DRAFT: Add support for grpc-web

This is a basic implementation of the grpc-web protocol over HTTP/2.

Do NOT use this as-is in production; it does not properly configure
HTTP access controls through CORS.

Unfortunately, some of the changes here are a bit at odds with the
current class structure:
- The Deframer is wrapped, but the code expects it *not* to be wrapped
  in some places
- The Framer uses Sink which we overwrite with custom implementations
  of framing (to implement Base64 encoding) and writeTrailers

It also also unclear to me under what circumstances headers may not be
written yet when trailers are sent.

Also note that this *DOES NOT* add support for grpc-web over HTTP/1.1.

Related to grpc#4823.

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

@@ -244,7 +244,7 @@ protected TransportState(
         int maxMessageSize,
         StatsTraceContext statsTraceCtx,
         TransportTracer transportTracer) {
-      super(maxMessageSize, statsTraceCtx, transportTracer);
+      super(maxMessageSize, statsTraceCtx, transportTracer, Protocol.GRPC);
       this.statsTraceCtx = checkNotNull(statsTraceCtx, "statsTraceCtx");
     }
 

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

@@ -171,7 +171,7 @@ public StatsTraceContext statsTraceContext() {
   }
 
   /**
-   * This should only called from the transport thread (except for private interactions with
+   * This should only be called from the transport thread (except for private interactions with
    * {@code AbstractServerStream}).
    */
   protected abstract static class TransportState extends AbstractStream.TransportState {
@@ -191,11 +191,13 @@ protected abstract static class TransportState extends AbstractStream.TransportS
     protected TransportState(
         int maxMessageSize,
         StatsTraceContext statsTraceCtx,
-        TransportTracer transportTracer) {
+        TransportTracer transportTracer,
+        Protocol protocol) {
       super(
           maxMessageSize,
           statsTraceCtx,
-          Preconditions.checkNotNull(transportTracer, "transportTracer"));
+          Preconditions.checkNotNull(transportTracer, "transportTracer"),
+          protocol);
       this.statsTraceCtx = Preconditions.checkNotNull(statsTraceCtx, "statsTraceCtx");
     }
 

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

@@ -148,7 +148,8 @@ public abstract static class TransportState
     protected TransportState(
         int maxMessageSize,
         StatsTraceContext statsTraceCtx,
-        TransportTracer transportTracer) {
+        TransportTracer transportTracer,
+        Protocol protocol) {
       this.statsTraceCtx = checkNotNull(statsTraceCtx, "statsTraceCtx");
       this.transportTracer = checkNotNull(transportTracer, "transportTracer");
       rawDeframer = new MessageDeframer(
@@ -158,7 +159,7 @@ protected TransportState(
           statsTraceCtx,
           transportTracer);
       // TODO(#7168): use MigratingThreadDeframer when enabling retry doesn't break.
-      deframer = rawDeframer;
+      deframer = protocol == Protocol.GRPC_WEB_TEXT ? new Base64Deframer(rawDeframer) : rawDeframer;
     }
 
     final void optimizeForDirectExecutor() {
@@ -168,6 +169,7 @@ final void optimizeForDirectExecutor() {
 
     protected void setFullStreamDecompressor(GzipInflatingBuffer fullStreamDecompressor) {
       rawDeframer.setFullStreamDecompressor(fullStreamDecompressor);
+      // TODO: Do we need to rewrap with Base64Deframer?
       deframer = new ApplicationThreadDeframer(this, this, rawDeframer);
     }
 

core/src/main/java/io/grpc/internal/Base64Deframer.java

@@ -0,0 +1,66 @@
+/*
+ * Copyright 2021 The gRPC Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package io.grpc.internal;
+
+import io.grpc.Decompressor;
+import java.util.Base64;
+
+public class Base64Deframer implements Deframer {
+  private final Deframer delegate;
+
+  public Base64Deframer(Deframer delegate) {
+    this.delegate = delegate;
+  }
+
+  @Override
+  public void setMaxInboundMessageSize(int messageSize) {
+    delegate.setMaxInboundMessageSize(messageSize);
+  }
+
+  @Override
+  public void setDecompressor(Decompressor decompressor) {
+    delegate.setDecompressor(decompressor);
+  }
+
+  @Override
+  public void setFullStreamDecompressor(GzipInflatingBuffer fullStreamDecompressor) {
+    delegate.setFullStreamDecompressor(fullStreamDecompressor);
+  }
+
+  @Override
+  public void request(int numMessages) {
+    delegate.request(numMessages);
+  }
+
+  @Override
+  public void deframe(ReadableBuffer data) {
+    // TODO: Make this more efficient.
+    byte[] decoded = Base64.getDecoder().decode(ReadableBuffers.readArray(data));
+    data.close();
+    delegate.deframe(ReadableBuffers.wrap(decoded));
+  }
+
+  @Override
+  public void closeWhenComplete() {
+    delegate.closeWhenComplete();
+  }
+
+  @Override
+  public void close() {
+    delegate.close();
+  }
+}

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

@@ -149,6 +149,10 @@ public byte[] parseAsciiString(byte[] serialized) {
    */
   public static final String CONTENT_TYPE_GRPC = "application/grpc";
 
+  public static final String CONTENT_TYPE_GRPC_WEB = "application/grpc-web";
+  public static final String CONTENT_TYPE_GRPC_WEB_TEXT = "application/grpc-web-text";
+  public static final String CONTENT_TYPE_GRPC_WEB_TEXT_PROTO = "application/grpc-web-text+proto";
+
   /**
    * The HTTP method used for GRPC requests.
    */
@@ -432,6 +436,14 @@ public static boolean isGrpcContentType(String contentType) {
     return nextChar == '+' || nextChar == ';';
   }
 
+  public static boolean isGrpcWebContentType(String contentType) {
+    if (contentType == null) {
+      return false;
+    }
+    // TODO: Also support grpc-web, grpc-web+proto, and grpc-web-text+proto.
+    return CONTENT_TYPE_GRPC_WEB_TEXT.equals(contentType.toLowerCase());
+  }
+
   /**
    * Gets the User-Agent string for the gRPC transport.
    */

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

@@ -0,0 +1,22 @@
+/*
+ * Copyright 2021 The gRPC Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package io.grpc.internal;
+
+public enum Protocol {
+  GRPC,
+  GRPC_WEB_TEXT;
+}

netty/src/main/java/io/grpc/netty/GrpcHttp2OutboundHeaders.java

@@ -16,6 +16,7 @@
 
 package io.grpc.netty;
 
+import io.grpc.internal.Protocol;
 import io.netty.handler.codec.http2.Http2Headers;
 import io.netty.util.AsciiString;
 import java.util.Iterator;
@@ -46,11 +47,22 @@ static GrpcHttp2OutboundHeaders clientRequestHeaders(byte[][] serializedMetadata
     return new GrpcHttp2OutboundHeaders(preHeaders, serializedMetadata);
   }
 
-  static GrpcHttp2OutboundHeaders serverResponseHeaders(byte[][] serializedMetadata) {
-    AsciiString[] preHeaders = new AsciiString[] {
-        Http2Headers.PseudoHeaderName.STATUS.value(), Utils.STATUS_OK,
-        Utils.CONTENT_TYPE_HEADER, Utils.CONTENT_TYPE_GRPC,
-    };
+  static GrpcHttp2OutboundHeaders serverResponseHeaders(byte[][] serializedMetadata,
+      Protocol protocol) {
+    AsciiString[] preHeaders;
+    if (protocol == Protocol.GRPC) {
+      preHeaders = new AsciiString[] {
+          Http2Headers.PseudoHeaderName.STATUS.value(), Utils.STATUS_OK,
+          Utils.CONTENT_TYPE_HEADER, Utils.CONTENT_TYPE_GRPC,
+      };
+    } else {
+      // TODO: Add CORS headers!
+      preHeaders =
+          new AsciiString[] {
+            Http2Headers.PseudoHeaderName.STATUS.value(), Utils.STATUS_OK,
+            Utils.CONTENT_TYPE_HEADER, Utils.CONTENT_TYPE_GRPC_WEB_TEXT_PROTO,
+          };
+    }
     return new GrpcHttp2OutboundHeaders(preHeaders, serializedMetadata);
   }
 

netty/src/main/java/io/grpc/netty/NettyServerHandler.java

@@ -43,6 +43,7 @@
 import io.grpc.internal.GrpcUtil;
 import io.grpc.internal.KeepAliveManager;
 import io.grpc.internal.LogExceptionRunnable;
+import io.grpc.internal.Protocol;
 import io.grpc.internal.ServerTransportListener;
 import io.grpc.internal.StatsTraceContext;
 import io.grpc.internal.TransportTracer;
@@ -417,19 +418,23 @@ private void onHeadersRead(ChannelHandlerContext ctx, int streamId, Http2Headers
         return;
       }
       String contentTypeString = contentType.toString();
-      if (!GrpcUtil.isGrpcContentType(contentTypeString)) {
+      boolean isGrpcWeb = GrpcUtil.isGrpcWebContentType(contentTypeString);
+      if (!isGrpcWeb && !GrpcUtil.isGrpcContentType(contentTypeString)) {
         respondWithHttpError(ctx, streamId, 415, Status.Code.INTERNAL,
             String.format("Content-Type '%s' is not supported", contentTypeString));
         return;
       }
+      Protocol protocol = isGrpcWeb ? Protocol.GRPC_WEB_TEXT : Protocol.GRPC;
 
       if (!HTTP_METHOD.contentEquals(headers.method())) {
         respondWithHttpError(ctx, streamId, 405, Status.Code.INTERNAL,
             String.format("Method '%s' is not supported", headers.method()));
         return;
       }
 
-      if (!teWarningLogged && !TE_TRAILERS.contentEquals(headers.get(TE_HEADER))) {
+      if ((protocol == Protocol.GRPC)
+          && !teWarningLogged
+          && !TE_TRAILERS.contentEquals(headers.get(TE_HEADER))) {
         logger.warning(String.format("Expected header TE: %s, but %s is received. This means "
                 + "some intermediate proxy may not support trailers",
             TE_TRAILERS, headers.get(TE_HEADER)));
@@ -451,7 +456,8 @@ private void onHeadersRead(ChannelHandlerContext ctx, int streamId, Http2Headers
           maxMessageSize,
           statsTraceCtx,
           transportTracer,
-          method);
+          method,
+          protocol);
 
       PerfMark.startTask("NettyServerHandler.onHeadersRead", state.tag());
       try {
@@ -462,7 +468,8 @@ private void onHeadersRead(ChannelHandlerContext ctx, int streamId, Http2Headers
             attributes,
             authority,
             statsTraceCtx,
-            transportTracer);
+            transportTracer,
+            protocol);
         transportListener.streamCreated(stream, method, metadata);
         state.onStreamAllocated();
         http2Stream.setProperty(streamKey, state);