flmodules

Raw Fledger modules

This crate holds the raw modules for Fledger. They are written in a way to be as reusable as possible. For this, most modules have the following structure:

• broker.rs - which contains the code to interact with the other modules
• module.rs - with the main code of the module, with at least a process_msg method that inputs a message and outputs a vector of answers
• data-structures - implementing the basic functionality of the module.

Currently the following modules are available:

• timer sends out one message per second and one message per minute
• random_connections takes a list of nodes and randomly selects enough nodes for a fully connected network
• ping uses random_connections to send regular messages to the connected nodes to make sure they answer. If a node doesn't answer in due time, a failure message is emitted.
• gossip_events exchanges events emitted by the nodes and updates the list. It works both in active mode - sending new messages to neighbours - as in passive mode - requesting list of available events from other nodes.
• network is the basic networking code to set up a new connection using the signalling server.
• web_proxy allows sending a http GET request to another node, using the other node as a proxy.

Adding your own modules

As described in the previous section, you should write your modules in three parts:

1. Core Logic: persistent data, configuration, methods. This part does not handle any messages to/from the system, but only provides the actual algorithm. This might include cryptographic calculations, caching, updating, and other tasks necessary for the functionality. Write it in a way that it can also be used by a non-fledger project.
2. Message Handling: create all messages that this module should receive or send during its lifetime. All messages defined here must be self-contained: this part must not depend directly on any other module's message definitions.
3. Translation: this part defines the interactions with the other modules. This is mostly done with defining a Translator which takes incoming messages and outputs messges defined in the Message Handling file.

Broker

I wanted to create a common code for both the libc- and wasm-implementation for Fledger. Unfortunately it is difficult by the fact that libc allows to use threads (and sometimes needs them), so some structures need to have the Send and Sync traits. But these traits are not available for all necessary websys-modules! So I came up with the idea of linking all modules using a Broker system.

In short, all input and output for a module are defined as messages. Then each module handles incoming messages and produces outgoing messages. Modules can be linked together by defining Translators that take messages from one module and translate them into messages for the other module.