From 1f40c7214ef1087b4f64025956b5b18711ec7aa7 Mon Sep 17 00:00:00 2001
From: Tadge Dryja <tadge@lightning.network>
Date: Wed, 20 Jan 2016 01:23:47 -0800
Subject: [PATCH] good enough storage of spent txs

---
 uspv/txstore.go | 15 +++++++++++----
 uspv/utxodb.go  | 49 +++++++++++++++++++++++++++++++++++++++++++++++--
 2 files changed, 58 insertions(+), 6 deletions(-)

diff --git a/uspv/txstore.go b/uspv/txstore.go
index a0332ee5..7c1abee3 100644
--- a/uspv/txstore.go
+++ b/uspv/txstore.go
@@ -83,7 +83,7 @@ func (t *TxStore) IngestTx(tx *wire.MsgTx) error {
 	if err != nil {
 		return err
 	}
-	err = t.ExpellTx(tx)
+	err = t.ExpellTx(tx, height)
 	if err != nil {
 		return err
 	}
@@ -115,7 +115,10 @@ func (t *TxStore) AbsorbTx(tx *wire.MsgTx, height int32) error {
 				newop.Hash = tx.TxSha()
 				newop.Index = uint32(i)
 				newu.Op = newop
-
+				err := newu.SaveToDB(t.StateDB)
+				if err != nil {
+					return err
+				}
 				t.Utxos = append(t.Utxos, newu)
 				break
 			}
@@ -127,7 +130,7 @@ func (t *TxStore) AbsorbTx(tx *wire.MsgTx, height int32) error {
 }
 
 // Expell money from wallet due to a tx
-func (t *TxStore) ExpellTx(tx *wire.MsgTx) error {
+func (t *TxStore) ExpellTx(tx *wire.MsgTx, height int32) error {
 	if tx == nil {
 		return fmt.Errorf("Tried to add nil tx")
 	}
@@ -139,7 +142,11 @@ func (t *TxStore) ExpellTx(tx *wire.MsgTx) error {
 			if myutxo.Op == in.PreviousOutPoint {
 				hits++
 				loss += myutxo.Txo.Value
-				// delete from my utxo set
+				err := t.MarkSpent(&myutxo.Op, height, tx)
+				if err != nil {
+					return err
+				}
+				// delete from my in-ram utxo set
 				t.Utxos = append(t.Utxos[:i], t.Utxos[i+1:]...)
 			}
 		}
diff --git a/uspv/utxodb.go b/uspv/utxodb.go
index abfb2f94..32fcf06b 100644
--- a/uspv/utxodb.go
+++ b/uspv/utxodb.go
@@ -5,6 +5,8 @@ import (
 	"encoding/binary"
 	"fmt"
 
+	"github.com/btcsuite/btcd/wire"
+
 	"github.com/boltdb/bolt"
 )
 
@@ -26,8 +28,32 @@ func (u *Utxo) SaveToDB(dbx *bolt.DB) error {
 	})
 }
 
-func (ts *TxStore) LoadUtxos() error {
+func (ts *TxStore) MarkSpent(op *wire.OutPoint, h int32, stx *wire.MsgTx) error {
 
+	// we write in key = outpoint (32 hash, 4 index)
+	// value = spending txid
+	// if we care about the spending tx we can store that in another bucket.
+	return ts.StateDB.Update(func(tx *bolt.Tx) error {
+		old := tx.Bucket(BKTOld)
+		opb, err := outPointToBytes(op)
+		if err != nil {
+			return err
+		}
+		var buf bytes.Buffer
+		err = binary.Write(&buf, binary.BigEndian, h)
+		if err != nil {
+			return err
+		}
+		sha := stx.TxSha()
+		err = old.Put(opb, sha.Bytes()) // write k:v outpoint:txid
+		if err != nil {
+			return err
+		}
+		return nil
+	})
+}
+
+func (ts *TxStore) LoadUtxos() error {
 	err := ts.StateDB.View(func(tx *bolt.Tx) error {
 		duf := tx.Bucket(BKTUtxos)
 		if duf == nil {
@@ -41,7 +67,8 @@ func (ts *TxStore) LoadUtxos() error {
 		duf.ForEach(func(k, v []byte) error {
 			// have to copy these here, otherwise append will crash it.
 			// not quite sure why but append does weird stuff I guess.
-			if spent.Get(k) == nil { // if it's not in the spent bucket
+			stx := spent.Get(k)
+			if stx == nil { // if it's not in the spent bucket
 				// create a new utxo
 				x := make([]byte, len(k)+len(v))
 				copy(x, k)
@@ -52,6 +79,9 @@ func (ts *TxStore) LoadUtxos() error {
 				}
 				// and add it to ram
 				ts.Utxos = append(ts.Utxos, newU)
+			} else {
+				fmt.Printf("had utxo %x but spent by tx %x...\n",
+					k, stx[:8])
 			}
 			return nil
 		})
@@ -63,6 +93,21 @@ func (ts *TxStore) LoadUtxos() error {
 	return nil
 }
 
+// outPointToBytes turns an outpoint into 36 bytes.
+func outPointToBytes(op *wire.OutPoint) ([]byte, error) {
+	var buf bytes.Buffer
+	_, err := buf.Write(op.Hash.Bytes())
+	if err != nil {
+		return nil, err
+	}
+	// write 4 byte outpoint index within the tx to spend
+	err = binary.Write(&buf, binary.BigEndian, op.Index)
+	if err != nil {
+		return nil, err
+	}
+	return buf.Bytes(), nil
+}
+
 // ToBytes turns a Utxo into some bytes.
 // note that the txid is the first 36 bytes and in our use cases will be stripped
 // off, but is left here for other applications