Enable tests to perform actions on behalf of the host (using service extensions)

[bartekpacia]

I want to embed an HTTP server in patrol_cli. Requests to that server would run shell commands (e.g adb, flutter screenshot) from within Dart test code running on a device.

This will enable us to solve the following:

• Take screenshot on failure option #534
• Always uninstall the app under test from device #73
• Close keyboard if opened #66
• Testing deep linking #556
• Run external program from within a test #606

I'd like to use gRPC for this (we already use it for Flutter <--> native communication within a device).

See also:

• this comment where the initial idea for this proposal was born

cc: @mateuszwojtczak, @jakubfijalkowski, @shilangyu

[jakubfijalkowski]

Since you already have gRPC there, and the use case for this is somewhat limited, maybe it is worth considering client streaming?

[bartekpacia]

Could you elaborate?

[jakubfijalkowski]

gRPC is unidirectional with a single exception - client streaming. You then don't need to open additional connection to send limited commands to the client.

I think this comment is somewhat irrelevant - I missed what parties you want to be connected. Sorry!

When it comes to CLI <-> Dart's part of the app comms, I personally would go with Dart VM's observatory service extension - there already is CLI <-> Dart communication (although somewhat hidden - it is maintained by the Flutter Driver but, if FD is used directly, you can attach to it) and then you can use events to send requests from tests to the CLI. This will be, IMO, much more Dart-native.

[bartekpacia]

@jakubfijalkowski Whoa, this is exactly a big-brain kind of idea I'd expect from you :D

This approach sounds very interesting, and I think I like it.

Concern:
It'll require more research from me than what I wrote in the first post (embedding a gRPC in the CLI), and I don't know what benefits we'll gain aside from being more Dart-native.

[jakubfijalkowski]

The main big advantage here is that you will need to maintain only one connection. With separate gRPC server you will have to have two of them, which gets funny when only one of them breaks in a silent manner ;P

[bartekpacia]

Another use case for the HTTP server:

• Testing deep linking #556

[bartekpacia]

Patrol 1.0 works only inside the host app, so this is not longer relevant. In the future, we'll research how we can add host feautres back, but they will only work when the host is available (so, for example, not on Firebase Test Lab).

See also #661.

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