Example for AppSync subscription resolver to work

Question

Hi
I was not able to make a working subscription resolver for my subscription field.

The sample schema is as follows:
```
type Message {
  user: String!
  body: String!
}

type Mutation {
  pushMessage(user: String!, body: String!): Message
}

type Query {
  	getMessages(user: String!): [Message]
}

type Subscription {
  onMessage(user: String!): Message @aws_subscribe(mutations: ["pushMessage"])
}

```

By referencing https://docs.aws.amazon.com/appsync/latest/devguide/security-authorization-use-cases.html#security-real-time-data, I was able to write
```
import { util } from '@aws-appsync/utils';

export function request(ctx) {
  const {identity, args} = ctx
  if (!!(identity?.resolverContext?.user)) {
    if (identity.resolverContext.user != args.user) {
      util.unauthorized()
    }
  }
  return {}
}

export function response(ctx) {
  return {}
}
```
as my resolver.

P.S I used the lambda authorization method to carry custom resolverContext to the ctx.

However, this did not work.

Can anyone give a robust example of how a subscription resolver can work? The official documentation has some flaws btw.

example errors from real-time websocket message
```
  "type": "error",
  "payload": {
    "errors": [
      {
        "errorType": "Code",
        "message": "Value for field '$[operation]' not found."
      }
    ]
  }
```

or 
```
.... null, request resource not match , something like that
```

Ben Chang · Accepted Answer

I found the solution,

As I am using data directly from the lambda resolver's context and the context arguments only, there is no need for other Dynamodb data source to be bound.
So I switch to NoneDataSource and have the following, then it works.

```
import { util } from '@aws-appsync/utils';

export function request(ctx) {
  return {
payload: ctx.args
}
}

export function response(ctx) {
    const {identity, args} = ctx
  if (!!(identity?.resolverContext?.user)) {
    if (identity.resolverContext.user != args.user) {
     return util.unauthorized()
    }
  }
}
```

As you can see, the request needs to comply with the data source format, the payload field must be specified for the NoneDataSource (good for just passing data), while the version and operation fields, etc need to be specified for the Dynamodb data source. That was why my resolver for the subscription did not work.

Example for AppSync subscription resolver to work

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