mirror of
https://github.com/vale981/apollo-server
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127 lines
3.9 KiB
Markdown
127 lines
3.9 KiB
Markdown
---
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title: Error handling
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description: Making errors actionable on the client and server
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---
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## Overview
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Apollo server provides a couple predefined errors, including `AuthenticationError`, `ForbiddenError`, and a generic `ApolloError`. These errors enhance before and during GraphQL execution. These errors focus on improving the ability to debug a server as well as enabling the client to take specific action based on an error.
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When an error occurs in Apollo server both inside and outside of resolvers, each error inside of the `errors` array will contain an object at `extensions` that contains additional information.
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## Default information
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The first step to improving the usability of a server is providing the error stack trace by default. The following example demonstrates the response returned from Apollo server with a resolver that throws a node [`SystemError`](https://nodejs.org/api/errors.html#errors_system_errors).
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```js line=4,15-17
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const {
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ApolloServer,
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gql,
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AuthenticationError,
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} = require('apollo-server');
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const typeDefs = gql`
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type Query {
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readError: String
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}
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`;
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const resolvers = {
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Query: {
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readError: (parent, args, context) => {
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fs.readFileSync('/does/not/exist');
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},
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},
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};
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```
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The response will return:
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> To disable stacktraces for production, pass `debug: false` to the Apollo server constructor or set the `NODE_ENV` environment variable to 'production' or 'test'
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## Codes
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In addition to stacktraces, Apollo Server's exported errors specify a human-readable string in the `code` field of `extensions` that enables the client to perform corrective actions. In addition to improving the client experience, the `code` field allows the server to categorize errors. For example, an `AuthenticationError` sets the code to `UNAUTHENTICATED`, which enables the client to reauthenticate and would generally be ignored as a server anomaly.
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```js line=4,15-17
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const {
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ApolloServer,
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gql,
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AuthenticationError,
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} = require('apollo-server');
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const typeDefs = gql`
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type Query {
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authenticationError: String
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}
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`;
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const resolvers = {
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Query: {
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authenticationError: (parent, args, context) => {
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throw AuthenticationError('must authenticate');
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},
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},
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};
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```
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The response will return:
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## Augmenting error details
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`ApolloError` can be augmented with additional information when the default information requires more context. This information could include a localized message that should be displayed to the user on an error or in the case of bad input a description of the fields that are invalid. The following example demonstrates adding extra information to a user input check.
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```js line=15-21
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const {
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ApolloServer,
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gql,
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AuthenticationError,
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} = require('apollo-server');
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const typeDefs = gql`
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type Mutation {
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userInputError(input: String): String
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}
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`;
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const resolvers = {
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Mutation: {
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userInputError: (parent, args, context, info) => {
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if(args.input !== 'expected') {
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throw ApolloError('Form Arguments invalid', 'BAD_USER_INPUT', {
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invalidArgs: Object.keys(args),
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});
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}
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},
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},
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};
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```
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The response will return:
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## Masking and logging errors
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The Apollo server constructor accepts a `formatError` function that is run on each error passed back to the client. This can be used to mask errors as well as logging.
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This example demonstrates masking
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```js line=4-7
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const server = new ApolloServer({
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typeDefs,
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resolvers,
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formatError: error => {
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console.log(error);
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return new Error('Internal server error');
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},
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});
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server.listen().then(({ url }) => {
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console.log(`🚀 Server ready at ${url}`);
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});
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```
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