Summary

This PR adds support for error handling in AppSync GraphQL described in the issue

Changes

• exceptionHandler method is introduced to register an exception and its handler.
• ExceptionHandlerRegistry is introduced to keep track of registered exception handlers
• exceptionHandler is also exposed as a decorator method
• Unit tests are written for 100% coverage
• Added documentation for exception handling with examples
• Minor housekeeping(ex: dockerfile nodejs version update due to error & endregion added)

Lambda handler:

import { AppSyncGraphQLResolver } from '@aws-lambda-powertools/event-handler/appsync-graphql';
import { Logger } from '@aws-lambda-powertools/logger';
import { AssertionError } from 'assert';
import type { Context } from 'aws-lambda';

const logger = new Logger({
  serviceName: 'MyService',
});
const app = new AppSyncGraphQLResolver({ logger });

app.exceptionHandler(AssertionError, async (error) => {
  return {
    error: {
      message: error.message,
      type: error.name,
    },
  };
});

app.onQuery('createSomething', async () => {
  throw new AssertionError({
    message: 'This is an assertion Error',
  });
});

export const handler = async (event: unknown, context: Context) =>
  app.resolve(event, context);

APPSYNC JS resolver

export function request(ctx) {
  return {
    operation: 'Invoke',
    payload: ctx,
  };
}

export function response(ctx) {
  if (ctx.result.error) {
    return util.error(ctx.result.error.message, ctx.result.error.type);
  }
  return ctx.result;
}

Response mapping template

#if (!$util.isNull($ctx.result.error))
  $util.error($ctx.result.error.message, $ctx.result.error.type)
#end

$utils.toJson($ctx.result)

Response:

{
  "data": {
    "createSomething": null
  },
  "errors": [
    {
      "path": [
        "createSomething"
      ],
      "data": null,
      "errorType": "AssertionError",
      "errorInfo": null,
      "locations": [
        {
          "line": 2,
          "column": 3,
          "sourceName": null
        }
      ],
      "message": "This is an assertion Error"
    }
  ]
}

Issue number: closes #4130

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