Add Pipe function to paster

handler/paste/paster.go

@@ -8,7 +8,10 @@ import (
 	"github.com/ollien/updown/repository"
 )
 
-const pasteFileMode = 0644
+const (
+	pasteFileMode = 0644
+	bufferSize    = 1024
+)
 
 // TruncatableFile implements reading, writing, seeking, truncation, and closing
 type TruncatableFile interface {
@@ -94,3 +97,19 @@ func (p *Paster) Close() error {
 
 	return p.file.Close()
 }
+
+// Pipe pours the entirety of the underlying pate into the given writer
+func (p *Paster) Pipe(w io.Writer) error {
+	buffer := make([]byte, bufferSize)
+	for {
+		n, err := p.Read(buffer)
+		if err == io.EOF {
+			break
+		} else if err != nil {
+			return err
+		}
+		w.Write(buffer[:n])
+	}
+
+	return nil
+}

handler/paste/paster_test.go

@@ -1,13 +1,16 @@
 package paste
 
 import (
+	"bytes"
 	"io"
+	"strings"
 	"testing"
 
 	"github.com/google/uuid"
 	"github.com/ollien/updown/repository"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/mock"
+	"github.com/stretchr/testify/require"
 )
 
 type MockFile struct {
@@ -109,3 +112,36 @@ func TestClose(t *testing.T) {
 	mockFile.AssertNotCalled(t, "Seek", mock.Anything)
 	mockFile.AssertNotCalled(t, "Read", mock.Anything)
 }
+
+func TestPipe(t *testing.T) {
+	paster := setupPaster()
+	mockFile := paster.file.(*MockFile)
+	// For subsequent calls to Read, we need to return different errors and paste contents
+	readCursor := 0
+	pasteContents := []string{"hello", " pipe", ""}
+	errors := []error{nil, nil, io.EOF}
+
+	readCall := mockFile.On("Read", mock.Anything).Return(len(pasteContents[0]), nil)
+	readCall.Run(func(args mock.Arguments) {
+		buffer := args.Get(0).([]byte)
+		singlePasteContents := pasteContents[readCursor]
+		// Dump pasteContents into the buffer
+		for i, char := range singlePasteContents {
+			buffer[i] = byte(char)
+		}
+		readCall.Return(len(singlePasteContents), errors[readCursor])
+
+		readCursor++
+		// Cannot call this more times than we have values for
+		require.True(t, func() bool {
+			return readCursor <= len(pasteContents)
+		}())
+	})
+	mockFile.On("Seek", int64(0), 0).Return(int64(0), nil)
+
+	pipeBuffer := bytes.NewBuffer([]byte{})
+	err := paster.Pipe(pipeBuffer)
+
+	assert.Nil(t, err)
+	assert.Equal(t, strings.Join(pasteContents, ""), pipeBuffer.String())
+}