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// Copyright 2021 Google Inc. All rights reserved.
//
// 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 h2
import (
"bytes"
"fmt"
"golang.org/x/net/http2"
)
// queuedFrame stores frames that belong to a stream and need to be kept in order. The need for
// this stems from flow control needed in the context of gRPC. Since a gRPC message can be split
// over multiple DATA frames, the proxy needs to buffer such frames so they can be reassembled
// into messages and edited before being forwarded.
//
// Note that the proxy does man-in-the-middle flow control independently to each endpoint instead
// of forwarding endpoint flow-control messages to each other directly. This is necessary because
// multiple DATA frames need to be captured before they can be forwarded. While the data frames are
// being held in the proxy, the destination of those frames cannot see them to send WINDOW_UPDATE
// acknowledgements and the sender will stop sending data. So the proxy must emit its own
// WINDOW_UPDATEs.
//
// Example: While DATA frames are being output-buffered due to pending WINDOW_UPDATE frames from
// the destination, it's possible for the source to send subsequent HEADER frames. Those HEADER
// frames must be queued after the DATA frames for consistency with HTTP/2's total ordering of
// frames within a stream.
//
// While the example only illustrates the need for HEADER frame buffering, a similar argument
// applies to other types of stream frames. WINDOW_UPDATE is a special case that is associated
// with a stream but does not require buffering or special ordering. This is because WINDOW_UPDATEs
// are basically acknowledgements for messages coming from the peer endpoint. In other words,
// WINDOW_UPDATE frames are associated with messages being received instead of messages being sent.
// The asynchrony of receiving remote messages should allow reordering freedom.
type queuedFrame interface {
// StreamID is the stream ID for the frame.
StreamID() uint32
// flowControlSize returns the size of this frame for the purposes of flow control. It is only
// non-zero for DATA frames.
flowControlSize() int
// send writes the frame to the provided framer. This is not thread-safe and the caller should be
// holding appropriate locks.
send(*http2.Framer) error
}
type queuedDataFrame struct {
streamID uint32
endStream bool
data []byte
}
func (f *queuedDataFrame) StreamID() uint32 {
return f.streamID
}
func (f *queuedDataFrame) flowControlSize() int {
return len(f.data)
}
func (f *queuedDataFrame) send(dest *http2.Framer) error {
return dest.WriteData(f.streamID, f.endStream, f.data)
}
func (f *queuedDataFrame) String() string {
return fmt.Sprintf("data[id=%d, endStream=%t, len=%d]", f.streamID, f.endStream, len(f.data))
}
type queuedHeaderFrame struct {
streamID uint32
endStream bool
priority http2.PriorityParam
chunks [][]byte
}
func (f *queuedHeaderFrame) StreamID() uint32 {
return f.streamID
}
func (*queuedHeaderFrame) flowControlSize() int {
return 0
}
func (f *queuedHeaderFrame) send(dest *http2.Framer) error {
if err := dest.WriteHeaders(http2.HeadersFrameParam{
StreamID: f.streamID,
BlockFragment: f.chunks[0],
EndStream: f.endStream,
EndHeaders: len(f.chunks) <= 1,
PadLength: 0,
Priority: f.priority,
}); err != nil {
return fmt.Errorf("sending header %v: %w", f, err)
}
for i := 1; i < len(f.chunks); i++ {
headersEnded := i == len(f.chunks)-1
if err := dest.WriteContinuation(f.streamID, headersEnded, f.chunks[i]); err != nil {
return fmt.Errorf("sending header continuations %v: %w", f, err)
}
}
return nil
}
func (f *queuedHeaderFrame) String() string {
var buf bytes.Buffer // strings.Builder is not available on App Engine.
fmt.Fprintf(&buf, "header[id=%d, endStream=%t", f.streamID, f.endStream)
fmt.Fprintf(&buf, ", priority=%v, chunk lengths=[", f.priority)
for i, c := range f.chunks {
if i > 0 {
fmt.Fprintf(&buf, ",")
}
fmt.Fprintf(&buf, "%d", len(c))
}
fmt.Fprintf(&buf, "]]")
return buf.String()
}
type queuedPushPromiseFrame struct {
streamID uint32
promiseID uint32
chunks [][]byte
}
func (f *queuedPushPromiseFrame) StreamID() uint32 {
return f.streamID
}
func (*queuedPushPromiseFrame) flowControlSize() int {
return 0
}
func (f *queuedPushPromiseFrame) send(dest *http2.Framer) error {
if err := dest.WritePushPromise(http2.PushPromiseParam{
StreamID: f.streamID,
PromiseID: f.promiseID,
BlockFragment: f.chunks[0],
EndHeaders: len(f.chunks) <= 1,
PadLength: 0,
}); err != nil {
return fmt.Errorf("sending push promise %v: %w", f, err)
}
for i := 1; i < len(f.chunks); i++ {
headersEnded := i == len(f.chunks)-1
if err := dest.WriteContinuation(f.streamID, headersEnded, f.chunks[i]); err != nil {
return fmt.Errorf("sending push promise continuations %v: %w", f, err)
}
}
return nil
}
func (f *queuedPushPromiseFrame) String() string {
var buf bytes.Buffer
fmt.Fprintf(&buf, "push promise[streamID=%d, promiseID= %d", f.streamID, f.promiseID)
fmt.Fprintf(&buf, ", chunk lengths=[")
for i, c := range f.chunks {
if i > 0 {
fmt.Fprintf(&buf, ",")
}
fmt.Fprintf(&buf, "%d", len(c))
}
fmt.Fprintf(&buf, "]]")
return buf.String()
}
type queuedPriorityFrame struct {
streamID uint32
priority http2.PriorityParam
}
func (f *queuedPriorityFrame) StreamID() uint32 {
return f.streamID
}
func (*queuedPriorityFrame) flowControlSize() int {
return 0
}
func (f *queuedPriorityFrame) send(dest *http2.Framer) error {
if err := dest.WritePriority(f.streamID, f.priority); err != nil {
return fmt.Errorf("sending %v: %w", f, err)
}
return nil
}
func (f *queuedPriorityFrame) String() string {
return fmt.Sprintf("priority[id=%d, priority=%v]", f.streamID, f.priority)
}
type queuedRSTStreamFrame struct {
streamID uint32
errCode http2.ErrCode
}
func (f *queuedRSTStreamFrame) StreamID() uint32 {
return f.streamID
}
func (*queuedRSTStreamFrame) flowControlSize() int {
return 0
}
func (f *queuedRSTStreamFrame) send(dest *http2.Framer) error {
if err := dest.WriteRSTStream(f.streamID, f.errCode); err != nil {
return fmt.Errorf("sending %v: %w", f, err)
}
return nil
}
func (f *queuedRSTStreamFrame) String() string {
return fmt.Sprintf("RSTStream[id=%d, errCode=%v]", f.streamID, f.errCode)
}
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