Issue #6715: Add module for compression using the LZMA algorithm.

1 files changed, 398 insertions, 0 deletions

diff --git a/Lib/lzma.py b/Lib/lzma.py
new file mode 100644
index 0000000000..780c666eeb
--- /dev/null
+++ b/Lib/lzma.py
@@ -0,0 +1,398 @@
+"""Interface to the liblzma compression library.
+
+This module provides a class for reading and writing compressed files,
+classes for incremental (de)compression, and convenience functions for
+one-shot (de)compression.
+
+These classes and functions support both the XZ and legacy LZMA
+container formats, as well as raw compressed data streams.
+"""
+
+__all__ = [
+    "CHECK_NONE", "CHECK_CRC32", "CHECK_CRC64", "CHECK_SHA256",
+    "CHECK_ID_MAX", "CHECK_UNKNOWN",
+    "FILTER_LZMA1", "FILTER_LZMA2", "FILTER_DELTA", "FILTER_X86", "FILTER_IA64",
+    "FILTER_ARM", "FILTER_ARMTHUMB", "FILTER_POWERPC", "FILTER_SPARC",
+    "FORMAT_AUTO", "FORMAT_XZ", "FORMAT_ALONE", "FORMAT_RAW",
+    "MF_HC3", "MF_HC4", "MF_BT2", "MF_BT3", "MF_BT4",
+    "MODE_FAST", "MODE_NORMAL", "PRESET_DEFAULT", "PRESET_EXTREME",
+
+    "LZMACompressor", "LZMADecompressor", "LZMAFile", "LZMAError",
+    "compress", "decompress", "check_is_supported",
+]
+
+import io
+from _lzma import *
+
+
+_MODE_CLOSED   = 0
+_MODE_READ     = 1
+_MODE_READ_EOF = 2
+_MODE_WRITE    = 3
+
+_BUFFER_SIZE = 8192
+
+
+class LZMAFile(io.BufferedIOBase):
+
+    """A file object providing transparent LZMA (de)compression.
+
+    An LZMAFile can act as a wrapper for an existing file object, or
+    refer directly to a named file on disk.
+
+    Note that LZMAFile provides a *binary* file interface - data read
+    is returned as bytes, and data to be written must be given as bytes.
+    """
+
+    def __init__(self, filename=None, mode="r", *,
+                 fileobj=None, format=None, check=-1,
+                 preset=None, filters=None):
+        """Open an LZMA-compressed file.
+
+        If filename is given, open the named file. Otherwise, operate on
+        the file object given by fileobj. Exactly one of these two
+        parameters should be provided.
+
+        mode can be "r" for reading (default), "w" for (over)writing, or
+        "a" for appending.
+
+        format specifies the container format to use for the file.
+        If mode is "r", this defaults to FORMAT_AUTO. Otherwise, the
+        default is FORMAT_XZ.
+
+        check specifies the integrity check to use. This argument can
+        only be used when opening a file for writing. For FORMAT_XZ,
+        the default is CHECK_CRC64. FORMAT_ALONE and FORMAT_RAW do not
+        support integrity checks - for these formats, check must be
+        omitted, or be CHECK_NONE.
+
+        When opening a file for reading, the *preset* argument is not
+        meaningful, and should be omitted. The *filters* argument should
+        also be omitted, except when format is FORMAT_RAW (in which case
+        it is required).
+
+        When opening a file for writing, the settings used by the
+        compressor can be specified either as a preset compression
+        level (with the *preset* argument), or in detail as a custom
+        filter chain (with the *filters* argument). For FORMAT_XZ and
+        FORMAT_ALONE, the default is to use the PRESET_DEFAULT preset
+        level. For FORMAT_RAW, the caller must always specify a filter
+        chain; the raw compressor does not support preset compression
+        levels.
+
+        preset (if provided) should be an integer in the range 0-9,
+        optionally OR-ed with the constant PRESET_EXTREME.
+
+        filters (if provided) should be a sequence of dicts. Each dict
+        should have an entry for "id" indicating ID of the filter, plus
+        additional entries for options to the filter.
+        """
+        self._fp = None
+        self._closefp = False
+        self._mode = _MODE_CLOSED
+        self._pos = 0
+        self._size = -1
+
+        if mode == "r":
+            if check != -1:
+                raise ValueError("Cannot specify an integrity check "
+                                 "when opening a file for reading")
+            if preset is not None:
+                raise ValueError("Cannot specify a preset compression "
+                                 "level when opening a file for reading")
+            if format is None:
+                format = FORMAT_AUTO
+            mode_code = _MODE_READ
+            # Save the args to pass to the LZMADecompressor initializer.
+            # If the file contains multiple compressed streams, each
+            # stream will need a separate decompressor object.
+            self._init_args = {"format":format, "filters":filters}
+            self._decompressor = LZMADecompressor(**self._init_args)
+            self._buffer = None
+        elif mode in ("w", "a"):
+            if format is None:
+                format = FORMAT_XZ
+            mode_code = _MODE_WRITE
+            self._compressor = LZMACompressor(format=format, check=check,
+                                              preset=preset, filters=filters)
+        else:
+            raise ValueError("Invalid mode: {!r}".format(mode))
+
+        if filename is not None and fileobj is None:
+            mode += "b"
+            self._fp = open(filename, mode)
+            self._closefp = True
+            self._mode = mode_code
+        elif fileobj is not None and filename is None:
+            self._fp = fileobj
+            self._mode = mode_code
+        else:
+            raise ValueError("Must give exactly one of filename and fileobj")
+
+    def close(self):
+        """Flush and close the file.
+
+        May be called more than once without error. Once the file is
+        closed, any other operation on it will raise a ValueError.
+        """
+        if self._mode == _MODE_CLOSED:
+            return
+        try:
+            if self._mode in (_MODE_READ, _MODE_READ_EOF):
+                self._decompressor = None
+                self._buffer = None
+            elif self._mode == _MODE_WRITE:
+                self._fp.write(self._compressor.flush())
+                self._compressor = None
+        finally:
+            try:
+                if self._closefp:
+                    self._fp.close()
+            finally:
+                self._fp = None
+                self._closefp = False
+                self._mode = _MODE_CLOSED
+
+    @property
+    def closed(self):
+        """True if this file is closed."""
+        return self._mode == _MODE_CLOSED
+
+    def fileno(self):
+        """Return the file descriptor for the underlying file."""
+        self._check_not_closed()
+        return self._fp.fileno()
+
+    def seekable(self):
+        """Return whether the file supports seeking."""
+        return self.readable()
+
+    def readable(self):
+        """Return whether the file was opened for reading."""
+        self._check_not_closed()
+        return self._mode in (_MODE_READ, _MODE_READ_EOF)
+
+    def writable(self):
+        """Return whether the file was opened for writing."""
+        self._check_not_closed()
+        return self._mode == _MODE_WRITE
+
+    # Mode-checking helper functions.
+
+    def _check_not_closed(self):
+        if self.closed:
+            raise ValueError("I/O operation on closed file")
+
+    def _check_can_read(self):
+        if not self.readable():
+            raise io.UnsupportedOperation("File not open for reading")
+
+    def _check_can_write(self):
+        if not self.writable():
+            raise io.UnsupportedOperation("File not open for writing")
+
+    def _check_can_seek(self):
+        if not self.seekable():
+            raise io.UnsupportedOperation("Seeking is only supported "
+                                          "on files open for reading")
+
+    # Fill the readahead buffer if it is empty. Returns False on EOF.
+    def _fill_buffer(self):
+        if self._buffer:
+            return True
+
+        if self._decompressor.unused_data:
+            rawblock = self._decompressor.unused_data
+        else:
+            rawblock = self._fp.read(_BUFFER_SIZE)
+
+        if not rawblock:
+            if self._decompressor.eof:
+                self._mode = _MODE_READ_EOF
+                self._size = self._pos
+                return False
+            else:
+                raise EOFError("Compressed file ended before the "
+                               "end-of-stream marker was reached")
+
+        # Continue to next stream.
+        if self._decompressor.eof:
+            self._decompressor = LZMADecompressor(**self._init_args)
+
+        self._buffer = self._decompressor.decompress(rawblock)
+        return True
+
+    # Read data until EOF.
+    # If return_data is false, consume the data without returning it.
+    def _read_all(self, return_data=True):
+        blocks = []
+        while self._fill_buffer():
+            if return_data:
+                blocks.append(self._buffer)
+            self._pos += len(self._buffer)
+            self._buffer = None
+        if return_data:
+            return b"".join(blocks)
+
+    # Read a block of up to n bytes.
+    # If return_data is false, consume the data without returning it.
+    def _read_block(self, n, return_data=True):
+        blocks = []
+        while n > 0 and self._fill_buffer():
+            if n < len(self._buffer):
+                data = self._buffer[:n]
+                self._buffer = self._buffer[n:]
+            else:
+                data = self._buffer
+                self._buffer = None
+            if return_data:
+                blocks.append(data)
+            self._pos += len(data)
+            n -= len(data)
+        if return_data:
+            return b"".join(blocks)
+
+    def peek(self, size=-1):
+        """Return buffered data without advancing the file position.
+
+        Always returns at least one byte of data, unless at EOF.
+        The exact number of bytes returned is unspecified.
+        """
+        self._check_can_read()
+        if self._mode == _MODE_READ_EOF or not self._fill_buffer():
+            return b""
+        return self._buffer
+
+    def read(self, size=-1):
+        """Read up to size uncompressed bytes from the file.
+
+        If size is negative or omitted, read until EOF is reached.
+        Returns b"" if the file is already at EOF.
+        """
+        self._check_can_read()
+        if self._mode == _MODE_READ_EOF or size == 0:
+            return b""
+        elif size < 0:
+            return self._read_all()
+        else:
+            return self._read_block(size)
+
+    def read1(self, size=-1):
+        """Read up to size uncompressed bytes with at most one read
+        from the underlying stream.
+
+        Returns b"" if the file is at EOF.
+        """
+        self._check_can_read()
+        if (size == 0 or self._mode == _MODE_READ_EOF or
+            not self._fill_buffer()):
+            return b""
+        if 0 < size < len(self._buffer):
+            data = self._buffer[:size]
+            self._buffer = self._buffer[size:]
+        else:
+            data = self._buffer
+            self._buffer = None
+        self._pos += len(data)
+        return data
+
+    def write(self, data):
+        """Write a bytes object to the file.
+
+        Returns the number of uncompressed bytes written, which is
+        always len(data). Note that due to buffering, the file on disk
+        may not reflect the data written until close() is called.
+        """
+        self._check_can_write()
+        compressed = self._compressor.compress(data)
+        self._fp.write(compressed)
+        self._pos += len(data)
+        return len(data)
+
+    # Rewind the file to the beginning of the data stream.
+    def _rewind(self):
+        self._fp.seek(0, 0)
+        self._mode = _MODE_READ
+        self._pos = 0
+        self._decompressor = LZMADecompressor(**self._init_args)
+        self._buffer = None
+
+    def seek(self, offset, whence=0):
+        """Change the file position.
+
+        The new position is specified by offset, relative to the
+        position indicated by whence. Possible values for whence are:
+
+            0: start of stream (default): offset must not be negative
+            1: current stream position
+            2: end of stream; offset must not be positive
+
+        Returns the new file position.
+
+        Note that seeking is emulated, sp depending on the parameters,
+        this operation may be extremely slow.
+        """
+        self._check_can_seek()
+
+        # Recalculate offset as an absolute file position.
+        if whence == 0:
+            pass
+        elif whence == 1:
+            offset = self._pos + offset
+        elif whence == 2:
+            # Seeking relative to EOF - we need to know the file's size.
+            if self._size < 0:
+                self._read_all(return_data=False)
+            offset = self._size + offset
+        else:
+            raise ValueError("Invalid value for whence: {}".format(whence))
+
+        # Make it so that offset is the number of bytes to skip forward.
+        if offset < self._pos:
+            self._rewind()
+        else:
+            offset -= self._pos
+
+        # Read and discard data until we reach the desired position.
+        if self._mode != _MODE_READ_EOF:
+            self._read_block(offset, return_data=False)
+
+        return self._pos
+
+    def tell(self):
+        """Return the current file position."""
+        self._check_not_closed()
+        return self._pos
+
+
+def compress(data, format=FORMAT_XZ, check=-1, preset=None, filters=None):
+    """Compress a block of data.
+
+    Refer to LZMACompressor's docstring for a description of the
+    optional arguments *format*, *check*, *preset* and *filters*.
+
+    For incremental compression, use an LZMACompressor object instead.
+    """
+    comp = LZMACompressor(format, check, preset, filters)
+    return comp.compress(data) + comp.flush()
+
+
+def decompress(data, format=FORMAT_AUTO, memlimit=None, filters=None):
+    """Decompress a block of data.
+
+    Refer to LZMADecompressor's docstring for a description of the
+    optional arguments *format*, *check* and *filters*.
+
+    For incremental decompression, use a LZMADecompressor object instead.
+    """
+    results = []
+    while True:
+        decomp = LZMADecompressor(format, memlimit, filters)
+        results.append(decomp.decompress(data))
+        if not decomp.eof:
+            raise LZMAError("Compressed data ended before the "
+                            "end-of-stream marker was reached")
+        if not decomp.unused_data:
+            return b"".join(results)
+        # There is unused data left over. Proceed to next stream.
+        data = decomp.unused_data