httpr, a Record/Replay Proxy

httpr is an HTTP proxy that records and replays traffic. It is designed specifically for Google APIs that use HTTP exclusively. These include the Google Cloud Storage and BigQuery clients, as well as the clients in the github.com/google/google-api-*-client repos.

If you are writing Go code, you should use the cloud.google.com/go/httpreplay package, which is a simpler way to use the proxy.

Using a Record/Replay Proxy

A record/replay proxy lets you run an "integration" test that accesses a backend like a Google service and record the interaction. Subsequent runs of the test can replay the server's responses without actually contacting the server, turning the integration test into a fast and inexpensive unit test.

Usage

First, obtain the httpr binary. If you have the Go toolchain, you can run go get -u cloud.google.com/go/httpreplay/cmd/httpr. Otherwise, precompiled binaries for various architectures and operating systems are available from the releases page.

Recording

Start httpr in record mode by passing it the -record flag with a filename:
```
httpr -record myclient.replay
```
By default, httpr will run on port 8080, and open a control port on 8181. You can change these with the -port and -control-port flags. You will want to run httpr in the background or in another window.
In order for httpr to record HTTPS traffic, your client must trust it. It does so by installing a CA certificate created by httpr during the recording session. To obtain the certificate in PEM form, GET the URL http://localhost:8181/authority.cer. (If you changed the control port, use it in place of 8181.) Consult your language to determine how to install the certificate. Note that the certificate is different for each run of httpr.
Arrange for your test program to use httpr as a proxy. This may be as simple as setting the HTTPS_PROXY environment variable.
Run your test program, using whatever authentication for your Google API clients that you wish.
Send httpr a SIGINT signal (kill -2). httpr will write the replay file, then exit.

Replaying

Start httpr in replay mode, in the background or another window:
```
httpr -replay myclient.replay
```
Install the CA certificate as described above.
Have your test program treat httpr as a proxy, as described above.
Run your test program. Your Google API clients should use no authentication.

Tips

You must remove all randomness from your interaction while recording, so that the replay is fully deterministic.

Note that BigQuery clients choose random values for job IDs and insert ID if you do not supply them. Either supply your own, or seed the client's random number generator if possible.

Examples

Examples of running httpr can be found in examples under this file's directory.

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