_io.py

"""
Python implementation of the io module.
"""

class _UnsupportedModuleWrapper:
    def __init__(self, module):
        self.__module = module
    def __getattr__(self, attr):
        raise RuntimeError(f"the {self.__module!r} module isn't available")
    def __bool__(self):
        return False

import sys
try:
    if 'posix' in sys.builtin_module_names:
        import posix as os
        linesep = '\n'
    else:
        import nt as os
        linesep = '\r\n'
except ImportError:
    os = _UnsupportedModuleWrapper("_os")
import codecs
import errno
import stat
# Import _thread instead of threading to reduce startup cost
try:
    from _thread import allocate_lock as Lock
except ImportError:
    from _dummy_thread import allocate_lock as Lock
if sys.platform in {'win32', 'cygwin'}:
    from msvcrt import setmode as _setmode
else:
    _setmode = None

del _UnsupportedModuleWrapper


SEEK_SET = 0
SEEK_CUR = 1
SEEK_END = 2

valid_seek_flags = {0, 1, 2}  # Hardwired values
if os and hasattr(os, 'SEEK_HOLE') :
    valid_seek_flags.add(os.SEEK_HOLE)
    valid_seek_flags.add(os.SEEK_DATA)

# open() uses st_blksize whenever we can
DEFAULT_BUFFER_SIZE = 8 * 1024  # bytes

# Rebind for compatibility
BlockingIOError = BlockingIOError


def open(file, mode="r", buffering=-1, encoding=None, errors=None,
         newline=None, closefd=True, opener=None):

    r"""Open file and return a stream.  Raise OSError upon failure.

    file is either a text or byte string giving the name (and the path
    if the file isn't in the current working directory) of the file to
    be opened or an integer file descriptor of the file to be
    wrapped. (If a file descriptor is given, it is closed when the
    returned I/O object is closed, unless closefd is set to False.)

    mode is an optional string that specifies the mode in which the file is
    opened. It defaults to 'r' which means open for reading in text mode. Other
    common values are 'w' for writing (truncating the file if it already
    exists), 'x' for exclusive creation of a new file, and 'a' for appending
    (which on some Unix systems, means that all writes append to the end of the
    file regardless of the current seek position). In text mode, if encoding is
    not specified the encoding used is platform dependent. (For reading and
    writing raw bytes use binary mode and leave encoding unspecified.) The
    available modes are:

    ========= ===============================================================
    Character Meaning
    --------- ---------------------------------------------------------------
    'r'       open for reading (default)
    'w'       open for writing, truncating the file first
    'x'       create a new file and open it for writing
    'a'       open for writing, appending to the end of the file if it exists
    'b'       binary mode
    't'       text mode (default)
    '+'       open a disk file for updating (reading and writing)
    'U'       universal newline mode (deprecated)
    ========= ===============================================================

    The default mode is 'rt' (open for reading text). For binary random
    access, the mode 'w+b' opens and truncates the file to 0 bytes, while
    'r+b' opens the file without truncation. The 'x' mode implies 'w' and
    raises an `FileExistsError` if the file already exists.

    Python distinguishes between files opened in binary and text modes,
    even when the underlying operating system doesn't. Files opened in
    binary mode (appending 'b' to the mode argument) return contents as
    bytes objects without any decoding. In text mode (the default, or when
    't' is appended to the mode argument), the contents of the file are
    returned as strings, the bytes having been first decoded using a
    platform-dependent encoding or using the specified encoding if given.

    'U' mode is deprecated and will raise an exception in future versions
    of Python.  It has no effect in Python 3.  Use newline to control
    universal newlines mode.

    buffering is an optional integer used to set the buffering policy.
    Pass 0 to switch buffering off (only allowed in binary mode), 1 to select
    line buffering (only usable in text mode), and an integer > 1 to indicate
    the size of a fixed-size chunk buffer.  When no buffering argument is
    given, the default buffering policy works as follows:

    * Binary files are buffered in fixed-size chunks; the size of the buffer
      is chosen using a heuristic trying to determine the underlying device's
      "block size" and falling back on `io.DEFAULT_BUFFER_SIZE`.
      On many systems, the buffer will typically be 4096 or 8192 bytes long.

    * "Interactive" text files (files for which isatty() returns True)
      use line buffering.  Other text files use the policy described above
      for binary files.

    encoding is the str name of the encoding used to decode or encode the
    file. This should only be used in text mode. The default encoding is
    platform dependent, but any encoding supported by Python can be
    passed.  See the codecs module for the list of supported encodings.

    errors is an optional string that specifies how encoding errors are to
    be handled---this argument should not be used in binary mode. Pass
    'strict' to raise a ValueError exception if there is an encoding error
    (the default of None has the same effect), or pass 'ignore' to ignore
    errors. (Note that ignoring encoding errors can lead to data loss.)
    See the documentation for codecs.register for a list of the permitted
    encoding error strings.

    newline is a string controlling how universal newlines works (it only
    applies to text mode). It can be None, '', '\n', '\r', and '\r\n'.  It works
    as follows:

    * On input, if newline is None, universal newlines mode is
      enabled. Lines in the input can end in '\n', '\r', or '\r\n', and
      these are translated into '\n' before being returned to the
      caller. If it is '', universal newline mode is enabled, but line
      endings are returned to the caller untranslated. If it has any of
      the other legal values, input lines are only terminated by the given
      string, and the line ending is returned to the caller untranslated.

    * On output, if newline is None, any '\n' characters written are
      translated to the system default line separator, os.linesep. If
      newline is '', no translation takes place. If newline is any of the
      other legal values, any '\n' characters written are translated to
      the given string.

    closedfd is a bool. If closefd is False, the underlying file descriptor will
    be kept open when the file is closed. This does not work when a file name is
    given and must be True in that case.

    The newly created file is non-inheritable.

    A custom opener can be used by passing a callable as *opener*. The
    underlying file descriptor for the file object is then obtained by calling
    *opener* with (*file*, *flags*). *opener* must return an open file
    descriptor (passing os.open as *opener* results in functionality similar to
    passing None).

    open() returns a file object whose type depends on the mode, and
    through which the standard file operations such as reading and writing
    are performed. When open() is used to open a file in a text mode ('w',
    'r', 'wt', 'rt', etc.), it returns a TextIOWrapper. When used to open
    a file in a binary mode, the returned class varies: in read binary
    mode, it returns a BufferedReader; in write binary and append binary
    modes, it returns a BufferedWriter, and in read/write mode, it returns
    a BufferedRandom.

    It is also possible to use a string or bytearray as a file for both
    reading and writing. For strings StringIO can be used like a file
    opened in a text mode, and for bytes a BytesIO can be used like a file
    opened in a binary mode.
    """
    if not isinstance(file, int):
        file = os.fspath(file)
    if not isinstance(file, (str, bytes, int)):
        raise TypeError("invalid file: %r" % file)
    if not isinstance(mode, str):
        raise TypeError("invalid mode: %r" % mode)
    if not isinstance(buffering, int):
        raise TypeError("invalid buffering: %r" % buffering)
    if encoding is not None and not isinstance(encoding, str):
        raise TypeError("invalid encoding: %r" % encoding)
    if errors is not None and not isinstance(errors, str):
        raise TypeError("invalid errors: %r" % errors)
    modes = set(mode)
    if modes - set("axrwb+tU") or len(mode) > len(modes):
        raise ValueError("invalid mode: %r" % mode)
    creating = "x" in modes
    reading = "r" in modes
    writing = "w" in modes
    appending = "a" in modes
    updating = "+" in modes
    text = "t" in modes
    binary = "b" in modes
    if "U" in modes:
        if creating or writing or appending or updating:
            raise ValueError("mode U cannot be combined with 'x', 'w', 'a', or '+'")
        import warnings
        warnings.warn("'U' mode is deprecated",
                      DeprecationWarning, 2)
        reading = True
    if text and binary:
        raise ValueError("can't have text and binary mode at once")
    if creating + reading + writing + appending > 1:
        raise ValueError("can't have read/write/append mode at once")
    if not (creating or reading or writing or appending):
        raise ValueError("must have exactly one of read/write/append mode")
    if binary and encoding is not None:
        raise ValueError("binary mode doesn't take an encoding argument")
    if binary and errors is not None:
        raise ValueError("binary mode doesn't take an errors argument")
    if binary and newline is not None:
        raise ValueError("binary mode doesn't take a newline argument")
    raw = FileIO(file,
                 (creating and "x" or "") +
                 (reading and "r" or "") +
                 (writing and "w" or "") +
                 (appending and "a" or "") +
                 (updating and "+" or ""),
                 closefd, opener=opener)
    result = raw
    try:
        line_buffering = False
        if buffering == 1 or buffering < 0 and raw.isatty():
            buffering = -1
            line_buffering = True
        if buffering < 0:
            buffering = DEFAULT_BUFFER_SIZE
            try:
                bs = os.fstat(raw.fileno()).st_blksize
            except (OSError, AttributeError):
                pass
            else:
                if bs > 1:
                    buffering = bs
        if buffering < 0:
            raise ValueError("invalid buffering size")
        if buffering == 0:
            if binary:
                return result
            raise ValueError("can't have unbuffered text I/O")
        if updating:
            buffer = BufferedRandom(raw, buffering)
        elif creating or writing or appending:
            buffer = BufferedWriter(raw, buffering)
        elif reading:
            buffer = BufferedReader(raw, buffering)
        else:
            raise ValueError("unknown mode: %r" % mode)
        result = buffer
        if binary:
            return result
        text = TextIOWrapper(buffer, encoding, errors, newline, line_buffering)
        result = text
        text.mode = mode
        return result
    except:
        result.close()
        raise


def open_code(path):
    """Opens the provided file with mode ``'rb'``. This function
    should be used when the intent is to treat the contents as
    executable code.

    ``path`` should be an absolute path.

    When supported by the runtime, this function can be hooked
    in order to allow embedders more control over code files.
    This functionality is not supported on the current runtime.
    """
    # XXX RustPython TODO: hooks?
    return open(path, "rb")


class DocDescriptor:
    """Helper for builtins.open.__doc__
    """
    def __get__(self, obj, typ):
        return (
            "open(file, mode='r', buffering=-1, encoding=None, "
                 "errors=None, newline=None, closefd=True)\n\n" +
            open.__doc__)

class OpenWrapper:
    """Wrapper for builtins.open

    Trick so that open won't become a bound method when stored
    as a class variable (as dbm.dumb does).

    See initstdio() in Python/pylifecycle.c.
    """
    __doc__ = DocDescriptor()

    def __new__(cls, *args, **kwargs):
        return open(*args, **kwargs)


class UnsupportedOperation(OSError, ValueError):
    pass


class _IOBase:

    """The abstract base class for all I/O classes, acting on streams of
    bytes. There is no public constructor.

    This class provides dummy implementations for many methods that
    derived classes can override selectively; the default implementations
    represent a file that cannot be read, written or seeked.

    Even though IOBase does not declare read, readinto, or write because
    their signatures will vary, implementations and clients should
    consider those methods part of the interface. Also, implementations
    may raise UnsupportedOperation when operations they do not support are
    called.

    The basic type used for binary data read from or written to a file is
    bytes. Other bytes-like objects are accepted as method arguments too. In
    some cases (such as readinto), a writable object is required. Text I/O
    classes work with str data.

    Note that calling any method (even inquiries) on a closed stream is
    undefined. Implementations may raise OSError in this case.

    IOBase (and its subclasses) support the iterator protocol, meaning
    that an IOBase object can be iterated over yielding the lines in a
    stream.

    IOBase also supports the :keyword:`with` statement. In this example,
    fp is closed after the suite of the with statement is complete:

    with open('spam.txt', 'r') as fp:
        fp.write('Spam and eggs!')
    """

    ### Internal ###

    def _unsupported(self, name):
        """Internal: raise an OSError exception for unsupported operations."""
        raise UnsupportedOperation("%s.%s() not supported" %
                                   (self.__class__.__name__, name))

    ### Positioning ###

    def seek(self, pos, whence=0):
        """Change stream position.

        Change the stream position to byte offset pos. Argument pos is
        interpreted relative to the position indicated by whence.  Values
        for whence are ints:

        * 0 -- start of stream (the default); offset should be zero or positive
        * 1 -- current stream position; offset may be negative
        * 2 -- end of stream; offset is usually negative
        Some operating systems / file systems could provide additional values.

        Return an int indicating the new absolute position.
        """
        self._unsupported("seek")

    def tell(self):
        """Return an int indicating the current stream position."""
        return self.seek(0, 1)

    def truncate(self, pos=None):
        """Truncate file to size bytes.

        Size defaults to the current IO position as reported by tell().  Return
        the new size.
        """
        self._unsupported("truncate")

    ### Flush and close ###

    def flush(self):
        """Flush write buffers, if applicable.

        This is not implemented for read-only and non-blocking streams.
        """
        self._checkClosed()
        # XXX Should this return the number of bytes written???

    __closed = False

    def close(self):
        """Flush and close the IO object.

        This method has no effect if the file is already closed.
        """
        if not self.__closed:
            try:
                self.flush()
            finally:
                self.__closed = True

    def __del__(self):
        """Destructor.  Calls close()."""
        # The try/except block is in case this is called at program
        # exit time, when it's possible that globals have already been
        # deleted, and then the close() call might fail.  Since
        # there's nothing we can do about such failures and they annoy
        # the end users, we suppress the traceback.
        try:
            self.close()
        except:
            pass

    ### Inquiries ###

    def seekable(self):
        """Return a bool indicating whether object supports random access.

        If False, seek(), tell() and truncate() will raise OSError.
        This method may need to do a test seek().
        """
        return False

    def _checkSeekable(self, msg=None):
        """Internal: raise UnsupportedOperation if file is not seekable
        """
        if not self.seekable():
            raise UnsupportedOperation("File or stream is not seekable."
                                       if msg is None else msg)

    def readable(self):
        """Return a bool indicating whether object was opened for reading.

        If False, read() will raise OSError.
        """
        return False

    def _checkReadable(self, msg=None):
        """Internal: raise UnsupportedOperation if file is not readable
        """
        if not self.readable():
            raise UnsupportedOperation("File or stream is not readable."
                                       if msg is None else msg)

    def writable(self):
        """Return a bool indicating whether object was opened for writing.

        If False, write() and truncate() will raise OSError.
        """
        return False

    def _checkWritable(self, msg=None):
        """Internal: raise UnsupportedOperation if file is not writable
        """
        if not self.writable():
            raise UnsupportedOperation("File or stream is not writable."
                                       if msg is None else msg)

    @property
    def closed(self):
        """closed: bool.  True iff the file has been closed.

        For backwards compatibility, this is a property, not a predicate.
        """
        return self.__closed

    def _checkClosed(self, msg=None):
        """Internal: raise a ValueError if file is closed
        """
        if self.closed:
            raise ValueError("I/O operation on closed file."
                             if msg is None else msg)

    ### Context manager ###

    def __enter__(self):  # That's a forward reference
        """Context management protocol.  Returns self (an instance of IOBase)."""
        self._checkClosed()
        return self

    def __exit__(self, *args):
        """Context management protocol.  Calls close()"""
        self.close()

    ### Lower-level APIs ###

    # XXX Should these be present even if unimplemented?

    def fileno(self):
        """Returns underlying file descriptor (an int) if one exists.

        An OSError is raised if the IO object does not use a file descriptor.
        """
        self._unsupported("fileno")

    def isatty(self):
        """Return a bool indicating whether this is an 'interactive' stream.

        Return False if it can't be determined.
        """
        self._checkClosed()
        return False

    ### Readline[s] and writelines ###

    def readline(self, size=-1):
        r"""Read and return a line of bytes from the stream.

        If size is specified, at most size bytes will be read.
        Size should be an int.

        The line terminator is always b'\n' for binary files; for text
        files, the newlines argument to open can be used to select the line
        terminator(s) recognized.
        """
        # For backwards compatibility, a (slowish) readline().
        if hasattr(self, "peek"):
            def nreadahead():
                readahead = self.peek(1)
                if not readahead:
                    return 1
                n = (readahead.find(b"\n") + 1) or len(readahead)
                if size >= 0:
                    n = min(n, size)
                return n
        else:
            def nreadahead():
                return 1
        if size is None:
            size = -1
        elif not isinstance(size, int):
            raise TypeError("size must be an integer")
        res = bytearray()
        while size < 0 or len(res) < size:
            b = self.read(nreadahead())
            if not b:
                break
            res += b
            if res.endswith(b"\n"):
                break
        return bytes(res)

    def __iter__(self):
        self._checkClosed()
        return self

    def __next__(self):
        line = self.readline()
        if not line:
            raise StopIteration
        return line

    def readlines(self, hint=None):
        """Return a list of lines from the stream.

        hint can be specified to control the number of lines read: no more
        lines will be read if the total size (in bytes/characters) of all
        lines so far exceeds hint.
        """
        if hint is None or hint <= 0:
            return list(self)
        n = 0
        lines = []
        for line in self:
            lines.append(line)
            n += len(line)
            if n >= hint:
                break
        return lines

    def writelines(self, lines):
        self._checkClosed()
        for line in lines:
            self.write(line)


class _RawIOBase(_IOBase):

    """Base class for raw binary I/O."""

    # The read() method is implemented by calling readinto(); derived
    # classes that want to support read() only need to implement
    # readinto() as a primitive operation.  In general, readinto() can be
    # more efficient than read().

    # (It would be tempting to also provide an implementation of
    # readinto() in terms of read(), in case the latter is a more suitable
    # primitive operation, but that would lead to nasty recursion in case
    # a subclass doesn't implement either.)

    def read(self, size=-1):
        """Read and return up to size bytes, where size is an int.

        Returns an empty bytes object on EOF, or None if the object is
        set not to block and has no data to read.
        """
        if size is None:
            size = -1
        if size < 0:
            return self.readall()
        b = bytearray(size.__index__())
        n = self.readinto(b)
        if n is None:
            return None
        del b[n:]
        return bytes(b)

    def readall(self):
        """Read until EOF, using multiple read() call."""
        res = bytearray()
        while True:
            data = self.read(DEFAULT_BUFFER_SIZE)
            if not data:
                break
            res += data
        if res:
            return bytes(res)
        else:
            # b'' or None
            return data

    def readinto(self, b):
        """Read bytes into a pre-allocated bytes-like object b.

        Returns an int representing the number of bytes read (0 for EOF), or
        None if the object is set not to block and has no data to read.
        """
        self._unsupported("readinto")

    def write(self, b):
        """Write the given buffer to the IO stream.

        Returns the number of bytes written, which may be less than the
        length of b in bytes.
        """
        self._unsupported("write")


class _BufferedIOBase(_IOBase):

    """Base class for buffered IO objects.

    The main difference with RawIOBase is that the read() method
    supports omitting the size argument, and does not have a default
    implementation that defers to readinto().

    In addition, read(), readinto() and write() may raise
    BlockingIOError if the underlying raw stream is in non-blocking
    mode and not ready; unlike their raw counterparts, they will never
    return None.

    A typical implementation should not inherit from a RawIOBase
    implementation, but wrap one.
    """

    def read(self, size=None):
        """Read and return up to size bytes, where size is an int.

        If the argument is omitted, None, or negative, reads and
        returns all data until EOF.

        If the argument is positive, and the underlying raw stream is
        not 'interactive', multiple raw reads may be issued to satisfy
        the byte count (unless EOF is reached first).  But for
        interactive raw streams (XXX and for pipes?), at most one raw
        read will be issued, and a short result does not imply that
        EOF is imminent.

        Returns an empty bytes array on EOF.

        Raises BlockingIOError if the underlying raw stream has no
        data at the moment.
        """
        self._unsupported("read")

    def read1(self, size=None):
        """Read up to size bytes with at most one read() system call,
        where size is an int.
        """
        self._unsupported("read1")

    def readinto(self, b):
        """Read bytes into a pre-allocated bytes-like object b.

        Like read(), this may issue multiple reads to the underlying raw
        stream, unless the latter is 'interactive'.

        Returns an int representing the number of bytes read (0 for EOF).

        Raises BlockingIOError if the underlying raw stream has no
        data at the moment.
        """

        return self._readinto(b, read1=False)

    def readinto1(self, b):
        """Read bytes into buffer *b*, using at most one system call

        Returns an int representing the number of bytes read (0 for EOF).

        Raises BlockingIOError if the underlying raw stream has no
        data at the moment.
        """

        return self._readinto(b, read1=True)

    def _readinto(self, b, read1):
        # XXX RustPython TODO: proper memoryview implementation
        # if not isinstance(b, memoryview):
        #     b = memoryview(b)
        # b = b.cast('B')

        if read1:
            data = self.read1(len(b))
        else:
            data = self.read(len(b))
        n = len(data)

        b[:n] = data

        return n

    def write(self, b):
        """Write the given bytes buffer to the IO stream.

        Return the number of bytes written, which is always the length of b
        in bytes.

        Raises BlockingIOError if the buffer is full and the
        underlying raw stream cannot accept more data at the moment.
        """
        self._unsupported("write")

    def detach(self):
        """
        Separate the underlying raw stream from the buffer and return it.

        After the raw stream has been detached, the buffer is in an unusable
        state.
        """
        self._unsupported("detach")


class _BufferedIOMixin(_BufferedIOBase):

    """A mixin implementation of BufferedIOBase with an underlying raw stream.

    This passes most requests on to the underlying raw stream.  It
    does *not* provide implementations of read(), readinto() or
    write().
    """

    def __init__(self, raw):
        self._raw = raw

    ### Positioning ###

    def seek(self, pos, whence=0):
        new_position = self.raw.seek(pos, whence)
        if new_position < 0:
            raise OSError("seek() returned an invalid position")
        return new_position

    def tell(self):
        pos = self.raw.tell()
        if pos < 0:
            raise OSError("tell() returned an invalid position")
        return pos

    def truncate(self, pos=None):
        # Flush the stream.  We're mixing buffered I/O with lower-level I/O,
        # and a flush may be necessary to synch both views of the current
        # file state.
        self.flush()

        if pos is None:
            pos = self.tell()
        # XXX: Should seek() be used, instead of passing the position
        # XXX  directly to truncate?
        return self.raw.truncate(pos)

    ### Flush and close ###

    def flush(self):
        if self.closed:
            raise ValueError("flush of closed file")
        self.raw.flush()

    def close(self):
        if self.raw is not None and not self.closed:
            try:
                # may raise BlockingIOError or BrokenPipeError etc
                self.flush()
            finally:
                self.raw.close()

    def detach(self):
        if self.raw is None:
            raise ValueError("raw stream already detached")
        self.flush()
        raw = self._raw
        self._raw = None
        return raw

    ### Inquiries ###

    def seekable(self):
        return self.raw.seekable()

    @property
    def raw(self):
        return self._raw

    @property
    def closed(self):
        return self.raw.closed

    @property
    def name(self):
        return self.raw.name

    @property
    def mode(self):
        return self.raw.mode

    def __getstate__(self):
        raise TypeError("can not serialize a '{0}' object"
                        .format(self.__class__.__name__))

    def __repr__(self):
        modname = self.__class__.__module__
        clsname = self.__class__.__qualname__
        try:
            name = self.name
        except Exception:
            return "<{}.{}>".format(modname, clsname)
        else:
            return "<{}.{} name={!r}>".format(modname, clsname, name)

    ### Lower-level APIs ###

    def fileno(self):
        return self.raw.fileno()

    def isatty(self):
        return self.raw.isatty()


class BytesIO(_BufferedIOBase):

    """Buffered I/O implementation using an in-memory bytes buffer."""

    def __init__(self, initial_bytes=None):
        buf = bytearray()
        if initial_bytes is not None:
            buf += initial_bytes
        self._buffer = buf
        self._pos = 0

    def __getstate__(self):
        if self.closed:
            raise ValueError("__getstate__ on closed file")
        return self.__dict__.copy()

    def getvalue(self):
        """Return the bytes value (contents) of the buffer
        """
        if self.closed:
            raise ValueError("getvalue on closed file")
        return bytes(self._buffer)

    def getbuffer(self):
        """Return a readable and writable view of the buffer.
        """
        if self.closed:
            raise ValueError("getbuffer on closed file")
        return memoryview(self._buffer)

    def close(self):
        self._buffer.clear()
        super().close()

    def read(self, size=None):
        if self.closed:
            raise ValueError("read from closed file")
        if size is None:
            size = -1
        if size < 0:
            size = len(self._buffer)
        if len(self._buffer) <= self._pos:
            return b""
        newpos = min(len(self._buffer), self._pos + size)
        b = self._buffer[self._pos : newpos]
        self._pos = newpos
        return bytes(b)

    def read1(self, size):
        """This is the same as read.
        """
        return self.read(size)

    def write(self, b):
        if self.closed:
            raise ValueError("write to closed file")
        if isinstance(b, str):
            raise TypeError("can't write str to binary stream")
        # XXX RustPython TODO: proper memoryview implementation
        # with memoryview(b) as view:
        #     n = view.nbytes  # Size of any bytes-like object
        n = len(b)
        if n == 0:
            return 0
        pos = self._pos
        if pos > len(self._buffer):
            # Inserts null bytes between the current end of the file
            # and the new write position.
            padding = b'\x00' * (pos - len(self._buffer))
            self._buffer += padding
        self._buffer[pos:pos + n] = b
        self._pos += n
        return n

    def seek(self, pos, whence=0):
        if self.closed:
            raise ValueError("seek on closed file")
        try:
            pos.__index__
        except AttributeError as err:
            raise TypeError("an integer is required") from err
        if whence == 0:
            if pos < 0:
                raise ValueError("negative seek position %r" % (pos,))
            self._pos = pos
        elif whence == 1:
            self._pos = max(0, self._pos + pos)
        elif whence == 2:
            self._pos = max(0, len(self._buffer) + pos)
        else:
            raise ValueError("unsupported whence value")
        return self._pos

    def tell(self):
        if self.closed:
            raise ValueError("tell on closed file")
        return self._pos

    def truncate(self, pos=None):
        if self.closed:
            raise ValueError("truncate on closed file")
        if pos is None:
            pos = self._pos
        else:
            try:
                pos.__index__
            except AttributeError as err:
                raise TypeError("an integer is required") from err
            if pos < 0:
                raise ValueError("negative truncate position %r" % (pos,))
        del self._buffer[pos:]
        return pos

    def readable(self):
        if self.closed:
            raise ValueError("I/O operation on closed file.")
        return True

    def writable(self):
        if self.closed:
            raise ValueError("I/O operation on closed file.")
        return True

    def seekable(self):
        if self.closed:
            raise ValueError("I/O operation on closed file.")
        return True


class BufferedReader(_BufferedIOMixin):

    """BufferedReader(raw[, buffer_size])

    A buffer for a readable, sequential BaseRawIO object.

    The constructor creates a BufferedReader for the given readable raw
    stream and buffer_size. If buffer_size is omitted, DEFAULT_BUFFER_SIZE
    is used.
    """

    def __init__(self, raw, buffer_size=DEFAULT_BUFFER_SIZE):
        """Create a new buffered reader using the given readable raw IO object.
        """
        if not raw.readable():
            raise OSError('"raw" argument must be readable.')

        _BufferedIOMixin.__init__(self, raw)
        if buffer_size <= 0:
            raise ValueError("invalid buffer size")
        self.buffer_size = buffer_size
        self._reset_read_buf()