Socket programming 1: using fork() to realize the most basic concurrency mode

tcp_server.c

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

int main(int argc, char **argv)
{
    // create socket
    int socketServerListen = socket(AF_INET, SOCK_STREAM, 0);
    if (socketServerListen < 0) {
        perror("socket");
        exit(1);
    }

    struct sockaddr_in serverAddr;
    bzero(&serverAddr, sizeof(serverAddr));
    serverAddr.sin_family = AF_INET;

    // atoi,  Don't use atoi It can lead to connection refused.
    serverAddr.sin_port = htons(atoi(argv[2]));
    serverAddr.sin_addr.s_addr = inet_addr(argv[1]);

    // bind, notice: it use the standard struct: sockaddr, not sockaddr_in
    if (bind(socketServerListen, (struct sockaddr*)&serverAddr, sizeof(struct sockaddr)) < 0) {
        perror("bind");
        exit(2);
    }

    // listen
    if (listen(socketServerListen, 30) < 0) {
        perror("listen");
        exit(3);
    }

    struct sockaddr_in clientAddr;
    bzero(&clientAddr, sizeof(clientAddr));
    int connFd;

    // Invalid argument, if not initialized.
    //  If not initialized , stay accept China will directly report : Invalid argument.
    socklen_t clientAddrLen = 0;

    while (1) {
        // accpet was different with bind, the parameters 3 was socklen_t*, but not socklen_t.
        if (connFd = accept(socketServerListen, (struct sockaddr*)&clientAddr, &clientAddrLen) < 0) {
            perror("accept");
            continue;
        }

        printf("tcp_server: client addr is:%s, client port is:%d\n",
            inet_ntoa(clientAddr.sin_addr),  ntohs(clientAddr.sin_port));

        pid_t pid = fork();
        if (pid < 0) { // error
            perror("fork");
        } else if (pid == 0) { // child
            // in child, it should close the socketServerListen, keep the connFd.
            close(socketServerListen);
            char buf[1024] = {0};
            ssize_t len = 0;

            // read the data from the connFd
            while (len = read(connFd, buf, 1024) > 0) {
                printf("read the data:%s\n", buf);
                //write(connFd, buf, len);
            }
        } else {
            // in father, it should close the connFd, just keep the socketServerListen
            close(connFd);
        }
    }

    return 0;
}

tcp_client.c

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

int main(int argc, char **argv)
{
    // socket
    int clientSockFd = socket(AF_INET, SOCK_STREAM, 0);
    if (clientSockFd < 0) {
        perror("clientSockFd");
        exit(1);
    }

    struct sockaddr_in serverAddr;
    bzero(&serverAddr, sizeof(serverAddr));

    serverAddr.sin_family = AF_INET;

    // atoi, if not use this ,connect will fail.
    serverAddr.sin_port = htons(atoi(argv[2]));
    // use inet_addr to transfer the address
    serverAddr.sin_addr.s_addr = inet_addr(argv[1]);
    //serverAddr.sin_addr.s_addr = htons(INADDR_ANY);

    // connect
    if (connect(clientSockFd, (struct sockaddr*)&serverAddr, sizeof(struct sockaddr)) < 0) {
        perror("connect");
        exit(2);
    }

    // get the data from standard input. (keyboard)
    char buf[1024] = {0};
    while (1) {
        read(0, buf, 1024);
        write(clientSockFd, buf, 1024);
        fflush(0);
    }
    return 0;
}