Add fastpath implementation for Unpooled.copiedBuffer(CharSequence, Charset) when UTF-8 or US-ASCII is used (#10206)

Motivation:

We can make use of our optimized implementations for UTF-8 and US-ASCII if the user request a copy of a sequence for these charsets

Modifications:

- Add fastpath implementation
- Add unit tests

Result:

Fixes https://github.com/netty/netty/issues/10205

buffer/src/main/java/io/netty/buffer/Unpooled.java

@@ -18,6 +18,7 @@ package io.netty.buffer;
 import static java.util.Objects.requireNonNull;
 
 import io.netty.buffer.CompositeByteBuf.ByteWrapper;
+import io.netty.util.CharsetUtil;
 import io.netty.util.internal.PlatformDependent;
 
 import java.nio.ByteBuffer;
@@ -579,6 +580,12 @@ public final class Unpooled {
     public static ByteBuf copiedBuffer(CharSequence string, Charset charset) {
         requireNonNull(string, "string");
 
+        if (CharsetUtil.UTF_8.equals(charset)) {
+            return copiedBufferUtf8(string);
+        }
+        if (CharsetUtil.US_ASCII.equals(charset)) {
+            return copiedBufferAscii(string);
+        }
         if (string instanceof CharBuffer) {
             return copiedBuffer((CharBuffer) string, charset);
         }
@@ -586,6 +593,36 @@ public final class Unpooled {
         return copiedBuffer(CharBuffer.wrap(string), charset);
     }
 
+    private static ByteBuf copiedBufferUtf8(CharSequence string) {
+        boolean release = true;
+        // Mimic the same behavior as other copiedBuffer implementations.
+        ByteBuf buffer = ALLOC.heapBuffer(ByteBufUtil.utf8Bytes(string));
+        try {
+            ByteBufUtil.writeUtf8(buffer, string);
+            release = false;
+            return buffer;
+        } finally {
+            if (release) {
+                buffer.release();
+            }
+        }
+    }
+
+    private static ByteBuf copiedBufferAscii(CharSequence string) {
+        boolean release = true;
+        // Mimic the same behavior as other copiedBuffer implementations.
+        ByteBuf buffer = ALLOC.heapBuffer(string.length());
+        try {
+            ByteBufUtil.writeAscii(buffer, string);
+            release = false;
+            return buffer;
+        } finally {
+            if (release) {
+                buffer.release();
+            }
+        }
+    }
+
     /**
      * Creates a new big-endian buffer whose content is a subregion of
      * the specified {@code string} encoded in the specified {@code charset}.

buffer/src/test/java/io/netty/buffer/UnpooledTest.java

@@ -15,12 +15,14 @@
  */
 package io.netty.buffer;
 
+import io.netty.util.CharsetUtil;
 import org.junit.Test;
 import org.mockito.Mockito;
 
 import java.io.InputStream;
 import java.nio.ByteBuffer;
 import java.nio.channels.ScatteringByteChannel;
+import java.nio.charset.Charset;
 import java.util.ArrayList;
 import java.util.LinkedHashMap;
 import java.util.List;
@@ -308,6 +310,30 @@ public class UnpooledTest {
         assertEquals(0, buf2.refCnt());
     }
 
+    @Test
+    public void testCopiedBufferUtf8() {
+        testCopiedBufferCharSequence("Some UTF_8 like äÄ∏ŒŒ", CharsetUtil.UTF_8);
+    }
+
+    @Test
+    public void testCopiedBufferAscii() {
+        testCopiedBufferCharSequence("Some US_ASCII", CharsetUtil.US_ASCII);
+    }
+
+    @Test
+    public void testCopiedBufferSomeOtherCharset() {
+        testCopiedBufferCharSequence("Some ISO_8859_1", CharsetUtil.ISO_8859_1);
+    }
+
+    private static void testCopiedBufferCharSequence(CharSequence sequence, Charset charset) {
+        ByteBuf copied = copiedBuffer(sequence, charset);
+        try {
+            assertEquals(sequence, copied.toString(charset));
+        } finally {
+            copied.release();
+        }
+    }
+
     @Test
     public void testCopiedBuffer() {
         ByteBuf copied = copiedBuffer(ByteBuffer.allocateDirect(16));