more tests, handle unexported and tagged fields moar better

decode.go

@@ -31,13 +31,12 @@ 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)
-
 	// v is nil, skip this line and proceed.
-	if rv.Kind() == reflect.Invalid {
+	if v == nil {
 		_, err := d.read()
 		return err
 	}
+	rv := reflect.ValueOf(v)
 	if rv.Kind() != reflect.Ptr {
 		return errors.New("must be pointer")
 	}

decode_test.go

@@ -25,15 +25,15 @@ d,e,f
 	}, {
 		// Rows that only have partial data are only partially filled.
 		data: `Foo,Bar,Baz
-a,,
-,b,
+a,"",""
+"",b,""
 `,
 		out: []row{{"a", "", ""}, {"", "b", ""}},
 	}, {
 		// Rows that don't define all the columns are partially filled.
 		data: `Foo,Bar
-a,
-,b
+a,""
+"",b
 `,
 		out: []row{{"a", "", ""}, {"", "b", ""}},
 	}, {

encode.go

@@ -14,7 +14,7 @@ type Encoder interface {
 
 type encoder struct {
 	w  csv.Writer
-	hw bool
+	hm map[string]int
 }
 
 // NewEncoder returns an encoder that writes to w.
@@ -24,52 +24,81 @@ func NewEncoder(w io.Writer) Encoder {
 
 // EncodeNext writes the CSV encoding of v to the stream.
 func (e *encoder) EncodeNext(v interface{}) error {
+	if v == nil {
+		return nil
+	}
+
 	t := reflect.ValueOf(v).Type()
-	if !e.hw {
-		headers := make([]string, t.NumField())
+	if e.hm == nil {
+		e.hm = make(map[string]int)
+		headers := []string{}
 		for i := 0; i < t.NumField(); i++ {
 			f := t.Field(i)
 			if f.PkgPath != "" { // Filter unexported fields
 				continue
 			}
-			h := f.Name
+			n := f.Name
 			if f.Tag.Get("csv") != "" {
-				h = f.Tag.Get("csv")
+				n = f.Tag.Get("csv")
+				if n == "-" {
+					continue
+				}
 			}
-			headers[i] = h
+			headers = append(headers, n)
+			e.hm[n] = i
 		}
 		if err := e.w.Write(headers); err != nil {
 			return err
 		}
-		e.hw = true
 	}
 
 	rv := reflect.ValueOf(v)
-	row := make([]string, t.NumField())
+	row := []string{}
+	add := false // Whether there has been a row to write in this call.
 	for i := 0; i < t.NumField(); i++ {
 		f := t.Field(i)
 		if f.PkgPath != "" { // Filter unexported fields
 			continue
 		}
+		n := f.Name
+		if f.Tag.Get("csv") != "" {
+			n = f.Tag.Get("csv")
+		}
+
+		fi, ok := e.hm[n]
+		if !ok {
+			// Unmapped header value
+			continue
+		}
+
+		// Increase the row size to fit the new row.
+		for fi >= len(row) {
+			row = append(row, "")
+		}
+
+		add = true
 		vf := rv.Field(i)
 		switch vf.Kind() {
 		case reflect.String:
-			row[i] = vf.String()
+			row[fi] = vf.String()
 		case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
-			row[i] = fmt.Sprintf("%d", vf.Int())
+			row[fi] = fmt.Sprintf("%d", vf.Int())
 		case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64:
-			row[i] = fmt.Sprintf("%d", vf.Uint())
+			row[fi] = fmt.Sprintf("%d", vf.Uint())
 		case reflect.Float64:
-			row[i] = fmt.Sprintf("%f", vf.Float())
+			row[fi] = fmt.Sprintf("%f", vf.Float())
 		case reflect.Bool:
-			row[i] = fmt.Sprintf("%t", vf.Bool())
+			row[fi] = fmt.Sprintf("%t", vf.Bool())
 		default:
 			return fmt.Errorf("can't decode type %v", f.Type)
 		}
 	}
+	if !add {
+		return nil
+	}
 	if err := e.w.Write(row); err != nil {
 		return err
 	}
 	e.w.Flush()
-	return nil
+	return e.w.Error()
 }

encode_test.go

@@ -18,6 +18,18 @@ func TestEncodeNext(t *testing.T) {
 		`Foo,Bar,Baz
 a,b,c
 d,e,f
+`,
+	}, {
+		[]row{{"a", "", ""}, {"", "b", ""}},
+		`Foo,Bar,Baz
+a,"",""
+"",b,""
+`,
+	}, {
+		[]row{{"a", "", ""}, {"", "b", ""}},
+		`Foo,Bar,Baz
+a,"",""
+"",b,""
 `,
 	}} {
 		var buf bytes.Buffer
@@ -33,3 +45,90 @@ d,e,f
 		}
 	}
 }
+
+func TestEncode_Unexported(t *testing.T) {
+	r := struct {
+		Exported, unexported string
+	}{"a", "b"}
+	var buf bytes.Buffer
+	if err := NewEncoder(&buf).EncodeNext(r); err != nil {
+		t.Errorf("unexpected error: %v", err)
+	}
+	exp := `Exported
+a
+`
+	got := buf.String()
+	if got != exp {
+		t.Errorf("unexpected result, got %s, want %s", got, exp)
+	}
+}
+
+func TestEncode_Tags(t *testing.T) {
+	type row struct {
+		Foo     string `csv:"renamed_foo"`
+		Bar     string
+		Ignored string `csv:"-"`
+	}
+	var buf bytes.Buffer
+	if err := NewEncoder(&buf).EncodeNext(row{"a", "b", "c"}); err != nil {
+		t.Errorf("unexpected error: %v", err)
+	}
+	exp := `renamed_foo,Bar
+a,b
+`
+	got := buf.String()
+	if got != exp {
+		t.Errorf("unexpected result, got %s, want %s", got, exp)
+	}
+}
+
+func TestEncode_NonStrings(t *testing.T) {
+	r := struct {
+		Int     int
+		Int64   int64
+		Uint64  uint64
+		Float64 float64
+		Bool    bool
+	}{123, -123456789, 123456789, 123.456, true}
+	var buf bytes.Buffer
+	if err := NewEncoder(&buf).EncodeNext(r); err != nil {
+		t.Errorf("unexpected error: %v", err)
+	}
+	exp := `Int,Int64,Uint64,Float64,Bool
+123,-123456789,123456789,123.456000,true
+`
+	got := buf.String()
+	if got != exp {
+		t.Errorf("unexpected result, got %s, want %s", got, exp)
+	}
+}
+
+func TestEncodeDifferent(t *testing.T) {
+	type row1 struct {
+		Foo, Bar string
+	}
+	type row2 struct {
+		Baz string
+	}
+	type row3 struct {
+		Bar, Baz string
+	}
+	var buf bytes.Buffer
+	e := NewEncoder(&buf)
+	// Headers are taken from the fields in the first call to EncodeNext.
+	// Further calls add whatever fields they can, and if no fields are
+	// shared then the row is not written.
+	for _, r := range []interface{}{row1{"foo", "bar"}, row2{"baz"}, row3{"bar", "baz"}} {
+		if err := e.EncodeNext(r); err != nil {
+			t.Errorf("unexpected error: %v", err)
+		}
+	}
+	exp := `Foo,Bar
+foo,bar
+"",bar
+`
+	got := buf.String()
+	if got != exp {
+		t.Errorf("unexpected result, got %s, want %s", got, exp)
+	}
+}