http - Delphi - 使用 Synapse 下载有进度的文件

Question

我使用 Synapse 已有一段时间了，主要是为了发送电子邮件。今天我正在创建一个简单的安装程序，并尝试通过 HTTP 下载应用程序 exe 文件。该文件大小约为 9 MB，因此我想向用户添加进度状态，但我不理解我找到的示例。这是我到目前为止得到的:

type
  THookSocketStatus = Procedure(Sender: TObject; Reason: THookSocketReason; const Value: String) of Object;
  CallBack = class
    Class Procedure Status(Sender: TObject; Reason: THookSocketReason; const Value: String);
  end;


Class Procedure CallBack.Status(Sender: TObject; Reason: THookSocketReason; const Value: String);
var
  V: String;
Begin
  V := GetEnumName(TypeInfo(THookSocketReason), Integer(Reason)) + ' ' + Value;
  Form1.mem1.Lines.Add(V);
  application.ProcessMessages;
end;

procedure TForm1.btn1Click(Sender: TObject);
var
  HTTP: THTTPSend;
  MSTM: TMemoryStream;
begin
  Screen.Cursor := crHourGlass;
  HTTP := THTTPSend.Create;
  MSTM := TMemoryStream.Create;
  Try
    Try
      HTTP.Sock.OnStatus := CallBack.Status;
      If HTTP.HTTPMethod('GET', edt1.Text) Then
      Begin
        MSTM.Seek(0, soFromBeginning);
        MSTM.CopyFrom(HTTP.Document, 0);
        MSTM.SaveToFile(ExtractFilePath(Application.ExeName) + 'test.exe');
      end;
    Except
    end;
  Finally
    MSTM.Free;
    HTTP.Free;
    Screen.Cursor := crDefault;
  end;
end;

在这个简单的测试中我得到了这个结果:

HR_SocketClose
HR_ResolvingBegin www.website.com:80
HR_ResolvingEnd 176.102.295.18:80
HR_SocketCreate IPv4
HR_Connect www.website.com:80
HR_WriteCount 158
HR_CanRead
HR_ReadCount 288
HR_CanRead
HR_ReadCount 8192
HR_ReadCount 8192
HR_ReadCount 8192
HR_ReadCount 6720
HR_CanRead
HR_ReadCount 3299
.
.
.
HR_ReadCount 8192
HR_ReadCount 8192
HR_ReadCount 7828
HR_SocketClose
HR_SocketClose

请问，WriteCount 和 ReadCount 是什么意思？如何在开始下载之前获取总文件大小以设置进度条？

谢谢大家!

Answer 1

我遇到了同样的问题，通过扩展上面的代码找到了解决方案。文件长度可通过使用 header 信息获得，如上所示。

这是我的代码:

unit uhttpdownloader;


{$mode Delphi}{$H+}

interface

uses
  Classes, SysUtils, httpsend, blcksock, typinfo;

//Interface for notifications about the progress
type
  IProgress = interface
    procedure ProgressNotification(Text: String; CurrentProgress : integer; MaxProgress : integer);
  end;

type
  { THttpDownloader }

  THttpDownloader = class
  public
    function DownloadHTTP(URL, TargetFile: string; ProgressMonitor : IProgress): Boolean;
  private
    Bytes : Integer;
    MaxBytes : Integer;
    HTTPSender: THTTPSend;
    ProgressMonitor : IProgress;
    procedure Status(Sender: TObject; Reason: THookSocketReason; const Value: String);
    function GetSizeFromHeader(Header: String):integer;
  end;

implementation

function THttpDownloader.DownloadHTTP(URL, TargetFile: string; ProgressMonitor : IProgress): Boolean;
var
  HTTPGetResult: Boolean;
begin
  Result := False;
  Bytes:= 0;
  MaxBytes:= -1;
  Self.ProgressMonitor:= ProgressMonitor;

  HTTPSender := THTTPSend.Create;
  try
    //add callback function for status updates
    HTTPSender.Sock.OnStatus:= Status;
    HTTPGetResult := HTTPSender.HTTPMethod('GET', URL);
    if (HTTPSender.ResultCode >= 100) and (HTTPSender.ResultCode<=299) then begin
      HTTPSender.Document.SaveToFile(TargetFile);
      Result := True;
    end;
  finally
    HTTPSender.Free;
  end;
end;

//Callback function for status events
procedure THttpDownloader.Status(Sender: TObject; Reason: THookSocketReason; const Value: String);
var
  V, currentHeader: String;
  i: integer;
begin
  //try to get filesize from headers
  if (MaxBytes = -1) then
  begin
    for i:= 0 to HTTPSender.Headers.Count - 1 do
    begin
      currentHeader:= HTTPSender.Headers[i];
      MaxBytes:= GetSizeFromHeader(currentHeader);
      if MaxBytes <> -1 then break;
    end;
  end;

  V := GetEnumName(TypeInfo(THookSocketReason), Integer(Reason)) + ' ' + Value;

  //HR_ReadCount contains the number of bytes since the last event
  if Reason = THookSocketReason.HR_ReadCount then
  begin
    Bytes:= Bytes + StrToInt(Value);
    ProgressMonitor.ProgressNotification(V, Bytes, MaxBytes);
  end;
end;

function THttpDownloader.GetSizeFromHeader(Header: String): integer;
var
  item : TStringList;
begin
  //the download size is contained in the header (e.g.: Content-Length: 3737722)
  Result:= -1;

  if Pos('Content-Length:', Header) <> 0 then
  begin
    item:= TStringList.Create();
    item.Delimiter:= ':';
    item.StrictDelimiter:=true;
    item.DelimitedText:=Header;
    if item.Count = 2 then
    begin
      Result:= StrToInt(Trim(item[1]));
    end;
  end;
end;
end.

完整的源代码和示例也可以在这里下载: http://andydunkel.net/lazarus/delphi/2015/09/09/lazarus_synapse_progress.html

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