Exposes TCP keepalive configuration via listener and dialer metadata:
keepalive: true
keepalive.idle: 30s
keepalive.interval: 10s
keepalive.count: 6
When enabled, the OS sends keepalive probes after the idle period and
tears down the socket if the remote does not respond. This causes any
blocked Read() on a dead connection to return promptly, releasing
goroutines and memory — covering both legs of a CONNECT tunnel (the
inbound client connection via the listener, and the outbound upstream
connection via the dialer).
This is the correct alternative to a hard application-level read
deadline (SetReadDeadline) for detecting dead connections, as it
distinguishes truly dead connections from legitimately idle ones.
Relates to: https://github.com/go-gost/x/issues/91
Andrew Beresford
cf70a0cbe1