Request IDs

The request ID extractor uses a fixed practical precedence:

1. X-Request-Id;
2. Request-Id, only when the preferred field is absent.

The selected value is returned unchanged. An empty X-Request-Id therefore returns Some("") and does not fall back. Duplicate selected fields and non-text values fail without including the value in the error.

#![allow(unused)]
fn main() {
use http_extract::{Request, extract_request_request_id};

let request = Request::builder()
    .header("request-id", "fallback")
    .header("x-request-id", "preferred")
    .body(())?;
assert_eq!(
    extract_request_request_id(&request)?,
    Some("preferred")
);
Ok::<(), Box<dyn std::error::Error>>(())
}

These are crate-configured common field names, not a claim that either is a universal IETF-standard request ID field. The crate does not generate, validate, or propagate identifiers. The distinction from standardized fields is summarized in Standards and compatibility.