Optimize routing resolution allocations with state machine refactoring

ktor-http/common/src/io/ktor/http/HttpProtocolVersion.kt

@@ -2,6 +2,9 @@
 * Copyright 2014-2021 JetBrains s.r.o and contributors. Use of this source code is governed by the Apache 2.0 license.
 */
 
+// ABOUTME: Represents HTTP protocol version (e.g., HTTP/1.1, HTTP/2.0).
+// ABOUTME: Provides cached instances for common versions and zero-allocation parsing for HTTP protocol.
+
 package io.ktor.http
 
 /**
@@ -77,16 +80,59 @@ public data class HttpProtocolVersion(val name: String, val major: Int, val mino
          * [Report a problem](https://ktor.io/feedback/?fqname=io.ktor.http.HttpProtocolVersion.Companion.parse)
          */
         public fun parse(value: CharSequence): HttpProtocolVersion {
-            /**
-             * Format: protocol/major.minor
-             */
-                val (protocol, major, minor) = value.split("/", ".").also {
-                check(it.size == 3) {
+            // Format: protocol/major.minor
+            // Zero-allocation fast path for common HTTP versions
+            val slashIndex = value.indexOf('/')
+            val dotIndex = if (slashIndex >= 0) value.indexOf('.', slashIndex + 1) else -1
+
+            if (slashIndex < 0 || dotIndex < 0) {
+                throw IllegalArgumentException(
                     "Failed to parse HttpProtocolVersion. Expected format: protocol/major.minor, but actual: $value"
+                )
+            }
+
+            val major = parseDigits(value, slashIndex + 1, dotIndex)
+            val minor = parseDigits(value, dotIndex + 1, value.length)
+
+            if (major < 0 || minor < 0) {
+                throw IllegalArgumentException(
+                    "Failed to parse HttpProtocolVersion. Expected format: protocol/major.minor, but actual: $value"
+                )
+            }
+
+            // Fast path for HTTP (most common) - returns cached instances, no allocation
+            if (isHttp(value, slashIndex)) {
+                return when {
+                    major == 1 && minor == 0 -> HTTP_1_0
+                    major == 1 && minor == 1 -> HTTP_1_1
+                    major == 2 && minor == 0 -> HTTP_2_0
+                    major == 3 && minor == 0 -> HTTP_3_0
+                    else -> HttpProtocolVersion("HTTP", major, minor)
                 }
             }
 
-            return fromValue(protocol, major.toInt(), minor.toInt())
+            // Slow path for other protocols - needs string allocation
+            val protocol = value.substring(0, slashIndex)
+            return fromValue(protocol, major, minor)
+        }
+
+        private fun isHttp(value: CharSequence, slashIndex: Int): Boolean {
+            return slashIndex == 4 &&
+                value[0] == 'H' &&
+                value[1] == 'T' &&
+                value[2] == 'T' &&
+                value[3] == 'P'
+        }
+
+        private fun parseDigits(value: CharSequence, start: Int, end: Int): Int {
+            if (start >= end) return -1
+            var result = 0
+            for (i in start until end) {
+                val c = value[i]
+                if (c !in '0'..'9') return -1
+                result = result * 10 + (c - '0')
+            }
+            return result
         }
     }
 

ktor-io/api/ktor-io.api

@@ -594,6 +594,11 @@ public final class io/ktor/utils/io/jvm/javaio/WritingKt {
 	public static synthetic fun copyTo$default (Lio/ktor/utils/io/ByteReadChannel;Ljava/io/OutputStream;JLkotlin/coroutines/Continuation;ILjava/lang/Object;)Ljava/lang/Object;
 }
 
+public final class io/ktor/utils/io/jvm/nio/ByteBufferHolder {
+	public fun <init> ()V
+	public final fun getOrCreate ([BII)Ljava/nio/ByteBuffer;
+}
+
 public final class io/ktor/utils/io/jvm/nio/ReadingKt {
 	public static final fun asSource (Ljava/nio/channels/ReadableByteChannel;)Lkotlinx/io/RawSource;
 	public static final fun toByteReadChannel (Ljava/nio/channels/ReadableByteChannel;Lkotlin/coroutines/CoroutineContext;)Lio/ktor/utils/io/ByteReadChannel;
@@ -609,6 +614,7 @@ public final class io/ktor/utils/io/jvm/nio/WriteSuspendSession {
 }
 
 public final class io/ktor/utils/io/jvm/nio/WriteSuspendSessionKt {
+	public static final fun getThreadLocalByteBufferHolder ()Ljava/lang/ThreadLocal;
 	public static final fun writeSuspendSession (Lio/ktor/utils/io/ByteWriteChannel;Lkotlin/jvm/functions/Function2;Lkotlin/coroutines/Continuation;)Ljava/lang/Object;
 	public static final fun writeWhile (Lio/ktor/utils/io/ByteWriteChannel;Lkotlin/jvm/functions/Function1;Lkotlin/coroutines/Continuation;)Ljava/lang/Object;
 }