RELOAD: Client/server mode

In a previous post I quickly talked about an extension called “Client connected to bootstrap node”, which is now implemented in version 0.7.0 of the libreload-java package that was released few minutes ago.

Section 3.2.1 of the RELOAD specification talks about the two modes that a RELOAD client can be using to interact with an overlay. In the first mode, the client attaches itself to the responsible peer and process Update messages to always be connected to the current responsible peer. In the second mode, a client attaches itself to any peer and store a destination list somewhere in the overlay so other node can reach it (P2P SIP can use both of theses modes).

I think that there is a third mode that is missing in the specification, so I added it in my list of extensions. In this mode, the client is connected to one of the bootstrap peer, so it is similar to the second mode described above, but without having to send an Attach. One interesting characteristic of his mode is that this is the initial mode for all nodes. Client in either of the two modes described above have to start with this third mode. Peers have to start with this third mode, then switch to the first mode, then go to the peer mode. So describing it is, in my opinion, kind of a fundamental step.

Another interesting characteristic of that mode is that an overlay made of only bootstrap peers and clients using this mode is in fact our good old client/server architecture. Bootstrap peers replicates the data between each other and help establish direct connections between clients, all in a secure way.

The new version of the package contains only the code for the client side, and only implement the Store message at this time. Because having this code is not that useful without a bootstrap node, I also installed one in the test server (see the this post for instruction on how to retrieve the configuration file and request a certificate. The configuration file now contains the address of the bootstrap server to use with the client).

The Node class is the fundamental abstraction that application developers need to care about. A Node object is instantiated with 3 parameters, a Configuration object that contains the initial configuration of the overlay to join (and especially the list of bootstrap servers), a SignerIdentity object that contains the identity of the node to create, and the private key that was used to create the identity.

After creating the node the application can store or modify data in the bootstrap peers by calling the modify method. Here is an example of code that stores the certificate of the node in the bootstrap servers:

Set<DataModel<? extends Value>> kinds = new HashSet<DataModel<? extends Value>>();
Certificate certificate = new Certificate(signer.certificateChain().get(0));
CertificateByNode certificatesByNode = new CertificateByNode();
node.modify(signer.nodeId().toBytes(), kinds);

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