用http下载图片只下载它的一小部分

Question

我想使用http协议GET来请求服务器发送给我一张图片。它编译并将要求图片，但服务器只会给我一小部分。

我的代码是：

#include <iostream> 
#include <string> 
#include <Windows.h> 
#include <fstream> 

#include <stdlib.h> 
#include <winsock.h> 

#pragma comment(lib, "wsock32.lib") 

using namespace std; 

#define BUFFERSIZE 1024 
void die_with_error(char *errorMessage); 
void die_with_wserror(char *errorMessage); 

int main(int argc, char *argv[]) 
{ 
string request; 
string response; 
int resp_leng; 

char buffer[BUFFERSIZE]; 
struct sockaddr_in serveraddr; 
int sock; 

WSADATA wsaData; 
char *ipaddress = "210.125.167.240"; 
int port = 80; 

//http://cwc.ghc.ac.kr/skin/base/board/view_brit2.gif 
request+="GET /skin/base/board/view_brit2.gif HTTP/1.0\r\n"; 
request+="Host: cwc.ghc.ac.kr\r\n"; 
request+="\r\n"; 

//init winsock 
if (WSAStartup(MAKEWORD(2, 0), &wsaData) != 0) 
    die_with_wserror("WSAStartup() failed"); 

//open socket 
if ((sock = socket(PF_INET, SOCK_STREAM, IPPROTO_TCP)) < 0) 
    die_with_wserror("socket() failed"); 

//connect 
memset(&serveraddr, 0, sizeof(serveraddr)); 
serveraddr.sin_family  = AF_INET; 
serveraddr.sin_addr.s_addr = inet_addr(ipaddress); 
serveraddr.sin_port  = htons((unsigned short) port); 
if (connect(sock, (struct sockaddr *) &serveraddr, sizeof(serveraddr)) < 0) 
    die_with_wserror("connect() failed"); 

//send request 
if (send(sock, request.c_str(), request.length(), 0) != request.length()) 
    die_with_wserror("send() sent a different number of bytes than expected"); 

//get response 
response = ""; 
resp_leng= BUFFERSIZE; 
while (resp_leng == BUFFERSIZE) 
{ 
    resp_leng= recv(sock, (char*)&buffer, BUFFERSIZE, 0); 
    if (resp_leng>0) 
     response+= string(buffer).substr(0,resp_leng); 
} 

ofstream myfile; 
myfile.open ("C:\\a\\example.gif"); 

//display response 
cout << response << endl; 

//get response 
response = ""; 
resp_leng= BUFFERSIZE; 
while (resp_leng == BUFFERSIZE) 
{ 
    resp_leng= recv(sock, (char*)&buffer, BUFFERSIZE, 0); 
    if (resp_leng>0) 
     response+= string(buffer).substr(0,resp_leng); 
} 


//display response 
cout << response << endl; 


myfile << response; 
myfile.close(); 

//disconnect 
closesocket(sock); 

//cleanup 
WSACleanup(); 
return 0; 
} 

void die_with_error(char *errorMessage) 
{ 
cerr << errorMessage << endl; 
    exit(1); 
} 

void die_with_wserror(char *errorMessage) 
{ 
    cerr << errorMessage << ": " << WSAGetLastError() << endl; 
    exit(1); 
} 

/* 

It compiles and runs fine the output is: 

HTTP/1.1 200 OK 
Server: Apache-Coyote/1.1 
ETag: W/"60-1144808550000" 
Last-Modified: Wed, 12 Apr 2006 02:22:30 GMT 
Content-Type: image/gif 
Content-Length: 60 
Date: Wed, 22 Feb 2012 04:29:04 GMT 
Connection: close 

GIF89a 
*/ 

什么是错的，为什么它不能下载的全貌？

Answer 1

它看起来像这样循环的问题是：

while (resp_leng == BUFFERSIZE) 
{ 
    resp_leng= recv(sock, (char*)&buffer, BUFFERSIZE, 0); 
    if (resp_leng>0) 
     response+= string(buffer).substr(0,resp_leng); 
} 

调用recv()会给你一定数量的字节，从插座中，可能小于你要求什么。因此，与读取文件不同，询问BUFFERSIZE字节可能会返回1到BUFFERSIZE之间的任何字节。

相反，循环，直到你到插座的末尾：

while (true) 
{ 
    resp_leng= recv(sock, (char*)&buffer, BUFFERSIZE, 0); 
    if (resp_leng <= 0) { 
     break; 
    } 
    response+= string(buffer,resp_leng); 
} 

请注意，我也改变了调用string()构造上循环的最后一行（你的工作，但会做比必要的更多的努力）。

Answer 2

此外，您应该清除每个周期的接收缓冲区。把它作为循环中的第一行。

ZeroMemory（buffer，sizeof（buffer））;

您可以在缓冲区中留下二进制数据，以获得许多意想不到的结果。