Refactor file transfer header encoding into protocol sub-module.

protocol/File Transfer.go

@@ -0,0 +1,49 @@
+/*
+File Name:  File Transfer.go
+Copyright:  2021 Peernet s.r.o.
+Author:     Peter Kleissner
+
+Encoding of file transfer protocol. Each transfer starts with a header:
+Offset  Size   Info
+0       8      Total File Size
+8       8      Transfer Size
+*/
+
+package protocol
+
+import (
+	"encoding/binary"
+	"errors"
+	"io"
+)
+
+// FileTransferWriteHeader starts writing the header for a file transfer.
+func FileTransferWriteHeader(writer io.Writer, fileSize, transferSize uint64) (err error) {
+	// Send the header: Total File Size and Transfer Size.
+	header := make([]byte, 16)
+	binary.LittleEndian.PutUint64(header[0:8], fileSize)
+	binary.LittleEndian.PutUint64(header[8:16], transferSize)
+	if n, err := writer.Write(header); err != nil {
+		return err
+	} else if n != len(header) {
+		return errors.New("error sending header")
+	}
+
+	return nil
+}
+
+// FileTransferReadHeader starts reading the header for a file transfer. It will only read the header and keeps the connection open.
+func FileTransferReadHeader(reader io.Reader) (fileSize, transferSize uint64, err error) {
+	// read the header
+	header := make([]byte, 16)
+	if n, err := reader.Read(header); err != nil {
+		return 0, 0, err
+	} else if n != len(header) {
+		return 0, 0, errors.New("error reading header")
+	}
+
+	fileSize = binary.LittleEndian.Uint64(header[0:8])
+	transferSize = binary.LittleEndian.Uint64(header[8:16])
+
+	return fileSize, transferSize, nil
+}