Adding progressbar to wininet http upload C++ - c++

Question

I'm having code for uploading binary files on HTTP-server with POST method:
http_upload_file(PCHAR szServer, PCHAR szScript, PCHAR szParam, PCHAR szValue, PCHAR szFile)
{
PCHAR szHeaders = "Content-Type: multipart/form-data; boundary=----qwerty";
PCHAR szData = "------qwerty\r\n"
"Content-Disposition: form-data; name=\"%s\"\r\n\r\n%s\r\n"
"------qwerty\r\n"
"Content-Disposition: form-data; name=\"files[]\"; filename=\"%s\"\r\n"
"Content-Type: application/octet-stream\r\n"
"Content-Transfer-Encoding: binary\r\n\r\n";
PCHAR szDataEnd = "\r\n------qwerty--\r\n";
char szHeader[512];
HINTERNET hSession, hConnect, hRequest;
DWORD dwFileSize, dwBytesRead, dwContentLength,dwBytesWritten;
hSession = InternetOpen(NULL, INTERNET_OPEN_TYPE_DIRECT, NULL, NULL, 0);
if (hSession)
{
hConnect = InternetConnect(hSession, szServer, INTERNET_DEFAULT_HTTP_PORT, NULL, NULL, INTERNET_SERVICE_HTTP,0, 0);
if (hConnect)
{
hRequest = HttpOpenRequest(hConnect, "POST", szScript, NULL, NULL, 0, 0, 0);
if (hRequest)
{
HANDLE hFile = CreateFile(szFile, GENERIC_READ, FILE_SHARE_READ, NULL, OPEN_EXISTING, NULL, NULL);
if (hFile != INVALID_HANDLE_VALUE)
{
dwFileSize = GetFileSize(hFile, NULL);
wsprintf(szHeader, szData, szParam, szValue, szFile);
dwContentLength = lstrlen(szHeader) + dwFileSize + lstrlen(szDataEnd);
LPBYTE pBuf = (LPBYTE)malloc(dwContentLength);
CopyMemory(&pBuf[0], szHeader, lstrlen(szHeader));
ReadFile(hFile, &pBuf[lstrlen(szHeader)], dwFileSize, &dwBytesRead, NULL);
CopyMemory(&pBuf[lstrlen(szHeader) + dwFileSize], szDataEnd, lstrlen(szDataEnd));
HttpSendRequest(hRequest, szHeaders, lstrlen(szHeaders), pBuf, dwContentLength);
CloseHandle(hFile);
free(pBuf);
}
}
InternetCloseHandle(hRequest);
}
InternetCloseHandle(hConnect);
}
InternetCloseHandle(hSession);
}
It's working fine, but I would like to add some proggess information while file is uploading.
Can I get size of transfered content, while HttpSendRequest(hRequest, szHeaders, lstrlen(szHeaders), pBuf, dwContentLength); is executing? The problem is that when uploading big file my Form is freezing and user can't watch how much data already uploaded. Because of this I want to add ProggessBar for displaying size of data transfering, but dont know how get this transfering data...
I will be glad for any advice.

Answer 1

You can split the upload into small pieces and update the progress bar after sending each piece.
Call InternetConnect() and HttpOpenRequest() as usual.
Instead of HttpSendRequest() call HttpSendRequestEx(). Define the total file size via the lpBuffersIn parameter. For parameter dwFlags pass the value HSR_INITIATE to tell the API that you want iterative data transfer. There is a doc bug in the reference page, the dwFlags parameter is not reserved. Everyone is using it, for example MFC.
INTERNET_BUFFERS buffer{ sizeof(buffer) };
buffer.dwBufferTotal = totalFileSizeInBytes;
BOOL success = HttpSendRequestEx( hRequest, &buffer, nullptr, HSR_INITIATE, 0 );
Call InternetWriteFile() in a loop to upload the file in pieces. Use a buffer size that is not too small to reduce overhead of API (say 16k). After each call to this API you could measure difference between current time and time of last progress bar update and only update progress bar if difference is big enough (say 1/10 s) to reduce API overhead of updating GUI.
When you are finished uploading the file, tell it the API by calling HttpEndRequest(). Of course close handles, check for errors, etc. pp.
All of this should be done in a separate thread to keep the GUI thread responsive. Report the progress to the GUI thread by calling PostMessage() with a message ID of WM_APP + x. You can pass the progress info with the wParam and lParam. Then only in the GUI thread you would actually update the progress bar to keep business logic and GUI clearly separated.