WinInet编程中如何使用异步

在WinInet编程中，同步的使用方法如下：
InternetOpen->InternetOpenUrl->HttpQueryInfo->InternetReadFile->InternetCloseHandle;在InternetOpenUrl和InternetReadFile时会导致程序阻塞，知道操作完成，同步的好处就是比较简单，调试方便。
异步的使用方法如下：
1)InternetOpen，需指定是异步；
2)InternetSetStatusCallback,设置回调；
3)InternetOpenUrl,需指定回调参数；
4)WaitForSingObject或WaitForMultipleObjects，接收信号量；
5)HttpQueryInfo；
6)InternetReadFileEx，需指定回调参数(CE或mobile下是InternetReadFileExA)；
7)WaitForSingObject或WaitForMultipleObjects，接收信号量；
8)InternetSetStatusCallback,卸载回调；
9)InternetCloseHandle。

异步比同步要复杂了不少，重点在于回调函数。在回调中，系统会及时返回各种系统定义的HTTP消息，我们根据这些消息来设置某些信号量。在WaitForSingObject或WaitForMultipleObjects里，等待这些信号(当然也可以等待用户的取消动作)。当有正确的信号返回时，继续往下的操作。下面一个例子代码：上面的理论同样适用于wince或windows mobile平台

#include<windows.h>
#include<wininet.h>
#include<iostream.h>

DWORD dwNumKSent;
DWORD dwNumKToSend;
DWORD dwNumBytesComplete = 0;
char lpOutBuf[1024];
HANDLE hConnectedEvent, hRequestCompleteEvent;
HINTERNET hInstance, hConnect, hRequest;
char *lpszUrl, *lpszServer;

BOOL bAllDone = FALSE;

void __stdcall Callback(HINTERNET hInternet,
              DWORD dwContext,
              DWORD dwInternetStatus,
              LPVOID lpStatusInfo,
              DWORD dwStatusInfoLen);

void main(int argc, char *argv[])
{
    if (argc != 4)
    {
        cout << "Usage: sendreqexasync <server> <url> <size in kilobytes>" << endl;
        cout << "   Example: sendreqexasync www.foo.com /postfolder/upload.exe 256" << endl;
        return;
    }

    lpszServer = argv[1];
    lpszUrl = argv[2];
    dwNumKToSend = atoi(argv[3]);

    FillMemory(lpOutBuf, 1024, 'A');
    hConnectedEvent = CreateEvent(NULL, FALSE, FALSE, NULL);
    hRequestCompleteEvent = CreateEvent(NULL, FALSE, FALSE, NULL);

    hInstance = InternetOpen("sendreqexasync", 
                                       INTERNET_OPEN_TYPE_PRECONFIG,
                                       NULL,
                                       NULL,
                                       INTERNET_FLAG_ASYNC);

    if (hInstance == NULL)
    {
        cout << "InternetOpen failed, error " << GetLastError();
        return;
    }

    if (InternetSetStatusCallback(hInstance,
                                  (INTERNET_STATUS_CALLBACK)&Callback) == INTERNET_INVALID_STATUS_CALLBACK)
    {
        cout << "InternetSetStatusCallback failed, error " << GetLastError();
        return;
    }

    hConnect = InternetConnect(hInstance, 
                               lpszServer, 
                               INTERNET_DEFAULT_HTTP_PORT,
                               NULL,
                               NULL,
                               INTERNET_SERVICE_HTTP,
                               0,
                               1);
    if (hConnect == NULL)
    {
        if (GetLastError() != ERROR_IO_PENDING)
        {
            cout << "InternetConnect failed, error " << GetLastError();
            return;
        }
        WaitForSingleObject(hConnectedEvent, INFINITE);
    }

    hRequest = HttpOpenRequest(hConnect, 
                               "POST", 
                               lpszUrl,
                               NULL,
                               NULL,
                               NULL,
                               INTERNET_FLAG_RELOAD | INTERNET_FLAG_NO_CACHE_WRITE,
                               2);
    if (hRequest == NULL)
    {
        if (GetLastError() != ERROR_IO_PENDING)
        {
            cout << "HttpOpenRequest failed, error " << GetLastError();
            return;
        }
        WaitForSingleObject(hRequestCompleteEvent, INFINITE);
    }

    INTERNET_BUFFERS IntBuff;

    FillMemory(&IntBuff, sizeof(IntBuff), 0);
    IntBuff.dwStructSize= sizeof(IntBuff);
    IntBuff.dwBufferTotal = 1024*dwNumKToSend;
    IntBuff.lpcszHeader = "Content-Type: text/text\r\n";
    IntBuff.dwHeadersLength = lstrlen(IntBuff.lpcszHeader);

    if (!HttpSendRequestEx(hRequest, 
                           &IntBuff, 
                           NULL, 
                           0,
                           2))
    {
        if (GetLastError() != ERROR_IO_PENDING)
        {
            cout << "HttpSendRequestEx failed, error " << GetLastError();
            return;
        }
        cout << "HttpSendRequestEx called successfully" << endl;
        cout.flush();

        WaitForSingleObject(hRequestCompleteEvent, INFINITE);
    }

    for (dwNumKSent = 0; dwNumKSent < dwNumKToSend; dwNumKSent++)
    {
        DWORD dwBytesWritten;

        if(!InternetWriteFile(hRequest,
                               lpOutBuf,
                               1024,
                               &dwBytesWritten))
        {
            if (GetLastError() != ERROR_IO_PENDING)
            {
                cout << "InternetWriteFile failed, error " << GetLastError();
                return;
            }
            else
            {
                cout << "InternetWriteFile completing asynchronously" << endl;
                cout.flush();
                WaitForSingleObject(hRequestCompleteEvent, INFINITE);
            }
        }
    }

    cout << "Calling HttpEndRequest" << endl;
    cout.flush();
    if (!HttpEndRequest(hRequest, NULL, HSR_INITIATE, 2))
    {
        if (GetLastError() == ERROR_IO_PENDING)
        {
            cout << "HttpEndRequest called" << endl;
            cout.flush();
            WaitForSingleObject(hRequestCompleteEvent, INFINITE);
        }
        else
        {
            cout << "HttpEndRequest failed, error " << GetLastError() << endl;
            return;
        }
    }


    cout << "------------------- Read the response -------------------" << endl;
    char lpReadBuff[256];

    do
    {
        INTERNET_BUFFERS InetBuff;
        FillMemory(&InetBuff, sizeof(InetBuff), 0);
        InetBuff.dwStructSize = sizeof(InetBuff);
        InetBuff.lpvBuffer = lpReadBuff;
        InetBuff.dwBufferLength = sizeof(lpReadBuff) - 1;
        
        cout << "Calling InternetReadFileEx" << endl;
        cout.flush();

        if (!InternetReadFileEx(hRequest,
                              &InetBuff,
                              0, 2))
        {
            if (GetLastError() == ERROR_IO_PENDING)
            {
                cout << "Waiting for InternetReadFile to complete" << endl;
                cout.flush();
                WaitForSingleObject(hRequestCompleteEvent, INFINITE);
            }
            else
            {
                cout << "InternetReadFileEx failed, error " << GetLastError();
                cout.flush();
                return;
            }
        }

        lpReadBuff[InetBuff.dwBufferLength] = 0;
        cout << lpReadBuff;
        cout.flush();

        if (InetBuff.dwBufferLength == 0) 
            bAllDone = TRUE;

    } while (bAllDone == FALSE);

    cout << endl << endl << "------------------- Request Complete ----------------" << endl;

}

void __stdcall Callback(HINTERNET hInternet,
              DWORD dwContext,
              DWORD dwInternetStatus,
              LPVOID lpStatusInfo,
              DWORD dwStatusInfoLen)
{
    cout << "Callback dwInternetStatus: " << dwInternetStatus << " Context: " << dwContext << endl;
    cout.flush();

    switch(dwContext)
    {
    case 1: // Connection handle
        if (dwInternetStatus == INTERNET_STATUS_HANDLE_CREATED)
        {
            INTERNET_ASYNC_RESULT *pRes = (INTERNET_ASYNC_RESULT *)lpStatusInfo;
            hConnect = (HINTERNET)pRes->dwResult;
            cout << "Connect handle created" << endl;
            cout.flush();
            SetEvent(hConnectedEvent);
        }
        break;
    case 2: // Request handle
        switch(dwInternetStatus)
        {
        case INTERNET_STATUS_HANDLE_CREATED:
            {
                INTERNET_ASYNC_RESULT *pRes = (INTERNET_ASYNC_RESULT *)lpStatusInfo;
                hRequest = (HINTERNET)pRes->dwResult;
                cout << "Request handle created" << endl;
                cout.flush();
            }
            break;
        case INTERNET_STATUS_REQUEST_SENT:
            {
                DWORD *lpBytesSent = (DWORD*)lpStatusInfo;
                cout << "Bytes Sent: " << *lpBytesSent << endl;
                dwNumBytesComplete += *lpBytesSent;
            }
            break;
        case INTERNET_STATUS_REQUEST_COMPLETE:
            {
                INTERNET_ASYNC_RESULT *pAsyncRes = (INTERNET_ASYNC_RESULT *)lpStatusInfo;
                cout << "Function call finished" << endl;
                cout << "dwResult: " << pAsyncRes->dwResult << endl;
                cout << "dwError:  " << pAsyncRes->dwError << endl;
                cout.flush();
                SetEvent(hRequestCompleteEvent);
            }
            break;
        case INTERNET_STATUS_RECEIVING_RESPONSE:
            cout << "Receiving Response" << endl;
            cout.flush();
            break;
        case INTERNET_STATUS_RESPONSE_RECEIVED:
            {
                DWORD *dwBytesReceived = (DWORD*)lpStatusInfo;
                cout << "Received " << *dwBytesReceived << endl;
                cout.flush();
            }

        }

    }

}

参考的异步类：

include <wininet.h>
#include <mmsystem.h>

class AsyncWinINet
{
public:
  typedef void (*notify_fp)(const StringMap&);
 
  class thread_info
  {
  public:
   thread_info(const String& _url,     //请求下载的地址(in)
    const StringMap& _request_headrs,   //请求头request_headrs(in)
    const notify_fp& _pfp,      //下载进度通知回调函数指针
    const StringMap& _pfp_param,
    String& _response_headrs,     //返回头response_headrs(out)  
    const String& _saved_filename,    //下载内容保存文件名(in)
    String& _response_content,     //返回内容(out)
    size_t _read_content_size)     //控制保存在response_content中内容的长度(in)) : 
    : request_headrs(_request_headrs), pfp(_pfp),
    pfp_param(_pfp_param),      //pfp函数传回参数
    response_headrs(_response_headrs), saved_filename(_saved_filename),
    response_content(_response_content), read_content_size(_read_content_size) 
   {
    this->response_headrs.clear();
    this->response_content.clear();
    this->url = StringUtil::EncodeURIComponent(_url);
    for(int i = 0; i < 3; ++i)
    {
     this->hEvent[i] = CreateEvent(NULL,TRUE,FALSE,NULL);
    }
   }

   HANDLE hThread;
   DWORD dwThreadID;
   HANDLE hCallbackThread;
   DWORD dwCallbackThreadID;
   HANDLE hEvent[3];
   LPVOID hInternet;
   LPVOID hFile;
   DWORD dwStatusCode;
   DWORD dwContentLength;

   String url;         //请求下载的地址(in)
   const StringMap& request_headrs;   //请求头request_headrs(in)
   const notify_fp& pfp;      //下载进度通知回调函数指针
   const StringMap& pfp_param;     //pfp函数传回参数

   String& response_headrs;     //返回头response_headrs(out)  
   const String& saved_filename;    //下载内容保存文件名(in)
   String& response_content;     //返回内容(out)
   size_t read_content_size;     //控制保存在response_content中内容的长度(in)
  };

  /*******************************************************************************
  * 函数：download
  * 功能：下载，返回WinINet_ERR_CODE值
  *   说明：关于notify_fp 类型说明: 函数的参数为StringMap类型，传回的变量名与变量值
  * 2007-12
  *******************************************************************************/
  static DWORD download(const String& url, //请求下载的地址(in)
   const StringMap& request_headrs,   //请求头request_headrs(in)
   const notify_fp& pfp,      //下载进度通知回调函数指针
   const StringMap& pfp_param,     //pfp函数传回参数
   String& response_headrs,     //返回头response_headrs(out)  
   const String& saved_filename,    //下载内容保存文件名(in)
   String& response_content,     //返回内容(out)
   size_t read_content_size = 0);    //控制保存在response_content中内容的长度(in)

protected:
  static BOOL WaitExitEvent(thread_info *p);
  static DWORD WINAPI AsyncThread(LPVOID lpParameter);
  static DWORD WINAPI AsyncCallbackThread(LPVOID lpParameter);
  static VOID CALLBACK AsyncInternetCallback(HINTERNET hInternet,
   DWORD dwContext,
   DWORD dwInternetStatus,
   LPVOID lpvStatusInformation,
   DWORD dwStatusInformationLength);

};

#include "AsyncWinINet.h"

#include "stdafx.h"

#pragma comment(lib, "Winmm.lib")
#pragma comment(lib, "Wininet.lib")

DWORD AsyncWinINet::download(const Fagex::String &url, const Fagex::StringMap &request_headrs, 
  const Fagex::AsyncWinINet::notify_fp &pfp, const Fagex::StringMap &pfp_param, Fagex::String &response_headrs, 
  const Fagex::String &saved_filename, Fagex::String &response_content, size_t read_content_size)
{
  thread_info info(url, request_headrs, pfp,
   pfp_param, response_headrs, saved_filename,
   response_content, read_content_size);

  info.hThread = CreateThread(NULL, 
   0,
   AsyncWinINet::AsyncThread,
   &info,
   NULL,
   &info.dwThreadID);

  WaitForSingleObject(info.hThread, INFINITE); //等待子线程安全退出
  CloseHandle(info.hThread);//关闭线程句柄

  return TRUE;
}

//---------------------------------------------------------------------
DWORD WINAPI AsyncWinINet::AsyncThread(LPVOID lpParameter)
{
  thread_info* p = (thread_info*)lpParameter;

  //a. 使用标记 INTERNET_FLAG_ASYNC 初始化 InternetOpen
  String user_agent("Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 5.1; TencentTraveler ; .NET CLR 2.0.50727)");
  StringMap iheadrs(p->request_headrs.begin(), p->request_headrs.end());
  StringMap::iterator it = iheadrs.find("User-Agent");
  if(it == iheadrs.end()) iheadrs["User-Agent"] = user_agent;
  else user_agent = it->second;

  p->hInternet = InternetOpen(user_agent.c_str(),
   INTERNET_OPEN_TYPE_PRECONFIG,
   NULL,
   NULL,
   INTERNET_FLAG_ASYNC);

  //ResetEvent(p->hEvent[0]);
  //p->hCallbackThread = CreateThread(NULL,
  // 0,
  // AsyncWinINet::AsyncCallbackThread,
  // p,
  // NULL,
  // &p->dwCallbackThreadID);
  //WaitForSingleObject(p->hEvent[0], INFINITE);//等待回调函数设置成功事件
  InternetSetStatusCallback(p->hInternet, AsyncWinINet::AsyncInternetCallback);

  String sheadrs;
  for(it = iheadrs.begin(); it != iheadrs.end(); ++it)
  {
   sheadrs += it->first + ":" + it->second;
   if(it->second.find(StringUtil::enter) == String::npos) { sheadrs += StringUtil::enter; }
  }
  sheadrs += StringUtil::enter;
 
  DWORD start_time = timeGetTime();
  ResetEvent(p->hEvent[0]); //重置句柄被创建事件
  p->hFile = InternetOpenUrl(p->hInternet, p->url.c_str(), sheadrs.c_str(), sheadrs.length(), 
   INTERNET_FLAG_DONT_CACHE | INTERNET_FLAG_RELOAD, (DWORD)p);

  FILE *fp = fopen(p->saved_filename.c_str(), "w+");
  while(true)
  {
   if (NULL == p->hFile)
   {
    DWORD dwError = ::GetLastError();
    if (ERROR_IO_PENDING == dwError || ERROR_SUCCESS == dwError)
    {
     if (WaitExitEvent(p)) { break; }
    }
    else break;
   }

   //读取返回文件头
   DWORD dwLength = 0;
   LPVOID lpOutBuffer = NULL;
   while(true) //读取response_headrs数据
   {
    if(!HttpQueryInfo(p->hFile, HTTP_QUERY_RAW_HEADERS_CRLF,
       lpOutBuffer, &dwLength, NULL))
    {
     DWORD err_code = GetLastError();
     if (err_code == ERROR_HTTP_HEADER_NOT_FOUND) break; 
     else if(err_code == ERROR_INSUFFICIENT_BUFFER)
     {
      lpOutBuffer = new char[dwLength];
      continue; 
     }
     else break;
    }
    break;
   }
   if(lpOutBuffer != NULL)
   {
    p->response_headrs.append((char*)lpOutBuffer,dwLength);
    delete [] lpOutBuffer;
   }

   //e. 使用 HttpQueryInfo 分析头信息 HttpQueryInfo 使用非阻塞方式，所以不用等待
   DWORD dwStatusSize = sizeof(p->dwStatusCode);
   if (FALSE == HttpQueryInfo(p->hFile, //获取返回状态码
    HTTP_QUERY_STATUS_CODE | HTTP_QUERY_FLAG_NUMBER,
    &p->dwStatusCode, &dwStatusSize, NULL)) { break; }
  
   //判断状态码是不是 200
   if (HTTP_STATUS_OK != p->dwStatusCode) break;
  
   StringMap msgMap(p->pfp_param.begin(), p->pfp_param.end());
   msgMap["url"] = p->url;

   //获取返回的Content-Length
   //DWORD dwLengthSize = sizeof(p->dwContentLength); 
   //if (FALSE == HttpQueryInfo(p->hFile,
   //HTTP_QUERY_CONTENT_LENGTH | HTTP_QUERY_FLAG_NUMBER,
   //&p->dwContentLength, &dwLengthSize, NULL)) { p->dwContentLength = 0; }

   //f. 使用标记 IRF_ASYNC 读数据 InternetReadFileEx
   //为了向主线程报告进度，我们设置每次读数据最多 1024 字节

   char lpvBuffer[1024];
   p->dwContentLength = 0; //Content-Length: 202749
   while(true)
   {
    INTERNET_BUFFERS i_buf = {0};
    i_buf.dwStructSize = sizeof(INTERNET_BUFFERS);
    i_buf.lpvBuffer = lpvBuffer;
    i_buf.dwBufferLength = 1024;
      
    //重置读数据事件
    ResetEvent(p->hEvent[0]);
    if (FALSE == InternetReadFileEx(p->hFile, &i_buf, IRF_ASYNC, (DWORD)p))
    {
     if (ERROR_IO_PENDING == ::GetLastError())
     {
      if (WaitExitEvent(p)) break; 
     }
     else break; 
    }
    else
    {
     //在网络传输速度快，步长较小的情况下，InternetReadFileEx 经常会直接返回成功，
     //因此要判断是否发生了用户要求终止子线程事件。
     if (WAIT_OBJECT_0 == WaitForSingleObject(p->hEvent[2], 0))
     {
      ResetEvent(p->hEvent[2]);
      break;
     }
    }

    if(i_buf.dwBufferLength == 0) 
    {
     DWORD time = timeGetTime() - start_time;
     if(time != 0)
     {
      Real speed = (Real)p->dwContentLength;
      speed /= ((Real)time)/1000.0f;
      speed /= 1024.0f;
      msgMap["speed"] = StringUtil::toString((DWORD)speed);
     }
     if(p->pfp) p->pfp(msgMap);
     break;
    }
    if(fp)
    {
     fwrite(i_buf.lpvBuffer, sizeof(char), i_buf.dwBufferLength, fp);
    }
    if(p->read_content_size > p->response_content.size())
    {
     p->response_content.append((char*)i_buf.lpvBuffer, i_buf.dwBufferLength);
    }
    p->dwContentLength += i_buf.dwBufferLength;
   }
   break;
  }
 
  if(fp)
  {
   fflush(fp); fclose(fp); fp = NULL;
  }

  if(p->hFile)
  {
   InternetCloseHandle(p->hFile);//关闭 m_hFile
   while (!WaitExitEvent(p)) //等待句柄被关闭事件或者要求子线程退出事件
   {
    ResetEvent(p->hEvent[0]);
   }
  }

  //设置子线程退出事件，通知回调线程退出
  SetEvent(p->hEvent[2]);
 
  //等待回调线程安全退出
  //WaitForSingleObject(p->hCallbackThread, INFINITE);
  //CloseHandle(p->hCallbackThread);
 
  //注销回调函数
  InternetSetStatusCallback(p->hInternet, NULL);
  InternetCloseHandle(p->hInternet);

  return TRUE;
}

//------------------------------------------------------------------------------------
DWORD WINAPI AsyncWinINet::AsyncCallbackThread(LPVOID lpParameter)
{
  thread_info *p = (thread_info*)lpParameter;
  InternetSetStatusCallback(p->hInternet, AsyncWinINet::AsyncInternetCallback);

  //通知子线程回调函数设置成功，子线程可以继续工作
  SetEvent(p->hEvent[0]);

  //等待用户终止事件或者子线程结束事件
  //子线程结束前需要设置子线程结束事件，并等待回调线程结束
  WaitForSingleObject(p->hEvent[2], INFINITE);

  return 0;
}

//----------------------------------------------------------------------------
VOID CALLBACK AsyncWinINet::AsyncInternetCallback(HINTERNET hInternet,
   DWORD dwContext,
   DWORD dwInternetStatus,
   LPVOID lpvStatusInformation,
   DWORD dwStatusInformationLength)
{
  thread_info* p = (thread_info*)dwContext;
 
  //在我们的应用中，我们只关心下面三个状态
  switch(dwInternetStatus)
  {
  //句柄被创建
  case INTERNET_STATUS_HANDLE_CREATED:
   p->hFile = (HINTERNET)(((LPINTERNET_ASYNC_RESULT)
    (lpvStatusInformation))->dwResult);
   break;
 
  //句柄被关闭
  case INTERNET_STATUS_HANDLE_CLOSING:
   SetEvent(p->hEvent[1]);
   break;

  //一个请求完成，比如一次句柄创建的请求，或者一次读数据的请求
  case INTERNET_STATUS_REQUEST_COMPLETE:
   if (ERROR_SUCCESS == ((LPINTERNET_ASYNC_RESULT)
    (lpvStatusInformation))->dwError)
   { 
    //设置句柄被创建事件或者读数据成功完成事件
    SetEvent(p->hEvent[0]);
   }
   else
   { 
    //如果发生错误，则设置子线程退出事件 这里也是一个陷阱，经常会忽视处理这个错误，
    SetEvent(p->hEvent[2]);
   }
   break;

  case INTERNET_STATUS_CONNECTION_CLOSED:
   SetEvent(p->hEvent[2]);
   break;

  }
}

//--------------------------------------------------------------------
BOOL AsyncWinINet::WaitExitEvent(thread_info *p)
{
  DWORD dwRet = WaitForMultipleObjects(3, p->hEvent, FALSE, INFINITE);
 
  switch (dwRet)
  {
  case WAIT_OBJECT_0://句柄被创建事件或者读数据请求成功完成事件
  case WAIT_OBJECT_0+1://句柄被关闭事件
  case WAIT_OBJECT_0+2://用户要求终止子线程事件或者发生错误事件
   break;
  }
  return WAIT_OBJECT_0 != dwRet;
}