[Delphi] 簡単に http 非同期ファイル取得を行うには

unit HTTPSyncFileDownloaderThread;

interface

uses
  Classes, Windows, SysUtils, WinInet, Forms;

type
  THTTPSyncFileDownloader = class(TThread)
  private
    UserAgent, URL, Headers: String;
    LastModified: TDateTime;
  protected
    procedure Execute; override;
  public
    stream: TStream;
    constructor Create(aUserAgent, aURL, aHeaders: String;
                         pfnCallback: TNotifyEvent; aStream: TStream); overload;
  end;

implementation

// THTTPSyncFileDownloader

procedure THTTPSyncFileDownloader.Execute;
var
  hSession: HINTERNET;
  hService: HINTERNET;
  lpBuffer: array[0..1024] of Byte;
  dwBytesRead: DWORD;
  szHeader: string;
  dwSize, Reserved: DWORD;
  ft1, ft2: FILETIME;
  httpLastModified: TSystemTime;
begin
  inherited;

  hSession := InternetOpen(PChar(UserAgent), INTERNET_OPEN_TYPE_PRECONFIG, nil, nil, 0);
  try
    if Assigned(hSession) then
    begin
      szheader := Headers;
      SetLength(szHeader, Length(szHeader));
      hService := InternetOpenUrl(hSession, PChar(URL), PChar(szHeader), $ffffffff,
                                  INTERNET_FLAG_RELOAD, 0);
      try
        if Assigned(hService) then
        begin
          dwBytesRead := 1024;
          while dwBytesRead = 1024 do
          begin
            // 同期モードのため，InternetReadFile() は，
            // データがまだ来ていないときには待ち続ける。
            // そのため，dwBytesRead
            // 理由が何であれダウンロードが終了したと
            // 考えることができる。
            InternetReadFile(hService, @lpBuffer, 1024, dwBytesRead);
            stream.WriteBuffer(lpBuffer, dwBytesRead);
            Sleep(10);
          end;

          // touch. 必要なければ削除しても良い。
          dwSize := sizeof(httpLastModified);
          Reserved := 0;
          HttpQueryInfo(hService, HTTP_QUERY_LAST_MODIFIED or HTTP_QUERY_FLAG_SYSTEMTIME,
                                  @httpLastModified, dwSize, Reserved);
          SystemTimeToFileTime(httpLastModified, ft2);
          FileTimeToLocalFileTime(ft2, ft1); // かなり適当
          FileTimeToSystemTime(ft1, httpLastModified);

          LastModified := SystemTimeToDateTime(httpLastModified);
          // touch ここまで
        end;
      finally
        InternetCloseHandle(hService);
      end;
    end;
  finally
    InternetCloseHandle(hSession);
  end;
end;

constructor THTTPSyncFileDownloader.Create(aUserAgent, aURL, aHeaders: String;
                                          pfnCallback: TNotifyEvent; aStream: TStream);
begin
  inherited Create(false);
  FreeOnTerminate := true;

  UserAgent := aUserAgent;
  URL := aURL;
  Headers := aHeaders;

  OnTerminate := pfnCallback;
  stream := aStream;
end;
end.