c - 无法让我的代理服务器向客户端发送http请求的信息 - Socket编程

Question

我的程序目标是实现一个可以由单个客户端连接并且只允许 http 请求的代理服务器。

要求

1. 使用套接字创建基于 C 的客户端-服务器架构
2. 代理服务器应该能够接受并服务单个客户端的 http 请求

<小时/>

代码

客户端.c

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


    int main(int argc, char *argv[]){

int sockfd, portnum, n;
struct sockaddr_in serv_addr;
struct hostent *server;

char buffer[256];
if(argc < 3){
  fprintf(stderr, "usage %s hostname port\n", argv[0]);
  exit(1);
}
portnum = atoi(argv[2]);
sockfd= socket(AF_INET, SOCK_STREAM, 0);

if(sockfd <0){
 perror("ERROR opening Socket");
 exit(1);
}
server= gethostbyname(argv[1]);
if(sockfd  == NULL){
 fprintf(stderr,"ERROR, no such host\n");
 exit(1);
}
bzero((char *) &serv_addr, sizeof(serv_addr));
serv_addr.sin_family = AF_INET;
bcopy((char *)server->h_addr,
     (char *)&serv_addr.sin_addr.s_addr,
      server->h_length); 
serv_addr.sin_port = htons(portnum);

if(connect(sockfd,(struct sockaddr *)&serv_addr,sizeof(serv_addr)) <0){
 fprintf(stderr,"ERROR, on connecting");
 exit(1);
}
printf("Please enter the Host name: ");
bzero(buffer,256);
fgets(buffer,255,stdin);
n=write(sockfd,buffer,strlen(buffer));
if(n<0){
 printf("Error writing to socket");
 exit(1);
}

bzero(buffer,256);
n=read(sockfd,buffer,255);
if(n<0){
 printf("ERROR reading from socket");
 exit(1);
}
printf("%s\n", buffer);


    return 0;
    }

代理服务器.c

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



    int main(int argc, char *argv[]){

int sockfd, newsockfd, portnum, clilen;
char buffer[256], hostname[256];
pid_t p_id;
struct sockaddr_in serv_addr, cli_addr;
int n, pid;

if(argc < 2){
    fprintf(stderr, "ERROR, NO PORT PROVIDED!\n");
    exit(1);
}
sockfd = socket(AF_INET, SOCK_STREAM, 0);//socket is made

if(sockfd < 0){
    fprintf(stderr,"ERROR opening socket!!");
    exit(1);
}
bzero((char *) &serv_addr, sizeof(serv_addr));
portnum = atoi(argv[1]);//port num

serv_addr.sin_family = AF_INET;
serv_addr.sin_addr.s_addr = htonl(INADDR_ANY);
serv_addr.sin_port = htons(portnum);


if(bind(sockfd, (struct sockaddr*)&serv_addr, sizeof(serv_addr)) < 0){
    fprintf(stderr,"ERROR on binding");
    exit(1);
}

if( listen(sockfd, 5) < 0){
 printf("ERROR ON LISTEN");
 exit(1);
}

    // accept
        clilen = sizeof(cli_addr);
    do{

newsockfd = accept(sockfd, (struct sockaddr *) &cli_addr, &clilen);
if(newsockfd<0){
    fprintf(stderr,"ERROR on accept\n");
    exit(1);
}

    pid=fork();
    if(pid==0){ 
bzero(buffer, 256);
n= read(newsockfd, buffer, 255);

if(n<0){//message from client
 fprintf(stderr,"ERROR Reading from socket\n");
 exit(1);
}   

strcpy(hostname, buffer);
printf("Here is the hostname : %s\n", hostname);

//variables used for acsessing webserver?
int sockwb, wbport, x;
struct sockaddr_in webser_addr;
struct hostent *wbhost;
char webbuf[510];//sending to webserver

wbport =80;//port used to access web server


    sockwb = socket(AF_INET, SOCK_STREAM, 0);
    if(sockwb <0){
        printf("error opeing websocket\n");
        exit(1);
    }
    wbhost= gethostbyname(hostname);
    printf("%s", wbhost->h_name);
    if(sockwb == -1){
        printf("NO SUCH web HOST\n");
        exit(1);
    }
    bzero((char*) &webser_addr, sizeof(webser_addr));
    webser_addr.sin_family = AF_INET;

        bcopy((char *)wbhost->h_addr,               
            (char *)&webser_addr.sin_addr.s_addr,       
            wbhost->h_length);              

    webser_addr.sin_port = htons(wbport);   
    if(connect(sockwb,(struct sockaddr *)&webser_addr,sizeof(webser_addr)) < 0){
        printf("error on web connecting\n");
        exit(1);
    }
    bzero(webbuf,510);
    strcpy(webbuf, "GET http://");
    strcat(webbuf, hostname);
    strcat(webbuf, " HTTP/1.1");

    printf("%s\n", webbuf);
    x=write(sockwb,webbuf,strlen(webbuf));
    if(x<0){
        printf("error writing to web sock");
        exit(1);
    }   
    bzero(webbuf,510);
    x=read(sockwb,webbuf,510);
    if(n<0){    
        printf("error reading from web socket");
        exit(1);
    }   

n = write(newsockfd, webbuf,255 );//write back to client

if (n<0){
   fprintf(stderr,"ERROR WRITING to socket");
   exit(1);
}

printf("%s\n", webbuf);
}//end of if pid==0

printf("closing client");
close(newsockfd);//closing client socket


    }while(1);
    return 0;
    }

<小时/>

我已经能够使用套接字实现简单的客户端-服务器交换，我的问题是 Http 请求。我必须使用 GET 方法通过端口 80 访问 Web 服务器。

我将客户端发送到代理服务器的输入的方式应该是:www.NAME.com

在与客户端初始连接后，服务器似乎没有执行任何操作。

Answer 1

与往常一样，此处未正确管理以空字符结尾的字符串。当使用以下结构时

send(sock, buff, strlen(buf));

不发送尾随空终止字符。在接收方，有两个问题。首先，recv(sock, buff, sizeof(buff)); 可以接收不可预测的字节数量 - 从 1 到提供的字符串大小。所以你需要阅读直到读完所有消息。困境来了——你怎么知道实际消息有多长？答案是，您要么提前同意所有字符串的大小，然后总是发送那么多字节(无论实际字符串长度如何)，要么在消息中使用字符串的大小作为前缀。第二个问题是，即使幸运地读取了整个字符串，它也不是以 null 结尾的，因此在程序中无法使用。它已被手动以 null 终止。