kvdb+etcd: assert on bucket/value key when putting value/bucket

This commit extends compatibility with the bbolt kvdb implementation,
which returns ErrIncompatibleValue in case of a bucket/value key
collision. Furthermore the commit also adds an extra precondition to the
transaction when a key doesn't exist. This is needed as we fix reads to
a snapshot revision and other writers may commit the key otherwise.

channeldb/kvdb/etcd/readwrite_bucket.go

@@ -116,6 +116,20 @@ func (b *readWriteBucket) NestedReadWriteBucket(key []byte) walletdb.ReadWriteBu
 	return newReadWriteBucket(b.tx, bucketKey, bucketVal)
 }
 
+// assertNoValue checks if the value for the passed key exists.
+func (b *readWriteBucket) assertNoValue(key []byte) error {
+	val, err := b.tx.stm.Get(string(makeValueKey(b.id, key)))
+	if err != nil {
+		return err
+	}
+
+	if val != nil {
+		return walletdb.ErrIncompatibleValue
+	}
+
+	return nil
+}
+
 // CreateBucket creates and returns a new nested bucket with the given
 // key. Returns ErrBucketExists if the bucket already exists,
 // ErrBucketNameRequired if the key is empty, or ErrIncompatibleValue
@@ -141,11 +155,15 @@ func (b *readWriteBucket) CreateBucket(key []byte) (
 		return nil, walletdb.ErrBucketExists
 	}
 
+	if err := b.assertNoValue(key); err != nil {
+		return nil, err
+	}
+
 	// Create a deterministic bucket id from the bucket key.
 	newID := makeBucketID(bucketKey)
 
 	// Create the bucket.
-	b.tx.put(string(bucketKey), string(newID[:]))
+	b.tx.stm.Put(string(bucketKey), string(newID[:]))
 
 	return newReadWriteBucket(b.tx, bucketKey, newID[:]), nil
 }
@@ -171,8 +189,12 @@ func (b *readWriteBucket) CreateBucketIfNotExists(key []byte) (
 	}
 
 	if !isValidBucketID(bucketVal) {
+		if err := b.assertNoValue(key); err != nil {
+			return nil, err
+		}
+
 		newID := makeBucketID(bucketKey)
-		b.tx.put(string(bucketKey), string(newID[:]))
+		b.tx.stm.Put(string(bucketKey), string(newID[:]))
 
 		return newReadWriteBucket(b.tx, bucketKey, newID[:]), nil
 	}
@@ -220,7 +242,7 @@ func (b *readWriteBucket) DeleteNestedBucket(key []byte) error {
 		}
 
 		for kv != nil {
-			b.tx.del(kv.key)
+			b.tx.stm.Del(kv.key)
 
 			if isBucketKey(kv.key) {
 				queue = append(queue, []byte(kv.val))
@@ -233,12 +255,12 @@ func (b *readWriteBucket) DeleteNestedBucket(key []byte) error {
 		}
 
 		// Finally delete the sequence key for the bucket.
-		b.tx.del(string(makeSequenceKey(id)))
+		b.tx.stm.Del(string(makeSequenceKey(id)))
 	}
 
 	// Delete the top level bucket and sequence key.
-	b.tx.del(bucketKey)
-	b.tx.del(string(makeSequenceKey(bucketVal)))
+	b.tx.stm.Del(bucketKey)
+	b.tx.stm.Del(string(makeSequenceKey(bucketVal)))
 
 	return nil
 }
@@ -250,8 +272,17 @@ func (b *readWriteBucket) Put(key, value []byte) error {
 		return walletdb.ErrKeyRequired
 	}
 
+	val, err := b.tx.stm.Get(string(makeBucketKey(b.id, key)))
+	if err != nil {
+		return err
+	}
+
+	if val != nil {
+		return walletdb.ErrIncompatibleValue
+	}
+
 	// Update the transaction with the new value.
-	b.tx.put(string(makeValueKey(b.id, key)), string(value))
+	b.tx.stm.Put(string(makeValueKey(b.id, key)), string(value))
 
 	return nil
 }
@@ -264,7 +295,7 @@ func (b *readWriteBucket) Delete(key []byte) error {
 	}
 
 	// Update the transaction to delete the key/value.
-	b.tx.del(string(makeValueKey(b.id, key)))
+	b.tx.stm.Del(string(makeValueKey(b.id, key)))
 
 	return nil
 }
@@ -294,7 +325,7 @@ func (b *readWriteBucket) SetSequence(v uint64) error {
 	val := strconv.FormatUint(v, 10)
 
 	// Update the transaction with the new value for the sequence key.
-	b.tx.put(string(makeSequenceKey(b.id)), val)
+	b.tx.stm.Put(string(makeSequenceKey(b.id)), val)
 
 	return nil
 }

channeldb/kvdb/etcd/readwrite_bucket_test.go

@@ -403,3 +403,121 @@ func TestBucketSequence(t *testing.T) {
 
 	require.Nil(t, err)
 }
+
+// TestKeyClash tests that one cannot create a bucket if a value with the same
+// key exists and the same is true in reverse: that a value cannot be put if
+// a bucket with the same key exists.
+func TestKeyClash(t *testing.T) {
+	t.Parallel()
+
+	f := NewEtcdTestFixture(t)
+	defer f.Cleanup()
+
+	db, err := newEtcdBackend(f.BackendConfig())
+	require.NoError(t, err)
+
+	// First:
+	// put: /apple/key -> val
+	// create bucket: /apple/banana
+	err = db.Update(func(tx walletdb.ReadWriteTx) error {
+		apple, err := tx.CreateTopLevelBucket([]byte("apple"))
+		require.Nil(t, err)
+		require.NotNil(t, apple)
+
+		require.NoError(t, apple.Put([]byte("key"), []byte("val")))
+
+		banana, err := apple.CreateBucket([]byte("banana"))
+		require.Nil(t, err)
+		require.NotNil(t, banana)
+
+		return nil
+	})
+
+	require.Nil(t, err)
+
+	// Next try to:
+	// put: /apple/banana -> val => will fail (as /apple/banana is a bucket)
+	// create bucket: /apple/key => will fail (as /apple/key is a value)
+	err = db.Update(func(tx walletdb.ReadWriteTx) error {
+		apple, err := tx.CreateTopLevelBucket([]byte("apple"))
+		require.Nil(t, err)
+		require.NotNil(t, apple)
+
+		require.Error(t,
+			walletdb.ErrIncompatibleValue,
+			apple.Put([]byte("banana"), []byte("val")),
+		)
+
+		b, err := apple.CreateBucket([]byte("key"))
+		require.Nil(t, b)
+		require.Error(t, walletdb.ErrIncompatibleValue, b)
+
+		b, err = apple.CreateBucketIfNotExists([]byte("key"))
+		require.Nil(t, b)
+		require.Error(t, walletdb.ErrIncompatibleValue, b)
+
+		return nil
+	})
+
+	require.Nil(t, err)
+
+	// Except that the only existing items in the db are:
+	// bucket: /apple
+	// bucket: /apple/banana
+	// value: /apple/key -> val
+	expected := map[string]string{
+		bkey("apple"):           bval("apple"),
+		bkey("apple", "banana"): bval("apple", "banana"),
+		vkey("key", "apple"):    "val",
+	}
+	require.Equal(t, expected, f.Dump())
+
+}
+
+// TestBucketCreateDelete tests that creating then deleting then creating a
+// bucket suceeds.
+func TestBucketCreateDelete(t *testing.T) {
+	t.Parallel()
+	f := NewEtcdTestFixture(t)
+	defer f.Cleanup()
+
+	db, err := newEtcdBackend(f.BackendConfig())
+	require.NoError(t, err)
+
+	err = db.Update(func(tx walletdb.ReadWriteTx) error {
+		apple, err := tx.CreateTopLevelBucket([]byte("apple"))
+		require.NoError(t, err)
+		require.NotNil(t, apple)
+
+		banana, err := apple.CreateBucket([]byte("banana"))
+		require.NoError(t, err)
+		require.NotNil(t, banana)
+
+		return nil
+	})
+	require.NoError(t, err)
+
+	err = db.Update(func(tx walletdb.ReadWriteTx) error {
+		apple := tx.ReadWriteBucket([]byte("apple"))
+		require.NotNil(t, apple)
+		require.NoError(t, apple.DeleteNestedBucket([]byte("banana")))
+
+		return nil
+	})
+	require.NoError(t, err)
+
+	err = db.Update(func(tx walletdb.ReadWriteTx) error {
+		apple := tx.ReadWriteBucket([]byte("apple"))
+		require.NotNil(t, apple)
+		require.NoError(t, apple.Put([]byte("banana"), []byte("value")))
+
+		return nil
+	})
+	require.NoError(t, err)
+
+	expected := map[string]string{
+		vkey("banana", "apple"): "value",
+		bkey("apple"):           bval("apple"),
+	}
+	require.Equal(t, expected, f.Dump())
+}

channeldb/kvdb/etcd/readwrite_tx.go

@@ -34,16 +34,6 @@ func rootBucket(tx *readWriteTx) *readWriteBucket {
 	return newReadWriteBucket(tx, tx.rootBucketID[:], tx.rootBucketID[:])
 }
 
-// put updates the passed key/value.
-func (tx *readWriteTx) put(key, val string) {
-	tx.stm.Put(key, val)
-}
-
-// del marks the passed key deleted.
-func (tx *readWriteTx) del(key string) {
-	tx.stm.Del(key)
-}
-
 // ReadBucket opens the root bucket for read only access.  If the bucket
 // described by the key does not exist, nil is returned.
 func (tx *readWriteTx) ReadBucket(key []byte) walletdb.ReadBucket {

channeldb/kvdb/etcd/stm.go

@@ -352,6 +352,15 @@ func (s *stm) fetch(key string, opts ...v3.OpOption) ([]KV, error) {
 		}
 	}
 
+	if len(resp.Kvs) == 0 {
+		// Add assertion to the read set which will extend our commit
+		// constraint such that the commit will fail if the key is
+		// present in the database.
+		s.rset[key] = stmGet{
+			rev: 0,
+		}
+	}
+
 	var result []KV
 
 	// Fill the read set with key/values returned.
@@ -395,12 +404,22 @@ func (s *stm) Get(key string) ([]byte, error) {
 	// the prefetch set.
 	if getValue, ok := s.prefetch[key]; ok {
 		delete(s.prefetch, key)
-		s.rset[key] = getValue
+
+		// Use the prefetched value only if it is for
+		// an existing key.
+		if getValue.rev != 0 {
+			s.rset[key] = getValue
+		}
 	}
 
 	// Return value if alread in read set.
-	if getVal, ok := s.rset[key]; ok {
-		return []byte(getVal.val), nil
+	if getValue, ok := s.rset[key]; ok {
+		// Return the value if the rset contains an existing key.
+		if getValue.rev != 0 {
+			return []byte(getValue.val), nil
+		} else {
+			return nil, nil
+		}
 	}
 
 	// Fetch and return value.