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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 protectedProcedure will ensure that the user is an "admin" before executing.

ts
import { TRPCError, initTRPC } from '@trpc/server';
interface Context {
user?: {
id: string;
isAdmin: boolean;
// [..]
};
}
export const t = initTRPC.context<Context>().create();
const isAdmin = t.middleware(async ({ ctx, next }) => {
if (!ctx.user?.isAdmin) {
throw new TRPCError({ code: 'UNAUTHORIZED' });
}
return next({
ctx: {
user: ctx.user,
},
});
});
const adminProcedure = t.procedure.use(isAdmin);
const adminRouter = t.router({
secretPlace: adminProcedure.query(() => 'a key'),
});
export const appRouter = t.router({
foo: t.procedure.query(() => 'bar'),
admin: adminRouter,
});
ts
import { TRPCError, initTRPC } from '@trpc/server';
interface Context {
user?: {
id: string;
isAdmin: boolean;
// [..]
};
}
export const t = initTRPC.context<Context>().create();
const isAdmin = t.middleware(async ({ ctx, next }) => {
if (!ctx.user?.isAdmin) {
throw new TRPCError({ code: 'UNAUTHORIZED' });
}
return next({
ctx: {
user: ctx.user,
},
});
});
const adminProcedure = t.procedure.use(isAdmin);
const adminRouter = t.router({
secretPlace: adminProcedure.query(() => 'a key'),
});
export const appRouter = t.router({
foo: t.procedure.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
import { initTRPC } from '@trpc/server';
export const t = initTRPC.context<Context>().create();
const logger = t.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;
});
const loggedProcedure = t.procedure.use(logger);
export const appRouter = t.router({
foo: loggedProcedure.query(() => 'bar'),
abc: loggedProcedure.query(() => 'def'),
});
ts
import { initTRPC } from '@trpc/server';
export const t = initTRPC.context<Context>().create();
const logger = t.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;
});
const loggedProcedure = t.procedure.use(logger);
export const appRouter = t.router({
foo: loggedProcedure.query(() => 'bar'),
abc: loggedProcedure.query(() => 'def'),
});

Context Swapping

A middleware can change 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);
 
export const appRouter = router({
userId: protectedProcedure.query(({ ctx }) => ctx.user.id),
(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);
 
export const appRouter = router({
userId: protectedProcedure.query(({ ctx }) => ctx.user.id),
(property) user: { id: string; }
});