[snh]

What

Extends the /metrics endpoint (enabled with PROME on) with metrics for each input and output. The existing global ais_stat_* metrics are unchanged.

Inputs

Labels: input, type, description. description is the user-supplied value from the config, falling back to a derived name when empty.

Metric	Notes
ais_input_count	Messages decoded
ais_input_bytes_in	Raw bytes received
ais_input_up	Streaming and not lost (a UDP input is up once its socket is bound)
ais_input_last_message_timestamp_seconds	0 until the first message
ais_input_errors{error}	checksum, undersized, oversized
ais_input_connect_ok, ais_input_connect_fail, ais_input_reconnects, ais_input_connected	RTLTCP and SpyServer only

Outputs

Labels: output, type, description.

Metric	Notes
ais_output_count	Messages passing the output's filter, counted once per message
ais_output_bytes_out	Wire bytes sent. For the TCP listener this is the total across clients
ais_output_bytes_in
ais_output_dropped	For the TCP listener, one per client disconnected for not reading
ais_output_connect_ok, ais_output_connect_fail, ais_output_reconnects, ais_output_connected	Connection-based outputs only. For the TCP listener, connected is the client count

Supporting changes

• Receiver::description now keeps the JSON config description (it was parsed and discarded).
• IO::OutputStats gains messages, which is also included in the JSON output.
• New Device::isUp() has no side effects. isStreaming() can read the WAV file and feed the decoder, so it isn't safe to call from the metrics path.
• New Device::getConnectionStats(), overridden by RTLTCP and SpyServer.
• New OutputMessage::hasConnection(), so connectionless outputs skip the connection metrics.
• DatabaseOutput now counts messages.
• New Dockerfile.dev builds from the checkout. The main Dockerfile installs the upstream release, so it can't be used to test local changes.