Move common libs to libs/common

libs/common/xdg/Mime.py

@@ -0,0 +1,781 @@
+"""
+This module is based on a rox module (LGPL):
+
+http://cvs.sourceforge.net/viewcvs.py/rox/ROX-Lib2/python/rox/mime.py?rev=1.21&view=log
+
+This module provides access to the shared MIME database.
+
+types is a dictionary of all known MIME types, indexed by the type name, e.g.
+types['application/x-python']
+
+Applications can install information about MIME types by storing an
+XML file as <MIME>/packages/<application>.xml and running the
+update-mime-database command, which is provided by the freedesktop.org
+shared mime database package.
+
+See http://www.freedesktop.org/standards/shared-mime-info-spec/ for
+information about the format of these files.
+
+(based on version 0.13)
+"""
+
+import os
+import re
+import stat
+import sys
+import fnmatch
+
+from xdg import BaseDirectory
+import xdg.Locale
+
+from xml.dom import minidom, XML_NAMESPACE
+from collections import defaultdict
+
+FREE_NS = 'http://www.freedesktop.org/standards/shared-mime-info'
+
+types = {}      # Maps MIME names to type objects
+
+exts = None     # Maps extensions to types
+globs = None    # List of (glob, type) pairs
+literals = None # Maps liternal names to types
+magic = None
+
+PY3 = (sys.version_info[0] >= 3)
+
+def _get_node_data(node):
+    """Get text of XML node"""
+    return ''.join([n.nodeValue for n in node.childNodes]).strip()
+
+def lookup(media, subtype = None):
+    """Get the MIMEtype object for the given type.
+    
+    This remains for backwards compatibility; calling MIMEtype now does
+    the same thing.
+    
+    The name can either be passed as one part ('text/plain'), or as two
+    ('text', 'plain').
+    """
+    return MIMEtype(media, subtype)
+
+class MIMEtype(object):
+    """Class holding data about a MIME type.
+    
+    Calling the class will return a cached instance, so there is only one 
+    instance for each MIME type. The name can either be passed as one part
+    ('text/plain'), or as two ('text', 'plain').
+    """
+    def __new__(cls, media, subtype=None):
+        if subtype is None and '/' in media:
+            media, subtype = media.split('/', 1)
+        assert '/' not in subtype
+        media = media.lower()
+        subtype = subtype.lower()
+        
+        try:
+            return types[(media, subtype)]
+        except KeyError:
+            mtype = super(MIMEtype, cls).__new__(cls)
+            mtype._init(media, subtype)
+            types[(media, subtype)] = mtype
+            return mtype
+
+    # If this is done in __init__, it is automatically called again each time
+    # the MIMEtype is returned by __new__, which we don't want. So we call it
+    # explicitly only when we construct a new instance.
+    def _init(self, media, subtype):
+        self.media = media
+        self.subtype = subtype
+        self._comment = None
+
+    def _load(self):
+        "Loads comment for current language. Use get_comment() instead."
+        resource = os.path.join('mime', self.media, self.subtype + '.xml')
+        for path in BaseDirectory.load_data_paths(resource):
+            doc = minidom.parse(path)
+            if doc is None:
+                continue
+            for comment in doc.documentElement.getElementsByTagNameNS(FREE_NS, 'comment'):
+                lang = comment.getAttributeNS(XML_NAMESPACE, 'lang') or 'en'
+                goodness = 1 + (lang in xdg.Locale.langs)
+                if goodness > self._comment[0]:
+                    self._comment = (goodness, _get_node_data(comment))
+                if goodness == 2: return
+
+    # FIXME: add get_icon method
+    def get_comment(self):
+        """Returns comment for current language, loading it if needed."""
+        # Should we ever reload?
+        if self._comment is None:
+            self._comment = (0, str(self))
+            self._load()
+        return self._comment[1]
+    
+    def canonical(self):
+        """Returns the canonical MimeType object if this is an alias."""
+        update_cache()
+        s = str(self)
+        if s in aliases:
+            return lookup(aliases[s])
+        return self
+    
+    def inherits_from(self):
+        """Returns a set of Mime types which this inherits from."""
+        update_cache()
+        return set(lookup(t) for t in inheritance[str(self)])
+
+    def __str__(self):
+        return self.media + '/' + self.subtype
+
+    def __repr__(self):
+        return 'MIMEtype(%r, %r)' % (self.media, self.subtype)
+    
+    def __hash__(self):
+        return hash(self.media) ^ hash(self.subtype)
+
+class UnknownMagicRuleFormat(ValueError):
+    pass
+
+class DiscardMagicRules(Exception):
+    "Raised when __NOMAGIC__ is found, and caught to discard previous rules."
+    pass
+
+class MagicRule:
+    also = None
+    
+    def __init__(self, start, value, mask, word, range):
+        self.start = start
+        self.value = value
+        self.mask = mask
+        self.word = word
+        self.range = range
+    
+    rule_ending_re = re.compile(br'(?:~(\d+))?(?:\+(\d+))?\n$')
+    
+    @classmethod
+    def from_file(cls, f):
+        """Read a rule from the binary magics file. Returns a 2-tuple of
+        the nesting depth and the MagicRule."""
+        line = f.readline()
+        #print line
+        
+        # [indent] '>'
+        nest_depth, line = line.split(b'>', 1)
+        nest_depth = int(nest_depth) if nest_depth else 0
+
+        # start-offset '='
+        start, line = line.split(b'=', 1)
+        start = int(start)
+        
+        if line == b'__NOMAGIC__\n':
+            raise DiscardMagicRules
+        
+        # value length (2 bytes, big endian)
+        if sys.version_info[0] >= 3:
+            lenvalue = int.from_bytes(line[:2], byteorder='big')
+        else:
+            lenvalue = (ord(line[0])<<8)+ord(line[1])
+        line = line[2:]
+        
+        # value
+        #   This can contain newlines, so we may need to read more lines
+        while len(line) <= lenvalue:
+            line += f.readline()
+        value, line = line[:lenvalue], line[lenvalue:]
+
+        # ['&' mask]
+        if line.startswith(b'&'):
+            # This can contain newlines, so we may need to read more lines
+            while len(line) <= lenvalue:
+                line += f.readline()
+            mask, line = line[1:lenvalue+1], line[lenvalue+1:]
+        else:
+            mask = None
+
+        # ['~' word-size] ['+' range-length]
+        ending = cls.rule_ending_re.match(line)
+        if not ending:
+            # Per the spec, this will be caught and ignored, to allow
+            # for future extensions.
+            raise UnknownMagicRuleFormat(repr(line))
+        
+        word, range = ending.groups()
+        word = int(word) if (word is not None) else 1
+        range = int(range) if (range is not None) else 1
+        
+        return nest_depth, cls(start, value, mask, word, range)
+
+    def maxlen(self):
+        l = self.start + len(self.value) + self.range
+        if self.also:
+            return max(l, self.also.maxlen())
+        return l
+
+    def match(self, buffer):
+        if self.match0(buffer):
+            if self.also:
+                return self.also.match(buffer)
+            return True
+
+    def match0(self, buffer):
+        l=len(buffer)
+        lenvalue = len(self.value)
+        for o in range(self.range):
+            s=self.start+o
+            e=s+lenvalue
+            if l<e:
+                return False
+            if self.mask:
+                test=''
+                for i in range(lenvalue):
+                    if PY3:
+                        c = buffer[s+i] & self.mask[i]
+                    else:
+                        c = ord(buffer[s+i]) & ord(self.mask[i])
+                    test += chr(c)
+            else:
+                test = buffer[s:e]
+
+            if test==self.value:
+                return True
+
+    def __repr__(self):
+        return 'MagicRule(start=%r, value=%r, mask=%r, word=%r, range=%r)' %(
+                                  self.start,
+                                  self.value,
+                                  self.mask,
+                                  self.word,
+                                  self.range)
+
+
+class MagicMatchAny(object):
+    """Match any of a set of magic rules.
+    
+    This has a similar interface to MagicRule objects (i.e. its match() and
+    maxlen() methods), to allow for duck typing.
+    """
+    def __init__(self, rules):
+        self.rules = rules
+    
+    def match(self, buffer):
+        return any(r.match(buffer) for r in self.rules)
+    
+    def maxlen(self):
+        return max(r.maxlen() for r in self.rules)
+    
+    @classmethod
+    def from_file(cls, f):
+        """Read a set of rules from the binary magic file."""
+        c=f.read(1)
+        f.seek(-1, 1)
+        depths_rules = []
+        while c and c != b'[':
+            try:
+                depths_rules.append(MagicRule.from_file(f))
+            except UnknownMagicRuleFormat:
+                # Ignored to allow for extensions to the rule format.
+                pass
+            c=f.read(1)
+            if c:
+                f.seek(-1, 1)
+        
+        # Build the rule tree
+        tree = []  # (rule, [(subrule,[subsubrule,...]), ...])
+        insert_points = {0:tree}
+        for depth, rule in depths_rules:
+            subrules = []
+            insert_points[depth].append((rule, subrules))
+            insert_points[depth+1] = subrules
+        
+        return cls.from_rule_tree(tree)
+    
+    @classmethod
+    def from_rule_tree(cls, tree):
+        """From a nested list of (rule, subrules) pairs, build a MagicMatchAny
+        instance, recursing down the tree.
+        
+        Where there's only one top-level rule, this is returned directly,
+        to simplify the nested structure. Returns None if no rules were read.
+        """
+        rules = []
+        for rule, subrules in tree:
+            if subrules:
+                rule.also = cls.from_rule_tree(subrules)
+            rules.append(rule)
+        
+        if len(rules)==0:
+            return None
+        if len(rules)==1:
+            return rules[0]
+        return cls(rules)        
+    
+class MagicDB:
+    def __init__(self):
+        self.bytype   = defaultdict(list)  # mimetype -> [(priority, rule), ...] 
+
+    def merge_file(self, fname):
+        """Read a magic binary file, and add its rules to this MagicDB."""
+        with open(fname, 'rb') as f:
+            line = f.readline()
+            if line != b'MIME-Magic\0\n':
+                raise IOError('Not a MIME magic file')
+
+            while True:
+                shead = f.readline().decode('ascii')
+                #print(shead)
+                if not shead:
+                    break
+                if shead[0] != '[' or shead[-2:] != ']\n':
+                    raise ValueError('Malformed section heading', shead)
+                pri, tname = shead[1:-2].split(':')
+                #print shead[1:-2]
+                pri = int(pri)
+                mtype = lookup(tname)
+                try:
+                    rule = MagicMatchAny.from_file(f)
+                except DiscardMagicRules:
+                    self.bytype.pop(mtype, None)
+                    rule = MagicMatchAny.from_file(f)
+                if rule is None:
+                    continue
+                #print rule
+
+                self.bytype[mtype].append((pri, rule))
+
+    def finalise(self):
+        """Prepare the MagicDB for matching.
+        
+        This should be called after all rules have been merged into it.
+        """
+        maxlen = 0
+        self.alltypes = []  # (priority, mimetype, rule)
+
+        for mtype, rules in self.bytype.items():
+            for pri, rule in rules:
+                self.alltypes.append((pri, mtype, rule))
+                maxlen = max(maxlen, rule.maxlen())
+
+        self.maxlen = maxlen  # Number of bytes to read from files
+        self.alltypes.sort(key=lambda x: x[0], reverse=True)
+
+    def match_data(self, data, max_pri=100, min_pri=0, possible=None):
+        """Do magic sniffing on some bytes.
+        
+        max_pri & min_pri can be used to specify the maximum & minimum priority
+        rules to look for. possible can be a list of mimetypes to check, or None
+        (the default) to check all mimetypes until one matches.
+        
+        Returns the MIMEtype found, or None if no entries match.
+        """
+        if possible is not None:
+            types = []
+            for mt in possible:
+                for pri, rule in self.bytype[mt]:
+                    types.append((pri, mt, rule))
+            types.sort(key=lambda x: x[0])
+        else:
+            types = self.alltypes
+        
+        for priority, mimetype, rule in types:
+            #print priority, max_pri, min_pri
+            if priority > max_pri:
+                continue
+            if priority < min_pri:
+                break
+            
+            if rule.match(data):
+                return mimetype
+
+    def match(self, path, max_pri=100, min_pri=0, possible=None):
+        """Read data from the file and do magic sniffing on it.
+        
+        max_pri & min_pri can be used to specify the maximum & minimum priority
+        rules to look for. possible can be a list of mimetypes to check, or None
+        (the default) to check all mimetypes until one matches.
+        
+        Returns the MIMEtype found, or None if no entries match. Raises IOError
+        if the file can't be opened.
+        """
+        with open(path, 'rb') as f:
+            buf = f.read(self.maxlen)
+        return self.match_data(buf, max_pri, min_pri, possible)
+    
+    def __repr__(self):
+        return '<MagicDB (%d types)>' % len(self.alltypes)
+
+class GlobDB(object):
+    def __init__(self):
+        """Prepare the GlobDB. It can't actually be used until .finalise() is
+        called, but merge_file() can be used to add data before that.
+        """
+        # Maps mimetype to {(weight, glob, flags), ...}
+        self.allglobs = defaultdict(set)
+
+    def merge_file(self, path):
+        """Loads name matching information from a globs2 file."""#
+        allglobs = self.allglobs
+        with open(path) as f:
+            for line in f:
+                if line.startswith('#'): continue   # Comment
+                
+                fields = line[:-1].split(':')
+                weight, type_name, pattern = fields[:3]
+                weight = int(weight)
+                mtype = lookup(type_name)
+                if len(fields) > 3:
+                    flags = fields[3].split(',')
+                else:
+                    flags = ()
+                    
+                if pattern == '__NOGLOBS__':
+                    # This signals to discard any previous globs
+                    allglobs.pop(mtype, None)
+                    continue
+                
+                allglobs[mtype].add((weight, pattern, tuple(flags)))
+    
+    def finalise(self):
+        """Prepare the GlobDB for matching.
+        
+        This should be called after all files have been merged into it.
+        """
+        self.exts = defaultdict(list)  # Maps extensions to [(type, weight),...]
+        self.cased_exts = defaultdict(list)
+        self.globs = []                # List of (regex, type, weight) triplets
+        self.literals = {}             # Maps literal names to (type, weight)
+        self.cased_literals = {}
+        
+        for mtype, globs in self.allglobs.items():
+          mtype = mtype.canonical()
+          for weight, pattern, flags in globs:
+        
+            cased = 'cs' in flags
+
+            if pattern.startswith('*.'):
+                # *.foo -- extension pattern
+                rest = pattern[2:]
+                if not ('*' in rest or '[' in rest or '?' in rest):
+                    if cased:
+                        self.cased_exts[rest].append((mtype, weight))
+                    else:
+                        self.exts[rest.lower()].append((mtype, weight))
+                    continue
+            
+            if ('*' in pattern or '[' in pattern or '?' in pattern):
+                # Translate the glob pattern to a regex & compile it
+                re_flags = 0 if cased else re.I
+                pattern = re.compile(fnmatch.translate(pattern), flags=re_flags)
+                self.globs.append((pattern, mtype, weight))
+            else:
+                # No wildcards - literal pattern
+                if cased:
+                    self.cased_literals[pattern] = (mtype, weight)
+                else:
+                    self.literals[pattern.lower()] = (mtype, weight)
+        
+        # Sort globs by weight & length
+        self.globs.sort(reverse=True, key=lambda x: (x[2], len(x[0].pattern)) )
+    
+    def first_match(self, path):
+        """Return the first match found for a given path, or None if no match
+        is found."""
+        try:
+            return next(self._match_path(path))[0]
+        except StopIteration:
+            return None
+    
+    def all_matches(self, path):
+        """Return a list of (MIMEtype, glob weight) pairs for the path."""
+        return list(self._match_path(path))
+    
+    def _match_path(self, path):
+        """Yields pairs of (mimetype, glob weight)."""
+        leaf = os.path.basename(path)
+
+        # Literals (no wildcards)
+        if leaf in self.cased_literals:
+            yield self.cased_literals[leaf]
+
+        lleaf = leaf.lower()
+        if lleaf in self.literals:
+            yield self.literals[lleaf]
+
+        # Extensions
+        ext = leaf
+        while 1:
+            p = ext.find('.')
+            if p < 0: break
+            ext = ext[p + 1:]
+            if ext in self.cased_exts:
+                for res in self.cased_exts[ext]:
+                    yield res
+        ext = lleaf
+        while 1:
+            p = ext.find('.')
+            if p < 0: break
+            ext = ext[p+1:]
+            if ext in self.exts:
+                for res in self.exts[ext]:
+                    yield res
+        
+        # Other globs
+        for (regex, mime_type, weight) in self.globs:
+            if regex.match(leaf):
+                yield (mime_type, weight)
+
+# Some well-known types
+text = lookup('text', 'plain')
+octet_stream = lookup('application', 'octet-stream')
+inode_block = lookup('inode', 'blockdevice')
+inode_char = lookup('inode', 'chardevice')
+inode_dir = lookup('inode', 'directory')
+inode_fifo = lookup('inode', 'fifo')
+inode_socket = lookup('inode', 'socket')
+inode_symlink = lookup('inode', 'symlink')
+inode_door = lookup('inode', 'door')
+app_exe = lookup('application', 'executable')
+
+_cache_uptodate = False
+
+def _cache_database():
+    global globs, magic, aliases, inheritance, _cache_uptodate
+
+    _cache_uptodate = True
+
+    aliases = {}    # Maps alias Mime types to canonical names
+    inheritance = defaultdict(set) # Maps to sets of parent mime types.
+    
+    # Load aliases
+    for path in BaseDirectory.load_data_paths(os.path.join('mime', 'aliases')):
+        with open(path, 'r') as f:
+            for line in f:
+                alias, canonical = line.strip().split(None, 1)
+                aliases[alias] = canonical
+    
+    # Load filename patterns (globs)
+    globs = GlobDB()
+    for path in BaseDirectory.load_data_paths(os.path.join('mime', 'globs2')):
+        globs.merge_file(path)
+    globs.finalise()
+    
+    # Load magic sniffing data
+    magic = MagicDB()    
+    for path in BaseDirectory.load_data_paths(os.path.join('mime', 'magic')):
+        magic.merge_file(path)
+    magic.finalise()
+    
+    # Load subclasses
+    for path in BaseDirectory.load_data_paths(os.path.join('mime', 'subclasses')):
+        with open(path, 'r') as f:
+            for line in f:
+                sub, parent = line.strip().split(None, 1)
+                inheritance[sub].add(parent)
+
+def update_cache():
+    if not _cache_uptodate:
+        _cache_database()
+
+def get_type_by_name(path):
+    """Returns type of file by its name, or None if not known"""
+    update_cache()
+    return globs.first_match(path)
+
+def get_type_by_contents(path, max_pri=100, min_pri=0):
+    """Returns type of file by its contents, or None if not known"""
+    update_cache()
+
+    return magic.match(path, max_pri, min_pri)
+
+def get_type_by_data(data, max_pri=100, min_pri=0):
+    """Returns type of the data, which should be bytes."""
+    update_cache()
+
+    return magic.match_data(data, max_pri, min_pri)
+
+def _get_type_by_stat(st_mode):
+    """Match special filesystem objects to Mimetypes."""
+    if stat.S_ISDIR(st_mode): return inode_dir
+    elif stat.S_ISCHR(st_mode): return inode_char
+    elif stat.S_ISBLK(st_mode): return inode_block
+    elif stat.S_ISFIFO(st_mode): return inode_fifo
+    elif stat.S_ISLNK(st_mode): return inode_symlink
+    elif stat.S_ISSOCK(st_mode): return inode_socket
+    return inode_door
+
+def get_type(path, follow=True, name_pri=100):
+    """Returns type of file indicated by path.
+    
+    This function is *deprecated* - :func:`get_type2` is more accurate.
+    
+    :param path: pathname to check (need not exist)
+    :param follow: when reading file, follow symbolic links
+    :param name_pri: Priority to do name matches. 100=override magic
+    
+    This tries to use the contents of the file, and falls back to the name. It
+    can also handle special filesystem objects like directories and sockets.
+    """
+    update_cache()
+    
+    try:
+        if follow:
+            st = os.stat(path)
+        else:
+            st = os.lstat(path)
+    except:
+        t = get_type_by_name(path)
+        return t or text
+
+    if stat.S_ISREG(st.st_mode):
+        # Regular file
+        t = get_type_by_contents(path, min_pri=name_pri)
+        if not t: t = get_type_by_name(path)
+        if not t: t = get_type_by_contents(path, max_pri=name_pri)
+        if t is None:
+            if stat.S_IMODE(st.st_mode) & 0o111:
+                return app_exe
+            else:
+                return text
+        return t
+    else:
+        return _get_type_by_stat(st.st_mode)
+
+def get_type2(path, follow=True):
+    """Find the MIMEtype of a file using the XDG recommended checking order.
+    
+    This first checks the filename, then uses file contents if the name doesn't
+    give an unambiguous MIMEtype. It can also handle special filesystem objects
+    like directories and sockets.
+    
+    :param path: file path to examine (need not exist)
+    :param follow: whether to follow symlinks
+    
+    :rtype: :class:`MIMEtype`
+    
+    .. versionadded:: 1.0
+    """
+    update_cache()
+    
+    try:
+        st = os.stat(path) if follow else os.lstat(path)
+    except OSError:
+        return get_type_by_name(path) or octet_stream
+    
+    if not stat.S_ISREG(st.st_mode):
+        # Special filesystem objects
+        return _get_type_by_stat(st.st_mode)
+    
+    mtypes = sorted(globs.all_matches(path), key=(lambda x: x[1]), reverse=True)
+    if mtypes:
+        max_weight = mtypes[0][1]
+        i = 1
+        for mt, w in mtypes[1:]:
+            if w < max_weight:
+                break
+            i += 1
+        mtypes = mtypes[:i]
+        if len(mtypes) == 1:
+            return mtypes[0][0]
+    
+        possible = [mt for mt,w in mtypes]
+    else:
+        possible = None   # Try all magic matches
+    
+    try:
+        t = magic.match(path, possible=possible)
+    except IOError:
+        t = None
+    
+    if t:
+        return t
+    elif mtypes:
+        return mtypes[0][0]
+    elif stat.S_IMODE(st.st_mode) & 0o111:
+        return app_exe
+    else:
+        return text if is_text_file(path) else octet_stream
+
+def is_text_file(path):
+    """Guess whether a file contains text or binary data.
+    
+    Heuristic: binary if the first 32 bytes include ASCII control characters.
+    This rule may change in future versions.
+    
+    .. versionadded:: 1.0
+    """
+    try:
+        f = open(path, 'rb')
+    except IOError:
+        return False
+    
+    with f:
+        return _is_text(f.read(32))
+
+if PY3:
+    def _is_text(data):
+        return not any(b <= 0x8 or 0xe <= b < 0x20 or b == 0x7f for b in data)
+else:
+    def _is_text(data):
+        return not any(b <= '\x08' or '\x0e' <= b < '\x20' or b == '\x7f' \
+                            for b in data)
+
+_mime2ext_cache = None
+_mime2ext_cache_uptodate = False
+
+def get_extensions(mimetype):
+    """Retrieve the set of filename extensions matching a given MIMEtype.
+    
+    Extensions are returned without a leading dot, e.g. 'py'. If no extensions
+    are registered for the MIMEtype, returns an empty set.
+    
+    The extensions are stored in a cache the first time this is called.
+    
+    .. versionadded:: 1.0
+    """
+    global _mime2ext_cache, _mime2ext_cache_uptodate
+    update_cache()
+    if not _mime2ext_cache_uptodate:
+        _mime2ext_cache = defaultdict(set)
+        for ext, mtypes in globs.exts.items():
+            for mtype, prio in mtypes:
+                _mime2ext_cache[mtype].add(ext)
+        _mime2ext_cache_uptodate = True
+    
+    return _mime2ext_cache[mimetype]
+        
+
+def install_mime_info(application, package_file):
+    """Copy 'package_file' as ``~/.local/share/mime/packages/<application>.xml.``
+    If package_file is None, install ``<app_dir>/<application>.xml``.
+    If already installed, does nothing. May overwrite an existing
+    file with the same name (if the contents are different)"""
+    application += '.xml'
+
+    new_data = open(package_file).read()
+
+    # See if the file is already installed
+    package_dir = os.path.join('mime', 'packages')
+    resource = os.path.join(package_dir, application)
+    for x in BaseDirectory.load_data_paths(resource):
+        try:
+            old_data = open(x).read()
+        except:
+            continue
+        if old_data == new_data:
+            return  # Already installed
+
+    global _cache_uptodate
+    _cache_uptodate = False
+
+    # Not already installed; add a new copy
+    # Create the directory structure...
+    new_file = os.path.join(BaseDirectory.save_data_path(package_dir), application)
+
+    # Write the file...
+    open(new_file, 'w').write(new_data)
+
+    # Update the database...
+    command = 'update-mime-database'
+    if os.spawnlp(os.P_WAIT, command, command, BaseDirectory.save_data_path('mime')):
+        os.unlink(new_file)
+        raise Exception("The '%s' command returned an error code!\n" \
+                  "Make sure you have the freedesktop.org shared MIME package:\n" \
+                  "http://standards.freedesktop.org/shared-mime-info/" % command)