[fpc-pascal] Improved FPC JSON-RPC support

[Michael Van Canneyt via fpc-pascal]

Hello,

Thanks to the magic of RTTI and Invoke(), creating a JSON-RPC server has
just become significantly easier !

Given an interface definition:

  IMyOtherInterface = interface ['{4D52BEE3-F709-44AC-BD31-870CBFF44632}']
    Function SayHello : string;
    function Echo(args : TStringArray) : String;
  end;

Creating a JSON-RPC server for this is now as simple as:

// Create a class that implements the interface
Type
  TIntf2Impl = class(TInterfacedObject, IMyOtherInterface)
  public
    function Echo(args: TStringArray): String;
    function SayHello: string;
  end;

function TIntf2Impl.Echo(args: TStringArray): String;

var
  S : String;

begin
  Result:='';
  For S in Args do
    begin
    if Result<>'' then
      Result:=Result+' ';
    Result:=Result+S;
    end
end;

function TIntf2Impl.SayHello: string;
begin
  Result:='Hello, World!';
end;

// Register the class using an interface factory:

Function GetMyOtherInterface(Const aName : string) : IInterface;

begin
  Result:=TIntf2Impl.Create as IInterface;
end;

initialization
  
RTTIJSONRPCRegistry.Add(TypeInfo(IMyOtherInterface),@GetMyOtherInterface,'Service2');
end.


And calling it from a client program is even more simple:

var
  client: IMyOtherInterface;
  aRPCClient: TFPRPCClient;

begin
  // Register interface with name 'Service2'
  RPCServiceRegistry.Add(TypeInfo(IMyOtherInterface),'Service2');
  // Create client
  aRPCClient:=TFPRPCClient.Create(Nil);
  aRPCClient.BaseURL:='http://localhost:8080/RPC';

  // Just typecast the client to the desired interface
  Client:=aRPCClient as IMyotherInterface;

  // or explitly create using the registered service name
  // Client:=RPC.Specialize CreateService<IMyotherInterface>('Service2');

  Writeln('Sayhello: ',client.SayHello);
  Writeln('Sayhello: ',client.Echo(['This','is','Sparta']));
end.

The service can also be consumed by pas2js.

The support for various argument types is still limited, but this will improve 
soon.
Currently simple types and arrays of simple types are improved. Proper
support for records and other structured types needs extended RTTI...

An example server and client programs have been committed to the FPC repo.
(packages/fcl-web/examples/jsonrpc/rtti)

With many thanks to Sven Barth for putting me on the right track...

Enjoy!

Michael.
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