Akka HTTP & java.time: ISO‑8601 Date Header Parsing Compatibility

Integration Boundary: Akka HTTP & java.time

The goal is to ensure that HTTP requests containing an ISO‑8601 formatted Date header are correctly interpreted by an Akka HTTP service that otherwise relies on java.time for time‑zone handling. Akka HTTP’s current HttpDate parser accepts only RFC1123, RFC1036, and ANSI C asctime formats, omitting ISO‑8601 and explicit time‑zone offsets. This mismatch forces application code to perform manual parsing or to reject otherwise valid requests.

Constraints include maintaining backward compatibility with existing Akka HTTP releases, avoiding invasive changes to the core HTTP layer, and preserving the lightweight nature of the framework. The uncertainty lies in whether Akka HTTP should expose ISO‑8601 parsing directly or delegate entirely to java.time in a future release.

Key questions for the community:

• Should Akka HTTP add native ISO‑8601 parsing to its HttpDate implementation, and if so, how should time‑zone offsets be handled?
• What is the recommended pattern for integrating java.time parsing in the request pipeline without duplicating logic across services?
• Is there a design trade‑off between extending Akka HTTP’s parser and maintaining a clear separation between HTTP protocol handling and application‑level date logic?