__init__.py

"""
This module handles SSH Connections
"""
import subprocess

class SshAgentException(Exception):
    def __init__(self,message=None):
        super(SshAgentException,self).__init__(message)
    """
    Raised if an SSH Agent isn't running (Normally the SPA client should invoke the agent
    before trying to execute anythign or create any tunnels)
    """
class SshValidationException(Exception):
    """
    Raised if any parameters passed to SSH don't look valid,
    eg hostnames are not hostnames, ports are not numbers, usernames are
    not the correct format
    """
    pass

class SshCtrlException(Exception):
    """
    Raised if the ssh control socket is not valid.
    """
    def __init__(self,message=None):
        super(SshCtrlException,self).__init__(message)

class SshExecException(Exception):
    """
    Raised if the ssh can't run a remote program. Possibly a bug on the other end 
    """
    def __init__(self,message=None):
        super(SshExecException,self).__init__(message)

class SftpException(Exception):
    pass
class SftpPermissionException(Exception):
    pass


class Ssh:
    """
    Ssh class can execute or create tunnelstat
    """
    TIMEOUT=30
    SSHOPTS = [ '-o', 'StrictHostKeyChecking=no',
                '-o', 'UserKnownHostsFile=/dev/null',
                '-o', 'IdentityFile=/dev/null',
                '-o', 'PreferredAuthentications=publickey',
                '-o', 'UpdateHostKeys=no',
                '-o', 'LogLevel=error',
#                '-o', 'ServerAliveInterval=30',
#                '-o', 'ServerAliveCountMax=4'
              ]
    SSHCMDWITHOPTS = ['ssh']
    SSHCMDWITHOPTS.extend(SSHOPTS)
    SFTPCMDWITHOPTS = ['sftp']
    SFTPCMDWITHOPTS.extend(SSHOPTS)

    @staticmethod
    def validate_port(port):
        "validate that the port we're being asked to connect to is an integer"
        try:
            port = int(port)
        except:
            raise SshValidationException("port number {} was not an integer".format(port))

    @staticmethod
    def validate_username(user):
        """
        ensure that the username conforms to posix standards
        Some systems do not conform to this standard, and linux still works
        but for the moment, lets assume they do conform.
        """
        import re
        username_re = re.compile(r'^[a-z_]([a-z0-9_-]{0,31}|[a-z0-9_\.-]{0,30}\$)$')
        if not username_re.match(user):
            raise SshValidationException("username {} is not valid according to " \
                                         "posix standards".format(user))

    @staticmethod
    def validate_hostname(host):
        "ensure that the hostname at least conforms to naming standards"
        import re
        hostname_re = re.compile(r'^[a-zA-Z0-9_\.-]+$')
        if not hostname_re.match(host):
            raise SshValidationException("hostname {} is not valid".format(host))

    @staticmethod
    def validate_command(cmd):
        """So in theory, due the the format of the Popen command
        we can take any input as a commnand to execute on the login host, including
        ; and other forms of injection,
        and the worst that can happen is the user screws up their own account
        """
        pass

    @staticmethod
    def check_ctrlsocket(sess, ctrlsocket):
        cmd = ['ssh','-S',ctrlsocket,'-O','check','-l','noone','nohost']
        check_p = None
        try:
            check_p = subprocess.Popen(cmd,start_new_session=True,stdout=subprocess.PIPE,stderr=subprocess.PIPE,stdin=None)
            (stderr,stdout) = check_p.communicate(timeout=Ssh.TIMEOUT)
        except subprocess.TimeoutExpired as e:
            if check_p is not None:
                check_p.kill()
                (stderr, stdout) = check_p.communicate()
            raise e
        return check_p.returncode == 0

    @staticmethod
    def get_ctrl_master_socket(sess, host, user, sshport):
        """
        Returns the socket for the control master process
        Opens it if needed.
        """
        import os
        import stat
        import logging
        logger = logging.getLogger()
        ctrlsocket = "/tmp/cm-{}-{}-{}".format(user,host,sess.sshsessid)
        sess.lock.acquire()
        try:
            if Ssh.check_ctrlsocket(sess,ctrlsocket):
                sess.lock.release()
                return ctrlsocket
        except subprocess.TimeoutExpired as e:
            sess.lock.release()
            raise e

        try:
            mode = os.stat(ctrlsocket).st_mode
            logger.debug(f'removing stale control socket for {user}')
            os.unlink(ctrlsocket) # This might occur if a container was restarted and the file wasn't removed
        # This is expected: It indicates there is not yet a control master for this user on this login node
        except FileNotFoundError as e:
            pass

        try:
            sshcmd = Ssh.SSHCMDWITHOPTS.copy()
            sshcmd.extend([
                    "-S", ctrlsocket,
                    "-M", '-o', 'ControlPersist=60s',
                    '-p', sshport, '-N','-l', user, host])
            env = os.environ.copy()
            if sess.socket is None:
                sess.lock.release()
                logger.debug("Exception get_ctrl_master_socket")
                raise SshAgentException("No ssh-agent yet")
            env['SSH_AUTH_SOCK'] = sess.socket
            logger.debug(f'creating master socket for {user}')
            logger.debug(" ".join(sshcmd))
            ctrl_p = subprocess.Popen(sshcmd,
                                    stdout=subprocess.PIPE, stderr=subprocess.PIPE,
                                    stdin=None,
                                    start_new_session=True,
                                    env=env)
            (stderr,stdout) = ctrl_p.communicate() # The process should exit, while the mux persists
        except Exception as e:
            sess.lock.release()
            raise e
        if ctrl_p.returncode == 0:
            sess.lock.release()
            return ctrlsocket
        else:
            sess.lock.release()
            try:
                certs = sess.get_certs()
                if b'The agent has no identities.\n' == certs:
                    raise SshCtrlException(certs.decode())
            except Exception as e:
                pass
            raise SshCtrlException(stderr.decode())

    @staticmethod
    def parse_sftp_output(output):
        import logging
        logger = logging.getLogger()
        rv = []
        pwd = None
        import dateutil.parser
        for l in output.splitlines():

            fields = l.split(None,8)
            fd = {}
            if len(fields) == 9:

                fd['name'] = fields[8]
                fd['mode'] = fields[0]
                fd['hardlinks'] = fields[1]
                fd['user'] = fields[2]
                fd['group'] = fields[3]
                fd['size'] = fields[4]
                fd['mtime'] = dateutil.parser.parse("{} {} {}".format(fields[5],fields[6],fields[7])).isoformat()
                fd['name'] = fields[8]
                rv.append(fd)
            remotestr = "Remote working directory: "
            if remotestr in l:
                pwd = l[len(remotestr):].rstrip()
        return ({'pwd':pwd,'files':rv})

    @staticmethod
    def sftpmkdir(sess, host, user, path, name, sshport):
        """
        Use sftp to run mkdir.
        """
        import os
        import logging
        logger = logging.getLogger()
        env = os.environ.copy()
        if path is None:
            path = "."
        if sess.socket is None:
            raise SshAgentException("No ssh-agent yet")
        env['SSH_AUTH_SOCK'] = sess.socket
        #Ssh.validate_username(user)
        Ssh.validate_hostname(host)
        ctrlsocket = Ssh.get_ctrl_master_socket(sess, host, user, sshport)
        sftpcmd = Ssh.SFTPCMDWITHOPTS.copy()
        sftpcmd.extend(['-P', sshport, 
                                   '-o', 'ControlPath={}'.format(ctrlsocket),
                                   '{}@{}'.format(user, host)])
        exec_p = subprocess.Popen(sftpcmd,
                                  stdout=subprocess.PIPE, stderr=subprocess.PIPE,
                                  stdin=subprocess.PIPE, env=env)

        sftpcmd="cd {}\n mkdir \"{}\"\n".format(path,name)

        (stdout, stderr) = exec_p.communicate(sftpcmd.encode())
        if stderr is not None:
            if not (stderr == b''):
                logger.error('sftp failure')
                logger.error(stdout.decode())
                logger.error(stderr.decode())
                if ('Couldn\'t create directory: Failure' in stderr.decode()):
                    raise SftpPermissionException()
                    return
                if ('Couldn\'t canonicalize: No such file or directory' in stderr.decode()):
                    logger.error('can\'t change to that directory')
                    raise SftpException()
                if ('Permission denied' in stderr.decode()):
                    logger.error('can\'t change to that directory')
                    raise SftpPermissionException()
                logger.error(stdout.decode())
                logger.error(stderr.decode())
                raise SftpException()
        return

    @staticmethod
    def sftpls(sess, host, user, sshport, path=".",changepath="."):
        """
        Use sftp to run an ls on the given path.
        Return the directory listing (as a list) and the cwd
        """
        import os
        import logging
        logger = logging.getLogger()
        env = os.environ.copy()
        if sess.socket is None:
            raise SshAgentException("No ssh-agent yet")
        env['SSH_AUTH_SOCK'] = sess.socket
        #Ssh.validate_username(user)
        Ssh.validate_hostname(host)
        ctrlsocket = Ssh.get_ctrl_master_socket(sess, host, user, sshport)
        if (path is None or path == ""):
            path="."
        if (changepath is None or changepath == ""):
            changepath="."
        sftpcmd = Ssh.SFTPCMDWITHOPTS.copy()
        sftpcmd.extend([ '-P', sshport, 
                                                  '-o', 'ControlPath={}'.format(ctrlsocket),
                                                  '{}@{}'.format(user, host)])
        exec_p = subprocess.Popen(sftpcmd,
                                  stdout=subprocess.PIPE, stderr=subprocess.PIPE,
                                  stdin=subprocess.PIPE, env=env)

        sftpcmd="cd {}\n cd {}\n pwd\nls -al\n".format(path,changepath)

        (stdout, stderr) = exec_p.communicate(sftpcmd.encode())
        if stderr is not None:
            if not (stderr == b''):
                logger.error('sftp failure')
                if ('Couldn\'t canonicalize: No such file or directory' in stderr.decode()):
                    logger.error('can\'t change to that directory')
                    return Ssh.sftpls(sess,host,user,sshport, path,changepath='.')
                if ('Permission denied' in stderr.decode()):
                    logger.error('can\'t change to that directory')
                    return Ssh.sftpls(sess,host,user,sshport, path,changepath='.')

                logger.error(stderr.decode())
                logger.error(('Permission denied' in stderr.decode()))
                logger.error('Couldn\'t canonicalize: No such file or directory' in stderr.decode())
                raise SshCtrlException(stderr.decode())

        dirlist = Ssh.parse_sftp_output(stdout.decode())
        return dirlist


    @staticmethod
    def execute(sess,  host, user, cmd, bastion=None, stdin=None, sshport="22", bastionsshport="22"):
        """
        execute the command cmd on the host via ssh
        # assume the environment is already setup with an
        # SSH_AUTH_SOCK that allows login
        """
        import os
        import logging
        logger = logging.getLogger()
        if cmd is None and stdin is None:
            return {'stdout': b'', 'stderr': b'No command given to execute'}
        env = os.environ.copy()
        if sess.socket is None:
            raise SshAgentException("No ssh-agent yet")
        env['SSH_AUTH_SOCK'] = sess.socket
        if ":" in host:
            host,sshport = host.split(':')
        if bastion is not None and ":" in bastion:
            bastion,bastionsshport = bastion.split(':')
        #Ssh.validate_username(user)
        Ssh.validate_hostname(host)
        Ssh.validate_command(cmd)
        if bastion == None:
            ctrlsocket = Ssh.get_ctrl_master_socket(sess, host, user, sshport)
        else:
            ctrlsocket = Ssh.get_ctrl_master_socket(sess, bastion, user, bastionsshport)
        if bastion == None:
            # we are executing this command on the login node, so no more magic is needed
            sshcmd = Ssh.SSHCMDWITHOPTS.copy()
            sshcmd.extend([
                      '-S', ctrlsocket, '-p', sshport,
                      '-l', user, host, cmd])
        else:
            # we are executing on a node (e.g. a compute/batch node) using a bastion (e.g. login node)
            # at the moment I'll assume the ssh port for the batch host is the same as the ssh port for the bastion/login host
            proxycmd = " ".join(Ssh.SSHCMDWITHOPTS)
            proxycmd = proxycmd + " {user}@{bastion} -W {host}:{sshport} -S {ctrlsocket}".format(
                user=user, host=host,
                ctrlsocket=ctrlsocket,
                sshport=sshport,
                bastion=bastion)
            sshcmd = Ssh.SSHCMDWITHOPTS.copy()
            sshcmd.extend([
                      '-o', "ProxyCommand={}".format(proxycmd),
                      '-p', str(bastionsshport), '-l', user, bastion, cmd])
        exec_p = subprocess.Popen(sshcmd,start_new_session=True,stdout=subprocess.PIPE,stderr=subprocess.PIPE,stdin=subprocess.PIPE,env=env)

        try:
            if stdin is not None:
                (stdout, stderr) = exec_p.communicate(stdin.encode(),timeout=Ssh.TIMEOUT)
            else:
                (stdout, stderr) = exec_p.communicate(timeout=Ssh.TIMEOUT)
        except subprocess.TimeoutExpired as e:
                logger.debug('cmd timed out')
                exec_p.kill()
                (stdout,stderr) = exec_p.communicate()
                raise e
                #raise SshExecException(message="A program timed out on the backend server")
        if exec_p.returncode == 255:
            logger.error(stderr)
            if b'client_loop' in stderr:
                raise SshExecException(message="It looks like your job died for some reason. Please check the log files")
            else:
                logger.error('ssh execute returned error code 255, killing the session')
                #sess.kill()
                raise SshCtrlException(message="Ssh was unable to login. It's likely you're credentials need to be renewed by loggin in again")
# this error condition should now be handled in  get_control_socket
#        if exec_p.returncode != 0 or b'Control socket connect' in stderr:
#            try:
#                ctrl_p = sess.ctrl_processes[ctrlsocket]
#            except KeyError as e:
#                # If the process is restarted and the agents all get restarted, but the control socket /tmp/cm-* is not removed
#                # This can happen
#                import os
#                try:
#                    os.unlink(ctrlsocket)
#                except FileNotFoundError as e:
#                    pass
#                raise SshCtrlException(message="ssh execute failed, there was a problem with the control socket. Did the docker backend get restartd?")

#            logger.error('ran command {}'.format(" ".join(sshcmd)))
#            logger.error('got return code {} stderr {} stdout {}'.format(exec_p.returncode,stderr,stdout))
#            logger.debug("exception execute")
#            raise SshExecException(message="{}".format(stderr.decode()))
            #sess.kill()
            #raise SshCtrlException(message="ssh execute failed, killing off the agent. Log in again")
        # If the return code is non-zero, its likely something went wrong logging in. We should perhaps consider killing the ssh session, or at least the ctrl socket processes
        # And allowing the client to retry them
        # I haven't decided yet whether we should kill the whole agent or just the ctrl process

        if exec_p.returncode != 0:
            if stderr  == b'':
                msg = "The program {} on {} failed".format(cmd,host)
            else:
                msg = "The program {} on {} failed. The error message was {}".format(cmd,host,stderr.decode())
            raise SshExecException(message=msg)
        # Because people often put stuff in their bashrc which casuses stderr to be non-empty, we will swallow errors in the bashrc without comment
        if b'bashrc' in stderr or b'locale' in stderr:
            return {'stdout':stdout,'stderr':b''}
        else:
            return {'stdout':stdout, 'stderr':stderr}

    @staticmethod
    def tunnel(sess, port, batchhost, user, host, internalfirewall = True, localbind = True, authtok = None, sshport="22"):
        """
        the ProxyCommand is used if the server we run on the batch host is only
        addressable on localhost
        e.g. jupyter in its default config runs on localhost:8888 so a web
        browser on the login node can not connect to it
        If the server port is directly accessible from the login host (eg the
        ssh server port is directly accessible) or the batchhost IS the login host
        (i.e. batchhost = localhost) we can use -O forward -S <control socket>
        """
        import os
        import logging
        logger = logging.getLogger()
        env = os.environ.copy()
        env['SSH_AUTH_SOCK'] = sess.socket
        if ":" in host:
            host,sshport = host.split(':')
        Ssh.validate_port(port)
        Ssh.validate_hostname(batchhost)
        #Ssh.validate_username(user)
        Ssh.validate_hostname(host)
        ctrlsocket = Ssh.get_ctrl_master_socket(sess, host, user, sshport)
        localport = Ssh.get_free_port()

        if port == 22 or (not internalfirewall and not localbind):
            # Can we use the existing control master connection and just add a
            # port forward to the batch node
            sshcmd = Ssh.SSHCMDWITHOPTS.copy()
            sshcmd.extend([
                '-L', '127.0.0.1:{localport}:{batchhost}:{port}'.
                      format(port=port, localport=localport, batchhost=batchhost),
                      '-N',
                      '-O', 'forward', '-S', ctrlsocket,
                      '-p', sshport, '-l', user, host])
        else:
            # Create an ssh tunnel to the batch node using a proxycommand.
            # The proxy command should utilise
            # the existing control master connection
            proxycmd = " ".join(Ssh.SSHCMDWITHOPTS) + " {user}@{host} -W {batchhost}:22 -S {ctrlsocket}".format(
                user=user, host=host,
                ctrlsocket=ctrlsocket,
                batchhost=batchhost)
            sshcmd = Ssh.SSHCMDWITHOPTS.copy()
            sshcmd.extend([
                '-o', "ProxyCommand={}".format(proxycmd),
                      '-L', '127.0.0.1:{localport}:localhost:{port}'.
                      format(port=port, localport=localport),
                      '-N',
                      '-p', sshport, '-l', user, batchhost])

        tunnel_p = subprocess.Popen(sshcmd, start_new_session=True, stdout=subprocess.PIPE, stderr=subprocess.PIPE, env=env)

        try:
            if not Ssh.wait_for_tunnel(localport):
                logger.error('tunnel failed to open')
                (stdout,stderr) = tunnel_p.communicate(timeout=Ssh.TIMEOUT) 
                logger.error('Ssh.tunnel: stdout {}'.format(stdout.decode()))
                logger.error('Ssh.tunnel: stderr {}'.format(stderr.decode()))
                raise SshCtrlException(message="failed to open a tunnel")
        except SshCtrlException as e:
            raise(e)
        except Exception as e:
            import traceback
            logger.error('exception waiting for tunnel')
            logger.error(e)
            logger.error(traceback.format_exc())
            return None, []
        if sess.port is None:
            sess.port = {}
        sess.port.update({authtok: localport})
        sess.pids.append(tunnel_p.pid)
        sess.tunnels.append(tunnel_p)
        return localport, [tunnel_p.pid]

    # @staticmethod
    # def addkey(sess, key, cert):
    #     ""
    #     pass

    @staticmethod
    def wait_for_tunnel(localport):
        notopen = True
        import socket
        import time
        import logging
        logger = logging.getLogger()
        while notopen:
            ssock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
            ssock.setblocking(True)
            try:
                ssock.connect(('127.0.0.1', localport))
                notopen = False
                ssock.close()
            except socket.error:
                time.sleep(0.1)
                ssock.close()
        return True


        """
        In order to avoid a race condition, we wait for the tunnel to be established
        If the tunnel hasn't been establised before TIMEOUT, perhaps something has gone wrong
        """
        """
        import socket
        import time
        import logging
        logger = logging.getLogger()
        ssock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
        ssock.settimeout(TIMEOUT)
        for retry in range(0,10):
            try:
                ssock.connect(('127.0.0.1', localport))
                ssock.close()
                return True
            except Exception as e:
                logger.debug('socket exception {}'.format(e))
                ssock.close()
            time.sleep(1)
        return False
        """

    @staticmethod
    def get_free_port():
        """
        # Finds a port which the local server can listen on.
        """
        import socket
        serversocket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
        for testport in range(1025, 65500):
            try:
                serversocket.bind(('127.0.0.1', testport))
                port = testport
                serversocket.close()
                return port
            except OSError:
                pass