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我正在使用WinINet并尝试从互联网下载binary file，但出于某种原因，当我到达使用InternetReadFile()实际下载该文件的时候，它返回什么都没读（读取0字节的信息）。运行Visual Studio 2012 debugger向我透露了详细信息，因为我提供给API调用的HINTERNET处理程序肯定有数据肯定。我只是不明白我做错了什么。也许你们可以帮忙吗？
我的程序的基本要点是我从网上下载二进制文件，并将其保存到临时目录中的临时文件中。将内容复制到临时文件后，我将该临时文件的二进制数据内容传输到另一个本地文件（这次是在有效目录中）。这是我到目前为止所拥有的。希望在我提供的逻辑细分的情况下，尽管代码长度，你们仍然可以关注它......
#include "httpfileretrieval.h" // contains all handlers (hInstance, etc.)
bool downloadFile(const char* lpszServer, const char* lpszUrl, const char* destPath)
{
FILE *tempFile = NULL;
FILE *localFile = NULL;
const int bufsize = 4096;
DWORD tempDirBytes;
DWORD dwSize = 4096; // experiment - ignore the fact this is the same as bufsize
DWORD dwRead = 0;
char lpszDataBuffer[bufsize];
lpszDataBuffer[bufsize] = '\0';
char tempPath[MAX_PATH];
char tempFileName[bufsize]; // will hold the FULL temp file path
std::string srcPath;
srcPath.append(lpszServer);
srcPath.append(lpszUrl); // http://www.domain.com/url into srcPath
hInstance = InternetOpen("httpfret",
INTERNET_OPEN_TYPE_PRECONFIG,
NULL,
NULL,
INTERNET_FLAG_ASYNC); // ASYNC Flag
if (!hInstance)
{
DWORD errorNum = GetLastError();
fprintf(stderr, "InternetOpen Failed! Windows Error %d\n", errorNum);
return false;
}
// Setup callback function due to INTERNET_FLAG_ASYNC
if (InternetSetStatusCallback(hInstance,(INTERNET_STATUS_CALLBACK)&Callback)
== INTERNET_INVALID_STATUS_CALLBACK)
{
DWORD errorNum = GetLastError();
fprintf(stderr, "InternetSetStatusCallback Failed! Windows Error %d\n", errorNum);
return false;
}
// First call that will actually complete asynchronously even though
// there is no network traffic
hConnect = InternetConnect(hInstance,
lpszServer,
INTERNET_DEFAULT_HTTP_PORT,
NULL,
NULL,hg
INTERNET_SERVICE_HTTP,
0,
1); // Connection handle's Context
if (!hConnect)
{
if (GetLastError() != ERROR_IO_PENDING)
{
DWORD errorNum = GetLastError();
fprintf(stderr, "InternetConnect Failed! Windows Error %d\n", errorNum);
InternetCloseHandle(hInstance);
return false;
}
// Wait until we get the connection handle
WaitForSingleObject(hConnectedEvent, INFINITE);
}
// Open the request
hRequest = HttpOpenRequest(hConnect, "GET", lpszUrl, NULL, NULL, NULL,
INTERNET_FLAG_RELOAD | INTERNET_FLAG_NO_CACHE_WRITE,
2); // Request handle's context
if (!hRequest)
{
if (GetLastError() != ERROR_IO_PENDING)
{
DWORD errorNum = GetLastError();
fprintf(stderr, "HttpOpenRequest Failed! Windows Error %d\n", errorNum);
InternetCloseHandle(hConnect);
InternetCloseHandle(hInstance);h
return false;
}
// Wait until we get the request handle
WaitForSingleObject(hRequestOpenedEvent, INFINITE);
}
// Send the request
if (!HttpSendRequest(hRequest, NULL, 0, NULL, 0))
{
if (GetLastError() != ERROR_IO_PENDING)
{
DWORD errorNum = GetLastError();
fprintf(stderr, "HttpSendRequest Failed! Windows Error %d\n", errorNum);
InternetCloseHandle(hRequest);
InternetCloseHandle(hConnect);
InternetCloseHandle(hInstance);
return false;
}
}
if (bVerbose)
{
printf("HttpSendRequest called successfully\n");
}
WaitForSingleObject(hRequestCompleteEvent, INFINITE);
// Before downloading file...
// 1. Get the temp directory
if (!(tempDirBytes = GetTempPathA(MAX_PATH, tempPath)))
{
fprintf(stderr, "Could not get temporary directory\n");
InternetCloseHandle(hRequest);
InternetCloseHandle(hConnect);
InternetCloseHandle(hInstance);
return false;
}
// 2. Get temp file name (full name: tempPath\temp.tmp)
srand(GetTickCount());
sprintf(tempFileName, "%s\\%08X.tmp", tempPath, rand());
// Error check the end of temp file name for ending double slash
if (tempFileName[bufsize] == '\\')
tempFileName[bufsize] = '\0';
// 3. Create temp file
printf("Creating temp file %s\nto store %s\n", tempFileName, srcPath.c_str());
tempFile = fopen(tempFileName, "wb"); // Open the file for writing
if (!tempFile)
{
DWORD errorNum = GetLastError();
fprintf(stderr, "Could not create temp file! Error %d\n", errorNum);
InternetCloseHandle(hRequest);
InternetCloseHandle(hConnect);
InternetCloseHandle(hInstance);
return false;
}
printf("Done!\n\n");
printf("------------------- Read the response -------------------\n");
unsigned long n = 0;
unsigned long sum = 0;
printf("Copying %s\n to %s\n", srcPath.c_str(), tempFileName);
// WHERE THE MAGIC HAPPENS - AND WHERE EVERYTHING FAILS!
while ( InternetReadFile(hRequest, lpszDataBuffer, dwSize, &dwRead) && !(bAllDone) )
{
if (dwRead != 0)
{
sum = 0;
fwrite(lpszDataBuffer, 1, dwRead, tempFile);
for (unsigned long i = 0; i < dwRead; ++i)
{
sum += lpszDataBuffer[i];
sum %= 0xFFFF;
}
printf("Received 4KB block %d. Sum %04X\r", n++, sum);
}
else
{
bAllDone = TRUE;
printf("\n");
break;
}
}
printf("\n\n------------------- Request Complete ----------------\n");
fclose(tempFile); // Done writing to file
tempFile = fopen(tempFileName, "rb"); // Reopen for reading
//Create the local file
printf("Creating local file %s\n", destPath);
localFile = fopen(destPath, "wb");
if (!localFile)
{
DWORD errorNum = GetLastError();
fprintf(stderr, "Could not create local file! Windows Error %d\n", errorNum);
fclose(tempFile);
remove(tempFileName); // delete temporary file from machine
InternetCloseHandle(hRequest);
InternetCloseHandle(hConnect);
InternetCloseHandle(hInstance);
return false;
}
printf("Done!\n\n");
// Copy the contents from the temp file to the local file
printf("Copying temp file %s contents\nto local file %s\n", tempFileName, destPath);
if (!copyFile(tempFile, localFile))
{
DWORD errorNum = GetLastError();
fprintf(stderr, "Could not copy temp file to local directory! Windows Error\n", errorNum);
fclose(tempFile);
remove(tempFileName); // delete temporary file from machine
fclose(localFile);
InternetCloseHandle(hRequest);
InternetCloseHandle(hConnect);
InternetCloseHandle(hInstance);
return false;
}
printf("Done!\n\n");
// end of logic housekeeping
fclose(tempFile);
printf("Deleting temp file %s\n", tempFileName);
remove(tempFileName); // delete temporary file from machine
printf("Done!\n\n");
fclose(localFile);
printf("Ending Internet Session\n");
InternetCloseHandle(hRequest);
InternetCloseHandle(hConnect);
InternetCloseHandle(hInstance);
printf("Done!\n");
printf("Press Enter to continue\n");
std::cin.get();
return true;
}
答案 0 :(得分：3)
您的代码适合我。您确定服务器返回非空响应吗？您可以使用Fiddler2之类的工具进行检查。此代码中存在相当多的问题，包括缓冲区溢出：lpszDataBuffer[bufsize] = '\0';。此外，您正在使用异步模式，但在读取循环中没有任何异步处理。我建议您在此处发布代码以供审核：https://codereview.stackexchange.com/。
最后一点说明。如果您只是等待每个操作完成，那么异步执行操作没有任何好处。你可以不用INTERNET_FLAG_ASYNC标志。这将使您的功能更加简单。