Indication of connection loss on downstream TCP and HTTP requests

Title: Indication of connection loss on downstream TCP and HTTP requests

Description: Hi Ladies and Gents,

This ticket is the continuation of 21294 that ended with proposal on requesting solution for the described issue as feature.

The request is to:

Indicate TCP connection level issues of downstream client when:

• connection was established earlier
• there were http requests received and answered
• then there is no active http request ongoing
• something happens on client side with the connection
  • loss of connectivity with client
  • RST is sent from client

With error log information:

• TCP connection ID
• and Connection closure reason

In:

• listener access log

TCP connection listener access log was configured and tried out. Used configuration: base_envoy_config_with_listener_accesslogs.txt.tar.gz Example output that appeared: [2022-06-07T13:43:30.306Z] TCP Connection 100.109.96.1:38321 196 - 0 1780 -

Expected that might %CONNECTION_TERMINATION_DETAILS% operator holds additional information on the connection loss, but showed only "-"

Annotated TCP dump describing visualizing the use case: downstream_client_loss_annotated.pcapng.tar.gz