Allow SSH agent to daemonize when invoked with `-d` flag

This change adds the support for "eval `trezor-agent -d`" invocation.

libagent/ssh/__init__.py

@@ -5,6 +5,7 @@ import io
 import logging
 import os
 import re
+import signal
 import subprocess
 import sys
 import tempfile
@@ -12,6 +13,7 @@ import threading
 
 import pkg_resources
 import configargparse
+import daemon
 
 from .. import device, formats, server, util
 from . import client, protocol
@@ -80,6 +82,8 @@ def create_agent_parser(device_type):
                    help='log SSH protocol messages for debugging.')
 
     g = p.add_mutually_exclusive_group()
+    g.add_argument('-d', '--daemonize', default=False, action='store_true',
+                   help='Daemonize the agent and print its UNIX socket path')
     g.add_argument('-s', '--shell', default=False, action='store_true',
                    help=('run ${SHELL} as subprocess under SSH agent, allowing '
                          'regular SSH-based tools to be used in the shell'))
@@ -96,7 +100,7 @@ def create_agent_parser(device_type):
 
 
 @contextlib.contextmanager
-def serve(handler, sock_path=None, timeout=UNIX_SOCKET_TIMEOUT):
+def serve(handler, sock_path, timeout=UNIX_SOCKET_TIMEOUT):
     """
     Start the ssh-agent server on a UNIX-domain socket.
 
@@ -106,9 +110,6 @@ def serve(handler, sock_path=None, timeout=UNIX_SOCKET_TIMEOUT):
     ssh_version = subprocess.check_output(['ssh', '-V'],
                                           stderr=subprocess.STDOUT)
     log.debug('local SSH version: %r', ssh_version)
-    if sock_path is None:
-        sock_path = tempfile.mktemp(prefix='trezor-ssh-agent-')
-
     environ = {'SSH_AUTH_SOCK': sock_path, 'SSH_AGENT_PID': str(os.getpid())}
     device_mutex = threading.Lock()
     with server.unix_domain_socket_server(sock_path) as sock:
@@ -128,12 +129,17 @@ def serve(handler, sock_path=None, timeout=UNIX_SOCKET_TIMEOUT):
                 quit_event.set()
 
 
-def run_server(conn, command, debug, timeout):
+def run_server(conn, command, sock_path, debug, timeout):
     """Common code for run_agent and run_git below."""
     try:
         handler = protocol.Handler(conn=conn, debug=debug)
-        with serve(handler=handler, timeout=timeout) as env:
-            return server.run_process(command=command, environ=env)
+        with serve(handler=handler, sock_path=sock_path,
+                   timeout=timeout) as env:
+            if command is None:
+                signal.pause()  # wait for signal
+                return 0
+            else:
+                return server.run_process(command=command, environ=env)
     except KeyboardInterrupt:
         log.info('server stopped')
 
@@ -195,6 +201,11 @@ class JustInTimeConnection(object):
         return conn.sign_ssh_challenge(blob=blob, identity=identity)
 
 
+@contextlib.contextmanager
+def _dummy_context():
+    yield
+
+
 @handle_connection_error
 def main(device_type):
     """Run ssh-agent using given hardware client factory."""
@@ -216,10 +227,21 @@ def main(device_type):
         identity.identity_dict['proto'] = u'ssh'
         log.info('identity #%d: %s', index, identity.to_string())
 
+    sock_path = tempfile.mktemp(prefix='trezor-ssh-agent-')
+
+    command = None
+    context = _dummy_context()
     if args.connect:
         command = ['ssh'] + ssh_args(args.identity) + args.command
     elif args.mosh:
         command = ['mosh'] + mosh_args(args.identity) + args.command
+    elif args.daemonize:
+        msg = ('SSH_AUTH_SOCK={0}; export SSH_AUTH_SOCK;\n'
+               'SSH_AGENT_PID={1}; export SSH_AGENT_PID;\n'
+               'echo Agent pid {1};\n'.format(sock_path, os.getpid()))
+        sys.stdout.write(msg)
+        sys.stdout.flush()
+        context = daemon.DaemonContext()
     else:
         command = args.command
 
@@ -231,9 +253,11 @@ def main(device_type):
     conn = JustInTimeConnection(
         conn_factory=lambda: client.Client(device_type()),
         identities=identities, public_keys=public_keys)
-    if command:
-        return run_server(conn=conn, command=command, debug=args.debug,
-                          timeout=args.timeout)
+
+    if command or args.daemonize:
+        with context:
+            return run_server(conn=conn, command=command, sock_path=sock_path,
+                              debug=args.debug, timeout=args.timeout)
     else:
         for pk in conn.public_keys():
             sys.stdout.write(pk)

setup.py

@@ -17,6 +17,7 @@ setup(
     install_requires=[
         'backports.shutil_which>=3.5.1',
         'ConfigArgParse>=0.12.0',
+        'python-daemon>=2.1.2',
         'ecdsa>=0.13',
         'ed25519>=1.4',
         'pymsgbox>=1.0.6',