[Draft] File system service minimum chunk size is 301 bytes

[Ignatius Bramananditya Rivaldi]

Description
I set transfer_chunk_size to 256 bytes according to https://docs.kubos.com/1.21.0/ecosystem/services/file.html#configuration as to simulate ground to OBC link, we used SLIP with default MTU of 296 bytes. But when I checked actual UDP packet size on the wire using Wireshark, the size is 302 bytes instead of 256 bytes, which results in huge amount of IP fragmentation, and eventually ICMP fragment reassembly time exceeded and then the file transfer failed

System Details

• KubOS HW: Beaglebone Black
• KubOS version: Linux Kubos 4.4.23-KubOS-1.21.0 #1 Fri Apr 3 16:07:34 UTC 2020 armv7l GNU/Linux

Severity

• Medium - Irritating bug, but there's a workaround

To Reproduce
Steps to reproduce the behavior:

1. Use file-client to download big file from OBC
2. Check network activity using Wireshark

Workaround
Increase SLIP MTU by using ip link set dev sl0 mtu 512 on both sides of connection