Provide a way to disable tls12 feature for rustls

[andylizi]

ureq is a lightweight HTTP client often used to communicate with one or a few hardcoded servers (e.g. making API calls). TLS 1.2 support is mostly unnecessary in those situations because we can know for sure if the hardcoded servers support TLS 1.3¹ or not.

TLS 1.2 in rustls often requires separate code paths to handle. Disabling the tls12 feature can reduce binary size by ~100kb. It'd be great if ureq can provide a way to do so.

Footnotes

1. Which is also highly likely, as 70% of sites now support TLS 1.3 according to https://www.ssllabs.com/ssl-pulse/ ↩

[algesten]

Good idea! Thanks!

[algesten]

Me testing to do a simple binary with/without tls12 enabled.

-rwxr-xr-x   1 martin  staff  2714424 Oct  8 18:19 foo-no-tls12*
-rwxr-xr-x   1 martin  staff  2821384 Oct  8 18:21 foo-with-tls12*

[algesten]

(2821384-2714424)/2821384 = 0.038

So tls12 takes 3.8% of a macOS binary. Now, the question is: the complication of having this as a separate feature, is it worth 3.8% potential reduction in size?

[algesten]

This complicates the feature flag situation for a rather small gain. I don't want this, for now.