feat(app): parse json-stream reports into structured events

The native layer now emits one JSON object per report, so the service parses
each into a sealed Iperf3Event — start, interval, end, error — and publishes
those instead of opaque lines. Interval samples carry bytes, bits per second,
retransmits and per-stream socket/cwnd/rtt detail; the end event carries sent
and received totals and CPU utilisation. None of that was available while the
output was scraped text.

Anything unrecognised — non-JSON, malformed JSON, an event name a future
iperf3 adds — becomes an Iperf3LogLine rather than being dropped, so
unexpected output still reaches the user.

Failures arrive as an `error` event rather than a non-zero return from
iperf_run_client, so that event is what now marks a run as failed. The
result's rawOutput keeps the JSON lines verbatim, since that is what the
native layer actually produced.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

lib/data/services/iperf3_service.dart

@@ -2,6 +2,7 @@ import 'dart:async';
 
 import 'package:flutter/foundation.dart';
 import 'package:flutter/services.dart';
+import 'package:iperf3gui/domain/models/iperf3_event.dart';
 import 'package:iperf3gui/domain/models/iperf3_result.dart';
 import 'package:iperf3gui/domain/models/test_configuration.dart';
 
@@ -10,9 +11,11 @@ import 'package:iperf3gui/domain/models/test_configuration.dart';
 /// On Android, iperf3 is compiled into the app as a shared library (.so).
 /// This avoids SELinux restrictions on executing ELF binaries from assets.
 ///
-/// The service talks to the native layer over a MethodChannel. Native output
-/// arrives line by line on [outputLines] while the test runs; [run] resolves
-/// with the accumulated transcript once the native layer reports completion.
+/// The service talks to the native layer over a MethodChannel. The test runs
+/// in `--json-stream` mode, so each native report arrives as one JSON object;
+/// they are parsed and published on [events] while the test runs. [run]
+/// resolves once the native layer reports completion, carrying the raw JSON
+/// lines as the result's output.
 class Iperf3Service {
   Iperf3Service() {
     _channel.setMethodCallHandler(_handleNativeCall);
@@ -33,16 +36,15 @@ class Iperf3Service {
   /// Exit code reported when the native layer never signalled completion.
   static const int exitCodeTimeout = -3;
 
-  /// Lines emitted by the native layer during the current run.
-  final StreamController<String> _outputController =
-      StreamController<String>.broadcast();
+  /// Events parsed from the native layer during the current run.
+  final StreamController<Iperf3Event> _eventController =
+      StreamController<Iperf3Event>.broadcast();
 
-  /// Live output, one line per event. Use this to render progress; [run]'s
-  /// result carries the same text joined together.
-  Stream<String> get outputLines => _outputController.stream;
+  /// Live reports, one event per native report. Use this to render progress.
+  Stream<Iperf3Event> get events => _eventController.stream;
 
-  /// Transcript of the current (or most recent) run.
-  final List<String> _outputBuffer = [];
+  /// Raw JSON lines received during the current (or most recent) run.
+  final List<String> _rawLines = [];
 
   /// Completer that resolves when the native iperf3 test finishes.
   Completer<Iperf3Result>? _runCompleter;
@@ -71,7 +73,7 @@ class Iperf3Service {
   /// Release the stream controller. Call from the owner's dispose().
   Future<void> dispose() async {
     _channel.setMethodCallHandler(null);
-    await _outputController.close();
+    await _eventController.close();
   }
 
   /// Run iperf3 with the given configuration.
@@ -88,7 +90,7 @@ class Iperf3Service {
     _isRunning = true;
     _sawError = false;
     _stopRequested = false;
-    _outputBuffer.clear();
+    _rawLines.clear();
 
     final args = config.toCliArgs();
     debugPrint('Iperf3Service: running: ${args.join(" ")}');
@@ -121,9 +123,9 @@ class Iperf3Service {
             debugPrint('Iperf3Service: error stopping after timeout: $e');
             return null;
           });
-          _emit('[ERROR] Timed out waiting for iperf3 to finish.');
+          _publish(const Iperf3Error('Timed out waiting for iperf3 to finish.'));
           return Iperf3Result(
-            rawOutput: _transcript(),
+            rawOutput: _rawOutput(),
             exitCode: exitCodeTimeout,
           );
         },
@@ -145,7 +147,12 @@ class Iperf3Service {
       case 'onOutput':
         final output = call.arguments['output'] as String?;
         if (output != null) {
-          _emit(output);
+          _rawLines.add(output);
+          final event = Iperf3Event.parse(output);
+          // iperf3 reports a failed test as an `error` event rather than a
+          // non-zero return, so this is where most failures surface.
+          if (event is Iperf3Error) _sawError = true;
+          _publish(event);
         }
       case 'onError':
         final error = call.arguments['error'] as String?;
@@ -153,7 +160,7 @@ class Iperf3Service {
           // Not terminal on its own — iperf3 reports the failure reason and
           // then completes, so wait for onComplete before resolving.
           _sawError = true;
-          _emit('[ERROR] $error');
+          _publish(Iperf3Error(error));
         }
       case 'onComplete':
         debugPrint('Iperf3Service: test completed');
@@ -161,7 +168,7 @@ class Iperf3Service {
         if (completer != null && !completer.isCompleted) {
           completer.complete(
             Iperf3Result(
-              rawOutput: _transcript(),
+              rawOutput: _rawOutput(),
               // A user-requested stop is a normal outcome, not a failure.
               exitCode:
                   (_sawError && !_stopRequested) ? exitCodeNativeError : 0,
@@ -174,17 +181,14 @@ class Iperf3Service {
     }
   }
 
-  void _emit(String line) {
-    _outputBuffer.add(line);
-    if (!_outputController.isClosed) {
-      _outputController.add(line);
+  void _publish(Iperf3Event event) {
+    if (!_eventController.isClosed) {
+      _eventController.add(event);
     }
-    debugPrint('Iperf3Service output: ${line.trimRight()}');
   }
 
-  /// Native output already carries its own newlines; keep it verbatim except
-  /// for lines we synthesised ourselves.
-  String _transcript() => _outputBuffer
+  /// The raw JSON stream as received, one event per line.
+  String _rawOutput() => _rawLines
       .map((line) => line.endsWith('\n') ? line : '$line\n')
       .join();