update.go

// Copyright 2018 The go-ethereum Authors
// This file is part of the go-ethereum library.
//
// The go-ethereum library is free software: you can redistribute it and/or modify
// it under the terms of the GNU Lesser General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// The go-ethereum library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public License
// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.

package feed

import (
	"fmt"
	"strconv"

	"github.com/ethersphere/swarm/chunk"
)

// ProtocolVersion defines the current version of the protocol that will be included in each update message
const ProtocolVersion uint8 = 0

const headerLength = 8

// Header defines a update message header including a protocol version byte
type Header struct {
	Version uint8                   // Protocol version
	Padding [headerLength - 1]uint8 // reserved for future use
}

// Update encapsulates the information sent as part of a feed update
type Update struct {
	Header Header //
	ID            // Feed Update identifying information
	data   []byte // actual data payload
}

const minimumUpdateDataLength = idLength + headerLength + 1

//MaxUpdateDataLength indicates the maximum payload size for a feed update
const MaxUpdateDataLength = chunk.DefaultSize - signatureLength - idLength - headerLength

// binaryPut serializes the feed update information into the given slice
func (r *Update) binaryPut(serializedData []byte) error {
	datalength := len(r.data)
	if datalength == 0 {
		return NewError(ErrInvalidValue, "a feed update must contain data")
	}

	if datalength > MaxUpdateDataLength {
		return NewErrorf(ErrInvalidValue, "feed update data is too big (length=%d). Max length=%d", datalength, MaxUpdateDataLength)
	}

	if len(serializedData) != r.binaryLength() {
		return NewErrorf(ErrInvalidValue, "slice passed to putBinary must be of exact size. Expected %d bytes", r.binaryLength())
	}

	var cursor int
	// serialize Header
	serializedData[cursor] = r.Header.Version
	copy(serializedData[cursor+1:headerLength], r.Header.Padding[:headerLength-1])
	cursor += headerLength

	// serialize ID
	if err := r.ID.binaryPut(serializedData[cursor : cursor+idLength]); err != nil {
		return err
	}
	cursor += idLength

	// add the data
	copy(serializedData[cursor:], r.data)
	cursor += datalength

	return nil
}

// binaryLength returns the expected number of bytes this structure will take to encode
func (r *Update) binaryLength() int {
	return idLength + headerLength + len(r.data)
}

// binaryGet populates this instance from the information contained in the passed byte slice
func (r *Update) binaryGet(serializedData []byte) error {
	if len(serializedData) < minimumUpdateDataLength {
		return NewErrorf(ErrNothingToReturn, "chunk less than %d bytes cannot be a feed update chunk", minimumUpdateDataLength)
	}
	dataLength := len(serializedData) - idLength - headerLength
	// at this point we can be satisfied that we have the correct data length to read

	var cursor int

	// deserialize Header
	r.Header.Version = serializedData[cursor]                                      // extract the protocol version
	copy(r.Header.Padding[:headerLength-1], serializedData[cursor+1:headerLength]) // extract the padding
	cursor += headerLength

	if err := r.ID.binaryGet(serializedData[cursor : cursor+idLength]); err != nil {
		return err
	}
	cursor += idLength

	data := serializedData[cursor : cursor+dataLength]
	cursor += dataLength

	// now that all checks have passed, copy data into structure
	r.data = make([]byte, dataLength)
	copy(r.data, data)

	return nil

}

// FromValues deserializes this instance from a string key-value store
// useful to parse query strings
func (r *Update) FromValues(values Values, data []byte) error {
	r.data = data
	version, _ := strconv.ParseUint(values.Get("protocolVersion"), 10, 32)
	r.Header.Version = uint8(version)
	return r.ID.FromValues(values)
}

// AppendValues serializes this structure into the provided string key-value store
// useful to build query strings
func (r *Update) AppendValues(values Values) []byte {
	r.ID.AppendValues(values)
	values.Set("protocolVersion", fmt.Sprintf("%d", r.Header.Version))
	return r.data
}