feat(server): enhance error handling for malformed requests

packages/server/src/adapters/standard/handler.test.ts

@@ -213,6 +213,73 @@ describe('standardHandler', () => {
     })
   })
 
+  it('on decode error', async () => {
+    matcher.match.mockResolvedValue({
+      path: ['ping'],
+      procedure: ping,
+      params: { id: '__id__' },
+    })
+
+    const error = new Error('Something bad')
+    codec.decode.mockRejectedValueOnce(error)
+    const client = vi.fn()
+    vi.mocked(createProcedureClient).mockReturnValueOnce(client)
+
+    codec.decode.mockReturnValueOnce('__input__')
+
+    codec.encodeError.mockReturnValueOnce(response)
+
+    const result = await handler.handle(request, {
+      context: { db: 'postgres' },
+      prefix: '/api/v1',
+    })
+
+    expect(result).toEqual({ matched: true, response })
+
+    expect(matcher.match).toHaveBeenCalledOnce()
+    expect(matcher.match).toHaveBeenCalledWith('GET', '/users/1')
+
+    expect(createProcedureClient).toHaveBeenCalledOnce()
+    expect(createProcedureClient).toHaveBeenCalledWith(ping, {
+      context: { db: 'postgres' },
+      path: ['ping'],
+    })
+
+    expect(codec.decode).toHaveBeenCalledOnce()
+    expect(codec.decode).toHaveBeenCalledWith(request, { id: '__id__' }, ping)
+
+    expect(client).not.toHaveBeenCalledOnce()
+    expect(codec.encode).not.toBeCalled()
+
+    expect(codec.encodeError).toHaveBeenCalledOnce()
+    expect(codec.encodeError.mock.calls[0]![0]).toSatisfy((e: any) => {
+      expect(e).toBeInstanceOf(ORPCError)
+      expect(e.code).toEqual('BAD_REQUEST')
+      expect(e.message).toEqual(
+        `Malformed request. Ensure the request body is properly formatted and the 'Content-Type' header is set correctly.`,
+      )
+      expect(e.cause).toEqual(error)
+
+      return true
+    })
+
+    expect(interceptor).toHaveBeenCalledOnce()
+    expect(interceptor).toHaveBeenCalledWith({
+      request,
+      next: expect.any(Function),
+      context: { db: 'postgres' },
+      prefix: '/api/v1',
+    })
+
+    expect(interceptorRoot).toHaveBeenCalledOnce()
+    expect(interceptorRoot).toHaveBeenCalledWith({
+      request,
+      next: expect.any(Function),
+      context: { db: 'postgres' },
+      prefix: '/api/v1',
+    })
+  })
+
   it('work without context and prefix', async () => {
     matcher.match.mockResolvedValue({
       path: ['ping'],

packages/server/src/adapters/standard/handler.ts

@@ -6,7 +6,7 @@ import type { Plugin } from '../../plugins'
 import type { CreateProcedureClientOptions } from '../../procedure-client'
 import type { Router } from '../../router'
 import type { StandardCodec, StandardMatcher } from './types'
-import { toORPCError } from '@orpc/contract'
+import { ORPCError, toORPCError } from '@orpc/contract'
 import { intercept, trim } from '@orpc/shared'
 import { CompositePlugin } from '../../plugins'
 import { createProcedureClient } from '../../procedure-client'
@@ -64,6 +64,8 @@ export class StandardHandler<T extends Context> {
         context: options?.context ?? {} as T, // context is optional only when all fields are optional so we can safely force it to have a context
       },
       async (interceptorOptions) => {
+        let isDecoding = false
+
         try {
           return await intercept(
             this.options.interceptors ?? [],
@@ -88,7 +90,9 @@ export class StandardHandler<T extends Context> {
 
               const client = createProcedureClient(match.procedure, clientOptions)
 
+              isDecoding = true
               const input = await this.codec.decode(request, match.params, match.procedure)
+              isDecoding = false
 
               const output = await client(input, { signal: request.signal })
 
@@ -102,7 +106,12 @@ export class StandardHandler<T extends Context> {
           )
         }
         catch (e) {
-          const error = toORPCError(e)
+          const error = isDecoding
+            ? new ORPCError('BAD_REQUEST', {
+              message: `Malformed request. Ensure the request body is properly formatted and the 'Content-Type' header is set correctly.`,
+              cause: e,
+            })
+            : toORPCError(e)
 
           const response = this.codec.encodeError(error)