feedbus

Work in progress.

This is a broker based message bus written in Java with clients in multiple languages.

It supports broadcast and select feed architectures.

Architecture

This is a publish subscribe broker based message bus.

At the heart of the system is the message broker server, or distributor. Clients connect to the distributor, then send and receive messages.

The following messages are supported:

• Subscribe
• Publish
• Notify
• Send

Messages

Subscribe

A client may add or remove a subscription. When a client has subscribed it will receive updates whenever the target of it's subscription changes.

When a client subscribes to data it sends a message to the distributor with the following content.

• Feed
• Topic
• IsAdd

The feed is a string which can be used as a namespace. For example financial data from the London Stock Exchange may have a feed "LSE".

The topic is a string which identifies the item of data within the feed. For example Barclays PLC might be represented as the topic "BARC".

The IsAdd is a boolean indicating if the subscription is being added or removed.

Publish

When a client publishes data, the data will be forwarded to all subscribers.

The publication has the following content:

• Feed
• Topic
• IsImage
• Data

The feed and topic have the same meanings as given above.

The IsImage is a boolean which indicates whether the data sent was complete, or a subset.

The Data is an array of bytes.

Notify

A client may request notifications of subscriptions to data.

The notification request has the following content:

• Feed
• IsAdd

The feed has the same meaning given above.

The IsAdd is a boolean indicating whether the notification is being added or removed.

When another client adds or removes a subscription to a topic on this feed the subscription is forwarded to this client with the following content.

• ClientId
• Feed
• Topic
• IsAdd

The feed, topic, and isAdd have the same meanings as given above.

The ClientId is a string which identifies the client made the subscription request.

Send

A client can send data to a specific client.

The send message has the following content.

• ClientId
• Feed
• Topic
• IsImage
• Data

The fields have the same meanins as described above.

Feed types

A message bus is typically described as broadcast or select feed. Both types are supported.

Broadcast feed

In a broadcast feed a data provided publishes all data, regardless of whether any clients are listening. An example of this is a feed from an exchange.

This is a simple architecture. The data providers send publish messages and the clients request subscriptions.

Select feed

A select feed only publishes data when clients have subscribed.

This is a more complicated arcitecture. The clients still request subscriptions, but the data provider is more structured.

It first requests notifications for it's feed with a notify request.

When it is notified of a subscription it first sends a complete set of data using the clientId it received with the forwarded subscription.

Subsequently any data received on the topic is published.

When notified of a subscription removal the data provider checks if any subscriptions remain, and stops publishing if no one is listening.