Issue #5863: Rewrite BZ2File in pure Python, and allow it to accept

file-like objects using a new `fileobj` constructor argument.  Patch by
Nadeem Vawda.

1 files changed, 392 insertions, 0 deletions

diff --git a/Lib/bz2.py b/Lib/bz2.py
new file mode 100644
index 0000000..667fffd
--- /dev/null
+++ b/Lib/bz2.py
@@ -0,0 +1,392 @@
+"""Interface to the libbzip2 compression library.
+
+This module provides a file interface, classes for incremental
+(de)compression, and functions for one-shot (de)compression.
+"""
+
+__all__ = ["BZ2File", "BZ2Compressor", "BZ2Decompressor", "compress",
+           "decompress"]
+
+__author__ = "Nadeem Vawda <nadeem.vawda@gmail.com>"
+
+import io
+import threading
+import warnings
+
+from _bz2 import BZ2Compressor, BZ2Decompressor
+
+
+_MODE_CLOSED   = 0
+_MODE_READ     = 1
+_MODE_READ_EOF = 2
+_MODE_WRITE    = 3
+
+_BUFFER_SIZE = 8192
+
+
+class BZ2File(io.BufferedIOBase):
+
+    """A file object providing transparent bzip2 (de)compression.
+
+    A BZ2File can act as a wrapper for an existing file object, or refer
+    directly to a named file on disk.
+
+    Note that BZ2File provides a *binary* file interface - data read is
+    returned as bytes, and data to be written should be given as bytes.
+    """
+
+    def __init__(self, filename=None, mode="r", buffering=None,
+                 compresslevel=9, fileobj=None):
+        """Open a bzip2-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), or 'w' for writing.
+
+        buffering is ignored. Its use is deprecated.
+
+        If mode is 'w', compresslevel can be a number between 1 and 9
+        specifying the level of compression: 1 produces the least
+        compression, and 9 (default) produces the most compression.
+        """
+        # This lock must be recursive, so that BufferedIOBase's
+        # readline(), readlines() and writelines() don't deadlock.
+        self._lock = threading.RLock()
+        self._fp = None
+        self._closefp = False
+        self._mode = _MODE_CLOSED
+        self._pos = 0
+        self._size = -1
+
+        if buffering is not None:
+            warnings.warn("Use of 'buffering' argument is deprecated",
+                          DeprecationWarning)
+
+        if not (1 <= compresslevel <= 9):
+            raise ValueError("compresslevel must be between 1 and 9")
+
+        if mode in ("", "r", "rb"):
+            mode = "rb"
+            mode_code = _MODE_READ
+            self._decompressor = BZ2Decompressor()
+            self._buffer = None
+        elif mode in ("w", "wb"):
+            mode = "wb"
+            mode_code = _MODE_WRITE
+            self._compressor = BZ2Compressor()
+        else:
+            raise ValueError("Invalid mode: {!r}".format(mode))
+
+        if filename is not None and fileobj is None:
+            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.
+        """
+        with self._lock:
+            if self._mode == _MODE_CLOSED:
+                return
+            try:
+                if self._mode in (_MODE_READ, _MODE_READ_EOF):
+                    self._decompressor = 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
+                    self._buffer = None
+
+    @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."""
+        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."""
+        return self._mode in (_MODE_READ, _MODE_READ_EOF)
+
+    def writable(self):
+        """Return whether the file was opened for writing."""
+        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():
+            self._check_not_closed()
+            raise io.UnsupportedOperation("File not open for reading")
+
+    def _check_can_write(self):
+        if not self.writable():
+            self._check_not_closed()
+            raise io.UnsupportedOperation("File not open for writing")
+
+    def _check_can_seek(self):
+        if not self.seekable():
+            self._check_not_closed()
+            raise io.UnsupportedOperation("Seeking is only supported "
+                                          "on files opening 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.eof:
+            self._mode = _MODE_READ_EOF
+            self._size = self._pos
+            return False
+        rawblock = self._fp.read(_BUFFER_SIZE)
+        if not rawblock:
+            raise EOFError("Compressed file ended before the "
+                           "end-of-stream marker was reached")
+        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, n=0):
+        """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.
+        """
+        with self._lock:
+            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.
+        """
+        with self._lock:
+            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.
+        """
+        with self._lock:
+            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 readinto(self, b):
+        """Read up to len(b) bytes into b.
+        
+        Returns the number of bytes read (0 for EOF).
+        """
+        with self._lock:
+            return io.BufferedIOBase.readinto(self, b)
+
+    def readline(self, size=-1):
+        """Read a line of uncompressed bytes from the file.
+
+        The terminating newline (if present) is retained. If size is
+        non-negative, no more than size bytes will be read (in which
+        case the line may be incomplete). Returns b'' if already at EOF.
+        """
+        if not hasattr(size, "__index__"):
+            raise TypeError("Integer argument expected")
+        size = size.__index__()
+        with self._lock:
+            return io.BufferedIOBase.readline(self, size)
+
+    def readlines(self, size=-1):
+        """Read a list of lines of uncompressed bytes from the file.
+
+        size can be specified to control the number of lines read: no
+        further lines will be read once the total size of the lines read
+        so far equals or exceeds size.
+        """
+        if not hasattr(size, "__index__"):
+            raise TypeError("Integer argument expected")
+        size = size.__index__()
+        with self._lock:
+            return io.BufferedIOBase.readlines(self, size)
+
+    def write(self, data):
+        """Write a byte string 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.
+        """
+        with self._lock:
+            self._check_can_write()
+            compressed = self._compressor.compress(data)
+            self._fp.write(compressed)
+            self._pos += len(data)
+            return len(data)
+
+    def writelines(self, seq):
+        """Write a sequence of byte strings to the file.
+
+        Returns the number of uncompressed bytes written.
+        seq can be any iterable yielding byte strings.
+
+        Line separators are not added between the written byte strings.
+        """
+        with self._lock:
+            return io.BufferedIOBase.writelines(self, seq)
+
+    # 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 = BZ2Decompressor()
+        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. 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, so depending on the parameters,
+        this operation may be extremely slow.
+        """
+        with self._lock:
+            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."""
+        with self._lock:
+            self._check_not_closed()
+            return self._pos
+
+
+def compress(data, compresslevel=9):
+    """Compress a block of data.
+
+    compresslevel, if given, must be a number between 1 and 9.
+
+    For incremental compression, use a BZ2Compressor object instead.
+    """
+    comp = BZ2Compressor(compresslevel)
+    return comp.compress(data) + comp.flush()
+
+
+def decompress(data):
+    """Decompress a block of data.
+
+    For incremental decompression, use a BZ2Decompressor object instead.
+    """
+    if len(data) == 0:
+        return b""
+    decomp = BZ2Decompressor()
+    result = decomp.decompress(data)
+    if not decomp.eof:
+        raise ValueError("Compressed data ended before the "
+                         "end-of-stream marker was reached")
+    return result