reader/fetcher: add brotli content encoding support

internal/reader/fetcher/encoding_wrappers.go

@@ -0,0 +1,55 @@
+package fetcher
+
+import (
+	"compress/gzip"
+	"io"
+
+	"github.com/andybalholm/brotli"
+)
+
+type brotliReadCloser struct {
+	body         io.ReadCloser
+	brotliReader io.Reader
+}
+
+func NewBrotliReadCloser(body io.ReadCloser) *brotliReadCloser {
+	return &brotliReadCloser{
+		body:         body,
+		brotliReader: brotli.NewReader(body),
+	}
+}
+
+func (b *brotliReadCloser) Read(p []byte) (n int, err error) {
+	return b.brotliReader.Read(p)
+}
+
+func (b *brotliReadCloser) Close() error {
+	return b.body.Close()
+}
+
+type gzipReadCloser struct {
+	body       io.ReadCloser
+	gzipReader io.Reader
+	gzipErr    error
+}
+
+func NewGzipReadCloser(body io.ReadCloser) *gzipReadCloser {
+	return &gzipReadCloser{body: body}
+}
+
+func (gz *gzipReadCloser) Read(p []byte) (n int, err error) {
+	if gz.gzipReader == nil {
+		if gz.gzipErr == nil {
+			gz.gzipReader, gz.gzipErr = gzip.NewReader(gz.body)
+		}
+		if gz.gzipErr != nil {
+			return 0, gz.gzipErr
+		}
+	}
+
+	return gz.gzipReader.Read(p)
+}
+
+func (gz *gzipReadCloser) Close() error {
+	return gz.body.Close()
+}