Add TxOutput struct, some Marshal/Hash functions and skeleton validit…

…y logic

blockchain/block.go

@@ -0,0 +1,57 @@
+package blockchain
+
+// BlockHeader contains metadata about a block
+import (
+	"crypto/sha256"
+	"encoding/binary"
+	"encoding/gob"
+	"io"
+)
+
+// BlockHeader contains metadata about a block
+type BlockHeader struct {
+	blockNumber uint32
+	lastBlock   Hash
+	miner       Wallet
+}
+
+// Marshal converts a BlockHeader to a byte slice
+func (bh *BlockHeader) Marshal() []byte {
+	buf := []byte{}
+	binary.LittleEndian.PutUint32(buf, bh.blockNumber)
+	for _, b := range bh.lastBlock {
+		buf = append(buf, b)
+	}
+	buf = append(buf, bh.miner.Marshal()...)
+	return buf
+}
+
+// Block represents a block in the blockchain. Contains transactions and header metadata.
+type Block struct {
+	BlockHeader
+	transactions []*Transaction
+}
+
+// Marshal converts a Block to a byte slice
+func (b *Block) Marshal() []byte {
+	buf := b.BlockHeader.Marshal()
+	for _, t := range b.transactions {
+		buf = append(buf, t.Marshal()...)
+	}
+	return buf
+}
+
+// Encode writes the marshalled block to the given io.Writer
+func (b *Block) Encode(w io.Writer) {
+	gob.NewEncoder(w).Encode(b)
+}
+
+// Decode reads the marshalled block from the given io.Reader
+func (b *Block) Decode(r io.Reader) {
+	gob.NewDecoder(r).Decode(b)
+}
+
+// Hash computes and returns the SHA256 hash of the block
+func (b *Block) Hash() Hash {
+	return sha256.Sum256(b.Marshal())
+}

blockchain/blockchain.go

@@ -1,75 +1,45 @@
 package blockchain
 
 import (
-	"crypto/sha256"
-	"encoding/binary"
 	"encoding/gob"
 	"io"
 )
 
-// Hash represents a hash of a block or transaction
+// Hash represents a 256-bit hash of a block or transaction
 type Hash [32]byte
 
-// BlockHeader contains metadata about a block
-type BlockHeader struct {
-	blockNumber uint32
-	lastBlock   Hash
-	miner       Wallet
-}
-
-// Marshal converts a BlockHeader to a byte slice
-func (bh *BlockHeader) Marshal() []byte {
-	buf := []byte{}
-	binary.LittleEndian.PutUint32(buf, bh.blockNumber)
-	for _, b := range bh.lastBlock {
-		buf = append(buf, b)
-	}
-	buf = append(buf, bh.miner.Marshal()...)
-	return buf
-}
-
-// Block represents a block in the blockchain. Contains transactions and header metadata.
-type Block struct {
-	BlockHeader
-	transactions []*Transaction
-}
-
-// Marshal converts a Block to a byte slice
-func (b *Block) Marshal() []byte {
-	buf := b.BlockHeader.Marshal()
-	for _, t := range b.transactions {
-		buf = append(buf, t.Marshal()...)
-	}
-	return buf
-}
-
-// Encode writes the marshalled block to the given io.Writer
-func (b *Block) Encode(w io.Writer) {
-	gob.NewEncoder(w).Encode(b)
-}
-
-// Encode reads the marshalled block from the given io.Reader
-func (b *Block) Decode(r io.Reader) {
-	gob.NewDecoder(r).Decode(b)
-}
-
-// Hash computes and returns the SHA256 hash of the block
-func (b *Block) Hash() Hash {
-	return sha256.Sum256(b.Marshal())
-}
-
 // BlockChain represents a linked list of blocks
 type BlockChain struct {
 	blocks []*Block
 	head   Hash
 }
 
 // Encode writes the marshalled blockchain to the given io.Writer
-func (b *BlockChain) Encode(w io.Writer) {
-	gob.NewEncoder(w).Encode(b)
+func (bc *BlockChain) Encode(w io.Writer) {
+	gob.NewEncoder(w).Encode(bc)
 }
 
-// Encode reads the marshalled blockchain from the given io.Reader
-func (b *BlockChain) Decode(r io.Reader) {
-	gob.NewDecoder(r).Decode(b)
+// Decode reads the marshalled blockchain from the given io.Reader
+func (bc *BlockChain) Decode(r io.Reader) {
+	gob.NewDecoder(r).Decode(bc)
+}
+
+// ValidTransaction checks whether a transaction is valid, assuming the blockchain is valid.
+func (bc *BlockChain) ValidTransaction(t *Transaction) bool {
+	// Find the transaction input (I) in the chain (by hash)
+	// Check that output to sender in I is equal to outputs in T
+	// Verify signature of T
+	return false
+}
+
+// ValidBlock checks whether a block is valid
+func (bc *BlockChain) ValidBlock(b *Block) bool {
+	for _, t := range b.transactions {
+		if !bc.ValidTransaction(t) {
+			return false
+		}
+	}
+	// Check that block number is one greater than last block
+	// Check that hash of last block is correct
+	return false
 }

blockchain/transaction.go

@@ -1,6 +1,9 @@
 package blockchain
 
-import "encoding/binary"
+import (
+	"crypto/sha256"
+	"encoding/binary"
+)
 
 // TxHashPointer is a reference to a transaction on the blockchain.
 type TxHashPointer struct {
@@ -18,35 +21,51 @@ func (thp TxHashPointer) Marshal() []byte {
 	return buf
 }
 
-// TxBody contains all relevant information about a transaction.
+// TxOutput defines an output to a transaction
+type TxOutput struct {
+	amount    uint64
+	recipient Wallet
+}
+
+// Marshal converts a TxOutput to a byte slice
+func (to TxOutput) Marshal() []byte {
+	buf := []byte{}
+	binary.LittleEndian.PutUint64(buf, to.amount)
+	buf = append(buf, to.recipient.Marshal()...)
+	return buf
+}
+
+// TxBody contains all relevant information about a transaction
 type TxBody struct {
-	sender Wallet
-	input  TxHashPointer
-	output TxHashPointer
+	sender  Wallet
+	input   TxHashPointer
+	outputs []TxOutput
 }
 
 // Marshal converts a TxBody to a byte slice
 func (tb TxBody) Marshal() []byte {
 	buf := tb.sender.Marshal()
 	buf = append(buf, tb.input.Marshal()...)
-	buf = append(buf, tb.output.Marshal()...)
+	for _, out := range tb.outputs {
+		buf = append(buf, out.Marshal()...)
+	}
 	return buf
 }
 
-// Transaction contains a TxBody and a signature verifying it.
+// Transaction contains a TxBody and a signature verifying it
 type Transaction struct {
 	TxBody
-	hash Hash
-	sig  Signature
+	sig Signature
 }
 
 // Marshal converts a Transaction to a byte slice
 func (t *Transaction) Marshal() []byte {
 	buf := t.TxBody.Marshal()
-	for _, b := range t.hash {
-		buf = append(buf, b)
-	}
-	buf = append(buf, t.sig.X.Bytes()...)
-	buf = append(buf, t.sig.Y.Bytes()...)
+	buf = append(buf, t.sig.Marshal()...)
 	return buf
 }
+
+// Hash returns the SHA256 hash of a transaction
+func (t *Transaction) Hash() Hash {
+	return sha256.Sum256(t.Marshal())
+}

blockchain/wallet.go

@@ -20,6 +20,11 @@ type Signature struct {
 	Y big.Int
 }
 
+// Marshal converts a signature to a byte slice
+func (s *Signature) Marshal() []byte {
+	return append(s.X.Bytes(), s.Y.Bytes()...)
+}
+
 // New creates a new Wallet backed by a ECC key pair. Uses system entropy.
 func newWallet() (*Wallet, error) {
 	k, err := ecdsa.GenerateKey(curve, rand.Reader)