Fix regression in handling badly formed JSON

lib/routes.js

@@ -135,14 +135,27 @@ module.exports = async function (app, opts) {
   const errorFormatter = typeof opts.errorFormatter === 'function' ? opts.errorFormatter : defaultErrorFormatter
 
   if (typeof opts.errorHandler === 'function') {
-    app.setErrorHandler(opts.errorHandler)
+    app.setErrorHandler((error, request, reply) => {
+      const errorHandler = opts.errorHandler
+      if (!request[kRequestContext]) {
+        // Generate the context for this request
+        request[kRequestContext] = { reply, app }
+      }
+
+      return errorHandler(error, request, reply)
+    })
   } else if (opts.errorHandler === true || opts.errorHandler === undefined) {
     app.setErrorHandler((error, request, reply) => {
+      if (!request[kRequestContext]) {
+        // Generate the context for this request
+        request[kRequestContext] = { reply, app }
+      }
+
       const { statusCode, response } = errorFormatter(
         error,
         request[kRequestContext]
       )
-      reply.code(statusCode).send(response)
+      return reply.code(statusCode).send(response)
     })
   }
   const contextFn = opts.context

test/errors.js

@@ -767,3 +767,90 @@ test('errors - should override statusCode to 200 if the data is present', async
 
   t.equal(res.statusCode, 200)
 })
+
+test('bad json', async (t) => {
+  const schema = `
+    type Query {
+      successful: String
+    }
+  `
+
+  const resolvers = {
+    Query: {
+      successful () {
+        t.fail('Should not be called')
+        return 'Runs OK'
+      }
+    }
+  }
+
+  const app = Fastify()
+
+  app.register(GQL, {
+    schema,
+    resolvers
+  })
+
+  await app.ready()
+
+  const res = await app.inject({
+    method: 'POST',
+    headers: {
+      'content-type': 'application/json'
+    },
+    body: 'this is not a json',
+    url: '/graphql'
+  })
+
+  t.equal(res.statusCode, 400)
+  t.same(res.json(),
+    { data: null, errors: [{ message: 'Unexpected token h in JSON at position 1' }] }
+  )
+})
+
+test('bad json with custom error handler', async (t) => {
+  t.plan(3)
+  const schema = `
+    type Query {
+      successful: String
+    }
+  `
+
+  const resolvers = {
+    Query: {
+      successful () {
+        t.fail('Should not be called')
+        return 'Runs OK'
+      }
+    }
+  }
+
+  const app = Fastify()
+
+  app.register(GQL, {
+    schema,
+    resolvers,
+    errorHandler: (_, request, reply) => {
+      t.pass('custom error handler called')
+      reply.code(400).send({
+        is: 'error'
+      })
+    }
+  })
+
+  await app.ready()
+
+  const res = await app.inject({
+    method: 'POST',
+    headers: {
+      'content-type': 'application/json'
+    },
+    body: 'this is not a json',
+    url: '/graphql'
+  })
+
+  t.equal(res.statusCode, 400)
+  t.same(res.json(), {
+    is: 'error'
+  })
+})