IWinHttpRequest::WaitForResponse method

Article
01/07/2021

The WaitForResponse method waits for an asynchronous Send method to complete, with optional time-out value, in seconds.

Syntax

HRESULT WaitForResponse(
  [in, optional] VARIANT      Timeout,
  [out, retval]  VARIANT_BOOL *Succeeded
);

Parameters

Timeout [in, optional]

Time-out value, in seconds. Default time-out is infinite. To explicitly set time-out to infinite, use the value -1.

Succeeded [out, retval]

Receives one of the following values.

Value	Meaning
VARIANT_TRUE	A response has been received.
VARIANT_FALSE	The specified time-out period was exceeded.

Return value

The return value is S_OK on success or an error value otherwise.

Remarks

This method suspends execution while waiting for a response to an asynchronous request. This method should be called after a Send. Calling applications can specify an optional Timeout value, in seconds. If this method times out, the request is not aborted. This way, the calling application can continue to wait for the request, if desired, in a subsequent call to this method.

Calling this property after a synchronous Send method returns immediately and has no effect.

Note

For Windows XP and Windows 2000, see the Run-Time Requirements section of the WinHTTP Start Page.

Examples

The following example shows how to open an asynchronous HTTP connection, send an HTTP request, wait for the response and read the response text.

#include <windows.h>
#include <stdio.h>
#include <objbase.h>

#include "httprequest.h"

#pragma comment(lib, "ole32.lib")
#pragma comment(lib, "oleaut32.lib")

// IID for IWinHttpRequest.
const IID IID_IWinHttpRequest =
{
  0x06f29373,
  0x5c5a,
  0x4b54,
  {0xb0, 0x25, 0x6e, 0xf1, 0xbf, 0x8a, 0xbf, 0x0e}
};

int main()
{
    // Variable for return value
    HRESULT    hr;

    // Initialize COM.
    hr = CoInitialize( NULL );

    IWinHttpRequest *  pIWinHttpRequest = NULL;

    BSTR            bstrResponse = NULL;
    VARIANT         varTrue;
    VARIANT         varEmpty;

    CLSID           clsid;

    VariantInit(&varTrue);
    V_VT(&varTrue)   = VT_BOOL;
    V_BOOL(&varTrue) = VARIANT_TRUE;

    VariantInit(&varEmpty);
    V_VT(&varEmpty) = VT_ERROR;

    hr = CLSIDFromProgID(L"WinHttp.WinHttpRequest.5.1", &clsid);

    if (SUCCEEDED(hr))
    {
        hr = CoCreateInstance(clsid, NULL,
                              CLSCTX_INPROC_SERVER,
                              IID_IWinHttpRequest,
                              (void **)&pIWinHttpRequest);
    }
    if (SUCCEEDED(hr))
    {    // Open WinHttpRequest.
        BSTR bstrMethod  = SysAllocString(L"GET");
        BSTR bstrUrl = SysAllocString(L"https://microsoft.com");
        hr = pIWinHttpRequest->Open(bstrMethod, bstrUrl, varTrue);
        SysFreeString(bstrMethod);
        SysFreeString(bstrUrl);
    }
    if (SUCCEEDED(hr))
    {    // Send Request.
        hr = pIWinHttpRequest->Send(varEmpty);
    }
    if (SUCCEEDED(hr))
    {    // Wait for response.
        VARIANT_BOOL varResult;
        hr = pIWinHttpRequest->WaitForResponse(varEmpty, &varResult);
    }
    if (SUCCEEDED(hr))
    {    // Get Response text.
        hr = pIWinHttpRequest->get_ResponseText(&bstrResponse);
    }
    if (SUCCEEDED(hr))
    {    // Print the response to a console.
        wprintf(L"%.256s",bstrResponse);
    }

    // Release memory.
    if (pIWinHttpRequest)
        pIWinHttpRequest->Release();
    if (bstrResponse)
        SysFreeString(bstrResponse);

    CoUninitialize();
    return 0;
}

The following scripting example shows how to open an asynchronous HTTP connection, send an HTTP request, wait for a response, and read the response text.

// Instantiate a WinHttpRequest object.
var WinHttpReq = new ActiveXObject("WinHttp.WinHttpRequest.5.1");

// Initialize an HTTP request.  
WinHttpReq.Open("GET", "https://www.microsoft.com", true);

// Send the HTTP request.
WinHttpReq.Send(); 

// Wait for the response.
WinHttpReq.WaitForResponse();

// Display the response text.
WScript.Echo( WinHttpReq.ResponseText);

Requirements

Requirement	Value
Minimum supported client	Windows XP, Windows 2000 Professional with SP3 [desktop apps only]
Minimum supported server	Windows Server 2003, Windows 2000 Server with SP3 [desktop apps only]
Redistributable	WinHTTP 5.0 and Internet Explorer 5.01 or later on Windows XP and Windows 2000.
IDL	HttpRequest.idl
Library	Winhttp.lib
DLL	Winhttp.dll

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