rustls-tls-native-roots does blocking IO during .build

[chebbyChefNEQ]

repro
Cargo.toml

[package]
name = "test-rs"
version = "0.1.0"
edition = "2021"

[dependencies]
reqwest = { version = "~0.12", default_features = false, features = ["rustls-tls-native-roots"] }

use reqwest::ClientBuilder;

fn main() {
    for _ in 0..10 {
        let start = std::time::Instant::now();
        ClientBuilder::new().build().unwrap();
        println!("built in: {:?}", start.elapsed());
    }
}

this produces the following flamegraph, which include loading certs std::fs.

Not sure what's a nice solution as wrapping the load in tokio::spawn_blocking would introduce a breaking change.

[chebbyChefNEQ]

oops forgot the attach the flamegraph

[seanmonstar]

Peeking in the source, yep, it does load a file from the disk. Thinking more about what exactly it's doing, that's not surprising. I'd recommend trying to only build one or a couple clients and sharing them.

I suppose one option is that you could load the native cert yourself manually (asynchronously), add it as a root certificate to the reqwest builder, and not use the rustls-tls-native-roots feature.

[chebbyChefNEQ]

loading the certs manually certainly sounds like a good solution. Let me try that, thanks for the suggestion!