JSON-RPC 2.0

Unreleased, synchronous typed methods without a transport dependency.

This optional adapter is unreleased source functionality, not part of the published rydantic = "0.8.0" package. Use the repository checkout to run the example. No package version or existing wire format is changed by enabling it.

cargo run -p rydantic --example jsonrpc --no-default-features --features derive,jsonrpc --locked

Register typed methods

use rydantic::{Model, jsonrpc::{Params, Router}};

#[derive(Model)]
struct Hello {
    #[model(trim, min_length = 2)]
    name: String,
}
#[derive(Model)]
struct Reply { greeting: String }

fn main() -> Result<(), rydantic::jsonrpc::RegistrationError> {
    let mut router = Router::new();
    router.register("hello", Params::Named, |input: Hello| {
        Ok(Reply { greeting: format!("Hello, {}!", input.name) })
    })?;
    let response = router.handle_json(
        r#"{"jsonrpc":"2.0","method":"hello","params":{"name":" Alice "},"id":1}"#,
    );
    assert_eq!(response.unwrap()["result"]["greeting"], "Hello, Alice!");
    Ok(())
}

Params::Named accepts objects. Params::Positional accepts arrays, for example a #[derive(Model)] struct Pair(i32, i32). The adapter never converts an array to field names or an object to positional arguments. Omitted params becomes {} or [] according to the registered mode; the model then decides whether that empty input is valid. Model aliases, extra-field policy and normalization apply exactly as in Model::parse_value. Choose the model policy for your method.

Output uses Model::dump, which revalidates and serializes but does not normalize a value constructed by the handler. Invalid output produces an internal error rather than a successful response. Handler effects are not rolled back.

Protocol boundary

The JSON-RPC 2.0 specification is the protocol reference. This adapter supports server-side single requests and sequential batches, not a client or service/code generator.

• Missing id means a notification; a valid notification executes but produces None, including when its method, parameters or output fail. Send no JSON body, not null or []. An explicit id: null still receives a response.
• String, number and null IDs are retained without numeric coercion. Fractional IDs are accepted although discouraged by the protocol. Arbitrary-precision JSON numbers retain their representation through the configured serde_json.
• Invalid JSON returns -32700; invalid envelopes return -32600 with null ID. A malformed object without an ID is not a valid notification. params must be an object or array when present, even for unknown methods.
• Unknown methods return -32601; wrong parameter mode or failed model parsing returns -32602; failed output revalidation/serialization returns -32603. Model error details and input values are not included in these messages.
• Empty batches return one invalid-request response. Invalid items (including nested arrays) each yield errors. Notification responses are omitted; an all-notification batch yields None, not an empty array. Items execute in order.
• Methods match case-sensitively. Duplicate registration and reserved rpc. method names are rejected. Extra envelope members are ignored. Duplicate JSON object keys follow a last-value policy. Private serde marker keys remain ordinary object data. JSON text nesting is bounded to 128 materialization levels; exceeding this parser limit returns -32700. No unbounded parser is implied.

A handler can return Error::application(code, message) with a non-reserved code (the constructor returns None for -32768..=-32000). That message is explicitly public: do not include secrets. No error data extension is supplied.

Application responsibilities

This module is synchronous. Async validators and context-dependent models are not supported; use a separately designed async/context integration rather than pretending this wrapper awaits rules or supplies business context. Panics propagate; there is no catch-unwind, transaction, timeout, concurrency or rollback boundary.

The caller owns HTTP/WebSocket/framing, authorization, authentication, request and batch limits, rate limits, cancellation and resource budgets. Bound input before calling the adapter. It is not a network server or a security boundary. Transport status codes for no-response notifications are the transport’s policy.

The adapter adds no dependency and is absent without the jsonrpc feature. Its minimal CI gate executes the complete protocol test inventory, checks the disabled feature control and runs the example; those synthetic checks are not production or external-adoption evidence.