rpc_util.go

/*
 *
 * Copyright 2014, Google Inc.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are
 * met:
 *
 *     * Redistributions of source code must retain the above copyright
 * notice, this list of conditions and the following disclaimer.
 *     * Redistributions in binary form must reproduce the above
 * copyright notice, this list of conditions and the following disclaimer
 * in the documentation and/or other materials provided with the
 * distribution.
 *     * Neither the name of Google Inc. nor the names of its
 * contributors may be used to endorse or promote products derived from
 * this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 *
 */

package grpc

import (
	"bytes"
	"encoding/binary"
	"fmt"
	"io"
	"math/rand"
	"os"
	"time"

	"github.com/coreos/etcd/Godeps/_workspace/src/github.com/golang/protobuf/proto"
	"github.com/coreos/etcd/Godeps/_workspace/src/golang.org/x/net/context"
	"github.com/coreos/etcd/Godeps/_workspace/src/google.golang.org/grpc/codes"
	"github.com/coreos/etcd/Godeps/_workspace/src/google.golang.org/grpc/metadata"
	"github.com/coreos/etcd/Godeps/_workspace/src/google.golang.org/grpc/transport"
)

// Codec defines the interface gRPC uses to encode and decode messages.
type Codec interface {
	// Marshal returns the wire format of v.
	Marshal(v interface{}) ([]byte, error)
	// Unmarshal parses the wire format into v.
	Unmarshal(data []byte, v interface{}) error
	// String returns the name of the Codec implementation. The returned
	// string will be used as part of content type in transmission.
	String() string
}

// protoCodec is a Codec implemetation with protobuf. It is the default codec for gRPC.
type protoCodec struct{}

func (protoCodec) Marshal(v interface{}) ([]byte, error) {
	return proto.Marshal(v.(proto.Message))
}

func (protoCodec) Unmarshal(data []byte, v interface{}) error {
	return proto.Unmarshal(data, v.(proto.Message))
}

func (protoCodec) String() string {
	return "proto"
}

// CallOption configures a Call before it starts or extracts information from
// a Call after it completes.
type CallOption interface {
	// before is called before the call is sent to any server.  If before
	// returns a non-nil error, the RPC fails with that error.
	before(*callInfo) error

	// after is called after the call has completed.  after cannot return an
	// error, so any failures should be reported via output parameters.
	after(*callInfo)
}

type beforeCall func(c *callInfo) error

func (o beforeCall) before(c *callInfo) error { return o(c) }
func (o beforeCall) after(c *callInfo)        {}

type afterCall func(c *callInfo)

func (o afterCall) before(c *callInfo) error { return nil }
func (o afterCall) after(c *callInfo)        { o(c) }

// Header returns a CallOptions that retrieves the header metadata
// for a unary RPC.
func Header(md *metadata.MD) CallOption {
	return afterCall(func(c *callInfo) {
		*md = c.headerMD
	})
}

// Trailer returns a CallOptions that retrieves the trailer metadata
// for a unary RPC.
func Trailer(md *metadata.MD) CallOption {
	return afterCall(func(c *callInfo) {
		*md = c.trailerMD
	})
}

// The format of the payload: compressed or not?
type payloadFormat uint8

const (
	compressionNone payloadFormat = iota // no compression
	compressionFlate
	// More formats
)

// parser reads complelete gRPC messages from the underlying reader.
type parser struct {
	s io.Reader
}

// msgFixedHeader defines the header of a gRPC message (go/grpc-wirefmt).
type msgFixedHeader struct {
	T      payloadFormat
	Length uint32
}

// recvMsg is to read a complete gRPC message from the stream. It is blocking if
// the message has not been complete yet. It returns the message and its type,
// EOF is returned with nil msg and 0 pf if the entire stream is done. Other
// non-nil error is returned if something is wrong on reading.
func (p *parser) recvMsg() (pf payloadFormat, msg []byte, err error) {
	var hdr msgFixedHeader
	if err := binary.Read(p.s, binary.BigEndian, &hdr); err != nil {
		return 0, nil, err
	}
	if hdr.Length == 0 {
		return hdr.T, nil, nil
	}
	msg = make([]byte, int(hdr.Length))
	if _, err := io.ReadFull(p.s, msg); err != nil {
		if err == io.EOF {
			err = io.ErrUnexpectedEOF
		}
		return 0, nil, err
	}
	return hdr.T, msg, nil
}

// encode serializes msg and prepends the message header. If msg is nil, it
// generates the message header of 0 message length.
func encode(c Codec, msg interface{}, pf payloadFormat) ([]byte, error) {
	var buf bytes.Buffer
	// Write message fixed header.
	buf.WriteByte(uint8(pf))
	var b []byte
	var length uint32
	if msg != nil {
		var err error
		// TODO(zhaoq): optimize to reduce memory alloc and copying.
		b, err = c.Marshal(msg)
		if err != nil {
			return nil, err
		}
		length = uint32(len(b))
	}
	var szHdr [4]byte
	binary.BigEndian.PutUint32(szHdr[:], length)
	buf.Write(szHdr[:])
	buf.Write(b)
	return buf.Bytes(), nil
}

func recv(p *parser, c Codec, m interface{}) error {
	pf, d, err := p.recvMsg()
	if err != nil {
		return err
	}
	switch pf {
	case compressionNone:
		if err := c.Unmarshal(d, m); err != nil {
			return Errorf(codes.Internal, "grpc: %v", err)
		}
	default:
		return Errorf(codes.Internal, "gprc: compression is not supported yet.")
	}
	return nil
}

// rpcError defines the status from an RPC.
type rpcError struct {
	code codes.Code
	desc string
}

func (e rpcError) Error() string {
	return fmt.Sprintf("rpc error: code = %d desc = %q", e.code, e.desc)
}

// Code returns the error code for err if it was produced by the rpc system.
// Otherwise, it returns codes.Unknown.
func Code(err error) codes.Code {
	if err == nil {
		return codes.OK
	}
	if e, ok := err.(rpcError); ok {
		return e.code
	}
	return codes.Unknown
}

// Errorf returns an error containing an error code and a description;
// Errorf returns nil if c is OK.
func Errorf(c codes.Code, format string, a ...interface{}) error {
	if c == codes.OK {
		return nil
	}
	return rpcError{
		code: c,
		desc: fmt.Sprintf(format, a...),
	}
}

// toRPCErr converts an error into a rpcError.
func toRPCErr(err error) error {
	switch e := err.(type) {
	case transport.StreamError:
		return rpcError{
			code: e.Code,
			desc: e.Desc,
		}
	case transport.ConnectionError:
		return rpcError{
			code: codes.Internal,
			desc: e.Desc,
		}
	}
	return Errorf(codes.Unknown, "%v", err)
}

// convertCode converts a standard Go error into its canonical code. Note that
// this is only used to translate the error returned by the server applications.
func convertCode(err error) codes.Code {
	switch err {
	case nil:
		return codes.OK
	case io.EOF:
		return codes.OutOfRange
	case io.ErrClosedPipe, io.ErrNoProgress, io.ErrShortBuffer, io.ErrShortWrite, io.ErrUnexpectedEOF:
		return codes.FailedPrecondition
	case os.ErrInvalid:
		return codes.InvalidArgument
	case context.Canceled:
		return codes.Canceled
	case context.DeadlineExceeded:
		return codes.DeadlineExceeded
	}
	switch {
	case os.IsExist(err):
		return codes.AlreadyExists
	case os.IsNotExist(err):
		return codes.NotFound
	case os.IsPermission(err):
		return codes.PermissionDenied
	}
	return codes.Unknown
}

const (
	// how long to wait after the first failure before retrying
	baseDelay = 1.0 * time.Second
	// upper bound on backoff delay
	maxDelay      = 120 * time.Second
	backoffFactor = 2.0 // backoff increases by this factor on each retry
	backoffRange  = 0.4 // backoff is randomized downwards by this factor
)

// backoff returns a value in [0, maxDelay] that increases exponentially with
// retries, starting from baseDelay.
func backoff(retries int) time.Duration {
	backoff, max := float64(baseDelay), float64(maxDelay)
	for backoff < max && retries > 0 {
		backoff = backoff * backoffFactor
		retries--
	}
	if backoff > max {
		backoff = max
	}

	// Randomize backoff delays so that if a cluster of requests start at
	// the same time, they won't operate in lockstep.  We just subtract up
	// to 40% so that we obey maxDelay.
	backoff -= backoff * backoffRange * rand.Float64()
	if backoff < 0 {
		return 0
	}
	return time.Duration(backoff)
}