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package shuttle
import (
// GzipFormatter is an HTTPFormatter that is built with a
// delegate HTTPFormatter but which compresses the request body
type GzipFormatter struct {
delegate HTTPFormatter
reader *io.PipeReader
writer *io.PipeWriter
once *sync.Once
// NewGzipFormatter builds a new GzipFormatter with the supplied delegate
func NewGzipFormatter(delegate HTTPFormatter) *GzipFormatter {
reader, writer := io.Pipe()
f := &GzipFormatter{
delegate: delegate,
reader: reader,
writer: writer,
once: new(sync.Once),
return f
func (g *GzipFormatter) writeGzip() {
gw := gzip.NewWriter(g.writer)
_, err := io.Copy(gw, g.delegate)
if err != nil {
} else {
// MsgCount return the number of messages contained in the formatted batch
func (g *GzipFormatter) MsgCount() int {
return g.delegate.MsgCount()
// Request returns a http.Request to be used with a http.Client
// The request has it's body and headers set as necessary
func (g *GzipFormatter) Request() (*http.Request, error) {
request, err := g.delegate.Request()
if err != nil {
return request, err
request.Body = ioutil.NopCloser(g)
request.Header.Add("Content-Encoding", "gzip")
return request, nil
// Read bytes from the formatter stream
func (g *GzipFormatter) Read(p []byte) (int, error) {
g.once.Do(func() {
go g.writeGzip()
return g.reader.Read(p)
// Close the stream
func (g *GzipFormatter) Close() error {
return g.reader.Close()