Revert "Switch to fasthttp"

This reverts commit 461d6f4a84.

utils.go

@@ -30,38 +30,3 @@ func doDeleteEncryptedContents(path string) error {
 		return nil
 	})
 }
-
-type BufferedWriter struct {
-	file             *os.File
-	downloaded       *int64
-	progressReporter ProgressReporter
-	buffer           []byte
-}
-
-func NewFileWriterWithProgress(file *os.File, downloaded *int64, progressReporter ProgressReporter) (*BufferedWriter, error) {
-	return &BufferedWriter{
-		file:             file,
-		downloaded:       downloaded,
-		progressReporter: progressReporter,
-		buffer:           make([]byte, BUFFER_SIZE),
-	}, nil
-}
-
-func (bw *BufferedWriter) Write(data []byte) (int, error) {
-	written := 0
-	for written < len(data) {
-		if bw.progressReporter.Cancelled() {
-			return written, nil
-		}
-		remaining := len(data) - written
-		toWrite := min(BUFFER_SIZE, uint64(remaining))
-		copy(bw.buffer, data[written:written+int(toWrite)])
-		n, err := bw.file.Write(bw.buffer[:toWrite])
-		if err != nil {
-			return written, err
-		}
-		written += n
-		*bw.downloaded += int64(n)
-	}
-	return written, nil
-}