check invalid strings and add fuzzing

thespine.go

@@ -1,8 +1,18 @@
 package thespine
 
+import (
+	"errors"
+	"unicode/utf8"
+)
+
 const THE_SIZE = 3
 
-func Decode(s string) string {
+var ErrInvalidString = errors.New("invalid string")
+
+func Decode(s string) (string, error) {
+	if !utf8.ValidString(s) {
+		return "", ErrInvalidString
+	}
 	sr := []rune(s)
 	l := len(sr)
 	g := make([][]rune, 0)
@@ -19,10 +29,13 @@ func Decode(s string) string {
 		gs := sr[si:ei]
 		g = append(g, gs)
 	}
-	return concat(g)
+	return concat(g), nil
 }
 
-func Encode(s string) string {
+func Encode(s string) (string, error) {
+	if !utf8.ValidString(s) {
+		return "", ErrInvalidString
+	}
 	sr := []rune(s)
 	l := len(sr)
 	g := make([][]rune, 0)
@@ -42,7 +55,7 @@ func Encode(s string) string {
 	for i, j := 0, len(g)-1; i < j; i, j = i+1, j-1 {
 		g[i], g[j] = g[j], g[i]
 	}
-	return concat(g)
+	return concat(g), nil
 }
 
 func concat(r [][]rune) string {

thespine_test.go

@@ -4,53 +4,131 @@ import (
 	"testing"
 )
 
-func Test_EncodeDecode(t *testing.T) {
+func Test_Decode(t *testing.T) {
 	tests := []struct {
-		str  string
-		name string
-		want string
+		str     string
+		name    string
+		want    string
+		wantErr bool
 	}{
 		{
-			str:  "",
-			name: "empty string",
-			want: "",
+			str:     "",
+			name:    "empty string",
+			want:    "",
+			wantErr: false,
 		},
 		{
-			str:  "erecshyrinol",
-			name: "the song",
-			want: "nolyricshere",
+			str:     "erecshyrinol",
+			name:    "the song",
+			want:    "nolyricshere",
+			wantErr: false,
 		},
 		{
-			str:  "nespithe",
-			name: "the album",
-			want: "thespine",
+			str:     "nespithe",
+			name:    "the album",
+			want:    "thespine",
+			wantErr: false,
 		},
 		{
-			str:  "seteernkub",
-			name: "the tech",
-			want: "kubernetes",
+			str:     "seteernkub",
+			name:    "the tech",
+			want:    "kubernetes",
+			wantErr: false,
 		},
 		{
-			str:  "ᚬᚩᚡᚣ",
-			name: "the runes",
-			want: "ᚩᚡᚣᚬ",
+			str:     "ᚬᚩᚡᚣ",
+			name:    "the runes",
+			want:    "ᚩᚡᚣᚬ",
+			wantErr: false,
 		},
 		{
-			str:  "\xf0\x9f\x9a\x80ketroc",
-			name: "the cringe",
-			want: "rocket\xf0\x9f\x9a\x80",
+			str:     "\xf2",
+			name:    "the invalid string",
+			want:    "",
+			wantErr: true,
+		},
+		{
+			str:     "\xf0\x9f\x9a\x80ketroc",
+			name:    "the cringe",
+			want:    "rocket\xf0\x9f\x9a\x80",
+			wantErr: false,
 		},
 	}
 	for _, test := range tests {
 		t.Run(test.name, func(t *testing.T) {
-			got := Decode(test.str)
+			got, err := Decode(test.str)
+			if test.wantErr && err == nil {
+				t.Fatalf("decode err wanted but got none")
+			}
 			if got != test.want {
 				t.Fatalf("decode got: %s\nwant: %s\n", got, test.want)
 			}
-			got = Encode(test.want)
-			if got != test.str {
-				t.Fatalf("encode got: %s\nwant: %s\n", got, test.str)
+		})
+	}
+}
+
+func Test_Encode(t *testing.T) {
+	tests := []struct {
+		str     string
+		name    string
+		want    string
+		wantErr bool
+	}{
+		{
+			str:     "",
+			name:    "empty string",
+			want:    "",
+			wantErr: false,
+		},
+		{
+			str:     "nolyricshere",
+			name:    "the song",
+			want:    "erecshyrinol",
+			wantErr: false,
+		},
+		{
+			str:     "\xf2",
+			name:    "the invalid string",
+			want:    "",
+			wantErr: true,
+		},
+		{
+			str:     "rocket\xf0\x9f\x9a\x80",
+			name:    "the cringe",
+			want:    "\xf0\x9f\x9a\x80ketroc",
+			wantErr: false,
+		},
+	}
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			enc, err := Encode(test.str)
+			if test.wantErr && err == nil {
+				t.Fatalf("encode err wanted but got none")
+			}
+			if enc != test.want {
+				t.Fatalf("encode got: %s\nwant: %s\n", enc, test.want)
 			}
 		})
 	}
 }
+
+func FuzzEncode(f *testing.F) {
+	tcs := []string{"rocket\xf0\x9f\x9a\x80", "abba acdc", "Hello, 世界!"}
+	for _, tc := range tcs {
+		f.Add(tc)
+	}
+	f.Fuzz(func(t *testing.T, og string) {
+		ec, _ := Encode(og)
+		if ec != "" {
+			dc, _ := Decode(ec)
+			ogr := []rune(og)
+			dcr := []rune(dc)
+			if og != dc {
+				t.Errorf("Before: '%q', after: '%q'", og, dc)
+			}
+			if len(ogr) != len(dcr) {
+				t.Errorf("Length before: %d, after: %d", len(og), len(dc))
+			}
+		}
+	})
+}