Delphi-JRPC: JSON-RPC 2.0 Library for Delphi

A modern, attribute-driven JSON-RPC 2.0 framework for Delphi, built on RTTI and the Neon serialization library.

🚀 Key Features

• Protocol Compliance: full support for the JSON-RPC 2.0 specification.
• Attribute-Driven: map Delphi methods to JSON-RPC endpoints with simple attributes like [JRPCMethod] and [JRPCParam].
• Automatic Marshaling: seamless conversion between JSON and Delphi types (integers, strings, enums, classes, records, arrays).
• Memory Management: built-in garbage collector for request-scoped objects.
• Context Injection: per-request dependency injection via the [Context] attribute.
• Flexible Routing: TRouteMatcher for URI-style template matching and parameter extraction.
• Flexible Naming: path + separator + method, a custom separator, or flat classes ([JRPCPath('')]) whose methods declare the full name (tools/call).
• High Performance: powered by Neon, with built-in TStopwatch [PERF] instrumentation in the invoker and the server.
• Transport Agnostic: integrate into any transport layer (HTTP, WebSockets, named pipes, STDIO) — on both sides: TJRPCServer takes a string and returns one, TJRPCClient is handed a function that does the same.
• Typed Client: call a remote method and get a Delphi value back — ExecuteAs<T> deserializes result through Neon, and an error member arrives as an exception.
• Batch Processing: multiple requests in a single batch.
• Notification Support: full JSON-RPC notification pattern.

📦 Core Components

Component	Description
JRPC.Core	Base protocol types, message classes (Request, Response, Notification, Error), error codes, serialization logic and the class registry (TJRPCRegistry).
JRPC.Invoker	Maps JSON-RPC requests to Delphi method calls using RTTI and attributes.
JRPC.Classes	Supporting utilities: garbage collection, context management, route matching.
JRPC.Server	Transport-agnostic server component (TJRPCServer) that parses, dispatches and answers requests, including batches.
JRPC.Client	Transport-agnostic client component (TJRPCClient): builds requests, correlates answers by id, deserializes result into a Delphi type and raises the peer's error.

🛠️ Quick Start

1. Define an API class

type
  [JRPCPath('math')]
  TMathApi = class
  public
    [JRPCMethod('sum')]
    function Sum([JRPCParam('a')] A: Integer; [JRPCParam('b')] B: Integer): Integer;

    [JRPCMethod('echo')]
    function Echo([JRPCParam('message')] const AMessage: string): string;
  end;

function TMathApi.Sum(A, B: Integer): Integer;
begin
  Result := A + B;
end;

2. Register and serve

uses
  JRPC.Core,
  JRPC.Server;

// Once, at startup:
TJRPCRegistry.Instance.RegisterClass(TMathApi);

// Per request (a transport feeds the raw JSON in, sends the JSON out):
var
  LServer: TJRPCServer;
  LResponse: string;
begin
  LServer := TJRPCServer.Create(nil);
  try
    LResponse := LServer.ProcessRequest(
      '{"jsonrpc":"2.0","id":1,"method":"math/sum","params":{"a":10,"b":20}}');
    // LResponse = {"result":30,"id":1,"jsonrpc":"2.0"}
  finally
    LServer.Free;
  end;
end;

ProcessRequest answers a single request with a single Response object, a batch with an array of Response objects, and a notification with an empty string (per the spec, a server never answers a notification).

3. Call it from a client

TJRPCClient is the mirror image: it links no transport either, so you hand it the one function that gets a payload to the peer and the answer back.

uses
  JRPC.Core,
  JRPC.Client;

var
  LClient: TJRPCClient;
begin
  LClient := TJRPCClient.Create(nil);
  try
    LClient.OnTransport :=
      function(const ARequest: string): string
      begin
        Result := MySocket.SendAndReadLine(ARequest);   // or LServer.ProcessRequest, to loop back
      end;

    // The id is generated, sent, and checked against the one echoed back.
    WriteLn(LClient.ExecuteAs<Integer>(
      TJRPCRequestBuilder.New
        .SetMethod('math/sum')
        .AddNamedParam('a', 10)
        .AddNamedParam('b', 20)));
  finally
    LClient.Free;
  end;
end;

A failure the peer reports arrives as EJRPCRemoteError, carrying its Code, Message and structured ErrorData; a failure of the call itself (no transport, unreadable answer, an id that does not match) arrives as EJRPCClientError. Assign OnError to log every failure in one place; it reports and the exception carries on as usual.

ExecuteAsJSONValue returns the raw TJSONValue instead and ExecuteAsJsonString its text, while Execute covers a call made for its effect and a notification, ExecuteBatch a batch, and ExecuteRaw a payload put on the wire untouched.

TJRPCRequestBuilder is interfaced, so the request is freed with it and no call site needs a try/finally. Build only lends the request out — the builder keeps ownership — so anything that adopts a request, TJRPCMessages in a batch above all, gets a plain TJRPCRequest.Create instead.

Because the transport is just a function, a client can be pointed straight at a TJRPCServer in the same process — which is how the suite tests it, with no socket involved.

4. Method naming

By default a method is addressed as path + separator + method, where the separator is / (or whatever a class declares with the separator= tag):

  [JRPCPath('math')]        // math/sum
  [JRPCPath('custom', 'separator=.')]  // custom.hello

A class that contributes no path - no attribute at all, or an explicitly empty [JRPCPath('')] - is flat: its methods declare the full JSON-RPC method name themselves, which is handy for protocols whose names are fixed (tools/list, resources/read, ...). Classes are registered explicitly, never discovered, so the attribute is only needed when it has something to say:

type
  TToolsApi = class          // no attribute needed
  public
    [JRPCMethod('tools/list')]
    function ToolsList: string;

    [JRPCMethod('tools/call')]
    function ToolsCall([JRPCParam('name')] const AName: string): string;

    [JRPCMethod('ping')]      // no separator needed at all
    function Ping: string;
  end;

Flat and path-based classes coexist in the same registry: a fully qualified flat name is resolved first, and everything else falls back to the usual path lookup. In a flat class every exposed method needs its [JRPCMethod] attribute - there is no implicit fallback to the Delphi method name, and two classes claiming the same flat name are rejected at registration time.

🧩 Context Injection & Memory Management

type
  [JRPCPath('ctx')]
  TContextApi = class
  private
    [Context] FGC: IGarbageCollector;
    [Context] Request: TJRPCRequest;
  public
    [JRPCMethod('method')]
    function GetRequestMethod: string;
  end;

function TContextApi.GetRequestMethod: string;
begin
  Result := 'request=' + Request.Method;

  // Objects registered with the garbage collector are freed automatically
  // when the request finishes - no manual Free here.
  var LScoped := TStringList.Create;
  FGC.Add(LScoped);
  LScoped.Add('freed with the request');
end;

🎯 Demo

Demo/JRPCDemo is a console test runner that exercises the library end to end: named/positional parameters, notifications, batches (including batches with invalid elements), all standard error codes, object results with default and per-class Neon casing, whole-params objects ([JRPCParams]), enum parameters, null-id round trips, context injection, garbage collection and custom separators. It exits with a non-zero code when any assertion fails, and it registers a Logify console adapter at startup so the [PERF] timing lines are printed between every request/response pair.

BuildDemo.bat

Demo/JRPCExample showcases a realistic example API - a notes CRUD service over an in-memory store (object params/results, array results, enums), plus custom separators, per-class Neon casing and context injection - as a guided showcase followed by an interactive prompt where any request can be typed and answered:

BuildExample.bat

⚙️ Requirements

• Delphi 11 or newer.

📦 Required dependencies

• Neon: high-performance JSON serialization for Delphi (github.com/paolo-rossi/delphi-neon).
• Logify: meta-logger used by the [PERF] instrumentation (github.com/delphi-blocks/Logify).

Clone both dependencies into Libs\ (the demo and test projects resolve them from there):

git clone https://github.com/paolo-rossi/delphi-neon Libs\Neon
git clone https://github.com/delphi-blocks/Logify Libs\Logify

📄 License

This project is licensed under the MIT License - see the LICENSE file for details.