README.in

## Hibiscus

An API specification for simple RPC clients.

## Motivation

Many [io7m](https://www.io7m.com/) projects implement some form of RPC client.
The Hibiscus API is an attempt to define some common interface types so that
unrelated projects nevertheless end up with a consistent look and feel across
client implementations.

## Architecture

![architecture](./src/site/resources/arch.png?raw=true)

1. A `Configuration` is passed to a `ClientFactory` to produce a `Client`.
2. The `Client` sends `ConnectionParameters` to the server to log in.
3. The `Server` sends back `Messages` indicating if the login succeeded or
   failed.
4. Assuming success, the `Client` sends `Messages` to the server to perform
   operations.
5. The `Server` sends `Messages` in response to `Messages`.

## State

Clients conform to a simple state machine:

![state](./src/site/resources/state.png?raw=true)

1. Clients begin in the `DISCONNECTED` state.
2. A `Login` operation moves the client into the `CONNECTING` state.
3. If the login succeeds, the client moves to the `CONNECTED` state after
   passing through the `CONNECTION_SUCCEEDED` state.
4. If the login fails, the client moves to the `DISCONNECTED` state after
   passing through the `CONNECTION_FAILED` state.

In the `CONNECTED` state, the client can:

* Disconnect, moving to the `DISCONNECTED` state.
* Send messages, remaining in the `CONNECTED` state.

A client maintains an internal [Transport](#transport) that performs
the actual communication.

## Transport

A _Transport_ represents an object that can be used to read and write messages.
A _Transport_ exposes the following operations:

  * `receive`: Read a message from the transport.
  * `sendAndForget`: Write a message to the transport, potentially discarding
                     any response that might come back.
  * `sendAndWait`: Write a message to the transport and wait for a response
                   to come back.
  * `send`: Write a message to the transport but do not wait for a response
            to come back. The response can be fetched later with `receive`.

The package includes multiple example transports:

  * [EUDP0Transport](com.io7m.hibiscus.examples/src/main/java/com/io7m/hibiscus/examples/udp0/EUDP0Transport.java) - A UDP transport
  * [ETCP0Transport](com.io7m.hibiscus.examples/src/main/java/com/io7m/hibiscus/examples/tcp0/ETCP0Transport.java) - A TCP transport
  * [EHTTP0Transport](com.io7m.hibiscus.examples/src/main/java/com/io7m/hibiscus/examples/http0/EHTTP0Transport.java) - An HTTP transport