path: root/swarm/storage/mru/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 mru

import (
    "encoding/binary"
    "errors"

    "github.com/ethereum/go-ethereum/swarm/chunk"
    "github.com/ethereum/go-ethereum/swarm/log"
    "github.com/ethereum/go-ethereum/swarm/multihash"
)

// resourceUpdate encapsulates the information sent as part of a resource update
type resourceUpdate struct {
    updateHeader        // metainformationa about this resource update
    data         []byte // actual data payload
}

// Update chunk layout
// Prefix:
// 2 bytes updateHeaderLength
// 2 bytes data length
const chunkPrefixLength = 2 + 2

// Header: (see updateHeader)
// Data:
// data (datalength bytes)
//
// Minimum size is Header + 1 (minimum data length, enforced)
const minimumUpdateDataLength = updateHeaderLength + 1
const maxUpdateDataLength = chunk.DefaultSize - signatureLength - updateHeaderLength - chunkPrefixLength

// binaryPut serializes the resource update information into the given slice
func (r *resourceUpdate) binaryPut(serializedData []byte) error {
    datalength := len(r.data)
    if datalength == 0 {
        return NewError(ErrInvalidValue, "cannot update a resource with no data")
    }

    if datalength > maxUpdateDataLength {
        return NewErrorf(ErrInvalidValue, "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())
    }

    if r.multihash {
        if _, _, err := multihash.GetMultihashLength(r.data); err != nil {
            return NewError(ErrInvalidValue, "Invalid multihash")
        }
    }

    // Add prefix: updateHeaderLength and actual data length
    cursor := 0
    binary.LittleEndian.PutUint16(serializedData[cursor:], uint16(updateHeaderLength))
    cursor += 2

    // data length
    binary.LittleEndian.PutUint16(serializedData[cursor:], uint16(datalength))
    cursor += 2

    // serialize header (see updateHeader)
    if err := r.updateHeader.binaryPut(serializedData[cursor : cursor+updateHeaderLength]); err != nil {
        return err
    }
    cursor += updateHeaderLength

    // 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 *resourceUpdate) binaryLength() int {
    return chunkPrefixLength + updateHeaderLength + len(r.data)
}

// binaryGet populates this instance from the information contained in the passed byte slice
func (r *resourceUpdate) binaryGet(serializedData []byte) error {
    if len(serializedData) < minimumUpdateDataLength {
        return NewErrorf(ErrNothingToReturn, "chunk less than %d bytes cannot be a resource update chunk", minimumUpdateDataLength)
    }
    cursor := 0
    declaredHeaderlength := binary.LittleEndian.Uint16(serializedData[cursor : cursor+2])
    if declaredHeaderlength != updateHeaderLength {
        return NewErrorf(ErrCorruptData, "Invalid header length. Expected %d, got %d", updateHeaderLength, declaredHeaderlength)
    }

    cursor += 2
    datalength := int(binary.LittleEndian.Uint16(serializedData[cursor : cursor+2]))
    cursor += 2

    if chunkPrefixLength+updateHeaderLength+datalength+signatureLength != len(serializedData) {
        return NewError(ErrNothingToReturn, "length specified in header is different than actual chunk size")
    }

    // at this point we can be satisfied that we have the correct data length to read
    if err := r.updateHeader.binaryGet(serializedData[cursor : cursor+updateHeaderLength]); err != nil {
        return err
    }
    cursor += updateHeaderLength

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

    // if multihash content is indicated we check the validity of the multihash
    if r.updateHeader.multihash {
        mhLength, mhHeaderLength, err := multihash.GetMultihashLength(data)
        if err != nil {
            log.Error("multihash parse error", "err", err)
            return err
        }
        if datalength != mhLength+mhHeaderLength {
            log.Debug("multihash error", "datalength", datalength, "mhLength", mhLength, "mhHeaderLength", mhHeaderLength)
            return errors.New("Corrupt multihash data")
        }
    }

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

    return nil

}

// Multihash specifies whether the resource data should be interpreted as multihash
func (r *resourceUpdate) Multihash() bool {
    return r.multihash
}