Architecture and Concepts

Spec and SDK Terms

Event: The canonical form of the attributes and payload of the occurrence.
Protocol: Protocol is the messaging protocol used to send/receive events. In sdk-go all supported Protocols are implemented through specific interfaces in protocol module.
Protocol Binding: Definition of how Events are mapped into Messages for the given Protocol. In sdk-go all supported Protocol bindings are implemented through specific interfaces in binding module.
Message: The encoded form of an Event for a given encoding and protocol. When a message is received in the sdk-go, the protocol implementation wraps it in a Message implementation specific to that protocol. This interface defines how to read the Message, given the Protocol.
Message Writer: Logic required to take in a Message in a specific encoding and write out to a given Protocol (request, message). A Message Writer can be a StructuredWriter, a BinaryWriter or both, depending on what encodings a Protocol supports.
Client: Interface to interact with a Protocol implementation to send/receive Events. Clients also provide protocol agnostic features that can be applied to events, such as extensions.
Extensions: Anything that extends the base requirements from the CloudEvents spec. There are several CloudEvents supported extensions.

The amount of the SDK adopters would like to use is up to the adopter. We support the following:

Resource Level: An adopter could use the Event data structure to interact with CloudEvents and marshal/unmarshal it to JSON.
Message Level: An adopter could use directly Messages implementations and Write* functions to read and write CloudEvents messages from/to the wire, handling by hand the connection, the consumption and the production of messages from/to the protocol specific APIs.
Protocol Level: An adopter could use Protocol implementations directly to consume/produce Messages without interacting with the protocol specific APIs.
Client Level: An adopter selects a Protocol implementation and Events can be directly sent and received without requiring interactions with Messages.

Producer, the “producer” is a specific instance, process or device that creates the data structure describing the CloudEvent.
Consumer, a “consumer” receives the event and acts upon it. It uses the context and data to execute some logic, which might lead to the occurrence of new events.
Intermediary, An “intermediary” receives a message containing an event for the purpose of forwarding it to the next receiver, which might be another intermediary or a Consumer. A typical task for an intermediary is to route the event to receivers based on the information in the Context.