Add fuzz test for FormatDSN

Run (go 1.18+): go test -fuzz FuzzFormatDSN Note: invalid host:addr values are currently ignored as they are known to break (ParseDSN doesn't strictly check address format).

Author: dolmen

dsn_fuzz_test.go

@@ -0,0 +1,47 @@
+//go:build go1.18
+// +build go1.18
+
+package mysql
+
+import (
+"net"
+"testing"
+)
+
+func FuzzFormatDSN(f *testing.F) {
+for _, test := range testDSNs { // See dsn_test.go
+f.Add(test.in)
+}
+
+f.Fuzz(func(t *testing.T, dsn1 string) {
+// Do not waste resources
+if len(dsn1) > 1000 {
+t.Skip("ignore: too long")
+}
+
+cfg1, err := ParseDSN(dsn1)
+if err != nil {
+t.Skipf("invalid DSN: %v", err)
+}
+
+dsn2 := cfg1.FormatDSN()
+if dsn2 == dsn1 {
+return
+}
+
+// Skip known cases of bad config that are not strictly checked by ParseDSN
+if _, _, err := net.SplitHostPort(cfg1.Addr); err != nil {
+t.Skipf("invalid addr: %v", err)
+}
+
+cfg2, err := ParseDSN(dsn2)
+if err != nil {
+t.Fatalf("%q rewritten as %q: %v", dsn1, dsn2, err)
+}
+
+dsn3 := cfg2.FormatDSN()
+if dsn3 != dsn2 {
+t.Errorf("%q rewritten as %q", dsn2, dsn3)
+}
+})
+}