delphi – 在下载之前使用WinInet来识别文件大小

检查这两个方法

WinInet的

如果要执行HEAD方法,则必须使用HttpOpenRequest,HttpSendRequest和HttpQueryInfo WinInet函数.

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

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

end;

印

还要检查这个代码使用indy.

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;