如何获取 BITS 下载作业中每个文件收到的最后一组 HTTP 标头

此示例演示如何使用新的 IBackgroundCopyJob5 接口的 GetProperty 方法获取后台智能传输服务 (BITS) 下载作业中每个文件收到的最后一组 HTTP 标头。 例如,可以使用 HTTP 标头中的信息来确定文件类型或在服务器上上次更改的时间。 在Windows 8和Windows Server 2012之前,BITS 不提供应用程序可以检索和检查已完成下载的 HTTP 响应标头的方法。 此示例演示如何使用 BITS API 创建包含多个 URL 的 BITS 作业,列出作业中的 URL,以及检索每个 URL 的 HTTP 响应标头。

需要了解的事项

技术

先决条件

  • Microsoft Visual Studio

说明

步骤 1:包括所需的 BITS 头文件

在源文件顶部插入以下标头指令。

#include <bits.h>

步骤 2:初始化 COM 并实例化 BITS 后台复制管理器对象接口

在实例化 IBackgroundCopyManager 接口之前, (用于创建 BITS 作业) ,必须初始化 COM 并设置所需的 COM 线程模型。

// Initialize COM and specify the appropriate COM threading model for your application.
IBackgroundCopyManager* pManager;

HRESULT hr = CoInitializeEx(NULL, COINIT_APARTMENTTHREADED);
if (SUCCEEDED(hr))
{
 hr = CoCreateInstance(__uuidof(BackgroundCopyManager), 
                       NULL,
                       CLSCTX_LOCAL_SERVER,
                       __uuidof(IBackgroundCopyManager),
                       (void**) &pManager);
}

步骤 3:创建 BITS 作业

只有创建作业或具有管理员权限的用户才能将文件添加到作业并更改作业的属性。

GUID guidJob;
IBackgroundCopyJob* pBackgroundCopyJob;

hr = pManager->CreateJob(L"TransferPolicy",
                         BG_JOB_TYPE_DOWNLOAD,
                         &guidJob,
                         (IBackgroundCopyJob **)&pBackgroundCopyJob);

步骤 4:将文件添加到 BITS 作业

以下示例从 Microsoft 下载中心下载公开可用的文档。 需要为特定环境更改这些值。

// Array that contains multiple DOWNLOAD_FILE data structures that represent the 
// files that will be added to the download job.
DOWNLOAD_FILE FileList[] =
{
 {
  L"https://download.microsoft.com/download/0/2/8/02809141-3329-4412-8AC4-AA41B406055C/WinRT81-HttpClient-BT-Socket-Poster.pdf",
  L"c:\\temp\\data\\WinRT81-HttpClient-BT-Socket-Poster.pdf"
 },
 {
  L"https://download.microsoft.com/download/6/6/2/662DD05E-BAD7-46EF-9431-135F9BAE6332/9781509302963_Microsoft%20Azure%20Essentials%20Fundamentals%20of%20Azure%202nd%20ed%20pdf.pdf",
  L"c:\\temp\\data\\Fundamentals of Azure.pdf"
 },
 {
  L"https://aka.ms/WinServ16/StndPDF",
  L"c:\\temp\\data\\IntroducingWindowsServer2016.pdf"
 }
};

...

// Add the files to the job.
for (int i=0; i < ARRAY_LENGTH(FileList); ++i)
{
 hr = Job->AddFile(FileList[i].RemoteFile,
                   FileList[i].LocalFile);
 ...
}

步骤 5:"开始"菜单 BITS 作业

设置 BITS 作业后,调用 IBackgroundCopyJob 接口的 Resume 函数以启动或继续下载。

// Start the BITS job. 
hr = pBackgroundJob->Resume();

步骤 6:监视和显示 BITS 作业的进度

MonitorJobProgress帮助程序函数采用 IBackgroundCopyJob 对象作为唯一参数,每 500 毫秒轮询一次状态。 在作业完成或取消之前,此函数不会返回。

HRESULT MonitorJobProgress(__in IBackgroundCopyJob* Job)
{ 
 HRESULT hr;
 LPWSTR JobName;
 BG_JOB_STATE State;
 int PreviousState = -1;
 bool Exit = false;
 int ProgressCounter = 0;
 hr = Job->GetDisplayName(&JobName);
 printf("Progress report for download job '%ws'.\n", JobName);
 CoTaskMemFree(JobName);

 // Display the download progress.
 while (!Exit)
 {
  hr = Job->GetState(&State);
  if (State != PreviousState)
  {
   switch(State)
   {
    case BG_JOB_STATE_QUEUED:
     printf("Job is in the queue and waiting to run.\n");
    break;
    case BG_JOB_STATE_CONNECTING:
     printf("BITS is trying to connect to the remote server.\n");    
    break;

    case BG_JOB_STATE_TRANSFERRING:
     printf("BITS has started downloading data.\n");  
     DisplayProgress( Job );
    break;

    case BG_JOB_STATE_ERROR:
     wprintf(L"ERROR: BITS has encountered a non-recoverable error.\n");
     DisplayError(Job);
     wprintf(L"       Exiting job.\n");
     Exit = true;
     break;

    case BG_JOB_STATE_TRANSIENT_ERROR:
     wprintf(L"ERROR: BITS has encountered a recoverable error.\n");
     DisplayError(Job);
     wprintf(L"       Continuing to retry.\n");
     break;

    case BG_JOB_STATE_TRANSFERRED:
     DisplayProgress(Job);
     printf("The job has been successfully completed.\n");
     printf("Finalizing local files.\n");
     Job->Complete();
    break;

    case BG_JOB_STATE_ACKNOWLEDGED:
     printf("Finalization complete.\n");
     Exit = true;
    break;

    case BG_JOB_STATE_CANCELLED:
     printf("WARNING: The job has been cancelled.\n");   
     Exit = true;
    break;

    default:
     printf("WARNING: Unknown BITS state %d.\n", State);    
     Exit = true;
   }

   PreviousState = State;
  }
  else if (State == BG_JOB_STATE_TRANSFERRING)
  {
   // Display job progress every 2 seconds.
   if (++ProgressCounter % TWO_SECOND_LOOP == 0)
   {
    DisplayProgress( Job );
   } 
  }
  Sleep(HALF_SECOND_AS_MILLISECONDS);
 }
 printf("\n");
 return hr;
}

// Display the current progress of the job in terms of the amount of data
// and number of files transferred.
VOID DisplayProgress(__in IBackgroundCopyJob *Job)
{
 HRESULT hr;
 BG_JOB_PROGRESS Progress;
 hr = Job->GetProgress(&Progress);
 if (SUCCEEDED(hr))
 {
  printf("%llu of %llu bytes transferred (%lu of %lu files).\n",
         Progress.BytesTransferred, Progress.BytesTotal,
         Progress.FilesTransferred, Progress.FilesTotal);
 }
}

步骤 7:显示下载的文件头

DisplayFileHeaders帮助程序函数枚举为 IBackgroundCopyJob 对象定义的作业。

// For each file in the job, obtain and display the HTTP header received server.
HRESULT DisplayFileHeaders(__in IBackgroundCopyJob *Job)
{
 HRESULT hr;
 IEnumBackgroundCopyFiles *FileEnumerator;
 
 hr = Job->EnumFiles(&FileEnumerator);
 if (SUCCEEDED(hr))
 {
  ULONG Count;

  hr = FileEnumerator->GetCount(&Count);
  if (SUCCEEDED(hr))
  {
   for (ULONG i=0; i < Count; ++i)
   {
    IBackgroundCopyFile *TempFile;

    hr = FileEnumerator->Next(1, &TempFile, NULL);
    if (SUCCEEDED(hr))
    {
     IBackgroundCopyFile5 *File;
     hr = TempFile->QueryInterface(__uuidof( IBackgroundCopyFile5 ), (void **) &File);
     if (SUCCEEDED(hr))
     {
      LPWSTR RemoteFileName;
      hr = File->GetRemoteName(&RemoteFileName);
      if (SUCCEEDED(hr))
      {
       printf("HTTP headers for remote file '%ws'\n", RemoteFileName );
       CoTaskMemFree( RemoteFileName );
       RemoteFileName = NULL;
      }

      BITS_FILE_PROPERTY_VALUE Value;
      hr = File->GetProperty(BITS_FILE_PROPERTY_ID_HTTP_RESPONSE_HEADERS, &Value);
      if (SUCCEEDED(hr) && Value.String)
      {
       printf("Headers: %ws\n", Headers );

       CoTaskMemFree(Value.String);
       Value.String = NULL;
      }

      File->Release();
      File = NULL;
     }

     TempFile->Release();
     TempFile = NULL;
    }
   }
  }

   FileEnumerator->Release();
   FileEnumerator = NULL;
 }

 return S_OK;
}

示例

下面的代码示例是一个完全正常工作的控制台应用程序,演示如何使用 BITS API 创建包含多个 URL 的 BITS 作业,列出作业中的 URL,以及检索每个 URL 的 HTTP 响应标头。

//*********************************************************
//
//    Copyright (c) Microsoft. All rights reserved.
//    This code is licensed under the Microsoft Public License.
//    THIS CODE IS PROVIDED *AS IS* WITHOUT WARRANTY OF
//    ANY KIND, EITHER EXPRESS OR IMPLIED, INCLUDING ANY
//    IMPLIED WARRANTIES OF FITNESS FOR A PARTICULAR
//    PURPOSE, MERCHANTABILITY, OR NON-INFRINGEMENT.
//
//*********************************************************

#define WIN32_LEAN_AND_MEAN // Exclude rarely-used stuff from Windows headers
#include <windows.h>
#include <bits.h>
#include <stdio.h> // needed for wprintf
#include <strsafe.h>

#define ARRAY_LENGTH(x) (sizeof(x) / sizeof( *(x) ))

// Definition of constants.
static const unsigned int HALF_SECOND_AS_MILLISECONDS = 500;
static const unsigned int TWO_SECOND_LOOP = 2000 / HALF_SECOND_AS_MILLISECONDS;

// Simple data structure that contains the remote and local names for a file.
typedef struct
{
 LPCWSTR RemoteFile;
 LPCWSTR LocalFile;
} DOWNLOAD_FILE;

// Array that contains sample DOWNLOAD_FILE data structures that represent the files
// that will be added to the download job.
DOWNLOAD_FILE FileList[] =
{
 {
  L"https://download.microsoft.com/download/0/2/8/02809141-3329-4412-8AC4-AA41B406055C/WinRT81-HttpClient-BT-Socket-Poster.pdf",
  L"c:\\temp\\data\\WinRT81-HttpClient-BT-Socket-Poster.pdf"
 },
 {
  L"https://download.microsoft.com/download/6/6/2/662DD05E-BAD7-46EF-9431-135F9BAE6332/9781509302963_Microsoft%20Azure%20Essentials%20Fundamentals%20of%20Azure%202nd%20ed%20pdf.pdf",
  L"c:\\temp\\data\\Fundamentals of Azure.pdf"
 },
 {
  L"https://aka.ms/WinServ16/StndPDF",
  L"c:\\temp\\data\\IntroducingWindowsServer2016.pdf"
 }
};

// Forward declaration of functions.
HRESULT GetBackgroundCopyManager(__out IBackgroundCopyManager **Manager);
HRESULT CreateDownloadJob(__in LPCWSTR Name, __in IBackgroundCopyManager *Manager, __out IBackgroundCopyJob **Job);
HRESULT MonitorJobProgress(__in IBackgroundCopyJob *Job);
HRESULT DisplayFileHeaders(__in IBackgroundCopyJob *Job);
VOID    DisplayProgress(__in IBackgroundCopyJob *Job);
VOID    DisplayHeaders(__in LPWSTR Headers);
VOID    DisplayError(__in IBackgroundCopyJob *Job);

// Main program entry point.
int wmain(int argc, wchar_t* argv[])
{
 HRESULT hr;
 IBackgroundCopyManager *Manager;

 // Get the BITS Background Copy Manager.
 hr = GetBackgroundCopyManager(&Manager);
 if (SUCCEEDED(hr))
 {
  IBackgroundCopyJob *Job;

  // Create a new download job.
  hr = CreateDownloadJob(L"MyJob", Manager, &Job);
  if (SUCCEEDED(hr))
  {
   // Add files to the job.
   for (int i = 0; i < ARRAY_LENGTH(FileList); ++i)
   {
    hr = Job->AddFile(FileList[i].RemoteFile, FileList[i].LocalFile);
    if (FAILED(hr))
    {
     wprintf(L"Error: Unable to add remote file '%ws' to the download job (error %08X).\n",
      FileList[i].RemoteFile,
      hr);
    }
    else
    {
     wprintf(L"Downloading remote file '%ws' to local file '%ws'\n",
      FileList[i].RemoteFile, FileList[i].LocalFile);
    }
   }

   // Start the job and display its progress.
   hr = Job->Resume();
   if (FAILED(hr))
   {
    wprintf(L"ERROR: Unable to start the BITS download job (error code %08X).\n", hr);
   }
   else
   {
    MonitorJobProgress(Job);
   }

   // Release the BITS IBackgroundCopyJob interface.
   Job->Release();
   Job = NULL;
  }

  // Release the IBackgroundCopyManager interface.
  Manager->Release();
  Manager = NULL;
 }

 return 0;
}

/**
 * Gets a pointer to the BITS Background Copy Manager.
 *
 * If successful, this function returns a success code and sets the
 * referenced IBackgroundCopyFileManager interface pointer to a
 * reference counted instance of the Background Copy Manager interface.
 */
HRESULT GetBackgroundCopyManager(__out IBackgroundCopyManager **Manager)
{
 HRESULT hr;

 //Specify the appropriate COM threading model for your application.
 hr = CoInitializeEx(NULL, COINIT_APARTMENTTHREADED);
 if (SUCCEEDED(hr))
 {
  hr = CoCreateInstance(__uuidof(BackgroundCopyManager),
   NULL,
   CLSCTX_LOCAL_SERVER,
   __uuidof(IBackgroundCopyManager),
   (void**)Manager);
 }
 else
 {
  wprintf(L"ERROR: Unable to initialize COM (error code %08X).\n", hr);
 }

 return hr;
}

/**
 * Creates a new download job with the specified name.
 */
HRESULT CreateDownloadJob(__in LPCWSTR Name, __in IBackgroundCopyManager *Manager, __out IBackgroundCopyJob **Job)
{
 GUID guid;
 return Manager->CreateJob(Name, BG_JOB_TYPE_DOWNLOAD, &guid, Job);
}

/**
 * Monitors and displays the progress of the download job.
 *
 * A new status message is output whenever the job's status changes or,
 * when transferring data, every 2 seconds displays how much data
 * has been transferred.
 */
HRESULT MonitorJobProgress(__in IBackgroundCopyJob *Job)
{
 HRESULT hr;
 LPWSTR JobName;
 BG_JOB_STATE State;
 int PreviousState = -1;
 bool Exit = false;
 int ProgressCounter = 0;

 hr = Job->GetDisplayName(&JobName);
 wprintf(L"Progress report for download job '%ws'.\n", JobName);
 CoTaskMemFree(JobName);

 // Display the download progress.
 while (!Exit)
 {
  hr = Job->GetState(&State);

  if (State != PreviousState)
  {
   switch (State)
   {
   case BG_JOB_STATE_QUEUED:
    wprintf(L"Job is in the queue and waiting to run.\n");
    break;

   case BG_JOB_STATE_CONNECTING:
    wprintf(L"BITS is trying to connect to the remote server.\n");
    break;

   case BG_JOB_STATE_TRANSFERRING:
    wprintf(L"BITS has started downloading data.\n");
    DisplayProgress(Job);
    break;

   case BG_JOB_STATE_ERROR:
    wprintf(L"ERROR: BITS has encountered a non-recoverable error.\n");
    DisplayError(Job);
    wprintf(L"       Exiting job.\n");
    Exit = true;
    break;

   case BG_JOB_STATE_TRANSIENT_ERROR:
    wprintf(L"ERROR: BITS has encountered a recoverable error.\n");
    DisplayError(Job);
    wprintf(L"       Continuing to retry.\n");
    break;

   case BG_JOB_STATE_TRANSFERRED:
    DisplayProgress(Job);
    wprintf(L"The job has been successfully completed.\n");
    wprintf(L"Finalizing local files.\n");
    Job->Complete();
    break;

   case BG_JOB_STATE_ACKNOWLEDGED:
    wprintf(L"Finalization complete.\n");
    Exit = true;
    break;

   case BG_JOB_STATE_CANCELLED:
    wprintf(L"WARNING: The job has been cancelled.\n");
    Exit = true;
    break;

   default:
    wprintf(L"WARNING: Unknown BITS state %d.\n", State);
    Exit = true;
   }

   PreviousState = State;
  }
  else if (State == BG_JOB_STATE_TRANSFERRING)
  {
   // Display job progress every 2 seconds.
   if (++ProgressCounter % TWO_SECOND_LOOP == 0)
   {
    DisplayProgress(Job);
   }
  }
  Sleep(HALF_SECOND_AS_MILLISECONDS);
 }

 wprintf(L"\n");

 if (SUCCEEDED(hr))
 {
  hr = DisplayFileHeaders(Job);
 }

 return hr;
}

/**
 * For each file in the job, obtains the (final) HTTP headers received from the
 * remote server that hosts the files and then displays the HTTP headers.
 */
HRESULT DisplayFileHeaders(__in IBackgroundCopyJob *Job)
{
 HRESULT hr;
 IEnumBackgroundCopyFiles *FileEnumerator;

 wprintf(L"Individual file information.\n");

 hr = Job->EnumFiles(&FileEnumerator);
 if (FAILED(hr))
 {
  wprintf(L"WARNING: Unable to obtain an IEnumBackgroundCopyFiles interface.\n");
  wprintf(L"         No further information can be provided about the files in the job.\n");
 }
 else
 {
  ULONG Count;

  hr = FileEnumerator->GetCount(&Count);
  if (FAILED(hr))
  {
   wprintf(L"WARNING: Unable to obtain a count of the number of files in the job.\n");
   wprintf(L"        No further information can be provided about the files in the job.\n");
  }
  else
  {
   for (ULONG i = 0; i < Count; ++i)
   {
    IBackgroundCopyFile *TempFile;

    hr = FileEnumerator->Next(1, &TempFile, NULL);
    if (FAILED(hr))
    {
     wprintf(L"WARNING: Unable to obtain an IBackgroundCopyFile interface for the next file in the job.\n");
     wprintf(L"        No further information can be provided about this file.\n");
    }
    else
    {
     IBackgroundCopyFile5 *File;
     hr = TempFile->QueryInterface(__uuidof(IBackgroundCopyFile5), (void **)&File);
     if (FAILED(hr))
     {
      wprintf(L"WARNING: Unable to obtain an IBackgroundCopyFile5 interface for the file.\n");
      wprintf(L"        No further information can be provided about this file.\n");
     }
     else
     {
      LPWSTR RemoteFileName;
      hr = File->GetRemoteName(&RemoteFileName);
      if (FAILED(hr))
      {
       wprintf(L"WARNING: Unable to obtain the remote file name for this file.\n");
      }
      else
      {
       wprintf(L"HTTP headers for remote file '%ws'\n", RemoteFileName);
       CoTaskMemFree(RemoteFileName);
       RemoteFileName = NULL;
      }

      BITS_FILE_PROPERTY_VALUE Value;
      hr = File->GetProperty(BITS_FILE_PROPERTY_ID_HTTP_RESPONSE_HEADERS, &Value);
      if (FAILED(hr))
      {
       wprintf(L"WARNING: Unable to obtain the HTTP headers for this file.\n");
      }
      else
      {
       if (Value.String)
       {
        DisplayHeaders(Value.String);
        CoTaskMemFree(Value.String);
        Value.String = NULL;
       }
      }

      File->Release();
      File = NULL;
     }

     TempFile->Release();
     TempFile = NULL;
    }
   }
  }

  FileEnumerator->Release();
  FileEnumerator = NULL;
 }

 return S_OK;
}


/**
 * Displays the current progress of the job in terms of the amount of data
 * and number of files transferred.
 */
VOID DisplayProgress(__in IBackgroundCopyJob *Job)
{
 HRESULT hr;
 BG_JOB_PROGRESS Progress;

 hr = Job->GetProgress(&Progress);
 if (SUCCEEDED(hr))
 {
  wprintf(L"%llu of %llu bytes transferred (%lu of %lu files).\n",
   Progress.BytesTransferred, Progress.BytesTotal,
   Progress.FilesTransferred, Progress.FilesTotal);
 }
 else
 {
  wprintf(L"ERROR: Unable to get job progress (error code %08X).\n", hr);
 }
}

/**
 * Parses the provided string that contains HTTP headers,
 * splits them apart and displays them to the user.
 */
VOID DisplayHeaders(__in LPWSTR Headers)
{
 wprintf(L"Headers: %ws\n", Headers);
}

VOID DisplayError(__in IBackgroundCopyJob *Job)
{
 HRESULT hr;
 IBackgroundCopyError *Error;
 LPWSTR ErrorDescription;

 hr = Job->GetError(&Error);
 if (FAILED(hr))
 {
  wprintf(L"WARNING: Unable to get job error information (code %08X)\n", hr);
 }
 else
 {
  BG_ERROR_CONTEXT ErrorContext;
  HRESULT ErrorResult;
  hr = Error->GetError(&ErrorContext, &ErrorResult);
  if (FAILED(hr))
  {
   wprintf(L"WARNING: Unable to get job error code information (code %08X)\n", hr);
  }
  else
  {
   hr = Error->GetErrorDescription(LANGIDFROMLCID(GetThreadLocale()), &ErrorDescription);
   if (FAILED(hr))
   {
    wprintf(L"WARNING: Unable to get job error description (code %08X) for %08X\n", hr, ErrorResult);
   }
   else
   {
    wprintf(L"   Error details: code %08X %ws\n", ErrorResult, ErrorDescription);
    CoTaskMemFree(ErrorDescription);
   }
  }

  Error->Release();
 }
}