kkrpc-interop

name	kkrpc-interop
description	Use when implementing kkrpc clients or servers in non-TypeScript languages, speaking the stable compact protocol, transports, and reference implementations in Go, Python, Rust, or Swift.
version	1.0.0
license	MIT
metadata	{"author":"kkrpc","domain":"cross-language-rpc","tags":["rpc","interop","protocol","go","python","rust","swift"]}
compatibility	Works with any language that can parse JSON and implement stdio/WebSocket transports

kkrpc Language Interop

Implement kkrpc clients and servers in non-JS languages by speaking the stable compact JSON protocol used by TypeScript kkrpc endpoints. Start with the default value-oriented protocol. Async iterable streaming and remote references are opt-in advanced protocols; implement them only when the interop boundary explicitly needs them.

Reference Implementations

Language	Location	Transports
Go	interop/go/kkrpc/	stdio, WebSocket
Python	interop/python/kkrpc/	stdio, WebSocket
Rust	interop/rust/src/	stdio, WebSocket
Swift	interop/swift/Sources/kkrpc/	stdio, WebSocket

Core Protocol

Interop uses JSON records. Stdio transports send newline-delimited UTF-8 JSON. WebSocket transports send the same JSON in text frames.

Request

{
	"t": "q",
	"id": "a1b2-c3d4",
	"op": "call",
	"p": ["math", "add"],
	"a": [1, 2]
}

Fields:

• t: message tag, always q for requests.
• id: unique request identifier.
• op: one of call, get, set, or new.
• p: method or property path as string segments.
• a: argument array for calls and constructors.
• v: value for property writes.

Response

{
	"t": "r",
	"id": "a1b2-c3d4",
	"v": 3
}

Errors use e with compact error fields:

{
	"t": "r",
	"id": "a1b2-c3d4",
	"e": {
		"n": "Error",
		"m": "Division by zero",
		"s": "optional stack"
	}
}

Callback Invocation

{
	"t": "cb",
	"id": "callback-id",
	"a": ["progress", 50]
}

Callback Argument Encoding

When sending a callable argument, generate an ID, store the callable locally, and replace the argument with a marker object.

{
	"__kkrpc_next_arg__": "callback",
	"id": "callback-id"
}

When receiving this marker, create a wrapper function. Invoking the wrapper sends t: "cb" with the marker ID and argument array.

When receiving callback arguments from JS, unwrap value envelopes before invoking local callbacks.

{
	"__kkrpc_next_arg__": "value",
	"v": "actual value"
}

Default callback invocation is fire-and-forget. If a non-JS implementation needs callback return values, object handles, or releaseProxy() behavior, it must also implement the kkrpc/remote-refs envelope and internal op: "ref" request flow.

Opt-in Advanced Protocols

kkrpc/streaming adds async iterable stream records:

• t: "sq" for stream pull/return/throw control requests
• t: "sr" for stream value/completion/error responses

kkrpc/remote-refs adds explicit proxy(value) envelopes with "__kkrpc_ref__": true plus internal op: "ref" requests for apply/get/set/call/release. Do not assume these features are present when connecting to a default kkrpc endpoint.

UUID Generation

Use any ID generator with low collision risk. IDs only need to match requests and responses within one connection.

import uuid

def generate_uuid() -> str:
    return str(uuid.uuid4())

Transport Layer

Every transport should provide these operations:

read() -> string?   # Read one message, null/None if closed
write(message)      # Write one JSON string
close()             # Close connection

Stdio transports append \n and flush immediately. WebSocket transports send and receive text frames containing a single JSON record.

Client Algorithm

1. Convert a dotted method name such as math.add to p: ["math", "add"].
2. Encode arguments, replacing callables with callback marker objects.
3. Send a request record with t: "q", unique id, op, p, and optional a or v.
4. Store a pending completion keyed by request ID.
5. In the read loop, resolve pending calls for t: "r" records.
6. In the read loop, dispatch t: "cb" records to stored callbacks.

Server Algorithm

1. Read JSON messages from the transport.
2. Ignore records that are not t: "q" unless your server also stores callbacks.
3. Dispatch op: "call" by joining p into the registered method name.
4. Dispatch op: "get" and op: "set" against registered property handlers if supported.
5. Encode successful results as { "t": "r", "id": requestId, "v": result }.
6. Encode failures as { "t": "r", "id": requestId, "e": { "n": name, "m": message } }.

Minimal Client Pseudocode

def call(method, *args):
    request_id = generate_uuid()
    payload = {
        "t": "q",
        "id": request_id,
        "op": "call",
        "p": method.split("."),
        "a": [encode_arg(arg) for arg in args],
    }
    transport.write(json.dumps(payload))
    response = wait_for_response(request_id)
    if "e" in response:
        raise RpcError(response["e"].get("m", "RPC error"))
    return response.get("v")

Minimal Server Pseudocode

def handle(message):
    if message.get("t") != "q":
        return
    try:
        method = ".".join(message.get("p", []))
        args = [decode_arg(arg) for arg in message.get("a", [])]
        result = api[method](*args)
        transport.write(json.dumps({"t": "r", "id": message["id"], "v": result}))
    except Exception as exc:
        transport.write(json.dumps({
            "t": "r",
            "id": message["id"],
            "e": {"n": exc.__class__.__name__, "m": str(exc)},
        }))

Testing Checklist

• Call JS server methods from the non-JS client.
• Call non-JS server methods from a JS client.
• Verify nested method paths.
• Verify property get and set if implemented.
• Verify callback marker encoding and t: "cb" dispatch.
• If implemented, verify streaming t: "sq"/t: "sr" flow control.
• If implemented, verify remote-reference op: "ref" apply/get/set/call/release behavior.
• Verify error responses preserve name and message.
• Verify stdio newline framing and WebSocket text framing.

Common Pitfalls

• Do not send dotted method names in the wire message. Use path arrays in p.
• Do not wrap responses in custom result objects. Put successful values in v.
• Do not use binary WebSocket frames for the JSON interop protocol.
• Do not forget to unwrap { "__kkrpc_next_arg__": "value", "v": ... } callback arguments.
• Do not rely on JS-specific transfer slots or structured clone in language interop.
• Do not assume async iterables or remote references are part of the default core protocol.
• Do not send op: "ref" to a default-core endpoint; only kkrpc/remote-refs endpoints implement those requests.