attachDirectives.ts

import {
  defaultFieldResolver,
  DirectiveNode,
  GraphQLField,
  GraphQLFieldResolver,
  GraphQLResolveInfo,
  GraphQLSchema,
} from 'graphql';
import { forEachField } from 'graphql-tools';
import { getArgumentValues } from 'graphql/execution/values';

export type NextResolverFn = () => Promise<any>;
export type DirectiveResolverFn<TSource, TContext> = (
 next: NextResolverFn,
 source: TSource,
 args: { [argName: string]: any },
 context: TContext,
 info: GraphQLResolveInfo,
) => any;

export interface IDirectiveResolvers<TSource, TContext> {
 [directiveName: string]: DirectiveResolverFn<TSource, TContext>;
}

 /**
 * Attach directive resolvers to Schema
 * https://github.com/apollographql/graphql-tools/issues/212#issuecomment-324447078
 *
 * @author Agon Bina <agon_bina@hotmail.com>
 * @author Giau. Tran Minh <giau.tmg@gmail.com>
 * @param resolvers: resolvers of directive
 * @param schema: GraphQL schema to attach directive resolvers
 */
export function attachDirectiveResolvers(
  schema: GraphQLSchema,
  directiveResolvers: IDirectiveResolvers<any, any>,
) {
  if (typeof directiveResolvers !== 'object') {
    throw new Error(
      `Expected directiveResolvers to be of type object, got ${typeof directiveResolvers}`,
    );
  }
  if (Array.isArray(directiveResolvers)) {
    throw new Error('Expected directiveResolvers to be of type object, got Array');
  }
  forEachField(schema, (field: GraphQLField<any, any>) => {
    const directives = field.astNode.directives;
    directives.forEach((directive: DirectiveNode) => {
      const directiveName = directive.name.value;
      const resolver = directiveResolvers[directiveName];

      if (resolver) {
        const originalResolver = field.resolve || defaultFieldResolver;
        const Directive = schema.getDirective(directiveName);
        if (typeof Directive === 'undefined') {
          throw new Error(`Directive @${directiveName} is undefined. ` +
            'Please define in schema before using');
        }
        const directiveArgs = getArgumentValues(Directive, directive);

        field.resolve = (...args: any[]) => {
          const [source, , context, info] = args;
          return resolver(() => {
            try {
              const promise = originalResolver.call(field, ...args);
              if (promise instanceof Promise) {
                return promise;
              }
              return Promise.resolve(promise);
            } catch (error) {
              return Promise.reject(error);
            }
          }, source, directiveArgs, context, info);
        };
      }
    });
  });
}

example.ts

import jwt from 'jsonwebtoken';
import { AuthorizationError } from './../errors';
import { NextResolver } from './attachDirectives';

export { attachDirectives } from './attachDirectives';

export const directiveResolvers = {
  upperCase(next: NextResolver, source, args, context) {
    return next().then((r) => {
      if (typeof(r) === 'string') {
        return r.toUpperCase();
      }
      return r;
    });
  },
  auth(next: NextResolver, source, args, { auth, scopes }) {
    if (auth) {
      const expected = args.scope;
      if (expected.length() === 0 || expected.some((e) => scopes.includes(e))) {
        return next();
      }

      throw new AuthorizationError({
        message: `You are not authorized. Expected scopes: ${expected.join(', ')}`,
      });
    }

    throw new AuthorizationError({
      message: 'You must supply a JWT for authorization!',
    });
  },
};

schema.graphql

directive @auth(scope: [String]) on QUERY | FIELD
directive @upperCase on QUERY | FIELD

# this is needed for upload to work
scalar Upload

type Query {
  uploads: [File]
  hello: String @upperCase
}

type Mutation {
  singleUpload(file: Upload!): File! @auth
  multipleUpload (files: [Upload!]!): [File!]!
}

type File {
  id: ID!
  path: String!
  filename: String!
  mimetype: String!
  encoding: String!
}