KTOR-7845 Fix for threading issue in flushAndClose for reader job channels (#4503)

Author: bjhham

ktor-io/api/ktor-io.api

@@ -173,6 +173,10 @@ public abstract interface class io/ktor/utils/io/ChannelJob {
 	public abstract fun getJob ()Lkotlinx/coroutines/Job;
 }
 
+public final class io/ktor/utils/io/CloseHookByteWriteChannelKt {
+	public static final fun onClose (Lio/ktor/utils/io/ByteWriteChannel;Lkotlin/jvm/functions/Function1;)Lio/ktor/utils/io/ByteWriteChannel;
+}
+
 public final class io/ktor/utils/io/ConcurrentIOException : java/lang/IllegalStateException {
 	public fun <init> (Ljava/lang/String;Ljava/lang/Throwable;)V
 	public synthetic fun <init> (Ljava/lang/String;Ljava/lang/Throwable;ILkotlin/jvm/internal/DefaultConstructorMarker;)V

ktor-io/api/ktor-io.klib.api

@@ -364,6 +364,7 @@ final fun (io.ktor.utils.io/ByteWriteChannel).io.ktor.utils.io/cancel() // io.kt
 final fun (io.ktor.utils.io/ByteWriteChannel).io.ktor.utils.io/close() // io.ktor.utils.io/close|[email protected](){}[0]
 final fun (io.ktor.utils.io/ByteWriteChannel).io.ktor.utils.io/close(kotlin/Throwable?) // io.ktor.utils.io/close|[email protected](kotlin.Throwable?){}[0]
 final fun (io.ktor.utils.io/ByteWriteChannel).io.ktor.utils.io/counted(): io.ktor.utils.io/CountedByteWriteChannel // io.ktor.utils.io/counted|[email protected](){}[0]
+final fun (io.ktor.utils.io/ByteWriteChannel).io.ktor.utils.io/onClose(kotlin.coroutines/SuspendFunction0<kotlin/Unit>): io.ktor.utils.io/ByteWriteChannel // io.ktor.utils.io/onClose|[email protected](kotlin.coroutines.SuspendFunction0<kotlin.Unit>){}[0]
 final fun (io.ktor.utils.io/ByteWriteChannel).io.ktor.utils.io/rethrowCloseCauseIfNeeded() // io.ktor.utils.io/rethrowCloseCauseIfNeeded|[email protected](){}[0]
 final fun (io.ktor.utils.io/ChannelJob).io.ktor.utils.io/cancel() // io.ktor.utils.io/cancel|[email protected](){}[0]
 final fun (io.ktor.utils.io/ChannelJob).io.ktor.utils.io/getCancellationException(): kotlin.coroutines.cancellation/CancellationException // io.ktor.utils.io/getCancellationException|[email protected](){}[0]

ktor-io/common/src/io/ktor/utils/io/ByteReadChannelOperations.kt

@@ -14,7 +14,6 @@ import kotlinx.io.Buffer
 import kotlinx.io.bytestring.*
 import kotlinx.io.unsafe.*
 import kotlin.coroutines.*
-import kotlin.jvm.*
 import kotlin.math.*
 
 @OptIn(InternalAPI::class)
@@ -309,7 +308,7 @@ public fun CoroutineScope.reader(
         }
     }
 
-    return ReaderJob(channel, job)
+    return ReaderJob(channel.onClose { job.join() }, job)
 }
 
 /**

ktor-io/common/src/io/ktor/utils/io/CloseHookByteWriteChannel.kt

@@ -0,0 +1,24 @@
+/*
+ * Copyright 2014-2024 JetBrains s.r.o and contributors. Use of this source code is governed by the Apache 2.0 license.
+ */
+
+package io.ktor.utils.io
+
+/**
+ * Wraps this channel to execute the provided action when closed using `flushAndClose()`.
+ *
+ * @param onClose The action to execute when the channel is closed.
+ * @return A new `ByteWriteChannel` that executes the given action upon closure.
+ */
+public fun ByteWriteChannel.onClose(onClose: suspend () -> Unit): ByteWriteChannel =
+    CloseHookByteWriteChannel(this, onClose)
+
+internal class CloseHookByteWriteChannel(
+    private val delegate: ByteWriteChannel,
+    private val onClose: suspend () -> Unit
+) : ByteWriteChannel by delegate {
+    override suspend fun flushAndClose() {
+        delegate.flushAndClose()
+        onClose()
+    }
+}

ktor-utils/jvm/test/io/ktor/tests/utils/FileChannelTest.kt

@@ -9,9 +9,11 @@ import io.ktor.util.cio.*
 import io.ktor.utils.io.*
 import io.ktor.utils.io.jvm.javaio.*
 import kotlinx.coroutines.*
+import kotlinx.coroutines.test.runTest
 import org.junit.jupiter.api.*
 import org.junit.jupiter.api.extension.*
 import java.io.*
+import java.nio.file.Files
 import kotlin.test.*
 import kotlin.test.Test
 
@@ -117,4 +119,23 @@ class FileChannelTest {
         // Assert (we cannot delete if there is a file handle open on it)
         assertTrue(temp.delete())
     }
+
+    @Test
+    fun `writeChannel finishes on close`() = runTest {
+        val file = Files.createTempFile("file", "txt").toFile()
+        val ch = file.writeChannel()
+        ch.writeStringUtf8("Hello")
+        ch.flushAndClose()
+        assertEquals(5, file.length())
+        assertEquals("Hello", file.readText())
+    }
+
+    @Test
+    fun `writeChannel writes to file on flush`() = runTest {
+        val file = Files.createTempFile("file", "txt").toFile()
+        val ch = file.writeChannel()
+        ch.writeStringUtf8("Hello")
+        ch.flush()
+        assertEquals("Hello", file.readText())
+    }
 }