test: add fuzz test for configloader

That PR contains an example of how fuzz tests can be written with Go 1.18.

It also fixes a few panics with invalid configs.

Signed-off-by: Alexey Palazhchenko <alexey.palazhchenko@talos-systems.com>

pkg/machinery/config/configloader/configloader_fuzz_test.go

@@ -0,0 +1,37 @@
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this
+// file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+//go:build go1.18
+// +build go1.18
+
+package configloader_test
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func FuzzConfigLoader(f *testing.F) {
+	files, err := filepath.Glob(filepath.Join("testdata", "*.test"))
+	require.NoError(f, err)
+
+	for _, file := range files {
+		b, err := os.ReadFile(file)
+		require.NoError(f, err)
+		f.Add(b)
+	}
+
+	f.Add([]byte(":   \xea"))
+	f.Add([]byte(nil))
+	f.Add([]byte(""))
+
+	f.Fuzz(func(t *testing.T, b []byte) {
+		t.Parallel()
+
+		testConfigLoaderBytes(t, b)
+	})
+}

pkg/machinery/config/configloader/configloader_test.go

@@ -2,42 +2,96 @@
 // License, v. 2.0. If a copy of the MPL was not distributed with this
 // file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
-//nolint:testpackage
-package configloader
+package configloader_test
 
 import (
+	"os"
+	"path/filepath"
+	"reflect"
 	"testing"
 
-	"github.com/stretchr/testify/suite"
+	"github.com/stretchr/testify/require"
+
+	"github.com/talos-systems/talos/pkg/machinery/config/configloader"
 )
 
-// docgen: nodoc
-type Suite struct {
-	suite.Suite
+// callMethods calls obj's "getter" methods recursively and fails on panic.
+func callMethods(t testing.TB, obj reflect.Value, chain ...string) {
+	t.Helper()
+
+	typ := obj.Type()
+
+	for i := 0; i < obj.NumMethod(); i++ {
+		method := obj.Method(i)
+
+		if method.Type().NumIn() != 0 {
+			continue
+		}
+
+		methodName := typ.Method(i).Name
+		nextChain := make([]string, len(chain)+1)
+		copy(nextChain, chain)
+		nextChain[len(nextChain)-1] = methodName
+		// t.Log(nextChain)
+
+		// skip known broken methods
+		switch methodName {
+		case "GetRSAKey", "GetEd25519Key", "GetECDSAKey", "GetCert", "GetKey":
+			fallthrough
+		case "MarshalYAML":
+			fallthrough
+		case "Endpoint":
+			// t.Logf("Skipping %v", nextChain)
+			continue
+		}
+
+		var resS []reflect.Value
+
+		require.NotPanics(t, func() { resS = method.Call(nil) }, "Method chain: %v", nextChain)
+
+		if len(resS) == 0 {
+			continue
+		}
+
+		res := resS[0]
+
+		// skip result if it has the same type
+		// to avoid infinite recursion on methods like DeepCopy
+		if res.Type() == typ {
+			continue
+		}
+
+		callMethods(t, res, nextChain...)
+	}
 }
 
-func TestSuite(t *testing.T) {
-	suite.Run(t, new(Suite))
+func testConfigLoaderBytes(t testing.TB, b []byte) {
+	t.Helper()
+
+	p, err := configloader.NewFromBytes(b)
+	if err != nil {
+		t.Skipf("Failed to load, skipping: %s.", err)
+	}
+
+	callMethods(t, reflect.ValueOf(p))
 }
 
-func (suite *Suite) SetupSuite() {}
-
-func (suite *Suite) TestNew() {
-	for _, tt := range []struct {
-		source      []byte
-		expectedErr string
-	}{
-		{
-			source:      []byte(":   \xea"),
-			expectedErr: "recovered: internal error: attempted to parse unknown event (please report): none",
-		},
-	} {
-		_, err := newConfig(tt.source)
-
-		if tt.expectedErr == "" {
-			suite.Require().NoError(err)
-		} else {
-			suite.Require().EqualError(err, tt.expectedErr)
-		}
+// TODO(aleksi): maybe remove once Go 1.18 is out; see https://github.com/golang/go/issues/47413
+func TestConfigLoader(t *testing.T) {
+	t.Parallel()
+
+	files, err := filepath.Glob(filepath.Join("testdata", "*.test"))
+	require.NoError(t, err)
+
+	for _, file := range files {
+		file := file
+		t.Run(file, func(t *testing.T) {
+			t.Parallel()
+
+			b, err := os.ReadFile(file)
+			require.NoError(t, err)
+
+			testConfigLoaderBytes(t, b)
+		})
 	}
 }