網絡編程——實現迭代服務器端/客戶端

時間 2019-11-18

原文原文鏈接

基於TCP的服務端編程——實現一個簡單的回聲服務器端/客戶端。即服務器端將客戶端傳輸的字符串數據原封不動地傳回客戶端，就像回聲同樣。編程

服務端：服務器

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <arpa/inet.h>
#include <sys/socket.h>
#define BUF_SIZE 1024

void ErrorHandling(char *message) {
    fputs(message, stderr);
    fputs("\n", stderr);
    exit(1);
}

int main(int argc, char * argv[]) {
    int serv_sock, clnt_sock;
    char message[BUF_SIZE];
    int str_len, i;

    struct sockaddr_in serv_adr, clnt_adr;
    socklen_t clnt_adr_sz;

    if(argc != 2) {
        printf("Usage : %s <port>\n", argv[0]);
        exit(1);
    }

    serv_sock  = socket(PF_INET, SOCK_STREAM, 0);
    if (serv_sock == -1)
        ErrorHandling("socket() error!");

    memset(&serv_adr, 0, sizeof(serv_adr));
    serv_adr.sin_family = AF_INET;
    serv_adr.sin_addr.s_addr = htonl(INADDR_ANY);
    serv_adr.sin_port = htons(atoi(argv[1]));

    if(bind(serv_sock, (struct sockaddr*)&serv_adr, sizeof(serv_adr)) == -1)
        ErrorHandling("bind() error!");

    if(listen(serv_sock, 5) == -1)
        ErrorHandling("listen() error!");

    clnt_adr_sz = sizeof(clnt_adr);
    for(int i = 0; i < 5; ++i)
    {
        clnt_sock = accept(serv_sock, (struct sockaddr*)&clnt_adr, &clnt_adr_sz);
        if (clnt_sock == -1)
            ErrorHandling("accept() error!");
        else
            printf("Connected client %d \n", i + 1);
        while ((str_len = read(clnt_sock, message, BUF_SIZE)) != 0)
            write(clnt_sock, message, str_len);

        close(clnt_sock);
    }
    close(serv_sock);
    return 0;
}

客戶端：socket

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <arpa/inet.h>
#include <sys/socket.h>
#define BUF_SIZE 1024

void ErrorHandling(char *message) {
    fputs(message, stderr);
    fputs("\n", stderr);
    exit(1);
}

int main(int argc, char *argv[]) {
    int sock;
    char message[BUF_SIZE];
    int str_len;
    struct sockaddr_in serv_adr;

    if (argc != 3) {
        printf("Usage: %s <IP> <port>\n", argv[0]);
        exit(1);
    }

    sock = socket(PF_INET, SOCK_STREAM, 0);
    if(sock == -1)
        ErrorHandling("socket() error!");

    memset(&serv_adr, 0, sizeof(serv_adr));
    serv_adr.sin_family = AF_INET;
    serv_adr.sin_addr.s_addr = inet_addr(argv[1]);
    serv_adr.sin_port = htons(atoi(argv[2]));

    if (connect(sock, (struct sockaddr*)&serv_adr, sizeof(serv_adr)) == -1)
        ErrorHandling("connect() error!");
    else
        printf("Connected.......\n");

    while(1){
        fputs("Input message(Q to quit): ", stdout);
        fgets(message, BUF_SIZE, stdin);

        if(!strcmp(message,"q\n") || !strcmp(message,"Q\n"))
            break;

        write(sock,message,strlen(message));
        str_len = read(sock,message,BUF_SIZE-1);
        message[str_len]=0;
        printf("Message from server: %s\n", message);
    }
    close(sock);
    return 0;
}

回聲客戶端存在的問題：函數

write(sock,message,strlen(message));
str_len = read(sock,message,BUF_SIZE-1);
message[str_len]=0;
printf("Message from server: %s\n", message);

因爲TCP不存在數據邊界，所以屢次調用write()函數傳遞的字符串就有可能一次性傳遞到服務器端。此時客戶端有可能從服務器端收到多個字符串。同時，服務器端但願經過調用1次write函數傳輸數據，但若是數據太大，操做系統就有可能把數據分紅多個數據包發送到客戶端。另外，在此過程當中，客戶端有可能在還沒有收到所有數據包時就調用read函數。ui

解決方法：提早確認接收數據的大小。若以前傳輸了20個字節，則在接受接收時循環調用read函數讀取20個字節便可。spa

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <arpa/inet.h>
#include <sys/socket.h>
#define BUF_SIZE 1024

void ErrorHandling(char *message) {
    fputs(message, stderr);
    fputs("\n", stderr);
    exit(1);
}

int main(int argc, char *argv[]) {
    int sock;
    char message[BUF_SIZE];
    int str_len, recv_len, recv_cnt;
    struct sockaddr_in serv_adr;

    if (argc != 3) {
        printf("Usage: %s <IP> <port>\n", argv[0]);
        exit(1);
    }

    sock = socket(PF_INET, SOCK_STREAM, 0);
    if (sock == -1)
        ErrorHandling("socket() error!");

    memset(&serv_adr, 0, sizeof(serv_adr));
    serv_adr.sin_family = AF_INET;
    serv_adr.sin_addr.s_addr = inet_addr(argv[1]);
    serv_adr.sin_port = htons(atoi(argv[2]));

    if (connect(sock, (struct sockaddr*)&serv_adr, sizeof(serv_adr)) == -1)
        ErrorHandling("connect() error!");
    else
        printf("Connected.......\n");

    while (1) {
        fputs("Input message(Q to quit): ", stdout);
        fgets(message, BUF_SIZE, stdin);

        if (!strcmp(message, "q\n") || !strcmp(message, "Q\n"))
            break;

        str_len = write(sock, message, strlen(message));

    recv_len = 0;
        //while循環確保接受到服務器端傳輸的全部數據
        while (recv_len != str_len) {
            recv_cnt = read(sock, message, BUF_SIZE - 1);
            if (recv_cnt == -1)
                ErrorHandling("read error");
            recv_len += recv_cnt;
        }
        message[recv_len] = 0;
        printf("Message from server: %s", message);
    }
    close(sock);
    return 0;
}