04-23 Async HTTPS

Today I made the httpmanager to use an async tcp library. For plain asynchronous http (no encryption) it works fine.

Problem

It turns out that the library doesnt support ssl. That is a problem, since my server upgrades all requests to https. The server errors out when it encounters a plain http request on port 80. Some developers are working on a pull request for TLS support in their free time. They are quite active, the last pull request was 7 days ago. They are not finished yet and the dev release is not stable.

Solutions

Make Server accept insecure HTTP on port 80

I can change the apache config to use plain http as well. This would allow the async client to work without me having to wait for tls support. It is a fairly easy fix since I only need to change a few lines in the configuration files. The drawback would be that I would be violating a requirement of my contract in which I stated that connections would be secure.

MQTT instead of HTTP

I could also switch from async HTTP to async MQTT. MQTT is more optimized for IoT traffic than HTTP and can be called asynchrously. It appears though that SSL only works with synchrounous MQTT. The async version uses the same asynctcp library from above that doesnt have ssl support. That would be the least of my problems if I switch to MQTT. The major drawback would be that I would need to redo my entire backend. I would need to set up port forwarding, disable firewall for port 8883 and set up a broker / publisher for the backend and esp32s. I would also have to change the entire backend on the server since Laravel php doesnt support MQTT. There are some packages for it on packagist but there is no official support. Having a codebase based on so many libraries also in the backend will be very fragile.

Go back to sync HTTPS without HTTPClient lib

I can just forget about asynchrounous communication and use the WifiClientSecure.h package from espressif systems directly. I already use it for all of my currenty connections but I havent directly used it to print HTTP headers to the socket as shown in this example. This needs no server reconfiguration and should not through connection refused -1 exceptions like when I used in in conjunction with the HTTPClient. It seemed to be the fault of the HTTPClient, which only provided a wrapper for easily setting request headers and the message body. I think there is potential to make it work without the httpclient.

https://github.com/espressif/arduino-esp32/issues/3449

Further actions

Both viable solutions have tradeoffs. In the I requirements for the project is for secure connections between clients and api. I think SSL is more or less a necessity and do not think that async traffic is super necessary. As long as the WifiClient is fast, I have no issues with using it synchronously.

Having working code now is more valuable than being promised some better code in the future. I will scrap the async http library and change the server config to not upgrade requests.