HTTP/1.1 Header Casing

To support these use cases, Envoy allows configuring a formatting scheme for the headers, which will have Envoy transform the header keys during serialization.

Currently Envoy supports two mutually exclusive types of header key formatters:

Stateful formatters

Stateful formatters are instantiated on decoding, called for every decoded header, attached to the header map, and are then available during encoding to format the headers prior to writing. Thus, they traverse the entire proxy stack. An example of this type of formatter is the preserve case formatter configured via the field. The following is an example configuration which will preserve HTTP/1 header case across the proxy.