Creating Procedures

Procedures in Actyx RPC are constructed using a procedure builder created by createProcedure(). This allows you to encapsulate and reuse shared server concerns, such as authentication, logging, global context, and centralized error mapping.

`createProcedure()`

To get started, instantiate a base procedure builder:


import { createProcedure } from "@explita/actyx-rpc";
 
const procedure = createProcedure({
  async createContext() {
    const session = await getSession();
 
    if (!session) {
      return { ok: false, reason: "UNAUTHORIZED" };
    }
 
    return {
      ok: true,
      ctx: {
        userId: session.user.id,
        role: session.user.role,
      },
    };
  },
  onContextError({ reason }) {
    if (reason === "UNAUTHORIZED") {
      return {
        _redirect: () => redirect("/login"),
        message: "Session expired or invalid",
      };
    }
  },
  onSuccess({ ctx, input, output, duration }) {
    console.log("Procedure completed successfully", { 
      handler: ctx.handlerName, 
      duration 
    });
  },
  inputMode: "strict", // "strict" | "form" | "partial"
});

Configuration Options

Option	Type	Description
`createContext`	`(prev) => Promise<ContextResult>`	Runs at the start of the request lifecycle to generate a shared context. Can return `{ ok: false, reason: string }` on failure.
`onContextError`	`(err) => any`	Called if `createContext` fails. Useful for global redirects or constructing unified error payloads.
`enrichInput`	`(ctx) => Promise<TEnrich> \| TEnrich`	Runs after context creation to attach global context keys (e.g., `userId`) into all procedure input objects.
`onSuccess`	`(props) => void`	Runs when a procedure finishes successfully. Receives context, input, output, and execution duration.
`onError`	`(props) => any`	Runs when a procedure throws or returns an error. Returns mapped error format.
`inputMode`	`InputMode`	The default caller input mode for procedures (`strict`, `form`, `partial`).
`middlewares`	`Middleware[]`	Array of global middlewares applied to all procedures generated from this builder.
`plugins`	`Plugin[]`	Array of global plugins applied to all procedures.
`cache`	`CacheAdapter`	The global cache adapter used for caching queries and rate-limit tracking (defaults to `MemoryCache`).
`compression`	`Compressor`	The global compressor instance used for response compression (defaults to `Compressor`).
`meta`	`TMeta`	Default global metadata attached to all child procedures.

Global Error Mapping

The onError hook is a powerful way to centralize error handling. Instead of polluting every query or mutation handler with identical try/catch blocks, let your handlers throw naturally.

When onError returns an object, that object becomes the official error response returned by the procedure to the client.


const procedure = createProcedure({
  // ...
  onError({ error, ctx }) {
    // If the procedure has a .name("..."), it's available in ctx.handlerName
    console.error(`Error in ${ctx.handlerName}:`, error);
 
    // Map database unique constraint violations globally
    if (error.code === "P2002") {
      return {
        success: false,
        message: "Conflict detected",
        reason: "VALIDATION_ERROR",
        errors: {
          [error.meta.target[0]]: "This value is already taken",
        },
      };
    }
  },
});

Now your actual query and mutation handlers can be clean and free of boilerplate:


const createUser = procedure.input(userResolver).mutation(async ({ input }) => {
  // Just throw! No try/catch needed here.
  return await db.user.create({ data: input });
});

Next.js Redirects in Context Failures

If you are using Next.js, you can return a _redirect callback in onContextError (or inside middlewares) to trigger a top-level redirect:


onContextError({ reason }) {
  if (reason === "INVALID_SESSION") {
    return {
      _redirect: () => redirect("/login"),
      message: "Session expired",
    };
  }
}

This is executed at the very start of the procedure response before returning to the caller.