(feature): emacs-lisp handling for roam:// links (#188)

We emulate org-protocol, and advise server-find-files, stripping the
roam protocol from the filename. This reduces the setup required to
open `roam://` links.

CHANGELOG.md

@@ -4,6 +4,7 @@
 
 ### New Features
 * [#182][gh-182] Support file name aliases via `#+ROAM_ALIAS`.
+* [#188][gh-188] Add `org-roam-protocol`, shifting `roam://` link handling into Emacs-lisp.
 
 ### Features
 * [#165][gh-165] Add templating functionality via `org-roam-templates`.
@@ -97,6 +98,7 @@ Mostly a documentation/cleanup release.
 [gh-143]: https://github.com/jethrokuan/org-roam/pull/143
 [gh-165]: https://github.com/jethrokuan/org-roam/pull/165
 [gh-182]: https://github.com/jethrokuan/org-roam/pull/182
+[gh-188]: https://github.com/jethrokuan/org-roam/pull/188
 
  # Local Variables:
  # eval: (auto-fill-mode -1)

doc/graph_setup.md

@@ -1,9 +1,15 @@
-The setup is similar to that of org-protocol. Here `roam://` links are
+The setup is the same as org-protocol. Here `roam://` links are
 defined, and need to be associated with an application. 
 
-The gist of the setup is setting up a Bash script to trim off the
-`roam://` prefix from the link, causing the desktop application to
-call `emacsclient path/to/org-roam-file.org`.
+Across all platforms, to enable `org-roam-protocol`, you have to add
+the following to your init file:
+
+```emacs-lisp
+(require 'org-roam-protocol)
+```
+
+We also need to create a desktop application for emacsclient. The
+instructions for various platforms are shown below:
 
 ## Linux
 
@@ -13,25 +19,14 @@ Create a desktop application. I place mine in
 ```
 [Desktop Entry]
 Name=Org-Roam Client
-Exec=/home/jethro/.local/bin/launch_emacs %u
+Exec=emacsclient %u
 Icon=emacs-icon
 Type=Application
 Terminal=false
 MimeType=x-scheme-handler/roam
 ```
 
-Note the `Exec` key is set to a bash script poorly named
-`launch_emacs`. You can set it to whatever you want.
-
-Create the corresponding bash script, and make it executable. Here's
-how it looks like:
-
-```bash
-#!/usr/bin/env bash
-emacsclient "${1#*:}"
-```
-
-Finally, associate `roam://` links with the desktop application by
+Associate `roam://` links with the desktop application by
 running in your shell:
 
 ```bash
@@ -55,10 +50,11 @@ sudo chmod 644 /etc/opt/chrome/policies/managed/external_protocol_dialog.json
 and then restart Chrome (for example, by navigating to <chrome://restart>) to
 make the new policy take effect.
 
-See [here](https://www.chromium.org/administrators/linux-quick-start) for more
-info on the `/etc/opt/chrome/policies/managed` directory and
+See [here](https://www.chromium.org/administrators/linux-quick-start)
+for more info on the `/etc/opt/chrome/policies/managed` directory and
 [here](https://cloud.google.com/docs/chrome-enterprise/policies/?policy=ExternalProtocolDialogShowAlwaysOpenCheckbox)
-for information on the `ExternalProtocolDialogShowAlwaysOpenCheckbox` policy.
+for information on the `ExternalProtocolDialogShowAlwaysOpenCheckbox`
+policy.
 
 
 ## Mac OS
@@ -68,24 +64,17 @@ One solution to this, recommended in [Issue
 [Platypus](https://github.com/sveinbjornt/Platypus). Here are the
 instructions for setting up with Platypus and Chrome:
 
-1. Create an executable `launch-emacs.sh` script:
-
-```sh
-#!/usr/bin/env bash
-/usr/local/bin/emacsclient --no-wait "${1#*:}"
-```
-
-2. Install and launch Platypus (with [Homebrew](https://brew.sh/)):
+1. Install and launch Platypus (with [Homebrew](https://brew.sh/)):
 
 ```sh
 brew cask install playtpus
 ```
 
-3. Playtpus settings:
+2. Platypus settings:
 
 - App Name: `OrgRoam`
 - Script Type: `env` and `/usr/bin/env`
-- Script Path: `/path/to/your/launch-emacs.sh`
+- Script Path: `/path/to/emacsclient $1`
 - Tick Accept dropped items and click Settings
 - Tick Accept dropped files
 - Tick Register as URI scheme handler

org-roam-protocol.el

@@ -0,0 +1,94 @@
+;;; org-roam-protocol.el --- Protocol handler for roam:// links
+
+;; Copyright © 2020 Jethro Kuan <jethrokuan95@gmail.com>
+;; Author: Jethro Kuan <jethrokuan95@gmail.com>
+;; URL: https://github.com/jethrokuan/org-roam
+;; Keywords: org-mode, roam, convenience
+;; Version: 0.1.2
+;; Package-Requires: ((emacs "26.1") (org "9.0"))
+
+;; This file is NOT part of GNU Emacs.
+
+;; This program 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, or (at your option)
+;; any later version.
+;;
+;; This program is distributed in the hope that it will be useful,
+;; but WITHOUT ANY WARRANTY; without even the implied warranty of
+;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;; GNU General Public License for more details.
+;;
+;; You should have received a copy of the GNU General Public License
+;; along with GNU Emacs; see the file COPYING.  If not, write to the
+;; Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
+;; Boston, MA 02110-1301, USA.
+
+;;; Commentary:
+;;
+;; Intercept calls from emacsclient for `roam://' links.
+;;
+;; This is done by advising `server-visit-files' to scan the list of filenames
+;; for `org-roam-protocol-the-protocol'.
+;;
+;; `roam://' links are expected to be absolute file locations, for example,
+;; `roam:///home/me/file.org'. The `roam://' prefix is stripped, and emacsclient
+;; opens the location as per usual.
+;;
+;; Any application that supports calling external programs with an URL as
+;; argument may be used with this functionality.
+;;
+;; Usage:
+;; ------
+;;
+;;    1.) Add this to your init file:
+;;        (add-to-list 'load-path "/path/to/org-roam-protocol.el"')
+;;        (require 'org-roam-protocol)
+;;
+;;    2.) Ensure emacs-server is up and running.
+;;    3.) Try this from the command line:
+;;        $ emacsclient roam:///tmp/test.org
+;;
+;;    If it works, you can now setup other applications for using this feature.
+
+(require 'org)
+
+;;; Variables:
+
+(defconst org-roam-protocol-the-protocol "roam"
+  "This is the protocol to detect if org-roam-protocol.el is loaded.
+You will have to define just one protocl handler OS-wide (MS-Windows)
+or per application (Linux). That protocol handler should call emacsclient.")
+
+;;; Code:
+(defun org-roam-protocol-check-filename-for-protocol (fname)
+  "Check if `org-roam-protocol-the-protocol' is used in FNAME.
+
+If the protocol is found, the protocol is stripped from fname,
+and the value is passed to the server as filename.
+
+If the function returns nil, the filename is removed from the
+list of filenames passed from emacsclient to the server. If the
+function returns a non-nil value, that value is passed to the
+server as filename."
+  (let ((the-protocol (concat (regexp-quote org-roam-protocol-the-protocol)
+				                      ":")))
+    (when (string-match the-protocol fname)
+      (cadr (split-string fname the-protocol)))))
+
+(defadvice server-visit-files (before org-roam-protocol-detect-protocol-server activate)
+  "Advice `server-visit-files' to strip the `roam:/' protocol.
+Default to `server-find-files' handling for file locations."
+  (let ((flist (ad-get-arg 0)))
+    (dolist (var flist)
+      ;; `\' to '/' on windows.
+      (let ((fname (expand-file-name (car var)))
+            org-roam-location)
+        (setq org-roam-location (org-roam-protocol-check-filename-for-protocol
+                                 fname))
+        (when (stringp org-roam-location) ; location for Org-roam file
+          (setcar var org-roam-location))))))
+
+(provide 'org-roam-protocol)
+
+;;; org-roam-protocol.el ends here