c++ - InternetReadFile() 似乎没有读取互联网数据

Question

我是这里网站的新人，所以如果我在这篇文章中做错了什么，请原谅我。

我正在使用 WinINet 并尝试从 Internet 下载一个 binary file 但是，由于某种原因，当我到达实际下载该文件时使用InternetReadFile()，它根本没有读取任何内容(读取了 0 个字节的信息)。运行 Visual Studio 2012 调试器 向我揭示了这个细节，因为我提供给 API 调用的 HINTERNET 处理程序肯定有数据。我只是不明白我做错了什么。也许你们可以帮忙？

我的程序的基本要点是我从网上下载一个二进制文件，并将其保存到临时目录中的一个临时文件中。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(这次是在一个有效目录中)。这是我到目前为止所拥有的。希望通过我提供的逻辑分解，尽管代码很长，你们也能理解...

#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;
}

Answer 1

您的代码对我有用。您确定服务器返回的是非空响应吗？可以使用Fiddler2之类的工具来检查。这段代码中有很多问题，包括这里的缓冲区溢出:lpszDataBuffer[bufsize] = '\0';。此外，您正在使用异步模式，但您的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。如果您只是要等待每个操作完成，那么异步执行操作就没有任何好处。您可以不使用 INTERNET_FLAG_ASYNC 标志。这将使您的功能更加简单。