* Introduction

~crdt.el~ is a real-time collaborative editing environment for Emacs
using Conflict-free Replicated Data Types.

Highlights:
- [[https://en.wikipedia.org/wiki/Conflict-free_replicated_data_type][CRDT]],
  darling child of collaborative editing researches...
- Share multiple buffer in one session
- See other users' cursor and region
- Synchronize Org mode folding status
- Org mode integration
- Comint derivatives integration (experimental)

* Usage

** Installation

~crdt.el~ is now on GNU ELPA! Just =M-x package-install crdt=.

*Caution!!!* Please make sure that you and your peers are on the same
~crdt.el~ version!  It turns out to be one of the most common causes
of ~crdt.el~ not working.  Because currently the network protocol is
not stablized, behavior when using mismatched versions is
unexpectable.
- Strictly speaking, it should work when =crdt-protocol-version= are
  defined (added after version =0.2.5=) and the same on all peers.
  But why not save some hassle and keep everyone on the latest
  version.
- To upgrade, just =M-x package-reinstall crdt=, then preferably
  restart Emacs. To check your ~crdt.el~ version, =M-x crdt-version=.

** Start a shared session

A shared session is a place that can contains multiple buffers (or
files), and multiple users can join to collaboratively edit those
buffers (or files).  Think about a meeting room with some people
working together on some papers.

In some buffer, =M-x crdt-share-buffer=. Then enter session name.
This add the current buffer to the existing session with that name.
If no such exists, it creates a new session with the provided session
name, and initially contains the current buffer as a shared buffer.

If a new session is to be created, you need to enter port (default to
6530), optional password and your display name (default to your
current =(user-full-name)=).

Experimental settings: "Secure Port" specifies TLS port, and "Command
Functions" specifies user permissions. It's ok to just use the default
values.

** Join a session

=M-x crdt-connect=, then enter address, port, and your display name.

If the server has provided the permission (this is the default case),
connected user may also add their buffers to the session via
=M-x crdt-share-buffer=.

** Navigate through sessions

- Sessions :: =M-x crdt-list-sessions= lists all sessions.
  
- Buffers :: =M-x crdt-list-buffers= lists all buffers in current
  session.  In the displayed buffer list, press ~RET~ in the session
  list to see buffers in the selected session.

  You can also use =M-x crdt-switch-to-buffer= to interactively switch
  to another buffer in the current session.

- Users :: In a CRDT shared buffer (either server or client), =M-x crdt-list-users=
  to list active users. In the displayed user list, press ~RET~ on an
  entry to goto that user's cursor position.  Press ~f~ to follow that
  user, and press ~f~ again or =M-x crdt-stop-follow= to stop following.

  You can also use =M-x crdt-goto-next-user= and =M-x crdt-goto-prev-user=
  to cycle through users' cursor positions from any CRDT shared buffer
  (don't need to be in the user list buffer).

** Stop sharing

=M-x crdt-stop-session= stops a session you've started and disconnect
all other users from it.  This will ask for your confirmation,
customize =crdt-confirm-stop-session= if you want to disable it.

You can also press ~k~ or ~d~ in the session list (show it by =M-x crdt-list-sessions=).

=M-x crdt-stop-share-buffer= removes current buffer from its CRDT
session (this operation is only allowed at server side). You can also
press ~k~ or ~d~ in the buffer list.

** Disconnect from a session

=M-x crdt-disconnect=, then choose a session to disconnect from.

You can also press ~k~ or ~d~ in the session list (show it by =M-x crdt-list-sessions=).

The server Emacs has the privilege to disconnect a user from a
session.  To do so, press ~k~ or ~d~ on an entry in the user list
(show it by =M-x crdt-list-users=).

** Fancy stuff
   
- Visualizing author of parts of the document ::    
  Turn on =crdt-visualize-author-mode= to color text based on which
  user authored it.

- Synchronizing Org folding status :: Turn on
  =crdt-org-sync-overlay-mode=. All peers that have this enabled have
  their folding status synchronized. Peers without enabling this minor
  mode are unaffected.

- Comint integration ::
  Just go ahead and share you comint REPL buffer! Tested: ~shell~ and
  ~cmuscheme~.  By default, when sharing a comint buffer, ~crdt.el~
  temporarily reset input history (as in =M-n= =M-p=) so others don't
  spy into your =.bash_history= and alike.  You can customize this
  behavior using variable =crdt-comint-share-input-history=.

** What if we don't have a public IP?

There're various workaround.

- You can use [[https://gitlab.com/gjedeer/tuntox][tuntox]] to proxy
  your connection over the [[https://tox.chat][Tox]] protocol.
  =crdt.el= has experimental built-in integration for =tuntox=.  To
  enable it, you need to install =tuntox=, set up the custom variable
  =crdt-tuntox-executable= accordingly (the path to your =tuntox=
  binary), and set the custom variable =crdt-use-tuntox=.  Setting it
  to =t= make =crdt.el= always create =tuntox= proxy for new server
  sessions, and setting it to ='confirm= make =crdt.el= ask you every
  time when creating new sessions.  After starting a session with
  =tuntox= proxy, you can =M-x crdt-copy-url= to copy a URL
  recognizable by =M-x crdt-connect= and share it to your friends.  Be
  aware that according to my experience, =tuntox= takes significant
  time to establish a connection (sometimes up to half a minute),
  however it gets much faster after the connection is established.

- You can use Teredo to get a public routable IPv6 address.  One free
  software implementation is Miredo. Get it from your favorite package
  manager or from [[https://www.remlab.net/miredo/][their website]].
  A typical usage is (run as root)
  #+BEGIN_SRC
# /usr/local/sbin/miredo
# ifconfig teredo
  #+END_SRC
  The =ifconfig= command should print the information of your IPv6
  address.  Now your traffic go through IPv6, and once you start a
  =crdt.el= session, your friends should be able to join using the
  IPv6 address.  For more information, see the user guide on the
  Miredo website.

- You can use SSH port forwarding if you have a VPS with public IP.
  Example usage:
  #+BEGIN_SRC 
$ ssh -R EXAMPLE.COM:6530:127.0.0.1:6530 EXAMPLE.COM
  #+END_SRC
  This make your =crdt.el= session on local port =6530= accessible
  from =EXAMPLE.COM:6530=.
  
  Note that you need to set the following =/etc/ssh/sshd_config=
  option on your VPS
  #+BEGIN_SRC 
GatewayPorts yes
  #+END_SRC
