Question

我对socket编程很新，我遇到了麻烦。我想实现一个服务器，根据某个客户端请求回答。在我的情况下，GET，HEAD或其他错误。请考虑以下代码

如果我在调用send()之前打印答案（请参阅下面的服务器端代码），则该消息是正确的。但是，我要从我发送的客户端说

GET
HEAD
GET
测试
GET

，从客户端打印的答案是

You want GET
You want HEAD
You want GETD
HTTP/1.1 400 Bad Request
You want GET Bad Request

所以看起来从服务器发送的消息有点'覆盖'，但这怎么可以避免呢？是否可以“清除服务器缓冲区”，如果这是问题呢？

这是完整的服务器端代码

#include <stdio.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <netdb.h>

#define BUFSIZE         1024
#define MAXPENDING      100

int main(){

    char get[] = "GET";
    char head[] = "HEAD";
    int serverSocket = socket(PF_INET, SOCK_STREAM, 0);

    struct sockaddr_in serverAddress;
    serverAddress.sin_family = AF_INET;
    serverAddress.sin_port = htons(8080);
    serverAddress.sin_addr.s_addr = htonl(INADDR_ANY);
    memset(&serverAddress.sin_zero, '\0', 8);

    bind(serverSocket, (struct sockaddr*)&serverAddress, sizeof(serverAddress));

    listen(serverSocket, MAXPENDING);

    for(;;){
        struct sockaddr_in clientAddress;
        int clientAddressLength = sizeof(clientAddress);
        int clientSocket;

        clientSocket = accept(serverSocket, (struct sockaddr*)&clientAddress, &clientAddressLength);

        char buf[BUFSIZE];
        int bytesRec;

        bytesRec = recv(clientSocket, buf, BUFSIZE, 0);
        while(bytesRec > 0){

            char *result;
            result = strtok(buf, " ");

            printf("result %s\n", result);

            if(strcmp(&buf, &get) == 0){
                char answer[] = "You want GET";
                send(clientSocket, answer, strlen(answer), 0);
            }else{
                if(strcmp(&buf, &head) == 0){
                    char answer[] = "You want HEAD";
                    send(clientSocket, answer, strlen(answer), 0);
                }else{
                    char answer[] = "HTTP/1.1 400 Bad Request";
                    send(clientSocket, answer, strlen(answer), 0); 
                }
            }

            bytesRec = recv(clientSocket, buf, BUFSIZE, 0);
        }

    return 0;
}

和客户端

#include <stdio.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <netdb.h>

int main(){

    int clientSocket = socket(PF_INET, SOCK_STREAM, 0);

    struct sockaddr_in clientAddress;
    clientAddress.sin_family = AF_INET;
    clientAddress.sin_port = 0;
    clientAddress.sin_addr.s_addr = htonl(INADDR_ANY);
    memset(&clientAddress.sin_zero, '\0', 8/*sizeof(clientAddress.sin_zero)*/);

    bind(clientSocket, (struct sockaddr*)&clientAddress, sizeof(clientAddress));

    struct sockaddr_in serverAddress;
    serverAddress.sin_family = AF_INET;
    serverAddress.sin_port = htons(8080);
    serverAddress.sin_addr.s_addr = inet_addr("127.0.0.1");
    memset(&serverAddress.sin_zero, '\0', 8);

    if(connect(clientSocket, (struct sockaddr*)&serverAddress, sizeof(serverAddress)) == -1){
        printf("error in connecting!\n");
        return 0;
    }

    char* serverReply[1024];

    for(;;){
        char request[100];
        printf("Enter your request: ");
        scanf("%s", &request);
        send(clientSocket, request, strlen(msg), 0);
        if(recv(clientSocket, serverReply, strlen(serverReply), 0) < 0){
            printf("failure in receiving from server!\n");
        }else{
            printf("%s\n", serverReply);
        }
    }

    close(clientSocket);

    return 0;
}

Answer 1

send(clientSocket, request, strlen(msg), 0);

这只发送字符串字符，不包括终止NULL。接收缓冲区不会终止服务器端收到的字符串。

这就是为什么你仍然看到上一条消息中的'D'字符。

You want GETD <-- 'D' is from the previous 'HEAD'

终止服务器上收到的字符串，

buf[bytesRec] = '\0';

编辑：正如@Zan指出的那样，不要这样做：

~~或从客户端发送NULL终止符。~~

~~send(clientSocket, request, strlen(msg) + 1, 0);~~

Answer 2

你的strcmp() in if错误

（1）而不是buf您需要与result进行比较，因为我可以从您的问题中了解到，请执行以下操作:(您在评论中说，结果打印为GET）

if(strcmp(result, get) == 0){

（2）正如@phihag所回答的应该是

if(strcmp(buf, get) == 0){
          ^   ^remove &

你在每个strcmp（）上都有类似的错误，因为buf，get，head都是包机数组。

（3） recv()不会终止读取缓冲区，因此在使用它之前最好添加null（\0）（我可以注意你使用buff作为字符串）

喜欢：

bytesRec = recv(clientSocket, buf, BUFSIZE, 0);
buf[bytesRec] = '\0'

感染您应该只读取BUFSIZE-1个字节，其中一个字符为空'\0'符号，如：

ytesRec = recv(clientSocket, buf, BUFSIZE-1, 0);
buf[bytesRec] = '\0'

C套接字编程，服务器发送缓冲区似乎不被清除

2 个答案: