context.done called twice within handler 'graphql' - node.js

Question

Attempting to create a project based off https://github.com/serverless/serverless-graphql/blob/master/app-backend/dynamodb/handler.js. The code works well, but for some reason, I always get a log warning telling me context.done called twice.
import { graphqlLambda, graphiqlLambda, LambdaHandler } from 'apollo-server-lambda'
import lambdaPlayground from 'graphql-playground-middleware-lambda'
import { makeExecutableSchema } from 'graphql-tools'
import { resolvers } from './resolvers'
const typeDefs = require('./schema.gql')
const schema = makeExecutableSchema({ typeDefs, resolvers, logger: console })
export const graphqlHandler: LambdaHandler = async (event, context) => {
const handler = graphqlLambda({ schema })
return handler(event, context, (error: Error | undefined, output: any) => {
output.headers['Access-Control-Allow-Origin'] = '*'
context.done(error, output)
})
}
export const playgroundHandler = lambdaPlayground({
endpoint: '/graphql',
})
export const graphiqlHandler: any = graphiqlLambda({
endpointURL: '/graphql',
})
This code gives me the following result:
Serverless: POST /graphql (λ: graphql)
Serverless: [200] {"statusCode":200,"headers":{"Content-Type":"application/json","Access-Control-Allow-Origin":"*"},"body":"{\"data\":{\"getUserInfo\":\"ads\"}}"}
Serverless: Warning: context.done called twice within handler 'graphql'!
What is even more strange is that if I comment the context.done call, I get the following output (the call stalls as expected):
Serverless: POST /graphql (λ: graphql)
Serverless: Warning: context.done called twice within handler 'graphql'!

Answer 1

I ran into a similar issue. Try remove async in your function if you are not going to use await. It looks like the function waits until you invoke callback or context.done when async is not there. But it runs through all the way with the async keyword. When it runs through though, whatever it returns at the end of your function is calling the context.done. Here is a sample working code.
Let me also share two useful resources about callback and context from aws lambda.
export const handler = (
{
headers,
pathParameters: pathParams,
queryStringParameters: queryParams,
body,
},
context,
callback
) => {
context.callbackWaitsForEmptyEventLoop = false;
const data = JSON.parse(body);
const params = {
TableName: process.env.EVENT_TABLE,
Item: {
id: uuid.v4(),
title: data.title,
creationDate: new Date().getTime(),
},
};
dynamoDb.put(params, (err, data) => {
if (err) {
callback(err);
}
callback(null, {
statusCode: 200,
body: JSON.stringify(data),
});
});
};

Answer 2

This appears to be already reported: https://github.com/dherault/serverless-offline/issues/405