JSON round-trip fails for MapSlice about coze

[horvski]

@clfs Would you mind sharing the fuzzing code you used to discover this?

[clfs]

Sure! Drop this in mapslice_test.go:

func FuzzMapSliceJSONRoundTrip(f *testing.F) {
	f.Add([]byte(`{"foo": [123, 456]}`))
	f.Fuzz(func(t *testing.T, b []byte) {
		var m MapSlice
		if err := json.Unmarshal(b, &m); err != nil {
			return
		}

		data, err := json.Marshal(m)
		if err != nil {
			t.Fatalf("marshal: %v", err)
		}

		var m2 MapSlice
		if err := json.Unmarshal(data, &m2); err != nil {
			t.Fatalf("unmarshal again: %v", err)
		}

		data2, err := json.Marshal(m2)
		if err != nil {
			t.Fatalf("marshal again: %v", err)
		}

		if !bytes.Equal(data, data2) {
			t.Fatalf("marshals differ: %q != %q", data, data2)
		}
	})
}

Then run it (I deleted the cache, so the failing input looks different):

calvin@mbp Coze % go test -fuzz FuzzMapSliceJSONRoundTrip .
fuzz: elapsed: 0s, gathering baseline coverage: 0/1 completed
fuzz: elapsed: 0s, gathering baseline coverage: 1/1 completed, now fuzzing with 10 workers
fuzz: elapsed: 3s, execs: 763910 (254609/sec), new interesting: 228 (total: 229)
fuzz: elapsed: 6s, execs: 1601985 (279341/sec), new interesting: 272 (total: 273)
fuzz: elapsed: 9s, execs: 2444368 (280836/sec), new interesting: 291 (total: 292)
fuzz: elapsed: 12s, execs: 3289903 (281844/sec), new interesting: 306 (total: 307)
fuzz: elapsed: 15s, execs: 4126384 (278823/sec), new interesting: 315 (total: 316)
fuzz: minimizing 88-byte failing input file
fuzz: elapsed: 18s, minimizing
fuzz: elapsed: 18s, minimizing
--- FAIL: FuzzMapSliceJSONRoundTrip (18.23s)
    --- FAIL: FuzzMapSliceJSONRoundTrip (0.00s)
        fuzz_test.go:68: marshal: json: error calling MarshalJSON for type coze.MapSlice: invalid character 'x' in string escape code

    Failing input written to testdata/fuzz/FuzzMapSliceJSONRoundTrip/db149316aeed8ab9
    To re-run:
    go test -run=FuzzMapSliceJSONRoundTrip/db149316aeed8ab9
FAIL
exit status 1
FAIL	github.com/cyphrme/coze	18.524s
calvin@mbp Coze % cat testdata/fuzz/FuzzMapSliceJSONRoundTrip/db149316aeed8ab9
go test fuzz v1
[]byte("{\"\x7f\":0}")
calvin@mbp Coze %

[zamicol]

We're taking a look.

[zamicol]

Fixed by b02966e. The problem was MapSlice.MarshalJSON was doing fmt with a %+q when it should just call Marshal again.