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;;; tramp-rpc-protocol.el --- JSON-RPC protocol for TRAMP-RPC -*- lexical-binding: t; -*-
;; Copyright (C) 2026 Arthur Heymans <arthur@aheymans.xyz>
;; Author: Arthur Heymans <arthur@aheymans.xyz>
;; Keywords: comm, processes
;; Package-Requires: ((emacs "30.1"))
;; This file is part of tramp-rpc.
;; tramp-rpc is free software: you can redistribute it and/or modify
;; it under the terms of the GNU General Public License as published by
;; the Free Software Foundation, either version 3 of the License, or
;; (at your option) any later version.
;;; Commentary:
;; This file provides the JSON-RPC 2.0 protocol implementation for
;; communicating with the tramp-rpc-server binary.
;;; Code:
(require 'json)
(defvar tramp-rpc-protocol--request-id 0
"Counter for generating unique request IDs.")
(defun tramp-rpc-protocol--next-id ()
"Generate the next request ID."
(cl-incf tramp-rpc-protocol--request-id))
(defun tramp-rpc-protocol-encode-request (method params)
"Encode a JSON-RPC 2.0 request for METHOD with PARAMS.
Returns a JSON string."
(let ((request `((jsonrpc . "2.0")
(id . ,(tramp-rpc-protocol--next-id))
(method . ,method)
(params . ,params))))
(json-encode request)))
(defun tramp-rpc-protocol-encode-request-with-id (method params)
"Encode a JSON-RPC 2.0 request for METHOD with PARAMS.
Returns a cons cell (ID . JSON-STRING) for pipelining support."
(let* ((id (tramp-rpc-protocol--next-id))
(request `((jsonrpc . "2.0")
(id . ,id)
(method . ,method)
(params . ,params))))
(cons id (json-encode request))))
(defun tramp-rpc-protocol-decode-response (json-string)
"Decode a JSON-RPC 2.0 response from JSON-STRING.
Returns a plist with :id, :result, and :error keys."
(let* ((response (json-parse-string json-string
:object-type 'alist
:false-object nil
:null-object nil))
(id (alist-get 'id response))
(result (alist-get 'result response))
(error-obj (alist-get 'error response)))
(list :id id
:result result
:error (when error-obj
(list :code (alist-get 'code error-obj)
:message (alist-get 'message error-obj)
:data (alist-get 'data error-obj))))))
(defun tramp-rpc-protocol-error-p (response)
"Return non-nil if RESPONSE contains an error."
(plist-get response :error))
(defun tramp-rpc-protocol-error-message (response)
"Extract the error message from RESPONSE."
(plist-get (plist-get response :error) :message))
(defun tramp-rpc-protocol-error-code (response)
"Extract the error code from RESPONSE."
(plist-get (plist-get response :error) :code))
;; Error codes
(defconst tramp-rpc-protocol-error-parse -32700)
(defconst tramp-rpc-protocol-error-invalid-request -32600)
(defconst tramp-rpc-protocol-error-method-not-found -32601)
(defconst tramp-rpc-protocol-error-invalid-params -32602)
(defconst tramp-rpc-protocol-error-internal -32603)
(defconst tramp-rpc-protocol-error-file-not-found -32001)
(defconst tramp-rpc-protocol-error-permission-denied -32002)
(defconst tramp-rpc-protocol-error-io -32003)
(defconst tramp-rpc-protocol-error-process -32004)
;; ============================================================================
;; Batch request support
;; ============================================================================
(defun tramp-rpc-protocol-encode-batch-request (requests)
"Encode a batch request containing multiple REQUESTS.
REQUESTS is a list of (METHOD . PARAMS) cons cells.
Returns a JSON string for a single RPC call to the batch method."
(let ((batch-requests
(mapcar (lambda (req)
`((method . ,(car req))
(params . ,(cdr req))))
requests)))
(tramp-rpc-protocol-encode-request
"batch"
`((requests . ,(vconcat batch-requests))))))
(defun tramp-rpc-protocol-encode-batch-request-with-id (requests)
"Encode a batch request containing multiple REQUESTS.
REQUESTS is a list of (METHOD . PARAMS) cons cells.
Returns a cons cell (ID . JSON-STRING) for ID tracking."
(let ((batch-requests
(mapcar (lambda (req)
`((method . ,(car req))
(params . ,(cdr req))))
requests)))
(tramp-rpc-protocol-encode-request-with-id
"batch"
`((requests . ,(vconcat batch-requests))))))
(defun tramp-rpc-protocol-decode-batch-response (response)
"Decode a batch response into a list of individual results.
RESPONSE is the decoded response plist from
`tramp-rpc-protocol-decode-response'.
Returns a list where each element is either:
- The result value (if successful)
- A plist (:error CODE :message MSG) if that sub-request failed."
(let ((results-array (alist-get 'results (plist-get response :result))))
(mapcar (lambda (result-obj)
(if-let ((error-obj (alist-get 'error result-obj)))
(list :error (alist-get 'code error-obj)
:message (alist-get 'message error-obj))
(alist-get 'result result-obj)))
results-array)))
(provide 'tramp-rpc-protocol)
;;; tramp-rpc-protocol.el ends here
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