Persisted queries

Unlike REST APIs that use a fixed URL to load data, GraphQL provides a rich query language that can be used to express the shape of application data requirements. This is a marvelous advancement in technology, but it comes at a cost: GraphQL query strings are often much longer than REST URLS—in some cases by many kilobytes.

In practice we've seen GraphQL query sizes ranging well above 10 KB just for the query text. This is significant overhead when compared with a simple URL of 50-100 characters. When paired with the fact that the uplink speed from the client is typically the most bandwidth-constrained part of the chain, large queries can become bottlenecks for client performance.

Malicious actors can exploit GraphQL APIs by sending large and complex requests that overwhelm servers and disrupt services. These attackers can abuse GraphQL's query flexibility to create deeply nested, resource-intensive queries that lead to excessive data fetching.

Solutions

Differences between persisted queries and APQ

Implementation steps

Because persisted queries requires you to preregister operations, it has additional implementation steps.

0. Requirements

Using persisted queries for safelisting has the following requirements:

• Apollo Client Web (v3.7.0+)
• The @apollo/generate-persisted-query-manifest package
• The @apollo/persisted-query-lists package
• GraphOS Router (v1.25.0+)
• GraphOS Enterprise plan

You can use APQ with the following versions of Apollo Client Web, Apollo Server, and Apollo Router Core:

• Apollo Client Web (v3.2.0+)
• Apollo Server (v1.0.0+)
• Apollo Router Core (v0.1.0+)

You can use either Apollo Server or Apollo Router Core for APQs. They don't need to be used together.

1. Generate operation manifests

This step is only required for persisted queries, not APQ.

An operation manifest acts as a safelist the GraphOS Router can check incoming requests against. You can generate the manifest using the @apollo/generate-persisted-query-manifest package:

1. Install the @apollo/generate-persisted-query-manifest package as a dev dependency:

npm install --save-dev @apollo/generate-persisted-query-manifest

2. Then use its CLI to extract queries from your app:

npx generate-persisted-query-manifest

The resulting operation manifest looks something like this:

{
  "format": "apollo-persisted-query-manifest",
  "version": 1,
  "operations": [
    {
      "id": "e0321f6b438bb42c022f633d38c19549dea9a2d55c908f64c5c6cb8403442fef",
      "body": "query GetItem { thing { __typename } }",
      "name": "GetItem",
      "type": "query"
    }
  ]
}

You can optionally create a configuration file in the root of your project to override the default options. Refer to the package's README for details.

To automatically update the manifest for each new app release, include the generate-persisted-query-manifest command in your CI/CD pipeline.

If you see a difference in the id generated in the manifest and the one your client is sending at runtime, read the options available in the @apollo/generate-persisted-query-manifest package to ensure the configuration matches your usage of Apollo Client.

This might also occur when you're not using the @apollo/persisted-query-lists package with PersistedQueryLink. The most common source of mismatches occurs because the @apollo/generate-persisted-query-manifest package sorts top-level definitions before generating the hash. If you're using a different terminating link, try using the sortTopLevelDefinitions function exported from @apollo/persisted-query-lists before generating the hash.

The following example uses sortTopLevelDefinitions before generating the query hash to ensure the hash matches the manifest file.

import { print } from "graphql";
import { sha256 } from "crypto-hash";
import { sortTopLevelDefinitions } from "@apollo/persisted-query-lists";

const link = new ApolloLink((operation, forward) => {
  const hash = sha256(print(sortTopLevelDefinitions(operation.query)));
  // ...
});

2. Publish manifests to a PQL

3. Enable persisted queries on ApolloClient

You use the persisted queries Apollo Link to send operations as IDs rather than full operation strings. The implementation details depend on whether you're using persisted queries or APQs.

Persisted queries implementation

The persisted queries link is included in the @apollo/client package:

npm install @apollo/client

A persisted queries implementation also requires the @apollo/persisted-query-lists package. This package contains helpers that work with the persisted queries link.

Install the @apollo/persisted-query-lists package:

npm install @apollo/persisted-query-lists

One of the package's utilities, generatePersistedQueryIdsFromManifest, reads operation IDs from your operation manifest so the client can use them to make requests. To do so, pass the loadManifest option a function that returns your manifest. We recommend using a dynamic import to avoid bundling the manifest configuration with your production build.

generatePersistedQueryIdsFromManifest({
  loadManifest: () => import("./path/to/persisted-query-manifest.json"),
});

Finally, combine the link that generatePersistedQueryIdsFromManifest returns with ApolloClient's HttpLink. The easiest way to use them together is to concat them into a single link.

import { HttpLink, InMemoryCache, ApolloClient } from "@apollo/client";
import { generatePersistedQueryIdsFromManifest } from "@apollo/persisted-query-lists";
import { PersistedQueryLink } from "@apollo/client/link/persisted-queries";

const persistedQueryLink = new PersistedQueryLink(
  generatePersistedQueryIdsFromManifest({
    loadManifest: () => import("./path/to/persisted-query-manifest.json"),
  })
);

const client = new ApolloClient({
  cache: new InMemoryCache(),
  link: persistedQueriesLink.concat(httpLink),
});

By including the persisted queries link in your client instantiation, your client sends operation IDs from your manifest instead of the full operation string.

The @apollo/persisted-query-lists package includes additional helpers you can use to verify that you've properly configured your operation manifest and generate operation IDs at runtime. Runtime generation is slower than fetching operation IDs from the manifest, but doesn't require making your manifest available to your client.

Refer to the package README for more information.

APQ implementation

The persisted queries Apollo Link used for APQs is included in the @apollo/client package:

npm install @apollo/client

This link requires but doesn't include a SHA-256 hash function. It does this to avoid forcing a particular hash function as a dependency. Developers should pick the most appropriate SHA-256 function (sync or async) for their needs and environment.

If you don't already have a SHA-256 based hashing function available in your application, install one separately. For example:

npm install crypto-hash

The link requires using ApolloClient's HttpLink. The easiest way to use them together is to concat them into a single link.

import { HttpLink, InMemoryCache, ApolloClient } from "@apollo/client";
import { PersistedQueryLink } from "@apollo/client/link/persisted-queries";
import { sha256 } from "crypto-hash";

const httpLink = new HttpLink({ uri: "/graphql" });
const persistedQueriesLink = new PersistedQueryLink({ sha256 });
const client = new ApolloClient({
  cache: new InMemoryCache(),
  link: persistedQueriesLink.concat(httpLink),
});

That's it! By including the persisted queries link in your client instantiation, your client sends operation IDs instead of the full operation string. This results in improved network performance, but doesn't include the security benefits of operation safelisting that persisted queries provide.

For more details on the options available to PersistedQueryLink, see its API reference documentation.

Apollo Studio

Apollo Studio supports receiving and fulfilling APQs. Simply adding this link into your client app will improve your network response times when using Apollo Studio.

Protocol

APQs are made up of three parts: the query signature, error responses, and the negotiation protocol.

Query Signature

The query signature for APQs is sent through the extensions field of a request from the client. This is a transport independent way to send extra information along with the operation.

{
  operationName: 'MyQuery',
  variables: null,
  extensions: {
    persistedQuery: {
      version: 1,
      sha256Hash: hashOfQuery
    }
  }
}

When sending an Automatic Persisted Query, the client omits the query field normally present, and instead sends an extension field with a persistedQuery object as shown above. The hash algorithm defaults to a sha256 hash of the query string.

If the client needs to register the hash, the query signature will be the same but include the full query text like so:

{
  operationName: 'MyQuery',
  variables: null,
  query: `query MyQuery { id }`,
  extensions: {
    persistedQuery: {
      version: 1,
      sha256Hash: hashOfQuery
    }
  }
}

This should only happen once across all clients when a new query is introduced into your application.

Error Responses

When the initial query signature is received by a backend, if it is unable to find the hash previously stored, it will send back the following response signature:

{
  errors: [{ message: "PersistedQueryNotFound" }];
}

If the backend doesn't support APQs, or does not want to support it for that particular client, it can send back the following which will tell the client to stop trying to send hashes:

{
  errors: [
    { message: 'PersistedQueryNotSupported' }
  ]
}

Negotiation Protocol

In order to support APQs, the client and server must follow the negotiation steps as outlined here:

Happy Path

1. Client sends query signature with no query field
2. Server looks up query based on hash, if found, it resolves the data
3. Client receives data and completes request

Missing hash path

1. Client sends query signature with no query field
2. Server looks up query based on hash, none is found
3. Server responds with NotFound error response
4. Client sends both hash and query string to Server
5. Server fulfills response and saves query string + hash for future lookup
6. Client receives data and completes request

Build time generation

If you want to avoid hashing in the browser, you can use a build script to include the hash as part of the request, then pass a function to retrieve that hash when the operation is run. This works well with projects like GraphQL Persisted Document Loader which uses webpack to generate hashes at build time.

If you use the above loader, you can pass { generateHash: ({ documentId }) => documentId } to the PersistedQueryLink class.