char buff[128] = {0};
    while(1){
        if(-1 == recv(acceptfd, buff, 128, 0)){
            ERRLOG("recv error");
        }
        printf(" client [%s] Send data [%s]\n", clientaddr.sun_path, buff);
        strcat(buff, "--hqyj");
        if(-1 == send(acceptfd, buff, 128, 0)){
            ERRLOG("send error");
        }
        memset(buff, 0, 128);
    }
    close(acceptfd);

    close(sockfd);

    return 0;
}

client

#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/un.h>
#include <string.h>
#include <unistd.h>
#include <stdlib.h>
#include <arpa/inet.h>

#define ERRLOG(errmsg) do{\
        printf("%s:%s:%d --", __FILE__, __func__, __LINE__);\
        perror(errmsg);\
        exit(-1);\
    }while(0)

int main(int argc, const char *argv[]){
    if(2 != argc){
        printf("Usage : %s <filename>\n", argv[0]);
        return -1;
    }

    // Create a streaming socket 
    int sockfd = socket(AF_UNIX, SOCK_STREAM, 0);
    if(-1 == sockfd){
        ERRLOG("socket error");
    }

    // Populate the server local information structure 
    struct sockaddr_un serveraddr;
    memset(&serveraddr, 0, sizeof(serveraddr));
    serveraddr.sun_family = AF_UNIX;
    strcpy(serveraddr.sun_path, argv[1]);

    socklen_t serveraddr_len = sizeof(serveraddr);


    // Define the client local information structure 
    struct sockaddr_un clientaddr;
    memset(&clientaddr, 0, sizeof(clientaddr));
    clientaddr.sun_family = AF_UNIX;
    strcpy(clientaddr.sun_path,"tcp_client_file");
    socklen_t clientaddr_len = sizeof(clientaddr);

    // Client needs binding , Otherwise, the server cannot receive the file name of the client 
    if(-1 == bind(sockfd, (struct sockaddr *)&clientaddr, clientaddr_len)){
        ERRLOG("bind error");
    }

    if(-1 == connect(sockfd, (struct sockaddr *)&serveraddr, serveraddr_len)){
        ERRLOG("accept error");
    }
    printf(" Successfully connected to the server \n");

    char buff[128] = {0};
    while(1){
        fgets(buff, 128, stdin);
        buff[strlen(buff)-1] = '\0';
        if(-1 == send(sockfd, buff, 128, 0)){
            ERRLOG("send error");
        }
        if(-1 == recv(sockfd, buff, 128, 0)){
            ERRLOG("recv error");
        }
        printf(" The reply [%s]\n", buff);
        memset(buff, 0, 128);
    }

    close(sockfd);

    return 0;
}

Two UDP Local communication

2.1 technological process

The server ：

Create socket socket( )

Populate the server local information structure sockaddr_un

Bind the socket to the server local information structure bind( )

communicate recvfrom( ) / sendto( )

client ：

Create socket socket( )

Fill in the client local information structure sockaddr_un

Bind the socket to the client local information structure bind()

Populate the server local information structure sockaddr_un

communicate sendto( ) / recvfrom( )

2.2 Code implementation

The server

#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/un.h>
#include <string.h>
#include <unistd.h>
#include <stdlib.h>
#include <arpa/inet.h>

#define ERRLOG(errmsg) do{\
        printf("%s:%s:%d --", __FILE__, __func__, __LINE__);\
        perror(errmsg);\
        exit(-1);\
    }while(0)

int main(int argc, const char *argv[]){
    if(2 != argc){
        printf("Usage : %s <filename>\n", argv[0]);
        return -1;
    }

    // Create user datagram socket 
    int sockfd = socket(AF_UNIX, SOCK_DGRAM, 0);
    if(-1 == sockfd){
        ERRLOG("socket error");
    }

    // Fill in the local information structure of server information 
    struct sockaddr_un serveraddr;
    memset(&serveraddr, 0, sizeof(serveraddr));
    serveraddr.sun_family = AF_UNIX;
    strcpy(serveraddr.sun_path, argv[1]);

    socklen_t serveraddr_len = sizeof(serveraddr);

    // binding 
    if(-1 == bind(sockfd, (struct sockaddr *)&serveraddr, serveraddr_len)){
        ERRLOG("bind error");
    }

    // Define the structure to save the information of the other party 
    struct sockaddr_un clientaddr;
    memset(&clientaddr, 0, sizeof(clientaddr));
    socklen_t clientaddr_len = sizeof(clientaddr);

    char buff[128] = {0};
    while(1){
        if(-1 == recvfrom(sockfd, buff, 128, 0, (struct sockaddr *)&clientaddr, &clientaddr_len)){
            ERRLOG("recv error");
        }
        printf(" client [%s] Send data [%s]\n", clientaddr.sun_path, buff);
        strcat(buff, "--hqyj");
        if(-1 == sendto(sockfd, buff, 128, 0, (struct sockaddr *)&clientaddr, clientaddr_len)){
            ERRLOG("send error");
        }
        memset(buff, 0, 128);
    }

    close(sockfd);

    return 0;
}

client

#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/un.h>
#include <string.h>
#include <unistd.h>
#include <stdlib.h>
#include <arpa/inet.h>

#define ERRLOG(errmsg) do{\
        printf("%s:%s:%d --", __FILE__, __func__, __LINE__);\
        perror(errmsg);\
        exit(-1);\
    }while(0)

int main(int argc, const char *argv[]){
    if(3 != argc){
        printf("Usage : %s <server_filename> <client_filename>\n", argv[0]);
        return -1;
    }

    // Create user datagram socket 
    int sockfd = socket(AF_LOCAL, SOCK_DGRAM, 0);
    if(-1 == sockfd){
        ERRLOG("socket error");
    }

    // Populate the server local information structure 
    struct sockaddr_un serveraddr;
    memset(&serveraddr, 0, sizeof(serveraddr));
    serveraddr.sun_family = AF_UNIX;
    strcpy(serveraddr.sun_path, argv[1]);

    socklen_t serveraddr_len = sizeof(serveraddr);


    // Define the client local information structure 
    struct sockaddr_un clientaddr;
    memset(&clientaddr, 0, sizeof(clientaddr));
    clientaddr.sun_family = AF_UNIX;
    strcpy(clientaddr.sun_path, argv[2]);
    socklen_t clientaddr_len = sizeof(clientaddr);

    // Client needs binding , Otherwise, the server cannot receive the file name of the client 
    if(-1 == bind(sockfd, (struct sockaddr *)&clientaddr, clientaddr_len)){
        ERRLOG("bind error");
    }

    char buff[128] = {0};
    while(1){
        fgets(buff, 128, stdin);
        buff[strlen(buff)-1] = '\0';
        if(-1 == sendto(sockfd, buff, 128, 0, (struct sockaddr *)&serveraddr, serveraddr_len)){
            ERRLOG("send error");
        }
        // because serveraddr No change.   So there is no need to save 
        if(-1 == recvfrom(sockfd, buff, 128, 0, NULL, NULL)){
            ERRLOG("recv error");
        }
        printf(" The reply [%s]\n", buff);
        memset(buff, 0, 128);
    }

    close(sockfd);

    return 0;
}