gzip telemetry events

[willwhite]

Make sure that we gzip telemetry events before sending them. gzip could reduce the time the mobile radio is working, especially on slower connections, and thus reduce battery impact.

/cc @boundsj

[friedbunny]

I'm surprised that we don't do this already.

[tobrun]

If content encoding is set to gzip, this is automatically handled in the background by Okhttp on Android.
You can verify this is the related unit-test, here they are showing Okhttp transparent gzipping in action.
update above is for response coming from server. Here is shown to add this to the request.

[boundsj]

There are 3rd party libs that make this transparent for iOS, too (https://github.com/AFNetworking/AFgzipRequestSerializer/blob/master/AFgzipRequestSerializer/AFgzipRequestSerializer.m?#L57) but we don't use a 3rd party dep in the iOS bindings

[mawajdak]

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[friedbunny]

Resources that we can draw upon for our own GZIP implementation:

• https://github.com/mattt/Godzippa (used in AFNetworking, per above)
• https://github.com/nicklockwood/GZIP

[tobrun]

What I mentioned in #3979 (comment) is not true.

To GZIP our communication we need to implement the following request interceptor on OkHttp: https://github.com/square/okhttp/blob/3f7a3344a4c85aa3bbb879dabac5ee625ab987f3/samples/guide/src/main/java/okhttp3/recipes/RequestBodyCompression.java#L73

This shouldn't be a big lift since we just need to copy/paste it into our telemetry web service code.

[ivovandongen]

@tobrun We're using something similar in Human too. Can take a look at that too if you want.

[mick]

The api already accepts gzip'd JSON as long as the following headers are set on the POST request:

Content-type: application/json
Content-Encoding: gzip

[bleege]

I've ticketed out the Android work in #5536.

[friedbunny]

This is done on the iOS side (#5490) and will be included in the final v3.3.0 release.

[zugaldia]

Work for Android was done in #5536 and for iOS in #5490. I think we're good to close here.