sshd: Add keepalive every 30s

Based on work by @prologic in #147
Fixes #89

sshd/terminal.go

@@ -4,11 +4,15 @@ import (
 	"errors"
 	"fmt"
 	"net"
+	"time"
 
 	"golang.org/x/crypto/ssh"
 	"golang.org/x/crypto/ssh/terminal"
 )
 
+var keepaliveInterval = time.Second * 30
+var keepaliveRequest = "keepalive@ssh-chat"
+
 // Connection is an interface with fields necessary to operate an sshd host.
 type Connection interface {
 	PublicKey() ssh.PublicKey
@@ -72,6 +76,17 @@ func NewTerminal(conn *ssh.ServerConn, ch ssh.NewChannel) (*Terminal, error) {
 		channel.Close()
 	}()
 
+	go func() {
+		for range time.Tick(keepaliveInterval) {
+			_, err := channel.SendRequest(keepaliveRequest, true, nil)
+			if err != nil {
+				// Connection is gone
+				conn.Close()
+				return
+			}
+		}
+	}()
+
 	return &term, nil
 }