Bug fixes, optimizations, fuzz testing.

driver/driver.go

@@ -99,12 +99,14 @@ func (c conn) Prepare(query string) (driver.Stmt, error) {
 	}
 	if tail != "" {
 		// Check if the tail contains any SQL.
-		s, _, err := c.conn.Prepare(tail)
+		st, _, err := c.conn.Prepare(tail)
 		if err != nil {
+			s.Close()
 			return nil, err
 		}
-		if s != nil {
+		if st != nil {
 			s.Close()
+			st.Close()
 			return nil, tailErr
 		}
 	}

driver/time.go

@@ -9,8 +9,22 @@ import (
 // if it roundtrips back to the same string.
 // This way times can be persisted to, and recovered from, the database,
 // but if a string is needed, [database.sql] will recover the same string.
-// TODO: optimize and fuzz test.
 func maybeDate(text string) driver.Value {
+	// Weed out (some) values that can't possibly be
+	// [time.RFC3339Nano] timestamps.
+	if len(text) < len("2006-01-02T15:04:05") {
+		return text
+	}
+	if text[4] != '-' || text[10] != 'T' || text[16] != ':' {
+		return text
+	}
+	for _, c := range []byte(text[:4]) {
+		if c < '0' || '9' < c {
+			return text
+		}
+	}
+
+	// Slow path.
 	date, err := time.Parse(time.RFC3339Nano, text)
 	if err == nil && date.Format(time.RFC3339Nano) == text {
 		return date

driver/time_test.go

@@ -0,0 +1,42 @@
+package driver
+
+import (
+	"testing"
+	"time"
+)
+
+func Fuzz_maybeDate(f *testing.F) {
+	f.Add("")
+	f.Add(" ")
+	f.Add("SQLite")
+	f.Add(time.RFC3339)
+	f.Add(time.RFC3339Nano)
+	f.Add(time.Layout)
+	f.Add(time.DateTime)
+	f.Add(time.DateOnly)
+	f.Add(time.TimeOnly)
+
+	f.Fuzz(func(t *testing.T, str string) {
+		value := maybeDate(str)
+
+		switch v := value.(type) {
+		case time.Time:
+			// Make sure times round-trip to the same string:
+			// https://pkg.go.dev/database/sql#Rows.Scan
+			if v.Format(time.RFC3339Nano) != str {
+				t.Fatalf("did not round-trip: %q", str)
+			}
+		case string:
+			if v != str {
+				t.Fatalf("did not round-trip: %q", str)
+			}
+
+			date, err := time.Parse(time.RFC3339Nano, str)
+			if err == nil && date.Format(time.RFC3339Nano) == str {
+				t.Fatalf("would round-trip: %q", str)
+			}
+		default:
+			t.Fatalf("invalid type %T: %q", v, str)
+		}
+	})
+}