HTTP/2 Headers Code Using String instead of AsciiString

Motivation:
The HTTP/2 headers code should be using binary string (currently AsciiString) objects instead of String objects. The DefaultHttp2HeadersEncoder was still using String for sensitiveHeaders.

Modifications:
- Remove the usage of String from DefaultHttp2HeadersEncoder.
- Introduce an interface to determine if a header name/value is sensitive or not to 1. prevent necessarily creating/copying sets. 2. Allow the name/value to be considered when checking if sensitive.

Result:
No more String in DefaultHttp2HeadersEncoder and less required set creation/operations.

codec-http2/src/main/java/io/netty/handler/codec/http2/DefaultHttp2HeadersEncoder.java

@@ -16,10 +16,11 @@
 package io.netty.handler.codec.http2;
 
 import static io.netty.handler.codec.http2.Http2CodecUtil.DEFAULT_HEADER_TABLE_SIZE;
-import static io.netty.handler.codec.http2.Http2Error.INTERNAL_ERROR;
 import static io.netty.handler.codec.http2.Http2Error.COMPRESSION_ERROR;
+import static io.netty.handler.codec.http2.Http2Error.INTERNAL_ERROR;
 import static io.netty.handler.codec.http2.Http2Error.PROTOCOL_ERROR;
 import static io.netty.handler.codec.http2.Http2Exception.connectionError;
+import static io.netty.util.internal.ObjectUtil.checkNotNull;
 import io.netty.buffer.ByteBuf;
 import io.netty.buffer.ByteBufOutputStream;
 import io.netty.handler.codec.AsciiString;
@@ -28,26 +29,23 @@
 import java.io.ByteArrayOutputStream;
 import java.io.IOException;
 import java.io.OutputStream;
-import java.util.Collections;
 import java.util.Map.Entry;
-import java.util.Set;
-import java.util.TreeSet;
 
 import com.twitter.hpack.Encoder;
 
 public class DefaultHttp2HeadersEncoder implements Http2HeadersEncoder, Http2HeadersEncoder.Configuration {
     private final Encoder encoder;
     private final ByteArrayOutputStream tableSizeChangeOutput = new ByteArrayOutputStream();
-    private final Set<String> sensitiveHeaders = new TreeSet<String>(String.CASE_INSENSITIVE_ORDER);
+    private final SensitivityDetector sensitivityDetector;
     private final Http2HeaderTable headerTable;
 
     public DefaultHttp2HeadersEncoder() {
-        this(DEFAULT_HEADER_TABLE_SIZE, Collections.<String>emptySet());
+        this(DEFAULT_HEADER_TABLE_SIZE, NEVER_SENSITIVE);
     }
 
-    public DefaultHttp2HeadersEncoder(int maxHeaderTableSize, Set<String> sensitiveHeaders) {
+    public DefaultHttp2HeadersEncoder(int maxHeaderTableSize, SensitivityDetector sensitivityDetector) {
+        this.sensitivityDetector = checkNotNull(sensitivityDetector, "sensitiveDetector");
         encoder = new Encoder(maxHeaderTableSize);
-        this.sensitiveHeaders.addAll(sensitiveHeaders);
         headerTable = new Http2HeaderTableEncoder();
     }
 
@@ -111,8 +109,7 @@ public Configuration configuration() {
     }
 
     private void encodeHeader(AsciiString key, AsciiString value, OutputStream stream) throws IOException {
-        boolean sensitive = sensitiveHeaders.contains(key.toString());
-        encoder.encodeHeader(stream, key.array(), value.array(), sensitive);
+        encoder.encodeHeader(stream, key.array(), value.array(), sensitivityDetector.isSensitive(key, value));
     }
 
     /**

codec-http2/src/main/java/io/netty/handler/codec/http2/Http2HeadersEncoder.java

@@ -16,6 +16,7 @@
 package io.netty.handler.codec.http2;
 
 import io.netty.buffer.ByteBuf;
+import io.netty.handler.codec.AsciiString;
 
 /**
  * Encodes {@link Http2Headers} into HPACK-encoded headers blocks.
@@ -31,6 +32,24 @@ interface Configuration {
         Http2HeaderTable headerTable();
     }
 
+    /**
+     * Determine if a header name/value pair is treated as
+     * <a href="http://tools.ietf.org/html/draft-ietf-httpbis-header-compression-12#section-7.1.3">sensitive</a>.
+     * If the object can be dynamically modified and shared across multiple connections it may need to be thread safe.
+     */
+    interface SensitivityDetector {
+        /**
+         * Determine if a header {@code name}/{@code value} pair should be treated as
+         * <a href="http://tools.ietf.org/html/draft-ietf-httpbis-header-compression-12#section-7.1.3">sensitive</a>.
+         * @param name The name for the header.
+         * @param value The value of the header.
+         * @return {@code true} if a header {@code name}/{@code value} pair should be treated as
+         * <a href="http://tools.ietf.org/html/draft-ietf-httpbis-header-compression-12#section-7.1.3">sensitive</a>.
+         * {@code false} otherwise.
+         */
+        boolean isSensitive(AsciiString name, AsciiString value);
+    }
+
     /**
      * Encodes the given headers and writes the output headers block to the given output buffer.
      *
@@ -43,4 +62,14 @@ interface Configuration {
      * Get the {@link Configuration} for this {@link Http2HeadersEncoder}
      */
     Configuration configuration();
+
+    /**
+     * Always return {@code false} for {@link SensitivityDetector#isSensitive(AsciiString, AsciiString)}.
+     */
+    SensitivityDetector NEVER_SENSITIVE = new SensitivityDetector() {
+        @Override
+        public boolean isSensitive(AsciiString name, AsciiString value) {
+            return false;
+        }
+    };
 }