diff options
Diffstat (limited to 'Lib/io.py')
| -rw-r--r-- | Lib/io.py | 284 |
1 files changed, 182 insertions, 102 deletions
@@ -802,11 +802,10 @@ class BufferedReader(_BufferedIOMixin): return self._read_buf def read1(self, n): - """Reads up to n bytes. + """Reads up to n bytes, with at most one read() system call. - Returns up to n bytes. If at least one byte is buffered, - we only return buffered bytes. Otherwise, we do one - raw read. + Returns up to n bytes. If at least one byte is buffered, we + only return buffered bytes. Otherwise, we do one raw read. """ if n <= 0: return b"" @@ -1180,10 +1179,24 @@ class TextIOWrapper(TextIOBase): self._writenl = newline or os.linesep self._encoder = None self._decoder = None - self._pending = "" - self._snapshot = None + self._decoded_text = "" # buffer for text produced by decoder + self._snapshot = None # info for reconstructing decoder state self._seekable = self._telling = self.buffer.seekable() + # A word about _snapshot. This attribute is either None, or a tuple + # (decoder_state, input_chunk, decoded_chars) where decoder_state is + # the second (integer) item of the decoder state, input_chunk is the + # chunk of bytes that was read, and decoded_chars is the number of + # characters rendered by the decoder after feeding it those bytes. + # We use this to reconstruct intermediate decoder states in tell(). + + # Naming convention: + # - integer variables ending in "_bytes" count input bytes + # - integer variables ending in "_chars" count decoded characters + + def __repr__(self): + return '<TIOW %x>' % id(self) + @property def encoding(self): return self._encoding @@ -1196,13 +1209,6 @@ class TextIOWrapper(TextIOBase): def line_buffering(self): return self._line_buffering - # A word about _snapshot. This attribute is either None, or a - # tuple (decoder_state, readahead, pending) where decoder_state is - # the second (integer) item of the decoder state, readahead is the - # chunk of bytes that was read, and pending is the characters that - # were rendered by the decoder after feeding it those bytes. We - # use this to reconstruct intermediate decoder states in tell(). - def seekable(self): return self._seekable @@ -1262,126 +1268,199 @@ class TextIOWrapper(TextIOBase): return decoder def _read_chunk(self): + """ + Read and decode the next chunk of data from the BufferedReader. + + Return a tuple of two elements: all the bytes that were read, and + the decoded string produced by the decoder. (The entire input + chunk is sent to the decoder, but some of it may remain buffered + in the decoder, yet to be converted.) + """ + if self._decoder is None: raise ValueError("no decoder") if not self._telling: - readahead = self.buffer.read1(self._CHUNK_SIZE) - pending = self._decoder.decode(readahead, not readahead) - return readahead, pending - decoder_buffer, decoder_state = self._decoder.getstate() - readahead = self.buffer.read1(self._CHUNK_SIZE) - pending = self._decoder.decode(readahead, not readahead) - self._snapshot = (decoder_state, decoder_buffer + readahead, pending) - return readahead, pending - - def _encode_decoder_state(self, ds, pos): - x = 0 - for i in bytes(ds): - x = x<<8 | i - return (x<<64) | pos - - def _decode_decoder_state(self, pos): - x, pos = divmod(pos, 1<<64) - if not x: - return None, pos - b = b"" - while x: - b.append(x&0xff) - x >>= 8 - return str(b[::-1]), pos + # No one should call tell(), so don't bother taking a snapshot. + input_chunk = self.buffer.read1(self._CHUNK_SIZE) + eof = not input_chunk + decoded = self._decoder.decode(input_chunk, eof) + return (input_chunk, decoded) + + # The cookie returned by tell() cannot include the contents of + # the decoder's buffer, so we need to snapshot a point in the + # input where the decoder has nothing in its input buffer. + + dec_buffer, dec_flags = self._decoder.getstate() + # The state tuple returned by getstate() contains the decoder's + # input buffer and an integer representing any other state. Thus, + # there is a valid snapshot point len(decoder_buffer) bytes ago in + # the input, with the state tuple (b'', decoder_state). + + input_chunk = self.buffer.read1(self._CHUNK_SIZE) + eof = not input_chunk + decoded = self._decoder.decode(input_chunk, eof) + + # At the snapshot point len(dec_buffer) bytes ago, the next input + # to be passed to the decoder is dec_buffer + input_chunk. Save + # len(decoded) so that later, tell() can figure out how much + # decoded data has been used up by TextIOWrapper.read(). + self._snapshot = (dec_flags, dec_buffer + input_chunk, len(decoded)) + return (input_chunk, decoded) + + def _encode_tell_cookie(self, position, dec_flags=0, + feed_bytes=0, need_eof=0, skip_chars=0): + # The meaning of a tell() cookie is: seek to position, set the + # decoder flags to dec_flags, read feed_bytes bytes, feed them + # into the decoder with need_eof as the EOF flag, then skip + # skip_chars characters of the decoded result. For most simple + # decoders, this should often just be the position. + return (position | (dec_flags<<64) | (feed_bytes<<128) | + (skip_chars<<192) | bool(need_eof)<<256) + + def _decode_tell_cookie(self, bigint): + rest, position = divmod(bigint, 1<<64) + rest, dec_flags = divmod(rest, 1<<64) + rest, feed_bytes = divmod(rest, 1<<64) + need_eof, skip_chars = divmod(rest, 1<<64) + return position, dec_flags, feed_bytes, need_eof, skip_chars def tell(self): if not self._seekable: - raise IOError("Underlying stream is not seekable") + raise IOError("underlying stream is not seekable") if not self._telling: - raise IOError("Telling position disabled by next() call") + raise IOError("telling position disabled by next() call") self.flush() position = self.buffer.tell() decoder = self._decoder if decoder is None or self._snapshot is None: - if self._pending: - raise ValueError("pending data") + if self._decoded_text: + # This should never happen. + raise AssertionError("pending decoded text") return position - decoder_state, readahead, pending = self._snapshot - position -= len(readahead) - needed = len(pending) - len(self._pending) - if not needed: - return self._encode_decoder_state(decoder_state, position) + + # Skip backward to the snapshot point (see _read_chunk). + dec_flags, next_input, decoded_chars = self._snapshot + position -= len(next_input) + + # How many decoded characters have been consumed since the snapshot? + skip_chars = decoded_chars - len(self._decoded_text) + if skip_chars == 0: + # We haven't moved from the snapshot point. + return self._encode_tell_cookie(position, dec_flags) + + # Walk the decoder forward, one byte at a time, to find the minimum + # input necessary to give us the decoded characters we need to skip. + # As we go, look for the "safe point" nearest to the current location + # (i.e. a point where the decoder has nothing buffered, so we can + # safely start from there when trying to return to this location). saved_state = decoder.getstate() try: - decoder.setstate((b"", decoder_state)) - n = 0 - bb = bytearray(1) - for i, bb[0] in enumerate(readahead): - n += len(decoder.decode(bb)) - if n >= needed: - decoder_buffer, decoder_state = decoder.getstate() - return self._encode_decoder_state( - decoder_state, - position + (i+1) - len(decoder_buffer) - (n - needed)) - raise IOError("Can't reconstruct logical file position") + decoder.setstate((b"", dec_flags)) + fed_bytes = 0 + decoded_chars = 0 + need_eof = 0 + last_safe_point = (dec_flags, 0, 0) + + next_byte = bytearray(1) + for next_byte[0] in next_input: + decoded = decoder.decode(next_byte) + fed_bytes += 1 + decoded_chars += len(decoded) + dec_buffer, dec_flags = decoder.getstate() + if not dec_buffer and decoded_chars <= skip_chars: + # Decoder buffer is empty, so it's safe to start from here. + last_safe_point = (dec_flags, fed_bytes, decoded_chars) + if decoded_chars >= skip_chars: + break + else: + # We didn't get enough decoded data; send EOF to get more. + decoded = decoder.decode(b"", True) + decoded_chars += len(decoded) + need_eof = 1 + if decoded_chars < skip_chars: + raise IOError("can't reconstruct logical file position") + + # Advance the starting position to the last safe point. + dec_flags, safe_fed_bytes, safe_decoded_chars = last_safe_point + position += safe_fed_bytes + fed_bytes -= safe_fed_bytes + skip_chars -= safe_decoded_chars + return self._encode_tell_cookie( + position, dec_flags, fed_bytes, need_eof, skip_chars) finally: decoder.setstate(saved_state) - def seek(self, pos, whence=0): + def seek(self, cookie, whence=0): if not self._seekable: - raise IOError("Underlying stream is not seekable") - if whence == 1: - if pos != 0: - raise IOError("Can't do nonzero cur-relative seeks") - pos = self.tell() + raise IOError("underlying stream is not seekable") + if whence == 1: # seek relative to current position + if cookie != 0: + raise IOError("can't do nonzero cur-relative seeks") + # Seeking to the current position should attempt to + # sync the underlying buffer with the current position. whence = 0 - if whence == 2: - if pos != 0: - raise IOError("Can't do nonzero end-relative seeks") + cookie = self.tell() + if whence == 2: # seek relative to end of file + if cookie != 0: + raise IOError("can't do nonzero end-relative seeks") self.flush() - pos = self.buffer.seek(0, 2) + position = self.buffer.seek(0, 2) + self._decoded_text = "" self._snapshot = None - self._pending = "" if self._decoder: self._decoder.reset() - return pos + return position if whence != 0: - raise ValueError("Invalid whence (%r, should be 0, 1 or 2)" % + raise ValueError("invalid whence (%r, should be 0, 1 or 2)" % (whence,)) - if pos < 0: - raise ValueError("Negative seek position %r" % (pos,)) + if cookie < 0: + raise ValueError("negative seek position %r" % (cookie,)) self.flush() - orig_pos = pos - ds, pos = self._decode_decoder_state(pos) - if not ds: - self.buffer.seek(pos) - self._snapshot = None - self._pending = "" - if self._decoder: - self._decoder.reset() - return pos - decoder = self._decoder or self._get_decoder() - decoder.set_state(("", ds)) - self.buffer.seek(pos) - self._snapshot = (ds, b"", "") - self._pending = "" - self._decoder = decoder - return orig_pos + + # Seek back to the snapshot point. + position, dec_flags, feed_bytes, need_eof, skip_chars = \ + self._decode_tell_cookie(cookie) + self.buffer.seek(position) + self._decoded_text = "" + self._snapshot = None + + if self._decoder or dec_flags or feed_bytes or need_eof: + # Restore the decoder flags to their values from the snapshot. + self._decoder = self._decoder or self._get_decoder() + self._decoder.setstate((b"", dec_flags)) + + if feed_bytes or need_eof: + # Feed feed_bytes bytes to the decoder. + input_chunk = self.buffer.read(feed_bytes) + decoded = self._decoder.decode(input_chunk, need_eof) + if len(decoded) < skip_chars: + raise IOError("can't restore logical file position") + + # Skip skip_chars of the decoded characters. + self._decoded_text = decoded[skip_chars:] + + # Restore the snapshot. + self._snapshot = (dec_flags, input_chunk, len(decoded)) + return cookie def read(self, n=None): if n is None: n = -1 decoder = self._decoder or self._get_decoder() - res = self._pending + result = self._decoded_text if n < 0: - res += decoder.decode(self.buffer.read(), True) - self._pending = "" + result += decoder.decode(self.buffer.read(), True) + self._decoded_text = "" self._snapshot = None - return res + return result else: - while len(res) < n: - readahead, pending = self._read_chunk() - res += pending - if not readahead: + while len(result) < n: + input_chunk, decoded = self._read_chunk() + result += decoded + if not input_chunk: break - self._pending = res[n:] - return res[:n] + self._decoded_text = result[n:] + return result[:n] def __next__(self): self._telling = False @@ -1400,10 +1479,11 @@ class TextIOWrapper(TextIOBase): line = self.readline() if len(line) <= limit: return line - line, self._pending = line[:limit], line[limit:] + self._pending + line, self._decoded_text = \ + line[:limit], line[limit:] + self._decoded_text return line - line = self._pending + line = self._decoded_text start = 0 decoder = self._decoder or self._get_decoder() @@ -1467,11 +1547,11 @@ class TextIOWrapper(TextIOBase): line += more_line else: # end of file - self._pending = '' + self._decoded_text = '' self._snapshot = None return line - self._pending = line[endpos:] + self._decoded_text = line[endpos:] return line[:endpos] @property |