fix(s2n-quic-platform): Fix compilation in non-pktinfo platforms

[dongcarl]

Clearly this was meant to be pktinfo_size

[camshaft]

I'm curious to know what platform you're using so we can add it to the CI. Ideally we would be testing for this 😄.

[dongcarl]

I'm actually on quite a strange platform: gramine.

Basically they LD_PRELOAD glibc and friends and implement a subset of Linux syscalls: https://gramine.readthedocs.io/en/latest/devel/features.html#tcp-ip-and-udp-ip-sockets

Since s2n-quic's feature detection in quic/s2n-quic-platform/build.rs is compilation and target_os-based, all the Linux features (sockopts) were enabled, which means it didn't run in gramine.

I had to patch build.rs like so:

diff --git a/quic/s2n-quic-platform/build.rs b/quic/s2n-quic-platform/build.rs
index 0777e6cf..0b65275f 100644
--- a/quic/s2n-quic-platform/build.rs
+++ b/quic/s2n-quic-platform/build.rs
@@ -6,6 +6,13 @@ use std::{fs::read_dir, io::Error, path::Path, process::Command};
 fn main() -> Result<(), Error> {
     let env = Env::new();

+    const SIMPLE_ENV_VAR: &str = "S2N_SIMPLE_ONLY";
+    println!("cargo:rerun-if-env-changed={}", SIMPLE_ENV_VAR);
+    let is_simple = std::env::var(SIMPLE_ENV_VAR).is_ok();
+    if is_simple {
+        return Ok(())
+    }
+
     for feature in read_dir("features")? {
         let path = feature?.path();
         if let Some(name) = path.file_stem() {

In order to turn off the features.

Thankfully the pktinfo_size change was all that was needed afterwards to make things compile and work (you guys did a great job abstracting away the platform).

Not sure if my build.rs patch is good but perhaps it'd make sense to have some flag that turns off all platform features to test the simple modules in your CI?

[camshaft]

Not sure if my build.rs patch is good but perhaps it'd make sense to have some flag that turns off all platform features to test the simple modules in your CI?

Yeah I think it would be a good idea to have some way to disable all of the features to prevent issues like this. Would you be able to open an issue for it and we can discuss it there?

[dongcarl]

Sure!

[dongcarl]

Opened: #1850