Building Context

In GraphQL, context is a value that is provided to every resolver and holds important contextual information that we can access in resolvers. (See Root fields & resolvers)

Benzene allows us to write a factory function that creates the context object in question. This context factory function will be used by downstream packages @benzene/http and @benzene/ws.

Writing the context factory function

The context factory function can be defined in contextFn when instantiating the Benzene instance.

const GQL = new Benzene({
  contextFn: ({ extra }) => {
    return { role: "admin" };
  },
});

It will receive an object with extra, which is the second argument passed into the handler function of downstream packages. For example:

import { Benzene, makeHandler } from "@benzene/ws";
 
const GQL = new Benzene({
  contextFn: ({ extra }) => {
    // extra is { user: "Niko", ip: "127.0.0.1" }
    return { user: extra.user };
  },
});
 
const graphqlWS = makeHandler(GQL);
 
function onConnection(socket, req) {
  const extra = {
    user: "Niko",
    ip: req.socket.remoteAddress,
  };
  graphqlWS(socket, extra);
}

Access the context in resolvers

This context will be created using the factory function on every request. We can access it in resolvers like so:

const resolvers = {
  Query: {
    catSecretPlan(obj, args, context, info) {
      if (context.user !== "Niko")
        throw new HttpError(401, "Only Niko can access this data");
      return thePlan;
    },
  },
};