Fix bug in putC/delC for mysql storage backend

When using encryption, the expected value (once encrypted) would never be the same as the encrypted value in the storage layer. As a result, it would never be possible to putC or delC a KV item.

Now the mysql package first gets the key from the storage layer, and then checks it’s decrypted value, before attempting to overwirte the value in the storage layer.

kvs/mysql/err.go

@@ -0,0 +1,22 @@
+// Copyright © 2016 Abcum Ltd
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package mysql
+
+import (
+	"errors"
+)
+
+// ErrKvNotExpectedValue occurs when conditionally putting or deleting a key-value item.
+var ErrTxNotExpectedValue = errors.New("KV val is not expected value")

kvs/mysql/sql.go

@@ -73,13 +73,6 @@ const sqlDel = `
 	LIMIT 1
 `
 
-const sqlDelC = `
-	DELETE FROM kv
-	WHERE t<=? AND k=? AND v=?
-	ORDER BY t DESC
-	LIMIT 1
-`
-
 const sqlDelP = `
 	DELETE q1 FROM kv
 	JOIN (
@@ -120,11 +113,3 @@ const sqlPutN = `
 	VALUES
 	(?, ?, ?)
 `
-
-const sqlPutC = `
-	UPDATE kv
-	SET v=?
-	WHERE t<=? AND k=? AND v=?
-	ORDER BY t DESC
-	LIMIT 1
-`

kvs/mysql/tx.go

@@ -36,12 +36,10 @@ type TX struct {
 		getP *sql.Stmt
 		getR *sql.Stmt
 		del  *sql.Stmt
-		delC *sql.Stmt
 		delP *sql.Stmt
 		delR *sql.Stmt
 		put  *sql.Stmt
 		putN *sql.Stmt
-		putC *sql.Stmt
 	}
 }
 
@@ -286,21 +284,41 @@ func (tx *TX) Del(ver int64, key []byte) (kvs.KV, error) {
 func (tx *TX) DelC(ver int64, key []byte, exp []byte) (kvs.KV, error) {
 
 	var err error
+	var now kvs.KV
 	var res *sql.Rows
 
-	exp, err = enc(exp)
-	if err != nil {
-		return nil, err
-	}
-
 	tx.lock.Lock()
 	defer tx.lock.Unlock()
 
-	if tx.stmt.delC == nil {
+	// Get the item at the key
-		tx.stmt.delC, _ = tx.pntr.Prepare(sqlDelC)
+
+	if tx.stmt.get == nil {
+		tx.stmt.get, _ = tx.pntr.Prepare(sqlGet)
 	}
 
-	res, err = tx.stmt.delC.Query(ver, key, exp)
+	res, err = tx.stmt.get.Query(ver, key)
+	if err != nil {
+		return nil, err
+	}
+
+	now, err = one(res, err)
+	if err != nil {
+		return nil, err
+	}
+
+	// Check if the values match
+
+	if !alter(now.Val(), exp) {
+		return nil, ErrTxNotExpectedValue
+	}
+
+	// If they match then delete
+
+	if tx.stmt.del == nil {
+		tx.stmt.del, _ = tx.pntr.Prepare(sqlDel)
+	}
+
+	res, err = tx.stmt.del.Query(ver, key)
 
 	return one(res, err)
 
@@ -376,6 +394,7 @@ func (tx *TX) Put(ver int64, key []byte, val []byte) (kvs.KV, error) {
 func (tx *TX) PutC(ver int64, key []byte, val []byte, exp []byte) (kvs.KV, error) {
 
 	var err error
+	var now kvs.KV
 	var res *sql.Rows
 
 	val, err = enc(val)
@@ -383,14 +402,6 @@ func (tx *TX) PutC(ver int64, key []byte, val []byte, exp []byte) (kvs.KV, error
 		return nil, err
 	}
 
-	exp, err = enc(exp)
-	if err != nil {
-		return nil, err
-	}
-
-	tx.lock.Lock()
-	defer tx.lock.Unlock()
-
 	switch exp {
 
 	case nil:
@@ -405,11 +416,35 @@ func (tx *TX) PutC(ver int64, key []byte, val []byte, exp []byte) (kvs.KV, error
 
 	default:
 
-		if tx.stmt.putC == nil {
+		// Get the item at the key
-			tx.stmt.putC, _ = tx.pntr.Prepare(sqlPutC)
+
+		if tx.stmt.get == nil {
+			tx.stmt.get, _ = tx.pntr.Prepare(sqlGet)
 		}
 
-		res, err = tx.stmt.putC.Query(val, ver, key, exp)
+		res, err = tx.stmt.get.Query(ver, key)
+		if err != nil {
+			return nil, err
+		}
+
+		now, err = one(res, err)
+		if err != nil {
+			return nil, err
+		}
+
+		// Check if the values match
+
+		if !check(now.Val(), exp) {
+			return nil, ErrTxNotExpectedValue
+		}
+
+		// If they match then delete
+
+		if tx.stmt.del == nil {
+			tx.stmt.put, _ = tx.pntr.Prepare(sqlPut)
+		}
+
+		res, err = tx.stmt.put.Query(ver, key, val, val)
 
 		return one(res, err)
 

kvs/mysql/util.go

@@ -15,6 +15,7 @@
 package mysql
 
 import (
+	"bytes"
 	"crypto/aes"
 	"crypto/cipher"
 	"crypto/rand"
@@ -23,6 +24,28 @@ import (
 
 var chars = []byte("ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789")
 
+// Used to see if we can conditionally put a value. We can only put
+// a value if the value is the same, or if both items are nil.
+func check(a, b []byte) bool {
+	if a != nil && b != nil {
+		return bytes.Equal(a, b)
+	} else if a == nil && b == nil {
+		return true
+	}
+	return false
+}
+
+// Used to see if we can conditionally del a value. We can only del
+// a value if the value is the same, and neither item is nil.
+func alter(a, b []byte) bool {
+	if a != nil && b != nil {
+		return bytes.Equal(a, b)
+	} else if a == nil && b == nil {
+		return false
+	}
+	return false
+}
+
 func encrypt(key []byte, src []byte) (dst []byte, err error) {
 
 	if key == nil || len(key) == 0 || len(src) == 0 {