Middleware is a good way to pre-process the request before handing it out to GraphQL.
We could add authentication that could check the auth token in the header or middleware that will log the request IPs. Let’s do the second one.

Adding middleware could be done the same way as we are doing it in Express app. Add the highlighted lines, and let’s see what they do.

var express = require('express');
var graphqlHTTP = require('express-graphql');
var { buildSchema } = require('graphql');
var dogs = require('./src/models/mock_data/dogs.js');
// Construct a schema, using GraphQL schema language
var schema = buildSchema(`
  type Mutation {
    setNewDog(id: String, breed: String, displayImage: String): String
  }  
  type dog {
    id: String,
    breed: String,
    displayImage: String
  }
  type dogsCatalog {
    getDogByBreed(breed: String): dog
  }
  type Query {
    queryDogs: dogsCatalog
  }  
`);
class dogsCatalog {
  
  getDogByBreed({breed}) {
    var result = dogs.find(function(dog){
      return breed == dog.breed ? dog : null;
    });
    return result;
  }
}
// The root provides a resolver function for each API endpoint
var root = {
  queryDogs: () => {
    return new dogsCatalog();
  },
  setNewDog: ({id, breed, displayImage}) => {
    var result = dogs.find(function(dog){
      return breed == dog.breed ? dog : null;
    });
    if(result != null) {
      return 'dog already exists!';
    }
    dogs.push({
      "breed": breed,
      "displayImage": displayImage,
      "id": id      
    });
    return 'dog added successfully !';
  }
};

// Logger middleware
var logger = function(req, res, next) {
  console.log("GOT REQUEST >", req.ip);
  next(); // Passing the request to the next handler in the stack.
}

var app = express();
app.use(logger);
app.use('/graphql', graphqlHTTP({
  schema: schema,
  rootValue: root,
  graphiql: true,
}));
app.listen(4001);
console.log('Running a GraphQL API server at localhost:4000/graphql');

 what we just did:
– we created the middleware object to log every request ip (lines 52-56)
– in the middleware we added the next() function to proceed to the next middleware none we are done with the request processing.
– we told Express to use our new middleware app.use(logger);

And as simple as that we created our own logging class.