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Proxay

CircleCI

Proxay (pronounced "prokseï") is a proxy server that helps you write faster tests.

Use Proxay as a layer between a client and its backend to record interactions and later replay them on demand.

You can use Proxay to proxy interactions between:

  • a web frontend and its backend
  • a mobile app and its backend
  • a server and another server (or a set of others, if using multiple Proxay instances)

Proxay can operate in several modes:

  • Record mode: Proxies requests to the backend and records interactions as "tapes" on disk.
  • Replay mode: Replays requests from your "tapes" on disk (no backend necessary).
  • Mimic mode: Records requests the first time it encounters them, then replays them (record then replay).
  • Passthrough mode: Proxies requests without persisting them (like a conventional proxy).

Proxay is language-agnostic: it's just a server. Your code doesn't need to be written in JavaScript to benefit from using it.

Installing

Make sure you have NPM installed, then run:

npm install --global proxay

# or if you're using Yarn
yarn global add proxay

Running

# Record mode (proxies requests)
proxay --mode record --host https://api.website.com --tapes-dir tapes/

# Replay mode (no proxying)
proxay --mode replay --tapes-dir tapes/

# Passthrough mode (proxies requests without persisting)
proxay --mode passthrough --host https://api.website.com

You can also run several instances of Proxay simultaneously on different ports (for example to proxy multiple backends). Just pick a different port (e.g. --port 3001).

If you want proxay to accept incoming requests on HTTPS in addition to HTTP, you can provide the HTTPS key and certificate files in PEM format on the --https-key and --https-cert arguments respectively. If the HTTPS certificate is self-signed, you probably also want to provide the CA certificate in PEM format on --https-ca. See the key, cert, and ca arguments to tls.createSecureContext for what these mean.

Specifying a tape

If you have several tests, you likely want to save recorded interactions into one tape per test, and replay from the correct tape for each test.

You can do this by sending a POST request to /__proxay/tape with the following payload:

{
  "tape": "test1/my tape"
}

In record mode, this will create a new file test1/my tape.yml within your tapes directory. In replay mode, this same file will be read from your tapes directory.

You can leverage this by picking a tape based on the current test's name in the beforeEach block of your test suite.

(Some) Options

--send-proxy-port: This flag enables the forwarding of the Proxay's local port number to the proxied host in the host header. It is particularly useful for handling redirect issues where the proxied host needs to be aware of the port on which Proxay is running to construct accurate redirect URLs. This is similar to nginx' proxy_set_header Host $host:$server_port;.

--ignore-headers <headers>: Allows users to specify a list of headers that should be ignored by Proxay's matching algorithm during request comparison. This is useful for bypassing headers that do not influence the behavior of the request but may cause mismatches, such as x-forwarded-for or x-real-ip. The headers should be provided as a comma-separated list.

Note: there is already a hardcoded list of headers that get ignored: accept, accept-encoding, age, cache-control, clear-site-data, connection, expires, from, host, postman-token, pragma, referer, referer-policy, te, trailer, transfer-encoding, user-agent, warning, x-datadog-trace-id, x-datadog-parent-id, traceparent

-r, --redact-headers <headers>: This option enables the redaction of specific HTTP header values, which are replaced by XXXX to maintain privacy or confidentiality during the recording of network interactions. The headers should be provided as a comma-separated list.

--debug-matcher-fails: When exact request matching is enabled, this flag provides some debug information on why a request did not match any recorded tape. It is useful for troubleshooting and refining the conditions under which requests are considered equivalent, focusing on differences in headers and query parameters.

Typical use case

Let's say you're writing tests for your client. You want your tests to run as fast as possible, but your backend is quite slow. Or worse, you have some tests already, but they're flaky because your backend or one of its dependencies isn't completely reliable.

Instead of pointing your client to your backend like you normally would, use Proxay as your backend. Tell Proxay to record requests going to the backend and run your tests once. This will create "tapes" which are records of each request/response between your client and your backend.

Then, run Proxay in replay mode and run your tests again. Your tests should still work, but you'll notice tests run a lot faster. That's because your backend is not used anymore. Instead, Proxay plays back responses from the tapes it had previously recorded.

This will make your tests faster and more stable. However, because you no longer use a real backend, you should still make sure to run your jobs in "record" mode on a regular basis (for example with a cron job on your CI) to test the implicit contract between your client and backend.

Comparison with alternatives

node-replay

node-replay is an inspiration for Proxay.

However, node-replay isn't a proxy per se: it simply replaces require('http').request in Node with its own method. This means that you can only use node-replay when running tests within Node.

Proxay is more versatile. It's "just a server". You can use it for anything you want, including as part of your test infrastructure for your web or mobile applications.

yakbak

Proxay is very similar to yakbak. There are a couple of differences:

  • Proxay is purely an HTTP server. You control it through HTTP as well (see Specifying a tape).
  • Proxay automatically replaces host headers so the backend doesn't reject mismatching requests.

vcr

VCR is a Ruby gem with a similar approach to node-replay. Just like node-replay, it cannot be used as a general-purpose proxy. It can only be used to test Ruby software.

MockServer

MockServer does a lot more things than Proxay.

If you need something more elaborate than Proxay, for example the ability to mock out specific URL patterns, you may need MockServer.

However, if all you need is a simple record/replay proxy layer, you'll probably find that Proxay is much easier to set up and run.

Releasing a new version of Proxay (for contributors)

To release a new version of Proxay, follow the following two steps:

Update the version in master

  1. Create a new branch.
  2. Update the version field in package.json.
  3. Send a PR with the changes (commit message Release [version]).
  4. Merge the PR into master.

Create a release on GitHub

  1. Visit the releases page to see what was last announced.
  2. Draft a new release:
    • Tag = v[version] (e.g. v2.1.1). Do not forget the v, which is required to trigger the NPM publish in GitHub Actions.
    • Title = Release v[version] (e.g. Release v2.1.1)
  3. Make sure to announce major changes since the last version in the description.
  4. Once published, check CircleCI to ensure publication was successful.