support DecodeNext(nil) to skip a line

csvstruct.go

@@ -1,4 +1,3 @@
-// TODO: support DecodeNext(nil) to skip a line
 // TODO: NewEncoder/EncodeNext -- header will be fields in first item...
 // TODO: Encode/Decode map[string]string
 
@@ -34,7 +33,13 @@ func NewDecoder(r io.Reader) Decoder {
 // DecodeNext reads the next CSV-encoded value from its input and stores it in the value pointed to by v.
 func (d *decoder) DecodeNext(v interface{}) error {
 	rv := reflect.ValueOf(v)
-	if rv.Kind() != reflect.Ptr || rv.IsNil() {
+
+	// v is nil, skip this line and proceed.
+	if rv.Kind() == reflect.Invalid {
+		_, err := d.read()
+		return err
+	}
+	if rv.Kind() != reflect.Ptr {
 		return errors.New("must be pointer")
 	}
 	rv = rv.Elem()

csvstruct_test.go

@@ -58,6 +58,9 @@ d
 		if !reflect.DeepEqual(rows, c.out) {
 			t.Errorf("unexpected result, got %v, want %v", rows, c.out)
 		}
+		if !isDone(d) {
+			t.Errorf("decoder unexpectedly not done")
+		}
 	}
 }
 
@@ -128,6 +131,33 @@ a,b`)).DecodeNext(&r); err != nil {
 	}
 }
 
+func TestDecode_DecodeNil(t *testing.T) {
+	type row struct {
+		Foo, Bar string
+	}
+	d := NewDecoder(strings.NewReader(`Foo,Bar
+ignore,this
+a,b`))
+	if err := d.DecodeNext(nil); err != nil {
+		t.Errorf("unexpected error while skipping line: %v", err)
+	}
+	var r row
+	if err := d.DecodeNext(&r); err != nil {
+		t.Errorf("unexpected error decoding after skip: %v", err)
+	}
+	exp := row{"a", "b"}
+	if r != exp {
+		t.Errorf("unexpected result, got %v, want %v", r, exp)
+	}
+	if !isDone(d) {
+		t.Errorf("decoder unexpectedly not done")
+	}
+}
+
+func isDone(d Decoder) bool {
+	return d.DecodeNext(nil) == io.EOF
+}
+
 func ExampleDecoder_DecodeNext() {
 	csv := `Foo,Bar,Baz
 a,b,c