core: speed up Status code and message parsing

This introduces the idea of a "Trusted" Ascii Marshaller, which is
known to always produce valid ASCII byte arrays.  This saves a
surprising amount of garbage, since String conversion involves
creating a new java.lang.StringCoding, and a sun.nio.cs.US_ASCII.

There are other types that can be converted (notably
Http2ClientStream's :status marshaller, which is particularly
wasteful).

Before:
Benchmark                              Mode     Cnt     Score    Error  Units
StatusBenchmark.codeDecode           sample  641278    88.889 ±  9.673  ns/op
StatusBenchmark.codeEncode           sample  430800    73.014 ±  1.444  ns/op
StatusBenchmark.messageDecodeEscape  sample  433467   441.078 ± 58.373  ns/op
StatusBenchmark.messageDecodePlain   sample  676526   268.620 ±  7.849  ns/op
StatusBenchmark.messageEncodeEscape  sample  547350  1211.243 ± 29.907  ns/op
StatusBenchmark.messageEncodePlain   sample  419318   223.263 ±  9.673  ns/op

After:
Benchmark                              Mode     Cnt    Score    Error  Units
StatusBenchmark.codeDecode           sample  442241   48.310 ±  2.409  ns/op
StatusBenchmark.codeEncode           sample  622026   35.475 ±  0.642  ns/op
StatusBenchmark.messageDecodeEscape  sample  595572  312.407 ± 15.870  ns/op
StatusBenchmark.messageDecodePlain   sample  565581   99.090 ±  8.799  ns/op
StatusBenchmark.messageEncodeEscape  sample  479147  201.422 ± 10.765  ns/op
StatusBenchmark.messageEncodePlain   sample  560957   94.722 ±  1.187  ns/op

Also fixes #2237

Before:
Result "unaryCall1024":
  mean = 155710.268 ±(99.9%) 149.278 ns/op

  Percentiles, ns/op:
      p(0.0000) =  63552.000 ns/op
     p(50.0000) = 151552.000 ns/op
     p(90.0000) = 188672.000 ns/op
     p(95.0000) = 207360.000 ns/op
     p(99.0000) = 260608.000 ns/op
     p(99.9000) = 358912.000 ns/op
     p(99.9900) = 1851425.792 ns/op
     p(99.9990) = 11161178.767 ns/op
     p(99.9999) = 14985005.383 ns/op
    p(100.0000) = 17235968.000 ns/op

Benchmark                         (direct)  (transport)    Mode      Cnt       Score     Error  Units
TransportBenchmark.unaryCall1024      true        NETTY  sample  3205966  155710.268 ± 149.278  ns/op

After:
Result "unaryCall1024":
  mean = 147474.794 ±(99.9%) 128.733 ns/op

  Percentiles, ns/op:
      p(0.0000) =  59520.000 ns/op
     p(50.0000) = 144640.000 ns/op
     p(90.0000) = 176128.000 ns/op
     p(95.0000) = 190464.000 ns/op
     p(99.0000) = 236544.000 ns/op
     p(99.9000) = 314880.000 ns/op
     p(99.9900) = 1113084.723 ns/op
     p(99.9990) = 10783126.979 ns/op
     p(99.9999) = 13887153.242 ns/op
    p(100.0000) = 15253504.000 ns/op

Benchmark                         (direct)  (transport)    Mode      Cnt       Score     Error  Units
TransportBenchmark.unaryCall1024      true        NETTY  sample  3385015  147474.794 ± 128.733  ns/op

Author: carl-mastrangelo

benchmarks/src/jmh/java/io/grpc/StatusBenchmark.java

@@ -0,0 +1,110 @@
+/*
+ * Copyright 2016, Google Inc. All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *    * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *    * Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following disclaimer
+ * in the documentation and/or other materials provided with the
+ * distribution.
+ *
+ *    * Neither the name of Google Inc. nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+package io.grpc;
+
+import org.openjdk.jmh.annotations.Benchmark;
+import org.openjdk.jmh.annotations.BenchmarkMode;
+import org.openjdk.jmh.annotations.Mode;
+import org.openjdk.jmh.annotations.OutputTimeUnit;
+import org.openjdk.jmh.annotations.Scope;
+import org.openjdk.jmh.annotations.State;
+
+import java.nio.charset.Charset;
+import java.util.concurrent.TimeUnit;
+
+/** StatusBenchmark. */
+@State(Scope.Benchmark)
+public class StatusBenchmark {
+
+  /**
+   * Javadoc comment.
+   */
+  @Benchmark
+  @BenchmarkMode(Mode.SampleTime)
+  @OutputTimeUnit(TimeUnit.NANOSECONDS)
+  public byte[] messageEncodePlain() {
+    return Status.MESSAGE_KEY.toBytes("Unexpected RST in stream");
+  }
+
+  /**
+   * Javadoc comment.
+   */
+  @Benchmark
+  @BenchmarkMode(Mode.SampleTime)
+  @OutputTimeUnit(TimeUnit.NANOSECONDS)
+  public byte[] messageEncodeEscape() {
+    return Status.MESSAGE_KEY.toBytes("Some Error\nWasabi and Horseradish are the same");
+  }
+
+  /**
+   * Javadoc comment.
+   */
+  @Benchmark
+  @BenchmarkMode(Mode.SampleTime)
+  @OutputTimeUnit(TimeUnit.NANOSECONDS)
+  public String messageDecodePlain() {
+    return Status.MESSAGE_KEY.parseBytes(
+        "Unexpected RST in stream".getBytes(Charset.forName("US-ASCII")));
+  }
+
+  /**
+   * Javadoc comment.
+   */
+  @Benchmark
+  @BenchmarkMode(Mode.SampleTime)
+  @OutputTimeUnit(TimeUnit.NANOSECONDS)
+  public String messageDecodeEscape() {
+    return Status.MESSAGE_KEY.parseBytes(
+        "Some Error%10Wasabi and Horseradish are the same".getBytes(Charset.forName("US-ASCII")));
+  }
+
+  /**
+   * Javadoc comment.
+   */
+  @Benchmark
+  @BenchmarkMode(Mode.SampleTime)
+  @OutputTimeUnit(TimeUnit.NANOSECONDS)
+  public byte[] codeEncode() {
+    return Status.CODE_KEY.toBytes(Status.DATA_LOSS);
+  }
+
+  /**
+   * Javadoc comment.
+   */
+  @Benchmark
+  @BenchmarkMode(Mode.SampleTime)
+  @OutputTimeUnit(TimeUnit.NANOSECONDS)
+  public Status codeDecode() {
+    return Status.CODE_KEY.parseBytes("15".getBytes(Charset.forName("US-ASCII")));
+  }
+}
+

core/src/main/java/io/grpc/InternalMetadata.java

@@ -0,0 +1,80 @@
+/*
+ * Copyright 2016, Google Inc. All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *    * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *    * Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following disclaimer
+ * in the documentation and/or other materials provided with the
+ * distribution.
+ *
+ *    * Neither the name of Google Inc. nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+package io.grpc;
+
+import io.grpc.Metadata.Key;
+
+import java.nio.charset.Charset;
+
+/**
+ * Internal {@link Metadata} accessor. This is intended for use by io.grpc.internal, and the
+ * specifically supported transport packages. If you *really* think you need to use this, contact
+ * the gRPC team first.
+ */
+@Internal
+public final class InternalMetadata {
+
+  /**
+   * A specialized plain ASCII marshaller. Both input and output are assumed to be valid header
+   * ASCII.
+   */
+  @Internal
+  public interface TrustedAsciiMarshaller<T> {
+    /**
+     * Serialize a metadata value to a ASCII string that contains only the characters listed in the
+     * class comment of {@link io.grpc.Metadata.AsciiMarshaller}. Otherwise the output may be
+     * considered invalid and discarded by the transport, or the call may fail.
+     *
+     * @param value to serialize
+     * @return serialized version of value, or null if value cannot be transmitted.
+     */
+    byte[] toAsciiString(T value);
+
+    /**
+     * Parse a serialized metadata value from an ASCII string.
+     *
+     * @param serialized value of metadata to parse
+     * @return a parsed instance of type T
+     */
+    T parseAsciiString(byte[] serialized);
+  }
+
+  /**
+   * Copy of StandardCharsets, which is only available on Java 1.7 and above.
+   */
+  public static final Charset US_ASCII = Charset.forName("US-ASCII");
+
+  @Internal
+  public static <T> Key<T> keyOf(String name, TrustedAsciiMarshaller<T> marshaller) {
+    return Metadata.Key.of(name, marshaller);
+  }
+}

core/src/main/java/io/grpc/Metadata.java

@@ -38,6 +38,8 @@
 import com.google.common.annotations.VisibleForTesting;
 import com.google.common.base.Preconditions;
 
+import io.grpc.InternalMetadata.TrustedAsciiMarshaller;
+
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.BitSet;
@@ -460,6 +462,10 @@ public static <T> Key<T> of(String name, AsciiMarshaller<T> marshaller) {
       return new AsciiKey<T>(name, marshaller);
     }
 
+    static <T> Key<T> of(String name, TrustedAsciiMarshaller<T> marshaller) {
+      return new TrustedAsciiKey<T>(name, marshaller);
+    }
+
     private final String originalName;
 
     private final String name;
@@ -603,7 +609,7 @@ private AsciiKey(String name, AsciiMarshaller<T> marshaller) {
       super(name);
       Preconditions.checkArgument(
           !name.endsWith(BINARY_HEADER_SUFFIX),
-          "ASCII header is named %s. It must not end with %s",
+          "ASCII header is named %s.  Only binary headers may end with %s",
           name, BINARY_HEADER_SUFFIX);
       this.marshaller = Preconditions.checkNotNull(marshaller, "marshaller");
     }
@@ -619,6 +625,32 @@ T parseBytes(byte[] serialized) {
     }
   }
 
+  private static final class TrustedAsciiKey<T> extends Key<T> {
+    private final TrustedAsciiMarshaller<T> marshaller;
+
+    /**
+     * Keys have a name and an ASCII marshaller used for serialization.
+     */
+    private TrustedAsciiKey(String name, TrustedAsciiMarshaller<T> marshaller) {
+      super(name);
+      Preconditions.checkArgument(
+          !name.endsWith(BINARY_HEADER_SUFFIX),
+          "ASCII header is named %s.  Only binary headers may end with %s",
+          name, BINARY_HEADER_SUFFIX);
+      this.marshaller = Preconditions.checkNotNull(marshaller, "marshaller");
+    }
+
+    @Override
+    byte[] toBytes(T value) {
+      return marshaller.toAsciiString(value);
+    }
+
+    @Override
+    T parseBytes(byte[] serialized) {
+      return marshaller.parseAsciiString(serialized);
+    }
+  }
+
   private static class MetadataEntry {
     Object parsed;