state: fix prefix index with the new pattern

Prefix queries are generally being used to match part of a partial
index. We can support these indexes by using a function that accept
different types for each subset of the index.

What I found interesting is that in the generic StringFieldIndexer the
implementation for PrefixFromArgs would remove the trailing null, but
at least in these 2 cases we actually want a null terminated string.
We simply want fewer components in the string.

agent/consul/state/catalog.go

@@ -28,7 +28,7 @@ const (
 	minUUIDLookupLen = 2
 )
 
-// Query is type used to query any single value index that may include an
+// Query is a type used to query any single value index that may include an
 // enterprise identifier.
 type Query struct {
 	Value string

agent/consul/state/catalog_oss.go

@@ -103,6 +103,17 @@ func indexFromServiceNode(raw interface{}) ([]byte, error) {
 	return b.Bytes(), nil
 }
 
+func prefixIndexFromQuery(arg interface{}) ([]byte, error) {
+	var b indexBuilder
+	switch v := arg.(type) {
+	case Query:
+		b.String(strings.ToLower(v.Value))
+		return b.Bytes(), nil
+	}
+
+	return nil, fmt.Errorf("unexpected type %T for NodeServiceQuery prefix index", arg)
+}
+
 func serviceIndexName(name string, _ *structs.EnterpriseMeta) string {
 	return fmt.Sprintf("service.%s", name)
 }

agent/consul/state/catalog_schema.go

@@ -72,9 +72,10 @@ func servicesTableSchema() *memdb.TableSchema {
 				Name:         indexID,
 				AllowMissing: false,
 				Unique:       true,
-				Indexer: indexerSingle{
-					readIndex:  readIndex(indexFromNodeServiceQuery),
-					writeIndex: writeIndex(indexFromServiceNode),
+				Indexer: indexerSingleWithPrefix{
+					readIndex:   readIndex(indexFromNodeServiceQuery),
+					writeIndex:  writeIndex(indexFromServiceNode),
+					prefixIndex: prefixIndex(prefixIndexFromQuery),
 				},
 			},
 			indexNode: {

agent/consul/state/indexer.go

@@ -53,7 +53,7 @@ func (f readIndex) FromArgs(args ...interface{}) ([]byte, error) {
 
 var errMissingValueForIndex = fmt.Errorf("object is missing a value for this index")
 
-// writeIndex implements memdb.SingleIndexer. It is used so that a function
+// writeIndex implements memdb.SingleIndexer. It exists so that a function
 // can be used to provide this interface.
 //
 // Instead of a bool return value, writeIndex expects errMissingValueForIndex to
@@ -69,7 +69,7 @@ func (f writeIndex) FromObject(raw interface{}) (bool, []byte, error) {
 	return err == nil, v, err
 }
 
-// writeIndexMulti implements memdb.MultiIndexer. It is used so that a function
+// writeIndexMulti implements memdb.MultiIndexer. It exists so that a function
 // can be used to provide this interface.
 //
 // Instead of a bool return value, writeIndexMulti expects errMissingValueForIndex to

agent/consul/state/testdata/TestStateStoreSchema.golden

@@ -150,7 +150,7 @@ table=services
   index=connect allow-missing
     indexer=github.com/hashicorp/consul/agent/consul/state.IndexConnectService
   index=id unique
-    indexer=github.com/hashicorp/consul/agent/consul/state.indexerSingle readIndex=github.com/hashicorp/consul/agent/consul/state.indexFromNodeServiceQuery writeIndex=github.com/hashicorp/consul/agent/consul/state.indexFromServiceNode
+    indexer=github.com/hashicorp/consul/agent/consul/state.indexerSingleWithPrefix readIndex=github.com/hashicorp/consul/agent/consul/state.indexFromNodeServiceQuery writeIndex=github.com/hashicorp/consul/agent/consul/state.indexFromServiceNode prefixIndex=github.com/hashicorp/consul/agent/consul/state.prefixIndexFromQuery
   index=kind
     indexer=github.com/hashicorp/consul/agent/consul/state.IndexServiceKind
   index=node