[disorder] / python / disorder.py.in

#
# Copyright (C) 2004, 2005 Richard Kettlewell
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 2 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful, but
# WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
# General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program; if not, write to the Free Software
# Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307
# USA
#

"""Python support for DisOrder

Provides disorder.client, a class for accessing a DisOrder server.

Example 1:

  #! /usr/bin/env python
  import disorder
  d = disorder.client()
  p = d.playing()
  if p:
    print p['track']

Example 2:

  #! /usr/bin/env python
  import disorder
  import sys
  d = disorder.client()
  for path in sys.argv[1:]:
    d.play(path)

"""

import re
import string
import os
import pwd
import socket
import binascii
import sha
import sys
import locale

_configfile = "pkgconfdir/config"
_dbhome = "pkgstatedir"
_userconf = True

# various regexps we'll use
_ws = re.compile(r"^[ \t\n\r]+")
_squote = re.compile("'(([^\\\\']|\\\\[\\\\\"'n])+)'")
_dquote = re.compile("\"(([^\\\\\"]|\\\\[\\\\\"'n])+)\"")
_unquoted = re.compile("[^\"' \\t\\n\\r][^ \t\n\r]*")

_response = re.compile("([0-9]{3}) ?(.*)")

version = "_version_"

########################################################################
# exception classes

class Error(Exception):
  """Base class for DisOrder exceptions."""

class _splitError(Error):
  # _split failed
  def __init__(self, value):
    self.value = value
  def __str__(self):
    return str(self.value)

class parseError(Error):
  """Error parsing the configuration file."""
  def __init__(self, path, line, details):
    self.path = path
    self.line = line
    self.details = details
  def __str__(self):
    return "%s:%d: %s" % (self.path, self.line, self.details)

class protocolError(Error):
  """DisOrder control protocol error.

  Indicates a mismatch between the client and server's understanding of
  the control protocol.
  """
  def __init__(self, who, error):
    self.who = who
    self.error = error
  def __str__(self):
    return "%s: %s" % (self.who, str(self.error))

class operationError(Error):
  """DisOrder control protocol error response.

  Indicates that an operation failed (e.g. an attempt to play a
  nonexistent track).  The connection should still be usable.
  """
  def __init__(self, res, details, cmd=None):
    self.res_ = int(res)
    self.cmd_ = cmd
    self.details_ = details
  def __str__(self):
    """Return the complete response string from the server, with the command
    if available.

    Excludes the final newline.
    """
    if self.cmd_ is None:
      return "%d %s" % (self.res_, self.details_)
    else:
      return "%d %s [%s]" % (self.res_, self.details_, self.cmd_)
  def response(self):
    """Return the response code from the server."""
    return self.res_
  def details(self):
    """Returns the detail string from the server."""
    return self.details_

class communicationError(Error):
  """DisOrder control protocol communication error.

  Indicates that communication with the server went wrong, perhaps
  because the server was restarted.  The caller could report an error to
  the user and wait for further user instructions, or even automatically
  retry the operation.
  """
  def __init__(self, who, error):
    self.who = who
    self.error = error
  def __str__(self):
    return "%s: %s" % (self.who, str(self.error))

########################################################################
# DisOrder-specific text processing

def _unescape(s):
  # Unescape the contents of a string
  #
  # Arguments:
  #
  # s -- string to unescape
  #
  s = re.sub("\\\\n", "\n", s)
  s = re.sub("\\\\(.)", "\\1", s)
  return s

def _split(s, *comments):
  # Split a string into fields according to the usual Disorder string splitting
  # conventions.
  #
  # Arguments:
  #
  # s        -- string to parse
  # comments -- if present, parse comments
  #
  # Return values:
  #
  # On success, a list of fields is returned.
  #
  # On error, disorder.parseError is thrown.
  #
  fields = []
  while s != "":
    # discard comments
    if comments and s[0] == '#':
      break
    # strip spaces
    m = _ws.match(s)
    if m:
      s = s[m.end():]
      continue
    # pick of quoted fields of both kinds
    m = _squote.match(s)
    if not m:
      m = _dquote.match(s)
    if m:
      fields.append(_unescape(m.group(1)))
      s = s[m.end():]
      continue
    # and unquoted fields
    m = _unquoted.match(s)
    if m:
      fields.append(m.group(0))
      s = s[m.end():]
      continue
    # anything left must be in error
    if s[0] == '"' or s[0] == '\'':
      raise _splitError("invalid quoted string")
    else:
      raise _splitError("syntax error")
  return fields

def _escape(s):
  # Escape the contents of a string
  #
  # Arguments:
  #
  # s -- string to escape
  #
  if re.search("[\\\\\"'\n \t\r]", s) or s == '':
    s = re.sub(r'[\\"]', r'\\\g<0>', s)
    s = re.sub("\n", r"\\n", s)
    return '"' + s + '"'
  else:
    return s

def _quote(list):
  # Quote a list of values
  return ' '.join(map(_escape, list))

def _sanitize(s):
  # Return the value of s in a form suitable for writing to stderr
  return s.encode(locale.nl_langinfo(locale.CODESET), 'replace')

def _list2dict(l):
  # Convert a list of the form [k1, v1, k2, v2, ..., kN, vN]
  # to a dictionary {k1:v1, k2:v2, ..., kN:vN}
  d = {}
  i = iter(l)
  try:
    while True:
      k = i.next()
      v = i.next()
      d[k] = v
  except StopIteration:
    pass
  return d

def _queueEntry(s):
  # parse a queue entry
  return _list2dict(_split(s))

########################################################################
# The client class

class client:
  """DisOrder client class.

  This class provides access to the DisOrder server either on this
  machine or across the internet.

  The server to connect to, and the username and password to use, are
  determined from the configuration files as described in 'man
  disorder_config'.

  All methods will connect if necessary, as soon as you have a
  disorder.client object you can start calling operational methods on
  it.

  However if the server is restarted then the next method called on a
  connection will throw an exception.  This may be considered a bug.

  All methods block until they complete.

  Operation methods raise communicationError if the connection breaks,
  protocolError if the response from the server is malformed, or
  operationError if the response is valid but indicates that the
  operation failed.
  """

  debug_proto = 0x0001
  debug_body = 0x0002

  def __init__(self):
    """Constructor for DisOrder client class.

    The constructor reads the configuration file, but does not connect
    to the server.

    If the environment variable DISORDER_PYTHON_DEBUG is set then the
    debug flags are initialised to that value.  This can be overridden
    with the debug() method below.

    The constructor Raises parseError() if the configuration file is not
    valid.
    """
    pw = pwd.getpwuid(os.getuid())
    self.debugging = int(os.getenv("DISORDER_PYTHON_DEBUG", 0))
    self.config = { 'collections': [],
                    'username': pw.pw_name,
                    'home': _dbhome }
    home = os.getenv("HOME")
    if not home:
      home = pw.pw_dir
    privconf = _configfile + "." + pw.pw_name
    passfile = home + os.sep + ".disorder" + os.sep + "passwd"
    self._readfile(_configfile)
    if os.path.exists(privconf):
      self._readfile(privconf)
    if os.path.exists(passfile) and _userconf:
      self._readfile(passfile)
    self.state = 'disconnected'

  def debug(self, bits):
    """Enable or disable protocol debugging.  Debug messages are written
    to sys.stderr.

    Arguments:
    bits -- bitmap of operations that should generate debug information

    Bitmap values:
    debug_proto -- dump control protocol messages (excluding bodies)
    debug_body -- dump control protocol message bodies
    """
    self.debugging = bits

  def _debug(self, bit, s):
    # debug output
    if self.debugging & bit:
      sys.stderr.write(_sanitize(s))
      sys.stderr.write("\n")
      sys.stderr.flush()

  def connect(self):
    """Connect to the DisOrder server and authenticate.

    Raises communicationError if connection fails and operationError if
    authentication fails (in which case disconnection is automatic).

    May be called more than once to retry connections (e.g. when the
    server is down).  If we are already connected and authenticated,
    this is a no-op.

    Other operations automatically connect if we're not already
    connected, so it is not strictly necessary to call this method.
    """
    if self.state == 'disconnected':
      try:
        self.state = 'connecting'
        if 'connect' in self.config and len(self.config['connect']) > 0:
          c = self.config['connect']
          self.who = repr(c)            # temporarily
          if len(c) == 1:
            a = socket.getaddrinfo(None, c[0],
                                   socket.AF_INET,
                                   socket.SOCK_STREAM,
                                   0,
                                   0)
          else:
            a = socket.getaddrinfo(c[0], c[1],
                                   socket.AF_INET,
                                   socket.SOCK_STREAM,
                                   0,
                                   0)
          a = a[0]
          s = socket.socket(a[0], a[1], a[2]);
          s.connect(a[4])
          self.who = "%s" % a[3]
        else:
          s = socket.socket(socket.AF_UNIX, socket.SOCK_STREAM);
          self.who = self.config['home'] + os.sep + "socket"
          s.connect(self.who)
        self.w = s.makefile("wb")
        self.r = s.makefile("rb")
        (res, challenge) = self._simple()
        h = sha.sha()
        h.update(self.config['password'])
        h.update(binascii.unhexlify(challenge))
        self._simple("user", self.config['username'], h.hexdigest())
        self.state = 'connected'
      except socket.error, e:
        self._disconnect()
        raise communicationError(self.who, e)
      except:
        self._disconnect()
        raise

  def _disconnect(self):
    # disconnect from the server, whatever state we are in
    try:
      del self.w
      del self.r
    except:
      pass
    self.state = 'disconnected'
    
  ########################################################################
  # Operations

  def become(self, who):
    """Become another user.

    Arguments:
    who -- the user to become.

    Only trusted users can perform this operation.
    """
    self._simple("become", who)

  def play(self, track):
    """Play a track.

    Arguments:
    track -- the path of the track to play.
    """
    self._simple("play", track)

  def remove(self, track):
    """Remove a track from the queue.

    Arguments:
    track -- the path or ID of the track to remove.
    """
    self._simple("remove", track)

  def enable(self):
    """Enable playing."""
    self._simple("enable")

  def disable(self, *now):
    """Disable playing.

    Arguments:
    now -- if present (with any value), the current track is stopped
           too.
    """
    if now:
      self._simple("disable", "now")
    else:
      self._simple("disable")

  def scratch(self, *id):
    """Scratch the currently playing track.

    Arguments:
    id -- if present, the ID of the track to scratch.
    """
    if id:
      self._simple("scratch", id[0])
    else:
      self._simple("scratch")

  def shutdown(self):
    """Shut down the server.

    Only trusted users can perform this operation.
    """
    self._simple("shutdown")

  def reconfigure(self):
    """Make the server reload its configuration.

    Only trusted users can perform this operation.
    """
    self._simple("reconfigure")

  def rescan(self, pattern):
    """Rescan one or more collections.

    Arguments:
    pattern -- glob pattern matching collections to rescan.

    Only trusted users can perform this operation.
    """
    self._simple("rescan", pattern)

  def version(self):
    """Return the server's version number."""
    return self._simple("version")[1]

  def playing(self):
    """Return the currently playing track.

    If a track is playing then it is returned as a dictionary.
    If no track is playing then None is returned."""
    res, details = self._simple("playing")
    if res % 10 != 9:
      try:
        return _queueEntry(details)
      except _splitError, s:
        raise protocolError(self.who, s.str())
    else:
      return None

  def _somequeue(self, command):
    self._simple(command)
    try:
      return map(lambda s: _queueEntry(s), self._body())
    except _splitError, s:
      raise protocolError(self.who, s.str())

  def recent(self):
    """Return a list of recently played tracks.

    The return value is a list of dictionaries corresponding to
    recently played tracks.  The oldest track comes first."""
    return self._somequeue("recent")

  def queue(self):
    """Return the current queue.

    The return value is a list of dictionaries corresponding to
    recently played tracks.  The next track to be played comes first."""
    return self._somequeue("queue")

  def _somedir(self, command, dir, re):
    if re:
      self._simple(command, dir, re[0])
    else:
      self._simple(command, dir)
    return self._body()

  def directories(self, dir, *re):
    """List subdirectories of a directory.

    Arguments:
    dir -- directory to list, or '' for the whole root.
    re -- regexp that results must match.  Optional.

    The return value is a list of the (nonempty) subdirectories of dir.
    If dir is '' then a list of top-level directories is returned.

    If a regexp is specified then the basename of each result must
    match.  Matching is case-independent.  See pcrepattern(3).
    """
    return self._somedir("dirs", dir, re)
  
  def files(self, dir, *re):
    """List files within a directory.

    Arguments:
    dir -- directory to list, or '' for the whole root.
    re -- regexp that results must match.  Optional.

    The return value is a list of playable files in dir.  If dir is ''
    then a list of top-level files is returned.

    If a regexp is specified then the basename of each result must
    match.  Matching is case-independent.  See pcrepattern(3).
    """
    return self._somedir("files", dir, re)

  def allfiles(self, dir, *re):
    """List subdirectories and files within a directory.

    Arguments:
    dir -- directory to list, or '' for the whole root.
    re -- regexp that results must match.  Optional.

    The return value is a list of all (nonempty) subdirectories and
    files within dir.  If dir is '' then a list of top-level files and
    directories is returned.
    
    If a regexp is specified then the basename of each result must
    match.  Matching is case-independent.  See pcrepattern(3).
    """
    return self._somedir("allfiles", dir, re)

  def set(self, track, key, value):
    """Set a preference value.

    Arguments:
    track -- the track to modify
    key -- the preference name
    value -- the new preference value
    """
    self._simple("set", track, key, value)

  def unset(self, track, key):
    """Unset a preference value.

    Arguments:
    track -- the track to modify
    key -- the preference to remove
    """
    self._simple("set", track, key, value)

  def get(self, track, key):
    """Get a preference value.

    Arguments:
    track -- the track to query
    key -- the preference to remove

    The return value is the preference 
    """
    ret, details = self._simple("get", track, key)
    return details

  def prefs(self, track):
    """Get all the preferences for a track.

    Arguments:
    track -- the track to query

    The return value is a dictionary of all the track's preferences.
    Note that even nominally numeric values remain encoded as strings.
    """
    self._simple("prefs", track)
    r = {}
    for line in self._body():
      try:
        kv = _split(line)
      except _splitError, s:
        raise protocolError(self.who, s.str())
      if len(kv) != 2:
        raise protocolError(self.who, "invalid prefs body line")
      r[kv[0]] = kv[1]
    return r

  def _boolean(self, s):
    return s[1] == 'yes'

  def exists(self, track):
    """Return true if a track exists

    Arguments:
    track -- the track to check for"""
    return self._boolean(self._simple("exists", track))

  def enabled(self):
    """Return true if playing is enabled"""
    return self._boolean(self._simple("enabled"))

  def random_enabled(self):
    """Return true if random play is enabled"""
    return self._boolean(self._simple("random-enabled"))

  def random_enable(self):
    """Enable random play."""
    self._simple("random-enable")

  def random_disable(self):
    """Disable random play."""
    self._simple("random-disable")

  def length(self, track):
    """Return the length of a track in seconds.

    Arguments:
    track -- the track to query.
    """
    ret, details = self._simple("length", track)
    return int(details)

  def search(self, words):
    """Search for tracks.

    Arguments:
    words -- the set of words to search for.

    The return value is a list of track path names, all of which contain
    all of the required words (in their path name, trackname
    preferences, etc.)
    """
    self._simple("search", _quote(words))
    return self._body()

  def stats(self):
    """Get server statistics.

    The return value is list of statistics.
    """
    self._simple("stats")
    return self._body()

  def dump(self):
    """Get all preferences.

    The return value is an encoded dump of the preferences database.
    """
    self._simple("dump")
    return self._body()

  def set_volume(self, left, right):
    """Set volume.

    Arguments:
    left -- volume for the left speaker.
    right --  volume for the right speaker.
    """
    self._simple("volume", left, right)

  def get_volume(self):
    """Get volume.

    The return value a tuple consisting of the left and right volumes.
    """
    ret, details = self._simple("volume")
    return map(int,string.split(details))

  def move(self, track, delta):
    """Move a track in the queue.

    Arguments:
    track -- the name or ID of the track to move
    delta -- the number of steps towards the head of the queue to move
    """
    ret, details = self._simple("move", track, str(delta))
    return int(details)

  def log(self, callback):
    """Read event log entries as they happen.

    Each event log entry is handled by passing it to callback.

    The callback takes two arguments, the first is the client and the
    second the line from the event log.
    
    The callback should return True to continue or False to stop (don't
    forget this, or your program will mysteriously misbehave).

    It is suggested that you use the disorder.monitor class instead of
    calling this method directly, but this is not mandatory.

    See disorder_protocol(5) for the event log syntax.

    Arguments:
    callback -- function to call with log entry
    """
    ret, details = self._simple("log")
    while True:
      l = self._line()
      self._debug(client.debug_body, "<<< %s" % l)
      if l != '' and l[0] == '.':
        if l == '.':
          return
        l = l[1:]
      if not callback(self, l):
        break
    # tell the server to stop sending, eat the remains of the body,
    # eat the response
    self._send("version")
    self._body()
    self._response()

  def pause(self):
    """Pause the current track."""
    self._simple("pause")

  def resume(self):
    """Resume after a pause."""
    self._simple("resume")

  def part(self, track, context, part):
    """Get a track name part

    Arguments:
    track -- the track to query
    context -- the context ('sort' or 'display')
    part -- the desired part (usually 'artist', 'album' or 'title')

    The return value is the preference 
    """
    ret, details = self._simple("part", track, context, part)
    return details

  def setglobal(self, key, value):
    """Set a global preference value.

    Arguments:
    key -- the preference name
    value -- the new preference value
    """
    self._simple("set-global", key, value)

  def unsetglobal(self, key):
    """Unset a global preference value.

    Arguments:
    key -- the preference to remove
    """
    self._simple("set-global", key, value)

  def getglobal(self, key):
    """Get a global preference value.

    Arguments:
    key -- the preference to look up

    The return value is the preference 
    """
    ret, details = self._simple("get-global", key)
    return details

  ########################################################################
  # I/O infrastructure

  def _line(self):
    # read one response line and return as some suitable string object
    #
    # If an I/O error occurs, disconnect from the server.
    #
    # XXX does readline() DTRT regarding character encodings?
    try:
      l = self.r.readline()
      if not re.search("\n", l):
        raise communicationError(self.who, "peer disconnected")
      l = l[:-1]
    except:
      self._disconnect()
      raise
    return unicode(l, "UTF-8")

  def _response(self):
    # read a response as a (code, details) tuple
    l = self._line()
    self._debug(client.debug_proto, "<== %s" % l)
    m = _response.match(l)
    if m:
      return int(m.group(1)), m.group(2)
    else:
      raise protocolError(self.who, "invalid response %s")

  def _send(self, *command):
    # Quote and send a command
    #
    # Returns the encoded command.
    quoted = _quote(command)
    self._debug(client.debug_proto, "==> %s" % quoted)
    encoded = quoted.encode("UTF-8")
    try:
      self.w.write(encoded)
      self.w.write("\n")
      self.w.flush()
      return encoded
    except IOError, e:
      # e.g. EPIPE
      self._disconnect()
      raise communicationError(self.who, e)
    except:
      self._disconnect()
      raise

  def _simple(self, *command):
    # Issue a simple command, throw an exception on error
    #
    # If an I/O error occurs, disconnect from the server.
    #
    # On success returns response as a (code, details) tuple
    #
    # On error raise operationError
    if self.state == 'disconnected':
      self.connect()
    if command:
      cmd = self._send(*command)
    else:
      cmd = None
    res, details = self._response()
    if res / 100 == 2:
      return res, details
    raise operationError(res, details, cmd)

  def _body(self):
    # Fetch a dot-stuffed body
    result = []
    while True:
      l = self._line()
      self._debug(client.debug_body, "<<< %s" % l)
      if l != '' and l[0] == '.':
        if l == '.':
          return result
        l = l[1:]
      result.append(l)

  ########################################################################
  # Configuration file parsing

  def _readfile(self, path):
    # Read a configuration file
    #
    # Arguments:
    #
    # path -- path of file to read

    # handlers for various commands
    def _collection(self, command, args):
      if len(args) != 3:
        return "'%s' takes three args" % command
      self.config["collections"].append(args)
      
    def _unary(self, command, args):
      if len(args) != 1:
        return "'%s' takes only one arg" % command
      self.config[command] = args[0]

    def _include(self, command, args):
      if len(args) != 1:
        return "'%s' takes only one arg" % command
      self._readfile(args[0])

    def _any(self, command, args):
      self.config[command] = args

    # mapping of options to handlers
    _options = { "collection": _collection,
                 "username": _unary,
                 "password": _unary,
                 "home": _unary,
                 "connect": _any,
                 "include": _include }

    # the parser
    for lno, line in enumerate(file(path, "r")):
      try:
        fields = _split(line, 'comments')
      except _splitError, s:
        raise parseError(path, lno + 1, str(s))
      if fields:
        command = fields[0]
        # we just ignore options we don't know about, so as to cope gracefully
        # with version skew (and nothing to do with implementor laziness)
        if command in _options:
          e = _options[command](self, command, fields[1:])
          if e:
            self._parseError(path, lno + 1, e)

  def _parseError(self, path, lno, s):
    raise parseError(path, lno, s)

########################################################################
# monitor class

class monitor:
  """DisOrder event log monitor class

  Intended to be subclassed with methods corresponding to event log messages
  the implementor cares about over-ridden."""

  def __init__(self, c=None):
    """Constructor for the monitor class

    Can be passed a client to use.  If none is specified then one
    will be created specially for the purpose.

    Arguments:
    c -- client"""
    if c == None:
      c = client();
    self.c = c

  def run(self):
    """Start monitoring logs.  Continues monitoring until one of the
    message-specific methods returns False.  Can be called more than once
    (but not recursively!)"""
    self.c.log(self._callback)

  def when(self):
    """Return the timestamp of the current (or most recent) event log entry"""
    return self.timestamp

  def _callback(self, c, line):
    try:
      bits = _split(line)
    except:
      return self.invalid(line)
    if(len(bits) < 2):
      return self.invalid(line)
    self.timestamp = int(bits[0], 16)
    keyword = bits[1]
    bits = bits[2:]
    if keyword == 'completed':
      if len(bits) == 1:
        return self.completed(bits[0])
    elif keyword == 'failed':
      if len(bits) == 2:
        return self.failed(bits[0], bits[1])
    elif keyword == 'moved':
      if len(bits) == 3:
        try:
          n = int(bits[1])
        except:
          return self.invalid(line)
        return self.moved(bits[0], n, bits[2])
    elif keyword == 'playing':
      if len(bits) == 1:
        return self.playing(bits[0], None)
      elif len(bits) == 2:
        return self.playing(bits[0], bits[1])
    elif keyword == 'queue' or keyword == 'recent-added':
      try:
        q = _list2dict(bits)
      except:
        return self.invalid(line)
      if keyword == 'queue':
        return self.queue(q)
      if keyword == 'recent-added':
        return self.recent_added(q)
    elif keyword == 'recent-removed':
      if len(bits) == 1:
        return self.recent_removed(bits[0])
    elif keyword == 'removed':
      if len(bits) == 1:
        return self.removed(bits[0], None)
      elif len(bits) == 2:
        return self.removed(bits[0], bits[1])
    elif keyword == 'scratched':
      if len(bits) == 2:
        return self.scratched(bits[0], bits[1])
    return self.invalid(line)

  def completed(self, track):
    """Called when a track completes.

    Arguments:
    track -- track that completed"""
    return True

  def failed(self, track, error):
    """Called when a player suffers an error.

    Arguments:
    track -- track that failed
    error -- error indicator"""
    return True

  def moved(self, id, offset, user):
    """Called when a track is moved in the queue.

    Arguments:
    id -- queue entry ID
    offset -- distance moved
    user -- user responsible"""
    return True

  def playing(self, track, user):
    """Called when a track starts playing.

    Arguments:
    track -- track that has started
    user -- user that submitted track, or None"""
    return True

  def queue(self, q):
    """Called when a track is added to the queue.

    Arguments:
    q -- dictionary of new queue entry"""
    return True

  def recent_added(self, q):
    """Called when a track is added to the recently played list

    Arguments:
    q -- dictionary of new queue entry"""
    return True

  def recent_removed(self, id):
    """Called when a track is removed from the recently played list

    Arguments:
    id -- ID of removed entry (always the oldest)"""
    return True

  def removed(self, id, user):
    """Called when a track is removed from the queue, either manually
    or in order to play it.

    Arguments:
    id -- ID of removed entry
    user -- user responsible (or None if we're playing this track)"""
    return True

  def scratched(self, track, user):
    """Called when a track is scratched

    Arguments:
    track -- track that was scratched
    user -- user responsible"""
    return True

  def invalid(self, line):
    """Called when an event log line cannot be interpreted

    Arguments:
    line -- line that could not be understood"""
    return True

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