Unexpected Content-Transfer-Encoding header for some multipart data

[pmstss]

Description

Multipart form-data default parameter value test is treated as base64 encoded

Steps to reproduce

Pass the my-schema.yaml (see below) to the oas2har as follows:

import { oas2har } from '@har-sdk/oas';
import { readFile } from 'fs';
import { promisify } from 'util';
import { load } from 'js-yaml';

const content = await promisify(readFile)(
  './my-schema.yaml',
  'utf8'
);

const result = oas2har(load(content) as OpenAPIV2.Document);

my-schema.yaml

swagger: '2.0'
info:
  title: Form-data parameter test
  version: 1.0.0
host: brightsec.com
basePath: /v1
schemes:
  - https
consumes:
  - multipart/form-data
produces:
  - application/json
paths:
  /example:
    post:
      consumes:
        - multipart/form-data
      parameters:
        - name: name
          in: formData
          type: string
          required: true
          default: test
      responses:
        201:
          description: Creation success

Actual result

Multipart form data in HAR entry postData contains Content-Transfer-Encoding: base64 header:

    "postData": {
      "mimeType": "multipart/form-data; boundary=956888039105887155673143",
      "text": "--956888039105887155673143\r\nContent-Disposition: form-data; name=\"name\"; filename=\"name\"\r\nContent-Type: application/octet-stream\r\nContent-Transfer-Encoding: base64\r\n\r\ntest\r\n--95688803910588715567314
3--"
    }

Expected result

    "postData": {
      "mimeType": "multipart/form-data; boundary=956888039105887155673143",
      "text": "--956888039105887155673143\r\nContent-Disposition: form-data; name=\"name\"\r\n\r\ntest\r\n--956888039105887155673143--"
    }

Additional info

Detection is performed by ^([A-Za-z0-9+/]{4})*([A-Za-z0-9+/]{3}=|[A-Za-z0-9+/]{2}==)?$ regular expression, that leads to false positives for some plain strings.

[derevnjuk]

@pmstss we can get rid of this header entirely due to https://www.rfc-editor.org/rfc/rfc7578#section-4.7