Hi,

I have been working on supporting jsonrpc 2.0 for one of my use case using huma.

The main features include:

• Support full jsonrpc message specification including request, response, notification and error
• Support batch requests
• Modular code with consumers having ability to stitch code as required. Conventional stitching helpers already present.
• Easy consumption by just importing the package and adding request/notification handlers
• Create a full openapi 3.1 schema for the supported requests/notifications with proper types

Things I have not added:

• Concurrent processing of requests inside a batch. This can be built incrementally on top of this without any impact on consumers.
• Errors that are supposed to be "Invalid Method Params" are not detected. Some details below.

Implementation notes:

• Given that jsonrpc supports batch or single requests and each request/response/notification is in itself is a multiplexed format, we need to start by adding a meta request that puts single/multiple requests inside a array and then processes them. This means that the schema generation for this meta handler and individual handlers cannot be directly done using the input struct. A custom schema needs to be created using a two level OneOf.
• Similar is true at one more level for responses as they must contain a error or a result.
• jsonrpc is to be served on a single post endpoint. Therefore the individual methods are available at registration time. Added a utility to create and append their schema as well.
• The whole schema generation took some time to get right because of the multi level multiplexing of jsonrpc and the use of "sum types" in the specification. I have mostly tried to do this by looking at huma's actual handling code. As I am very new to this, it is quite possible that there is a much simple/better way for doing this.
• An error handler to convert all errors to jsonrpc format errors is present. The error handler looks a bit all over the place. This is because I needed to deduce various scenarios in the handler from the error message (especially if it is a huma generated error). One scenario I was not able to handle was that of deducing whether the error was a request error or a method params error as all things are raised as a "validation failed" error. There may be better ways to do this but I was not able to figure this out.
• Unit tests are present. Some scenarios are tested using an example server/client test.

I understand that this is a direct pull request without sufficient discussion first and I am sorry if this is way out of line. The main rationale of doing a pull request directly was that the implementation looked involved enough that discussion using code seemed like a better idea.

If jsonrpc support doesn't really align with huma's goals, feel free to close this.

Thank you for your great work, I do love huma !!!