Http/2 Priority on CLOSED stream

Motivation:
The encoder/decoder currently do not handle streams which have previously existed but no longer exist because they were closed. The specification requires supporting this.

Modifications:
- encoder/decoder should tolerate the frame or the dependent frame not existing in the streams map due to the fact that it may have previously existed.

Result:
encoder/decoder are more compliant with the specification.

codec-http2/src/main/java/io/netty/handler/codec/http2/DefaultHttp2Connection.java

@@ -22,6 +22,7 @@
 import static io.netty.handler.codec.http2.Http2CodecUtil.immediateRemovalPolicy;
 import static io.netty.handler.codec.http2.Http2Error.PROTOCOL_ERROR;
 import static io.netty.handler.codec.http2.Http2Error.REFUSED_STREAM;
+import static io.netty.handler.codec.http2.Http2Exception.closedStreamError;
 import static io.netty.handler.codec.http2.Http2Exception.connectionError;
 import static io.netty.handler.codec.http2.Http2Exception.streamError;
 import static io.netty.handler.codec.http2.Http2Stream.State.CLOSED;
@@ -689,8 +690,7 @@ private final class DefaultEndpoint<F extends Http2FlowController> implements En
 
         @Override
         public int nextStreamId() {
-            // For manually created client-side streams, 1 is reserved for HTTP upgrade, so
-            // start at 3.
+            // For manually created client-side streams, 1 is reserved for HTTP upgrade, so start at 3.
             return nextStreamId > 1 ? nextStreamId : nextStreamId + 2;
         }
 
@@ -836,24 +836,22 @@ private void checkNewStreamAllowed(int streamId) throws Http2Exception {
             if (isGoAway()) {
                 throw connectionError(PROTOCOL_ERROR, "Cannot create a stream since the connection is going away");
             }
-            verifyStreamId(streamId);
-            if (!canCreateStream()) {
-                throw connectionError(REFUSED_STREAM, "Maximum streams exceeded for this endpoint.");
-            }
-        }
-
-        private void verifyStreamId(int streamId) throws Http2Exception {
             if (streamId < 0) {
                 throw new Http2NoMoreStreamIdsException();
             }
-            if (streamId < nextStreamId) {
-                throw connectionError(PROTOCOL_ERROR, "Request stream %d is behind the next expected stream %d",
-                        streamId, nextStreamId);
-            }
             if (!createdStreamId(streamId)) {
                 throw connectionError(PROTOCOL_ERROR, "Request stream %d is not correct for %s connection",
                         streamId, server ? "server" : "client");
             }
+            // This check must be after all id validated checks, but before the max streams check because it may be
+            // recoverable to some degree for handling frames which can be sent on closed streams.
+            if (streamId < nextStreamId) {
+                throw closedStreamError(PROTOCOL_ERROR, "Request stream %d is behind the next expected stream %d",
+                        streamId, nextStreamId);
+            }
+            if (!canCreateStream()) {
+                throw connectionError(REFUSED_STREAM, "Maximum streams exceeded for this endpoint.");
+            }
         }
 
         private boolean isLocal() {

codec-http2/src/main/java/io/netty/handler/codec/http2/DefaultHttp2ConnectionDecoder.java

@@ -24,6 +24,7 @@
 import static io.netty.util.internal.ObjectUtil.checkNotNull;
 import io.netty.buffer.ByteBuf;
 import io.netty.channel.ChannelHandlerContext;
+import io.netty.handler.codec.http2.Http2Exception.ClosedStreamCreationException;
 
 import java.util.List;
 
@@ -374,15 +375,20 @@ public void onPriorityRead(ChannelHandlerContext ctx, int streamId, int streamDe
                 return;
             }
 
-            if (stream == null) {
-                // PRIORITY frames always identify a stream. This means that if a PRIORITY frame is the
-                // first frame to be received for a stream that we must create the stream.
-                stream = connection.remote().createStream(streamId);
-            }
+            try {
+                if (stream == null) {
+                    // PRIORITY frames always identify a stream. This means that if a PRIORITY frame is the
+                    // first frame to be received for a stream that we must create the stream.
+                    stream = connection.remote().createStream(streamId);
+                }
 
-            // This call will create a stream for streamDependency if necessary.
-            // For this reason it must be done before notifying the listener.
-            stream.setPriority(streamDependency, weight, exclusive);
+                // This call will create a stream for streamDependency if necessary.
+                // For this reason it must be done before notifying the listener.
+                stream.setPriority(streamDependency, weight, exclusive);
+            } catch (ClosedStreamCreationException ignored) {
+                // It is possible that either the stream for this frame or the parent stream is closed.
+                // In this case we should ignore the exception and allow the frame to be sent.
+            }
 
             listener.onPriorityRead(ctx, streamId, streamDependency, weight, exclusive);
         }

codec-http2/src/main/java/io/netty/handler/codec/http2/DefaultHttp2ConnectionEncoder.java

@@ -24,6 +24,7 @@
 import io.netty.channel.ChannelFutureListener;
 import io.netty.channel.ChannelHandlerContext;
 import io.netty.channel.ChannelPromise;
+import io.netty.handler.codec.http2.Http2Exception.ClosedStreamCreationException;
 import io.netty.util.ReferenceCountUtil;
 
 import java.util.ArrayDeque;
@@ -238,9 +239,14 @@ public ChannelFuture writePriority(ChannelHandlerContext ctx, int streamId, int
                 stream = connection.local().createStream(streamId);
             }
 
+            // The set priority operation must be done before sending the frame. The parent may not yet exist
+            // and the priority tree may also be modified before sending.
             stream.setPriority(streamDependency, weight, exclusive);
-        } catch (Throwable e) {
-            return promise.setFailure(e);
+        } catch (ClosedStreamCreationException ignored) {
+            // It is possible that either the stream for this frame or the parent stream is closed.
+            // In this case we should ignore the exception and allow the frame to be sent.
+        } catch (Throwable t) {
+            return promise.setFailure(t);
         }
 
         ChannelFuture future = frameWriter.writePriority(ctx, streamId, streamDependency, weight, exclusive, promise);

codec-http2/src/main/java/io/netty/handler/codec/http2/Http2Exception.java

@@ -72,6 +72,18 @@ public static Http2Exception connectionError(Http2Error error, Throwable cause,
         return new Http2Exception(error, String.format(fmt, args), cause);
     }
 
+    /**
+     * Use if an error has occurred which can not be isolated to a single stream, but instead applies
+     * to the entire connection.
+     * @param error The type of error as defined by the HTTP/2 specification.
+     * @param fmt String with the content and format for the additional debug data.
+     * @param args Objects which fit into the format defined by {@code fmt}.
+     * @return An exception which can be translated into a HTTP/2 error.
+     */
+    public static Http2Exception closedStreamError(Http2Error error, String fmt, Object... args) {
+        return new ClosedStreamCreationException(error, String.format(fmt, args));
+    }
+
     /**
      * Use if an error which can be isolated to a single stream has occurred.  If the {@code id} is not
      * {@link Http2CodecUtil#CONNECTION_STREAM_ID} then a {@link Http2Exception.StreamException} will be returned.
@@ -130,6 +142,25 @@ public static int streamId(Http2Exception e) {
         return isStreamError(e) ? ((StreamException) e).streamId() : CONNECTION_STREAM_ID;
     }
 
+    /**
+     * Used when a stream creation attempt fails but may be because the stream was previously closed.
+     */
+    public static final class ClosedStreamCreationException extends Http2Exception {
+        private static final long serialVersionUID = -1911637707391622439L;
+
+        public ClosedStreamCreationException(Http2Error error) {
+            super(error);
+        }
+
+        public ClosedStreamCreationException(Http2Error error, String message) {
+            super(error, message);
+        }
+
+        public ClosedStreamCreationException(Http2Error error, String message, Throwable cause) {
+            super(error, message, cause);
+        }
+    }
+
     /**
      * Represents an exception that can be isolated to a single stream (as opposed to the entire connection).
      */

codec-http2/src/main/java/io/netty/handler/codec/http2/Http2FrameListener.java

@@ -46,10 +46,10 @@ int onDataRead(ChannelHandlerContext ctx, int streamId, ByteBuf data, int paddin
             boolean endOfStream) throws Http2Exception;
 
     /**
-     * Handles an inbound HEADERS frame.
+     * Handles an inbound {@code HEADERS} frame.
      * <p>
-     * Only one of the following methods will be called for each HEADERS frame sequence.
-     * One will be called when the END_HEADERS flag has been received.
+     * Only one of the following methods will be called for each {@code HEADERS} frame sequence.
+     * One will be called when the {@code END_HEADERS} flag has been received.
      * <ul>
      * <li>{@link #onHeadersRead(ChannelHandlerContext, int, Http2Headers, int, boolean)}</li>
      * <li>{@link #onHeadersRead(ChannelHandlerContext, int, Http2Headers, int, short, boolean, int, boolean)}</li>
@@ -70,11 +70,11 @@ void onHeadersRead(ChannelHandlerContext ctx, int streamId, Http2Headers headers
             boolean endOfStream) throws Http2Exception;
 
     /**
-     * Handles an inbound HEADERS frame with priority information specified. Only called if END_HEADERS encountered.
-     *
+     * Handles an inbound {@code HEADERS} frame with priority information specified.
+     * Only called if {@code END_HEADERS} encountered.
      * <p>
-     * Only one of the following methods will be called for each HEADERS frame sequence.
-     * One will be called when the END_HEADERS flag has been received.
+     * Only one of the following methods will be called for each {@code HEADERS} frame sequence.
+     * One will be called when the {@code END_HEADERS} flag has been received.
      * <ul>
      * <li>{@link #onHeadersRead(ChannelHandlerContext, int, Http2Headers, int, boolean)}</li>
      * <li>{@link #onHeadersRead(ChannelHandlerContext, int, Http2Headers, int, short, boolean, int, boolean)}</li>
@@ -100,7 +100,11 @@ void onHeadersRead(ChannelHandlerContext ctx, int streamId, Http2Headers headers
             throws Http2Exception;
 
     /**
-     * Handles an inbound PRIORITY frame.
+     * Handles an inbound {@code PRIORITY} frame.
+     * <p>
+     * Note that is it possible to have this method called and no stream object exist for either
+     * {@code streamId}, {@code streamDependency}, or both. This is because the {@code PRIORITY} frame can be
+     * sent/received when streams are in the {@code CLOSED} state.
      *
      * @param ctx the context from the handler where the frame was read.
      * @param streamId the subject stream for the frame.
@@ -113,7 +117,7 @@ void onPriorityRead(ChannelHandlerContext ctx, int streamId, int streamDependenc
             short weight, boolean exclusive) throws Http2Exception;
 
     /**
-     * Handles an inbound RST_STREAM frame.
+     * Handles an inbound {@code RST_STREAM} frame.
      *
      * @param ctx the context from the handler where the frame was read.
      * @param streamId the stream that is terminating.
@@ -122,21 +126,21 @@ void onPriorityRead(ChannelHandlerContext ctx, int streamId, int streamDependenc
     void onRstStreamRead(ChannelHandlerContext ctx, int streamId, long errorCode) throws Http2Exception;
 
     /**
-     * Handles an inbound SETTINGS acknowledgment frame.
+     * Handles an inbound {@code SETTINGS} acknowledgment frame.
      * @param ctx the context from the handler where the frame was read.
      */
     void onSettingsAckRead(ChannelHandlerContext ctx) throws Http2Exception;
 
     /**
-     * Handles an inbound SETTINGS frame.
+     * Handles an inbound {@code SETTINGS} frame.
      *
      * @param ctx the context from the handler where the frame was read.
      * @param settings the settings received from the remote endpoint.
      */
     void onSettingsRead(ChannelHandlerContext ctx, Http2Settings settings) throws Http2Exception;
 
     /**
-     * Handles an inbound PING frame.
+     * Handles an inbound {@code PING} frame.
      *
      * @param ctx the context from the handler where the frame was read.
      * @param data the payload of the frame. If this buffer needs to be retained by the listener
@@ -145,7 +149,7 @@ void onPriorityRead(ChannelHandlerContext ctx, int streamId, int streamDependenc
     void onPingRead(ChannelHandlerContext ctx, ByteBuf data) throws Http2Exception;
 
     /**
-     * Handles an inbound PING acknowledgment.
+     * Handles an inbound {@code PING} acknowledgment.
      *
      * @param ctx the context from the handler where the frame was read.
      * @param data the payload of the frame. If this buffer needs to be retained by the listener
@@ -154,13 +158,13 @@ void onPriorityRead(ChannelHandlerContext ctx, int streamId, int streamDependenc
     void onPingAckRead(ChannelHandlerContext ctx, ByteBuf data) throws Http2Exception;
 
     /**
-     * Handles an inbound PUSH_PROMISE frame. Only called if END_HEADERS encountered.
+     * Handles an inbound {@code PUSH_PROMISE} frame. Only called if {@code END_HEADERS} encountered.
      * <p>
      * Promised requests MUST be authoritative, cacheable, and safe.
      * See <a href="https://tools.ietf.org/html/draft-ietf-httpbis-http2-17#section-8.2">[RFC http2], Seciton 8.2</a>.
      * <p>
-     * Only one of the following methods will be called for each HEADERS frame sequence.
-     * One will be called when the END_HEADERS flag has been received.
+     * Only one of the following methods will be called for each {@code HEADERS} frame sequence.
+     * One will be called when the {@code END_HEADERS} flag has been received.
      * <ul>
      * <li>{@link #onHeadersRead(ChannelHandlerContext, int, Http2Headers, int, boolean)}</li>
      * <li>{@link #onHeadersRead(ChannelHandlerContext, int, Http2Headers, int, short, boolean, int, boolean)}</li>
@@ -180,7 +184,7 @@ void onPushPromiseRead(ChannelHandlerContext ctx, int streamId, int promisedStre
             Http2Headers headers, int padding) throws Http2Exception;
 
     /**
-     * Handles an inbound GO_AWAY frame.
+     * Handles an inbound {@code GO_AWAY} frame.
      *
      * @param ctx the context from the handler where the frame was read.
      * @param lastStreamId the last known stream of the remote endpoint.
@@ -192,7 +196,7 @@ void onGoAwayRead(ChannelHandlerContext ctx, int lastStreamId, long errorCode, B
             throws Http2Exception;
 
     /**
-     * Handles an inbound WINDOW_UPDATE frame.
+     * Handles an inbound {@code WINDOW_UPDATE} frame.
      *
      * @param ctx the context from the handler where the frame was read.
      * @param streamId the stream the frame was sent on.

codec-http2/src/test/java/io/netty/handler/codec/http2/DefaultHttp2ConnectionDecoderTest.java

@@ -45,6 +45,7 @@
 import io.netty.channel.ChannelHandlerContext;
 import io.netty.channel.ChannelPromise;
 import io.netty.channel.DefaultChannelPromise;
+import io.netty.handler.codec.http2.Http2Exception.ClosedStreamCreationException;
 
 import java.util.Collections;
 import java.util.concurrent.atomic.AtomicInteger;
@@ -379,6 +380,40 @@ public void priorityReadShouldSucceed() throws Exception {
         verify(stream, never()).open(anyBoolean());
     }
 
+    @Test
+    public void priorityReadOnPreviouslyExistingStreamShouldSucceed() throws Exception {
+        doAnswer(new Answer<Http2Stream>() {
+            @Override
+            public Http2Stream answer(InvocationOnMock in) throws Throwable {
+                throw new ClosedStreamCreationException(Http2Error.INTERNAL_ERROR);
+            }
+        }).when(remote).createStream(eq(STREAM_ID));
+        when(connection.stream(STREAM_ID)).thenReturn(null);
+        when(connection.requireStream(STREAM_ID)).thenReturn(null);
+        // Just return the stream object as the connection stream to ensure the dependent stream "exists"
+        when(connection.stream(0)).thenReturn(stream);
+        when(connection.requireStream(0)).thenReturn(stream);
+        decode().onPriorityRead(ctx, STREAM_ID, 0, (short) 255, true);
+        verify(stream, never()).setPriority(anyInt(), anyShort(), anyBoolean());
+        verify(listener).onPriorityRead(eq(ctx), eq(STREAM_ID), eq(0), eq((short) 255), eq(true));
+        verify(remote).createStream(STREAM_ID);
+    }
+
+    @Test
+    public void priorityReadOnPreviouslyParentExistingStreamShouldSucceed() throws Exception {
+        doAnswer(new Answer<Http2Stream>() {
+            @Override
+            public Http2Stream answer(InvocationOnMock in) throws Throwable {
+                throw new ClosedStreamCreationException(Http2Error.INTERNAL_ERROR);
+            }
+        }).when(stream).setPriority(eq(0), eq((short) 255), eq(true));
+        when(connection.stream(STREAM_ID)).thenReturn(stream);
+        when(connection.requireStream(STREAM_ID)).thenReturn(stream);
+        decode().onPriorityRead(ctx, STREAM_ID, 0, (short) 255, true);
+        verify(stream).setPriority(eq(0), eq((short) 255), eq(true));
+        verify(listener).onPriorityRead(eq(ctx), eq(STREAM_ID), eq(0), eq((short) 255), eq(true));
+    }
+
     @Test
     public void windowUpdateReadAfterGoAwayShouldBeIgnored() throws Exception {
         when(connection.goAwaySent()).thenReturn(true);