Speedup HTTP headers lowercase transformation

src/main/java/io/vertx/core/http/impl/HttpUtils.java

@@ -704,18 +704,32 @@ static String getWebSocketLocation(HttpServerRequest req, boolean ssl) throws Ex
   }
 
   /**
+   * This is optimized for Http headers, which are usually in the form:<br>
+   * eg Content-Length, content-length
+   *
    * @return convert the {@code sequence} to a lower case instance
    */
   public static CharSequence toLowerCase(CharSequence sequence) {
-    StringBuilder buffer = null;
+    if (sequence instanceof AsciiString) {
+      return ((AsciiString) sequence).toLowerCase();
+    }
+    return toCharSequenceLowerCase(sequence);
+  }
+
+  private static CharSequence toCharSequenceLowerCase(CharSequence sequence) {
     int len = sequence.length();
+    StringBuilder buffer = null;
     for (int index = 0; index < len; index++) {
       char c = sequence.charAt(index);
       if (c >= 'A' && c <= 'Z') {
         if (buffer == null) {
+          if (sequence instanceof String) {
+            return toLowerCase(((String) sequence).toCharArray(), index, len);
+          }
+          // just copy the lowercase part
           buffer = new StringBuilder(sequence);
         }
-        buffer.setCharAt(index, (char)(c + ('a' - 'A')));
+        buffer.setCharAt(index, (char) (c + ('a' - 'A')));
       }
     }
     if (buffer != null) {
@@ -725,6 +739,17 @@ public static CharSequence toLowerCase(CharSequence sequence) {
     }
   }
 
+  private static CharSequence toLowerCase(char[] chars, int firstUpperCase, int length) {
+    assert chars[firstUpperCase] >= 'A' && chars[firstUpperCase] <= 'Z';
+    for (int i = firstUpperCase; i < length; i++) {
+      char c = chars[i];
+      if (c >= 'A' && c <= 'Z') {
+        chars[i] = (char) (c + ('a' - 'A'));
+      }
+    }
+    return new String(chars, 0, length == chars.length? chars.length : length);
+  }
+
   static HttpVersion toNettyHttpVersion(io.vertx.core.http.HttpVersion version) {
     switch (version) {
       case HTTP_1_0: {

src/test/benchmarks/io/vertx/benchmarks/HttpUtilsAsciiToLowerCaseBenchmark.java

@@ -0,0 +1,72 @@
+/*
+ * Copyright (c) 2011-2019 Contributors to the Eclipse Foundation
+ *
+ * This program and the accompanying materials are made available under the
+ * terms of the Eclipse Public License 2.0 which is available at
+ * http://www.eclipse.org/legal/epl-2.0, or the Apache License, Version 2.0
+ * which is available at https://www.apache.org/licenses/LICENSE-2.0.
+ *
+ * SPDX-License-Identifier: EPL-2.0 OR Apache-2.0
+ */
+
+package io.vertx.benchmarks;
+
+import io.netty.util.AsciiString;
+import io.vertx.core.http.impl.HttpUtils;
+import org.openjdk.jmh.annotations.Benchmark;
+import org.openjdk.jmh.annotations.BenchmarkMode;
+import org.openjdk.jmh.annotations.Fork;
+import org.openjdk.jmh.annotations.Measurement;
+import org.openjdk.jmh.annotations.Mode;
+import org.openjdk.jmh.annotations.OutputTimeUnit;
+import org.openjdk.jmh.annotations.Param;
+import org.openjdk.jmh.annotations.Scope;
+import org.openjdk.jmh.annotations.Setup;
+import org.openjdk.jmh.annotations.State;
+import org.openjdk.jmh.annotations.Warmup;
+
+import java.util.concurrent.TimeUnit;
+
+import static java.util.concurrent.TimeUnit.MILLISECONDS;
+import static java.util.concurrent.TimeUnit.NANOSECONDS;
+
+@State(Scope.Benchmark)
+@Warmup(iterations = 20, time = 200, timeUnit = TimeUnit.MILLISECONDS)
+@Measurement(iterations = 10, time = 200, timeUnit = MILLISECONDS)
+@BenchmarkMode(Mode.AverageTime)
+@OutputTimeUnit(NANOSECONDS)
+@Fork(2)
+public class HttpUtilsAsciiToLowerCaseBenchmark {
+
+  @Param({"ascii", "string", "builder"})
+  public String type;
+
+  @Param({"false", "true"})
+  public boolean lowerCase;
+  private CharSequence sequence;
+
+  @Setup
+  public void init() {
+    sequence = create(type, lowerCase ? "content-length" : "Content-Length");
+  }
+
+  private CharSequence create(String type, String content) {
+
+    switch (type) {
+      case "ascii":
+        return new AsciiString(content);
+      case "string":
+        return content;
+      case "builder":
+        return new StringBuilder(content);
+      default:
+        throw new IllegalStateException();
+    }
+  }
+
+  @Benchmark
+  public CharSequence toLowerCase() {
+    return HttpUtils.toLowerCase(sequence);
+  }
+
+}