csv: Add SkipWriteFields (#39)

csv/writer.go

@@ -31,6 +31,10 @@ func NewWriter(w io.Writer, utf8bom bool) *Writer {
 	}
 }
 
+func (w *Writer) SkipWriteFields() {
+	w.fieldsWritten = true
+}
+
 // WriteFields writes fieldnames to w along with necessary utf8bom bytes. The fields must be a
 // non-zero field struct or a non-zero length string slice, otherwise an error will be return.
 // It can be run only once.
@@ -164,7 +168,7 @@ func (w *Writer) Write(record any) error {
 			if len(rec) == 0 {
 				return nil
 			}
-			return w.Writer.Write(r)
+			return w.Writer.Write(rec)
 		} else if d, ok := record.(D); ok {
 			for i, field := range w.fields {
 				for _, e := range d {

csv/writer_test.go

@@ -10,10 +10,10 @@ import (
 func TestWriteFields(t *testing.T) {
 	w := NewWriter(io.Discard, false)
 	if err := w.Write(map[string]string{"test": "test"}); err == nil {
-		t.Error("gave nil error; want error")
+		t.Fatal("gave nil error; want error")
 	}
 	if err := w.WriteFields(map[string]string{"test": "test"}); err == nil {
-		t.Error("gave nil error; want error")
+		t.Fatal("gave nil error; want error")
 	}
 	if err := w.WriteFields(struct {
 		A string
@@ -27,6 +27,30 @@ func TestWriteFields(t *testing.T) {
 	}
 }
 
+func TestSkipWriteFields(t *testing.T) {
+	var buf bytes.Buffer
+	w := NewWriter(&buf, false)
+	if err := w.WriteFields([]string{"A", "B"}); err != nil {
+		t.Fatal(err)
+	}
+	if err := w.Write([]string{"a", "b"}); err != nil {
+		t.Fatal(err)
+	}
+	w.Flush()
+	w = NewWriter(&buf, false)
+	if err := w.Write([]string{"c", "d"}); err == nil {
+		t.Fatal("gave nil error; want error")
+	}
+	w.SkipWriteFields()
+	if err := w.Write([]string{"c", "d"}); err != nil {
+		t.Fatal(err)
+	}
+	w.Flush()
+	if result, r := "A,B\na,b\nc,d\n", buf.String(); r != result {
+		t.Errorf("expected %q; got %q", result, r)
+	}
+}
+
 func TestWriter(t *testing.T) {
 	result := `A|B
 a|b