senders.io - Blog

Venturing back into C

For the past two weeks or so I have been diving back into C - programming. I've found it to be a very fun and refreshing experience - coming off of a slog of Java 11 updates at work. I've found comfort - in its simplicity and frustrations in my "I can do this without an - IDE" mindset.

I started C programming in College during a 8 AM course of which all I - can remember is that it was at 8 AM. I loved programming in C, dealing - with memory, pointers, no strings, structs, no strings, linking, no - strings. It was a really interesting difference from the web and Java - programming I had done previously. Obviously the lack of the - "string" type made things interesting and initially a challenge - for me back then. In my most recent endevour I found char * to be perfectly suitable for every case I came - across. It was usually a separate library that was failing me, not a - fixed char array. This was mostly due to the types of programs I was - writting in college were text adventures where all of what I did was - using strings. And my lack of understanding of what was actually - happening in C was really what was causing all the issues.

The Project

I started working on an application I had been meaning to develop - called reminder.d. This daemon - would monitor for reminder notifications I would send via a CLI. It queue - them up based on some time set to send the notification. I ended up - writing both the CLI and the daemon in this past week, both in C.

The Beginning

This project started with an outline (as a README) which I think was - the reason this ended up as an actually successful project. I had been - thinking about this for a long time, and had begun using a calendar to - keep track of long term reminders/dates etc. First, I outlined the - architecture "how would I actually do want to send myself - remidners". Since half my day is spent infront of a computer, with a - terminal open or at least two keystrokes away, a CLI would do the trick. - Then how do I actually send myself notifications... writing them down. So - I can use the CLI to write to a file and have a daemon pick up the - changes and notify me once it hits the desired time posted.

The CLI

The CLI remindme took in messages and appened them to a file. - This file would be monitored by the daemon later on. Each reminder - consisted of three parts:

Message - The body of the notification.
Time - This is either a datetime or a period for when the - notification should send.
Flag - The Flag was set by the CLI when written to the file, - this marks the status of the reminder

After a notification is written the daemon will pick up the - notification and notify if the time set is now/past. -

The Daemon

The Daemon reminder-daemon opened and tailed a file at - /usr/local/etc/reminder.d/$USER.list. It would tail the file - monitoring any incoming lines parsing them into reminders. The syntax of - the reminder is FLAG EPOCHSEC MESSAGE . - Tokenizing on spaces it was then added to a linked-list sorted by time. - Every second it checks the file for any new lines, adding reminders as - they come in, then check the head of the list. If the reminder at the - head is ready to be notified the daemon pops it off the list and sends - the notification. After a notification is sent successfully the daemon - modifies that line in file updating its FLAG - to 'd'. This is so when the daemon starts back up it skips the - reminder. Notifications are sent via libnotify: Reminder - $DATETIME with the message body. They are also - set to last until dismissed manually, this way if were to walk away, once - I sat down I'd see the stale reminder waiting.

Future Plans for Reminder.d

Having a system to create and send myself notifications is incredibly - useful but having them limit to just the computer I sent them on makes - them a very limited. I have been using them at work for the last few days - and its nice to be able to tell myself to remeber to email a person after - lunch. But I would like to be able to tell myself things later in the - day. I have planned since the beginning to have a remote server I can - sync the reminders through. In addition having an application running on - my phone that also gets and sets reminders.

Remote syncing would change entirely how I deal with reminders in the - file.

-
- struct remnode { 
-   long fileptr; 
-   struct reminder* reminder; 
-   struct remnode* next; 
- }; 
-

Is currently the struct I use to keep track of the reminders. - fileptr is the line of the file where the - reminder is, so I can fseek back to the - location and overwrite its flag. I cannot currently think of a way to - keep the files perfectly identical without introducing countless - edgecases. What I do think might work is providing some form of UUID. - When a remote pull tells the systems daemon that a notification has been - cleared it can mark it by ID. Right now the fileptr is effectively its - ID, but that will not work anymore. A composite key of the daemons own id - (generated at install?) with a new ID of each incoming message would help - ensure uniqueness across ID generations across multiple systems.

What I've learned

First off, I probably could've done this in bash. With - date notify-send git awk cron and a few other - useful commands I could very easily keep track of file changes and push - notifications at a certain time. But seeing as I scrap together bash - scripts all the time I though C would make things more fun.

Writing manpages was the probably the most fun I had working on the - project. They have a simple elegance to them, similar to C. That being - said you could FEEL the age of the language. Every single decision is - there to make things simple to parse. Even compared to modern markup the - explicit direct nature of the language made it so easy to learn. Every - tag served a specific purpose and each objective I had had a flag to do - it.


-.TH REMINDME 1 
-.SH NAME
- remindme \- Send yourself reminders at a specific time on one or more devices
-.SH SYNOPSIS
-.B remindme
-[\fB\-t\fR \fITIME\fR]
-[\fB\-\-at \fITIME\fR]
-[\fB\-i\fR \fIPERIOD\fR]
-[\fB\-\-in\fR \fIPERIOD\fR]
-        
-

Libnotify was insanely easy to work with, from a programming - perspective.


-  NotifyNotification *notif = notify_notification_new(title, rem->message, "info");
-  notify_notification_set_app_name(notif, APP_NAME);
-  notify_notification_set_timeout(notif, NOTIFY_EXPIRES_NEVER);
-
-  GError* error = NULL;
-  gboolean shown = notify_notification_show(notif, &error);
-        
-

In closing

Overall, this was an extremely fun first week of engineering. I look - forward to what I am able to do syncing and sending notifications on - android.

For the zero people reading, grab a beer and outline your project. - Full through. Think about the how, then write it down. Don't worry - about getting in the weeds of how to write a manfile, thats what is fun - about programming. I thought I botched my debian/sid environment - uninstalling and reinstalling a notification daemon. Infact I think its - caused me to take a stance on the whole systemd thing. Either way, start - a private repo (they're free now) write a README and a LICENSE file - and iterate on the README until you realize "oh shit this is - something I can do". Then do it. This project still needs some work, - but for an MVP, its actually done. And now I can dive in the deep end of - trying to actually make it easy to setup on a fresh PC. Or dive into - modern android development and server syncing...