core: Emit bin-headers with unpadded encoding

Following the [grpc PROTOCOL-HTTP2 spec](https://github.com/grpc/grpc/blob/master/doc/PROTOCOL-HTTP2.md)
"Note that HTTP2 does not allow arbitrary octet sequences for header values so binary header values must be encoded using Base64 as per https://tools.ietf.org/html/rfc4648#section-4. Implementations MUST accept padded and un-padded values and should emit un-padded values. "

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

@@ -16,6 +16,7 @@
 
 package io.grpc;
 
+import com.google.common.io.BaseEncoding;
 import io.grpc.Metadata.AsciiMarshaller;
 import io.grpc.Metadata.Key;
 import java.nio.charset.Charset;
@@ -43,6 +44,13 @@ public final class InternalMetadata {
   @Internal
   public static final Charset US_ASCII = Charset.forName("US-ASCII");
 
+  /**
+   * An instance of base64 encoder that omits padding.
+   */
+  @Internal
+  public static final BaseEncoding BASE64_ENCODING_OMIT_PADDING
+      = Metadata.BASE64_ENCODING_OMIT_PADDING;
+
   @Internal
   public static <T> Key<T> keyOf(String name, TrustedAsciiMarshaller<T> marshaller) {
     boolean isPseudo = name != null && !name.isEmpty() && name.charAt(0) == ':';

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

@@ -104,6 +104,8 @@ public final class Metadata {
         }
       };
 
+  static final BaseEncoding BASE64_ENCODING_OMIT_PADDING = BaseEncoding.base64().omitPadding();
+
   /**
    * Constructor called by the transport layer when it receives binary metadata. Metadata will
    * mutate the passed in array.
@@ -466,7 +468,7 @@ public final class Metadata {
       String headerName = new String(name(i), US_ASCII);
       sb.append(headerName).append('=');
       if (headerName.endsWith(BINARY_HEADER_SUFFIX)) {
-        sb.append(BaseEncoding.base64().encode(value(i)));
+        sb.append(BASE64_ENCODING_OMIT_PADDING.encode(value(i)));
       } else {
         String headerValue = new String(value(i), US_ASCII);
         sb.append(headerValue);

core/src/main/java/io/grpc/internal/TransportFrameUtil.java

@@ -61,7 +61,8 @@ public final class TransportFrameUtil {
       if (endsWith(key, binaryHeaderSuffixBytes)) {
         // Binary header.
         serializedHeaders[k] = key;
-        serializedHeaders[k + 1] = BaseEncoding.base64().encode(value).getBytes(US_ASCII);
+        serializedHeaders[k + 1]
+            = InternalMetadata.BASE64_ENCODING_OMIT_PADDING.encode(value).getBytes(US_ASCII);
         k += 2;
       } else {
         // Non-binary header.

core/src/test/java/io/grpc/internal/TransportFrameUtilTest.java

@@ -140,7 +140,7 @@ public class TransportFrameUtilTest {
   }
 
   private static byte[] base64Encode(byte[] input) {
-    return BaseEncoding.base64().encode(input).getBytes(US_ASCII);
+    return InternalMetadata.BASE64_ENCODING_OMIT_PADDING.encode(input).getBytes(US_ASCII);
   }
 
 }

netty/src/test/java/io/grpc/netty/GrpcHttp2InboundHeadersTest.java

@@ -16,12 +16,12 @@
 
 package io.grpc.netty;
 
+import static io.grpc.InternalMetadata.BASE64_ENCODING_OMIT_PADDING;
 import static io.netty.util.AsciiString.of;
 import static junit.framework.TestCase.assertNotSame;
 import static org.junit.Assert.assertArrayEquals;
 import static org.junit.Assert.assertEquals;
 
-import com.google.common.io.BaseEncoding;
 import io.grpc.netty.GrpcHttp2HeadersUtils.GrpcHttp2InboundHeaders;
 import io.grpc.netty.GrpcHttp2HeadersUtils.GrpcHttp2RequestHeaders;
 import io.grpc.netty.GrpcHttp2HeadersUtils.GrpcHttp2ResponseHeaders;
@@ -69,7 +69,7 @@ public class GrpcHttp2InboundHeadersTest {
 
     byte[] data = new byte[100];
     new Random().nextBytes(data);
-    headers.add(of("foo-bin"), of(BaseEncoding.base64().encode(data)));
+    headers.add(of("foo-bin"), of(BASE64_ENCODING_OMIT_PADDING.encode(data)));
 
     assertEquals(1, headers.size());