Host2Hub File Sync Protocol

Packet Format 
 Each packet starts with a one byte long identifier followed by the arguments. The end of the packet is signalized by a  SUB (0x1A) byte. (This is subject to change and will likely be replaced by a NUL (0x00) byte in the future. The different packets are listed below. 
 Generally, the host sends a packet to the hub and the hub responds. The only cases in which the hub actively sends a packet are if it reports an error or delivers a print message. 
 Packet Types 
 The Host can send these Packets, the Hub must handle these packets: 
 
 
 
 Identifier 
 Type 
 Meaning 
 Argmuent 
 
 
 Y (0x59) 
 Actively Sent 
 Start SYNC Mode 
 
 
 
 D (0x44) 
 Actively Sent 
 Ensure Directory exists 
 /path/to/dir 
 
 
 F (0x46) 
 Actively Sent 
 Ensure File has same Hash 
 /path/to/file SHA256 
 
 
 C (0x43) 
 Response 
 CHUNK 
 192 Bytes of the file data (base64-encoded compressed file) 
 
 
 E (0x45) 
 Response 
 End Of File 
 
 
 
 N (0x4E) 
 Actively Sent 
 End SYNC Mode 
 
 
 
 R (0x52) 
 Actively Sent 
 Remove File or Directory 
 /path/to/file/or/diretory 
 
 
 P (0x50) 
 Actively Sent 
 Start Program (loop() from /__init__.py) 
 
 
 
 X (0x58) 
 Actively Sent 
 Stop Program 
 
 
 
 & (0x26) 
 Actively Sent 
 Reboot 
 
 
 
 = (0x3D) 
 Actively Sent 
 Sync Communication 
 timestamp 
 
 
 > (0x3E) 
 Actively Sent 
 Enter REPL 
 
 
 
 $ (0x24) 
 Actively Sent 
 Reset State 
 
 
 
 
 The Hub can send these Packets, the Host must handle these packets: 
 
 
 
 Identifier 
 Type 
 Meaning 
 Argmuent 
 
 
 K (0x4B) 
 Response 
 OK 
 
 
 
 = (0x3D) 
 Response 
 Sync Communication 
 given timestamp 
 
 
 U (0x55) 
 Response 
 Request File Contents 
 
 
 
 ! (0x21) 
 Actively Sent 
 Internal Error 
 traceback 
 
 
 E (0x45) 
 Actively Sent 
 User Error 
 traceback 
 
 
 P (0x50) 
 Actively Sent 
 Print 
 json-encoded args & kwargs 
 
 
 
 Packets written in italics are not yet documented below. 
 Examples 
 Sync all files 
 If a full tree needs to be synced to the hub, this is the right choice. 
 
 Host sends Y to start SYNC Mode. Hub responds with  K . 
 Here, Files and Directories are updated. Refer to Update an individual file and Update an individual directory . 
 Host sends  N to stop SYNC Mode . Hub responds with K . 
 
 Effect 
 Upon receiving N , the Hub deletes all files and directories that were not updated since Y was sent. 
 Update an individual file 
 
 Host sends F . The argument is the file's path and its SHA256 Hash, seperated by a space. The file path needs to start with  / . Hub responds with  K ,  or with  U . 
 If U was sent, Host repeatedly sends C with 192 bytes of the file as argmuent, or E if EOF is reached. Hub responds to each of these packets with K . Hub can respond with  U to E if the hash is still not matching. 
 
 Effect 
 The Hub checks whether the file exists and has the correct hash. If it is correct, it responds with K . Otherwise, it sends U and stores the file received in the following  C packets under the given file path. 
 Update an individual directory 
 
 Host sends D with the file path as argument. The file path needs to start with  / . Hub responds with  K . 
 
 Effect 
 The Hub ensures the directory exists. 
 Delete an individual file or directory 
 
 Host sends R with the file path as argument. The file path needs to start with  / . Hub responds with  K . 
 
 Effect 
 The Hub deletes the file or directory found under the given file path if it exists. Non-empty directories are cleared. 
 Start the program 
 
 Host sends P . Hub responds with  K . 
 
 Effect 
 The Hub stops the task it created when it received P the last time, if it exists. The Hub starts the loop() function it found in the /__init__.py file by creating a new task using asyncio . 
 Stop the program 
 
 Host sends X . Hub responds with  K . 
 
 Effect 
 The Hub stops the task it created when it received P the last time, if it exists. 
 Sync connection 
 
 Host sends = with arbitrary data as argument. Hub echos the packet. 
 
 Effect 
 Echo. Ping-Pong. Verify connection. 
 Open REPL 
 
 Host sends  > . 
 
 Effect 
 The Hub stops all running tasks and returns control to the Micropython REPL. 
 [OUTDATED: This is to be preferred in comparison to sending Ctrl-C (which also works), as it makes sure the print() function works as expected afterwards.] -> [NOTE: Ctrl-C should not work] 
 Reboot Hub 
 
 Host sends  & . 
 
 Effect 
 The Hub reboots. 
 Cancel sync 
 
 Host sends $ . Hub responds with  K . 
 
 Effect 
 The Hub resets its sync state. It is recommended to send this when a new connection is made.