Remove panic and replace by returning InvalidDecodeError

for issue-#7

Author: joeybloggs

decoder_test.go

@@ -1129,7 +1129,7 @@ func TestDecodeAllTypes(t *testing.T) {
 	Equal(t, phones[1].Label, "label2")
 }
 
-func TestDecoderPanics(t *testing.T) {
+func TestDecoderPanicsAndBadValues(t *testing.T) {
 
 	type Phone struct {
 		Number string
@@ -1152,7 +1152,28 @@ func TestDecoderPanics(t *testing.T) {
 	PanicMatches(t, func() { decoder.Decode(&test, values) }, "Invalid formatting for key 'Phone[0.Number' missing ']' bracket")
 
 	i := 1
-	PanicMatches(t, func() { decoder.Decode(i, values) }, "interface must be a pointer")
+	err := decoder.Decode(i, values)
+	NotEqual(t, err, nil)
+
+	_, ok := err.(*InvalidDecoderError)
+	Equal(t, ok, true)
+	Equal(t, err.Error(), "form: Decode(non-pointer int)")
+
+	err = decoder.Decode(nil, values)
+	NotEqual(t, err, nil)
+
+	_, ok = err.(*InvalidDecoderError)
+	Equal(t, ok, true)
+	Equal(t, err.Error(), "form: Decode(nil)")
+
+	var ts *TestError
+
+	err = decoder.Decode(ts, values)
+	NotEqual(t, err, nil)
+
+	_, ok = err.(*InvalidDecoderError)
+	Equal(t, ok, true)
+	Equal(t, err.Error(), "form: Decode(nil *form.TestError)")
 
 	values = url.Values{
 		"Phone0].Number": []string{"1(111)111-1111"},
@@ -1357,7 +1378,12 @@ func TestDecoderInterface(t *testing.T) {
 
 	iface = i
 
-	PanicMatches(t, func() { d.Decode(iface, values) }, "interface must be a pointer")
+	err = d.Decode(iface, values)
+	NotEqual(t, err, nil)
+
+	_, ok := err.(*InvalidDecoderError)
+	Equal(t, ok, true)
+	Equal(t, err.Error(), "form: Decode(non-pointer int)")
 
 	values = map[string][]string{
 		"Value": {"testVal"},
@@ -1377,5 +1403,10 @@ func TestDecoderInterface(t *testing.T) {
 
 	iface = tst
 
-	PanicMatches(t, func() { d.Decode(iface, values) }, "interface must be a pointer")
+	err = d.Decode(iface, values)
+	NotEqual(t, err, nil)
+
+	_, ok = err.(*InvalidDecoderError)
+	Equal(t, ok, true)
+	Equal(t, err.Error(), "form: Decode(non-pointer form.test)")
 }

form_decoder.go

@@ -28,6 +28,23 @@ func (d DecodeErrors) Error() string {
 	return strings.TrimSpace(buff.String())
 }
 
+// An InvalidDecoderError describes an invalid argument passed to Decode.
+// (The argument passed to Decode must be a non-nil pointer.)
+type InvalidDecoderError struct {
+	Type reflect.Type
+}
+
+func (e *InvalidDecoderError) Error() string {
+	if e.Type == nil {
+		return "form: Decode(nil)"
+	}
+
+	if e.Type.Kind() != reflect.Ptr {
+		return "form: Decode(non-pointer " + e.Type.String() + ")"
+	}
+	return "form: Decode(nil " + e.Type.String() + ")"
+}
+
 type key struct {
 	ivalue      int
 	value       string
@@ -92,7 +109,9 @@ func (d *Decoder) RegisterCustomTypeFunc(fn DecodeCustomTypeFunc, types ...inter
 	}
 }
 
-// Decode decodes the given values and sets the corresponding struct values
+// Decode parses the given values and sets the corresponding struct and/or type values
+//
+// Decode returns an InvalidDecoderError if interface passed is invalid.
 func (d *Decoder) Decode(v interface{}, values url.Values) (err error) {
 
 	dec := &decoder{
@@ -102,12 +121,12 @@ func (d *Decoder) Decode(v interface{}, values url.Values) (err error) {
 
 	val := reflect.ValueOf(v)
 
-	if val.Kind() != reflect.Ptr {
-		panic("interface must be a pointer")
+	if val.Kind() != reflect.Ptr || val.IsNil() {
+		return &InvalidDecoderError{reflect.TypeOf(v)}
+		// panic("interface must be a pointer")
 	}
 
 	val = val.Elem()
-
 	typ := val.Type()
 
 	if val.Kind() == reflect.Struct && typ != timeType {