contrib/knock.in: Can now be called from an ordinary shell.

[tripe] / contrib / knock.in

diff --git a/contrib/knock.in b/contrib/knock.in
index be55f2b95a0496b312842a6637c001fcf52cd162..b1754d931cc6169c5a4b3e3e46a907337f8ef87f 100755 (executable)
--- a/contrib/knock.in
+++ b/contrib/knock.in
@@ -3,21 +3,29 @@
 set -e
 
 ### This script performs the passive side of a dynamic association.  It is
-### intended to be set as the `tripe' user's shell, and invoked via ssh(1).
-### Specifically, for each dynamic peer, add a line to `.ssh/authorized_keys'
-### of the form
+### intended to be set as the forced command in an `.ssh/authorized_keys'
+### file.  Specifically, for each dynamic peer, add a line to
+### `.ssh/authorized_keys' of the form
 ###
-###    command="PEER" ssh-rsa ...
+###    environment="TRIPE_USER=PEER" ssh-rsa ...
 ###
 ### There's an additional wrinkle.  Suppose that the passive TrIPE endpoint
 ### is behind a NAT, and the SSH gateway is on a different machine.  The
 ### gateway should have its own `tripe' user, and this script should again be
 ### its shell.  On the gateway, add a `.ssh/authorized_keys' entry
 ###
-###    command="tripe@SERVER:PEER" ssh-rsa ...
+###    environment="TRIPE_USER=tripe@SERVER:PEER" ssh-rsa ...
 ###
 ### for the dynamic endpoint.  On the passive endpoint itself, you need an
-### entry for the gateway's `tripe' user's key, with no command.
+### entry for the gateway's `tripe' user's key, with `TRIPE_GATEWAY' set to
+### any value, like
+###
+###    environment="TRIPE_GATEWAY=t" ssh-rsa ...
+###
+### For backwards compatibility, it can also be set as the `tripe' user's
+### shell, with the `[tripe@SERVER:]PEER' indicator set as the forced
+### command.  If there are no forced command or `TRIPE_*' environment
+### variables then it is assumed that a gateway is calling.
 
 : ${prefix=@prefix@} ${exec_prefix=@exec_prefix@}
 : ${bindir=@bindir@}
@@ -25,23 +33,47 @@ set -e
 : ${tripectl=$bindir/tripectl}
 export TRIPEDIR TRIPESOCK
 
-case "$#,$1,$2" in
-
-  2,-c,*:*)
-    ## Proxy through to another server.
-    server=${2%:*} user=${2##*:}
-    exec ssh "$server" "$user"
+## Make sure we're being called properly, and figure out the peer identity.
+case "${TRIPE_USER+t},${TRIPE_GATEWAY+t},$#,$1" in
+  t,,0,) set -- "$TRIPE_USER" ;;
+  ,t,0,) set -- $SSH_ORIGINAL_COMMAND; unset SSH_ORIGINAL_COMMAND ;;
+  ,,2,-c) ;;
+  *)
+    echo >&2 "usage: $0 -c [SERVER:]PEER [ACTION]"
+    exit 1
     ;;
+esac
 
-  2,-c,*)
-    ## Connect to the local tripe server.
-    exec $tripectl SVCSUBMIT connect passive "$2"
-    ;;
+## Examine the peer identifier and work out how to proceed.
+case "$#,$1" in
+  0,*) echo >&2 "missing peer identifier"; exit 1 ;;
+  *:*) mode=proxy server=${1%:*} user=${1##*:} ;;
+  *) mode=local user=$1 ;;
+esac
+shift
+
+## Fetch the optional command from where SSH stashed it.
+case "$#" in 0) set -- $SSH_ORIGINAL_COMMAND ;; esac
+case "$#,$1" in
+  0, | 1,hello) act=hello ;;
+  1,goodbye) act=goodbye ;;
+  *) echo >&2 "$0: unknown action spec \`$*'"; exit 1 ;;
+esac
 
+## Now actually do something.
+case "$mode,$act" in
+  proxy,*)
+    exec ssh "$server" "$user" "$act"
+    ;;
+  local,hello)
+    exec $tripectl SVCSUBMIT connect passive "$user"
+    ;;
+  local,goodbye)
+    peer=$($tripectl SVCSUBMIT connect userpeer "$user")
+    exec $tripectl KILL "$peer"
+    ;;
   *)
-    ## Anything else is an error.
-    echo >&2 "usage: $0 -c [SERVER:]PEER"
+    echo >&2 "$0: unknown mode/action $mode/$act"
     exit 1
     ;;
-
 esac