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98 lines
3.9 KiB
Python
98 lines
3.9 KiB
Python
from __future__ import annotations
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import os
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import select
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from codecs import getincrementaldecoder
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__all__ = [
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"PosixStdinReader",
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]
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class PosixStdinReader:
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"""
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Wrapper around stdin which reads (nonblocking) the next available 1024
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bytes and decodes it.
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Note that you can't be sure that the input file is closed if the ``read``
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function returns an empty string. When ``errors=ignore`` is passed,
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``read`` can return an empty string if all malformed input was replaced by
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an empty string. (We can't block here and wait for more input.) So, because
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of that, check the ``closed`` attribute, to be sure that the file has been
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closed.
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:param stdin_fd: File descriptor from which we read.
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:param errors: Can be 'ignore', 'strict' or 'replace'.
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On Python3, this can be 'surrogateescape', which is the default.
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'surrogateescape' is preferred, because this allows us to transfer
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unrecognized bytes to the key bindings. Some terminals, like lxterminal
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and Guake, use the 'Mxx' notation to send mouse events, where each 'x'
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can be any possible byte.
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"""
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# By default, we want to 'ignore' errors here. The input stream can be full
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# of junk. One occurrence of this that I had was when using iTerm2 on OS X,
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# with "Option as Meta" checked (You should choose "Option as +Esc".)
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def __init__(
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self, stdin_fd: int, errors: str = "surrogateescape", encoding: str = "utf-8"
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) -> None:
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self.stdin_fd = stdin_fd
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self.errors = errors
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# Create incremental decoder for decoding stdin.
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# We can not just do `os.read(stdin.fileno(), 1024).decode('utf-8')`, because
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# it could be that we are in the middle of a utf-8 byte sequence.
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self._stdin_decoder_cls = getincrementaldecoder(encoding)
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self._stdin_decoder = self._stdin_decoder_cls(errors=errors)
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#: True when there is nothing anymore to read.
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self.closed = False
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def read(self, count: int = 1024) -> str:
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# By default we choose a rather small chunk size, because reading
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# big amounts of input at once, causes the event loop to process
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# all these key bindings also at once without going back to the
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# loop. This will make the application feel unresponsive.
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"""
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Read the input and return it as a string.
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Return the text. Note that this can return an empty string, even when
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the input stream was not yet closed. This means that something went
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wrong during the decoding.
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"""
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if self.closed:
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return ""
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# Check whether there is some input to read. `os.read` would block
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# otherwise.
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# (Actually, the event loop is responsible to make sure that this
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# function is only called when there is something to read, but for some
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# reason this happens in certain situations.)
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try:
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if not select.select([self.stdin_fd], [], [], 0)[0]:
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return ""
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except OSError:
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# Happens for instance when the file descriptor was closed.
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# (We had this in ptterm, where the FD became ready, a callback was
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# scheduled, but in the meantime another callback closed it already.)
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self.closed = True
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# Note: the following works better than wrapping `self.stdin` like
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# `codecs.getreader('utf-8')(stdin)` and doing `read(1)`.
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# Somehow that causes some latency when the escape
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# character is pressed. (Especially on combination with the `select`.)
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try:
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data = os.read(self.stdin_fd, count)
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# Nothing more to read, stream is closed.
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if data == b"":
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self.closed = True
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return ""
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except OSError:
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# In case of SIGWINCH
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data = b""
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return self._stdin_decoder.decode(data)
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