Marshaler returning nil creates malformed output #84
Description
If a value implementing the Marshaler interface returns a nil replacement value, the resulting encoding is malformed. The value's key is encoded but the value is silently skipped:
<plist version="1.0">
<dict>
<key>C</key>
</dict>
</plist>
The correct behaviour is to return an encoding error. The exception is if the non-nil Marshaler value has the omitempty structure tag and it returns a replacement of nil, then the entire key value pair should be omitted:
type S struct {
C CustomMarshaler `plist:"C,omitempty"`
}
Below are some tests to help isolate the problem:
type CustomMarshaler struct {
value interface{}
}
var _ plist.Marshaler = (*CustomMarshaler)(nil)
func (c *CustomMarshaler) MarshalPlist() (interface{}, error) {
return c.value, nil
}
func TestPlistMarshalerNil(t *testing.T) {
// Direct non-nil value encodes
t.Run("string", func(t *testing.T) {
c := &CustomMarshaler{value: "hello world"}
b, err := plist.Marshal(c, plist.XMLFormat)
if err != nil {
t.Error(err)
}
if len(b) == 0 {
t.Error("expect non-nil")
}
// <!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
// <plist version="1.0"><string>hello world</string></plist>
})
// Direct nil value correctly returns an error
t.Run("nil", func(t *testing.T) {
c := &CustomMarshaler{}
b, err := plist.Marshal(c, plist.XMLFormat)
if err == nil {
t.Error("expect error")
}
if len(b) != 0 {
t.Error("expect nil")
}
})
// Field nil value with omitempty correctly omitted
t.Run("ptr-omitempty", func(t *testing.T) {
type Structure struct {
C *CustomMarshaler `plist:"C,omitempty"`
}
s := &Structure{}
b, err := plist.Marshal(s, plist.XMLFormat)
if err != nil {
t.Error(err)
}
if len(b) == 0 {
t.Error("expect non-nil")
}
// <!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
// <plist version="1.0"><dict></dict></plist>
})
// Non-nil field returning marshaler nil value with omitempty should be omitted
t.Run("omitempty", func(t *testing.T) {
type Structure struct {
C CustomMarshaler `plist:"C,omitempty"`
}
s := &Structure{}
b, err := plist.Marshal(s, plist.XMLFormat)
if err != nil {
t.Error(err)
}
if len(b) == 0 {
t.Error("expect non-nil")
}
//t.Log(string(b))
// Unmarshal to prove malformed encoding
var dst Structure
if _, err := plist.Unmarshal(b, &dst); err != nil {
t.Error(err) // plist: error parsing XML property list: missing value in dictionary
}
// Get key without value and no error:
// <!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
// <plist version="1.0"><dict><key>C</key></dict></plist>
// Expect:
// <!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
// <plist version="1.0"><dict></dict></plist>
})
}