\section{Another application of Smallworld, the Dat Protocol}
\section{Another application of Smallworld, the Hypercore Protocol}
The Dat Protocol\footnote{\url{https://www.datprotocol.com/}}~\cite{Robinson2018} is a peer-to-peer protocol that allows sharing files in a distributed network. It is based on append-only logs like Secure-Scuttlebutt (SSB)~\cite{10.1145/3357150.3357396} but it provides more mature core libraries.
The Hypercore Protocol\footnote{\url{https://hypercore-protocol.org/}}~\cite{Robinson2018} is a peer-to-peer protocol that allows sharing files in a distributed network. It is based on append-only logs like Secure-Scuttlebutt (SSB)~\cite{10.1145/3357150.3357396} but it provides more mature core libraries.
As a distributed file sharing protocol, it differs from BitTorrent \footnote{\url{https://www.bittorrent.com/}} in that contents can be updated by their author.
This report aims at showing that Dat can be used with a Smallworld setup, to easily share files that could be often updated among peers, similarly to a Dropbox instance. We will explain how to configure Dat to replicate files, and we will cover a scenario where we replicate files between two clients A and B with the Raspberry Pi acting as an intermediary when only one of the clients is online at a given time.
\subsection{Real time synchronization with dat-store}
The Hypercore protocol\footnote{\url{https://hypercore-protocol.org/}} was created in 2016 as a way to provide the original protocol, called the Dat protocol\footnote{\url{https://www.datprotocol.com/}}, more abstract foundations that could be reused among several applications. From then, the Hyper project grew and it was decided in 2020 to separate Dat from Hypercore and to provide both with their own governance\footnote{An explanation video is available at \url{https://www.youtube.com/watch?v=mx52uO5SP7A}}.
The hypercore protocol extensively supports both local and remote peer-to-peer connexions using a DHT (Distributed Hash Tables), while the Dat protocol only supports a rendez-vous approach with a centralized server.
The Hypercore protocol is now incompatible with the Dat protocol and provides its own CLI tools and libraries.
This report aims at showing that Hypercore can be used with a Smallworld setup, to easily share files that could be often updated among peers, similarly to a Dropbox instance. We will explain how to configure Dat-store to replicate files, and we will cover a scenario where we replicate files between two clients A and B with the Raspberry Pi acting as an intermediary when only one of the clients is online at a given time.
\subsection{Real time synchronization with dat-store}
Dat-store is a command line tool that provides commands for downloading and syncing Dat archives, as well as a service that can be run in background, notably for remote control. \footnote{People usually recommend using a command line tool called \emph{dat-cli} 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.}\\
Dat-store is a command line tool that provides commands for downloading and syncing Hypercore archives, as well as a service that can be run in background, notably for remote control. \footnote{People usually recommend using a command line tool called \emph{dat-cli} 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.}\\
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. \\
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@@ -159,7 +158,7 @@ Then, client B executes the commands from \autoref{cmd:dat_store_example_B}.
Changes from A to the folder \emph{mydat} will be replicated by B, even if A is not connected at the same time.
\section{Beyond Dat}
\section{Beyond Hypercore}
We also experimented with Pushpin\footnote{\url{https://github.com/automerge/pushpin}}, which is a collaborative coarkboard app. We wanted to showcase a peer-to-peer application with a real-time interface. Pushpin 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.
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@@ -170,19 +169,16 @@ On top of that, we were unable to install Pushpin on the Raspberry Pi to have a
In the previous sections, we have shown how to use dat store to replicate files between devices and a simple usage scenario. Many extensions are possible.
First, while implementing this use case, we have noticed a major need shared between SSB and Dat, that is to provide a way to determine when two devices ended their synchronization.
One possible implementation for SSB could be to use the Node.js client\footnote{\url{https://github.com/ssbc/ssb-client}}as it 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.
First, while implementing this use case, we have noticed a major need shared between SSB and Hypercore, that is to provide a way to determine when two devices ended their synchronization.
One possible implementation for SSB could be to use the Node.js client\footnote{\url{https://github.com/ssbc/ssb-client}} 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. The user could also be notified directly on their device using \url{https://github.com/RangerMauve/hyperdrive-publisher}.
Second, it appears that much of the activity in the Dat community is migrating toward the Hypercore protocol. In the next section, we detail how to install it on the Raspberry Pi so that future students could extend our work using these libraries instead.
Second, Hypercore libraries offer the support of Bees, which are distributed key-value tables, but they are not supported by dat store. In the next section, we detail how to install Hypercore CLI, a CLI tool supporting Bees, on the Raspberry Pi so that future students could extend our work using these libraries instead.
\subsection{Dat migration to Hypercore protocol}
The Hypercore protocol\footnote{\url{https://hypercore-protocol.org/}} was created in 2016 as a way to provide to Dat more abstract foundations that could be reused among several applications. From then, the Hyper project grew and it was decided in 2020 to separate Dat from Hypercore and to provide both with their own governance\footnote{An explanation video is available at \url{https://www.youtube.com/watch?v=mx52uO5SP7A}}.
The Hypercore protocol is now incompatible with the Dat protocol and provides its own CLI tools and libraries.
\subsection{Hypercore CLI tool}
The main entry of the Hyperspace is the Hyperspace CLI\footnote{\url{https://github.com/hypercore-protocol/cli}}. It enables the creation of Hyperdrives, i.e.\ folders distributed on the Hyper network, and Bees, which are distributed key-value tables.
The Hyper community provides its own CLI tool in addition to the dat store CLI\footnote{\url{https://github.com/hypercore-protocol/cli}}. It enables the creation of Hyperdrives, i.e.\ folders distributed on the Hyper network, and Bees, which are distributed key-value tables.
In addition, Hypercore is the underlying library of Hyperspace CLI. It provides an actually decentralized implementation for remote peer-to-peer connexion based on DHT (Distributed Hash Tables), while the Dat protocol only supports a rendez-vous approach with a centralized server.\\
% In addition, Hypercore is the underlying library of Hyperspace CLI. \\
In order to run the Hypercore libraries, the documentation states that Node version 14 or more recent is required. However, Node 14 is not officially supported on the Raspberry Pi Zero as it is based on an ARMv6 CPU.
Thankfully, the NodeJs team is actually still providing unofficial (and "experimental") builds under \url{https://github.com/nodejs/unofficial-builds/} and those are usable on the Raspberry Pi. You may install them using the scripts provided by \url{https://github.com/sdesalas/node-pi-zero}. We tested successfully Node version 14.17.1. \\
