Re: Lazy load of org-protocol

[Jim Porter]

On 2/5/2022 3:54 AM, Max Nikulin wrote:
> I would prefer to avoid
>     (require 'org-protocol)
> in emacs init file and to postpone loading till invocation of 
> emacsclient with org-protocol URI.
>
> The problem is a hack in org-protocol. URIs are actually treated as 
> (relative) file names and magic is achieved in an advice for 
> `server-visit-files' function. So the advice must be installed in advance.
>
> My first idea was to avoid such magic and to create autoload function 
> org-protocol-from-argv with body similar to that advice. If it were 
> possible to get arguments from `command-line-args-left' then invocation 
> would look like
>
>     emacsclient --eval '(org-protocol-from-argv)' 
> 'org-protocol:/store-link?url=u1&title=t1'
>
> Unfortunately it is against design of emacs server protocol. If --eval 
> option is given than everything other is considered as independent 
> expressions. At the lower level there is no way to transfer `argv` as a 
> list from client to server process.

I've thought a bit about how to improve this too. One further issue with 
the current implementation is that when emacsclient invokes the 
alternate editor (usually to start the "main" emacs instance), 
org-protocol: links no longer work correctly. That's because only the 
emacsclient itself (through `server-visit-files') knows what to do with 
them.

I think the problem really starts in emacsclient's command line 
handling. You can see this in other situations too. For example, Emacs 
can be configured as your system's mailto: URL handler. (The file 
etc/emacsclient-mail.desktop in the Emacs repo does this.) The command 
to use for a new Emacs instance is simple:

  emacs -f message-mailto %u

However, doing this for emacsclient is harder:

  emacsclient --alternate-editor= --create-frame --eval 
"(message-mailto \\"%u\\")"

There's no problem with "--alternate-editor=" and "--create-frame", but 
the fact that emacsclient requires evaling the function call that way 
is: if %u holds a string with quotation marks, this will break, and 
worse, could even result in arbitrary code being executed. (In practice, 
this is probably rare, since URLs are generally URL-encoded, and so 
don't have literal quotes in them.)

As a result, I think a good first step might be to add support for 
"--funcall" to emacsclient, just like the regular emacs binary. (The 
"-f" shorthand won't work though, since emacsclient already uses that 
for "--server-file"). This would simplify the `message-mailto' case 
above and would also allow org-protocol to do something similar:

  emacsclient --funcall org-protocol-capture %u

Then, so long as `org-protocol-capture' has an autoload, this would Just 
Work, and org-protocol.el would be lazily loaded. Hopefully, this could 
also be forwarded onto the alternate editor so that when the user open 
an org-protocol: URL when Emacs is closed, it still handles the URL 
correctly.

That said, in the short term, you could try out something like:

  emacsclient --eval "(org-protocol-capture \\"%u\\")"

Of course, that has the quoting issues I mentioned above, but it could 
be helpful for developing a proof of concept.

- Jim