Serverless Calendar App
written by Matthias Endler
Every once in a while my buddies and I meet for dinner. I value these evenings, but the worst part is scheduling these events!
- We send out a message to the group.
- We wait for a response.
- We decide on a date.
- Someone sends out a calendar invite.
- Things finally happen.
None of that is fun except for the dinner.
Being the reasonable person you are, you would think: “Why don’t you just use a scheduling app?”.
I have tried many of them. None of them are any good. They are all…too much!
Just let me send out an invite and whoever wants can show up.
- I don’t want to have to create an account for your calendar/scheduling/whatever app.
- I don’t want to have to add my friends.
- I don’t want to have to add my friends’ friends.
- I don’t want to have to add my friends’ friends’ friends.
- You get the idea: I just want to send out an invite and get no response from you.
The nerdy, introvert engineer’s solution
💡 What we definitely need is yet another calendar app which allows us to create events and send out an invite with a link to that event! You probably didn’t see that coming now, did you?
Oh, and I don’t want to use Google Calendar to create the event because I don’t trust them.
Like any reasonable person, I wanted a way to create calendar entries from my terminal.
That’s how I pitched the idea to my buddies last time. The answer was: “I don’t know, sounds like a solution in search of a problem.” But you know what they say: Never ask a starfish for directions.
Show, don’t tell
That night I went home and built a website that would create a calendar entry
from GET
parameters.
It allows you to create a calendar event from the convenience of your command line:
You can then save that to a file and open it with your calendar app.
In a sense, it’s a “serverless calendar app”, haha. There is no state on the server, it just generates a calendar event on the fly and returns it.
How I built it
You probably noticed that the URL contains “shuttleapp.rs”. That’s because I’m using shuttle.rs to host the website.
Shuttle is a hosting service for Rust projects and I wanted to try it out for a long time.
To initialize the project using the awesome axum web framework, I’ve used
and I was greeted with everything I needed to get started:
Let’s quickly commit the changes:
To deploy the code, I needed to sign up for a shuttle account. This can be done over at https://console.shuttle.rs/.
It will ask you to authorize it to access your Github account.
Then:
and finally:
Now let’s head over to https://zerocal.shuttleapp.rs:
Hello World! Deploying the first version took less than 5 minutes. Nice! We’re all set for our custom calendar app.
Writing the app
To create the calendar event, I used the icalendar crate (shout out to hoodie for creating this nice library!). iCalendar is a standard for creating calendar events that is supported by most calendar apps.
Let’s create a demo calendar event:
Simple enough.
How to return a file!?
Now that we have a calendar event, we need to return it to the user. But how do we return it as a file?
There’s an example of how to return a file dynamically in axum here.
Some interesting things to note here:
- Every calendar file is a collection of events so we wrap the event in a
Calendar
object, which represents the collection. impl IntoResponse
is a trait that allows us to return any type that implements it.CalendarResponse
is a newtype wrapper around Calendar that implements IntoResponse.
Here is the CalendarResponse
implementation:
We just create a new Response
object and set the Content-Type
header to the
correct MIME type for iCalendar files: text/calendar
. Then we return the
response.
Add date parsing
This part is a bit hacky, so feel free to glance over it. We need to parse the date and duration from the query string. I used dateparser, because it supports sooo many different date formats.
Would be nice to support more date formats like now and tomorrow, but I’ll leave that for another time.
Let’s test it:
Nice, it works!
Opening it in the browser creates a new event in the calendar:
And for all the odd people who don’t use a terminal to create a calendar event, let’s also add a form to the website.
Add a form
I modified the calendar function a bit to return the form if the query string is empty:
After some more tweaking, we got ourselves a nice little form in all of its web 1.0 glory.
And that’s it! We now have a little web app that can create calendar events. Well, almost. We still need to deploy it.
Deploying
Right, that’s all. It’s that easy. Thanks to the folks over at shuttle.rs for making this possible.
The calendar app is now available at https://zerocal.shuttleapp.rs.
Now I can finally send my friends a link to a calendar event for our next pub crawl. They’ll surely appreciate it.yeahyeah
From zero to calendar in 100 lines of Rust
Boy it feels great to be writing plain HTML again. Building little apps never gets old.
Check out the source code on GitHub and help me make it better! 🙏
Here are some ideas:
- Add support for more human-readable date formats (e.g.
now
,tomorrow
). - Add support for recurring events. Add support for timezones.
- Add location support (e.g.
location=Berlin
orlocation=https://zoom.us/test
). Add Google calendar short-links (https://calendar.google.com/calendar/render?action=TEMPLATE&dates=20221003T224500Z%2F20221003T224500Z&details=&location=&text=
). - Add example bash command to create a calendar event from the command line.
- Shorten the URL (e.g.
zerocal.shuttleapp.rs/2022-11-04T20:00/3h/Birthday/Party
)?
Check out the issue tracker and feel free to open a PR!
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