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Hyperlinks in Terminal Emulators

This isn't made explicit, and I didn't see any concrete consensus in the discussions, how are arbitrary/non-standard URL schemes handled? From the looks of things, it's not the terminal's responsibility, they will just pass the URL to the OS's own file open routines. So if I wanted to generate a link to say, an IRC chatroom:

echo -e '\e]8;;irc://\a#lobby channel\e]8;;\a'

All I will need to do is make sure my IRC client is registered in the system to handle irc:// links. Is that correct?


egmontkob commented Apr 25, 2017

@evaryont You're right, we don't intend to go into such details. It's up to the terminal emulator to decide which schemes it supports and what action it takes on them, probably delegating this decision to some lower level OS routine.

Most terminal emulators already autodetect standard URLs appearing on the screen. On one hand, it's reasonable for them to take the same action, regardless whether e.g. "irc://..." is autodetected as a visible string, or specified explicitly via this new escape sequence. On the other hand, the new one is potentially more easily configurable by the users since they won't have to handcraft complicated regexes, so perhaps some terminal emulators will add a configuration option for this.

It might also make sense for terminal emulators to offer the possibility to override the OS-wide action because the OS-wide registry would probably prefer to open a graphical app, whereas if coming from a terminal emulator, you might want to prefer to open a terminal-based IRC client in a new window/tab of the same terminal emulator, or similarly, prefer a lynx-style browser for http/https rather than a graphical one.

This is an open ended question, leaving room for terminal emulators to come up with nice ideas.

ssbarnea commented Jun 21, 2017

This is really cool! I found this after looking for the same thing myself (and wasting some time with the reddit thread).
Is there any ANSI "coloring" python library already implementing this? I would love to start giving hyperlinks as output. The option to display them raw is not ok.

Foxboron commented Jul 8, 2017

Wouldn't this allow rather ugly attack vectors where the user doesn't understand what he/she is clicking?


egmontkob commented Jul 12, 2017

@ssbarnea Not that I'm aware of. Thanks for spreading the news of this feature and asking others to add support!


egmontkob commented Jul 12, 2017

@Foxboron I'm fairly sure there's no risk here at all. The situation shouldn't be any worse than clicking on a link on an untrusted webpage. In fact, webpages are worse. First, they can leak data via the Referer field which isn't filled out if you click from the terminal emulator. Second, they can do nasty JS tricks to alter the target just when you click on the link (sometimes this is actually used for good purposes, like to inject a redirector which hides the referring page). In the terminal emulator a malicious app can still probably overwrite the link target at any time, but it has no clue when you're about to click.

Any webpage that does harmful things (e.g. delete data stored on a server) by just visiting a link suffer from CSRF bug anyway which can be exploited from browsers (malicious websites) too.

What happens to "data:" urls or pure local (#) links? Any chance to get anything to STDIN or back to a terminal based app that doesn't involve registering a link handler with the window manager? Use case: local link handling inside a "pure" command-line app with hyperlink support.


egmontkob commented Sep 3, 2017

@stefanhaustein Interpretation of different schemes (or lack thereof) is up to the terminal emulator. E.g. with "data:" URLs they might show a popup with the content, or store in a temporary file and open that. Note that with the current limit of 2083 bytes for the URL in both VTE and iTerm2, the "data:" scheme isn't quite useful. I wouldn't want to significantly increase the limit (let alone remove it altogether) because then a malicious utility could cause the terminal emulator to eat tons of memory.

Handling the link inside the existing terminal emulator is alas again something that would be truly problematic. It would raise tons of questions like what to do if an app is already running or if you're ssh'd to a remote host, and probably a whole lot more. Not to mention that if we did anything like this, that would probably introduce serious security concerns.

The closest you can do with the current design is to specify a handler that opens a new terminal window and a specific app inside that, e.g. "lynx" for "http(s)" scheme. I'm not sure if iTerm2 allows you to configure this. GNOME Terminal takes the handler app from the global GNOME-wide configuration, hence it cannot differ from what's used for graphical apps. This is something we might improve on if there's a high demand – or other VTE-based apps might implement this.

@egmontkob: Malicious "utilities" aren't worth worrying about. If you're executing a malicious binary, you've got much bigger problems than a terminal emulator eating up memory. However, catting a text file could be a problem, as people expect text files to be safe to display. This is actually similar to an issue MS-DOS had with the ANSI.SYS driver, only that was much worse, as that allowed random text files to change what the keys on your keyboard do—for instance, making a common letter instead type a command that formats your hard drive and press Enter.


egmontkob commented Sep 13, 2017

@flarn2006 Thanks for the clarification, I indeed did not clearly distinguish these two. A malicious binary can also be a compromised binary on a remote system that you ssh into, in which case it's like locally cating a maliciously constructed text file (plus all the damage being done over there on the compromised system). As far as the terminal emulator is concerned, it's only the incoming byte stream that matters.

hdon commented Oct 10, 2017

A note to any maintainers of terminal emulators out there: please include a prominent option to scale back this feature. I've been using terminal emulators for 20 years and one behavior I find really annoying is clicking even what is obviously a URL and then having it come up in my browser. Sometimes I'm just trying to select text...

(Oh, and rectangle select is a nice feature, too, guys!)

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