C++ 为什么文件上传会在发送了几个数据块（使用多部分/表单数据）后停止？

我正在使用libcurl将固件文件上载到硬件设备。我使用的是多部分/表单数据，看起来文件上传启动正常，但不会加载整个文件。
我上传的文件是144855725字节，但似乎只发送了两个64k块

在发布的代码中，我使用了一个read回调函数。我还尝试将文件名传递给curl\u mime\u filedata函数，结果是一样的。
一个有趣的注意事项是，当我运行这个程序时，我会从curl\u easy\u执行程序中得到成功的响应，大约有一半的时间。另一半时间，我会收到错误56“从对等方接收数据时失败”。 另一个有趣的注意事项是，文件的大小（144855725）与curl认为的下载大小（144856042）略有差异。我认为这是因为它占用了正文中的所有字节（不仅仅是文件）。对吗

以下是我运行程序时的一些（精简）输出。
文件大小：144855725
总时间：0.000092
向上：0/0向下：0/0
上升：144856042的0下降：0的0
ReadCallback:Size=1，Nmemb=65267
我们从文件中读取了65267个字节
上升：144856042的65536下降：0的0
ReadCallback:Size=1，Nmemb=65536
我们从文件中读取了65536个字节
上升：131072/144856042下降：0/0
卷曲结果错误=
无法上载固件文件

size_t ReadCallback(char *BufferOut, size_t Size, size_t Nmemb, void *StreamIn)
{
   curl_off_t nread;
   size_t retcode = fread(BufferOut, Size, Nmemb, (FILE *)StreamIn);
   nread = (curl_off_t)retcode;
   cout << "ReadCallback: Size=" << Size << ", Nmemb=" << Nmemb << endl;
   cout << "We read " << nread << " bytes from the file" << endl;
   return retcode;
}

size\t ReadCallback（char*BufferOut、size\t size、size\t Nmemb、void*StreamIn）
{
卷曲，卷曲，卷曲；
size\u t retcode=fread（BufferOut，size，Nmemb，（FILE*）StreamIn）；
nread=（curl_off_t）retcode；
cout您没有正确填充
curl\u mime
结构。您显示的代码与您在以下文档中描述的mime格式不匹配：

--1a2fc07a-d882-4470-a1da-79716d34cd9b
内容处置：表单数据；name=“升级文件”filename=“”
内容类型：应用程序/八位字节流
//文件数据在这里//
--1a2fc07a-d882-4470-a1da-79716d34cd9b
内容处置：表单数据；name=“提交”
安装操作系统
--1a2fc07a-d882-4470-a1da-79716d34cd9b--
请尝试以下方法：

size_t ReadCallback(char *buffer, size_t size, size_t nitems, void *arg)
{
    cout << "ReadCallback: size=" << size << ", nitems=" << nitems << endl;
    size_t retcode = fread(buffer, size, nitems, (FILE *)arg);
    cout << "We read " << retcode << " bytes from the file" << endl;
    return retcode;
}

int SeekCallback(void *arg, curl_off_t offset, int origin)
{
    if (fseek((FILE *)arg, offset, origin) == 0)
        return CURL_SEEKFUNC_OK;
    else
        return CURL_SEEKFUNC_FAIL;
}

int main()
{
    CURL *pCurl;
    CURLcode res;
    struct curl_slist *headerList = NULL;
    string accessToken;
    struct TransferProgress transProgress;
    string filePath;
    FILE * pFile;
    long lSize;

    curl_global_init(CURL_GLOBAL_ALL);
    pCurl = curl_easy_init();
    if (pCurl)
    {
        EC520UutComms comms;
        curl_mime *multipart;
        curl_mimepart *part;

        accessToken = comms.GetAccessToken(pCurl);
        SetOptionsToDefault(pCurl);

        // Specify the target URL
        std::string str(comms.BaseURL() + kAPI_Upgrade);
        cout << "URL <" + str + ">" << endl;
        curl_easy_setopt(pCurl, CURLOPT_URL, str.c_str());

        multipart = curl_mime_init(pCurl);

        part = curl_mime_addpart(multipart);
        curl_mime_name(part, "upgrade_file");
        curl_mime_filename(part, "");
        curl_mime_type(part, "application/octet-stream");
        filePath = "C:\\Temp\\TestFile.tst";
        // curl_mime_filedata(part, filePath.c_str());
        fopen_s(&pFile, filePath.c_str(), "rb");
        // obtain file size:
        fseek(pFile, 0, SEEK_END);
        lSize = ftell(pFile);
        rewind(pFile);
        cout << "File size: " << lSize << endl;
        curl_mime_data_cb(part, lSize, ReadCallback, SeekCallback, NULL, pFile);

        part = curl_mime_addpart(multipart);
        curl_mime_name(part, "submit");
        curl_mime_data(part, "Install OS", CURL_ZERO_TERMINATED);

        curl_easy_setopt(pCurl, CURLOPT_MIMEPOST, multipart);

        // This is a long upload, disable the timeout
        curl_easy_setopt(pCurl, CURLOPT_TIMEOUT, 0L);

        // Create headers
        headerList = curl_slist_append(headerList, ("Authorization: Bearer " + accessToken).c_str());
        headerList = curl_slist_append(headerList, "Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8");

        curl_easy_setopt(pCurl, CURLOPT_HTTPHEADER, headerList);

        curl_easy_setopt(pCurl, CURLOPT_XFERINFOFUNCTION, TransferInfo);

        transProgress.curl = pCurl;
        curl_easy_setopt(pCurl, CURLOPT_XFERINFODATA, &transProgress);

        curl_easy_setopt(pCurl, CURLOPT_NOPROGRESS, 0L);

        // Now send the message
        res = curl_easy_perform(pCurl);

        fclose(pFile);
        curl_slist_free_all(headerList);
        curl_mime_free(multipart);

        if (res == CURLE_OK)
        {
            cout << "Firmware file successfully uploaded" << endl;
        }
        else
        {
            cout << "curl result ERROR = <" + to_string(res) + ": " + curl_easy_strerror(res) + ">" << endl;
            cout << "Failed to upload firmware file" << endl;
        }

        curl_easy_cleanup(pCurl);
    }

    return 0;
}

size\t ReadCallback（字符*缓冲区、大小、大小元素、void*arg）
{
cout您没有正确填充
curl\u mime
结构。您显示的代码与您在以下文档中描述的mime格式不匹配：

--1a2fc07a-d882-4470-a1da-79716d34cd9b
内容处置：表单数据；name=“升级文件”filename=“”
内容类型：应用程序/八位字节流
//文件数据在这里//
--1a2fc07a-d882-4470-a1da-79716d34cd9b
内容处置：表单数据；name=“提交”
安装操作系统
--1a2fc07a-d882-4470-a1da-79716d34cd9b--
请尝试以下方法：

size_t ReadCallback(char *buffer, size_t size, size_t nitems, void *arg)
{
    cout << "ReadCallback: size=" << size << ", nitems=" << nitems << endl;
    size_t retcode = fread(buffer, size, nitems, (FILE *)arg);
    cout << "We read " << retcode << " bytes from the file" << endl;
    return retcode;
}

int SeekCallback(void *arg, curl_off_t offset, int origin)
{
    if (fseek((FILE *)arg, offset, origin) == 0)
        return CURL_SEEKFUNC_OK;
    else
        return CURL_SEEKFUNC_FAIL;
}

int main()
{
    CURL *pCurl;
    CURLcode res;
    struct curl_slist *headerList = NULL;
    string accessToken;
    struct TransferProgress transProgress;
    string filePath;
    FILE * pFile;
    long lSize;

    curl_global_init(CURL_GLOBAL_ALL);
    pCurl = curl_easy_init();
    if (pCurl)
    {
        EC520UutComms comms;
        curl_mime *multipart;
        curl_mimepart *part;

        accessToken = comms.GetAccessToken(pCurl);
        SetOptionsToDefault(pCurl);

        // Specify the target URL
        std::string str(comms.BaseURL() + kAPI_Upgrade);
        cout << "URL <" + str + ">" << endl;
        curl_easy_setopt(pCurl, CURLOPT_URL, str.c_str());

        multipart = curl_mime_init(pCurl);

        part = curl_mime_addpart(multipart);
        curl_mime_name(part, "upgrade_file");
        curl_mime_filename(part, "");
        curl_mime_type(part, "application/octet-stream");
        filePath = "C:\\Temp\\TestFile.tst";
        // curl_mime_filedata(part, filePath.c_str());
        fopen_s(&pFile, filePath.c_str(), "rb");
        // obtain file size:
        fseek(pFile, 0, SEEK_END);
        lSize = ftell(pFile);
        rewind(pFile);
        cout << "File size: " << lSize << endl;
        curl_mime_data_cb(part, lSize, ReadCallback, SeekCallback, NULL, pFile);

        part = curl_mime_addpart(multipart);
        curl_mime_name(part, "submit");
        curl_mime_data(part, "Install OS", CURL_ZERO_TERMINATED);

        curl_easy_setopt(pCurl, CURLOPT_MIMEPOST, multipart);

        // This is a long upload, disable the timeout
        curl_easy_setopt(pCurl, CURLOPT_TIMEOUT, 0L);

        // Create headers
        headerList = curl_slist_append(headerList, ("Authorization: Bearer " + accessToken).c_str());
        headerList = curl_slist_append(headerList, "Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8");

        curl_easy_setopt(pCurl, CURLOPT_HTTPHEADER, headerList);

        curl_easy_setopt(pCurl, CURLOPT_XFERINFOFUNCTION, TransferInfo);

        transProgress.curl = pCurl;
        curl_easy_setopt(pCurl, CURLOPT_XFERINFODATA, &transProgress);

        curl_easy_setopt(pCurl, CURLOPT_NOPROGRESS, 0L);

        // Now send the message
        res = curl_easy_perform(pCurl);

        fclose(pFile);
        curl_slist_free_all(headerList);
        curl_mime_free(multipart);

        if (res == CURLE_OK)
        {
            cout << "Firmware file successfully uploaded" << endl;
        }
        else
        {
            cout << "curl result ERROR = <" + to_string(res) + ": " + curl_easy_strerror(res) + ">" << endl;
            cout << "Failed to upload firmware file" << endl;
        }

        curl_easy_cleanup(pCurl);
    }

    return 0;
}

size\t ReadCallback（字符*缓冲区、大小、大小元素、void*arg）
{
你的建议修改成功了。我感谢你的时间。非常感谢！你的建议修改成功了。我感谢你的时间。非常感谢！
size_t ReadCallback(char *buffer, size_t size, size_t nitems, void *arg)
{
    cout << "ReadCallback: size=" << size << ", nitems=" << nitems << endl;
    size_t retcode = fread(buffer, size, nitems, (FILE *)arg);
    cout << "We read " << retcode << " bytes from the file" << endl;
    return retcode;
}

int SeekCallback(void *arg, curl_off_t offset, int origin)
{
    if (fseek((FILE *)arg, offset, origin) == 0)
        return CURL_SEEKFUNC_OK;
    else
        return CURL_SEEKFUNC_FAIL;
}

int main()
{
    CURL *pCurl;
    CURLcode res;
    struct curl_slist *headerList = NULL;
    string accessToken;
    struct TransferProgress transProgress;
    string filePath;
    FILE * pFile;
    long lSize;

    curl_global_init(CURL_GLOBAL_ALL);
    pCurl = curl_easy_init();
    if (pCurl)
    {
        EC520UutComms comms;
        curl_mime *multipart;
        curl_mimepart *part;

        accessToken = comms.GetAccessToken(pCurl);
        SetOptionsToDefault(pCurl);

        // Specify the target URL
        std::string str(comms.BaseURL() + kAPI_Upgrade);
        cout << "URL <" + str + ">" << endl;
        curl_easy_setopt(pCurl, CURLOPT_URL, str.c_str());

        multipart = curl_mime_init(pCurl);

        part = curl_mime_addpart(multipart);
        curl_mime_name(part, "upgrade_file");
        curl_mime_filename(part, "");
        curl_mime_type(part, "application/octet-stream");
        filePath = "C:\\Temp\\TestFile.tst";
        // curl_mime_filedata(part, filePath.c_str());
        fopen_s(&pFile, filePath.c_str(), "rb");
        // obtain file size:
        fseek(pFile, 0, SEEK_END);
        lSize = ftell(pFile);
        rewind(pFile);
        cout << "File size: " << lSize << endl;
        curl_mime_data_cb(part, lSize, ReadCallback, SeekCallback, NULL, pFile);

        part = curl_mime_addpart(multipart);
        curl_mime_name(part, "submit");
        curl_mime_data(part, "Install OS", CURL_ZERO_TERMINATED);

        curl_easy_setopt(pCurl, CURLOPT_MIMEPOST, multipart);

        // This is a long upload, disable the timeout
        curl_easy_setopt(pCurl, CURLOPT_TIMEOUT, 0L);

        // Create headers
        headerList = curl_slist_append(headerList, ("Authorization: Bearer " + accessToken).c_str());
        headerList = curl_slist_append(headerList, "Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8");

        curl_easy_setopt(pCurl, CURLOPT_HTTPHEADER, headerList);

        curl_easy_setopt(pCurl, CURLOPT_XFERINFOFUNCTION, TransferInfo);

        transProgress.curl = pCurl;
        curl_easy_setopt(pCurl, CURLOPT_XFERINFODATA, &transProgress);

        curl_easy_setopt(pCurl, CURLOPT_NOPROGRESS, 0L);

        // Now send the message
        res = curl_easy_perform(pCurl);

        fclose(pFile);
        curl_slist_free_all(headerList);
        curl_mime_free(multipart);

        if (res == CURLE_OK)
        {
            cout << "Firmware file successfully uploaded" << endl;
        }
        else
        {
            cout << "curl result ERROR = <" + to_string(res) + ": " + curl_easy_strerror(res) + ">" << endl;
            cout << "Failed to upload firmware file" << endl;
        }

        curl_easy_cleanup(pCurl);
    }

    return 0;
}