纯C中使用IWebBrowser2发送POST请求，服务器无法接收参数问题

我需要用纯C编写基于IWebBrowser2的POST请求程序，微软文档指出：

PostData指定的POST数据需以SAFEARRAY数据结构传递。VARIANT应属于VT_ARRAY|VT_UI1类型，并指向SAFEARRAY数据类型。SAFEARRAY数据类型的元素类型应为VT_UI1、一维，且元素数量等于POST数据的字节数。

但当我把请求发送到本地服务器时，服务器完全接收不到$_POST['name']和$_POST['sub']变量，就像没发送任何数据一样。

我的代码如下：

INT32
WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLine, INT32 nShowCmd)
{
  HRESULT HResult = 0;
  CLSID CLSID_IE;
  IWebBrowser2 *pWebBrowser;
  VARIANT vEmpty;
  VARIANT_BOOL vBusy;

  VariantInit(&vEmpty);
  CoInitializeEx(0, COINIT_MULTITHREADED);
  CoInitializeSecurity(NULL, -1, NULL, NULL, RPC_C_AUTHN_LEVEL_DEFAULT, RPC_C_IMP_LEVEL_IMPERSONATE, NULL, EOAC_NONE, NULL);
  CoCreateInstance(&CLSID_InternetExplorer, 0, CLSCTX_ALL, &IID_IWebBrowser2, &pWebBrowser);
  IWebBrowser2_put_Visible(pWebBrowser, VARIANT_FALSE);

  /* process the formulary data */
  LPSTR pPostData = NULL;
  CHAR strFormulary[] = "sub=gt&name=sdfs";
  LPSAFEARRAY FormularyArray = SafeArrayCreateVector(VT_UI1, 0, sizeof(strFormulary));
  VARIANT PostData = FormularyArray;

  SafeArrayAccessData(FormularyArray, (LPVOID*)&pPostData);
  memcpy(pPostData, &strFormulary, sizeof(strFormulary));
  SafeArrayUnaccessData(FormularyArray);

  /* Set the headers data */
  VARIANT Headers;
  V_VT(&Headers) = VT_BSTR;
  V_BSTR(&Headers) = SysAllocString(L"Content-Type: application/x-www-form-urlencodedrn");

  /* Set POST request */
  BSTR bstrURL = SysAllocString(L"http://192.168.100.44/user.php");
  IWebBrowser2_Navigate(pWebBrowser, bstrURL, &vEmpty, &vEmpty, &PostData, &Headers);

  // Wait for page to load
  do {
    LARGE_INTEGER TimeOut;
    UINT32 Milliseconds = 2000;
    TimeOut.QuadPart = UInt32x32To64( Milliseconds, 1000 );
    TimeOut.QuadPart *= -1;
    NtDelayExecution(FALSE, &TimeOut);
    IWebBrowser2_get_Busy(pWebBrowser, &vBusy);
  } while(vBusy);

  // Get IDispatch interface
  IDispatch* pDispatch;
  IWebBrowser2_get_Document(pWebBrowser, &pDispatch);
  IHTMLDocument2* pDocument;
  IDispatch_QueryInterface(pDispatch, &IID_IHTMLDocument2 , &pDocument);
  IHTMLElement* lpBodyElm;
  IHTMLDocument2_get_body(pDocument, &lpBodyElm);
  IHTMLElement* lpParentElm;
  IHTMLElement_get_parentElement(lpBodyElm, &lpParentElm);

  // Get Inner HTML content content of the request
  BSTR bstrBody;
  lpParentElm->lpVtbl->get_innerHTML(lpParentElm, &bstrBody);

  wprintf(L"%ls\n\n", bstrBody);

  cleanup:
  SysFreeString(bstrURL);
  IWebBrowser2_Quit(pWebBrowser);
  IWebBrowser2_Release(pWebBrowser);
  IDispatch_Release(pDispatch);
  IHTMLDocument2_Release(pDocument);
  IHTMLElement_Release(lpBodyElm);
  lpParentElm->lpVtbl->Release(lpParentElm);
  CoUninitialize();
  RtlExitUserProcess(STATUS_SUCCESS);
}

问题根源及修复方案 #

1. VARIANT初始化错误 #

直接将LPSAFEARRAY赋值给VARIANT是错误的，必须正确设置VARIANT的类型标记：

VARIANT PostData;
VariantInit(&PostData);
PostData.vt = VT_ARRAY | VT_UI1;
PostData.parray = FormularyArray;

2. HTTP头部格式错误 #

头部中的换行符应该是\r\n，且HTTP头部需要以空行结尾，修正后的头部：

V_BSTR(&Headers) = SysAllocString(L"Content-Type: application/x-www-form-urlencoded\r\n\r\n");

3. POST数据长度错误 #

sizeof(strFormulary)会包含字符串末尾的\0终止符，导致数据多一个字节，改用strlen获取实际长度：

size_t postLen = strlen(strFormulary);
LPSAFEARRAY FormularyArray = SafeArrayCreateVector(VT_UI1, 0, postLen);

4. memcpy参数错误 #

数组名本身就是首地址，无需取地址，修正后的memcpy：

memcpy(pPostData, strFormulary, postLen);

修复后的关键代码片段 #

/* process the formulary data */
LPSTR pPostData = NULL;
CHAR strFormulary[] = "sub=gt&name=sdfs";
size_t postLen = strlen(strFormulary);
LPSAFEARRAY FormularyArray = SafeArrayCreateVector(VT_UI1, 0, postLen);

VARIANT PostData;
VariantInit(&PostData);
PostData.vt = VT_ARRAY | VT_UI1;
PostData.parray = FormularyArray;

SafeArrayAccessData(FormularyArray, (LPVOID*)&pPostData);
memcpy(pPostData, strFormulary, postLen);
SafeArrayUnaccessData(FormularyArray);

/* Set the headers data */
VARIANT Headers;
VariantInit(&Headers);
V_VT(&Headers) = VT_BSTR;
V_BSTR(&Headers) = SysAllocString(L"Content-Type: application/x-www-form-urlencoded\r\n\r\n");

内容的提问来源于stack exchange，提问作者steve woods