syncthing

This is syncthing, an open BitTorrent Sync alternative. It is currently far from ready for mass consumption, but it is a usable proof of concept and tech demo. The following are the project goals:

1. Define an open, secure, language neutral protocol usable for efficient synchronization of a file repository between an arbitrary number of nodes. This is the Block Exchange Protocol (BEP).

2. Provide the reference implementation to demonstrate the usability of said protocol. This is the syncthing utility.

The two are evolving together; the protocol is not to be considered stable until syncthing 1.0 is released, at which point it is locked down for incompatible changes.

Syncthing does not use the BitTorrent protocol. The reasons for this are

1. we don't know if BitTorrent Sync does either, so there's nothing to be compatible with, 2) BitTorrent includes a lot of functionality for making sure large swarms of selfish agents behave and somehow work towards a common goal. Here we have a much smaller swarm of cooperative agents and a simpler approach will suffice.

Features

The following features are currently implemented and working:

• The formation of a cluster of nodes, certificate authenticated and communicating over TLS over TCP.

• Synchronization of a single directory among the cluster nodes.

• Change detection by periodic scanning of the local repository.

• Static configuration of cluster nodes.

• Automatic discovery of cluster nodes on the local network. See discover.go for the protocol specification.

• Handling of deleted files. Deletes can be propagated or ignored per client.

• Synchronizing multiple unrelated directory tries by following symlinks directly below the repository level.

The following features are not yet implemented but planned:

• Change detection by listening to file system notifications instead of periodic scanning.

• HTTP GUI.

The following features are not implemented but may be implemented in the future:

• Syncing multiple directories from the same syncthing instance.

• Automatic remote node discovery using a DHT. This is not technically very difficult but requires one or more globally reachable root nodes. This is open for discussion -- perhaps we can piggyback on an existing DHT, or root nodes need to be established in some other manner.

• Automatic NAT handling via UPNP. Required for the above, not very useful without it.

• Conflict resolution. Currently whichever file has the newest modification time "wins". The correct behavior in the face of conflicts is open for discussion.

Security

Security is one of the primary project goals. This means that it should not be possible for an attacker to join a cluster uninvited, and it should not be possible to extract private information from intercepted traffic. Currently this is implemented as follows.

All traffic is protected by TLS. To prevent uninvited nodes from joining a cluster, the certificate fingerprint of each node is compared to a preset list of acceptable nodes at connection establishment. The fingerprint is computed as the SHA-1 hash of the certificate and displayed in BASE32 encoding to form a compact yet convenient string. Currently SHA-1 is deemed secure against preimage attacks.

Usage

go get github.com/calmh/syncthing

Check out the options:

$ syncthing --help
Usage:
  syncthing [options]

...

Run syncthing to let it create it's config directory and certificate:

$ syncthing
11:34:13 tls.go:61: OK: wrote cert.pem
11:34:13 tls.go:67: OK: wrote key.pem
11:34:13 main.go:66: INFO: My ID: NCTBZAAHXR6ZZP3D7SL3DLYFFQERMW4Q
11:34:13 main.go:90: FATAL: No config file

Take note of the "My ID: ..." line. Perform the same operation on another computer (or the same computer but with a different --home for testing) to create another node. Take note of that ID as well, and create a config file ~/.syncthing/syncthing.ini looking something like this:

[repository]
dir = /Users/jb/Synced

[nodes]
NCTBZAAHXR6ZZP3D7SL3DLYFFQERMW4Q = 172.16.32.1:22000 192.23.34.56:22000
CUGAE43Y5N64CRJU26YFH6MTWPSBLSUL = dynamic

This assumes that the first node is reachable on either of the two addresses listed (perhaps one internal and one port-forwarded external) and that the other node is not normally reachable from the outside. Save this config file, identically, to both nodes. If both nodes are running on the same network, you can set all addresses to 'dynamic' and they will find each other by local node discovery.

Start syncthing on both nodes. If you're running both on the same computer, one needs a different repository directory (in the config file) and listening port (set as a command line paramter). For the cautious, one side can be set to be read only.

$ syncthing --ro
13:30:55 main.go:102: INFO: My ID: NCTBZAAHXR6ZZP3D7SL3DLYFFQERMW4Q
13:30:55 main.go:149: INFO: Initial repository scan in progress
13:30:59 main.go:153: INFO: Listening for incoming connections
13:30:59 main.go:157: INFO: Attempting to connect to other nodes
13:30:59 main.go:247: INFO: Starting local discovery
13:30:59 main.go:165: OK: Ready to synchronize
13:31:04 discover.go:113: INFO: Discovered node CUGAE43Y5N64CRJU26YFH6MTWPSBLSUL at 172.16.32.24:23456
13:31:14 main.go:296: OK: Connected to node CUGAE43Y5N64CRJU26YFH6MTWPSBLSUL
13:31:19 main.go:345: INFO: Transferred 139 KiB in (14 KiB/s), 139 KiB out (14 KiB/s)
...

You should see the synchronization start and then finish a short while later. Add nodes to taste.

License

MIT