thesis.tex

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% Author: Mathias Payer <mathias.payer@epfl.ch>
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\title{Smallworld: Adding Dat support}
\author{Paulette Vazquez and Guilhem Niot}
\supervisor{Dr. Erick Lavoie}
\adviser{Professor Anne-Marie Kermarrec}

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\begin{document}
\maketitle

% \maketoc


\section{Another application of Smallworld, the Dat Protocol}



The Dat Protocol\footnote{\url{https://www.datprotocol.com/}} is a peer-to-peer protocol that allows sharing files in a distributed network. It is based on append-only logs Secure-Scuttlebutt (SSB) but its community is more active, and it provides more mature libraries.

As a distributed file sharing protocol, it differs from BitTorrent in that contents can be updated by their author.

This report aims at showing that Dat can be used with a Smallworld setup, to continuously replicate files among peers, similarly to a Dropbox instance. We will explain how to configure Dat to continously replicate files, and we will cover the case where we replicate files between two clients A and B with the Raspberry Pi acting as an intermediary in case only one of the clients is online at a given time.
% \subsection{Installation}

% The installation of Dat is quite straightforward. The dat-cli command utility allows to simply interact with Dat files. The commands in Figure \ref{cmd:dat_install} are used to install dat-cli.
% % TODO: try replicating remotely


% It must be installed on both the emitter and the receiver devices.

% \begin{figure}
%   \begin{lstlisting}[label=cmd:dat_install, caption=Installing dat-cli]
%     wget -qO- https://raw.githubusercontent.com/datproject/dat/master/download.sh | bash
    
%     # or
%     npm install -g dat-cli
%   \end{lstlisting}
% \end{figure}

\subsection{Real time synchronization with dat-store}

Dat provides a command tool called \emph{dat-cli} that is advised for downloading and syncing Dat archives, but it is not able to run in background, and cannot be remotely controlled and is thus not practical for this application. \\

A more suited tool is \emph{dat-store}. It implements the same commands as \emph{dat-cli} and on top of that it provides a service that can be run in background,  and can be remotely controlled. \\
Dat-store introduces the concept of provider. Providers are instances of dat-store running either locally or remotely. The default provider is your local instance, but you can also configure other providers, like the Raspberry Pi. 
This notion is particularly useful for remote control of other providers. \\

% It is possible to create a shared folder using \emph{dat share} in the folder to share. This command will give a dat url starting with \emph{dat://} that can be used to retrieve the files on other clients.

% A set of useful commands:
% \begin{itemize}
%   \item \emph{dat share}, to share a folder (starts a daemon that waits for incoming connexions)
%   \item \emph{dat sync}, tries to retrieve newer version of the files, and share the files for incoming connexions
%   \item \emph{dat clone <url> <folder>}, retrieves files from a dat url
%   \item \emph{dat pull}, tries to retrieve a newer version of the files
% \end{itemize}

% \subsubsection{Real time synchronization with dat-store}
% TODO: what's dat-store: reverse the order of the following
% A tool to do just that is . 

% On the opposite, Dat does not directly provide a daemon to run in background and automatically synchronize folders for you. \\


Dat-store should be installed on both the client and the Raspberry Pi using 
\begin{lstlisting}
  npm install -g dat-store
\end{lstlisting}

\textbf{Note:} In case you have permission errors, you may need to fix the permissions of your NPM installations. See the \href{https://docs.npmjs.com/resolving-eacces-permissions-errors-when-installing-packages-globally#manually-change-npms-default-directory}{manual guide}. Using sudo instead won't fix the problem.  \\

You should then configure a systemd service to run the store in background. You have to configure both your device and the Raspberry Pi. For the user device you can follow Configuration \ref{cmd:dat_store_systemd_user}. For the Raspberry Pi you can follow Configuration \ref{cmd:dat_store_systemd_rasp}.

\begin{figure}
  \begin{lstlisting}[label=cmd:dat_store_systemd_user, caption=Configure dat-store systemd service on the user device]
    
# This will create the service file.
sudo cat << EOF | sudo tee /etc/systemd/system/dat-store.service > /dev/null
[Unit]
Description=Dat storage provider, keeps dats alive in the background.

[Service]
Type=simple
# Check that dat-store is present at this location
# If it's not, replace the path with its location
ExecStart=$(which dat-store) run-service
Restart=always

[Install]
WantedBy=multi-user.target
EOF

sudo chmod 644 /etc/systemd/system/dat-store.service

sudo systemctl daemon-reload
sudo systemctl enable dat-store
sudo systemctl start dat-store

sudo systemctl status dat-store
  \end{lstlisting}
\end{figure}

\begin{figure}
  \begin{lstlisting}[label=cmd:dat_store_systemd_rasp, caption=Configure dat-store systemd service on the raspberry pi]
    
# This will create the service file.
sudo cat << EOF | sudo tee /etc/systemd/system/dat-store.service > /dev/null
[Unit]
Description=Dat storage provider exposed to the internet (for the raspberry pi).

[Service]
Type=simple
# Check that dat-store is present at this location
# If it's not, replace the path with its location
ExecStart=$(which dat-store) run-service --expose-to-internet
Restart=always

[Install]
WantedBy=multi-user.target
EOF

sudo chmod 644 /etc/systemd/system/dat-store.service

sudo systemctl daemon-reload
sudo systemctl enable dat-store
sudo systemctl start dat-store

sudo systemctl status dat-store
  \end{lstlisting}
\end{figure}

Dat-store provides interesting commands that we will use in our demo\footnote{See the documentation at \url{https://github.com/datproject/dat-store}.}
\begin{itemize}
  \item \emph{dat-store add <url|path> [provider]}: Adds a folder or a dat url to the dat-store of the specified provider.
  \item \emph{dat-store set-provider <url> [provider]}: Sets the url of the specified provider.
  \item \emph{dat-store list [provider]}: Retrieves the list of available Dats in the specified provider.
  \item \emph{dat-store clone <path> <url> [provider]}: Clones \emph{<url>} into a local folder.
\end{itemize}

\subsection{Demonstration with 2 clients, and a Raspberry Pi}

We can then imagine the case where we have two clients A and B and one Raspberry Pi used as a permanent store to synchronize a folder from A to B.

First, A executes the following commands:
\begin{lstlisting}[label=cmd:dat_store_example_A, caption=Commands executed by client A]

  dat-store set-provider http://raspberrypi.local:3472 raspberry
  mkdir mydat
  dat-store add ./mydat
  dat-store list
  dat-store add <url from previous command corresponding to ./mydat> raspberry
  # You can check that the content is actually replicated by accessing
  # http://raspberrypi.local/gateway/<token from hyper url corresponding to ./mydat>/
\end{lstlisting}

Then, client B executes:
\begin{lstlisting}[label=cmd:dat_store_example_A, caption=Commands executed by client B]

  dat-store set-provider http://raspberrypi.local:3472 raspberry
  dat-store list raspberry
  dat-store clone ./mydat <url obtained from the previous command>
\end{lstlisting}

\section{Beyond}

We also experimented with Pushpin\footnote{\url{https://github.com/automerge/pushpin}}, which is a collaborative coarkboard app. It is based on hypermerge\footnote{\url{https://github.com/automerge/hypermerge}}, a library providing a JSON-like structure that can be edited concurrently, without worrying about conflicts. And hypermerge is itself based on the Dat protocol.

However, while using it we suffered from a few instabilities, among them Electron crashes from time to time, and the synchronization stops until the window is reloaded. \\
On top of that, we were unable to install Pushpin on the Raspberry Pi to have a replicating node as it requires compiling Node 14 and the Raspberry Pi ran out of memory while doing the compilation.

\section{Possible improvements and future work}

A common need we noticed between SSB and Dat is to provide a way to determine when two devices ended their synchronization. SSB provides a Node.js client\footnote{\url{https://github.com/ssbc/ssb-client}} that can be used to determine when new posts are received. A proof of concept is showcased at \url{https://github.com/GuilhemN/ssb-copy-follows/tree/POSTS}. This script could be adapted to make a LED blink for instance to notify the user that the devices have synchronized.

Another possible improvement for SSB is the refactoring of the AutoFollow with \emph{ssb-client} to copy the follows of its owner. Similarly a proof of concept is available at \url{https://github.com/GuilhemN/ssb-copy-follows/blob/master/index.js}. It could be integrated to a web page exposed at \verb|http://raspberrypi.local/|.


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% TODO: talk about pushpin + reference and what we've observed: that it didn't sync well + npm issue on rasp

% TODO: need for knowing when the replication is done, state + motivate the problem, sketch the solutions