feat(parser): handle UTF-8 BOM in JSON input

parser/json/json.go

@@ -10,6 +10,10 @@ type Parser struct{}
 
 // Unmarshal unmarshals JSON files.
 func (p *Parser) Unmarshal(data []byte, v interface{}) error {
+	if len(data) > 2 && data[0] == 0xef && data[1] == 0xbb && data[2] == 0xbf {
+		data = data[3:] // Strip UTF-8 BOM, see https://www.rfc-editor.org/rfc/rfc8259#section-8.1
+	}
+
 	if err := json.Unmarshal(data, v); err != nil {
 		return fmt.Errorf("unmarshal json: %w", err)
 	}

parser/json/json_test.go

@@ -40,3 +40,45 @@ func TestJSONParser(t *testing.T) {
 		t.Error("there should be at least one item defined in the parsed file, but none found")
 	}
 }
+
+func TestJSONParserWithBOM(t *testing.T) {
+	tests := []struct {
+		name    string
+		input   []byte
+		want    map[string]any
+		wantErr bool
+	}{
+		{
+			name:  "valid JSON with BOM",
+			input: append([]byte{0xEF, 0xBB, 0xBF}, []byte(`{"test": "value"}`)...),
+			want:  map[string]any{"test": "value"},
+		},
+		{
+			name:  "valid JSON without BOM",
+			input: []byte(`{"test": "value"}`),
+			want:  map[string]any{"test": "value"},
+		},
+	}
+
+	parser := &Parser{}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			var got interface{}
+			err := parser.Unmarshal(tt.input, &got)
+			if (err != nil) != tt.wantErr {
+				t.Errorf("Unmarshal() error = %v, wantErr %v", err, tt.wantErr)
+				return
+			}
+			if !tt.wantErr && got == nil {
+				t.Fatal("expected parsed content, got nil")
+			}
+			if m, ok := got.(map[string]any); ok {
+				for k, want := range tt.want {
+					if got := m[k]; got != want {
+						t.Errorf("key %q = %v, want %v", k, got, want)
+					}
+				}
+			}
+		})
+	}
+}