don't return false positives when searching for a prefix of a tag value (#2919)

Fixes #2908

CHANGELOG_PENDING.md

@@ -37,6 +37,7 @@ program](https://hackerone.com/tendermint).
 - [blockchain] \#2731 Retry both blocks if either is bad to avoid getting stuck during fast sync (@goolAdapter)
 - [log] \#2868 fix module=main setting overriding all others
 - [rpc] \#2808 RPC validators calls IncrementAccum if necessary
+- [kv indexer] \#2908 don't return false positives when searching for a prefix of a tag value
 - [kv indexer] \#2775 order results by index if height is the same
 - [rpc] \#2759 fix tx.height range queries
 - [rpc] \#2811 Allow integer IDs in JSON-RPC requests

state/txindex/kv/kv.go

@@ -412,9 +412,9 @@ LOOP:
 func startKey(c query.Condition, height int64) []byte {
 	var key string
 	if height > 0 {
-		key = fmt.Sprintf("%s/%v/%d", c.Tag, c.Operand, height)
+		key = fmt.Sprintf("%s/%v/%d/", c.Tag, c.Operand, height)
 	} else {
-		key = fmt.Sprintf("%s/%v", c.Tag, c.Operand)
+		key = fmt.Sprintf("%s/%v/", c.Tag, c.Operand)
 	}
 	return []byte(key)
 }

state/txindex/kv/kv_test.go

@@ -73,6 +73,8 @@ func TestTxSearch(t *testing.T) {
 		{"account.number = 1 AND account.owner = 'Ivan'", 1},
 		// search by exact match (two tags)
 		{"account.number = 1 AND account.owner = 'Vlad'", 0},
+		// search using a prefix of the stored value
+		{"account.owner = 'Iv'", 0},
 		// search by range
 		{"account.number >= 1 AND account.number <= 5", 1},
 		// search by range (lower bound)