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grpc.go
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grpc.go
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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 grpc contains gRPC functionality for Martian proxy.
package grpc
import (
"bytes"
"compress/flate"
"compress/gzip"
"encoding/binary"
"fmt"
"io/ioutil"
"net/url"
"sync/atomic"
"github.com/golang/snappy"
"github.com/zema1/martian/h2"
"golang.org/x/net/http2"
"golang.org/x/net/http2/hpack"
)
// Encoding is the grpc-encoding type. See Content-Coding entry at:
// https://github.com/grpc/grpc/blob/master/doc/PROTOCOL-HTTP2.md#requests
type Encoding uint8
const (
// Identity indicates that no compression is used.
Identity Encoding = iota
// Gzip indicates that Gzip compression is used.
Gzip
// Deflate indicates that Deflate compression is used.
Deflate
// Snappy indicates that Snappy compression is used.
Snappy
)
// ProcessorFactory creates gRPC processors that implement the Processor interface, which abstracts
// away some of the details of the underlying HTTP/2 protocol. A processor must forward
// invocations to the given `server` or `client` processors, which will arrange to have the data
// forwarded to the destination, with possible edits. Nil values are safe to return and no
// processing occurs in such cases. NOTE: an interface may have a non-nil type with a nil value.
// Such values are treated as valid processors.
type ProcessorFactory func(url *url.URL, server, client Processor) (Processor, Processor)
// AsStreamProcessorFactory converts a ProcessorFactory into a StreamProcessorFactory. It creates
// an adapter that abstracts HTTP/2 frames into a representation that is closer to gRPC.
func AsStreamProcessorFactory(f ProcessorFactory) h2.StreamProcessorFactory {
return func(url *url.URL, sinks *h2.Processors) (h2.Processor, h2.Processor) {
var cToS, sToC h2.Processor
// A grpc.Processor is translated into an h2.Processor in layers.
//
// adapter → processor → emitter → sink
// \_____________________________↗
//
// * The adapter wraps the grpc.Processor interface so that it conforms with h2.Processor. It
// performs some processing to translate HTTP/2 frames into gRPC concepts. Frames that are
// not relevant to gRPC are forwarded directly to the sink.
// * The processor is the gRPC processing logic provided by the client factory.
// * The emitter wraps an h2.Processor sink and translates the processed gRPC data into HTTP/2
// frames.
cToSEmitter := &emitter{sink: sinks.ForDirection(h2.ClientToServer)}
sToCEmitter := &emitter{sink: sinks.ForDirection(h2.ServerToClient)}
cToSProcessor, sToCProcessor := f(url, cToSEmitter, sToCEmitter)
// enabled indicates whether the stream should be processed as gRPC. It is shared between the
// the two adapters because its detection is on a client-to-server HEADER frame and the state
// applies bidirectionally.
enabled := int32(0)
if cToSProcessor != nil {
cToSEmitter.adapter = &adapter{
enabled: &enabled,
dir: h2.ClientToServer,
processor: cToSProcessor,
sink: sinks.ForDirection(h2.ClientToServer),
}
cToS = cToSEmitter.adapter
}
if sToCProcessor != nil {
sToCEmitter.adapter = &adapter{
enabled: &enabled,
dir: h2.ServerToClient,
processor: sToCProcessor,
sink: sinks.ForDirection(h2.ServerToClient),
}
sToC = sToCEmitter.adapter
}
return cToS, sToC
}
}
// Processor processes gRPC traffic.
type Processor interface {
h2.HeaderProcessor
// Message receives serialized messages.
Message(data []byte, streamEnded bool) error
}
// dataState represents one of two possible states when consuming gRPC DATA frames.
type dataState uint8
const (
readingMetadata dataState = iota
readingMessageData
)
// adapter wraps the Processor interface with an h2.Processor interface. It filters streams that
// are not gRPC and handles decompressing the message data.
type adapter struct {
enabled *int32
dir h2.Direction
processor Processor
sink h2.Processor
encoding Encoding
// State for the data interpreter.
buffer bytes.Buffer
state dataState
compressed bool
length uint32
}
func (a *adapter) Header(
headers []hpack.HeaderField,
streamEnded bool,
priority http2.PriorityParam,
) error {
if !a.isEnabled() {
for _, h := range headers {
if h.Name == "content-type" && h.Value == "application/grpc" {
atomic.StoreInt32(a.enabled, 1)
break
}
}
if !a.isEnabled() {
return a.sink.Header(headers, streamEnded, priority)
}
}
for _, h := range headers {
if h.Name == "grpc-encoding" {
switch h.Value {
case "identity":
a.encoding = Identity
case "gzip":
a.encoding = Gzip
case "deflate":
a.encoding = Deflate
case "snappy":
a.encoding = Snappy
default:
return fmt.Errorf("unrecognized grpc-encoding %s in %v", h.Value, headers)
}
}
}
return a.processor.Header(headers, streamEnded, priority)
}
func (a *adapter) Data(data []byte, streamEnded bool) error {
if !a.isEnabled() {
return a.sink.Data(data, streamEnded)
}
a.buffer.Write(data)
for {
switch a.state {
case readingMetadata:
if streamEnded && a.buffer.Len() == 0 {
// gRPC may send empty DATA frames to end a stream.
if err := a.processor.Message(nil, true); err != nil {
return err
}
}
if a.buffer.Len() < 5 {
return nil
}
compressed, _ := a.buffer.ReadByte()
a.compressed = compressed > 0
if err := binary.Read(&a.buffer, binary.BigEndian, &a.length); err != nil {
return fmt.Errorf("reading message length: %w", err)
}
a.state = readingMessageData
case readingMessageData:
if uint32(a.buffer.Len()) < a.length {
return nil
}
data := make([]byte, a.length)
a.buffer.Read(data)
if a.compressed {
switch a.encoding {
case Identity:
case Gzip:
var err error
data, err = gunzip(data)
if err != nil {
return fmt.Errorf("gunzipping data: %w", err)
}
case Deflate:
var err error
data, err = deflate(data)
if err != nil {
return fmt.Errorf("deflating data: %w", err)
}
case Snappy:
var err error
data, err = ioutil.ReadAll(snappy.NewReader(bytes.NewReader(data)))
if err != nil {
return fmt.Errorf("uncompressing snappy: %w", err)
}
default:
panic(fmt.Sprintf("unexpected enocding: %v", a.encoding))
}
}
a.state = readingMetadata
// Only marks stream ended for the message if there is no data remaining. For ease of
// implementation, this proxy aligns messages with data frames. This means that if a data
// frame with stream ended contains multiple messages, the earlier ones should not be
// marked with stream ended.
//
// As explained in https://github.com/grpc/grpc/blob/master/doc/PROTOCOL-HTTP2.md#data-frames,
// this reframing is safe because gRPC implementations won't be making any assumptions about
// the framing.
if err := a.processor.Message(data, streamEnded && a.buffer.Len() == 0); err != nil {
return err
}
default:
panic(fmt.Sprintf("unexpected state: %v", a.state))
}
if a.buffer.Len() == 0 {
return nil
}
}
}
func (a *adapter) Priority(priority http2.PriorityParam) error {
return a.sink.Priority(priority)
}
func (a *adapter) RSTStream(errCode http2.ErrCode) error {
return a.sink.RSTStream(errCode)
}
func (a *adapter) PushPromise(promiseID uint32, headers []hpack.HeaderField) error {
return a.sink.PushPromise(promiseID, headers)
}
func (a *adapter) isEnabled() bool {
return atomic.LoadInt32(a.enabled) > 0
}
// emitter is a Processor implementation that wraps a h2.Processor instance, forwarding traffic to
// it. It handles recompression of the data.
type emitter struct {
sink h2.Processor
// adapter is a reference to the adapter needed to retrieve state.
adapter *adapter
}
func (e *emitter) Header(
headers []hpack.HeaderField,
streamEnded bool,
priority http2.PriorityParam,
) error {
return e.sink.Header(headers, streamEnded, priority)
}
func (e *emitter) Message(data []byte, streamEnded bool) error {
// Applies compression to `data` depending on `adapter`'s state.
if e.adapter.compressed {
switch e.adapter.encoding {
case Identity:
case Gzip:
var buf bytes.Buffer
w := gzip.NewWriter(&buf)
if _, err := w.Write(data); err != nil {
return fmt.Errorf("gzipping message data: %w", err)
}
if err := w.Close(); err != nil {
return fmt.Errorf("gzipping message data: %w", err)
}
data = buf.Bytes()
case Deflate:
var buf bytes.Buffer
w, _ := flate.NewWriter(&buf, -1)
if _, err := w.Write(data); err != nil {
return fmt.Errorf("flate compressing message data: %w", err)
}
if err := w.Close(); err != nil {
return fmt.Errorf("flate compressing message data: %w", err)
}
data = buf.Bytes()
case Snappy:
data = snappy.Encode(nil, data)
}
}
var buf bytes.Buffer
// Writes the compression status.
if e.adapter.compressed {
buf.WriteByte(1)
} else {
buf.WriteByte(0)
}
binary.Write(&buf, binary.BigEndian, uint32(len(data))) // Writes the length of the data.
buf.Write(data) // Writes the actual data.
return e.sink.Data(buf.Bytes(), streamEnded)
}
func gunzip(data []byte) ([]byte, error) {
r, err := gzip.NewReader(bytes.NewReader(data))
if err != nil {
return nil, err
}
return ioutil.ReadAll(r)
}
func deflate(data []byte) (_ []byte, rerr error) {
r := flate.NewReader(bytes.NewReader(data))
defer func() {
if err := r.Close(); err != nil && rerr != nil {
rerr = err
}
}()
return ioutil.ReadAll(r)
}