Non-deterministic recordings files

Description

I’m not sure how to minimally reproduce this, but using persister-fs, I’m getting non-deterministic orderings of requests. Context: I’m working on making our polly recordings idempotent; e.g. scrubbing timestamps and auth tokens. I have everything idempotent now, but some recordings (not all) keep changing the order of requests; e.g.

[
  <recording for /auth/login>,
  <recording for /users>,
  <recording for /users/4>,
]

will get reordered as

[
  <recording for /users/4>,
  <recording for /auth/login>,
  <recording for /users>,
]

It seems like Persister uses stringify from fast-json-stable-stringify, which should produce a deterministic JSON blob, but Persister-FS re-parses the JSON string as JSON, which makes the JSON blob non-deterministic again:

https://github.com/Netflix/pollyjs/blob/8f86fb372b6ac3e6efa36a9dee07d81d8e112847/packages/@pollyjs/persister-fs/src/index.js#L31

I also don’t see a unit test for deterministic recordings?

https://github.com/Netflix/pollyjs/blob/master/packages/@pollyjs/persister-fs/tests/unit/persister-test.js

Shareable Source

Haven’t found a minimal repro yet

Error Message & Stack Trace

See description

Config

Copy the config used to setup the Polly instance:

const { setupPolly } = require('setup-polly-jest')
setupPolly({
  adapters: ['node-http'],
  persister: 'fs',
  logging: false,
  recordFailedRequests: true,
  recordIfMissing: true,
  mode: recordMode,
  matchRequestsBy: {
    headers: {
      exclude: ['Authorization'],
    },
  },
})

Dependencies

Copy the @pollyjs dependencies from package.json:

{
    "@pollyjs/adapter-fetch": "^2.6.3",
    "@pollyjs/adapter-node-http": "^2.6.3",
    "@pollyjs/core": "^2.6.3",
    "@pollyjs/persister-fs": "^2.6.3",
    "@pollyjs/persister-rest": "^2.6.3",
}

Relevant Links

Environment

• Mac OS (darwin 18.7.0)
• Yarn: 1.17.3
• Node: v10.16.2

[offirgolan]

From the HAR 1.2 spec:

Sorting entries by startedDateTime (starting from the oldest) is preferred way how to export data since it can make importing faster.

See here

The sorting and deduping is done here: https://github.com/Netflix/pollyjs/blob/8f86fb372b6ac3e6efa36a9dee07d81d8e112847/packages/%40pollyjs/persister/src/har/log.js#L31-L45

Just as a note, Polly does depend on startedDateTime for features such as timing and expiration. Instead, maybe we can support a persister config option to disable sorting the entries.

[brandon-leapyear]

@pushred nope! our workaround has been working seamlessly for us (there are other idempotency problems, but this particular spot hasn’t given us any trouble)