Host2Hub File Sync Protocol

Packet Format

A packet always starts with a colon (:). This is to filter out unrelated data by e.g. micropython itself.
This is followed by a one byte long identifier specifying the packet type.

Without an argument

Without an argument, the packet is now closed with a closing bracket (]).

With an argmument

Four digits will specify the length of the following base64 encoded argument.

Packet Types

The Host can send these Packets, the Hub must handle these packets:

Identifier	Type	Meaning	Argmuent
Y	Actively Sent	Start SYNC Mode
D	Actively Sent	Ensure Directory exists	/path/to/dir
F	Actively Sent	Ensure File has same Hash	/path/to/file SHA256
C	Response	CHUNK	192 Bytes of file
E	Response	End Of File
N	Actively Sent	End SYNC Mode
R	Actively Sent	Remove File or Directory	/path/to/file/or/diretory
P	Actively Sent	Start Program (loop() from /__init__.py)
X	Actively Sent	Stop Program
&	Actively Sent	Reboot
=	Actively Sent	Sync Communication	timestamp
>	Actively Sent	Enter REPL
$	Actively Sent	Reset State

The Hub can send these Packets, the Host must handle these packets:

Identifier	Type	Meaning	Argmuent
K	Response	OK
=	Response	Sync Communication	given timestamp
U	Response	Request File Contents
!	Actively Sent	Internal Error	traceback
E	Actively Sent	User Error	traceback
$	Actively Sent	Please Reconnect
P	Actively Sent	Print	json-encoded args & kwargs
B	Actively Sent	Blocking call, will be inresponsive
D	Actively Sent	No more blocking call, will be responsive again

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.

1. Host sends Y to start SYNC Mode.
   Hub responds with K.
2. Here, Files and Directories are updated.
   Refer to Update an individual file and Update an individual directory.
3. 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

1. 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.
2. 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 stores the file under the given file path.

Update an individual directory

1. 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

1. 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.

Start the program

1. 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

1. 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

1. Host sends = with some uniwue identifier, eg. the current timestamp, as argument.
   Hub echos the packet.

Effect

The Host skips all packets until it receives the echo in order to ignore the hubs responses made before the connection was established. It is recommended to use this at the start of every connection.

Open REPL

1. Host sends >.

Effect

The Hub stops all running tasks and returns control to the Micropython REPL.
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.

Reboot Hub

1. Host sends &.

Effect

The Hub reboots.

Reset Connection

1. Host sends $.
   Hub responds with K.

Effect

The Hub resets its state. It is recommended to send this when a new connection is made.