Reduce allocations in isMatch in filestore/memstore

Otherwise long subjects could cause us to make the same reallocations
on each call to `tokenizeSubjectIntoSlice` without reusing the newly
sized underlying array for the next call.

Signed-off-by: Neil Twigg <[email protected]>

Author: neilalexander

server/filestore.go

@@ -2325,16 +2325,15 @@ func (mb *msgBlock) firstMatching(filter string, wc bool, start uint64, sm *Stor
 	lseq := atomic.LoadUint64(&mb.last.seq)
 
 	// Optionally build the isMatch for wildcard filters.
-	tsa := [32]string{}
-	fsa := [32]string{}
-	var fts []string
+	_tsa, _fsa := [32]string{}, [32]string{}
+	tsa, fsa := _tsa[:0], _fsa[:0]
 	var isMatch func(subj string) bool
 	// Decide to build.
 	if wc {
-		fts = tokenizeSubjectIntoSlice(fsa[:0], filter)
+		fsa = tokenizeSubjectIntoSlice(fsa[:0], filter)
 		isMatch = func(subj string) bool {
-			tts := tokenizeSubjectIntoSlice(tsa[:0], subj)
-			return isSubsetMatchTokenized(tts, fts)
+			tsa = tokenizeSubjectIntoSlice(tsa[:0], subj)
+			return isSubsetMatchTokenized(tsa, fsa)
 		}
 	}
 

server/memstore.go

@@ -389,9 +389,9 @@ func (ms *memStore) filteredStateLocked(sseq uint64, filter string, lastPerSubje
 		}
 	}
 
-	tsa := [32]string{}
-	fsa := [32]string{}
-	fts := tokenizeSubjectIntoSlice(fsa[:0], filter)
+	_tsa, _fsa := [32]string{}, [32]string{}
+	tsa, fsa := _tsa[:0], _fsa[:0]
+	fsa = tokenizeSubjectIntoSlice(fsa[:0], filter)
 	wc := subjectHasWildcard(filter)
 
 	// 1. See if we match any subs from fss.
@@ -405,8 +405,8 @@ func (ms *memStore) filteredStateLocked(sseq uint64, filter string, lastPerSubje
 		if !wc {
 			return subj == filter
 		}
-		tts := tokenizeSubjectIntoSlice(tsa[:0], subj)
-		return isSubsetMatchTokenized(tts, fts)
+		tsa = tokenizeSubjectIntoSlice(tsa[:0], subj)
+		return isSubsetMatchTokenized(tsa, fsa)
 	}
 
 	update := func(fss *SimpleState) {