grid_file.py

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# Copyright 2009-2010 10gen, Inc.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

"""Tools for representing files stored in GridFS."""

import datetime
import math
import os
try:
    from cStringIO import StringIO
except ImportError:
    from StringIO import StringIO

from bson.binary import Binary
from bson.objectid import ObjectId
from gridfs.errors import (CorruptGridFile,
                           FileExists,
                           NoFile,
                           UnsupportedAPI)
from pymongo import ASCENDING
from pymongo.collection import Collection
from pymongo.errors import DuplicateKeyError

try:
    _SEEK_SET = os.SEEK_SET
    _SEEK_CUR = os.SEEK_CUR
    _SEEK_END = os.SEEK_END
# before 2.5
except AttributeError:
    _SEEK_SET = 0
    _SEEK_CUR = 1
    _SEEK_END = 2


"""Default chunk size, in bytes."""
DEFAULT_CHUNK_SIZE = 256 * 1024


def _create_property(field_name, docstring,
                      read_only=False, closed_only=False):
    """Helper for creating properties to read/write to files.
    """
    def getter(self):
        if closed_only and not self._closed:
            raise AttributeError("can only get %r on a closed file" %
                                 field_name)
        return self._file.get(field_name, None)

    def setter(self, value):
        if self._closed:
            self._coll.files.update({"_id": self._file["_id"]},
                                    {"$set": {field_name: value}}, safe=True)
        self._file[field_name] = value

    if read_only:
        docstring = docstring + "\n\nThis attribute is read-only."
    elif closed_only:
        docstring = "%s\n\n%s" % (docstring, "This attribute is read-only and "
                                  "can only be read after :meth:`close` "
                                  "has been called.")

    if not read_only and not closed_only:
        return property(getter, setter, doc=docstring)
    return property(getter, doc=docstring)


class GridIn(object):
    """Class to write data to GridFS.
    """
    def __init__(self, root_collection, **kwargs):
        """Write a file to GridFS

        Application developers should generally not need to
        instantiate this class directly - instead see the methods
        provided by :class:`~gridfs.GridFS`.

        Raises :class:`TypeError` if `root_collection` is not an
        instance of :class:`~pymongo.collection.Collection`.

        Any of the file level options specified in the `GridFS Spec
        <http://dochub.mongodb.org/core/gridfsspec>`_ may be passed as
        keyword arguments. Any additional keyword arguments will be
        set as additional fields on the file document. Valid keyword
        arguments include:

          - ``"_id"``: unique ID for this file (default:
            :class:`~bson.objectid.ObjectId`) - this ``"_id"`` must
            not have already been used for another file

          - ``"filename"``: human name for the file

          - ``"contentType"`` or ``"content_type"``: valid mime-type
            for the file

          - ``"chunkSize"`` or ``"chunk_size"``: size of each of the
            chunks, in bytes (default: 256 kb)

          - ``"encoding"``: encoding used for this file - any
            :class:`unicode` that is written to the file will be
            converted to a :class:`str` with this encoding

        :Parameters:
          - `root_collection`: root collection to write to
          - `**kwargs` (optional): file level options (see above)
        """
        if not isinstance(root_collection, Collection):
            raise TypeError("root_collection must be an "
                            "instance of Collection")

        # Handle alternative naming
        if "content_type" in kwargs:
            kwargs["contentType"] = kwargs.pop("content_type")
        if "chunk_size" in kwargs:
            kwargs["chunkSize"] = kwargs.pop("chunk_size")

        # Defaults
        kwargs["_id"] = kwargs.get("_id", ObjectId())
        kwargs["chunkSize"] = kwargs.get("chunkSize", DEFAULT_CHUNK_SIZE)

        root_collection.chunks.ensure_index([("files_id", ASCENDING),
                                             ("n", ASCENDING)],
                                            unique=True)
        object.__setattr__(self, "_coll", root_collection)
        object.__setattr__(self, "_chunks", root_collection.chunks)
        object.__setattr__(self, "_file", kwargs)
        object.__setattr__(self, "_buffer", StringIO())
        object.__setattr__(self, "_position", 0)
        object.__setattr__(self, "_chunk_number", 0)
        object.__setattr__(self, "_closed", False)

    @property
    def closed(self):
        """Is this file closed?
        """
        return self._closed

    _id = _create_property("_id", "The ``'_id'`` value for this file.",
                            read_only=True)
    filename = _create_property("filename", "Name of this file.")
    content_type = _create_property("contentType", "Mime-type for this file.")
    length = _create_property("length", "Length (in bytes) of this file.",
                               closed_only=True)
    chunk_size = _create_property("chunkSize", "Chunk size for this file.",
                                   read_only=True)
    upload_date = _create_property("uploadDate",
                                    "Date that this file was uploaded.",
                                    closed_only=True)
    md5 = _create_property("md5", "MD5 of the contents of this file "
                            "(generated on the server).",
                            closed_only=True)

    def __getattr__(self, name):
        if name in self._file:
            return self._file[name]
        raise AttributeError("GridIn object has no attribute '%s'" % name)

    def __setattr__(self, name, value):
        object.__setattr__(self, name, value)
        if self._closed:
            self._coll.files.update({"_id": self._file["_id"]},
                                    {"$set": {name: value}}, safe=True)

    def __flush_data(self, data):
        """Flush `data` to a chunk.
        """
        if not data:
            return
        assert(len(data) <= self.chunk_size)

        chunk = {"files_id": self._file["_id"],
                 "n": self._chunk_number,
                 "data": Binary(data)}

        self._chunks.insert(chunk)
        self._chunk_number += 1
        self._position += len(data)

    def __flush_buffer(self):
        """Flush the buffer contents out to a chunk.
        """
        self.__flush_data(self._buffer.getvalue())
        self._buffer.close()
        self._buffer = StringIO()

    def __flush(self):
        """Flush the file to the database.
        """
        self.__flush_buffer()

        md5 = self._coll.database.command("filemd5", self._id,
                                          root=self._coll.name)["md5"]

        self._file["md5"] = md5
        self._file["length"] = self._position
        self._file["uploadDate"] = datetime.datetime.utcnow()

        try:
            return self._coll.files.insert(self._file, safe=True)
        except DuplicateKeyError:
            raise FileExists("file with _id %r already exists" % self._id)

    def close(self):
        """Flush the file and close it.

        A closed file cannot be written any more. Calling
        :meth:`close` more than once is allowed.
        """
        if not self._closed:
            self.__flush()
            self._closed = True

    def write(self, data):
        """Write data to the file. There is no return value.

        `data` can be either a string of bytes or a file-like object
        (implementing :meth:`read`). If the file has an
        :attr:`encoding` attribute, `data` can also be a
        :class:`unicode` instance, which will be encoded as
        :attr:`encoding` before being written.

        Due to buffering, the data may not actually be written to the
        database until the :meth:`close` method is called. Raises
        :class:`ValueError` if this file is already closed. Raises
        :class:`TypeError` if `data` is not an instance of
        :class:`str`, a file-like object, or an instance of
        :class:`unicode` (only allowed if the file has an
        :attr:`encoding` attribute).

        :Parameters:
          - `data`: string of bytes or file-like object to be written
            to the file

        .. versionadded:: 1.9
           The ability to write :class:`unicode`, if the file has an
           :attr:`encoding` attribute.
        """
        if self._closed:
            raise ValueError("cannot write to a closed file")

        # file-like
        try:
            if self._buffer.tell() > 0:
                space = self.chunk_size - self._buffer.tell()
                self._buffer.write(data.read(space))
                self.__flush_buffer()
            to_write = data.read(self.chunk_size)
            while to_write and len(to_write) == self.chunk_size:
                self.__flush_data(to_write)
                to_write = data.read(self.chunk_size)
            self._buffer.write(to_write)
        # string
        except AttributeError:
            if not isinstance(data, basestring):
                raise TypeError("can only write strings or file-like objects")

            if isinstance(data, unicode):
                try:
                    data = data.encode(self.encoding)
                except AttributeError:
                    raise TypeError("must specify an encoding for file in "
                                    "order to write unicode")

            while data:
                space = self.chunk_size - self._buffer.tell()

                if len(data) <= space:
                    self._buffer.write(data)
                    break
                else:
                    self._buffer.write(data[:space])
                    self.__flush_buffer()
                    data = data[space:]

    def writelines(self, sequence):
        """Write a sequence of strings to the file.

        Does not add seperators.
        """
        for line in sequence:
            self.write(line)

    def __enter__(self):
        """Support for the context manager protocol.
        """
        return self

    def __exit__(self, exc_type, exc_val, exc_tb):
        """Support for the context manager protocol.

        Close the file and allow exceptions to propogate.
        """
        self.close()

        # propogate exceptions
        return False


class GridOut(object):
    """Class to read data out of GridFS.
    """
    def __init__(self, root_collection, file_id=None, file_document=None):
        """Read a file from GridFS

        Application developers should generally not need to
        instantiate this class directly - instead see the methods
        provided by :class:`~gridfs.GridFS`.

        Either `file_id` or `file_document` must be specified,
        `file_document` will be given priority if present. Raises
        :class:`TypeError` if `root_collection` is not an instance of
        :class:`~pymongo.collection.Collection`.

        :Parameters:
          - `root_collection`: root collection to read from
          - `file_id`: value of ``"_id"`` for the file to read
          - `file_document`: file document from `root_collection.files`

        .. versionadded:: 1.9
           The `file_document` parameter.
        """
        if not isinstance(root_collection, Collection):
            raise TypeError("root_collection must be an "
                            "instance of Collection")

        self.__chunks = root_collection.chunks

        files = root_collection.files
        self._file = file_document or files.find_one({"_id": file_id})

        if not self._file:
            raise NoFile("no file in gridfs collection %r with _id %r" %
                         (files, file_id))

        self.__buffer = ""
        self.__position = 0

    _id = _create_property("_id", "The ``'_id'`` value for this file.", True)
    name = _create_property("filename", "Name of this file.", True)
    content_type = _create_property("contentType", "Mime-type for this file.",
                                     True)
    length = _create_property("length", "Length (in bytes) of this file.",
                               True)
    chunk_size = _create_property("chunkSize", "Chunk size for this file.",
                                   True)
    upload_date = _create_property("uploadDate",
                                    "Date that this file was first uploaded.",
                                    True)
    aliases = _create_property("aliases", "List of aliases for this file.",
                                True)
    metadata = _create_property("metadata", "Metadata attached to this file.",
                                 True)
    md5 = _create_property("md5", "MD5 of the contents of this file "
                            "(generated on the server).", True)

    def __getattr__(self, name):
        if name in self._file:
            return self._file[name]
        raise AttributeError("GridIn object has no attribute '%s'" % name)

    def read(self, size=-1):
        """Read at most `size` bytes from the file (less if there
        isn't enough data).

        The bytes are returned as an instance of :class:`str`. If
        `size` is negative or omitted all data is read.

        :Parameters:
          - `size` (optional): the number of bytes to read
        """
        if size == 0:
            return ""

        remainder = int(self.length) - self.__position
        if size < 0 or size > remainder:
            size = remainder

        received = len(self.__buffer)
        chunk_number = (received + self.__position) / self.chunk_size
        chunks = []

        while received < size:
            chunk = self.__chunks.find_one({"files_id": self._id,
                                            "n": chunk_number})
            if not chunk:
                raise CorruptGridFile("no chunk #%d" % chunk_number)

            if received:
                chunk_data = chunk["data"]
            else:
                chunk_data = chunk["data"][self.__position % self.chunk_size:]

            received += len(chunk_data)
            chunks.append(chunk_data)
            chunk_number += 1

        data = "".join([self.__buffer] + chunks)
        self.__position += size
        to_return = data[:size]
        self.__buffer = data[size:]
        return to_return

    def readline(self, size=-1):
        """Read one line or up to `size` bytes from the file.

        :Parameters:
         - `size` (optional): the maximum number of bytes to read

        .. versionadded:: 1.9
        """
        bytes = ""
        while len(bytes) != size:
            byte = self.read(1)
            bytes += byte
            if byte == "" or byte == "\n":
                break
        return bytes

    def tell(self):
        """Return the current position of this file.
        """
        return self.__position

    def seek(self, pos, whence=_SEEK_SET):
        """Set the current position of this file.

        :Parameters:
         - `pos`: the position (or offset if using relative
           positioning) to seek to
         - `whence` (optional): where to seek
           from. :attr:`os.SEEK_SET` (``0``) for absolute file
           positioning, :attr:`os.SEEK_CUR` (``1``) to seek relative
           to the current position, :attr:`os.SEEK_END` (``2``) to
           seek relative to the file's end.
        """
        if whence == _SEEK_SET:
            new_pos = pos
        elif whence == _SEEK_CUR:
            new_pos = self.__position + pos
        elif whence == _SEEK_END:
            new_pos = int(self.length) + pos
        else:
            raise IOError(22, "Invalid value for `whence`")

        if new_pos < 0:
            raise IOError(22, "Invalid value for `pos` - must be positive")

        self.__position = new_pos
        self.__buffer = ""

    def __iter__(self):
        """Return an iterator over all of this file's data.

        The iterator will return chunk-sized instances of
        :class:`str`. This can be useful when serving files using a
        webserver that handles such an iterator efficiently.
        """
        return GridOutIterator(self, self.__chunks)


class GridOutIterator(object):
    def __init__(self, grid_out, chunks):
        self.__id = grid_out._id
        self.__chunks = chunks
        self.__current_chunk = 0
        self.__max_chunk = math.ceil(float(grid_out.length) /
                                     grid_out.chunk_size)

    def __iter__(self):
        return self

    def next(self):
        if self.__current_chunk >= self.__max_chunk:
            raise StopIteration
        chunk = self.__chunks.find_one({"files_id": self.__id,
                                        "n": self.__current_chunk})
        if not chunk:
            raise CorruptGridFile("no chunk #%d" % self.__current_chunk)
        self.__current_chunk += 1
        return str(chunk["data"])


class GridFile(object):
    """No longer supported.

    .. versionchanged:: 1.6
       The GridFile class is no longer supported.
    """
    def __init__(self, *args, **kwargs):
        raise UnsupportedAPI("The GridFile class is no longer supported. "
                             "Please use GridIn or GridOut instead.")

---

pymongo
Author(s): Bhaskara Marthi
autogenerated on Fri Jan 11 10:09:03 2013