A highly evolved GraphQL HTTP Server 🧬

GraphQL Helix is a collection of utility functions for building your own GraphQL HTTP server. You can check out Building a GraphQL server with GraphQL Helix on DEV for a detailed tutorial on getting started.

Features

• Framework and runtime agnostic. Use whatever HTTP library you want. GraphQL Helix works in Node, Deno and in the browser.
• HTTP first. GraphQL Helix allows you to create a GraphQL over HTTP specification-compliant server, while exposing a single HTTP endpoint for everything from documentation to subscriptions.
• Server push and client pull. GraphQL Helix supports real-time requests with both subscriptions and @defer and @stream directives.
• Flexible. GraphQL Helix abstracts away logic that's common to all GraphQL HTTP servers, while leaving the implementation to you. Implement the features you want and take full control of your transport layer.
• Minimal. No bloat. No paid platform intergration. Zero dependencies outside of graphql-js.

Installation

npm install graphql-helix

Basic Usage

The following example shows how to integrate GraphQL Helix with Node.js using Express. This example shows how to implement all the basic features, including a GraphiQL interface, subscriptions and support for @stream and @defer. See the rest of the examples for implementations using other frameworks and runtimes. For implementing additional features, see the Recipes section below.

import express, { RequestHandler } from "express";
import {
  getGraphQLParameters,
  processRequest,
  renderGraphiQL,
  shouldRenderGraphiQL,
} from "../lib";
import { schema } from "./schema";

const app = express();

app.use(express.json());

app.use("/graphql", async (req, res) => {
  // Create a generic Request object that can be consumed by Graphql Helix's API
  const request = {
    body: req.body,
    headers: req.headers,
    method: req.method,
    query: req.query,
  };

  // Determine whether we should render GraphiQL instead of returning an API response
  if (shouldRenderGraphiQL(request)) {
    res.send(renderGraphiQL());
  } else {
    // Extract the GraphQL parameters from the request
    const { operationName, query, variables } = getGraphQLParameters(request);

    // Validate and execute the query
    const result = await processRequest({
      operationName,
      query,
      variables,
      request,
      schema,
    });

    // processRequest returns one of three types of results depending on how the server should respond
    // 1) RESPONSE: a regular JSON payload
    // 2) MULTIPART RESPONSE: a multipart response (when @stream or @defer directives are used)
    // 3) PUSH: a stream of events to push back down the client for a subscription
    if (result.type === "RESPONSE") {
      // We set the provided status and headers and just the send the payload back to the client
      result.headers.forEach(({ name, value }) => res.setHeader(name, value));
      res.status(result.status);
      res.json(result.payload);
    } else if (result.type === "MULTIPART_RESPONSE") {
      // Indicate we're sending a multipart response
      res.writeHead(200, {
        Connection: "keep-alive",
        "Content-Type": 'multipart/mixed; boundary="-"',
        "Transfer-Encoding": "chunked",
      });

      // If the request is closed by the client, we unsubscribe and stop executing the request
      req.on("close", () => {
        result.unsubscribe();
      });

      res.write("---");

      // Subscribe and send back each result as a separate chunk. We await the subscribe
      // call. Once we're done executing the request and there are no more results to send
      // to the client, the Promise returned by subscribe will resolve and we can end the response.
      await result.subscribe((result) => {
        const chunk = Buffer.from(JSON.stringify(result), "utf8");
        const data = [
          "",
          "Content-Type: application/json; charset=utf-8",
          "Content-Length: " + String(chunk.length),
          "",
          chunk,
        ];

        if (result.hasNext) {
          data.push("---");
        }

        res.write(data.join("\r\n"));
      });

      res.write("\r\n-----\r\n");
      res.end();
    } else {
      // Indicate we're sending an event stream to the client
      res.writeHead(200, {
        "Content-Type": "text/event-stream",
        Connection: "keep-alive",
        "Cache-Control": "no-cache",
      });

      // If the request is closed by the client, we unsubscribe and stop executing the request
      req.on("close", () => {
        result.unsubscribe();
      });

      // We subscribe to the event stream and push any new events to the client
      await result.subscribe((result) => {
        res.write(`data: ${JSON.stringify(result)}\n\n`);
      });
    }
  }
});

const port = process.env.PORT || 4000;

app.listen(port, () => {
  console.log(`GraphQL server is running on port ${port}.`);
});

API

getGraphQLParameters

function getGraphQLParameters(request: Request): GraphQLParams;

Extracts the query, variables and operationName values from the request.

processRequest

function processRequest<TContext, TRootValue>(
  options: ProcessRequestOptions<TContext, TRootValue>
): Promise<ProcessRequestResult<TContext, TRootValue>>;

Takes the schema, request, query, variables, operationName and a number of other optional parameters and returns one of three kinds of results, depending on the sort of response the server should send back.

renderGraphiQL

function renderGraphiQL(options: RenderGraphiQLOptions = {}): string;

Returns the HTML to render a GraphiQL instance.

shouldRenderGraphiQL

function shouldRenderGraphiQL(request: Request): boolean;

Uses the method and headers in the request to determine whether a GraphiQL instance should be returned instead of processing an API request.

Types

export interface GraphQLParams {
  operationName?: string;
  query?: string;
  variables?: string | { [name: string]: any };
}

export interface RenderGraphiQLOptions {
  /**
   * An optional GraphQL string to use when no query is provided and no stored
   * query exists from a previous session.  If undefined is provided, GraphiQL
   * will use its own default query.
   */
  defaultQuery?: string;
  /**
   * Whether to open the variable editor by default. Defaults to `true`.
   */
  defaultVariableEditorOpen?: boolean;
  /**
   * The endpoint requests should be sent. Defaults to `"/graphql"`.
   */
  endpoint?: string;
  /**
   * The initial headers to render inside the header editor. Defaults to `"{}"`.
   */
  headers?: string;
  /**
   * Whether the header editor is enabled. Defaults to `true`.
   */
  headerEditorEnabled?: boolean;
  /**
   * A cryptographic nonce for use with Content-Security-Policy.
   */
  nonce?: string;
  /**
   * The endpoint subscription requests should be sent to. Defaults to the value of the `endpoint` parameter.
   */
  subscriptionsEndpoint?: string;
}

export interface ProcessRequestOptions<TContext, TRootValue> {
  /**
   * A function whose return value is passed in as the `context` to `execute`.
   */
  contextFactory?: (
    executionContext: ExecutionContext
  ) => Promise<TContext> | TContext;
  /**
   * An optional function which will be used to execute instead of default `execute` from `graphql-js`.
   */
  execute?: typeof execute;
  /**
   * The name of the Operation in the Document to execute.
   */
  operationName?: string;
  /**
   * An optional function which will be used to create a document instead of the default `parse` from `graphql-js`.
   */
  parse?: typeof parse;
  /**
   * A Document containing GraphQL Operations and Fragments to execute.
   */
  query?: string | DocumentNode;
  /**
   * An object describing the HTTP request.
   */
  request: Request;
  /**
   * A function whose return value is passed in as the `rootValue` to `execute`.
   */
  rootValueFactory?: (
    executionContext: ExecutionContext
  ) => Promise<TRootValue> | TRootValue;
  /**
   * The GraphQL schema used to process the request.
   */
  schema: GraphQLSchema;
  /**
   * An optional function which will be used to subscribe instead of default `subscribe` from `graphql-js`.
   */
  subscribe?: typeof subscribe;
  /**
   * An optional function which will be used to validate instead of default `validate` from `graphql-js`.
   */
  validate?: typeof validate;
  /**
   * An optional array of validation rules that will be applied to the document
   * in place of those defined by the GraphQL specification.
   */
  validationRules?: ReadonlyArray<ValidationRule>;
  /**
   * Values for any Variables defined by the Operation.
   */
  variables?: string | { [name: string]: any };
}

export interface ExecutionContext {
  document: DocumentNode;
  operation: OperationDefinitionNode;
  variables?: { readonly [name: string]: unknown };
}

export interface Request {
  body?: any;
  headers: Headers;
  method: string;
  query: any;
}

export type Headers =
  | Record<string, string | string[] | undefined>
  | { get(name: string): string | null };

export interface Response<TContext, TRootValue> {
  type: "RESPONSE";
  status: number;
  headers: { name: string; value: string }[];
  payload: ExecutionResult;
  context?: TContext;
  rootValue?: TRootValue;
  document?: DocumentNode;
  operation?: OperationDefinitionNode;
}

export interface MultipartResponse<TContext, TRootValue> {
  type: "MULTIPART_RESPONSE";
  subscribe: (onResult: (result: ExecutionResult) => void) => Promise<void>;
  unsubscribe: () => void;
  context?: TContext;
  rootValue?: TRootValue;
  document?: DocumentNode;
  operation?: OperationDefinitionNode;
}

export interface Push<TContext, TRootValue> {
  type: "PUSH";
  subscribe: (onResult: (result: ExecutionResult) => void) => Promise<void>;
  unsubscribe: () => void;
  context?: TContext;
  rootValue?: TRootValue;
  document?: DocumentNode;
  operation?: OperationDefinitionNode;
}

export type ProcessRequestResult<TContext, TRootValue> =
  | Response<TContext, TRootValue>
  | MultipartResponse<TContext, TRootValue>
  | Push<TContext, TRootValue>;

Recipes

• Log the response using your favorite logger.
• Format your errors and mask them in production.
• Add an extensions field to the response with additional metadata to send to the client

See here for a basic example of error handling.

app.use("/graphql", async (req, res) => {
  ...

  const result = await processRequest({
    operationName,
    query,
    variables,
    request,
    schema,
    contextFactory: () => ({
      req,
    }),
  });
}

The contextFactory can be asyncronous and return a Promise. The function is called with a single parameter, an object with the following properties:

export interface ExecutionContext {
  document: DocumentNode;
  operation: OperationDefinitionNode;
  variables?: { readonly [name: string]: unknown };
}

GraphQL Helix provides this information to contextFactory in case you want to modify the context based on the operation that will be executed.

With contextFactory, we have a mechanism for doing authentication and authorization inside our application. We can determine who is accessing our API and capture that information inside the context. Our resolvers can then use the context to determine whether a particular field can be resolved and how to resolve it. Check out this example for basic contextFactory usage. If you're looking for a robust authorization solution, I highly recommend GraphQL Shield.

When the operation being executed is a subscription, processRequest will return a PUSH result, which you can then use to return a text/event-stream response. Here's what a basic implementation looks like:

if (result.type === "PUSH") {
  // Indicate that we're sending a stream of events and should keep the connection open.
  res.writeHead(200, {
    "Content-Type": "text/event-stream",
    Connection: "keep-alive",
    "Cache-Control": "no-cache",
  });

  // If the client closes the connection, we unsubscribe to prevent memory leaks.
  req.on("close", () => {
    result.unsubscribe();
  });

  // We subscribe to any new events and push them down to the client that initiated the subscription.
  await result.subscribe((result) => {
    res.write(`data: ${JSON.stringify(result)}\n\n`);
  });
}

On the client-side, we use the EventSource API to listen to these events. Our EventSource instance should reconnect in the event the connection is closed, but this behavior varies widely from browser to browser. Therefore, it's a good idea to implement a keep-alive mechanism in production to ensure your connection stays persistent. Check out this StackOverflow post for additional details. On the back end, you can just use setInterval to periodically send the keep alive message to the client (just make sure to clear the timer when you unsubscribe).

Implementing SSE on the client-side is equally simple, but you can use sse-z to make it even easier. If you're adding keep-alive to your implementation, sse-z provides a nice abstraction for that as well.

If SSE is not your cup of tea and you want to use WebSocket as the transport for your subscriptions instead, you can still do that. For example, we can use both GraphQL Helix and graphql-ws

import express from "express";
import {
  getGraphQLParameters,
  processRequest,
  renderGraphiQL,
  shouldRenderGraphiQL,
} from "graphql-helix";
import { execute, subscribe } from "graphql";
import { createServer } from "graphql-ws";
import { schema } from "./schema";

const app = express();

app.use(express.json());

app.use("/graphql", async (req, res) => {
  // handle the request using processRequest as shown before
});

const port = process.env.PORT || 4000;

const server = app.listen(port, () => {
  createServer(
    {
      schema,
      execute,
      subscribe,
    },
    {
      server,
      path: "/graphql",
    }
  );

  console.log(`GraphQL server is running on port ${port}.`);
});

A complete example can be found here. If you'd prefer you use socket.io, take a look at socket-io-graphql-server instead.

See here for an example.

if (result.type === "MULTIPART_RESPONSE") {
  // Indicate that this is a multipart response and the connection should be kept open.
  res.writeHead(200, {
    Connection: "keep-alive",
    "Content-Type": 'multipart/mixed; boundary="-"',
    "Transfer-Encoding": "chunked",
  });

  // If the client closes the connection, we unsubscribe to prevent memory leaks.
  req.on("close", () => {
    result.unsubscribe();
  });

  res.write("---");

  // Subscribe to new results. The callback will be called with the
  // ExecutionResult object that should be sent back to the client for each chunk.
  await result.subscribe((result) => {
    const chunk = Buffer.from(JSON.stringify(formatResult(result)), "utf8");
    const data = [
      "Content-Type: application/json; charset=utf-8",
      "Content-Length: " + String(chunk.length),
      "",
      chunk,
    ];

    if (result.hasNext) {
      data.push("---");
    }

    res.write(data.join("\r\n"));
  });

  // The Promise returned by `subscribe` will only resolve once all chunks have been emitted,
  // at which point we can end the request.
  res.write("\r\n-----\r\n");
  res.end();
}

See the here for a complete example.

The examples used in this repo are compatible with client-side libraries like meros and fetch-multipart-graphql.

With GraphQL Helix, it's as simple as adding the directive to your schema and utilizing the alternative execute function provided by @n1ru4l/in-memory-live-query-store.

import { InMemoryLiveQueryStore } from "@n1ru4l/in-memory-live-query-store";

const liveQueryStore = new InMemoryLiveQueryStore();

...

const result = await processRequest({
  operationName,
  query,
  variables,
  request,
  schema,
  contextFactory: () => ({
    liveQueryStore,
  }),
  execute: liveQueryStore.execute,
});

You can checkout the complete example here.

The query value that's passed to processQuery can be an already-parsed DocumentNode object instead of a string. This lets us fetch the query from memory based on some other value, like a queryId parameter. A rudimentary implementation could be as simple as this:

let queryId: string;
let operationName: string | undefined;
let variables: any;

if (req.method === "POST") {
  queryId = req.body.queryId;
  operationName = req.body.operationName;
  variables = req.body.variables;
} else {
  queryId = req.query.queryId as string;
  operationName = req.query.operationName as string;
  variables = req.query.variables;
}

const query = queryMap[queryId];

if (!query) {
  res.status(400);
  res.json({
    errors: [
      new GraphQLError(
        `Could not find a persisted query with an id of ${queryId}`
      ),
    ],
  });
  return;
}

const result = await processRequest({
  operationName,
  query,
  variables,
  request,
  schema,
});

See here for a more complete example. A more robust solution can be implemented using a library like relay-compiler-plus.

const result = await processRequest({
  // ...
  execute: (
    schema,
    documentAst,
    rootValue,
    contextValue,
    variableValues,
    operationName
  ) => {
    const compiledQuery = compileQuery(schema, documentAst, operationName);

    if (isCompiledQuery(compiledQuery)) {
      return compiledQuery.query(rootValue, contextValue, variableValues || {});
    }

    return compiledQuery;
  },
});

⚠️ GraphQL JIT is an experimental library that is still lacking some features required by the GraphQL specification. You probably should not use it in production unless you know what you're getting yourself into.

The ability to provide custom implementations of parse and validate means we can also optimize the performance of those individual steps by introducing caching. This allows us to bypass these steps for queries we've processed before.

For example, we can create a simple in-memory cache

import lru from "tiny-lru";

const cache = lru(1000, 3600000);

and then use it to cache our parsed queries so we can skip that step for subsequent requests:

import { parse } from "graphql";

const result = await processRequest({
  operationName,
  query,
  variables,
  request,
  schema,
  parse: (source, options) => {
    if (!cache.get(query)) {
      cache.set(query, parse(source, options));
    }

    return cache.get(query);
  },
});

We can take a similar approach with validate and even cache the result of compileQuery if we're using GraphQL JIT. See this example for a more complete implementation.