storages.py

"""custom storages for the system source"""
from os import unlink, path as osp

from yams.schema import role_name

from cubicweb import Binary
from cubicweb.server import hook

def set_attribute_storage(repo, etype, attr, storage):
    repo.system_source.set_storage(etype, attr, storage)

def unset_attribute_storage(repo, etype, attr):
    repo.system_source.unset_storage(etype, attr)

class Storage(object):
    """abstract storage

    * If `source_callback` is true (by default), the callback will be run during
      query result process of fetched attribute's valu and should have the
      following prototype::

        callback(self, source, value)

      where `value` is the value actually stored in the backend. None values
      will be skipped (eg callback won't be called).

    * if `source_callback` is false, the callback will be run during sql
      generation when some attribute with a custom storage is accessed and
      should have the following prototype::

        callback(self, generator, relation, linkedvar)

      where `generator` is the sql generator, `relation` the current rql syntax
      tree relation and linkedvar the principal syntax tree variable holding the
      attribute.
    """
    is_source_callback = True

    def callback(self, *args):
        """see docstring for prototype, which vary according to is_source_callback
        """
        raise NotImplementedError()

    def entity_added(self, entity, attr):
        """an entity using this storage for attr has been added"""
        raise NotImplementedError()
    def entity_updated(self, entity, attr):
        """an entity using this storage for attr has been updatded"""
        raise NotImplementedError()
    def entity_deleted(self, entity, attr):
        """an entity using this storage for attr has been deleted"""
        raise NotImplementedError()

# TODO
# * make it configurable without code
# * better file path attribution
# * handle backup/restore

def uniquify_path(dirpath, basename):
    """return a unique file name for `basename` in `dirpath`, or None
    if all attemps failed.

    XXX subject to race condition.
    """
    path = osp.join(dirpath, basename)
    if not osp.isfile(path):
        return path
    base, ext = osp.splitext(path)
    for i in xrange(1, 256):
        path = '%s%s%s' % (base, i, ext)
        if not osp.isfile(path):
            return path
    return None

class BytesFileSystemStorage(Storage):
    """store Bytes attribute value on the file system"""
    def __init__(self, defaultdir, fsencoding='utf-8'):
        self.default_directory = defaultdir
        self.fsencoding = fsencoding

    def callback(self, source, value):
        """sql generator callback when some attribute with a custom storage is
        accessed
        """
        fpath = source.binary_to_str(value)
        try:
            return Binary(file(fpath).read())
        except OSError, ex:
            source.critical("can't open %s: %s", value, ex)
            return None

    def entity_added(self, entity, attr):
        """an entity using this storage for attr has been added"""
        if entity._cw.transaction_data.get('fs_importing'):
            binary = Binary(file(entity[attr].getvalue()).read())
        else:
            binary = entity.pop(attr)
            fpath = self.new_fs_path(entity, attr)
            # bytes storage used to store file's path
            entity[attr] = Binary(fpath)
            file(fpath, 'w').write(binary.getvalue())
            hook.set_operation(entity._cw, 'bfss_added', fpath, AddFileOp)
        return binary

    def entity_updated(self, entity, attr):
        """an entity using this storage for attr has been updatded"""
        if entity._cw.transaction_data.get('fs_importing'):
            oldpath = self.current_fs_path(entity, attr)
            fpath = entity[attr].getvalue()
            if oldpath != fpath:
                hook.set_operation(entity._cw, 'bfss_deleted', oldpath,
                                   DeleteFileOp)
            binary = Binary(file(fpath).read())
        else:
            binary = entity.pop(attr)
            fpath = self.current_fs_path(entity, attr)
            UpdateFileOp(entity._cw, filepath=fpath, filedata=binary.getvalue())
        return binary

    def entity_deleted(self, entity, attr):
        """an entity using this storage for attr has been deleted"""
        fpath = self.current_fs_path(entity, attr)
        hook.set_operation(entity._cw, 'bfss_deleted', fpath, DeleteFileOp)

    def new_fs_path(self, entity, attr):
        # We try to get some hint about how to name the file using attribute's
        # name metadata, so we use the real file name and extension when
        # available. Keeping the extension is useful for example in the case of
        # PIL processing that use filename extension to detect content-type, as
        # well as providing more understandable file names on the fs.
        basename = [str(entity.eid), attr]
        name = entity.attr_metadata(attr, 'name')
        if name is not None:
            basename.append(name.encode(self.fsencoding))
        fspath = uniquify_path(self.default_directory, '_'.join(basename))
        if fspath is None:
            msg = entity._cw._('failed to uniquify path (%s, %s)') % (
                dirpath, '_'.join(basename))
            raise ValidationError(entity.eid, {role_name(attr, 'subject'): msg})
        return fspath

    def current_fs_path(self, entity, attr):
        sysource = entity._cw.pool.source('system')
        cu = sysource.doexec(entity._cw,
                             'SELECT cw_%s FROM cw_%s WHERE cw_eid=%s' % (
                             attr, entity.__regid__, entity.eid))
        rawvalue = cu.fetchone()[0]
        if rawvalue is None: # no previous value
            return self.new_fs_path(entity, attr)
        return sysource._process_value(rawvalue, cu.description[0],
                                       binarywrap=str)



class AddFileOp(hook.Operation):
    def rollback_event(self):
        for filepath in self.session.transaction_data.pop('bfss_added'):
            try:
                unlink(filepath)
            except Exception, ex:
                self.error('cant remove %s: %s' % (filepath, ex))

class DeleteFileOp(hook.Operation):
    def commit_event(self):
        for filepath in self.session.transaction_data.pop('bfss_deleted'):
            try:
                unlink(filepath)
            except Exception, ex:
                self.error('cant remove %s: %s' % (filepath, ex))

class UpdateFileOp(hook.Operation):
    def precommit_event(self):
        try:
            file(self.filepath, 'w').write(self.filedata)
        except Exception, ex:
            self.exception(str(ex))