Architecture

Network I/O layer

This layer is responsible for transmitting octets of data between endpoints (local and remote)

• Classic: based on java.net.Socket / java.io.OutputStream / java.io.InputStream APIs.
• Event-driven (async): based on java.nio.channels.Selector and java.nio.channels.Channel APIs

Both implementations are provided by HttpCore.

Potentially there can be other network layer implementations, for example, QUIC based or Netty based.

Transport Security Layer

This layer implements Transport Layer Security on top of the network I/O layer as defined by the TLS protocol. Both the classic and async implementations rely on the TLS protocol functionality provided by the standard JSSE security provider. Alternative JSSE providers such as Conscrypt can be used as well.

Protocol Transport Layer

This layer is responsible for transport of messages between endpoints based on a communication protocol.

• HTTP/1.1 with HTTP/1.0 compatibility
• HTTP/2

The classic implementation supports HTTP/1.1. The async implementation supports HTTP/1.1 and HTTP/2.

Both implementations are provided by HttpCore.

Please note that the classic I/O model work well with request / response oriented protocols such as HTTP/1.1 but does not lend itself well to multiplexing protocols such as HTTP/2. This is the reason the classic I/O based clients presently support HTTP/1.1 only.

Connection Management Layer

This layer facilitates efficient creation and re-use of connections. It also aims at harmonising the connection management APIs across different netweok I/O models and protocols and making those APIs as compatible and consistent as possible. This layer is responsible for connection creation, initialization, upgrade to TLS and re-use by maintaining pools of reusable persistent connection that can be leased to execute message exchanges and released back to the pool.

Both Classic and Async I/O models are supported.

Connection pool implementations are provided by HttpCore.

Message Exchange Protocol Layer

This layer is responsible for execution of complex message exchanges that may involve complex routing, authentication, state management, automatic re-execution or recovery and transparent compression / decompression of content. It also aims at harmonising the request execution APIs across different transport models and protocols and making those APIs as compatible and consistent as possible.

Both Classic and Async I/O models are supported.

Caching Protocol Layer

This layer implements HTTP caching protocol on top of a message exchange protocol layer.

Both Classic and Async I/O models are supported.

This layer is optional.

Reactive Streams Layer

This layer provides Reactive Streams Bindings on top of the async message exchange protocol layer.

The bindings implementation is provided by HttpCore.

This layer is optional.

Classic Over Async Facade

This layer provides compatibility bindings with the classic java.io.OutputStream / java.io.InputStream based APIs on top of the asnyc message exchange protocol layer.

This layer is optional and is still considered experimental.