preloader.go

/*
 *
 * Copyright 2019 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 grpc

import (
	"google.golang.org/grpc/codes"
	"google.golang.org/grpc/status"
)

// PreparedMsg is responsible for creating a Marshalled and Compressed object.
//
// This API is EXPERIMENTAL.
type PreparedMsg struct {
	// Struct for preparing msg before sending them
	encodedData  []byte
	hdr          []byte
	payload      []byte
	returnBuffer func()
}

// Encode marshalls and compresses the message using the codec and compressor for the stream.
func (p *PreparedMsg) Encode(s Stream, msg interface{}) error {
	ctx := s.Context()
	rpcInfo, ok := rpcInfoFromContext(ctx)
	if !ok {
		return status.Errorf(codes.Internal, "grpc: unable to get rpcInfo")
	}

	// check if the context has the relevant information to prepareMsg
	if rpcInfo.preloaderInfo == nil {
		return status.Errorf(codes.Internal, "grpc: rpcInfo.preloaderInfo is nil")
	}
	if rpcInfo.preloaderInfo.codec == nil {
		return status.Errorf(codes.Internal, "grpc: rpcInfo.preloaderInfo.codec is nil")
	}

	// prepare the msg
	data, err := encode(rpcInfo.preloaderInfo.codec, msg)
	if err != nil {
		return err
	}
	p.encodedData = data
	if cap(data) >= bufferReuseThreshold {
		if bcodec, ok := rpcInfo.preloaderInfo.codec.(bufferReturner); ok {
			p.returnBuffer = func() {
				bcodec.ReturnBuffer(data)
			}
		}
	}

	compData, err := compress(data, rpcInfo.preloaderInfo.cp, rpcInfo.preloaderInfo.comp)
	if err != nil {
		return err
	}
	p.hdr, p.payload = msgHeader(data, compData)
	return nil
}