ammar

In my post about esp-visualize I declared my intention to “query my tasks list from my caldav server and display different types of messages that act as a reminder” using my esp32-s3 board.

Well, this seems to be harder than I thought it would be, if you have the energy and the time, dive with me into one of the problems.

So let’s start the story from the beginning.

I had a wifi module working, it connects to my network and gets an ip address from dhcp, and it can send an HTTP request to some random website successfully, hooray!

I change the url to be my caldav’s server (It’s a radicale instance behind a traefik reverse proxy), and voila… nothing happens.

After accidentally realizing that I can log panic information in rust in the `#[panic_handler]` (duh!), I see it’s a handshake failure, not sure if I felt frustrated or excited, I need to ask my therapist about this!

My first assumption was a certificate issue, so I looked up the documentation of the crate I’m using (reqwless) and I found that the code I copied from the book already disables certificate verification (note to future self, spend few more minutes understanding the config you copy from tutorials).

I also found that reqwless is using `embedded-tls` which only supports tls1.3 (It can be made to use `esp-mbedtls` which supports tls1.2 and tls1.3 but I didn’t try that yet).

My next assumption is that my traefik instance doesn’t support tls1.3, life would have been simple if that was the case but a simple openssl command proved me wrong

openssl s_client -connect <domain>:443 -tls1_3

As we see, life isn’t fair, and now I have to figure out how do packet capture to get more information, urghh.

My router runs openwrt, so I looked up how to do packet capture and found this pretty cool guide.

So what was the situation? A client hello packet followed by a tls alert, the alert is handshake failure (40), no certificate exchange so that confirms it is not a certificate verification issue, so why the server didn’t like my client hello?

Luckily openssl has the option `-trace` which shows exchanged packets so I can compare them, and here is what we found!

First, the low hanging fruit, the cipher suites, my esp32 was sending a single one(TLSAES128GCMSHA256) so adding `-ciphersuites TLSAES128GCMSHA256` option to the openssl command immediately ruled this out.

Next, “Extension: supported_groups”™ was different, my esp32 was sending a single value for secp256r1 and openssl was sending that plus other values.

Using the option `-groups secp256r1` reproduced the issue, this is great, I go to the Coop-cloud’s traefik recipe I use, and I modify it to support the supported group (https://git.coopcloud.tech/coop-cloud/traefik/pulls/73).

I use openssl to verify and now handshake works fine with `secp256r1` so I do another cargo run and guess what? It’s still a handshake failure!!

Okay, that was enough to take in for today I guess, I will stare at client hello packets and compare their bytes again on another day.

After reading few chapters of the rust book, I decided that I need a project to keep myself going and excited.

map battle was supposed to be that project, but after the pilot game without another game scheduled there was not much motivation to continue.

I still plan to get back to map battle but I wanted to keep learning rust and I wanted another project.

I found myself with an esp32-s3 board and a couple of 64x32 led matrix, and with a [quick] online search I found Embedded Rust (no_std) on Espressif and impl Rust for ESP32.

So what do I do? I start making esp-visualize!

What does it do? not much yet :D

The idea is to have it query my tasks list from my caldav server and display different types of messages that act as a reminder.

Maybe I’ll allow it to be configured and managed using BLE? I’ll keep getting more ideas as I go I guess, figuring out how to connect to wifi and send HTTP requests took me longer than I thought it would and I’m not fully sure I understand every line of code I have in there, so there is a lot for me to learn about the chip, no_std rust, and how to debug low-level implementation of modules like BLE and WIFI.

I expect this to be a pretty fun and maybe a useful project!