一、注意的問題

• 客戶端的0號檔案描述要設定成非阻塞，這樣才能接受其他客戶端發的訊息。
• 客戶端的讀寫操作也必須設定成非阻塞。
• 對服務端使用setsockopt函式，允許建立多個埠號相同的套接字（解決伺服器先關閉而引發TIME_WAIT狀態的一系列問題）

二、原始碼

comm.h

#ifndef __COMM_H__
#define __COMM_H__

#define NAMESIZE 16
#define DATASIZE 1024

#include <stdio.h>
#include <unistd.h>
#include <string.h>
 

#include <stdlib.h>
#include <netinet/in.h>
#include <pthread.h>
#include <sys/socket.h>
#include <assert.h>
#include <arpa/inet.h>
#include <fcntl.h>
#include <signal.h>

typedef struct Msg
{
    char name[NAMESIZE];
    char data[DATASIZE];
}Msg;

server.c

#include "comm.h"

typedef struct sockfd_node{
    int fd;
    struct sockfd_node* _prev;
    struct sockfd_node* _next;
}sockfd_node;

sockfd_node* phead = NULL;

sockfd_node* buy_node(int client_fd)
{
    sockfd_node* new_node = (sockfd_node*)malloc(sizeof(sockfd_node));
    assert(new_node != NULL);

    new_node->fd = client_fd;
    new_node->_prev = NULL;
    new_node->_next = NULL;
    return
 
 new_node;
}

void push_back(sockfd_node* new_node)
{
    if(phead->_next == NULL){
        phead->_next = new_node;
        phead->_prev = new_node;
        new_node->_next = phead;
        new_node->_prev = phead;
    }else{
        new_node->_prev = phead->_prev;
        new_node->_next = phead;
        phead->_prev->_next = new_node;
        phead->_prev = new_node;
    }
}

// 刪除節點
void erase(sockfd_node* del)
{
    del->_prev->_next = del->_next;
    del->_next->_prev = del->_prev;
    free(del);
}

// 接收到 Ctrl+C 產生的 資訊後，執行此函式
void handler(int n)
{
    sockfd_node* cur = phead->_next;
    while(cur != phead){
        sockfd_node* next = cur->_next;
        free(cur);
        cur = next;
    }
    free(phead);
    printf("伺服器退出\n");
    exit(0);
}

void* thread_work(void* attr)
{
    sockfd_node* cur = (sockfd_node*)attr;

    // 儲存客戶端發來的訊息以及客戶端的姓名
    Msg msg;
    memset(&msg, 0, sizeof(msg));

    for(;;){
        // 讀取客戶端資訊
        int read_size = recv(cur->fd, &msg, sizeof(msg), 0);
        // 讀到的位元組個數為0，代表客戶端斷開連線
        if(read_size == 0){
            printf("< < < < < %s 已下線 < < < < <\n", msg.name);
            erase(cur);
            break;
        }else{
            if(read_size < 0){
                perror("recv");
                break;
            }
        }

        printf("%s say : %s\n", msg.name, msg.data);

        // 把收到訊息給所有使用者傳送
        sockfd_node* p = phead->_next;
        while(p != phead){
            if(p != cur){
                send(p->fd, &msg, sizeof(msg), 0);
            }
            p = p->_next;
        }
    }
}

void server_work(int argc, char* argv[])
{
    int server_fd = socket(AF_INET, SOCK_STREAM, 0);
    if(server_fd < 0){
        perror("socket");
    }

    // 允許建立多個埠號相同的套接字
    // 解決：如果伺服器主動斷開連線會進入 TIME_WAIT 狀態的問題
    int opt = 1;
    setsockopt(server_fd, SOL_SOCKET, SO_REUSEADDR, &opt, sizeof(opt));

    struct sockaddr_in server_socket;
    server_socket.sin_family = AF_INET;
    server_socket.sin_addr.s_addr = inet_addr(argv[1]);
    server_socket.sin_port = htons(atoi(argv[2]));

    int ret = bind(server_fd, (struct sockaddr*)&server_socket, sizeof(server_socket));
    if(ret < 0){
        perror("bind()");
        close(server_fd);
    }

    if(listen(server_fd, 5) < 0){
        perror("listen");
        close(server_fd);
    }


    printf("bind and listen success, wait accept...\n");

    for(;;){
        struct sockaddr_in client_socket;
        socklen_t len = sizeof(client_socket);

        // 與客戶端建立連線
        int client_fd = accept(server_fd, (struct sockaddr*)&client_socket, &len);
        if(client_fd < 0){
            continue;
        }
        char* ip = inet_ntoa(client_socket.sin_addr);
        int port = ntohs(client_socket.sin_port);
        printf("get accept, ip : %s, port : %d\n", ip, port);

        // 把連線的客戶端的資訊存放在連結串列裡，統一管理
        sockfd_node* new_node = buy_node(client_fd);
        push_back(new_node);

        pthread_t tid = 0;
        pthread_create(&tid, NULL, thread_work, (void*)new_node);

        // 把執行緒設定成分離狀態，使其結束後被作業系統自動回收（不會阻塞主執行緒）
        pthread_detach(tid);
    }
    close(server_fd);
}

int main(int argc, char* argv[])
{
    // 把伺服器設定成守護程序
    //daemon(0, 0);
    phead = buy_node(0);
    if(argc != 3){
        printf("Usage ./server [ip] [port]\n");
        return 1;
    }

    // 當按下 Ctrl+C 時，先銷燬連結串列釋放空間，然後伺服器退出
    signal(SIGINT, handler);
    server_work(argc, argv);

    return 0;
}

client.c

#include "comm.h"


int client_work(int argc, char* argv[])
{
    int server_fd = socket(AF_INET, SOCK_STREAM, 0);
    if(server_fd < 0){
        perror("socket");
        return 2;
    }

    struct sockaddr_in server_socket;
    //struct sockaddr_in client_socket;
    server_socket.sin_family = AF_INET;
    server_socket.sin_addr.s_addr = inet_addr(argv[1]);
    server_socket.sin_port = htons(atoi(argv[2]));

    int ret = connect(server_fd, (struct sockaddr*)&server_socket, sizeof(server_socket));
    if(ret < 0){
        perror("connect");
        return 3;
    }

    printf("%s connect success...\n", argv[3]);

    if(fcntl(0, F_SETFL, FNDELAY) < 0){
        perror("fcntl");
        return 4;
    }

    Msg msg;
    for(;;){
        memset(&msg, 0, sizeof(msg));
        strcpy(msg.name, argv[3]);
        int read_size = read(0, msg.data, sizeof(msg.data));
        if(read_size > 0){
            msg.data[read_size-1] = '\0';
            send(server_fd, &msg, sizeof(msg), MSG_DONTWAIT);
        }

        int recv_size = recv(server_fd, &msg, sizeof(msg), MSG_DONTWAIT);
        if(recv_size > 0){
            printf("\t\t%s say : %s\n", msg.name, msg.data);
        }
    }
}

int main(int argc, char* argv[])
{
    if(argc != 4){
        printf("Usage ./server [ip] [port] [name]\n");
        return 1;
    }
    client_work(argc, argv);

    return 0;
}