Description:
When envoy processes request with enabled buffering it reads the whole request into memory before sending headers to an upstream.
Is is possible to make Envoy populate content-length header in this case? It would help with some http/1.0 backends (which unfortunately still exist in the wild).

Another option would be to add http/1.0-compliant behavior as cluster option (based on the precedent of existing accept_http10 option).

Without either of this options Envoy tries to send chunked-encoded data, which is observed as empty body by http/1.0 server.

Relevant Links:

• https://www.envoyproxy.io/docs/envoy/latest/configuration/http_filters/buffer_filter