network: add uncompressed payload size

Closes #1212

pkg/network/compress.go

@@ -1,28 +1,32 @@
 package network
 
 import (
+ "encoding/binary"
+ "errors"
+
  "github.com/nspcc-dev/neo-go/pkg/network/payload"
  "github.com/pierrec/lz4"
 )
 
 // compress compresses bytes using lz4.
 func compress(source []byte) ([]byte, error) {
- dest := make([]byte, lz4.CompressBlockBound(len(source)))
- size, err := lz4.CompressBlock(source, dest, nil)
+ dest := make([]byte, 4+lz4.CompressBlockBound(len(source)))
+ size, err := lz4.CompressBlock(source, dest[4:], nil)
  if err != nil {
  return nil, err
  }
- return dest[:size], nil
+ binary.LittleEndian.PutUint32(dest[:4], uint32(len(source)))
+ return dest[:size+4], nil
 }
 
 // decompress decompresses bytes using lz4.
 func decompress(source []byte) ([]byte, error) {
- maxSize := len(source) * 255
- if maxSize > payload.MaxSize {
- maxSize = payload.MaxSize
+ length := binary.LittleEndian.Uint32(source[:4])
+ if length < 0 || length > payload.MaxSize {
+ return nil, errors.New("invalid uncompressed payload length")
  }
- dest := make([]byte, maxSize)
- size, err := lz4.UncompressBlock(source, dest)
+ dest := make([]byte, length)
+ size, err := lz4.UncompressBlock(source[4:], dest)
  if err != nil {
  return nil, err
  }