如何使用C套接字编程下载文件

Question

如何使像互联网下载管理器这样的程序从互联网上下载给定链接的文件.可以使用套接字编程C从Internet下载文件.

我们将不胜感激.谢谢.

Answer 1

1. 使用创建套接字 socket()
2. 打电话connect()给它.
3. GET /path/filename HTTP/1.0\r\n\r\n使用send()或write()正确发送请求.
4. 使用recv()或read()正确接收响应.
5. 解析响应以查明请求是否成功以及文件数据的格式是什么格式.
6. 使用recv()或接收文件数据(如果存在)read().
7. 使用关闭套接字close().

进一步阅读:

• http://tools.ietf.org/html/rfc7230#section-2.1
• http://unpbook.com

Answer 2

#include<stdio.h>
#include<string.h>    
#include<sys/socket.h>
#include<arpa/inet.h>

// www.axmag.com/download/pdfurl-guide.pdf
int main(int argc , char *argv[])
{
    int socket_desc;

    char *message;
    char server_reply[10000];
    char *filename = "file.pdf";
    int total_len = 0;
    int file_len = 99352;

    int len; 

    FILE *file = NULL;
    struct sockaddr_in server;

    //Create socket
    socket_desc = socket(AF_INET , SOCK_STREAM , 0);
    if (socket_desc == -1)
    {
        printf("Could not create socket");
    }

    server.sin_addr.s_addr = inet_addr("198.11.181.184");
    server.sin_family = AF_INET;
    server.sin_port = htons( 80 );

    //Connect to remote server
    if (connect(socket_desc , (struct sockaddr *)&server , sizeof(server)) < 0)
    {
        puts("connect error");
        return 1;
    }

    puts("Connected\n");

    //Send request
    message = "GET /download/pdfurl-guide.pdf HTTP/1.1\r\nHost: www.axmag.com\r\n\r\n Connection: keep-alive\r\n\r\n Keep-Alive: 300\r\n";

    if( send(socket_desc , message , strlen(message) , 0) < 0)
    {
        puts("Send failed");
        return 1;
    }

    puts("Data Send\n"); 

    remove(filename);
    file = fopen(filename, "ab");

    if(file == NULL){
        printf("File could not opened");
    }   

    while(1)
    {
        int received_len = recv(socket_desc, server_reply , sizeof server_reply , 0);

        if( received_len < 0 ){
            puts("recv failed");
            break;
        }

        total_len += received_len;

        //puts(server_reply);   
        fwrite(server_reply , received_len , 1, file);

        printf("\nReceived byte size = %d\nTotal lenght = %d", received_len, total_len);

        if( total_len >= file_len ){
            break;
        }   
    }

    puts("Reply received\n");

    fclose(file);

    return 0;
}