Stubbing "multipart-form-data" request with part array

[aeoncl]

Description

Hi 😁, here's the issue:

In a multipart-form-data, you can have an array of parts by specifing the same partname multiple times.

Here is how it looks in the OpenApi definition (pdfFiles):

requestBody:
  content:
    multipart/form-data:
      schema:
        type: object
        properties:
          sendMessageRequest:
            $ref: "#/components/schemas/SendMessageRequest"
          pdfFiles:
            type: array
            items:
              type: string
              format: binary
        required:
          - sendMessageRequest
          - pdfFiles

We expect this to be an array of pdfFiles:

If i send this request to the Specmatic Stub, i get the following error:

This happens because Specmatic thinks a multipart part of type array should contain an array, and not be one:
Internally this is interpreted as a ListPattern which matches only if the value is an array.

Snippet from ListPattern.kt

If i change my part value to an array, it works, but that's not the behaviour i expected:

Steps to reproduce

1. Create a stub using the following OpenApi Definition:

openapi: 3.0.3
info:
  title: Multipart With Array Example
  description: Service to add context to a github issue
  version: 1.0.0

servers:
  - url: "http://{hostname}:{port}/{basePath}/"
    variables:
      hostname:
        default: localhost
      port:
        default: "8080"
      basePath:
        default: rest
tags:
  - name: UploadFile
paths:
  "/message":
    post:
      tags:
        - UploadFile
      operationId: sendMessage
      requestBody:
        content:
          multipart/form-data:
            schema:
              type: object
              properties:
                sendMessageRequest:
                  $ref: "#/components/schemas/SendMessageRequest"
                pdfFiles:
                  type: array
                  items:
                    type: string
                    format: binary
              required:
                - sendMessageRequest
                - pdfFiles
            encoding:
              sendMessageRequest:
                contentType: application/json
      responses:
        "200":
          description: "Send Message Response"
          content:
            multipart/form-data:
              schema:
                type: object
                properties:
                  filename:
                    type: string
                    description: filename for associated file content
components:
  schemas:
    SendMessageRequest:
      type: object
      title: SendMessageRequest
      properties:
        foobar:
          type: string
          maxLength: 255
          minLength: 1
      required:
        - foobar

2. Make an HTTP POST request to the /message endpoint containing the following parts:

Expected behavior
I expect to receive a 200 OK generated response

System Information:

• OS & version: Windows 11
• Browser & version: Postman 10.16.0
• Specmatic version: 0.73.0
• JDK version: OpenJDK 17

Additional context
To fix it, we'll need to change the way Specmatic interprets "type: array" on multipart parts. Changing the meaning from "contains a json array" to "expect to have the same part multiple times"

[jaydeepk]

Thanks for reporting this @aeoncl.
We'll have a look at this and get back to you.

[aeoncl]

Hi guys, i've started working on this. i'll submit a PR in the coming days for you to review

[jaydeepk]

Hi @aeoncl, really appreciate the initiative.
Please do let us know if you have any queries regarding the code.

[harikrishnan83]

@aeoncl Thank you for your patience. The reason we were taking time on this PR is to make sure we also understood the http RFC around this. And it does look like the expected behaviour in your bug description is valid as per this section in RFC 7578. We are now reviewing your PR in this regard. cc @jaydeepk