framework/rpc/server.go

// Copyright (C) 2016 The Android Open Source Project
//
// 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 rpc

import (
	"bufio"
	"io"

	"sync/atomic"

	"android.googlesource.com/platform/tools/gpu/framework/binary"
	"android.googlesource.com/platform/tools/gpu/framework/binary/cyclic"
	"android.googlesource.com/platform/tools/gpu/framework/binary/vle"
	"android.googlesource.com/platform/tools/gpu/framework/log"
	"android.googlesource.com/platform/tools/gpu/framework/multiplexer"
)

// Handler is the signature for a function that handles incoming rpc calls.
type Handler func(log.Context, interface{}) (binary.Object, error)

var lastRPCID = uint32(1)

// Serve implements the receiving side of a client server rpc pair.
// It listens on the reader for calls, and dispatches them to the supplied handler.
// Any result returned from the handler is then sent back down the writer.
func Serve(ctx log.Context, s io.ReadWriteCloser, mtu int, handler Handler) {
	multiplexer.New(ctx, s, mtu, func(ctx log.Context, channel io.ReadWriteCloser) {
		// If Close fails, multiplexer already knows, so we ignore the error
		defer channel.Close()

		ctx = ctx.V("RPC", atomic.AddUint32(&lastRPCID, 1))

		w := bufio.NewWriterSize(channel, mtu)
		// Flush only fails if channel fails, multiplexer already knows, so we ignore the error
		defer w.Flush()

		d := cyclic.Decoder(vle.Reader(channel))
		e := cyclic.Encoder(vle.Writer(w))

		// Function used for encoding an error
		encErr := func(err error) {
			if rpcErr, ok := err.(Err); ok {
				e.Object(rpcErr)
			} else {
				e.Object(&Error{Msg: err.Error()})
			}
		}

		// Check the RPC header
		var h [4]byte
		d.Data(h[:])

		switch h {
		case headerV0:
			// Legacy support for a single string error message type.
			encErr = func(err error) { e.Object(&Error{Msg: err.Error()}) }
		case headerV1:
		default:
			err := &ErrInvalidHeader{Header: h}
			ctx.Fail(err, "")
			encErr(err)
			return
		}

		// Decode the call
		val := d.Object()
		if err := d.Error(); err != nil {
			ctx.Error().Fail(err, "Decoding call")
			encErr(&ErrDecodingCall{Reason: err.Error()})
			return
		}

		// Invoke the call
		res, err := handler(ctx, val)

		// Encode the call result
		if err == nil {
			e.Object(res) // Success
		} else {
			encErr(err) // Failure
		}

		if err := e.Error(); err != nil {
			ctx.Error().V("value", val).Fail(err, "Encoding result")
			return
		}
	})
}