读DataSnap源代码（五）

 function TDSHTTPWebDispatcher.DispatchRequest(Sender: TObject;
   Request: TWebRequest; Response: TWebResponse): Boolean;
 begin
   try
     if Owner is TWebModule then
       DataSnapWebModule := TWebModule(Owner);
     try
       try
         RequiresServer;
         TDSHTTPServerWebBroker(Self.FHttpServer).DispatchDataSnap(Request, Response);
         Result := True;
       except
         on E: Exception do
         begin
           { Default to 500, like web services. }
           Response.StatusCode := ;
           Result := True;
         end;
       end;
     except
       { Swallow any unexpected exception, it will bring down some web servers }
       Result := False;
     end;
   finally
     { Reset current DataSnapWebModule }
     DataSnapWebModule := nil;
   end;
 end;

第10行代码中，请求被分配到TDSHTTPServerWebBorker中处理了。

 procedure TDSHTTPServerWebBroker.DispatchDataSnap(ARequest: TWebRequest;
   AResponse: TWebResponse);
 var
   LDispatch: TDSHTTPDispatch;
   LContext: TDSHTTPContextWebBroker;
 begin
   LDispatch := TDSHTTPApplication.Instance.HTTPDispatch;
   if LDispatch <> nil then
     DoCommand(LDispatch.Context, LDispatch.Request, LDispatch.Response)
   else
   begin
     LContext := TDSHTTPContextWebBroker.Create(ARequest, AResponse);
     try
       DoCommand(LContext, LContext.FRequest, LContext.FResponse);
     finally
       LContext.Free;
     end;
   end;
 end;

上面的第14行代码最终会转到TDSRESTServer类处理。

procedure TDSRESTServer.DoCommand(AContext: TDSHTTPContext; ARequestInfo: TDSHTTPRequest;
                                  AResponseInfo: TDSHTTPResponse);

 procedure TDSRESTServer.DoCommand(AContext: TDSHTTPContext; ARequestInfo: TDSHTTPRequest;
                                   AResponseInfo: TDSHTTPResponse);
 var
   Request: string;
   NextRequest: string;
   NextContext: string;
   RestCtxt: string;
   StartDispatch: Boolean;
 begin

   // HTTPDispatch object if necessary
   StartDispatch := not TDSHTTPApplication.Instance.Dispatching;
   if StartDispatch then
     TDSHTTPApplication.Instance.StartDispatch(AContext, ARequestInfo, AResponseInfo);
   try
 {$IFNDEF POSIX}
   if CoInitFlags = - then
     CoInitializeEx(nil, COINIT_MULTITHREADED)
   else
     CoInitializeEx(nil, CoInitFlags);
 {$ENDIF}
   try
     // check for context, if not found send the appropriate error message
     Request := ARequestInfo.URI;
     if Consume(FDSContext, Request, NextRequest) then
     begin
       Request := NextRequest;
       if Consume(FRESTContext, Request, NextRequest) then
       begin
         // datasnap/rest
         DoDSRESTCommand(ARequestInfo, AResponseInfo, NextRequest);
       end
       else if ConsumeOtherContext(Request, NextContext, NextRequest) then
       begin
         DoDSOtherCommand(AContext, ARequestInfo, AResponseInfo, NextContext, NextRequest, FDSServerName <> EmptyStr);
       end
       else
       begin
         RestCtxt := Trim(FRESTContext);
         if RestCtxt = EmptyStr then
           RestCtxt := SProtocolRestEmpty;

         AResponseInfo.ResponseNo := ; {rest or other service not found in URI}
         AResponseInfo.ContentText := Format(SProtocolNotSupported, [Request, RestCtxt]);
         AResponseInfo.CloseConnection := true;
       end;
     end
     else
     begin
       // This may dispatch .js files for example
       DoCommandOtherContext(AContext, ARequestInfo, AResponseInfo, Request);
     end;
     if Assigned(Self.FTrace ) then
     begin
       FTrace(Self, AContext, ARequestInfo, AResponseInfo);
     end;
   finally

     ClearInvocationMetadata();
 {$IFNDEF POSIX}
     CoUnInitialize;
 {$ENDIF}
   end;
   finally
     if StartDispatch then
       TDSHTTPApplication.Instance.EndDispatch;
   end;
 end;

上面阴影的代码，一步一步的推进，先判断URI中是否包括Datasnap，再往判断是否包括REST，然后再继续处理。

到目前，代码已经从TWebModule到TDSHTTPWebDispatcher再到TDSRESTServer类中了。

而Delphi中，我们可以创建三种类型的DataSanp Server程序:

一是DataSanp REST App

二是DataSnap App

三是DataSnap WebBroker App

目前来看， Rest App和WebBroder App是很相似的。而 DataSanp App有些不同：

一是没有WebModule。

二是用 TDSHTTPService 代替了 TDSHTTPWebDispatcher。

三是Form1中代码简化了很多了，虽然project中也出现了  IdHTTPWebBrokerBridge，但也是不同的。（可以和rest app的比较）

 program Project1;

 uses
   Vcl.Forms,
   Web.WebReq,
   IdHTTPWebBrokerBridge,
   Unit1 in 'Unit1.pas' {Form1},
   ServerMethodsUnit1 in 'ServerMethodsUnit1.pas',
   ServerContainerUnit1 in 'ServerContainerUnit1.pas' {ServerContainer1: TDataModule};

 {$R *.res}

 begin
   Application.Initialize;
   Application.MainFormOnTaskbar := True;
   Application.CreateForm(TForm1, Form1);
   Application.CreateForm(TServerContainer1, ServerContainer1);
   Application.Run;
 end.

机制有何不同?