GUACAMOLE-2220: Kubernetes: add support for terminal-type.

[bbennett-ks]

Related PRs

GUACAMOLE-2220 (server 637)
GUACAMOLE-2220 (manual 291)

Overview

Unlike SSH and Telnet, Kubernetes sessions do not automatically pass a terminal type. Kubernetes exposes stdin, stdout, and stderr, but has no built-in way to propagate the TERM environment variable.

Kubernetes supports two connection modes:

• Attach: connect stdin/stdout/stderr to the main process already running in the container.
• Exec: start a new process in the container and connect to that process.

Because Kubernetes does not pass the terminal type itself, this change adds a server-side substitution mechanism for Exec sessions: Any $TERM in the Exec command line is replaced with the configured terminal type when the session starts. This lets users decide whether and how to pass the terminal type, for example:

env TERM=$TERM /bin/bash

Attach mode has no command line, so the terminal type is not propagated automatically.

• Adds support for terminal-type for Kubernetes sessions.
• Adds conditionalLabel for Field, so a form field can replace its label based on another field's value.
• conditionalLabel is used for the Kubernetes terminal-type label:
  • If exec-command is empty, the label uses the default Terminal type (set manually in session):.

- Else, (a command was specified), the label switches to `Terminal type (available as $TERM in command):`.