fix(decoder): panic raised on fuzzer inputs.

Handle yaml_NO_EVENT event type to raise a parsing
error vs panic.

ref go-yaml#833

Signed-off-by: Thibault Normand <me@zenithar.org>

decode.go

@@ -159,6 +159,9 @@ func (p *parser) parse() *Node {
 		return nil
 	case yaml_TAIL_COMMENT_EVENT:
 		panic("internal error: unexpected tail comment event (please report)")
+	case yaml_NO_EVENT:
+		failf("unable to build a node from none event")
+		return nil
 	default:
 		panic("internal error: attempted to parse unknown event (please report): " + p.event.typ.String())
 	}

decode_test.go

@@ -767,7 +767,7 @@ var unmarshalTests = []struct {
 		M{"a": 123456e1},
 	}, {
 		"a: 123456E1\n",
-		M{"a": 123456E1},
+		M{"a": 123456e1},
 	},
 	// yaml-test-suite 3GZX: Spec Example 7.1. Alias Nodes
 	{
@@ -802,7 +802,6 @@ var unmarshalTests = []struct {
 			"c": []interface{}{"d", "e"},
 		},
 	},
-
 }
 
 type M map[string]interface{}
@@ -934,6 +933,8 @@ func (s *S) TestUnmarshalDurationInt(c *C) {
 var unmarshalErrorTests = []struct {
 	data, error string
 }{
+	{"! !00 \xf6", "yaml: unable to build a node from none event"},
+	{"! !!0 \xf7", "yaml: unable to build a node from none event"},
 	{"v: !!float 'error'", "yaml: cannot decode !!str `error` as a !!float"},
 	{"v: [A,", "yaml: line 1: did not find expected node content"},
 	{"v:\n- [A,", "yaml: line 2: did not find expected node content"},
@@ -950,14 +951,14 @@ var unmarshalErrorTests = []struct {
 	{"a: 1\nb: 2\nc 2\nd: 3\n", "^yaml: line 3: could not find expected ':'$"},
 	{
 		"a: &a [00,00,00,00,00,00,00,00,00]\n" +
-		"b: &b [*a,*a,*a,*a,*a,*a,*a,*a,*a]\n" +
-		"c: &c [*b,*b,*b,*b,*b,*b,*b,*b,*b]\n" +
-		"d: &d [*c,*c,*c,*c,*c,*c,*c,*c,*c]\n" +
-		"e: &e [*d,*d,*d,*d,*d,*d,*d,*d,*d]\n" +
-		"f: &f [*e,*e,*e,*e,*e,*e,*e,*e,*e]\n" +
-		"g: &g [*f,*f,*f,*f,*f,*f,*f,*f,*f]\n" +
-		"h: &h [*g,*g,*g,*g,*g,*g,*g,*g,*g]\n" +
-		"i: &i [*h,*h,*h,*h,*h,*h,*h,*h,*h]\n",
+			"b: &b [*a,*a,*a,*a,*a,*a,*a,*a,*a]\n" +
+			"c: &c [*b,*b,*b,*b,*b,*b,*b,*b,*b]\n" +
+			"d: &d [*c,*c,*c,*c,*c,*c,*c,*c,*c]\n" +
+			"e: &e [*d,*d,*d,*d,*d,*d,*d,*d,*d]\n" +
+			"f: &f [*e,*e,*e,*e,*e,*e,*e,*e,*e]\n" +
+			"g: &g [*f,*f,*f,*f,*f,*f,*f,*f,*f]\n" +
+			"h: &h [*g,*g,*g,*g,*g,*g,*g,*g,*g]\n" +
+			"i: &i [*h,*h,*h,*h,*h,*h,*h,*h,*h]\n",
 		"yaml: document contains excessive aliasing",
 	},
 }
@@ -1436,7 +1437,10 @@ func (s *S) TestMergeStruct(c *C) {
 	}
 }
 
-var unmarshalNullTests = []struct{ input string; pristine, expected func() interface{} }{{
+var unmarshalNullTests = []struct {
+	input              string
+	pristine, expected func() interface{}
+}{{
 	"null",
 	func() interface{} { var v interface{}; v = "v"; return &v },
 	func() interface{} { var v interface{}; v = nil; return &v },
@@ -1487,7 +1491,7 @@ func (s *S) TestUnmarshalNull(c *C) {
 func (s *S) TestUnmarshalPreservesData(c *C) {
 	var v struct {
 		A, B int
-		C int `yaml:"-"`
+		C    int `yaml:"-"`
 	}
 	v.A = 42
 	v.C = 88