feature: end-to-end type safety with native tRPC (trpc.io) integration

docs/asciidoc/tRPC.adoc

@@ -0,0 +1,184 @@
+=== tRPC
+
+The tRPC module provides end-to-end type safety by integrating the https://trpc.io/[tRPC] protocol directly into Jooby.
+
+Because the `io.jooby.trpc` package is included in Jooby core, there are no extra dependencies to add to your project. This integration allows you to write standard Java/Kotlin controllers and consume them directly in the browser using the official `@trpc/client`—complete with 100% type safety, autocomplete, and zero manual client generation.
+
+==== Usage
+
+Because tRPC relies heavily on JSON serialization to communicate with the frontend client, a JSON module **must** be installed prior to the `TrpcModule`.
+
+NOTE: Currently, Jooby only provides the required `TrpcParser` SPI implementation for two JSON engines: **Jackson 2/3** and **AvajeJsonbModule** . Using other JSON modules (like Gson) will result in a missing service exception at startup.
+
+[source, java]
+----
+import io.jooby.Jooby;
+import io.jooby.json.JacksonModule;
+import io.jooby.trpc.TrpcModule;
+
+public class App extends Jooby {
+  {
+    install(new JacksonModule()); // <1>
+
+    install(new TrpcModule());    // <2>
+
+    install(new MovieService_()); // <3>
+  }
+}
+----
+
+1. Install a supported JSON engine (Jackson or Avaje)
+2. Install the tRPC extension
+3. Register your @Trpc annotated controllers (using the APT generated route)
+
+==== Writing a Service
+
+You can define your procedures using explicit tRPC annotations or a hybrid approach combining tRPC with standard HTTP methods:
+
+* **Explicit Annotations:** Use `@Trpc.Query` (maps to `GET`) and `@Trpc.Mutation` (maps to `POST`).
+* **Hybrid Annotations:** Combine the base `@Trpc` annotation with Jooby's standard HTTP annotations. A `@GET` resolves to a tRPC query, while state-changing methods (`@POST`, `@PUT`, `@DELETE`) resolve to tRPC mutations.
+
+.MovieService
+[source, java]
+----
+import io.jooby.annotation.Trpc;
+import io.jooby.annotation.DELETE;
+
+public record Movie(int id, String title, int year) {}
+
+@Trpc("movies") // Defines the 'movies' namespace
+public class MovieService {
+
+  // 1. Explicit tRPC Query
+  @Trpc.Query
+  public Movie getById(int id) {
+    return new Movie(id, "Pulp Fiction", 1994);
+  }
+
+  // 2. Explicit tRPC Mutation
+  @Trpc.Mutation
+  public Movie create(Movie movie) {
+    // Save to database logic here
+    return movie;
+  }
+
+  // 3. Hybrid Mutation
+  @Trpc
+  @DELETE
+  public void delete(int id) {
+    // Delete from database
+  }
+}
+----
+
+==== Build Tool Configuration
+
+To generate the `trpc.d.ts` TypeScript definitions, you must configure the Jooby build plugin for your project. The generator parses your source code and emits the definitions during the compilation phase.
+
+.pom.xml
+[source, xml, role = "primary", subs="verbatim,attributes"]
+----
+<plugin>
+  <groupId>io.jooby</groupId>
+  <artifactId>jooby-maven-plugin</artifactId>
+  <version>${jooby.version}</version>
+  <executions>
+    <execution>
+      <goals>
+        <goal>trpc</goal>
+      </goals>
+    </execution>
+  </executions>
+  <configuration>
+    <jsonLibrary>jackson2</jsonLibrary>
+    <outputDir>${project.build.outputDirectory}</outputDir>
+  </configuration>
+</plugin>
+----
+
+.gradle.build
+[source, groovy, role = "secondary", subs="verbatim,attributes"]
+----
+plugins {
+  id 'io.jooby.trpc' version "${joobyVersion}"
+}
+
+trpc {
+  // Optional settings
+  jsonLibrary = 'jackson2'
+}
+----
+
+==== Consuming the API (Frontend)
+
+Once the project is compiled, the build plugin generates a `trpc.d.ts` file containing your exact `AppRouter` shape. You can then use the official client in your TypeScript frontend:
+
+[source, bash]
+----
+npm install @trpc/client
+----
+
+[source, typescript]
+----
+import { createTRPCProxyClient, httpLink } from '@trpc/client';
+import type { AppRouter } from './target/classes/trpc'; // Path to generated file
+
+// Initialize the strongly-typed client
+export const trpc = createTRPCProxyClient<AppRouter>({
+  links: [
+    httpLink({
+      url: 'http://localhost:8080/trpc',
+    }),
+  ],
+});
+
+// 100% Type-safe! IDEs will autocomplete namespaces, inputs, and outputs.
+const movie = await trpc.movies.getById.query(1);
+console.log(`Fetched: ${movie.title} (${movie.year})`);
+----
+
+==== Advanced Configuration
+
+===== Custom Exception Mapping
+The tRPC protocol expects specific JSON-RPC error codes (e.g., `-32600` for Bad Request). `TrpcModule` automatically registers a specialized error handler to format these errors.
+
+If you throw custom domain exceptions, you can map them directly to tRPC error codes using the service registry so the frontend client receives the correct error state:
+
+[source, java]
+----
+import io.jooby.trpc.TrpcErrorCode;
+
+{
+  install(new TrpcModule());
+
+  // Map your custom business exception to a standard tRPC error code
+  getServices().mapOf(Class.class, TrpcErrorCode.class)
+    .put(IllegalArgumentException.class, TrpcErrorCode.BAD_REQUEST)
+    .put(MovieNotFoundException.class, TrpcErrorCode.NOT_FOUND);
+}
+----
+
+===== Custom TypeScript Mappings
+Sometimes you have custom Java types (like `java.util.UUID` or `java.math.BigDecimal`) that you want translated into specific TypeScript primitives. You can define these overrides in your build tool:
+
+**Maven:**
+[source, xml]
+----
+<configuration>
+  <customTypeMappings>
+    <java.util.UUID>string</java.util.UUID>
+    <java.math.BigDecimal>number</java.math.BigDecimal>
+  </customTypeMappings>
+</configuration>
+----
+
+**Gradle:**
+[source, groovy]
+----
+trpc {
+  customTypeMappings = [
+    'java.util.UUID': 'string',
+    'java.math.BigDecimal': 'number'
+  ]
+}
+----

docs/asciidoc/web.adoc

@@ -10,4 +10,6 @@ include::session.adoc[]
 
 include::server-sent-event.adoc[]
 
+include::tRPC.adoc[]
+
 include::websocket.adoc[]

jooby/src/main/java/io/jooby/StatusCode.java

@@ -738,6 +738,14 @@ public final class StatusCode {
   public static final StatusCode REQUEST_HEADER_FIELDS_TOO_LARGE =
       new StatusCode(REQUEST_HEADER_FIELDS_TOO_LARGE_CODE, "Request Header Fields Too Large");
 
+  /** {@code 499 The client aborted the request before completion}. */
+  public static final int CLIENT_CLOSED_REQUEST_CODE = 499;
+
+  /** {@code 499 The client aborted the request before completion}. */
+  public static final StatusCode CLIENT_CLOSED_REQUEST =
+      new StatusCode(
+          CLIENT_CLOSED_REQUEST_CODE, "The client aborted the request before completion");
+
   // --- 5xx Server Error ---
 
   /**
@@ -1025,6 +1033,7 @@ public static StatusCode valueOf(final int statusCode) {
       case PRECONDITION_REQUIRED_CODE -> PRECONDITION_REQUIRED;
       case TOO_MANY_REQUESTS_CODE -> TOO_MANY_REQUESTS;
       case REQUEST_HEADER_FIELDS_TOO_LARGE_CODE -> REQUEST_HEADER_FIELDS_TOO_LARGE;
+      case CLIENT_CLOSED_REQUEST_CODE -> CLIENT_CLOSED_REQUEST;
       case SERVER_ERROR_CODE -> SERVER_ERROR;
       case NOT_IMPLEMENTED_CODE -> NOT_IMPLEMENTED;
       case BAD_GATEWAY_CODE -> BAD_GATEWAY;

jooby/src/main/java/io/jooby/annotation/Trpc.java

@@ -0,0 +1,111 @@
+/*
+ * Jooby https://jooby.io
+ * Apache License Version 2.0 https://jooby.io/LICENSE.txt
+ * Copyright 2014 Edgar Espina
+ */
+package io.jooby.annotation;
+
+import java.lang.annotation.Documented;
+import java.lang.annotation.ElementType;
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+import java.lang.annotation.Target;
+
+/**
+ * Marks a controller class or a specific route method for tRPC TypeScript generation.
+ *
+ * <p>When applied to a class, it defines a namespace for the tRPC router. All tRPC-annotated
+ * methods within the class will be grouped under this namespace in the generated TypeScript {@code
+ * AppRouter}.
+ *
+ * <p><b>Defining Procedures:</b>
+ *
+ * <p>There are two ways to expose a method as a tRPC procedure:
+ *
+ * <ul>
+ *   <li><b>Explicit tRPC Annotations:</b> Use {@link Trpc.Query} for read-only operations (mapped
+ *       to HTTP GET) and {@link Trpc.Mutation} for state-changing operations (mapped to HTTP POST).
+ *   <li><b>Hybrid HTTP Annotations:</b> Combine the base {@code @Trpc} annotation with standard
+ *       HTTP annotations. A {@code @GET} annotation maps to a query, while {@code @POST},
+ *       {@code @PUT}, {@code @PATCH}, and {@code @DELETE} map to a mutation.
+ * </ul>
+ *
+ * <p><b>Network Payloads:</b>
+ *
+ * <p>Because tRPC natively supports only a single input payload, Java methods with multiple
+ * parameters will automatically require a JSON array (Tuple) from the frontend client. Framework
+ * parameters like {@code io.jooby.Context} are ignored during payload calculation.
+ *
+ * <p><b>Example:</b>
+ *
+ * <pre>{@code
+ * @Trpc("movies") // Defines the 'movies' namespace
+ * public class MovieService {
+ *
+ * @Trpc.Query // Becomes 'movies.list' query
+ * public List<Movie> list() { ... }
+ *
+ * @Trpc // Hybrid approach: Becomes 'movies.delete' mutation
+ * @DELETE
+ * public void delete(int id) { ... }
+ * }
+ * }</pre>
+ */
+@Target({ElementType.TYPE, ElementType.METHOD})
+@Retention(RetentionPolicy.RUNTIME)
+@Documented
+public @interface Trpc {
+
+  /**
+   * Marks a method as a tRPC mutation.
+   *
+   * <p>Mutations are used for creating, updating, or deleting data. Under the hood, Jooby will
+   * automatically expose this method as an HTTP POST route on the {@code /trpc} endpoint.
+   */
+  @Target(ElementType.METHOD)
+  @Retention(RetentionPolicy.RUNTIME)
+  @Documented
+  @interface Mutation {
+    /**
+     * Custom name for the tRPC mutation.
+     *
+     * <p>This overrides the generated procedure name in the TypeScript router.
+     *
+     * @return The custom procedure name. Empty by default, which means the generator will use the
+     *     Java method name.
+     */
+    String value() default "";
+  }
+
+  /**
+   * Marks a method as a tRPC query.
+   *
+   * <p>Queries are strictly used for fetching data. Under the hood, Jooby will automatically expose
+   * this method as an HTTP GET route on the {@code /trpc} endpoint.
+   */
+  @Target(ElementType.METHOD)
+  @Retention(RetentionPolicy.RUNTIME)
+  @Documented
+  @interface Query {
+    /**
+     * Custom name for the tRPC query.
+     *
+     * <p>This overrides the generated procedure name in the TypeScript router.
+     *
+     * @return The custom procedure name. Empty by default, which means the generator will use the
+     *     Java method name.
+     */
+    String value() default "";
+  }
+
+  /**
+   * Custom name for the tRPC procedure or namespace.
+   *
+   * <p>If applied to a method, this overrides the generated procedure name. If applied to a class,
+   * this overrides the generated namespace in the {@code AppRouter}.
+   *
+   * @return The custom procedure or namespace name. Empty by default, which means the generator
+   *     will use the Java method or class name.
+   */
+  String value() default "";
+}

jooby/src/main/java/io/jooby/trpc/TrpcDecoder.java

@@ -0,0 +1,42 @@
+/*
+ * Jooby https://jooby.io
+ * Apache License Version 2.0 https://jooby.io/LICENSE.txt
+ * Copyright 2014 Edgar Espina
+ */
+package io.jooby.trpc;
+
+/**
+ * A pre-resolved decoder used at runtime to deserialize tRPC network payloads into complex Java
+ * objects.
+ *
+ * <p>This interface is heavily utilized by the Jooby Annotation Processor (APT). When compiling
+ * tRPC-annotated controllers, the APT generates highly optimized routing code that resolves the
+ * appropriate {@code TrpcDecoder} for each method argument. By pre-resolving these decoders, Jooby
+ * efficiently parses incoming JSON payloads without incurring reflection overhead on every request.
+ *
+ * <p>Note: Primitive types and standard wrappers (like {@code int}, {@code String}, {@code
+ * boolean}) are typically handled directly by the {@code TrpcReader} rather than requiring a
+ * dedicated decoder.
+ *
+ * @param <T> The target Java type this decoder produces.
+ */
+public interface TrpcDecoder<T> {
+
+  /**
+   * Decodes a raw byte array payload into the target Java object.
+   *
+   * @param name The name of the parameter being decoded (useful for error reporting or wrapping).
+   * @param payload The raw JSON byte array received from the network.
+   * @return The fully deserialized Java object.
+   */
+  T decode(String name, byte[] payload);
+
+  /**
+   * Decodes a string payload into the target Java object.
+   *
+   * @param name The name of the parameter being decoded (useful for error reporting or wrapping).
+   * @param payload The JSON string received from the network.
+   * @return The fully deserialized Java object.
+   */
+  T decode(String name, String payload);
+}