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  • Committer: Canonical.com Patch Queue Manager
  • Date: 2007-08-02 06:33:21 UTC
  • mfrom: (2661.2.3 pack)
  • Revision ID: pqm@pqm.ubuntu.com-20070802063321-lpx3oazcxyac24oa
(robertc) Add support to the bzrlib.pack interface for arbitrary-record access via a readv adapter for transports. (Robert Collins)

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bzrlib/pack.py
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"Containers" and "records" are described in doc/developers/container-format.txt.
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"""
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from cStringIO import StringIO
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import re
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from bzrlib import errors
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        :param write_func: a callable that will be called when this
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            ContainerWriter needs to write some bytes.
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        """
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        self.write_func = write_func
 
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        self._write_func = write_func
 
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        self.current_offset = 0
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    def begin(self):
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        """Begin writing a container."""
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        self.write_func(FORMAT_ONE + "\n")
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    def write_func(self, bytes):
 
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        self._write_func(bytes)
 
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        self.current_offset += len(bytes)
 
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    def end(self):
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        """Finish writing a container."""
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        self.write_func("E")
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    def add_bytes_record(self, bytes, names):
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        """Add a Bytes record with the given names."""
 
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        """Add a Bytes record with the given names.
 
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        :param bytes: The bytes to insert.
 
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        :param names: The names to give the inserted bytes.
 
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        :return: An offset, length tuple. The offset is the offset
 
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            of the record within the container, and the length is the
 
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            length of data that will need to be read to reconstitute the
 
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            record. These offset and length can only be used with the pack
 
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            interface - they might be offset by headers or other such details
 
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            and thus are only suitable for use by a ContainerReader.
 
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        """
 
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        current_offset = self.current_offset
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        # Kind marker
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        self.write_func("B")
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        # Length
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        self.write_func("\n")
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        # Finally, the contents.
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        self.write_func(bytes)
 
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        # return a memo of where we wrote data to allow random access.
 
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        return current_offset, self.current_offset - current_offset
 
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class ReadVFile(object):
 
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    """Adapt a readv result iterator to a file like protocol."""
 
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    def __init__(self, readv_result):
 
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        self.readv_result = readv_result
 
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        # the most recent readv result block
 
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        self._string = None
 
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    def _next(self):
 
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        if (self._string is None or
 
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            self._string.tell() == self._string_length):
 
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            length, data = self.readv_result.next()
 
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            self._string_length = len(data)
 
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            self._string = StringIO(data)
 
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    def read(self, length):
 
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        self._next()
 
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        result = self._string.read(length)
 
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        if len(result) < length:
 
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            raise errors.BzrError('request for too much data from a readv hunk.')
 
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        return result
 
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    def readline(self):
 
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        """Note that readline will not cross readv segments."""
 
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        self._next()
 
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        result = self._string.readline()
 
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        if self._string.tell() == self._string_length and result[-1] != '\n':
 
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            raise errors.BzrError('short readline in the readvfile hunk.')
 
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        return result
 
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def make_readv_reader(transport, filename, requested_records):
 
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    """Create a ContainerReader that will read selected records only.
 
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    :param transport: The transport the pack file is located on.
 
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    :param filename: The filename of the pack file.
 
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    :param requested_records: The record offset, length tuples as returned
 
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        by add_bytes_record for the desired records.
 
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    """
 
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    readv_blocks = [(0, len(FORMAT_ONE)+1)]
 
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    readv_blocks.extend(requested_records)
 
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    result = ContainerReader(ReadVFile(
 
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        transport.readv(filename, readv_blocks)))
 
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    return result
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class BaseReader(object):