Merge pull request #6 from fossil-engineering/feature/add-reader-writ…

…e-error

Define errors for Reader and Write functions.

buffer.go

@@ -4,12 +4,22 @@ package multibuf
 
 import (
 	"bytes"
+	"errors"
 	"fmt"
 	"io"
 	"io/ioutil"
 	"os"
 )
 
+var (
+	// ErrNoDataReady is an error when getting the reader while the data is not
+	// ready.
+	ErrNoDataReady = errors.New("mailgun/multibuf: no data ready")
+	// ErrReaderHasBeenCalled is an error when getting the reader or writing
+	// while the reader has been called.
+	ErrReaderHasBeenCalled = errors.New("mailgun/multibuf: reader has been called")
+)
+
 // MultiReader provides Read, Close, Seek and Size methods. In addition to that it supports WriterTo interface
 // to provide efficient writing schemes, as functions like io.Copy use WriterTo when it's available.
 type MultiReader interface {
@@ -337,7 +347,7 @@ func (w *writerOnce) write(p []byte) (int, error) {
 	}
 	switch w.state {
 	case writerCalledRead:
-		return 0, fmt.Errorf("can not write after reader has been called")
+		return 0, ErrReaderHasBeenCalled
 	case writerInit:
 		w.mem = &bytes.Buffer{}
 		w.state = writerMem
@@ -388,9 +398,9 @@ func (w *writerOnce) initFile() error {
 func (w *writerOnce) Reader() (MultiReader, error) {
 	switch w.state {
 	case writerInit:
-		return nil, fmt.Errorf("no data ready")
+		return nil, ErrNoDataReady
 	case writerCalledRead:
-		return nil, fmt.Errorf("reader has been called")
+		return nil, ErrReaderHasBeenCalled
 	case writerMem:
 		w.state = writerCalledRead
 		return newBuf(w.total, nil, bytes.NewReader(w.mem.Bytes())), nil

buffer_test.go

@@ -264,16 +264,16 @@ func TestWriterReaderCalled(t *testing.T) {
 
 	// Subsequent calls to write and get reader will fail
 	_, err = w.Reader()
-	assert.Error(t, err)
+	assert.EqualError(t, err, ErrReaderHasBeenCalled.Error())
 
 	_, err = w.Write([]byte{1})
-	assert.Error(t, err)
+	assert.EqualError(t, err, ErrReaderHasBeenCalled.Error())
 }
 
 func TestWriterNoData(t *testing.T) {
 	w, err := NewWriterOnce()
 	assert.NoError(t, err)
 
 	_, err = w.Reader()
-	assert.Error(t, err)
+	assert.EqualError(t, err, ErrNoDataReady.Error())
 }