path: root/bzrlib/tuned_gzip.py

# Copyright (C) 2006-2011 Canonical Ltd
# Written by Robert Collins <robert.collins@canonical.com>
#
# 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., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA

"""Bzrlib specific gzip tunings. We plan to feed these to the upstream gzip."""

from __future__ import absolute_import

from cStringIO import StringIO

# make GzipFile faster:
import gzip
from gzip import FEXTRA, FCOMMENT, FNAME, FHCRC
import sys
import struct
import zlib

# we want a \n preserved, break on \n only splitlines.
from bzrlib import symbol_versioning

__all__ = ["GzipFile", "bytes_to_gzip"]


def U32(i):
    """Return i as an unsigned integer, assuming it fits in 32 bits.

    If it's >= 2GB when viewed as a 32-bit unsigned int, return a long.
    """
    if i < 0:
        i += 1L << 32
    return i


def LOWU32(i):
    """Return the low-order 32 bits of an int, as a non-negative int."""
    return i & 0xFFFFFFFFL


def bytes_to_gzip(bytes, factory=zlib.compressobj,
    level=zlib.Z_DEFAULT_COMPRESSION, method=zlib.DEFLATED,
    width=-zlib.MAX_WBITS, mem=zlib.DEF_MEM_LEVEL,
    crc32=zlib.crc32):
    """Create a gzip file containing bytes and return its content."""
    return chunks_to_gzip([bytes])


def chunks_to_gzip(chunks, factory=zlib.compressobj,
    level=zlib.Z_DEFAULT_COMPRESSION, method=zlib.DEFLATED,
    width=-zlib.MAX_WBITS, mem=zlib.DEF_MEM_LEVEL,
    crc32=zlib.crc32):
    """Create a gzip file containing chunks and return its content.

    :param chunks: An iterable of strings. Each string can have arbitrary
        layout.
    """
    result = [
        '\037\213'  # self.fileobj.write('\037\213')  # magic header
        '\010'      # self.fileobj.write('\010')      # compression method
                    # fname = self.filename[:-3]
                    # flags = 0
                    # if fname:
                    #     flags = FNAME
        '\x00'      # self.fileobj.write(chr(flags))
        '\0\0\0\0'  # write32u(self.fileobj, long(time.time()))
        '\002'      # self.fileobj.write('\002')
        '\377'      # self.fileobj.write('\377')
                    # if fname:
        ''          #     self.fileobj.write(fname + '\000')
        ]
    # using a compressobj avoids a small header and trailer that the compress()
    # utility function adds.
    compress = factory(level, method, width, mem, 0)
    crc = 0
    total_len = 0
    for chunk in chunks:
        crc = crc32(chunk, crc)
        total_len += len(chunk)
        zbytes = compress.compress(chunk)
        if zbytes:
            result.append(zbytes)
    result.append(compress.flush())
    # size may exceed 2GB, or even 4GB
    result.append(struct.pack("<LL", LOWU32(crc), LOWU32(total_len)))
    return ''.join(result)


class GzipFile(gzip.GzipFile):
    """Knit tuned version of GzipFile.

    This is based on the following lsprof stats:
    python 2.4 stock GzipFile write:
    58971      0   5644.3090   2721.4730   gzip:193(write)
    +58971     0   1159.5530   1159.5530   +<built-in method compress>
    +176913    0    987.0320    987.0320   +<len>
    +58971     0    423.1450    423.1450   +<zlib.crc32>
    +58971     0    353.1060    353.1060   +<method 'write' of 'cStringIO.
                                            StringO' objects>
    tuned GzipFile write:
    58971      0   4477.2590   2103.1120   bzrlib.knit:1250(write)
    +58971     0   1297.7620   1297.7620   +<built-in method compress>
    +58971     0    406.2160    406.2160   +<zlib.crc32>
    +58971     0    341.9020    341.9020   +<method 'write' of 'cStringIO.
                                            StringO' objects>
    +58971     0    328.2670    328.2670   +<len>


    Yes, its only 1.6 seconds, but they add up.
    """

    def __init__(self, *args, **kwargs):
        symbol_versioning.warn(
            symbol_versioning.deprecated_in((2, 3, 0))
            % 'bzrlib.tuned_gzip.GzipFile',
            DeprecationWarning, stacklevel=2)
        gzip.GzipFile.__init__(self, *args, **kwargs)

    def _add_read_data(self, data):
        # 4169 calls in 183
        # temp var for len(data) and switch to +='s.
        # 4169 in 139
        len_data = len(data)
        self.crc = zlib.crc32(data, self.crc)
        self.extrabuf += data
        self.extrasize += len_data
        self.size += len_data

    def _write_gzip_header(self):
        """A tuned version of gzip._write_gzip_header

        We have some extra constrains that plain Gzip does not.
        1) We want to write the whole blob at once. rather than multiple
           calls to fileobj.write().
        2) We never have a filename
        3) We don't care about the time
        """
        self.fileobj.write(
           '\037\213'   # self.fileobj.write('\037\213')  # magic header
            '\010'      # self.fileobj.write('\010')      # compression method
                        # fname = self.filename[:-3]
                        # flags = 0
                        # if fname:
                        #     flags = FNAME
            '\x00'      # self.fileobj.write(chr(flags))
            '\0\0\0\0'  # write32u(self.fileobj, long(time.time()))
            '\002'      # self.fileobj.write('\002')
            '\377'      # self.fileobj.write('\377')
                        # if fname:
            ''          #     self.fileobj.write(fname + '\000')
            )

    def _read(self, size=1024):
        # various optimisations:
        # reduces lsprof count from 2500 to
        # 8337 calls in 1272, 365 internal
        if self.fileobj is None:
            raise EOFError, "Reached EOF"

        if self._new_member:
            # If the _new_member flag is set, we have to
            # jump to the next member, if there is one.
            #
            # First, check if we're at the end of the file;
            # if so, it's time to stop; no more members to read.
            next_header_bytes = self.fileobj.read(10)
            if next_header_bytes == '':
                raise EOFError, "Reached EOF"

            self._init_read()
            self._read_gzip_header(next_header_bytes)
            self.decompress = zlib.decompressobj(-zlib.MAX_WBITS)
            self._new_member = False

        # Read a chunk of data from the file
        buf = self.fileobj.read(size)

        # If the EOF has been reached, flush the decompression object
        # and mark this object as finished.

        if buf == "":
            self._add_read_data(self.decompress.flush())
            if len(self.decompress.unused_data) < 8:
                raise AssertionError("what does flush do?")
            self._gzip_tail = self.decompress.unused_data[0:8]
            self._read_eof()
            # tell the driving read() call we have stuffed all the data
            # in self.extrabuf
            raise EOFError, 'Reached EOF'

        self._add_read_data(self.decompress.decompress(buf))

        if self.decompress.unused_data != "":
            # Ending case: we've come to the end of a member in the file,
            # so seek back to the start of the data for the next member which
            # is the length of the decompress objects unused data - the first
            # 8 bytes for the end crc and size records.
            #
            # so seek back to the start of the unused data, finish up
            # this member, and read a new gzip header.
            # (The number of bytes to seek back is the length of the unused
            # data, minus 8 because those 8 bytes are part of this member.
            seek_length = len (self.decompress.unused_data) - 8
            if seek_length > 0:
                # we read too much data
                self.fileobj.seek(-seek_length, 1)
                self._gzip_tail = self.decompress.unused_data[0:8]
            elif seek_length < 0:
                # we haven't read enough to check the checksum.
                if not (-8 < seek_length):
                    raise AssertionError("too great a seek")
                buf = self.fileobj.read(-seek_length)
                self._gzip_tail = self.decompress.unused_data + buf
            else:
                self._gzip_tail = self.decompress.unused_data

            # Check the CRC and file size, and set the flag so we read
            # a new member on the next call
            self._read_eof()
            self._new_member = True

    def _read_eof(self):
        """tuned to reduce function calls and eliminate file seeking:
        pass 1:
        reduces lsprof count from 800 to 288
        4168 in 296
        avoid U32 call by using struct format L
        4168 in 200
        """
        # We've read to the end of the file, so we should have 8 bytes of
        # unused data in the decompressor. If we don't, there is a corrupt file.
        # We use these 8 bytes to calculate the CRC and the recorded file size.
        # We then check the that the computed CRC and size of the
        # uncompressed data matches the stored values.  Note that the size
        # stored is the true file size mod 2**32.
        if not (len(self._gzip_tail) == 8):
            raise AssertionError("gzip trailer is incorrect length.")
        crc32, isize = struct.unpack("<LL", self._gzip_tail)
        # note that isize is unsigned - it can exceed 2GB
        if crc32 != U32(self.crc):
            raise IOError, "CRC check failed %d %d" % (crc32, U32(self.crc))
        elif isize != LOWU32(self.size):
            raise IOError, "Incorrect length of data produced"

    def _read_gzip_header(self, bytes=None):
        """Supply bytes if the minimum header size is already read.

        :param bytes: 10 bytes of header data.
        """
        """starting cost: 300 in 3998
        15998 reads from 3998 calls
        final cost 168
        """
        if bytes is None:
            bytes = self.fileobj.read(10)
        magic = bytes[0:2]
        if magic != '\037\213':
            raise IOError, 'Not a gzipped file'
        method = ord(bytes[2:3])
        if method != 8:
            raise IOError, 'Unknown compression method'
        flag = ord(bytes[3:4])
        # modtime = self.fileobj.read(4) (bytes [4:8])
        # extraflag = self.fileobj.read(1) (bytes[8:9])
        # os = self.fileobj.read(1) (bytes[9:10])
        # self.fileobj.read(6)

        if flag & FEXTRA:
            # Read & discard the extra field, if present
            xlen = ord(self.fileobj.read(1))
            xlen = xlen + 256*ord(self.fileobj.read(1))
            self.fileobj.read(xlen)
        if flag & FNAME:
            # Read and discard a null-terminated string containing the filename
            while True:
                s = self.fileobj.read(1)
                if not s or s=='\000':
                    break
        if flag & FCOMMENT:
            # Read and discard a null-terminated string containing a comment
            while True:
                s = self.fileobj.read(1)
                if not s or s=='\000':
                    break
        if flag & FHCRC:
            self.fileobj.read(2)     # Read & discard the 16-bit header CRC

    def readline(self, size=-1):
        """Tuned to remove buffer length calls in _unread and...

        also removes multiple len(c) calls, inlines _unread,
        total savings - lsprof 5800 to 5300
        phase 2:
        4168 calls in 2233
        8176 calls to read() in 1684
        changing the min chunk size to 200 halved all the cache misses
        leading to a drop to:
        4168 calls in 1977
        4168 call to read() in 1646
        - i.e. just reduced the function call overhead. May be worth
          keeping.
        """
        if size < 0: size = sys.maxint
        bufs = []
        readsize = min(200, size)    # Read from the file in small chunks
        while True:
            if size == 0:
                return "".join(bufs) # Return resulting line

            # c is the chunk
            c = self.read(readsize)
            # number of bytes read
            len_c = len(c)
            i = c.find('\n')
            if size is not None:
                # We set i=size to break out of the loop under two
                # conditions: 1) there's no newline, and the chunk is
                # larger than size, or 2) there is a newline, but the
                # resulting line would be longer than 'size'.
                if i==-1 and len_c > size: i=size-1
                elif size <= i: i = size -1

            if i >= 0 or c == '':
                # if i>= 0 we have a newline or have triggered the above
                # if size is not None condition.
                # if c == '' its EOF.
                bufs.append(c[:i+1])    # Add portion of last chunk
                # -- inlined self._unread --
                ## self._unread(c[i+1:], len_c - i)   # Push back rest of chunk
                self.extrabuf = c[i+1:] + self.extrabuf
                self.extrasize = len_c - i + self.extrasize
                self.offset -= len_c - i
                # -- end inlined self._unread --
                return ''.join(bufs)    # Return resulting line

            # Append chunk to list, decrease 'size',
            bufs.append(c)
            size = size - len_c
            readsize = min(size, readsize * 2)

    def readlines(self, sizehint=0):
        # optimise to avoid all the buffer manipulation
        # lsprof changed from:
        # 4168 calls in 5472 with 32000 calls to readline()
        # to :
        # 4168 calls in 417.
        # Negative numbers result in reading all the lines

        # python's gzip routine uses sizehint. This is a more efficient way
        # than python uses to honor it. But it is even more efficient to
        # just read the entire thing and use cStringIO to split into lines.
        # if sizehint <= 0:
        #     sizehint = -1
        # content = self.read(sizehint)
        # return bzrlib.osutils.split_lines(content)
        content = StringIO(self.read(-1))
        return content.readlines()

    def _unread(self, buf, len_buf=None):
        """tuned to remove unneeded len calls.

        because this is such an inner routine in readline, and readline is
        in many inner loops, this has been inlined into readline().

        The len_buf parameter combined with the reduction in len calls dropped
        the lsprof ms count for this routine on my test data from 800 to 200 -
        a 75% saving.
        """
        if len_buf is None:
            len_buf = len(buf)
        self.extrabuf = buf + self.extrabuf
        self.extrasize = len_buf + self.extrasize
        self.offset -= len_buf

    def write(self, data):
        if self.mode != gzip.WRITE:
            import errno
            raise IOError(errno.EBADF, "write() on read-only GzipFile object")

        if self.fileobj is None:
            raise ValueError, "write() on closed GzipFile object"
        data_len = len(data)
        if data_len > 0:
            self.size = self.size + data_len
            self.crc = zlib.crc32(data, self.crc)
            self.fileobj.write( self.compress.compress(data) )
            self.offset += data_len

    def writelines(self, lines):
        # profiling indicated a significant overhead
        # calling write for each line.
        # this batch call is a lot faster :).
        # (4 seconds to 1 seconds for the sample upgrades I was testing).
        self.write(''.join(lines))

    if sys.version_info > (2, 7):
        # As of Python 2.7 the crc32 must be positive when close is called
        def close(self):
            if self.fileobj is None:
                return
            if self.mode == gzip.WRITE:
                self.crc &= 0xFFFFFFFFL
            gzip.GzipFile.close(self)