KTOR-7904 Fix Servlet response body is corrupted due to the wrong off…

…set (#4527)

ktor-server/ktor-server-servlet-jakarta/jvm/src/io/ktor/server/servlet/jakarta/ServletWriter.kt

@@ -77,7 +77,7 @@ private class ServletWriter(val output: ServletOutputStream) : WriteListener {
                 }
 
                 awaitReady()
-                output.write(buffer, 0, rc)
+                output.write(buffer, start, rc)
                 awaitReady()
                 rc
             }

ktor-server/ktor-server-servlet-jakarta/jvm/test/io/ktor/tests/servlet/jakarta/ServletWriterJakartaTest.kt

@@ -0,0 +1,55 @@
+/*
+ * 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.tests.servlet.jakarta
+
+import io.ktor.server.servlet.*
+import io.ktor.server.servlet.jakarta.servletWriter
+import io.ktor.utils.io.*
+import io.ktor.utils.io.core.*
+import jakarta.servlet.ServletOutputStream
+import jakarta.servlet.WriteListener
+import kotlinx.coroutines.coroutineScope
+import kotlinx.coroutines.runBlocking
+import kotlinx.io.readByteArray
+import kotlin.test.Test
+import kotlin.test.assertEquals
+
+class ServletWriterJakartaTest {
+
+    @Test
+    fun testWriteBufferWithPositivePosition() = runBlocking {
+        val content = withServletWriter {
+            val buffer = ByteReadPacket("1234567890".toByteArray())
+            buffer.readByte()
+
+            writeBuffer(buffer)
+            flushAndClose()
+        }
+
+        assertEquals("234567890", content.decodeToString())
+    }
+
+    suspend fun withServletWriter(block: suspend ByteWriteChannel.() -> Unit): ByteArray {
+        val content = BytePacketBuilder()
+        val output = object : ServletOutputStream() {
+            override fun isReady(): Boolean = true
+            override fun setWriteListener(writeListener: WriteListener) {
+                writeListener.onWritePossible()
+            }
+
+            override fun write(b: Int) {
+                content.writeByte((b and 0xff).toByte())
+            }
+        }
+
+        coroutineScope {
+            val channel = servletWriter(output).channel
+            block(channel)
+            channel.flushAndClose()
+        }
+
+        return content.build().readByteArray()
+    }
+}

ktor-server/ktor-server-servlet/jvm/src/io/ktor/server/servlet/ServletWriter.kt

@@ -77,7 +77,7 @@ private class ServletWriter(val output: ServletOutputStream) : WriteListener {
                 }
 
                 awaitReady()
-                output.write(buffer, 0, rc)
+                output.write(buffer, start, rc)
                 awaitReady()
                 rc
             }

ktor-server/ktor-server-servlet/jvm/test/io/ktor/tests/servlet/ServletWriterTest.kt

@@ -0,0 +1,55 @@
+/*
+ * 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.tests.servlet
+
+import io.ktor.server.servlet.*
+import io.ktor.utils.io.*
+import io.ktor.utils.io.core.*
+import kotlinx.coroutines.coroutineScope
+import kotlinx.coroutines.runBlocking
+import kotlinx.io.readByteArray
+import javax.servlet.ServletOutputStream
+import javax.servlet.WriteListener
+import kotlin.test.Test
+import kotlin.test.assertEquals
+
+class ServletWriterTest {
+
+    @Test
+    fun testWriteBufferWithPositivePosition() = runBlocking {
+        val content = withServletWriter {
+            val buffer = ByteReadPacket("1234567890".toByteArray())
+            buffer.readByte()
+
+            writeBuffer(buffer)
+            flushAndClose()
+        }
+
+        assertEquals("234567890", content.decodeToString())
+    }
+
+    suspend fun withServletWriter(block: suspend ByteWriteChannel.() -> Unit): ByteArray {
+        val content = BytePacketBuilder()
+        val output = object : ServletOutputStream() {
+            override fun isReady(): Boolean = true
+
+            override fun setWriteListener(writeListener: WriteListener) {
+                writeListener.onWritePossible()
+            }
+
+            override fun write(b: Int) {
+                content.writeByte((b and 0xff).toByte())
+            }
+        }
+
+        coroutineScope {
+            val channel = servletWriter(output).channel
+            block(channel)
+            channel.flushAndClose()
+        }
+
+        return content.build().readByteArray()
+    }
+}

ktor-server/ktor-server-tests/build.gradle.kts

@@ -15,6 +15,7 @@ kotlin.sourceSets {
     jvmTest {
         dependencies {
             implementation(libs.jansi)
+            implementation(project(":ktor-client:ktor-client-plugins:ktor-client-encoding"))
             api(project(":ktor-server:ktor-server-core", configuration = "testOutput"))
             api(libs.logback.classic)
             api(project(":ktor-server:ktor-server-plugins:ktor-server-sse"))

ktor-server/ktor-server-tests/jvm/test/io/ktor/server/plugins/CompressionTest.kt

@@ -22,11 +22,16 @@ import io.ktor.server.testing.*
 import io.ktor.util.*
 import io.ktor.utils.io.*
 import io.ktor.utils.io.jvm.javaio.*
-import kotlinx.coroutines.*
-import kotlinx.io.*
-import java.time.*
-import java.util.zip.*
-import kotlin.coroutines.*
+import kotlinx.coroutines.Job
+import kotlinx.coroutines.coroutineScope
+import kotlinx.coroutines.launch
+import kotlinx.io.readByteArray
+import java.time.ZoneId
+import java.time.ZonedDateTime
+import java.util.zip.GZIPInputStream
+import java.util.zip.Inflater
+import java.util.zip.InflaterInputStream
+import kotlin.coroutines.CoroutineContext
 import kotlin.test.*
 
 class CompressionTest {