Version: 10.x

Middlewares

You are able to add middleware(s) to a procedure with the t.procedure.use() method. The middleware(s) will wrap the invocation of the procedure and must pass through its return value.

Authorization

In the example below, any call to a adminProcedure will ensure that the user is an "admin" before executing.

ts
import { TRPCError, initTRPC } from '@trpc/server';
 
interface Context {
  user?: {
    id: string;
    isAdmin: boolean;
    // [..]
  };
}
 
const t = initTRPC.context<Context>().create();
export const middleware = t.middleware;
export const publicProcedure = t.procedure;
export const router = t.router;
 
const isAdmin = middleware(async ({ ctx, next }) => {
  if (!ctx.user?.isAdmin) {
    throw new TRPCError({ code: 'UNAUTHORIZED' });
  }
  return next({
    ctx: {
      user: ctx.user,
    },
  });
});
 
export const adminProcedure = publicProcedure.use(isAdmin);

ts
import { TRPCError, initTRPC } from '@trpc/server';
 
interface Context {
  user?: {
    id: string;
    isAdmin: boolean;
    // [..]
  };
}
 
const t = initTRPC.context<Context>().create();
export const middleware = t.middleware;
export const publicProcedure = t.procedure;
export const router = t.router;
 
const isAdmin = middleware(async ({ ctx, next }) => {
  if (!ctx.user?.isAdmin) {
    throw new TRPCError({ code: 'UNAUTHORIZED' });
  }
  return next({
    ctx: {
      user: ctx.user,
    },
  });
});
 
export const adminProcedure = publicProcedure.use(isAdmin);

ts
import { adminProcedure, publicProcedure, router } from './trpc';
 
const adminRouter = router({
  secretPlace: adminProcedure.query(() => 'a key'),
});
 
export const appRouter = router({
  foo: publicProcedure.query(() => 'bar'),
  admin: adminRouter,
});

ts
import { adminProcedure, publicProcedure, router } from './trpc';
 
const adminRouter = router({
  secretPlace: adminProcedure.query(() => 'a key'),
});
 
export const appRouter = router({
  foo: publicProcedure.query(() => 'bar'),
  admin: adminRouter,
});

tip

See Error Handling to learn more about the TRPCError thrown in the above example.

Logging

In the example below timings for queries are logged automatically.

ts
const loggerMiddleware = middleware(async ({ path, type, next }) => {
  const start = Date.now();
  const result = await next();
  const durationMs = Date.now() - start;
  result.ok
    ? logMock('OK request timing:', { path, type, durationMs })
    : logMock('Non-OK request timing', { path, type, durationMs });
 
  return result;
});
 
export const loggedProcedure = publicProcedure.use(loggerMiddleware);

ts
const loggerMiddleware = middleware(async ({ path, type, next }) => {
  const start = Date.now();
  const result = await next();
  const durationMs = Date.now() - start;
  result.ok
    ? logMock('OK request timing:', { path, type, durationMs })
    : logMock('Non-OK request timing', { path, type, durationMs });
 
  return result;
});
 
export const loggedProcedure = publicProcedure.use(loggerMiddleware);

ts
import { loggedProcedure, router } from './trpc';
 
export const appRouter = router({
  foo: loggedProcedure.query(() => 'bar'),
  abc: loggedProcedure.query(() => 'def'),
});

ts
import { loggedProcedure, router } from './trpc';
 
export const appRouter = router({
  foo: loggedProcedure.query(() => 'bar'),
  abc: loggedProcedure.query(() => 'def'),
});

Context Swapping

Context swapping in tRPC is a very powerful feature that allows you to create base procedures that dynamically infers new context in a flexible and typesafe manner.

Below we have an example of a middleware that changes properties of the context, and procedures will receive the new context value:

ts
type Context = {
  // user is nullable
  user?: {
    id: string;
  };
};
 
const isAuthed = middleware(({ ctx, next }) => {
  // `ctx.user` is nullable
  if (!ctx.user) {
            (property) user?: {
    id: string;
} | undefined
    throw new TRPCError({ code: 'UNAUTHORIZED' });
  }
 
  return next({
    ctx: {
      // ✅ user value is known to be non-null now
      user: ctx.user,
       (property) user: {
    id: string;
}
    },
  });
});
 
const protectedProcedure = publicProcedure.use(isAuthed);
protectedProcedure.query(({ ctx }) => ctx.user);
                                           (property) user: {
    id: string;
}

ts
type Context = {
  // user is nullable
  user?: {
    id: string;
  };
};
 
const isAuthed = middleware(({ ctx, next }) => {
  // `ctx.user` is nullable
  if (!ctx.user) {
            (property) user?: {
    id: string;
} | undefined
    throw new TRPCError({ code: 'UNAUTHORIZED' });
  }
 
  return next({
    ctx: {
      // ✅ user value is known to be non-null now
      user: ctx.user,
       (property) user: {
    id: string;
}
    },
  });
});
 
const protectedProcedure = publicProcedure.use(isAuthed);
protectedProcedure.query(({ ctx }) => ctx.user);
                                           (property) user: {
    id: string;
}

Extending middlewares

info

We have prefixed this as unstable_ as it's a new API, but you're safe to use it! Read more.

We have a powerful feature called .pipe() which allows you to extend middlewares in a typesafe manner.

Below we have an example of a middleware that extends a base middleware(foo). Like the context swapping example above, piping middlewares will change properties of the context, and procedures will receive the new context value.

ts
const fooMiddleware = middleware(({ next }) => {
  return next({
    ctx: {
      foo: 'foo' as const,
    },
  });
});
 
const barMiddleware = fooMiddleware.unstable_pipe(({ ctx, next }) => {
  ctx.foo;
      
(property) foo: "foo"
  return next({
    ctx: {
      bar: 'bar' as const,
    },
  });
});
 
const barProcedure = publicProcedure.use(barMiddleware);
barProcedure.query(({ ctx }) => ctx.bar);
                      (parameter) ctx: {
    foo: "foo";
    bar: "bar";
}

ts
const fooMiddleware = middleware(({ next }) => {
  return next({
    ctx: {
      foo: 'foo' as const,
    },
  });
});
 
const barMiddleware = fooMiddleware.unstable_pipe(({ ctx, next }) => {
  ctx.foo;
      
(property) foo: "foo"
  return next({
    ctx: {
      bar: 'bar' as const,
    },
  });
});
 
const barProcedure = publicProcedure.use(barMiddleware);
barProcedure.query(({ ctx }) => ctx.bar);
                      (parameter) ctx: {
    foo: "foo";
    bar: "bar";
}

Beware that the order in which you pipe your middlewares matter and that the context must overlap. An example of a forbidden pipe is shown below. Here, the fooMiddleware overrides the ctx.a while barMiddleware still expects the root context from the initialization in initTRPC - so piping fooMiddleware with barMiddleware would not work, while piping barMiddleware with fooMiddleware does work.

ts
import { initTRPC } from '@trpc/server';
 
const t = initTRPC
  .context<{
    a: {
      b: 'a';
    };
  }>()
  .create();
 
const fooMiddleware = t.middleware(({ ctx, next }) => {
  ctx.a; // 👈 fooMiddleware expects `ctx.a` to be an object
     (property) a: {
    b: 'a';
}
  return next({
    ctx: {
      a: 'a' as const, // 👈 `ctx.a` is no longer an object
    },
  });
});
 
const barMiddleware = t.middleware(({ ctx, next }) => {
  ctx.a; // 👈 barMiddleware expects `ctx.a` to be an object
     (property) a: {
    b: 'a';
}
  return next({
    ctx: {
      foo: 'foo' as const,
    },
  });
});
 
// ❌ `ctx.a` does not overlap from `fooMiddleware` to `barMiddleware`
fooMiddleware.unstable_pipe(barMiddleware);
Argument of type 'MiddlewareBuilder<{ _config: RootConfig<{ ctx: { a: { b: "a"; }; }; meta: object; errorShape: DefaultErrorShape; transformer: DefaultDataTransformer; }>; ... 5 more ...; _meta: object; }, { ...; }>' is not assignable to parameter of type 'MiddlewareBuilder<{ _config: RootConfig<{ ctx: { a: { b: "a"; }; }; meta: object; errorShape: DefaultErrorShape; transformer: DefaultDataTransformer; }>; ... 5 more ...; _output_out: unknown; }, { ...; }> | MiddlewareFunction<...>'.
  Type 'MiddlewareBuilder<{ _config: RootConfig<{ ctx: { a: { b: "a"; }; }; meta: object; errorShape: DefaultErrorShape; transformer: DefaultDataTransformer; }>; ... 5 more ...; _meta: object; }, { ...; }>' is not assignable to type 'MiddlewareBuilder<{ _config: RootConfig<{ ctx: { a: { b: "a"; }; }; meta: object; errorShape: DefaultErrorShape; transformer: DefaultDataTransformer; }>; ... 5 more ...; _output_out: unknown; }, { ...; }>'.
    Types of property 'unstable_pipe' are incompatible.
      Type '<$Params extends import("/vercel/path0/www/node_modules/@trpc/server/dist/core/procedure").ProcedureParams<import("/vercel/path0/www/node_modules/@trpc/server/dist/core/internals/config").AnyRootConfig, unknown, unknown, unknown, unknown, unknown, unknown>>(fn: import("/vercel/path0/www/node_modules/@trpc/server/dis...' is not assignable to type '<$Params extends import("/vercel/path0/www/node_modules/@trpc/server/dist/core/procedure").ProcedureParams<import("/vercel/path0/www/node_modules/@trpc/server/dist/core/internals/config").AnyRootConfig, unknown, unknown, unknown, unknown, unknown, unknown>>(fn: import("/vercel/path0/www/node_modules/@trpc/server/dis...'. Two different types with this name exist, but they are unrelated.
        Types of parameters 'fn' and 'fn' are incompatible.
          Type 'import("/vercel/path0/www/node_modules/@trpc/server/dist/core/middleware").MiddlewareBuilder<{ _config: import("/vercel/path0/www/node_modules/@trpc/server/dist/core/internals/config").RootConfig<{ ctx: { a: { b: "a"; }; }; meta: object; errorShape: import("/vercel/path0/www/node_modules/@trpc/server/dist/error/form...' is not assignable to type 'import("/vercel/path0/www/node_modules/@trpc/server/dist/core/middleware").MiddlewareBuilder<{ _config: import("/vercel/path0/www/node_modules/@trpc/server/dist/core/internals/config").RootConfig<{ ctx: { a: { b: "a"; }; }; meta: object; errorShape: import("/vercel/path0/www/node_modules/@trpc/server/dist/error/form...'. Two different types with this name exist, but they are unrelated.
            Type 'MiddlewareBuilder<{ _config: RootConfig<{ ctx: { a: { b: "a"; }; }; meta: object; errorShape: DefaultErrorShape; transformer: DefaultDataTransformer; }>; ... 5 more ...; _output_out: unknown; }, any>' is not assignable to type 'MiddlewareBuilder<{ _config: RootConfig<{ ctx: { a: { b: "a"; }; }; meta: object; errorShape: DefaultErrorShape; transformer: DefaultDataTransformer; }>; ... 5 more ...; _output_out: unknown; }, any> | MiddlewareFunction<...>'.
              Type 'import("/vercel/path0/www/node_modules/@trpc/server/dist/core/middleware").MiddlewareBuilder<{ _config: import("/vercel/path0/www/node_modules/@trpc/server/dist/core/internals/config").RootConfig<{ ctx: { a: { b: "a"; }; }; meta: object; errorShape: import("/vercel/path0/www/node_modules/@trpc/server/dist/error/form...' is not assignable to type 'import("/vercel/path0/www/node_modules/@trpc/server/dist/core/middleware").MiddlewareBuilder<{ _config: import("/vercel/path0/www/node_modules/@trpc/server/dist/core/internals/config").RootConfig<{ ctx: { a: { b: "a"; }; }; meta: object; errorShape: import("/vercel/path0/www/node_modules/@trpc/server/dist/error/form...'. Two different types with this name exist, but they are unrelated.
                Types of property '_middlewares' are incompatible.
                  Type 'import("/vercel/path0/www/node_modules/@trpc/server/dist/core/middleware").MiddlewareFunction<{ _config: import("/vercel/path0/www/node_modules/@trpc/server/dist/core/internals/config").RootConfig<{ ctx: { a: { b: "a"; }; }; meta: object; errorShape: import("/vercel/path0/www/node_modules/@trpc/server/dist/error/for...' is not assignable to type 'import("/vercel/path0/www/node_modules/@trpc/server/dist/core/middleware").MiddlewareFunction<{ _config: import("/vercel/path0/www/node_modules/@trpc/server/dist/core/internals/config").RootConfig<{ ctx: { a: { b: "a"; }; }; meta: object; errorShape: import("/vercel/path0/www/node_modules/@trpc/server/dist/error/for...'. Two different types with this name exist, but they are unrelated.
                    Type 'import("/vercel/path0/www/node_modules/@trpc/server/dist/core/middleware").MiddlewareFunction<{ _config: import("/vercel/path0/www/node_modules/@trpc/server/dist/core/internals/config").RootConfig<{ ctx: { a: { b: "a"; }; }; meta: object; errorShape: import("/vercel/path0/www/node_modules/@trpc/server/dist/error/for...' is not assignable to type 'import("/vercel/path0/www/node_modules/@trpc/server/dist/core/middleware").MiddlewareFunction<{ _config: import("/vercel/path0/www/node_modules/@trpc/server/dist/core/internals/config").RootConfig<{ ctx: { a: { b: "a"; }; }; meta: object; errorShape: import("/vercel/path0/www/node_modules/@trpc/server/dist/error/for...'. Two different types with this name exist, but they are unrelated.
                      Type '{ _config: import("/vercel/path0/www/node_modules/@trpc/server/dist/core/internals/config").RootConfig<{ ctx: { a: { b: "a"; }; }; meta: object; errorShape: import("/vercel/path0/www/node_modules/@trpc/server/dist/error/formatter").DefaultErrorShape; transformer: import("/vercel/path0/www/node_modules/@trpc/server/d...' is not assignable to type '{ _config: import("/vercel/path0/www/node_modules/@trpc/server/dist/core/internals/config").RootConfig<{ ctx: { a: { b: "a"; }; }; meta: object; errorShape: import("/vercel/path0/www/node_modules/@trpc/server/dist/error/formatter").DefaultErrorShape; transformer: import("/vercel/path0/www/node_modules/@trpc/server/d...'. Two different types with this name exist, but they are unrelated.
                        Types of property '_ctx_out' are incompatible.
                          Type 'Overwrite<{ a: { b: "a"; }; }, { foo: "foo"; }>' is not assignable to type 'Overwrite<Overwrite<{ a: { b: "a"; }; }, { a: "a"; }>, { foo: "foo"; }>'.
                            Type 'Overwrite<{ a: { b: "a"; }; }, { foo: "foo"; }>' is not assignable to type 'Omit<Overwrite<{ a: { b: "a"; }; }, { a: "a"; }>, "foo">'.
                              Types of property 'a' are incompatible.
                                Type '{ b: "a"; }' is not assignable to type '"a"'.2345Argument of type 'MiddlewareBuilder<{ _config: RootConfig<{ ctx: { a: { b: "a"; }; }; meta: object; errorShape: DefaultErrorShape; transformer: DefaultDataTransformer; }>; ... 5 more ...; _meta: object; }, { ...; }>' is not assignable to parameter of type 'MiddlewareBuilder<{ _config: RootConfig<{ ctx: { a: { b: "a"; }; }; meta: object; errorShape: DefaultErrorShape; transformer: DefaultDataTransformer; }>; ... 5 more ...; _output_out: unknown; }, { ...; }> | MiddlewareFunction<...>'.
  Type 'MiddlewareBuilder<{ _config: RootConfig<{ ctx: { a: { b: "a"; }; }; meta: object; errorShape: DefaultErrorShape; transformer: DefaultDataTransformer; }>; ... 5 more ...; _meta: object; }, { ...; }>' is not assignable to type 'MiddlewareBuilder<{ _config: RootConfig<{ ctx: { a: { b: "a"; }; }; meta: object; errorShape: DefaultErrorShape; transformer: DefaultDataTransformer; }>; ... 5 more ...; _output_out: unknown; }, { ...; }>'.
    Types of property 'unstable_pipe' are incompatible.
      Type '<$Params extends import("/vercel/path0/www/node_modules/@trpc/server/dist/core/procedure").ProcedureParams<import("/vercel/path0/www/node_modules/@trpc/server/dist/core/internals/config").AnyRootConfig, unknown, unknown, unknown, unknown, unknown, unknown>>(fn: import("/vercel/path0/www/node_modules/@trpc/server/dis...' is not assignable to type '<$Params extends import("/vercel/path0/www/node_modules/@trpc/server/dist/core/procedure").ProcedureParams<import("/vercel/path0/www/node_modules/@trpc/server/dist/core/internals/config").AnyRootConfig, unknown, unknown, unknown, unknown, unknown, unknown>>(fn: import("/vercel/path0/www/node_modules/@trpc/server/dis...'. Two different types with this name exist, but they are unrelated.
        Types of parameters 'fn' and 'fn' are incompatible.
          Type 'import("/vercel/path0/www/node_modules/@trpc/server/dist/core/middleware").MiddlewareBuilder<{ _config: import("/vercel/path0/www/node_modules/@trpc/server/dist/core/internals/config").RootConfig<{ ctx: { a: { b: "a"; }; }; meta: object; errorShape: import("/vercel/path0/www/node_modules/@trpc/server/dist/error/form...' is not assignable to type 'import("/vercel/path0/www/node_modules/@trpc/server/dist/core/middleware").MiddlewareBuilder<{ _config: import("/vercel/path0/www/node_modules/@trpc/server/dist/core/internals/config").RootConfig<{ ctx: { a: { b: "a"; }; }; meta: object; errorShape: import("/vercel/path0/www/node_modules/@trpc/server/dist/error/form...'. Two different types with this name exist, but they are unrelated.
            Type 'MiddlewareBuilder<{ _config: RootConfig<{ ctx: { a: { b: "a"; }; }; meta: object; errorShape: DefaultErrorShape; transformer: DefaultDataTransformer; }>; ... 5 more ...; _output_out: unknown; }, any>' is not assignable to type 'MiddlewareBuilder<{ _config: RootConfig<{ ctx: { a: { b: "a"; }; }; meta: object; errorShape: DefaultErrorShape; transformer: DefaultDataTransformer; }>; ... 5 more ...; _output_out: unknown; }, any> | MiddlewareFunction<...>'.
              Type 'import("/vercel/path0/www/node_modules/@trpc/server/dist/core/middleware").MiddlewareBuilder<{ _config: import("/vercel/path0/www/node_modules/@trpc/server/dist/core/internals/config").RootConfig<{ ctx: { a: { b: "a"; }; }; meta: object; errorShape: import("/vercel/path0/www/node_modules/@trpc/server/dist/error/form...' is not assignable to type 'import("/vercel/path0/www/node_modules/@trpc/server/dist/core/middleware").MiddlewareBuilder<{ _config: import("/vercel/path0/www/node_modules/@trpc/server/dist/core/internals/config").RootConfig<{ ctx: { a: { b: "a"; }; }; meta: object; errorShape: import("/vercel/path0/www/node_modules/@trpc/server/dist/error/form...'. Two different types with this name exist, but they are unrelated.
                Types of property '_middlewares' are incompatible.
                  Type 'import("/vercel/path0/www/node_modules/@trpc/server/dist/core/middleware").MiddlewareFunction<{ _config: import("/vercel/path0/www/node_modules/@trpc/server/dist/core/internals/config").RootConfig<{ ctx: { a: { b: "a"; }; }; meta: object; errorShape: import("/vercel/path0/www/node_modules/@trpc/server/dist/error/for...' is not assignable to type 'import("/vercel/path0/www/node_modules/@trpc/server/dist/core/middleware").MiddlewareFunction<{ _config: import("/vercel/path0/www/node_modules/@trpc/server/dist/core/internals/config").RootConfig<{ ctx: { a: { b: "a"; }; }; meta: object; errorShape: import("/vercel/path0/www/node_modules/@trpc/server/dist/error/for...'. Two different types with this name exist, but they are unrelated.
                    Type 'import("/vercel/path0/www/node_modules/@trpc/server/dist/core/middleware").MiddlewareFunction<{ _config: import("/vercel/path0/www/node_modules/@trpc/server/dist/core/internals/config").RootConfig<{ ctx: { a: { b: "a"; }; }; meta: object; errorShape: import("/vercel/path0/www/node_modules/@trpc/server/dist/error/for...' is not assignable to type 'import("/vercel/path0/www/node_modules/@trpc/server/dist/core/middleware").MiddlewareFunction<{ _config: import("/vercel/path0/www/node_modules/@trpc/server/dist/core/internals/config").RootConfig<{ ctx: { a: { b: "a"; }; }; meta: object; errorShape: import("/vercel/path0/www/node_modules/@trpc/server/dist/error/for...'. Two different types with this name exist, but they are unrelated.
                      Type '{ _config: import("/vercel/path0/www/node_modules/@trpc/server/dist/core/internals/config").RootConfig<{ ctx: { a: { b: "a"; }; }; meta: object; errorShape: import("/vercel/path0/www/node_modules/@trpc/server/dist/error/formatter").DefaultErrorShape; transformer: import("/vercel/path0/www/node_modules/@trpc/server/d...' is not assignable to type '{ _config: import("/vercel/path0/www/node_modules/@trpc/server/dist/core/internals/config").RootConfig<{ ctx: { a: { b: "a"; }; }; meta: object; errorShape: import("/vercel/path0/www/node_modules/@trpc/server/dist/error/formatter").DefaultErrorShape; transformer: import("/vercel/path0/www/node_modules/@trpc/server/d...'. Two different types with this name exist, but they are unrelated.
                        Types of property '_ctx_out' are incompatible.
                          Type 'Overwrite<{ a: { b: "a"; }; }, { foo: "foo"; }>' is not assignable to type 'Overwrite<Overwrite<{ a: { b: "a"; }; }, { a: "a"; }>, { foo: "foo"; }>'.
                            Type 'Overwrite<{ a: { b: "a"; }; }, { foo: "foo"; }>' is not assignable to type 'Omit<Overwrite<{ a: { b: "a"; }; }, { a: "a"; }>, "foo">'.
                              Types of property 'a' are incompatible.
                                Type '{ b: "a"; }' is not assignable to type '"a"'. 
// ✅ `ctx.a` overlaps from `barMiddleware` and `fooMiddleware`
barMiddleware.unstable_pipe(fooMiddleware);

ts
import { initTRPC } from '@trpc/server';
 
const t = initTRPC
  .context<{
    a: {
      b: 'a';
    };
  }>()
  .create();
 
const fooMiddleware = t.middleware(({ ctx, next }) => {
  ctx.a; // 👈 fooMiddleware expects `ctx.a` to be an object
     (property) a: {
    b: 'a';
}
  return next({
    ctx: {
      a: 'a' as const, // 👈 `ctx.a` is no longer an object
    },
  });
});
 
const barMiddleware = t.middleware(({ ctx, next }) => {
  ctx.a; // 👈 barMiddleware expects `ctx.a` to be an object
     (property) a: {
    b: 'a';
}
  return next({
    ctx: {
      foo: 'foo' as const,
    },
  });
});
 
// ❌ `ctx.a` does not overlap from `fooMiddleware` to `barMiddleware`
fooMiddleware.unstable_pipe(barMiddleware);
Argument of type 'MiddlewareBuilder<{ _config: RootConfig<{ ctx: { a: { b: "a"; }; }; meta: object; errorShape: DefaultErrorShape; transformer: DefaultDataTransformer; }>; ... 5 more ...; _meta: object; }, { ...; }>' is not assignable to parameter of type 'MiddlewareBuilder<{ _config: RootConfig<{ ctx: { a: { b: "a"; }; }; meta: object; errorShape: DefaultErrorShape; transformer: DefaultDataTransformer; }>; ... 5 more ...; _output_out: unknown; }, { ...; }> | MiddlewareFunction<...>'.
  Type 'MiddlewareBuilder<{ _config: RootConfig<{ ctx: { a: { b: "a"; }; }; meta: object; errorShape: DefaultErrorShape; transformer: DefaultDataTransformer; }>; ... 5 more ...; _meta: object; }, { ...; }>' is not assignable to type 'MiddlewareBuilder<{ _config: RootConfig<{ ctx: { a: { b: "a"; }; }; meta: object; errorShape: DefaultErrorShape; transformer: DefaultDataTransformer; }>; ... 5 more ...; _output_out: unknown; }, { ...; }>'.
    Types of property 'unstable_pipe' are incompatible.
      Type '<$Params extends import("/vercel/path0/www/node_modules/@trpc/server/dist/core/procedure").ProcedureParams<import("/vercel/path0/www/node_modules/@trpc/server/dist/core/internals/config").AnyRootConfig, unknown, unknown, unknown, unknown, unknown, unknown>>(fn: import("/vercel/path0/www/node_modules/@trpc/server/dis...' is not assignable to type '<$Params extends import("/vercel/path0/www/node_modules/@trpc/server/dist/core/procedure").ProcedureParams<import("/vercel/path0/www/node_modules/@trpc/server/dist/core/internals/config").AnyRootConfig, unknown, unknown, unknown, unknown, unknown, unknown>>(fn: import("/vercel/path0/www/node_modules/@trpc/server/dis...'. Two different types with this name exist, but they are unrelated.
        Types of parameters 'fn' and 'fn' are incompatible.
          Type 'import("/vercel/path0/www/node_modules/@trpc/server/dist/core/middleware").MiddlewareBuilder<{ _config: import("/vercel/path0/www/node_modules/@trpc/server/dist/core/internals/config").RootConfig<{ ctx: { a: { b: "a"; }; }; meta: object; errorShape: import("/vercel/path0/www/node_modules/@trpc/server/dist/error/form...' is not assignable to type 'import("/vercel/path0/www/node_modules/@trpc/server/dist/core/middleware").MiddlewareBuilder<{ _config: import("/vercel/path0/www/node_modules/@trpc/server/dist/core/internals/config").RootConfig<{ ctx: { a: { b: "a"; }; }; meta: object; errorShape: import("/vercel/path0/www/node_modules/@trpc/server/dist/error/form...'. Two different types with this name exist, but they are unrelated.
            Type 'MiddlewareBuilder<{ _config: RootConfig<{ ctx: { a: { b: "a"; }; }; meta: object; errorShape: DefaultErrorShape; transformer: DefaultDataTransformer; }>; ... 5 more ...; _output_out: unknown; }, any>' is not assignable to type 'MiddlewareBuilder<{ _config: RootConfig<{ ctx: { a: { b: "a"; }; }; meta: object; errorShape: DefaultErrorShape; transformer: DefaultDataTransformer; }>; ... 5 more ...; _output_out: unknown; }, any> | MiddlewareFunction<...>'.
              Type 'import("/vercel/path0/www/node_modules/@trpc/server/dist/core/middleware").MiddlewareBuilder<{ _config: import("/vercel/path0/www/node_modules/@trpc/server/dist/core/internals/config").RootConfig<{ ctx: { a: { b: "a"; }; }; meta: object; errorShape: import("/vercel/path0/www/node_modules/@trpc/server/dist/error/form...' is not assignable to type 'import("/vercel/path0/www/node_modules/@trpc/server/dist/core/middleware").MiddlewareBuilder<{ _config: import("/vercel/path0/www/node_modules/@trpc/server/dist/core/internals/config").RootConfig<{ ctx: { a: { b: "a"; }; }; meta: object; errorShape: import("/vercel/path0/www/node_modules/@trpc/server/dist/error/form...'. Two different types with this name exist, but they are unrelated.
                Types of property '_middlewares' are incompatible.
                  Type 'import("/vercel/path0/www/node_modules/@trpc/server/dist/core/middleware").MiddlewareFunction<{ _config: import("/vercel/path0/www/node_modules/@trpc/server/dist/core/internals/config").RootConfig<{ ctx: { a: { b: "a"; }; }; meta: object; errorShape: import("/vercel/path0/www/node_modules/@trpc/server/dist/error/for...' is not assignable to type 'import("/vercel/path0/www/node_modules/@trpc/server/dist/core/middleware").MiddlewareFunction<{ _config: import("/vercel/path0/www/node_modules/@trpc/server/dist/core/internals/config").RootConfig<{ ctx: { a: { b: "a"; }; }; meta: object; errorShape: import("/vercel/path0/www/node_modules/@trpc/server/dist/error/for...'. Two different types with this name exist, but they are unrelated.
                    Type 'import("/vercel/path0/www/node_modules/@trpc/server/dist/core/middleware").MiddlewareFunction<{ _config: import("/vercel/path0/www/node_modules/@trpc/server/dist/core/internals/config").RootConfig<{ ctx: { a: { b: "a"; }; }; meta: object; errorShape: import("/vercel/path0/www/node_modules/@trpc/server/dist/error/for...' is not assignable to type 'import("/vercel/path0/www/node_modules/@trpc/server/dist/core/middleware").MiddlewareFunction<{ _config: import("/vercel/path0/www/node_modules/@trpc/server/dist/core/internals/config").RootConfig<{ ctx: { a: { b: "a"; }; }; meta: object; errorShape: import("/vercel/path0/www/node_modules/@trpc/server/dist/error/for...'. Two different types with this name exist, but they are unrelated.
                      Type '{ _config: import("/vercel/path0/www/node_modules/@trpc/server/dist/core/internals/config").RootConfig<{ ctx: { a: { b: "a"; }; }; meta: object; errorShape: import("/vercel/path0/www/node_modules/@trpc/server/dist/error/formatter").DefaultErrorShape; transformer: import("/vercel/path0/www/node_modules/@trpc/server/d...' is not assignable to type '{ _config: import("/vercel/path0/www/node_modules/@trpc/server/dist/core/internals/config").RootConfig<{ ctx: { a: { b: "a"; }; }; meta: object; errorShape: import("/vercel/path0/www/node_modules/@trpc/server/dist/error/formatter").DefaultErrorShape; transformer: import("/vercel/path0/www/node_modules/@trpc/server/d...'. Two different types with this name exist, but they are unrelated.
                        Types of property '_ctx_out' are incompatible.
                          Type 'Overwrite<{ a: { b: "a"; }; }, { foo: "foo"; }>' is not assignable to type 'Overwrite<Overwrite<{ a: { b: "a"; }; }, { a: "a"; }>, { foo: "foo"; }>'.
                            Type 'Overwrite<{ a: { b: "a"; }; }, { foo: "foo"; }>' is not assignable to type 'Omit<Overwrite<{ a: { b: "a"; }; }, { a: "a"; }>, "foo">'.
                              Types of property 'a' are incompatible.
                                Type '{ b: "a"; }' is not assignable to type '"a"'.2345Argument of type 'MiddlewareBuilder<{ _config: RootConfig<{ ctx: { a: { b: "a"; }; }; meta: object; errorShape: DefaultErrorShape; transformer: DefaultDataTransformer; }>; ... 5 more ...; _meta: object; }, { ...; }>' is not assignable to parameter of type 'MiddlewareBuilder<{ _config: RootConfig<{ ctx: { a: { b: "a"; }; }; meta: object; errorShape: DefaultErrorShape; transformer: DefaultDataTransformer; }>; ... 5 more ...; _output_out: unknown; }, { ...; }> | MiddlewareFunction<...>'.
  Type 'MiddlewareBuilder<{ _config: RootConfig<{ ctx: { a: { b: "a"; }; }; meta: object; errorShape: DefaultErrorShape; transformer: DefaultDataTransformer; }>; ... 5 more ...; _meta: object; }, { ...; }>' is not assignable to type 'MiddlewareBuilder<{ _config: RootConfig<{ ctx: { a: { b: "a"; }; }; meta: object; errorShape: DefaultErrorShape; transformer: DefaultDataTransformer; }>; ... 5 more ...; _output_out: unknown; }, { ...; }>'.
    Types of property 'unstable_pipe' are incompatible.
      Type '<$Params extends import("/vercel/path0/www/node_modules/@trpc/server/dist/core/procedure").ProcedureParams<import("/vercel/path0/www/node_modules/@trpc/server/dist/core/internals/config").AnyRootConfig, unknown, unknown, unknown, unknown, unknown, unknown>>(fn: import("/vercel/path0/www/node_modules/@trpc/server/dis...' is not assignable to type '<$Params extends import("/vercel/path0/www/node_modules/@trpc/server/dist/core/procedure").ProcedureParams<import("/vercel/path0/www/node_modules/@trpc/server/dist/core/internals/config").AnyRootConfig, unknown, unknown, unknown, unknown, unknown, unknown>>(fn: import("/vercel/path0/www/node_modules/@trpc/server/dis...'. Two different types with this name exist, but they are unrelated.
        Types of parameters 'fn' and 'fn' are incompatible.
          Type 'import("/vercel/path0/www/node_modules/@trpc/server/dist/core/middleware").MiddlewareBuilder<{ _config: import("/vercel/path0/www/node_modules/@trpc/server/dist/core/internals/config").RootConfig<{ ctx: { a: { b: "a"; }; }; meta: object; errorShape: import("/vercel/path0/www/node_modules/@trpc/server/dist/error/form...' is not assignable to type 'import("/vercel/path0/www/node_modules/@trpc/server/dist/core/middleware").MiddlewareBuilder<{ _config: import("/vercel/path0/www/node_modules/@trpc/server/dist/core/internals/config").RootConfig<{ ctx: { a: { b: "a"; }; }; meta: object; errorShape: import("/vercel/path0/www/node_modules/@trpc/server/dist/error/form...'. Two different types with this name exist, but they are unrelated.
            Type 'MiddlewareBuilder<{ _config: RootConfig<{ ctx: { a: { b: "a"; }; }; meta: object; errorShape: DefaultErrorShape; transformer: DefaultDataTransformer; }>; ... 5 more ...; _output_out: unknown; }, any>' is not assignable to type 'MiddlewareBuilder<{ _config: RootConfig<{ ctx: { a: { b: "a"; }; }; meta: object; errorShape: DefaultErrorShape; transformer: DefaultDataTransformer; }>; ... 5 more ...; _output_out: unknown; }, any> | MiddlewareFunction<...>'.
              Type 'import("/vercel/path0/www/node_modules/@trpc/server/dist/core/middleware").MiddlewareBuilder<{ _config: import("/vercel/path0/www/node_modules/@trpc/server/dist/core/internals/config").RootConfig<{ ctx: { a: { b: "a"; }; }; meta: object; errorShape: import("/vercel/path0/www/node_modules/@trpc/server/dist/error/form...' is not assignable to type 'import("/vercel/path0/www/node_modules/@trpc/server/dist/core/middleware").MiddlewareBuilder<{ _config: import("/vercel/path0/www/node_modules/@trpc/server/dist/core/internals/config").RootConfig<{ ctx: { a: { b: "a"; }; }; meta: object; errorShape: import("/vercel/path0/www/node_modules/@trpc/server/dist/error/form...'. Two different types with this name exist, but they are unrelated.
                Types of property '_middlewares' are incompatible.
                  Type 'import("/vercel/path0/www/node_modules/@trpc/server/dist/core/middleware").MiddlewareFunction<{ _config: import("/vercel/path0/www/node_modules/@trpc/server/dist/core/internals/config").RootConfig<{ ctx: { a: { b: "a"; }; }; meta: object; errorShape: import("/vercel/path0/www/node_modules/@trpc/server/dist/error/for...' is not assignable to type 'import("/vercel/path0/www/node_modules/@trpc/server/dist/core/middleware").MiddlewareFunction<{ _config: import("/vercel/path0/www/node_modules/@trpc/server/dist/core/internals/config").RootConfig<{ ctx: { a: { b: "a"; }; }; meta: object; errorShape: import("/vercel/path0/www/node_modules/@trpc/server/dist/error/for...'. Two different types with this name exist, but they are unrelated.
                    Type 'import("/vercel/path0/www/node_modules/@trpc/server/dist/core/middleware").MiddlewareFunction<{ _config: import("/vercel/path0/www/node_modules/@trpc/server/dist/core/internals/config").RootConfig<{ ctx: { a: { b: "a"; }; }; meta: object; errorShape: import("/vercel/path0/www/node_modules/@trpc/server/dist/error/for...' is not assignable to type 'import("/vercel/path0/www/node_modules/@trpc/server/dist/core/middleware").MiddlewareFunction<{ _config: import("/vercel/path0/www/node_modules/@trpc/server/dist/core/internals/config").RootConfig<{ ctx: { a: { b: "a"; }; }; meta: object; errorShape: import("/vercel/path0/www/node_modules/@trpc/server/dist/error/for...'. Two different types with this name exist, but they are unrelated.
                      Type '{ _config: import("/vercel/path0/www/node_modules/@trpc/server/dist/core/internals/config").RootConfig<{ ctx: { a: { b: "a"; }; }; meta: object; errorShape: import("/vercel/path0/www/node_modules/@trpc/server/dist/error/formatter").DefaultErrorShape; transformer: import("/vercel/path0/www/node_modules/@trpc/server/d...' is not assignable to type '{ _config: import("/vercel/path0/www/node_modules/@trpc/server/dist/core/internals/config").RootConfig<{ ctx: { a: { b: "a"; }; }; meta: object; errorShape: import("/vercel/path0/www/node_modules/@trpc/server/dist/error/formatter").DefaultErrorShape; transformer: import("/vercel/path0/www/node_modules/@trpc/server/d...'. Two different types with this name exist, but they are unrelated.
                        Types of property '_ctx_out' are incompatible.
                          Type 'Overwrite<{ a: { b: "a"; }; }, { foo: "foo"; }>' is not assignable to type 'Overwrite<Overwrite<{ a: { b: "a"; }; }, { a: "a"; }>, { foo: "foo"; }>'.
                            Type 'Overwrite<{ a: { b: "a"; }; }, { foo: "foo"; }>' is not assignable to type 'Omit<Overwrite<{ a: { b: "a"; }; }, { a: "a"; }>, "foo">'.
                              Types of property 'a' are incompatible.
                                Type '{ b: "a"; }' is not assignable to type '"a"'. 
// ✅ `ctx.a` overlaps from `barMiddleware` and `fooMiddleware`
barMiddleware.unstable_pipe(fooMiddleware);

Authorization​

Logging​

Context Swapping​

Extending middlewares​

Authorization

Logging

Context Swapping

Extending middlewares