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https://github.com/python/cpython
synced 2024-09-04 15:56:13 +00:00
Make TextIOWrapper's seek/tell work properly with stateful decoders;
document and rename things to make seek/tell workings a little clearer. Add a weird decoder for testing TextIOWrapper's seek/tell methods. Document the getstate/setstate protocol conventions for IncrementalDecoders.
This commit is contained in:
parent
b5dc90b5fa
commit
f44c7e8996
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@ -237,7 +237,7 @@ class IncrementalDecoder(object):
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"""
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def __init__(self, errors='strict'):
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"""
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Creates a IncrementalDecoder instance.
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Create a IncrementalDecoder instance.
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The IncrementalDecoder may use different error handling schemes by
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providing the errors keyword argument. See the module docstring
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@ -247,28 +247,35 @@ def __init__(self, errors='strict'):
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def decode(self, input, final=False):
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"""
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Decodes input and returns the resulting object.
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Decode input and returns the resulting object.
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"""
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raise NotImplementedError
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def reset(self):
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"""
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Resets the decoder to the initial state.
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Reset the decoder to the initial state.
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"""
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def getstate(self):
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"""
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Return the current state of the decoder. This must be a
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(buffered_input, additional_state_info) tuple. By convention,
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additional_state_info should represent the state of the decoder
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WITHOUT yet having processed the contents of buffered_input.
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Return the current state of the decoder.
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This must be a (buffered_input, additional_state_info) tuple.
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buffered_input must be a bytes object containing bytes that
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were passed to decode() that have not yet been converted.
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additional_state_info must be a non-negative integer
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representing the state of the decoder WITHOUT yet having
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processed the contents of buffered_input. In the initial state
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and after reset(), getstate() must return (b"", 0).
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"""
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return (b"", 0)
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def setstate(self, state):
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"""
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Set the current state of the decoder. state must have been
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returned by getstate().
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Set the current state of the decoder.
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state must have been returned by getstate(). The effect of
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setstate((b"", 0)) must be equivalent to reset().
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"""
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class BufferedIncrementalDecoder(IncrementalDecoder):
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280
Lib/io.py
280
Lib/io.py
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@ -802,11 +802,10 @@ def peek(self, n=0):
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return self._read_buf
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def read1(self, n):
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"""Reads up to n bytes.
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"""Reads up to n bytes, with at most one read() system call.
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Returns up to n bytes. If at least one byte is buffered,
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we only return buffered bytes. Otherwise, we do one
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raw read.
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Returns up to n bytes. If at least one byte is buffered, we
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only return buffered bytes. Otherwise, we do one raw read.
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"""
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if n <= 0:
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return b""
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@ -1180,10 +1179,24 @@ def __init__(self, buffer, encoding=None, errors=None, newline=None,
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self._writenl = newline or os.linesep
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self._encoder = None
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self._decoder = None
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self._pending = ""
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self._snapshot = None
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self._decoded_text = "" # buffer for text produced by decoder
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self._snapshot = None # info for reconstructing decoder state
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self._seekable = self._telling = self.buffer.seekable()
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# A word about _snapshot. This attribute is either None, or a tuple
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# (decoder_state, input_chunk, decoded_chars) where decoder_state is
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# the second (integer) item of the decoder state, input_chunk is the
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# chunk of bytes that was read, and decoded_chars is the number of
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# characters rendered by the decoder after feeding it those bytes.
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# We use this to reconstruct intermediate decoder states in tell().
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# Naming convention:
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# - integer variables ending in "_bytes" count input bytes
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# - integer variables ending in "_chars" count decoded characters
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def __repr__(self):
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return '<TIOW %x>' % id(self)
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@property
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def encoding(self):
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return self._encoding
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@ -1196,13 +1209,6 @@ def errors(self):
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def line_buffering(self):
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return self._line_buffering
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# A word about _snapshot. This attribute is either None, or a
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# tuple (decoder_state, readahead, pending) where decoder_state is
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# the second (integer) item of the decoder state, readahead is the
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# chunk of bytes that was read, and pending is the characters that
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# were rendered by the decoder after feeding it those bytes. We
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# use this to reconstruct intermediate decoder states in tell().
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def seekable(self):
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return self._seekable
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@ -1262,126 +1268,199 @@ def _get_decoder(self):
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return decoder
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def _read_chunk(self):
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"""
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Read and decode the next chunk of data from the BufferedReader.
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Return a tuple of two elements: all the bytes that were read, and
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the decoded string produced by the decoder. (The entire input
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chunk is sent to the decoder, but some of it may remain buffered
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in the decoder, yet to be converted.)
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"""
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if self._decoder is None:
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raise ValueError("no decoder")
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if not self._telling:
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readahead = self.buffer.read1(self._CHUNK_SIZE)
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pending = self._decoder.decode(readahead, not readahead)
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return readahead, pending
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decoder_buffer, decoder_state = self._decoder.getstate()
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readahead = self.buffer.read1(self._CHUNK_SIZE)
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pending = self._decoder.decode(readahead, not readahead)
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self._snapshot = (decoder_state, decoder_buffer + readahead, pending)
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return readahead, pending
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# No one should call tell(), so don't bother taking a snapshot.
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input_chunk = self.buffer.read1(self._CHUNK_SIZE)
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eof = not input_chunk
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decoded = self._decoder.decode(input_chunk, eof)
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return (input_chunk, decoded)
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def _encode_decoder_state(self, ds, pos):
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x = 0
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for i in bytes(ds):
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x = x<<8 | i
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return (x<<64) | pos
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# The cookie returned by tell() cannot include the contents of
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# the decoder's buffer, so we need to snapshot a point in the
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# input where the decoder has nothing in its input buffer.
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def _decode_decoder_state(self, pos):
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x, pos = divmod(pos, 1<<64)
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if not x:
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return None, pos
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b = b""
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while x:
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b.append(x&0xff)
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x >>= 8
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return str(b[::-1]), pos
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dec_buffer, dec_flags = self._decoder.getstate()
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# The state tuple returned by getstate() contains the decoder's
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# input buffer and an integer representing any other state. Thus,
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# there is a valid snapshot point len(decoder_buffer) bytes ago in
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# the input, with the state tuple (b'', decoder_state).
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input_chunk = self.buffer.read1(self._CHUNK_SIZE)
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eof = not input_chunk
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decoded = self._decoder.decode(input_chunk, eof)
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# At the snapshot point len(dec_buffer) bytes ago, the next input
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# to be passed to the decoder is dec_buffer + input_chunk. Save
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# len(decoded) so that later, tell() can figure out how much
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# decoded data has been used up by TextIOWrapper.read().
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self._snapshot = (dec_flags, dec_buffer + input_chunk, len(decoded))
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return (input_chunk, decoded)
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def _encode_tell_cookie(self, position, dec_flags=0,
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feed_bytes=0, need_eof=0, skip_chars=0):
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# The meaning of a tell() cookie is: seek to position, set the
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# decoder flags to dec_flags, read feed_bytes bytes, feed them
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# into the decoder with need_eof as the EOF flag, then skip
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# skip_chars characters of the decoded result. For most simple
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# decoders, this should often just be the position.
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return (position | (dec_flags<<64) | (feed_bytes<<128) |
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(skip_chars<<192) | bool(need_eof)<<256)
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def _decode_tell_cookie(self, bigint):
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rest, position = divmod(bigint, 1<<64)
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rest, dec_flags = divmod(rest, 1<<64)
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rest, feed_bytes = divmod(rest, 1<<64)
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need_eof, skip_chars = divmod(rest, 1<<64)
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return position, dec_flags, feed_bytes, need_eof, skip_chars
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def tell(self):
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if not self._seekable:
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raise IOError("Underlying stream is not seekable")
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raise IOError("underlying stream is not seekable")
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if not self._telling:
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raise IOError("Telling position disabled by next() call")
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raise IOError("telling position disabled by next() call")
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self.flush()
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position = self.buffer.tell()
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decoder = self._decoder
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if decoder is None or self._snapshot is None:
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if self._pending:
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raise ValueError("pending data")
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if self._decoded_text:
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# This should never happen.
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raise AssertionError("pending decoded text")
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return position
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decoder_state, readahead, pending = self._snapshot
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position -= len(readahead)
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needed = len(pending) - len(self._pending)
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if not needed:
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return self._encode_decoder_state(decoder_state, position)
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# Skip backward to the snapshot point (see _read_chunk).
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dec_flags, next_input, decoded_chars = self._snapshot
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position -= len(next_input)
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# How many decoded characters have been consumed since the snapshot?
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skip_chars = decoded_chars - len(self._decoded_text)
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if skip_chars == 0:
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# We haven't moved from the snapshot point.
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return self._encode_tell_cookie(position, dec_flags)
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# Walk the decoder forward, one byte at a time, to find the minimum
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# input necessary to give us the decoded characters we need to skip.
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# As we go, look for the "safe point" nearest to the current location
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# (i.e. a point where the decoder has nothing buffered, so we can
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# safely start from there when trying to return to this location).
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saved_state = decoder.getstate()
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try:
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decoder.setstate((b"", decoder_state))
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n = 0
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bb = bytearray(1)
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for i, bb[0] in enumerate(readahead):
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n += len(decoder.decode(bb))
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if n >= needed:
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decoder_buffer, decoder_state = decoder.getstate()
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return self._encode_decoder_state(
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decoder_state,
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position + (i+1) - len(decoder_buffer) - (n - needed))
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raise IOError("Can't reconstruct logical file position")
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decoder.setstate((b"", dec_flags))
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fed_bytes = 0
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decoded_chars = 0
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need_eof = 0
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last_safe_point = (dec_flags, 0, 0)
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next_byte = bytearray(1)
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for next_byte[0] in next_input:
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decoded = decoder.decode(next_byte)
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fed_bytes += 1
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decoded_chars += len(decoded)
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dec_buffer, dec_flags = decoder.getstate()
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if not dec_buffer and decoded_chars <= skip_chars:
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# Decoder buffer is empty, so it's safe to start from here.
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last_safe_point = (dec_flags, fed_bytes, decoded_chars)
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if decoded_chars >= skip_chars:
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break
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else:
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# We didn't get enough decoded data; send EOF to get more.
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decoded = decoder.decode(b"", True)
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decoded_chars += len(decoded)
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need_eof = 1
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if decoded_chars < skip_chars:
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raise IOError("can't reconstruct logical file position")
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# Advance the starting position to the last safe point.
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dec_flags, safe_fed_bytes, safe_decoded_chars = last_safe_point
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position += safe_fed_bytes
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fed_bytes -= safe_fed_bytes
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skip_chars -= safe_decoded_chars
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return self._encode_tell_cookie(
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position, dec_flags, fed_bytes, need_eof, skip_chars)
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finally:
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decoder.setstate(saved_state)
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def seek(self, pos, whence=0):
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def seek(self, cookie, whence=0):
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if not self._seekable:
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raise IOError("Underlying stream is not seekable")
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if whence == 1:
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if pos != 0:
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raise IOError("Can't do nonzero cur-relative seeks")
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pos = self.tell()
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raise IOError("underlying stream is not seekable")
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if whence == 1: # seek relative to current position
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if cookie != 0:
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raise IOError("can't do nonzero cur-relative seeks")
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# Seeking to the current position should attempt to
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# sync the underlying buffer with the current position.
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whence = 0
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if whence == 2:
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if pos != 0:
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raise IOError("Can't do nonzero end-relative seeks")
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cookie = self.tell()
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if whence == 2: # seek relative to end of file
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if cookie != 0:
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raise IOError("can't do nonzero end-relative seeks")
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self.flush()
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pos = self.buffer.seek(0, 2)
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position = self.buffer.seek(0, 2)
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self._decoded_text = ""
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self._snapshot = None
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self._pending = ""
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if self._decoder:
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self._decoder.reset()
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return pos
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return position
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if whence != 0:
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raise ValueError("Invalid whence (%r, should be 0, 1 or 2)" %
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raise ValueError("invalid whence (%r, should be 0, 1 or 2)" %
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(whence,))
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if pos < 0:
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raise ValueError("Negative seek position %r" % (pos,))
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if cookie < 0:
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raise ValueError("negative seek position %r" % (cookie,))
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self.flush()
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orig_pos = pos
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ds, pos = self._decode_decoder_state(pos)
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if not ds:
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self.buffer.seek(pos)
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self._snapshot = None
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self._pending = ""
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if self._decoder:
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self._decoder.reset()
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return pos
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decoder = self._decoder or self._get_decoder()
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decoder.set_state(("", ds))
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self.buffer.seek(pos)
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self._snapshot = (ds, b"", "")
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self._pending = ""
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self._decoder = decoder
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return orig_pos
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# Seek back to the snapshot point.
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position, dec_flags, feed_bytes, need_eof, skip_chars = \
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self._decode_tell_cookie(cookie)
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self.buffer.seek(position)
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self._decoded_text = ""
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self._snapshot = None
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if self._decoder or dec_flags or feed_bytes or need_eof:
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# Restore the decoder flags to their values from the snapshot.
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self._decoder = self._decoder or self._get_decoder()
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self._decoder.setstate((b"", dec_flags))
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if feed_bytes or need_eof:
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# Feed feed_bytes bytes to the decoder.
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input_chunk = self.buffer.read(feed_bytes)
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decoded = self._decoder.decode(input_chunk, need_eof)
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if len(decoded) < skip_chars:
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raise IOError("can't restore logical file position")
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# Skip skip_chars of the decoded characters.
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self._decoded_text = decoded[skip_chars:]
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# Restore the snapshot.
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self._snapshot = (dec_flags, input_chunk, len(decoded))
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return cookie
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def read(self, n=None):
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if n is None:
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n = -1
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decoder = self._decoder or self._get_decoder()
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res = self._pending
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result = self._decoded_text
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if n < 0:
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res += decoder.decode(self.buffer.read(), True)
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self._pending = ""
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result += decoder.decode(self.buffer.read(), True)
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self._decoded_text = ""
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self._snapshot = None
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return res
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return result
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else:
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while len(res) < n:
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readahead, pending = self._read_chunk()
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res += pending
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if not readahead:
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while len(result) < n:
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input_chunk, decoded = self._read_chunk()
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result += decoded
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if not input_chunk:
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break
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self._pending = res[n:]
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return res[:n]
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self._decoded_text = result[n:]
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return result[:n]
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def __next__(self):
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self._telling = False
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@ -1400,10 +1479,11 @@ def readline(self, limit=None):
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line = self.readline()
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if len(line) <= limit:
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return line
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line, self._pending = line[:limit], line[limit:] + self._pending
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line, self._decoded_text = \
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line[:limit], line[limit:] + self._decoded_text
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return line
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line = self._pending
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line = self._decoded_text
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start = 0
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decoder = self._decoder or self._get_decoder()
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@ -1467,11 +1547,11 @@ def readline(self, limit=None):
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line += more_line
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else:
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# end of file
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self._pending = ''
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self._decoded_text = ''
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self._snapshot = None
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return line
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self._pending = line[endpos:]
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self._decoded_text = line[endpos:]
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return line[:endpos]
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@property
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@ -8,6 +8,7 @@
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from itertools import chain
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from test import test_support
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import codecs
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import io # The module under test
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@ -486,6 +487,122 @@ def testSeekAndTell(self):
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self.assertEquals(b"fl", rw.read(11))
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self.assertRaises(TypeError, rw.seek, 0.0)
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# To fully exercise seek/tell, the StatefulIncrementalDecoder has these
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# properties:
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# - A single output character can correspond to many bytes of input.
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# - The number of input bytes to complete the character can be
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# undetermined until the last input byte is received.
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# - The number of input bytes can vary depending on previous input.
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# - A single input byte can correspond to many characters of output.
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# - The number of output characters can be undetermined until the
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# last input byte is received.
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# - The number of output characters can vary depending on previous input.
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class StatefulIncrementalDecoder(codecs.IncrementalDecoder):
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"""
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For testing seek/tell behavior with a stateful, buffering decoder.
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Input is a sequence of words. Words may be fixed-length (length set
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by input) or variable-length (period-terminated). In variable-length
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mode, extra periods are ignored. Possible words are:
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- 'i' followed by a number sets the input length, I (maximum 99).
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When I is set to 0, words are space-terminated.
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- 'o' followed by a number sets the output length, O (maximum 99).
|
||||
- Any other word is converted into a word followed by a period on
|
||||
the output. The output word consists of the input word truncated
|
||||
or padded out with hyphens to make its length equal to O. If O
|
||||
is 0, the word is output verbatim without truncating or padding.
|
||||
I and O are initially set to 1. When I changes, any buffered input is
|
||||
re-scanned according to the new I. EOF also terminates the last word.
|
||||
"""
|
||||
|
||||
def __init__(self, errors='strict'):
|
||||
codecs.IncrementalEncoder.__init__(self, errors)
|
||||
self.reset()
|
||||
|
||||
def __repr__(self):
|
||||
return '<SID %x>' % id(self)
|
||||
|
||||
def reset(self):
|
||||
self.i = 1
|
||||
self.o = 1
|
||||
self.buffer = bytearray()
|
||||
|
||||
def getstate(self):
|
||||
i, o = self.i ^ 1, self.o ^ 1 # so that flags = 0 after reset()
|
||||
return bytes(self.buffer), i*100 + o
|
||||
|
||||
def setstate(self, state):
|
||||
buffer, io = state
|
||||
self.buffer = bytearray(buffer)
|
||||
i, o = divmod(io, 100)
|
||||
self.i, self.o = i ^ 1, o ^ 1
|
||||
|
||||
def decode(self, input, final=False):
|
||||
output = ''
|
||||
for b in input:
|
||||
if self.i == 0: # variable-length, terminated with period
|
||||
if b == ord('.'):
|
||||
if self.buffer:
|
||||
output += self.process_word()
|
||||
else:
|
||||
self.buffer.append(b)
|
||||
else: # fixed-length, terminate after self.i bytes
|
||||
self.buffer.append(b)
|
||||
if len(self.buffer) == self.i:
|
||||
output += self.process_word()
|
||||
if final and self.buffer: # EOF terminates the last word
|
||||
output += self.process_word()
|
||||
return output
|
||||
|
||||
def process_word(self):
|
||||
output = ''
|
||||
if self.buffer[0] == ord('i'):
|
||||
self.i = min(99, int(self.buffer[1:] or 0)) # set input length
|
||||
elif self.buffer[0] == ord('o'):
|
||||
self.o = min(99, int(self.buffer[1:] or 0)) # set output length
|
||||
else:
|
||||
output = self.buffer.decode('ascii')
|
||||
if len(output) < self.o:
|
||||
output += '-'*self.o # pad out with hyphens
|
||||
if self.o:
|
||||
output = output[:self.o] # truncate to output length
|
||||
output += '.'
|
||||
self.buffer = bytearray()
|
||||
return output
|
||||
|
||||
class StatefulIncrementalDecoderTest(unittest.TestCase):
|
||||
"""
|
||||
Make sure the StatefulIncrementalDecoder actually works.
|
||||
"""
|
||||
|
||||
test_cases = [
|
||||
# I=1 fixed-length mode
|
||||
(b'abcd', False, 'a.b.c.d.'),
|
||||
# I=0, O=0, variable-length mode
|
||||
(b'oiabcd', True, 'abcd.'),
|
||||
# I=0, O=0, variable-length mode, should ignore extra periods
|
||||
(b'oi...abcd...', True, 'abcd.'),
|
||||
# I=0, O=6
|
||||
(b'i.o6.xyz.', False, 'xyz---.'),
|
||||
# I=2, O=6
|
||||
(b'i.i2.o6xyz', True, 'xy----.z-----.'),
|
||||
# I=0, O=3
|
||||
(b'i.o3.x.xyz.toolong.', False, 'x--.xyz.too.'),
|
||||
# I=6, O=3
|
||||
(b'i.o3.i6.abcdefghijklmnop', True, 'abc.ghi.mno.')
|
||||
]
|
||||
|
||||
def testDecoder(self):
|
||||
# Try a few one-shot test cases.
|
||||
for input, eof, output in self.test_cases:
|
||||
d = StatefulIncrementalDecoder()
|
||||
self.assertEquals(d.decode(input, eof), output)
|
||||
|
||||
# Also test an unfinished decode, followed by forcing EOF.
|
||||
d = StatefulIncrementalDecoder()
|
||||
self.assertEquals(d.decode(b'oiabcd'), '')
|
||||
self.assertEquals(d.decode(b'', 1), 'abcd.')
|
||||
|
||||
class TextIOWrapperTest(unittest.TestCase):
|
||||
|
||||
|
@ -765,6 +882,60 @@ def testSeekingToo(self):
|
|||
f.readline()
|
||||
f.tell()
|
||||
|
||||
def testSeekAndTell(self):
|
||||
"""Test seek/tell using the StatefulIncrementalDecoder."""
|
||||
|
||||
def lookupTestDecoder(name):
|
||||
if self.codecEnabled and name == 'test_decoder':
|
||||
return codecs.CodecInfo(
|
||||
name='test_decoder', encode=None, decode=None,
|
||||
incrementalencoder=None,
|
||||
streamreader=None, streamwriter=None,
|
||||
incrementaldecoder=StatefulIncrementalDecoder)
|
||||
|
||||
def testSeekAndTellWithData(data, min_pos=0):
|
||||
"""Tell/seek to various points within a data stream and ensure
|
||||
that the decoded data returned by read() is consistent."""
|
||||
f = io.open(test_support.TESTFN, 'wb')
|
||||
f.write(data)
|
||||
f.close()
|
||||
f = io.open(test_support.TESTFN, encoding='test_decoder')
|
||||
decoded = f.read()
|
||||
f.close()
|
||||
|
||||
for i in range(min_pos, len(decoded) + 1): # seek positions
|
||||
for j in [1, 5, len(decoded) - i]: # read lengths
|
||||
f = io.open(test_support.TESTFN, encoding='test_decoder')
|
||||
self.assertEquals(f.read(i), decoded[:i])
|
||||
cookie = f.tell()
|
||||
self.assertEquals(f.read(j), decoded[i:i + j])
|
||||
f.seek(cookie)
|
||||
self.assertEquals(f.read(), decoded[i:])
|
||||
f.close()
|
||||
|
||||
# Register a special incremental decoder for testing.
|
||||
codecs.register(lookupTestDecoder)
|
||||
self.codecEnabled = 1
|
||||
|
||||
# Run the tests.
|
||||
try:
|
||||
# Try each test case.
|
||||
for input, _, _ in StatefulIncrementalDecoderTest.test_cases:
|
||||
testSeekAndTellWithData(input)
|
||||
|
||||
# Position each test case so that it crosses a chunk boundary.
|
||||
CHUNK_SIZE = io.TextIOWrapper._CHUNK_SIZE
|
||||
for input, _, _ in StatefulIncrementalDecoderTest.test_cases:
|
||||
offset = CHUNK_SIZE - len(input)//2
|
||||
prefix = b'.'*offset
|
||||
# Don't bother seeking into the prefix (takes too long).
|
||||
min_pos = offset*2
|
||||
testSeekAndTellWithData(prefix + input, min_pos)
|
||||
|
||||
# Ensure our test decoder won't interfere with subsequent tests.
|
||||
finally:
|
||||
self.codecEnabled = 0
|
||||
|
||||
def testEncodedWrites(self):
|
||||
data = "1234567890"
|
||||
tests = ("utf-16",
|
||||
|
|
Loading…
Reference in a new issue