Converting WinHttp to WinInet API POST request - c++

Question

I am trying to convert some HTTP request code from using the WinHttp COM interface to using lower-level WinInet calls from <wininet.h>. The COM version is working but I am having difficulty translating the calls into the WinInet API.
This code works fine and gets the correct error response (as the request data is empty) to the POST request:
#import <winhttpcom.dll>
#include <iostream>
#include <string>
int main()
{
HRESULT hr = CoInitialize(NULL);
using namespace WinHttp;
IWinHttpRequestPtr pReq = NULL;
hr = pReq.CreateInstance(__uuidof(WinHttpRequest));
const char* pszReq = "";
if (SUCCEEDED(hr))
{
_bstr_t bstrMethod("POST");
_bstr_t bstrUrl("https://lite.realtime.nationalrail.co.uk/OpenLDBWS/ldb9.asmx");
hr = pReq->Open(bstrMethod, bstrUrl);
pReq->SetRequestHeader(_bstr_t("Content-Type"), _bstr_t("text/*"));
_variant_t vReq(pszReq);
hr = pReq->Send(vReq);
if (SUCCEEDED(hr))
{
_bstr_t bstrResp;
hr = pReq->get_ResponseText(&bstrResp.GetBSTR());
if (SUCCEEDED(hr))
{
std::cout << std::string(bstrResp) << "\n";
}
}
}
CoUninitialize();
}
Saving the output as html, gives this rendering of the response (which is what I expect, since I haven't provided any request data, which would usually include an access token).
This is the code (amended after comments below, and should be reproducible) that I am using to try and replicate this result using wininet.h and the low-level Win32 calls (I realize I haven't closed the handles).
#include <windows.h>
#include <WinInet.h>
#include <iostream>
int main()
{
const char* pszReq = "";
const char* pszUrl = "https://lite.realtime.nationalrail.co.uk/OpenLDBWS/ldb9.asmx";
char szHostName[256];
char szPath[256];
URL_COMPONENTSA comps = {};
comps.dwStructSize = sizeof(comps);
comps.lpszHostName = szHostName;
comps.dwHostNameLength = sizeof(szHostName);
comps.lpszUrlPath = szPath;
comps.dwUrlPathLength = sizeof(szPath);
if (!InternetCrackUrlA(pszUrl, strlen(pszUrl), 0, &comps)) return 1;
HINTERNET hOpen = InternetOpenA("XYZ",INTERNET_OPEN_TYPE_DIRECT,NULL,NULL,0);
if (!hOpen) return 1;
HINTERNET hConnect = InternetConnectA(hOpen,szHostName,comps.nPort,
NULL,NULL,INTERNET_SERVICE_HTTP,0,NULL);
if (!hConnect) return 1;
const char * rgpszAcceptTypes[] = { "text/*", NULL };
HINTERNET hOpenReq = HttpOpenRequestA(hConnect,"POST",szPath,NULL, NULL,
rgpszAcceptTypes, 0,NULL);
if (!hOpenReq) return 1;
const char* pszHeader = "Content-Type: text/xml;charset=UTF-8";
//*** This line returns FALSE ***
BOOL bRet = HttpSendRequestA(hOpenReq, pszHeader, strlen(pszHeader), (LPVOID)pszReq, strlen(pszReq));
//*** LastError is ERROR_HTTP_INVALID_SERVER_RESPONSE
DWORD dwErr = GetLastError();
return 0;
}
All the WinInet handles are non-zero, suggesting the calls are working, but the last HttpSendRequestA() is returning FALSE immediately, with LastError set to ERROR_HTTP_INVALID_SERVER_RESPONSE.
Clearly the COM route hides a lot of intermediate working, and presumably some constants are defaulted to specific values. It may also be adding other header information, I suppose.
Perhaps someone can suggest where I am going wrong?

Answer 1

There are some mistakes in your WinInet code:
the pszServerName value needs to be just the host name by itself, not a full URL. If you have a URL as input, you can parse it into its constituent pieces using InternetCrackUrlA().
the 3rd parameter of HttpOpenRequestA() is the requested resource relative to pszServerName. So, in your example, you need to use "/" to request the root resource.
the 1st parameter of HttpSendRequestA() needs to be hOpenReq, not hOpen. Also, you should not be including the null-terminators in your buffer sizes.
If you have not already done so, you should have a look at WinInet's documentation on HTTP Sessions.
With that said, try this:
#include <windows.h>
#include <WinInet.h>
#include <iostream>
const char * pszUrl = "https://someUrl";
const char * pszReq = "A string of request data";
const char* pszHeader = "Content-Type: text/xml;charset=UTF-8";
char szHostName[256];
char szPath[256];
URL_COMPONENTSA comps = {};
comps.dwStructSize = sizeof(comps);
comps.lpszHostName = szHostName;
comps.dwHostNameLength = sizeof(szHostName);
comps.lpszUrlPath = szPath;
comps.dwUrlPathLength = sizeof(szPath);
BOOL bRet = InternetCrackUrlA(pszUrl, strlen(pszUrl), 0, &comps);
if (!bRet) ...
HINTERNET hOpen = InternetOpenA("XYZ", INTERNET_OPEN_TYPE_DIRECT, NULL, NULL, 0);
if (!hOpen) ...
HINTERNET hConnect = InternetConnectA(hOpen, szHostName, comps.nPort, NULL, NULL, INTERNET_SERVICE_HTTP, 0, NULL);
if (!hConnect) ...
HINTERNET hOpenReq = HttpOpenRequestA(hConnect, "POST", szPath, NULL, NULL, NULL, comps.nScheme == INTERNET_SCHEME_HTTPS ? INTERNET_FLAG_SECURE : 0, NULL);
if (!hOpenReq) ...
bRet = HttpSendRequestA(hOpenReq, pszHeader, strlen(pszHeader), pszReq, strlen(pszReq));
if (!bRet) ...
...