From 5b7cffc72d0d4bc40696256612e5a2afd87f3438 Mon Sep 17 00:00:00 2001
From: Vitor Pamplona <vitor@vitorpamplona.com>
Date: Thu, 1 Oct 2026 10:38:28 -0400
Subject: [PATCH] fix(desktop): read now-playing command output while the
 command runs

runCommand waited for the process to exit before reading its stdout. On a
busy Mac `ps -A -o comm=` prints ~100 KB, past the pipe buffer, so ps blocked
on the write, waitFor hit the 5 s timeout and the macOS reader never saw
Spotify or Music (and every poll stalled 5 s). Read stdout to EOF while a
watchdog thread kills a command that outlives the timeout.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
---
 .../desktop/nowPlaying/OsNowPlayingReader.kt  | 24 +++++++++++++------
 .../nowPlaying/OsNowPlayingReaderTest.kt      | 22 +++++++++++++++++
 2 files changed, 39 insertions(+), 7 deletions(-)

diff --git a/desktopApp/src/jvmMain/kotlin/com/vitorpamplona/amethyst/desktop/nowPlaying/OsNowPlayingReader.kt b/desktopApp/src/jvmMain/kotlin/com/vitorpamplona/amethyst/desktop/nowPlaying/OsNowPlayingReader.kt
index 7a8cb58c6d..f8aad95b00 100644
--- a/desktopApp/src/jvmMain/kotlin/com/vitorpamplona/amethyst/desktop/nowPlaying/OsNowPlayingReader.kt
+++ b/desktopApp/src/jvmMain/kotlin/com/vitorpamplona/amethyst/desktop/nowPlaying/OsNowPlayingReader.kt
@@ -25,6 +25,7 @@ import com.vitorpamplona.quartz.utils.Log
 import kotlinx.coroutines.Dispatchers
 import kotlinx.coroutines.runInterruptible
 import java.util.concurrent.TimeUnit
+import kotlin.concurrent.thread
 
 /** Reads what the OS says another app is playing right now. */
 interface OsNowPlayingReader {
@@ -63,13 +64,22 @@ internal suspend fun runCommand(
                     .start()
             process = started
             started.outputStream.close()
-            // Wait before reading so a hung command cannot block the read forever. The outputs
-            // here are a few KB, well under the pipe buffer, so the command never blocks on it.
-            if (!started.waitFor(timeoutSeconds, TimeUnit.SECONDS) || started.exitValue() != 0) {
-                null
-            } else {
-                started.inputStream.bufferedReader(Charsets.UTF_8).use { it.readText() }
-            }
+            // Read while the command runs: `ps -A -o comm=` prints ~100 KB on a busy Mac, past the
+            // pipe buffer, so waiting for the exit before reading deadlocked until the timeout and
+            // the reader never saw a player. The watchdog still kills a command that hangs, which
+            // also ends the read.
+            val watchdog =
+                thread(isDaemon = true, name = "now-playing-command-timeout") {
+                    try {
+                        if (!started.waitFor(timeoutSeconds, TimeUnit.SECONDS)) started.destroyForcibly()
+                    } catch (_: InterruptedException) {
+                        // The command finished first.
+                    }
+                }
+            val output = started.inputStream.bufferedReader(Charsets.UTF_8).use { it.readText() }
+            val exited = started.waitFor(timeoutSeconds, TimeUnit.SECONDS)
+            watchdog.interrupt()
+            if (!exited || started.exitValue() != 0) null else output
         } catch (e: InterruptedException) {
             throw e
         } catch (e: Exception) {
diff --git a/desktopApp/src/jvmTest/kotlin/com/vitorpamplona/amethyst/desktop/nowPlaying/OsNowPlayingReaderTest.kt b/desktopApp/src/jvmTest/kotlin/com/vitorpamplona/amethyst/desktop/nowPlaying/OsNowPlayingReaderTest.kt
index 02e0bc97c2..36b29a93cc 100644
--- a/desktopApp/src/jvmTest/kotlin/com/vitorpamplona/amethyst/desktop/nowPlaying/OsNowPlayingReaderTest.kt
+++ b/desktopApp/src/jvmTest/kotlin/com/vitorpamplona/amethyst/desktop/nowPlaying/OsNowPlayingReaderTest.kt
@@ -22,9 +22,11 @@ package com.vitorpamplona.amethyst.desktop.nowPlaying
 
 import com.vitorpamplona.amethyst.commons.model.nip38UserStatuses.nowPlaying.NowPlayingSource
 import kotlinx.coroutines.test.runTest
+import java.io.File
 import kotlin.test.Test
 import kotlin.test.assertEquals
 import kotlin.test.assertNull
+import kotlin.test.assertTrue
 
 class OsNowPlayingReaderTest {
     private val listNames =
@@ -215,4 +217,24 @@ class OsNowPlayingReaderTest {
         assertEquals("ZuneMusic", WindowsNowPlayingReader.appLabel("Microsoft.ZuneMusic_8wekyb3d8bbwe!Microsoft.ZuneMusic"))
         assertEquals("308046B0AF4A39CB", WindowsNowPlayingReader.appLabel("308046B0AF4A39CB"))
     }
+
+    private val hasShell = File("/bin/sh").canExecute()
+
+    /** `ps -A -o comm=` prints ~100 KB on a busy Mac; reading only after the exit deadlocked on the pipe. */
+    @Test
+    fun runCommandReturnsOutputLargerThanThePipeBuffer() =
+        runTest {
+            if (!hasShell) return@runTest
+            val output = runCommand(listOf("/bin/sh", "-c", "i=0; while [ \$i -lt 4000 ]; do echo 0123456789012345678901234567890123456789012345678; i=\$((i+1)); done"))
+            assertEquals(4000 * 50, output?.length)
+        }
+
+    @Test
+    fun runCommandGivesUpOnAHungCommand() =
+        runTest {
+            if (!hasShell) return@runTest
+            val started = System.currentTimeMillis()
+            assertNull(runCommand(listOf("/bin/sh", "-c", "sleep 30"), timeoutSeconds = 1))
+            assertTrue(System.currentTimeMillis() - started < 10_000, "the timeout must end the call")
+        }
 }