sqlite: add DB.MemoryUsed accessor, add leak test to ExpandedSQL test

Updates tailscale/corp#34015

Signed-off-by: Brad Fitzpatrick <[email protected]>

Author: bradfitz

cgosqlite/cgosqlite.go

@@ -10,7 +10,6 @@ package cgosqlite
 
 #cgo CFLAGS: -DSQLITE_THREADSAFE=2
 #cgo CFLAGS: -DSQLITE_DQS=0
-#cgo CFLAGS: -DSQLITE_DEFAULT_MEMSTATUS=0
 #cgo CFLAGS: -DSQLITE_DEFAULT_WAL_SYNCHRONOUS=1
 #cgo CFLAGS: -DSQLITE_LIKE_DOESNT_MATCH_BLOBS
 #cgo CFLAGS: -DSQLITE_MAX_EXPR_DEPTH=0
@@ -143,6 +142,10 @@ func (db *DB) TotalChanges() int {
 	return int(C.sqlite3_total_changes(db.db))
 }
 
+func (db *DB) MemoryUsed() int64 {
+	return int64(C.sqlite3_memory_used())
+}
+
 func (db *DB) ExtendedErrCode() sqliteh.Code {
 	return sqliteh.Code(C.sqlite3_extended_errcode(db.db))
 }

go.mod

@@ -1,3 +1,3 @@
 module github.com/tailscale/sqlite
 
-go 1.21
+go 1.25

sqlite_test.go

@@ -1567,4 +1567,14 @@ func TestExpandedSQL(t *testing.T) {
 	if got, want := stmt.stmt.ExpandedSQL(), "SELECT 6 + 7"; got != want {
 		t.Errorf("wrong sql: got %q, want %q", got, want)
 	}
+	mem0 := conn.db.MemoryUsed()
+	for range 100 {
+		if got, want := stmt.stmt.ExpandedSQL(), "SELECT 6 + 7"; got != want {
+			t.Errorf("wrong sql: got %q, want %q", got, want)
+		}
+	}
+	mem1 := conn.db.MemoryUsed()
+	if mem1 > mem0 {
+		t.Errorf("memory leak detected: before=%v after=%v", mem0, mem1)
+	}
 }

sqliteh/sqliteh.go

@@ -37,6 +37,9 @@ type DB interface {
 	// TotalChanges is sqlite3_total_changes.
 	// https://sqlite.org/c3ref/total_changes.html
 	TotalChanges() int
+	// MemoryUsed is sqlite3_memory_used.
+	// https://sqlite.org/c3ref/memory_highwater.html
+	MemoryUsed() int64
 	// ExtendedErrCode is sqlite3_extended_errcode.
 	// https://sqlite.org/c3ref/errcode.html
 	ExtendedErrCode() Code