add first fuzzing test

fuzz_test.go

@@ -0,0 +1,58 @@
+//go:build go1.18
+// +build go1.18
+
+package cose_test
+
+import (
+	"encoding/json"
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+
+	"github.com/veraison/go-cose"
+)
+
+func FuzzSign1_Encode(f *testing.F) {
+	testdata, err := os.ReadDir("testdata")
+	if err != nil {
+		f.Fatalf("failed to read testdata directory: %s", err)
+	}
+	for _, de := range testdata {
+		if de.IsDir() || !strings.HasPrefix(de.Name(), "sign1-") || !strings.HasSuffix(de.Name(), ".json") {
+			continue
+		}
+		b, err := os.ReadFile(filepath.Join("testdata", de.Name()))
+		if err != nil {
+			f.Fatalf("failed to read testdata: %s", err)
+		}
+		type testCase struct {
+			Sign1   *Sign1   `json:"sign1::sign"`
+			Verify1 *Verify1 `json:"sign1::verify"`
+		}
+		var tc testCase
+		err = json.Unmarshal(b, &tc)
+		if err != nil {
+			f.Fatal(err)
+		}
+		if tc.Sign1 != nil {
+			f.Add(mustHexToBytes(tc.Sign1.Output.CBORHex))
+		} else if tc.Verify1 != nil {
+			f.Add(mustHexToBytes(tc.Verify1.TaggedCOSESign1.CBORHex))
+		}
+	}
+	f.Fuzz(func(t *testing.T, b []byte) {
+		var msg cose.Sign1Message
+		if err := msg.UnmarshalCBOR(b); err != nil {
+			return
+		}
+		_, err := msg.MarshalCBOR()
+		if err != nil {
+			t.Fatalf("failed to marshal valid message: %s", err)
+		}
+		// TODO: uncomment the roundtrip test once https://github.com/veraison/go-cose/pull/17 lands.
+		// if !bytes.Equal(b, got) {
+		// 	t.Fatalf("roundtripped message has changed, got: %v, want: %v", got, b)
+		// }
+	})
+}