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 := 500;
          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
{$IFNDEF POSIX}
  if CoInitFlags = -1 then
    CoInitializeEx(nil, COINIT_MULTITHREADED)
  else
    CoInitializeEx(nil, CoInitFlags);
{$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 := 501; {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?