amazon web services - Get detailed error messages from AWS API Gateway Request Validator

Question

Background

I have an API Gateway created using Swagger 2.0 definitions with API Gateway extensions.

I overrode the default API Gateway responses, for instance:

x-amazon-apigateway-gateway-responses:
  BAD_REQUEST_BODY:
    statusCode: 400
    responseTemplates:
      application/json: |
        {
          "error": {
            "code": 400,
            "stage": "$context.stage",
            "request": "$context.requestId",
            "message": "$context.error.message"
          }
        }

The $context in the above payload comes from API Gateway variables.

A sample resource/method in my API looks like this (always LAMBDA_PROXY integrations):

paths:
  /test:
    post:
      parameters:
        - in: body
          name: Test
          required: true
          schema:
          $ref: "#/definitions/Test"
      responses:
        201:
          description: Created
        400:
          description: Bad Request
        401:
          description: Unauthorized
        403:
          description: Forbidden
      x-amazon-apigateway-integration:
      uri: >-
        arn:aws:apigateway:${region}:lambda:path/2015-03-31/functions/${lambda}/invocations
      type: aws_proxy
      httpMethod: POST
      credentials: "${credentials}"
      passthroughBehavior: never

With the corresponding request payload definition:

definitions:
  Test:
    type: object
    title: Test
    required:
      - date
    properties:
      date:
        type: string
        pattern: "^20[0-9]{2}-(0[1-9]|1[012])-(0[1-9]|[12][0-9]|3[01])$"
        description: Date in YYYY-MM-DD Format

And the request validator extensions:

x-amazon-apigateway-request-validator: body
x-amazon-apigateway-request-validators:
  body:
    validateRequestBody: true
    validateRequestParameters: false

Problem

When I call this endpoint with a missing or invalid date, I always get the same response:

{
    "error": {
        "code": 400,
        "stage": "latest",
        "request": "6b7a64f5-e7f0-11e7-845b-f53ceb4cb049",
        "message": "Invalid request body"
    }
}

However, when I test it through the API Gateway console without the date property:

Request body does not match model schema for content type application/json: [
  object has missing required properties (["date"])
]

And with an invalid date:

Request body does not match model schema for content type application/json: [
  ECMA 262 regex "^20[0-9]{2}-(0[1-9]|1[012])-(0[1-9]|[12][0-9]|3[01])$" does not match input string "2017/12/25"
]

Question

How can I access the detailed error message so that I can enrich my error response with a more descriptive message than Invalid request body? I suspect that this must be possible, perhaps using x-amazon-apigateway-gateway-responses mapping, but so far I haven't been able to do it.

Answer 1

UPDATE:

This is now possible with gateway responses. Setup a BAD_REQUEST_BODY gateway response with the below template:

{"message": "$context.error.validationErrorString"}

---

(Developer on API Gateway)

Unfortunately, this is not supported right now. We are actively working on fixing this issue, but I can't give you any specific timelines by when this could be supported.