What is the recommended way to interface with a CorDapp via an API?

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I am designing a CorDapp, which would require user input as well as API integration, and I am considering various approaches to expose flows and vault queries to the outside world.

Default option seems to be to use Corda RPC. Unless I missed something, there are only Java bindings for it, which is effectively restricting the clients to only be JVM-based. This is somewhat inconvenient, and ideally I would like something like OpenAPI to make it more open and implementation-agnostic.

Another option is to use some kind of Corda RPC to OpenAPI proxy. I know about Braid, and I'm sure there are others. Braid seems to support deployment as a Corda service packed together with the flows into the CorDapp itself, effectively making it running embedded into the Corda JVM.

Braid can be deployed as a standalone proxy too, which I suppose is option three.

Instinctively I find the embedded mode more attractive, as it reduces the number of moving parts, as opposed to a standalone mode. However, I am concerned that such model may be in fact become discouraged at some point, either because Corda developers consider it to be a misuse of services facility, or because some organisations will not be keen to deploy such code onto their nodes, especially when they may be running multiple CorDapps. I would imagine anything deployed as part of Corda JVM would at least require more scrutiny due to potential impact on other things running there, which in turn would reduce the agility.

I wonder what approach to integrate with a CorDapp is actually recommended?

Edit 1: I know it is technically possible to embed a webserver into the node and expose a REST API from there, at least in the current version of Corda (4.3 at the time of writing). The question is more about whether it is a good idea to do so, or not, and why.

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1 Answers

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Take a look at the question I had asked on Stackoverflow regarding front end for CordApp. This might be of some help.

Following is the link -

"Corda: Can we develop Dapps that will be run by IIS webserver to talk to Corda platform?"

You can use any front-end technology you want.

As of Corda 3, your backend must be JVM-based, for two reasons:

  • You need to load various flow, state and other class definitions onto the classpath to pass as arguments to flows, retrieve objects from the vault, etc.

  • You need to use the CordaRPCClient library to create an RPC connection to the node

If you really need to write your back-end in another language, there are a few workarounds:

  • Create a thin Java webserver that sits between your main webserver and the node. The Java webserver translates HTTP requests from the main webserver into RPC calls to the node, and RPC responses from the node into HTTP responses to the main webserver

    • This is the approach taken by libraries such as Braid

  • Use a library such as GraalVM to compile non-JVM languages to JVM bytecode