merge original into coz repo (#10)

merged with the original repo.

pkg/core/block.go

@@ -1,20 +1,24 @@
 package core
 
 import (
+	"bytes"
+	"crypto/sha256"
 	"encoding/binary"
 	"io"
 
 	. "github.com/CityOfZion/neo-go/pkg/util"
 )
 
-// Block represents one block in the chain.
-type Block struct {
+// BlockBase holds the base info of a block
+type BlockBase struct {
 	Version uint32
 	// hash of the previous block.
 	PrevBlock Uint256
 	// Root hash of a transaction list.
 	MerkleRoot Uint256
-	// timestamp
+	// The time stamp of each block must be later than previous block's time stamp.
+	// Generally the difference of two block's time stamp is about 15 seconds and imprecision is allowed.
+	// The height of the block must be exactly equal to the height of the previous block plus 1.
 	Timestamp uint32
 	// height of the block
 	Height uint32
@@ -22,14 +26,40 @@ type Block struct {
 	Nonce uint64
 	// contract addresss of the next miner
 	NextMiner Uint160
-	// seperator ? fixed to 1
+	// fixed to 1
 	_sep uint8
 	// Script used to validate the block
 	Script *Witness
+}
+
+// BlockHead holds the head info of a block
+type BlockHead struct {
+	BlockBase
+	// fixed to 0
+	_sep1 uint8
+}
+
+// Block represents one block in the chain.
+type Block struct {
+	BlockBase
 	// transaction list
 	Transactions []*Transaction
 }
 
+// encodeHashableFields will only encode the fields used for hashing.
+// see Hash() for more information about the fields.
+func (b *Block) encodeHashableFields(w io.Writer) error {
+	err := binary.Write(w, binary.LittleEndian, &b.Version)
+	err = binary.Write(w, binary.LittleEndian, &b.PrevBlock)
+	err = binary.Write(w, binary.LittleEndian, &b.MerkleRoot)
+	err = binary.Write(w, binary.LittleEndian, &b.Timestamp)
+	err = binary.Write(w, binary.LittleEndian, &b.Height)
+	err = binary.Write(w, binary.LittleEndian, &b.Nonce)
+	err = binary.Write(w, binary.LittleEndian, &b.NextMiner)
+
+	return err
+}
+
 // EncodeBinary encodes the block to the given writer.
 func (b *Block) EncodeBinary(w io.Writer) error {
 	return nil
@@ -66,5 +96,20 @@ func (b *Block) DecodeBinary(r io.Reader) error {
 	return err
 }
 
+// Hash return the hash of the block.
+// When calculating the hash value of the block, instead of calculating the entire block,
+// only first seven fields in the block head will be calculated, which are
+// version, PrevBlock, MerkleRoot, timestamp, and height, the nonce, NextMiner.
+// Since MerkleRoot already contains the hash value of all transactions,
+// the modification of transaction will influence the hash value of the block.
+func (b *Block) Hash() (hash Uint256, err error) {
+	buf := new(bytes.Buffer)
+	if err = b.encodeHashableFields(buf); err != nil {
+		return
+	}
+	hash = sha256.Sum256(buf.Bytes())
+	return
+}
+
 // Size implements the payload interface.
 func (b *Block) Size() uint32 { return 0 }