241 lines
7.5 KiB
Markdown
241 lines
7.5 KiB
Markdown
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# Auto adapting signal to day-night scheme
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So I wanted to automatically change the day/night theme of my brand new Signal desktop app. The way that it is manually done is through the `File -> Preferences...` menu. Now that's not convinient for programatic person like me. Let's investigate!
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## `.config` folder
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My first stab is looking into the mostly standard `~/.config` folder in Linux for Signal if one actually exists. It turns out it does. Let's see. It even has a `~/.config/Signal/config.json` file. Unfortunately, that file doesn't contain the settings for the theme, just window positions.
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`grep -r`ing in the folder for any of `android` or `theme` just returns the logfile that Signal is writing to.
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```
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...
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./logs/log.log.1:{..."theme-setting changed to android-dark",...}
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...
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```
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No luck.
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Another stab is at `/opt/Signal` directory. Again - no luck. And the app is a binary ELF executable
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```
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$ file signal-desktop
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signal-desktop: ELF 64-bit LSB executable,...
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```
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## `strace`-ing
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My next attempt is to attach to attach to the Signal process via `strace`. Find the process by `ps aux|grep signal`, attach by `strace -p <pid>` and try to change the . Boy, this does a lot of stuff! Let's filter by writing:
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`strace -e write -p 12345`
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Still, too much but I saw something hapenning amid the writing to `40` and `71` file descriptors (fd).
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```bash
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#...
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write(40, "!", 1) = 1
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write(71, "\0", 1) = 1
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write(40, "!", 1) = 1
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write(1, "{\"name\":\"log\",\"hostname\":\"pi2-ho"..., 147) = 147
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write(12, "\1\0\0\0\0\0\0\0", 8) = 8
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write(71, "\0", 1) = 1
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write(40, "!", 1) = 1
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#...
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```
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All right, the `1` fd is the log that is being written that I already saw. How about that 12 fd? Let's explore within the `proc` fs:
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```bash
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$ cd /proc/1234/fd
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$ ls -la
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# ...
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lrwx------ 1 pi2 pi2 64 Mar 29 23:23 12 -> anon_inode:[eventfd]
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# ...
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```
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Oh boy, some wierd anonymous inode. So we are definately not dealing with a good old filesystem file but rather some on the fly created fd. Let's explore a bit more...
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## Signal is an Electron app
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Taking a look at the [github repo of the project](https://github.com/signalapp/Signal-Desktop). Searching for `dark` and `theme` reveals css, sass files. Okay
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Looking at the menus there is `View -> Toggle Developer Tools` and BAM - a good old Chrome developer tools console pops up! Inspecting the elements, it's pretty clear what is happening:
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```html
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<body class="android">
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<!-- changes to -->
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<body class="android-dark">
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```
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Brilliant, the change of theme just changes the class on the `body` element. Let's see if we have jquery or I have to go to the dark ages of javascript's `findElementByTagName`:
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```javascript
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> $
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< function ( selector, context ) {
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// The jQuery object is actually just the init constructor 'enhanced' ...
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```
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Good, we have. Now I "just" have to find a way to connect to chrome console via a good old terminal in some way...
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## Chrome remote debugging
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Searching the Internets, I find a [post](https://blog.chromium.org/2011/05/remote-debugging-with-chrome-developer.html) in Chromium blog from way back in 2011 that I can run Chrome with `--remote-debugging-port` flag which enables some sort of a remote console.
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Would the electron app do the same?
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```bash
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signal-desktop --remote-debugging-port=9222
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```
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Indeed it does. This console however is not just a simple tcp connection to the javascript console. Running `echo "alert('echo'); | netcat localhost 9222` does nothing. More reading to go...
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Turns out, Chrome DevTools has its [own protocol](https://chromedevtools.github.io/devtools-protocol/) that among other things exposes websockets. Let's see what clients exist for that
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[Quite a lot](https://github.com/ChromeDevTools/awesome-chrome-devtools).
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Any pythonic ones? [pychrome](https://github.com/fate0/pychrome) seems simple enough.
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Let's be modern, do python3:
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```bash
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pip3 install pychrome
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```
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And I will use my favourite repl, `ipython` and follow the Getting started tutorial:
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```python
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import pychrome
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browser = pychrome.Browser(url="http://127.0.0.1:9222")
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```
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Awesome, I have a connection. The tutorial goes into opening a tab. I don't want that, I assume I should alread have a tab. Exploring `browser` object (via my favourite [ipython repl](http://ipython.org/)):
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```python
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In [3]: dir(browser)
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Out[3]: [... _private_stuff
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'activate_tab',
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'close_tab',
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'dev_url',
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'list_tab',
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'new_tab',
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'version']
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In [4]: browser.list_tab()
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Out[4]: [<Tab [38473d8e-ad8d-4325-8cb6-81aaec36c124]>]
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In [5]: tab = browser.list_tab()[0]
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In [6]: dir(tab)
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Out[6]: [... _private_stuff
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'call_method',
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'debug',
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'del_all_listeners',
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'event_handlers',
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'event_queue',
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'get_listener',
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'id',
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'method_results',
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'set_listener',
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'start',
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'status',
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'status_initial',
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'status_started',
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'status_stopped',
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'stop',
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'type',
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'wait']
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```
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The README goes into navigating pages and the examples folder is also not what I am looking for. But they do tell me `call_method` is probably what I want, just need to find the proper string and parameters in the protocl. I want to execute a javascript call.
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Back to the [Chrome DevTools Protocol Viewer](https://chromedevtools.github.io/devtools-protocol/). I look through a few of the Domains listed and finally arrive at [Runtime.evaluate](https://chromedevtools.github.io/devtools-protocol/tot/Runtime#method-evaluate) method.
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```python
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In [7]: tab.start()
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In [8]: tab.call_method('Runtime.evaluate', expression='alert("hi");')
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# I GET AN ALERT IN THE BROWSER! Dismiss it.
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Out[8]: {'result': {'type': 'undefined'}}
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```
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Finally! I have access to my javascript console in the browser! Let's write the jquery change of theme:
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```python
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tab.call_method('Runtime.evaluate', expression='$("body").removeClass("android").addClass("android-dark");')
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```
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That worked!
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## Wrapping it up
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Let's write a propper python script now:
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```python
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#!/usr/bin/env python3
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import sys
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import pychrome
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sys_argv = sys.argv
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if len(sys_argv) < 2:
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print("first argument needs to be day|night")
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exit(1)
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command = sys_argv[1]
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if command == "night":
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expression = js_dark_to_light = """
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$("body").removeClass("android").addClass("android-dark");
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"""
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elif command == "day":
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expression = js_light_to_dark = """
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$("body").removeClass("android-dark").addClass("android");
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"""
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else:
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print("first argument needs to be day|night")
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exit(1)
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browser = pychrome.Browser(url="http://127.0.0.1:9222")
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tab = browser.list_tab()[0]
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tab.start()
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tab.call_method('Runtime.evaluate', expression=expression)
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tab.stop()
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```
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Running `./change_signal.py day` changes to white theme and `./change_signal.py night` goes to dark theme.
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I also want to change the `signal-desktop` app to always start with the remote-debug flag enabled, so I do that:
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```bash
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rm /usr/local/bin/signal-desktop
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cat > /usr/local/bin/signal-desktop << EOF
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#!/bin/bash
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/opt/Signal/signal-desktop --remote-debugging-port=9222
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EOF
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chmod +x /usr/local/bin/signal-desktop
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```
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And that's it. Code can be found in my [sun](https://gitlab.com/pisquared/sun) repo which also deals with other day-night related dark-light themes including a script to detect whether the sun has set or not:
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```bash
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$ ./calc_sun.py
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usage: calc --loc=location_name [--date-format]
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calc --lat=latitude --lon=longitude [--tz|--date-format]
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returns
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current_time sunrise sunset day|night
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$ ./calc_sun.py --lat=51.21 --lon=4.40 --tz=Europe/Brussels
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23:57 07:23 20:10 night
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```
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So now I can chain that:
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```bash
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state=`./current.sh | cut -f4 -d' '`
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./change_signal.py $state
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```
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Voala! That was fun 🙂😊
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