codec.go

// Copyright (C) 2019-2021, Ava Labs, Inc. All rights reserved.
// See the file LICENSE for licensing terms.

package message

import (
	"errors"
	"fmt"
	"math"
	"sync"
	"time"

	"github.com/prometheus/client_golang/prometheus"

	"github.com/MetalBlockchain/metalgo/ids"
	"github.com/MetalBlockchain/metalgo/utils/compression"
	"github.com/MetalBlockchain/metalgo/utils/constants"
	"github.com/MetalBlockchain/metalgo/utils/metric"
	"github.com/MetalBlockchain/metalgo/utils/timer/mockable"
	"github.com/MetalBlockchain/metalgo/utils/wrappers"
)

var (
	errMissingField = errors.New("message missing field")
	errBadOp        = errors.New("input field has invalid operation")

	_ Codec = &codec{}
)

type Packer interface {
	Pack(
		op Op,
		fieldValues map[Field]interface{},
		compress bool,
		bypassThrottling bool,
	) (OutboundMessage, error)
}

type Parser interface {
	SetTime(t time.Time) // useful in UTs

	// Parse reads given bytes as InboundMessage
	// Overrides client specified deadline in a message to maxDeadlineDuration
	Parse(bytes []byte, nodeID ids.ShortID, onFinishedHandling func()) (InboundMessage, error)
}

type Codec interface {
	Packer
	Parser
}

// codec defines the serialization and deserialization of network messages.
// It's safe for multiple goroutines to call Pack and Parse concurrently.
type codec struct {
	// Contains []byte. Used as an optimization.
	// Can be accessed by multiple goroutines concurrently.
	byteSlicePool sync.Pool

	clock mockable.Clock

	compressTimeMetrics   map[Op]metric.Averager
	decompressTimeMetrics map[Op]metric.Averager
	compressor            compression.Compressor
	maxMessageTimeout     time.Duration
}

func NewCodecWithMemoryPool(namespace string, metrics prometheus.Registerer, maxMessageSize int64, maxMessageTimeout time.Duration) (Codec, error) {
	c := &codec{
		byteSlicePool: sync.Pool{
			New: func() interface{} {
				return make([]byte, 0, constants.DefaultByteSliceCap)
			},
		},
		compressTimeMetrics:   make(map[Op]metric.Averager, len(ExternalOps)),
		decompressTimeMetrics: make(map[Op]metric.Averager, len(ExternalOps)),
		compressor:            compression.NewGzipCompressor(maxMessageSize),
		maxMessageTimeout:     maxMessageTimeout,
	}

	errs := wrappers.Errs{}
	for _, op := range ExternalOps {
		if !op.Compressible() {
			continue
		}

		c.compressTimeMetrics[op] = metric.NewAveragerWithErrs(
			namespace,
			fmt.Sprintf("%s_compress_time", op),
			fmt.Sprintf("time (in ns) to compress %s messages", op),
			metrics,
			&errs,
		)
		c.decompressTimeMetrics[op] = metric.NewAveragerWithErrs(
			namespace,
			fmt.Sprintf("%s_decompress_time", op),
			fmt.Sprintf("time (in ns) to decompress %s messages", op),
			metrics,
			&errs,
		)
	}
	return c, errs.Err
}

func (c *codec) SetTime(t time.Time) {
	c.clock.Set(t)
}

// Pack attempts to pack a map of fields into a message.
// The first byte of the message is the opcode of the message.
// Uses [buffer] to hold the message's byte repr.
// [buffer]'s contents may be overwritten by this method.
// [buffer] may be nil.
// If [compress], compress the payload.
// If [bypassThrottling], mark the message to avoid outbound throttling checks.
func (c *codec) Pack(
	op Op,
	fieldValues map[Field]interface{},
	compress bool,
	bypassThrottling bool,
) (OutboundMessage, error) {
	msgFields, ok := messages[op]
	if !ok {
		return nil, errBadOp
	}

	buffer := c.byteSlicePool.Get().([]byte)
	p := wrappers.Packer{
		MaxSize: math.MaxInt32,
		Bytes:   buffer[:0],
	}
	// Pack the op code (message type)
	p.PackByte(byte(op))

	// Optionally, pack whether the payload is compressed
	if op.Compressible() {
		p.PackBool(compress)
	}

	// Pack the uncompressed payload
	for _, field := range msgFields {
		data, ok := fieldValues[field]
		if !ok {
			return nil, errMissingField
		}
		field.Packer()(&p, data)
	}
	if p.Err != nil {
		return nil, p.Err
	}
	msg := &outboundMessage{
		op:               op,
		bytes:            p.Bytes,
		refs:             1,
		c:                c,
		bypassThrottling: bypassThrottling,
	}
	if !compress {
		return msg, nil
	}

	// If [compress], compress the payload (not the op code, not isCompressed).
	// The slice below is guaranteed to be in-bounds because [p.Err] == nil
	// implies that len(msg.bytes) >= 2
	payloadBytes := msg.bytes[wrappers.BoolLen+wrappers.ByteLen:]
	startTime := time.Now()
	compressedPayloadBytes, err := c.compressor.Compress(payloadBytes)
	if err != nil {
		return nil, fmt.Errorf("couldn't compress payload of %s message: %w", op, err)
	}
	c.compressTimeMetrics[op].Observe(float64(time.Since(startTime)))
	msg.bytesSavedCompression = len(payloadBytes) - len(compressedPayloadBytes) // may be negative
	// Remove the uncompressed payload (keep just the message type and isCompressed)
	msg.bytes = msg.bytes[:wrappers.BoolLen+wrappers.ByteLen]
	// Attach the compressed payload
	msg.bytes = append(msg.bytes, compressedPayloadBytes...)
	return msg, nil
}

// Parse attempts to convert bytes into a message.
// The first byte of the message is the opcode of the message.
// Overrides client specified deadline in a message to maxDeadlineDuration
func (c *codec) Parse(bytes []byte, nodeID ids.ShortID, onFinishedHandling func()) (InboundMessage, error) {
	p := wrappers.Packer{Bytes: bytes}

	// Unpack the op code (message type)
	op := Op(p.UnpackByte())

	msgFields, ok := messages[op]
	if !ok { // Unknown message type
		return nil, errBadOp
	}

	// See if messages of this type may be compressed
	compressed := false
	if op.Compressible() {
		compressed = p.UnpackBool()
	}
	if p.Err != nil {
		return nil, p.Err
	}

	bytesSaved := 0

	// If the payload is compressed, decompress it
	if compressed {
		// The slice below is guaranteed to be in-bounds because [p.Err] == nil
		compressedPayloadBytes := p.Bytes[wrappers.ByteLen+wrappers.BoolLen:]
		startTime := time.Now()
		payloadBytes, err := c.compressor.Decompress(compressedPayloadBytes)
		if err != nil {
			return nil, fmt.Errorf("couldn't decompress payload of %s message: %w", op, err)
		}
		c.decompressTimeMetrics[op].Observe(float64(time.Since(startTime)))
		// Replace the compressed payload with the decompressed payload.
		// Remove the compressed payload and isCompressed; keep just the message type
		p.Bytes = p.Bytes[:wrappers.ByteLen]
		// Rewind offset by 1 because we removed the bool flag
		// since the data now is uncompressed
		p.Offset -= wrappers.BoolLen
		// Attach the decompressed payload.
		p.Bytes = append(p.Bytes, payloadBytes...)
		bytesSaved = len(payloadBytes) - len(compressedPayloadBytes)
	}

	// Parse each field of the payload
	fieldValues := make(map[Field]interface{}, len(msgFields))
	for _, field := range msgFields {
		fieldValues[field] = field.Unpacker()(&p)
	}

	if p.Offset != len(p.Bytes) {
		return nil, fmt.Errorf("expected length %d but got %d", len(p.Bytes), p.Offset)
	}

	var expirationTime time.Time
	if deadline, hasDeadline := fieldValues[Deadline]; hasDeadline {
		deadlineDuration := time.Duration(deadline.(uint64))
		if deadlineDuration > c.maxMessageTimeout {
			deadlineDuration = c.maxMessageTimeout
		}
		expirationTime = c.clock.Time().Add(deadlineDuration)
	}

	return &inboundMessage{
		op:                    op,
		fields:                fieldValues,
		bytesSavedCompression: bytesSaved,
		nodeID:                nodeID,
		expirationTime:        expirationTime,
		onFinishedHandling:    onFinishedHandling,
	}, p.Err
}