Fix ESPHome transport by subscribing serial proxy instance

[balloob]

I was messing around with the ESPHome proxy PR with serialx and ran into an issue.

Below is written by AI:

Summary

Fix esphome:// serial transports so they explicitly subscribe to the selected serial-proxy instance before expecting RX data.

This restores end-to-end behavior for ESPHome serial proxy setups where writes succeed but no inbound bytes are delivered unless serial_proxy_subscribe(instance) is called.

Problem

With recent ESPHome serial proxy behavior, connecting and configuring a serial proxy instance is not enough to receive data events. The client must explicitly subscribe to that instance.

serialx currently:

• connects API client
• configures serial proxy port
• registers subscribe_serial_proxy_data(...) callback

…but never sends serial_proxy_subscribe(instance).

Observed failure mode

On a live setup (connect-proxy-sendspin at 192.168.1.227, Denon AVR-X2700H on RS232):

• serialx.open_serial_connection("esphome://192.168.1.227/1", baudrate=9600)
• writer.write(b"PW?\\r")
• reader.read(...) timed out with empty bytes repeatedly

At the same time, the exact same command path worked immediately when sending api.serial_proxy_subscribe(1) manually first.

Root Cause

subscribe_serial_proxy_data(...) registers a callback for data events, but does not itself request that the server begin streaming a specific serial instance.

The explicit instance request is done via:

• serial_proxy_subscribe(instance)
• and should be paired with serial_proxy_unsubscribe(instance) on close.

Changes

serialx/platforms/serial_esphome.py

• Add instance subscription lifecycle tracking:
  • self._instance_subscribed
  • _subscribe_instance()
  • _unsubscribe_instance()
• On open/connect:
  • call _subscribe_instance() before setting the data callback
• On close:
  • call _unsubscribe_instance() before API disconnect
• Apply this in both:
  • sync ESPHomeSerial path
  • async ESPHomeSerialTransport path

Backward compatibility

Some older aioesphomeapi variants may not expose subscribe/unsubscribe helpers.

To avoid regressions, this patch uses getattr(...) and no-ops when those methods are unavailable.

Tests

Added: tests/test_serial_esphome.py

1. test_transport_subscribes_instance_and_unsubscribes_on_close
   • verifies serial_proxy_subscribe(instance) is called on connect
   • verifies serial_proxy_unsubscribe(instance) is called on close
2. test_transport_works_without_instance_subscribe_api
   • verifies behavior remains functional when subscribe APIs do not exist

Verification

Unit

• pytest -q -o addopts='' tests/test_serial_esphome.py
• Result: 2 passed

Manual (live hardware)

On the setup above:

Before patch:

• esphome://.../1 writes sent, but RX stayed empty.

After patch:

• PW?\r over serialx returns PWON\r
• higher-level Denon client connection succeeds and power queries return PowerState.ON

This confirms the fix in real-world traffic and not only mocked tests.

[puddly]

If it runs on a real device then it's good enough for me 😄. We're still iterating on the flush() semantics for ESP8266 and other platforms so once the aioesphomeapi PR is finished we can start merging everything.

[codecov]

Codecov Report

❌ Patch coverage is 0% with 22 lines in your changes missing coverage. Please review.
✅ Project coverage is 59.51%. Comparing base (615c1b4) to head (b00ddbd).
⚠️ Report is 7 commits behind head on puddly/esphome.

Files with missing lines	Patch %	Lines
serialx/platforms/serial_esphome.py	0.00%	22 Missing ⚠️

Additional details and impacted files

@@                Coverage Diff                 @@
##           puddly/esphome      #29      +/-   ##
==================================================
- Coverage           63.20%   59.51%   -3.70%     
==================================================
  Files                  11       13       +2     
  Lines                1166     1408     +242     
==================================================
+ Hits                  737      838     +101     
- Misses                429      570     +141     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.