读DataSnap源代码（一）

Delphi的DataSnap用了一段时间了，但一直感觉有些地方还不够了解，所以花时间阅读了源代码，特作此烂笔头。

Datasnap是在之前的WebBorker基础上搭建的，DataSnap向导自动生成了基础的代码,所以就以基础代码为起点来看看DataSnap的内部机制。

首选创建一个 Stand-alone 的REST App,  向导至少会为我们生成一个Form1和一个WebModule1，

FormUnit1单元如下：

unit FormUnit1;
 
interface
 
uses
  Winapi.Messages, System.SysUtils, System.Variants,
  System.Classes, Vcl.Graphics, Vcl.Controls, Vcl.Forms, Vcl.Dialogs,
  Vcl.AppEvnts, Vcl.StdCtrls, IdHTTPWebBrokerBridge, Web.HTTPApp;
 
type
  TForm1 = class(TForm)
    ButtonStart: TButton;
    ButtonStop: TButton;
    EditPort: TEdit;
    Label1: TLabel;
    ApplicationEvents1: TApplicationEvents;
    ButtonOpenBrowser: TButton;
    procedure FormCreate(Sender: TObject);
    procedure ApplicationEvents1Idle(Sender: TObject; var Done: Boolean);
    procedure ButtonStartClick(Sender: TObject);
    procedure ButtonStopClick(Sender: TObject);
    procedure ButtonOpenBrowserClick(Sender: TObject);
  private
    FServer: TIdHTTPWebBrokerBridge;
    procedure StartServer;
    { Private declarations }
  public
    { Public declarations }
  end;
 
var
  Form1: TForm1;
 
implementation
 
{$R *.dfm}
 
uses
  WinApi.Windows, Winapi.ShellApi, Datasnap.DSSession;
 
procedure TForm1.ApplicationEvents1Idle(Sender: TObject; var Done: Boolean);
begin
  ButtonStart.Enabled := not FServer.Active;
  ButtonStop.Enabled := FServer.Active;
  EditPort.Enabled := not FServer.Active;
end;
 
procedure TForm1.ButtonOpenBrowserClick(Sender: TObject);
var
  LURL: string;
begin
  StartServer;
  LURL := Format('http://localhost:%s', [EditPort.Text]);
  ShellExecute(0,
        nil,
        PChar(LURL), nil, nil, SW_SHOWNOACTIVATE);
end;
 
procedure TForm1.ButtonStartClick(Sender: TObject);
begin
  StartServer;
end;
 
procedure TerminateThreads;
begin
  if TDSSessionManager.Instance <> nil then
    TDSSessionManager.Instance.TerminateAllSessions;
end;
 
procedure TForm1.ButtonStopClick(Sender: TObject);
begin
  TerminateThreads;
  FServer.Active := False;
  FServer.Bindings.Clear;
end;
 
procedure TForm1.FormCreate(Sender: TObject);
begin
  FServer := TIdHTTPWebBrokerBridge.Create(Self);
end;
 
procedure TForm1.StartServer;
begin
  if not FServer.Active then
  begin
    FServer.Bindings.Clear;
    FServer.DefaultPort := StrToInt(EditPort.Text);
    FServer.Active := True;
  end;
end;
 
end.

在Form1中，有一个FServer ,ButtonStart.Click事件中有FServer.Active := True;

TIdHTTPWebBrokerBridge 是  TIdHTTPWebBrokerBridge = class(TIdCustomHTTPServer)

到目前上为，至少知道Datasanp是基于Id组件的，那么Id（idHttpServer)和WebModule, DSServer, DSHTTPWebDispatcher1 是如何关连上的，又是如何调用到

DDServerClass实例方法呢？

   TIdHTTPWebBrokerBridge = class(TIdCustomHTTPServer)
   private
     procedure RunWebModuleClass(AThread: TIdContext; ARequestInfo: TIdHTTPRequestInfo;
      AResponseInfo: TIdHTTPResponseInfo);
   protected
     FWebModuleClass: TComponentClass;
     //
 8     procedure DoCommandGet(AThread: TIdContext; ARequestInfo: TIdHTTPRequestInfo;
 9      AResponseInfo: TIdHTTPResponseInfo); override;
10     procedure DoCommandOther(AThread: TIdContext; ARequestInfo: TIdHTTPRequestInfo;
11      AResponseInfo: TIdHTTPResponseInfo); override;
     procedure InitComponent; override;
   public
     procedure RegisterWebModuleClass(AClass: TComponentClass);
   end;

DoCommandGet的内部代码：

procedure TIdHTTPWebBrokerBridge.DoCommandGet(AThread: TIdContext;
 ARequestInfo: TIdHTTPRequestInfo; AResponseInfo: TIdHTTPResponseInfo);
begin
  if FWebModuleClass <> nil then begin
    // FWebModuleClass, RegisterWebModuleClass supported for backward compatability
    RunWebModuleClass(AThread, ARequestInfo, AResponseInfo)
  end else
  begin
    {$IFDEF HAS_CLASSVARS}
    TIdHTTPWebBrokerBridgeRequestHandler.FWebRequestHandler.Run(AThread, ARequestInfo, AResponseInfo);
    {$ELSE}
    IndyWebRequestHandler.Run(AThread, ARequestInfo, AResponseInfo);
    {$ENDIF}
  end;
end;

TIdHTTPWebBrokerBridgeRequestHandler的定义：

   TIdHTTPWebBrokerBridgeRequestHandler = class(TWebRequestHandler)
   {$IFDEF HAS_CLASSVARS}
   private
 4　   class var FWebRequestHandler: TIdHTTPWebBrokerBridgeRequestHandler;
   {$ENDIF}
   public
     constructor Create(AOwner: TComponent); override;
     {$IFDEF HAS_CLASSVARS}
       {$IFDEF HAS_CLASSDESTRUCTOR}
     class destructor Destroy;
       {$ENDIF}
     {$ENDIF}
     destructor Destroy; override;
14     procedure Run(AThread: TIdContext; ARequestInfo: TIdHTTPRequestInfo; AResponseInfo: TIdHTTPResponseInfo);
   end;

第4行，静态的，唯一的。

第14行 就是TIdHTTPWebBrokerBridge.DoCommandGet中被调用的。

Run内部代码：

 procedure TIdHTTPWebBrokerBridgeRequestHandler.Run(AThread: TIdContext; ARequestInfo: TIdHTTPRequestInfo; AResponseInfo: TIdHTTPResponseInfo);
 var
   LRequest: TIdHTTPAppRequest;
   LResponse: TIdHTTPAppResponse;
 begin
   try
     LRequest := TIdHTTPAppRequest.Create(AThread, ARequestInfo, AResponseInfo);
     try
       LResponse := TIdHTTPAppResponse.Create(LRequest, AThread, ARequestInfo, AResponseInfo);
       try
         // WebBroker will free it and we cannot change this behaviour
         AResponseInfo.FreeContentStream := False;
         HandleRequest(LRequest, LResponse);
       finally
         FreeAndNil(LResponse);
       end;
     finally
       FreeAndNil(LRequest);
     end;
   except
     // Let Indy handle this exception
     raise;
   end;
 end;