HTTP Retry-After Header Parser (src/retry_after.rs)

A utility to parse HTTP Retry-After headers, supporting both delta-seconds and HTTP-date formats. Use this to handle rate-limiting signals from LLM APIs reliably.

// Source: https://github.com/librefang/librefang | License: MIT | Copyright 2024 LibreFang Contributors
// Provided via justclaw.it.com; keep this notice with the code.
//! `Retry-After` HTTP header parsing.
//!
//! Per RFC 7231 §7.1.3 the `Retry-After` header value can be either:
//!
//! 1. **Delta-seconds** — a non-negative integer giving the number of
//!    seconds to wait, e.g. `Retry-After: 120`.
//! 2. **HTTP-date** — an absolute timestamp in IMF-fixdate format,
//!    e.g. `Retry-After: Wed, 21 Oct 2015 07:28:00 GMT`.
//!
//! Real LLM providers send delta-seconds in practice, but the spec
//! permits either form and a few middleware layers / CDNs do emit
//! HTTP-date.  Drivers that only handle the delta-seconds form silently
//! fall back to a hardcoded default whenever the serve

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