Add NewBlockFromReader and NewTxFromReader.

While here, remove the serializedTx field from Tx.  This field was
originally intended to be used to cache the bytes of the serialized
transaction, but it was never used and can effectively leak memory if
the Tx was created with a call to NewTxFromBytes.

ok @davecgh

block.go

@@ -8,6 +8,7 @@ import (
 	"bytes"
 	"fmt"
 	"github.com/conformal/btcwire"
+	"io"
 )
 
 // OutOfRangeError describes an error due to accessing an element that is out
@@ -206,18 +207,28 @@ func NewBlock(msgBlock *btcwire.MsgBlock) *Block {
 // NewBlockFromBytes returns a new instance of a bitcoin block given the
 // serialized bytes.  See Block.
 func NewBlockFromBytes(serializedBlock []byte) (*Block, error) {
+	br := bytes.NewReader(serializedBlock)
+	b, err := NewBlockFromReader(br)
+	if err != nil {
+		return nil, err
+	}
+	b.serializedBlock = serializedBlock
+	return b, nil
+}
+
+// NewBlockFromReader returns a new instance of a bitcoin block given a
+// Reader to deserialize the block.  See Block.
+func NewBlockFromReader(r io.Reader) (*Block, error) {
 	// Deserialize the bytes into a MsgBlock.
 	var msgBlock btcwire.MsgBlock
-	br := bytes.NewReader(serializedBlock)
-	err := msgBlock.Deserialize(br)
+	err := msgBlock.Deserialize(r)
 	if err != nil {
 		return nil, err
 	}
 
 	b := Block{
-		msgBlock:        &msgBlock,
-		serializedBlock: serializedBlock,
-		blockHeight:     BlockHeightUnknown,
+		msgBlock:    &msgBlock,
+		blockHeight: BlockHeightUnknown,
 	}
 	return &b, nil
 }

tx.go

@@ -7,6 +7,7 @@ package btcutil
 import (
 	"bytes"
 	"github.com/conformal/btcwire"
+	"io"
 )
 
 // TxIndexUnknown is the value returned for a transaction index that is unknown.
@@ -19,10 +20,9 @@ const TxIndexUnknown = -1
 // transaction on its first access so subsequent accesses don't have to repeat
 // the relatively expensive hashing operations.
 type Tx struct {
-	msgTx        *btcwire.MsgTx   // Underlying MsgTx
-	serializedTx []byte           // Serialized bytes for the transaction
-	txSha        *btcwire.ShaHash // Cached transaction hash
-	txIndex      int              // Position within a block or TxIndexUnknown
+	msgTx   *btcwire.MsgTx   // Underlying MsgTx
+	txSha   *btcwire.ShaHash // Cached transaction hash
+	txIndex int              // Position within a block or TxIndexUnknown
 }
 
 // MsgTx returns the underlying btcwire.MsgTx for the transaction.
@@ -72,18 +72,23 @@ func NewTx(msgTx *btcwire.MsgTx) *Tx {
 // NewTxFromBytes returns a new instance of a bitcoin transaction given the
 // serialized bytes.  See Tx.
 func NewTxFromBytes(serializedTx []byte) (*Tx, error) {
+	br := bytes.NewReader(serializedTx)
+	return NewTxFromReader(br)
+}
+
+// NewTxFromReader returns a new instance of a bitcoin transaction given a
+// Reader to deserialize the transaction.  See Tx.
+func NewTxFromReader(r io.Reader) (*Tx, error) {
 	// Deserialize the bytes into a MsgTx.
 	var msgTx btcwire.MsgTx
-	br := bytes.NewReader(serializedTx)
-	err := msgTx.Deserialize(br)
+	err := msgTx.Deserialize(r)
 	if err != nil {
 		return nil, err
 	}
 
 	t := Tx{
-		msgTx:        &msgTx,
-		serializedTx: serializedTx,
-		txIndex:      TxIndexUnknown,
+		msgTx:   &msgTx,
+		txIndex: TxIndexUnknown,
 	}
 	return &t, nil
 }