Polly.JS doesn't encode multipart/form-data requests properly

Description

This is a bug report.

Polly.JS appears to not send all of a multipart/form-data request to servers when it captures the initial server response. Most servers return an error when they cannot parse multipart form boundaries in a request.

Update: Polly.JS doesn’t pass multipart/form-data bodies with the right encoding. See comments below.

Shareable Source

I created a minimal reproduction here that uses request to upload a file to a simple express server: https://github.com/swashcap/pollyjs-multipart-form-data-error

Error Message & Stack Trace

Most servers return an error when they cannot parse multipart form boundaries in a request. Polly.JS emits an error similar to:

PollyError: [Polly] [persister:fs] Cannot persist response for [GET] http://localhost:3001/ because the status code was 400 and `recordFailedRequests` is `false`

Config

I’m using setup-polly-jest to run tests in Node.js. Here’s the config:

const AdapterNodeHTTP = require('@pollyjs/adapter-node-http')
const PersisterFS = require('@pollyjs/persister-fs')
const path = require('path')
const { Polly } = require('@pollyjs/core')
const { setupPolly } = require('setup-polly-jest')

Polly.register(AdapterNodeHTTP)
Polly.register(PersisterFS)

// ...

describe('this great test', () => {
  const context = setupPolly({
    adapters: ['node-http'],
    persister: 'fs'
  })

  // ...
})

(see the test here: https://github.com/swashcap/pollyjs-multipart-form-data-error/blob/master/src/upload.spec.js)

Dependencies

$ yarn list --pattern=polly --silent
├─ @pollyjs/adapter-node-http@2.6.2
├─ @pollyjs/adapter@2.6.0
├─ @pollyjs/core@2.6.2
├─ @pollyjs/node-server@2.6.0
├─ @pollyjs/persister-fs@2.6.2
├─ @pollyjs/persister@2.6.2
├─ @pollyjs/utils@2.6.0
└─ setup-polly-jest@0.5.2

Environment

$ node -e "var os=require('os');console.log('Node.js ' + process.version + '\n' + os.platform() + ' ' + os.release())"
Node.js v10.16.3
darwin 18.7.0
$ npm --version
6.9.0
$ yarn --version
1.17.3

[jasonmit]

This should actually be a pretty small fix; shall I open a PR?

Yes please 😃

[swashcap]

First off, thanks for diving into this.

No problem! We’re enjoying Polly.JS quite a bit 🙂

What do y’all think of a patch in Polly.JS that checks whether body is all hex right here?

Is the goal to avoid calling JSON.stringify on body if it’s all hex values?

The goal would be to correct the body’s encoding when it’s sent to the upstream server in HttpAdapter#passthroughRequest. Right now it’s hex, it should be decoded to utf8.

This should actually be a pretty small fix; shall I open a PR?