使用WinInet在下載文件之前確定總文件的大小

Question

我從第三方網站了解如何使用WinInet從互聯網下載文件。我對API不太熟悉，然後我看着WinInet單元，但沒有看到任何我需要的API調用。

我正在做的是添加報告下載文件進度的能力。這個程序我已經包裝在TThread裏面，一切正常。但是，只有一個缺失的部分：在下載之前查找源文件的總大小。

看下面我在哪裏發表評論//HOW TO GET TOTAL SIZE?這是我需要找出什麼是文件的總大小之前，我開始下載它。我如何去做這件事？因爲這個代碼似乎不知道文件的大小，直到它被完成下載 - 這使得這個添加不相關。

procedure TInetThread.Execute; 
const 
    BufferSize = 1024; 
var 
    hSession, hURL: HInternet; 
    Buffer: array[1..BufferSize] of Byte; 
    BufferLen: DWORD; 
    f: File; 
    S: Bool; 
    D: Integer; 
    T: Integer; 
    procedure DoWork(const Amt: Integer); 
    begin 
    if assigned(FOnWork) then 
     FOnWork(Self, FSource, FDest, Amt, T); 
    end; 
begin 
    S:= False; 
    try 
    try 
     if not DirectoryExists(ExtractFilePath(FDest)) then begin 
     ForceDirectories(ExtractFilePath(FDest)); 
     end; 
     hSession:= InternetOpen(PChar(FAppName), INTERNET_OPEN_TYPE_PRECONFIG, nil, nil, 0); 
     try 
     hURL:= InternetOpenURL(hSession, PChar(FSource), nil, 0, 0, 0); 
     try 
      AssignFile(f, FDest); 
      Rewrite(f, 1); 
      T:= 0; //HOW TO GET TOTAL SIZE? 
      D:= 0; 
      DoWork(D); 
      repeat 
      InternetReadFile(hURL, @Buffer, SizeOf(Buffer), BufferLen); 
      BlockWrite(f, Buffer, BufferLen); 
      D:= D + BufferLen; 
      DoWork(D); 
      until BufferLen = 0; 
      CloseFile(f); 
      S:= True; 
     finally 
      InternetCloseHandle(hURL); 
     end 
     finally 
     InternetCloseHandle(hSession); 
     end; 
    except 
     on e: exception do begin 
     S:= False; 
     end; 
    end; 
    finally 
    if assigned(FOnComplete) then 
     FOnComplete(Self, FSource, FDest, S); 
    end; 
end; 

Answer 1

您可以使用HEAD方法和檢查Content-Length檢索一個遠程文件的文件大小

檢查這兩種方法

的WinInet

如果你想執行HEAD方法您必須使用HttpOpenRequest,HttpSendRequest和HttpQueryInfo WinInet函數。

uses 
SysUtils, 
Windows, 
WinInet; 

function GetWinInetError(ErrorCode:Cardinal): string; 
const 
    winetdll = 'wininet.dll'; 
var 
    Len: Integer; 
    Buffer: PChar; 
begin 
    Len := FormatMessage(
    FORMAT_MESSAGE_FROM_HMODULE or FORMAT_MESSAGE_FROM_SYSTEM or 
    FORMAT_MESSAGE_ALLOCATE_BUFFER or FORMAT_MESSAGE_IGNORE_INSERTS or FORMAT_MESSAGE_ARGUMENT_ARRAY, 
    Pointer(GetModuleHandle(winetdll)), ErrorCode, 0, @Buffer, SizeOf(Buffer), nil); 
    try 
    while (Len > 0) and {$IFDEF UNICODE}(CharInSet(Buffer[Len - 1], [#0..#32, '.'])) {$ELSE}(Buffer[Len - 1] in [#0..#32, '.']) {$ENDIF} do Dec(Len); 
    SetString(Result, Buffer, Len); 
    finally 
    LocalFree(HLOCAL(Buffer)); 
    end; 
end; 


procedure ParseURL(const lpszUrl: string; var Host, Resource: string); 
var 
    lpszScheme  : array[0..INTERNET_MAX_SCHEME_LENGTH - 1] of Char; 
    lpszHostName : array[0..INTERNET_MAX_HOST_NAME_LENGTH - 1] of Char; 
    lpszUserName : array[0..INTERNET_MAX_USER_NAME_LENGTH - 1] of Char; 
    lpszPassword : array[0..INTERNET_MAX_PASSWORD_LENGTH - 1] of Char; 
    lpszUrlPath  : array[0..INTERNET_MAX_PATH_LENGTH - 1] of Char; 
    lpszExtraInfo : array[0..1024 - 1] of Char; 
    lpUrlComponents : TURLComponents; 
begin 
    ZeroMemory(@lpszScheme, SizeOf(lpszScheme)); 
    ZeroMemory(@lpszHostName, SizeOf(lpszHostName)); 
    ZeroMemory(@lpszUserName, SizeOf(lpszUserName)); 
    ZeroMemory(@lpszPassword, SizeOf(lpszPassword)); 
    ZeroMemory(@lpszUrlPath, SizeOf(lpszUrlPath)); 
    ZeroMemory(@lpszExtraInfo, SizeOf(lpszExtraInfo)); 
    ZeroMemory(@lpUrlComponents, SizeOf(TURLComponents)); 

    lpUrlComponents.dwStructSize  := SizeOf(TURLComponents); 
    lpUrlComponents.lpszScheme  := lpszScheme; 
    lpUrlComponents.dwSchemeLength := SizeOf(lpszScheme); 
    lpUrlComponents.lpszHostName  := lpszHostName; 
    lpUrlComponents.dwHostNameLength := SizeOf(lpszHostName); 
    lpUrlComponents.lpszUserName  := lpszUserName; 
    lpUrlComponents.dwUserNameLength := SizeOf(lpszUserName); 
    lpUrlComponents.lpszPassword  := lpszPassword; 
    lpUrlComponents.dwPasswordLength := SizeOf(lpszPassword); 
    lpUrlComponents.lpszUrlPath  := lpszUrlPath; 
    lpUrlComponents.dwUrlPathLength := SizeOf(lpszUrlPath); 
    lpUrlComponents.lpszExtraInfo  := lpszExtraInfo; 
    lpUrlComponents.dwExtraInfoLength := SizeOf(lpszExtraInfo); 

    InternetCrackUrl(PChar(lpszUrl), Length(lpszUrl), ICU_DECODE or ICU_ESCAPE, lpUrlComponents); 

    Host := lpszHostName; 
    Resource := lpszUrlPath; 
end; 

function GetRemoteFileSize(const Url : string): Integer; 
const 
    sUserAgent = 'Mozilla/5.001 (windows; U; NT4.0; en-US; rv:1.0) Gecko/25250101'; 

var 
    hInet : HINTERNET; 
    hConnect : HINTERNET; 
    hRequest : HINTERNET; 
    lpdwBufferLength: DWORD; 
    lpdwReserved : DWORD; 
    ServerName: string; 
    Resource: string; 
    ErrorCode : Cardinal; 
begin 
    ParseURL(Url,ServerName,Resource); 
    Result:=0; 

    hInet := InternetOpen(PChar(sUserAgent), INTERNET_OPEN_TYPE_PRECONFIG, nil, nil, 0); 
    if hInet=nil then 
    begin 
    ErrorCode:=GetLastError; 
    raise Exception.Create(Format('InternetOpen Error %d Description %s',[ErrorCode,GetWinInetError(ErrorCode)])); 
    end; 

    try 
    hConnect := InternetConnect(hInet, PChar(ServerName), INTERNET_DEFAULT_HTTP_PORT, nil, nil, INTERNET_SERVICE_HTTP, 0, 0); 
    if hConnect=nil then 
    begin 
     ErrorCode:=GetLastError; 
     raise Exception.Create(Format('InternetConnect Error %d Description %s',[ErrorCode,GetWinInetError(ErrorCode)])); 
    end; 

    try 
     hRequest := HttpOpenRequest(hConnect, PChar('HEAD'), PChar(Resource), nil, nil, nil, 0, 0); 
     if hRequest<>nil then 
     begin 
      try 
      lpdwBufferLength:=SizeOf(Result); 
      lpdwReserved :=0; 
      if not HttpSendRequest(hRequest, nil, 0, nil, 0) then 
      begin 
       ErrorCode:=GetLastError; 
       raise Exception.Create(Format('HttpOpenRequest Error %d Description %s',[ErrorCode,GetWinInetError(ErrorCode)])); 
      end; 

      if not HttpQueryInfo(hRequest, HTTP_QUERY_CONTENT_LENGTH or HTTP_QUERY_FLAG_NUMBER, @Result, lpdwBufferLength, lpdwReserved) then 
      begin 
       Result:=0; 
       ErrorCode:=GetLastError; 
       raise Exception.Create(Format('HttpQueryInfo Error %d Description %s',[ErrorCode,GetWinInetError(ErrorCode)])); 
      end; 
      finally 
      InternetCloseHandle(hRequest); 
      end; 
     end 
     else 
     begin 
      ErrorCode:=GetLastError; 
      raise Exception.Create(Format('HttpOpenRequest Error %d Description %s',[ErrorCode,GetWinInetError(ErrorCode)])); 
     end; 
    finally 
     InternetCloseHandle(hConnect); 
    end; 
    finally 
    InternetCloseHandle(hInet); 
    end; 

end; 

印

利用Indy還要檢查這些代碼。

function GetRemoteFilesize(const Url :string) : Integer; 
var 
    Http: TIdHTTP; 
begin 
    Http := TIdHTTP.Create(nil); 
    try 
    Http.Head(Url); 
    result:= Http.Response.ContentLength; 
    finally 
    Http.Free; 
    end; 
end; 

Answer 2

回答如何使用WinInet下載大小的問題。這是基於WinInet的文件下載器之一。

這是我用得到的下載大小的方法：

function TWebDownloader.GetContentLength(URLHandle: HINTERNET): Int64; 
// returns the expected download size. Returns -1 if one not provided 
    var 
    SBuffer: Array[1..20] of char; 
    SBufferSize: Integer; 
    srv: integer; 
    begin 
    srv := 0; 
    SBufferSize := 20; 
    if HttpQueryInfo(URLHandle, HTTP_QUERY_CONTENT_LENGTH, @SBuffer, SBufferSize, srv) then 
     Result := StrToFloat(String(SBuffer)) 
    else 
     Result := -1; 
    end; 

使用這種方法需要一個開放的要求處理，並且不需要讀取任何數據：

URLHandle := HttpOpenRequest(ConnectHandle, 'GET', Pchar(sitepath), nil, 
        nil, nil, INTERNET_FLAG_NO_CACHE_WRITE, 0); 
... 
DownloadSize := GetContentLength(URLHandle); 

HTH

Answer 3

固定後類型看起來好像這樣：

function GetContentLength(URLHandle:HINTERNET):Int64; 
// returns the expected download size. Returns -1 if one not provided 
var 
SBufferSize, srv:Cardinal; 
begin 
srv:=0; 
SBufferSize:=20; 
if Not HttpQueryInfo(URLHandle, HTTP_QUERY_CONTENT_LENGTH or HTTP_QUERY_FLAG_NUMBER, {@SBuffer} @Result, SBufferSize, srv) then Result:=-1; 
end; 

叫它：

{get the file handle} 
hURL:=InternetOpenURL(hSession, PChar(URL), nil, 0, 0, 0); 
if hURL=Nil then 
begin 
InternetCloseHandle(hSession); 
ShowMessage('The link is incorrect!'); 
exit; 
end; 
{get the file size} 
filesize:=GetContentLength(hURL);