forst-io

Asynchronous framework mostly inspired by Capn'Proto with the key difference of not using Promises, but more reusable Pipelines/Conveyors. This introduces some challenges since I can't assume that only one element gets passed along the chain, but it is managable. The advantage is that you have zero heap overhead by not recreating the chain after every use.
The asynchronous interfaces are very similar to Capn'Proto. At least similar to the 0.7.0 version.
The other elements like schema, serialization, network interfaces are designed in another manner.

Early stage of development. I am currently rewriting my software to find a good interface solution by checking if I am comfortable with the current design.
Schema description has been rewritten once already and the current version is probably here to stay. The default container will be changed in the future, so no parsing will be necessary with my binary format.

Dependencies

You will need

• A compiler (std=c++20) (g++/clang++)
• scons
• gnutls

Currently the build script explicitly calls clang++ due to some occasional internal compiler error on archlinux with g++.
Optional dependencies are

• clang-format

Build

Execute scons.
It's that simple.

scons test build the test cases.
scons format formats the sources.
scons install installs the library + headers locally.
scons all to format the sources and build the library and the tests.

Async

The main interface for async events is the Conveyor class.
This class is the builder object for creating new nodes in the graph of relations. At the same time it stores the end nodes of this graph.
Most of the times this async relationship graph is started by using newConveyorAndFeeder which return a connected input and output class. You can provide the templated data to the feeder and if you have built up a graph with the Conveyor class, it will get passed along the chain.

It is necessary to create an EventLoop instance and activate it on the current thread by creating a WaitScope class before using the Async features.

External events

Since a lot of external events may occur which originate from the OS in some way, we require an additional class called EventPort.
You can create your async context by calling setupAsyncIo() which creates this OS dependent EventPort for you.
Only the WaitScope has to be created afterwards so these classes are active on the current thread.
Most of the times you want to create the AsyncIoContext on the main thread while in the future other threads can or should have a custom implementation of EventPort to allow for external events arriving for these threads as well. In the context of threads external means outside of the mentioned thread.

Cross-Thread communication currently is implemented differently due to missing features. It is done either by implementing your own thread-safe data transfer or using the network features to communicate across threads.

Schema Structure

Message description is achieved by a series of templated schema description classes found in forstio/schema.h as seen below

using BasicStruct = schema::Struct<
	schema::NamedMember<Int32, "foo">,
	schema::NamedMember<String, "bar">	
>;

These schema classes are just meant to describe the schema structure. By itself, it can't do anything.
For a message we create an instance of any MessageRoot class such as HeapMessageRoot.
Using those schema classes and an appropriate container class, we can now build a message class as seen below.

HeapMessageRoot<BasicStruct, MessageContainer<BasicStruct>> buildBasicMessage(){
	auto root = heapMessageRoot<BasicStruct>();
	// This is equivalent to
	// auto root = heapMessageRoot<BasicStruct, MessageContainer<BasicStruct>>();

	auto builder = root.build();
	auto bar_build = builder.init<"bar">().set("banana");
	
	auto foo_build = builder.init<"foo">().set(5);

	return root;
}

The current default message container stores each value in stl containers such as std::string, std::vector, std::tuple, std::variant or in its primitive form.
Though it is planned to allow storing those directly in buffers.

Examples

Currently no examples except in test.
But forstio-graphics contains some programs which heavily use this library. Though no schema or io features are used there.

Roadmap

• Zerocopy for message templates during parsing
• Tls with gnutls (Client side partly done. Server side missing)
• Windows/Mac/Wasm Support
• Multithreaded conveyor communication
• Minimal logger implementation to help describe the async graphs with dot files
• Reintroduce JSON without dynamic message parsing or at least with more streaming support