Mercurial > hg
view mercurial/encoding.py @ 42044:bb271ec2fbfb
compression: introduce a `storage.revlog.zstd.level` configuration
This option control the zstd compression level used when compressing revlog
chunk. The usage of zstd for revlog compression has not graduated from
experimental yet, but we intend to fix that soon.
The option name for the compression level is more straight forward to pick, so
this changesets comes first. Having a dedicated option for each compression
engine is useful because they don't support the same range of values.
I ran the same measurement as for the zlib compression level (in the parent
changesets). The variation in repository size is stay mostly in the same (small)
range. The "read/write" performance see smallish variation, but are overall much
better than zlib. Write performance show the same tend of having better write
performance for when reaching high-end compression.
Again, we don't intend to change the default zstd compression level (currently:
3) in this series. However this is worth investigating in the future.
The Performance comparison of zlib vs zstd is quite impressive. The repository
size stay in the same range, but the performance are much better in all
situations.
Comparison summary
==================
We are looking at:
- performance range for zlib
- performance range for zstd
- comparison of default zstd (level-3) to default zlib (level 6)
- comparison of the slowest zstd time to the fastest zlib time
Read performance:
-----------------
| zlib | zstd | cmp | f2s
mercurial | 0.170159 - 0.189219 | 0.144127 - 0.149624 | 80% | 88%
pypy | 2.679217 - 2.768691 | 1.532317 - 1.705044 | 60% | 63%
netbeans | 122.477027 - 141.620281 | 72.996346 - 89.731560 | 58% | 73%
mozilla | 147.867662 - 170.572118 | 91.700995 - 105.853099 | 56% | 71%
Write performance:
------------------
| zlib | zstd | cmp | f2s
mercurial | 53.250304 - 56.2936129 | 40.877025 - 45.677286 | 75% | 86%
pypy | 460.721984 - 476.589918 | 270.545409 - 301.002219 | 63% | 65%
netbeans | 520.560316 - 715.930400 | 370.356311 - 428.329652 | 55% | 82%
mozilla | 739.803002 - 987.056093 | 505.152906 - 591.930683 | 57% | 80%
Raw data
--------
repo alg lvl .hg/store size 00manifest.d read write
mercurial zlib 1 49,402,813 5,963,475 0.170159 53.250304
mercurial zlib 6 47,197,397 5,875,730 0.182820 56.264320
mercurial zlib 9 47,121,596 5,849,781 0.189219 56.293612
mercurial zstd 1 49,737,084 5,966,355 0.144127 40.877025
mercurial zstd 3 48,961,867 5,895,208 0.146376 42.268142
mercurial zstd 5 48,200,592 5,938,676 0.149624 43.162875
mercurial zstd 10 47,833,520 5,913,353 0.145185 44.012489
mercurial zstd 15 47,314,604 5,728,679 0.147686 45.677286
mercurial zstd 20 47,330,502 5,830,539 0.145789 45.025407
mercurial zstd 22 47,330,076 5,830,539 0.143996 44.690460
pypy zlib 1 370,830,572 28,462,425 2.679217 460.721984
pypy zlib 6 340,112,317 27,648,747 2.768691 467.537158
pypy zlib 9 338,360,736 27,639,003 2.763495 476.589918
pypy zstd 1 362,377,479 27,916,214 1.532317 270.545409
pypy zstd 3 354,137,693 27,905,988 1.686718 294.951509
pypy zstd 5 342,640,043 27,655,774 1.705044 301.002219
pypy zstd 10 334,224,327 27,164,493 1.567287 285.186239
pypy zstd 15 329,000,363 26,645,965 1.637729 299.561332
pypy zstd 20 324,534,039 26,199,547 1.526813 302.149827
pypy zstd 22 324,530,595 26,198,932 1.525718 307.821218
netbeans zlib 1 1,281,847,810 165,495,457 122.477027 520.560316
netbeans zlib 6 1,205,284,353 159,161,207 139.876147 715.930400
netbeans zlib 9 1,197,135,671 155,034,586 141.620281 678.297064
netbeans zstd 1 1,259,581,737 160,840,613 72.996346 370.356311
netbeans zstd 3 1,232,978,122 157,691,551 81.622317 396.733087
netbeans zstd 5 1,208,034,075 160,246,880 83.080549 364.342626
netbeans zstd 10 1,188,624,176 156,083,417 79.323935 403.594602
netbeans zstd 15 1,176,973,589 153,859,477 89.731560 428.329652
netbeans zstd 20 1,162,958,258 151,147,535 82.842667 392.335349
netbeans zstd 22 1,162,707,029 151,150,220 82.565695 402.840655
mozilla zlib 1 2,775,497,186 298,527,987 147.867662 751.263721
mozilla zlib 6 2,596,856,420 286,597,671 170.572118 987.056093
mozilla zlib 9 2,587,542,494 287,018,264 163.622338 739.803002
mozilla zstd 1 2,723,159,348 286,617,532 91.700995 570.042751
mozilla zstd 3 2,665,055,001 286,152,013 95.240155 561.412805
mozilla zstd 5 2,607,819,817 288,060,030 101.978048 505.152906
mozilla zstd 10 2,558,761,085 283,967,648 104.113481 497.771202
mozilla zstd 15 2,526,216,060 275,581,300 105.853099 591.930683
mozilla zstd 20 2,485,114,806 266,478,859 95.268795 576.515389
mozilla zstd 22 2,484,869,080 266,456,505 94.429282 572.785537
author | Pierre-Yves David <pierre-yves.david@octobus.net> |
---|---|
date | Wed, 27 Mar 2019 18:35:59 +0100 |
parents | 25694a78e4a4 |
children | 2372284d9457 |
line wrap: on
line source
# encoding.py - character transcoding support for Mercurial # # Copyright 2005-2009 Matt Mackall <mpm@selenic.com> and others # # This software may be used and distributed according to the terms of the # GNU General Public License version 2 or any later version. from __future__ import absolute_import, print_function import locale import os import unicodedata from . import ( error, policy, pycompat, ) from .pure import ( charencode as charencodepure, ) charencode = policy.importmod(r'charencode') isasciistr = charencode.isasciistr asciilower = charencode.asciilower asciiupper = charencode.asciiupper _jsonescapeu8fast = charencode.jsonescapeu8fast _sysstr = pycompat.sysstr if pycompat.ispy3: unichr = chr # These unicode characters are ignored by HFS+ (Apple Technote 1150, # "Unicode Subtleties"), so we need to ignore them in some places for # sanity. _ignore = [unichr(int(x, 16)).encode("utf-8") for x in "200c 200d 200e 200f 202a 202b 202c 202d 202e " "206a 206b 206c 206d 206e 206f feff".split()] # verify the next function will work assert all(i.startswith(("\xe2", "\xef")) for i in _ignore) def hfsignoreclean(s): """Remove codepoints ignored by HFS+ from s. >>> hfsignoreclean(u'.h\u200cg'.encode('utf-8')) '.hg' >>> hfsignoreclean(u'.h\ufeffg'.encode('utf-8')) '.hg' """ if "\xe2" in s or "\xef" in s: for c in _ignore: s = s.replace(c, '') return s # encoding.environ is provided read-only, which may not be used to modify # the process environment _nativeenviron = (not pycompat.ispy3 or os.supports_bytes_environ) if not pycompat.ispy3: environ = os.environ # re-exports elif _nativeenviron: environ = os.environb # re-exports else: # preferred encoding isn't known yet; use utf-8 to avoid unicode error # and recreate it once encoding is settled environ = dict((k.encode(r'utf-8'), v.encode(r'utf-8')) for k, v in os.environ.items()) # re-exports _encodingrewrites = { '646': 'ascii', 'ANSI_X3.4-1968': 'ascii', } # cp65001 is a Windows variant of utf-8, which isn't supported on Python 2. # No idea if it should be rewritten to the canonical name 'utf-8' on Python 3. # https://bugs.python.org/issue13216 if pycompat.iswindows and not pycompat.ispy3: _encodingrewrites['cp65001'] = 'utf-8' try: encoding = environ.get("HGENCODING") if not encoding: encoding = locale.getpreferredencoding().encode('ascii') or 'ascii' encoding = _encodingrewrites.get(encoding, encoding) except locale.Error: encoding = 'ascii' encodingmode = environ.get("HGENCODINGMODE", "strict") fallbackencoding = 'ISO-8859-1' class localstr(bytes): '''This class allows strings that are unmodified to be round-tripped to the local encoding and back''' def __new__(cls, u, l): s = bytes.__new__(cls, l) s._utf8 = u return s def __hash__(self): return hash(self._utf8) # avoid collisions in local string space class safelocalstr(bytes): """Tagged string denoting it was previously an internal UTF-8 string, and can be converted back to UTF-8 losslessly >>> assert safelocalstr(b'\\xc3') == b'\\xc3' >>> assert b'\\xc3' == safelocalstr(b'\\xc3') >>> assert b'\\xc3' in {safelocalstr(b'\\xc3'): 0} >>> assert safelocalstr(b'\\xc3') in {b'\\xc3': 0} """ def tolocal(s): """ Convert a string from internal UTF-8 to local encoding All internal strings should be UTF-8 but some repos before the implementation of locale support may contain latin1 or possibly other character sets. We attempt to decode everything strictly using UTF-8, then Latin-1, and failing that, we use UTF-8 and replace unknown characters. The localstr class is used to cache the known UTF-8 encoding of strings next to their local representation to allow lossless round-trip conversion back to UTF-8. >>> u = b'foo: \\xc3\\xa4' # utf-8 >>> l = tolocal(u) >>> l 'foo: ?' >>> fromlocal(l) 'foo: \\xc3\\xa4' >>> u2 = b'foo: \\xc3\\xa1' >>> d = { l: 1, tolocal(u2): 2 } >>> len(d) # no collision 2 >>> b'foo: ?' in d False >>> l1 = b'foo: \\xe4' # historical latin1 fallback >>> l = tolocal(l1) >>> l 'foo: ?' >>> fromlocal(l) # magically in utf-8 'foo: \\xc3\\xa4' """ if isasciistr(s): return s try: try: # make sure string is actually stored in UTF-8 u = s.decode('UTF-8') if encoding == 'UTF-8': # fast path return s r = u.encode(_sysstr(encoding), r"replace") if u == r.decode(_sysstr(encoding)): # r is a safe, non-lossy encoding of s return safelocalstr(r) return localstr(s, r) except UnicodeDecodeError: # we should only get here if we're looking at an ancient changeset try: u = s.decode(_sysstr(fallbackencoding)) r = u.encode(_sysstr(encoding), r"replace") if u == r.decode(_sysstr(encoding)): # r is a safe, non-lossy encoding of s return safelocalstr(r) return localstr(u.encode('UTF-8'), r) except UnicodeDecodeError: u = s.decode("utf-8", "replace") # last ditch # can't round-trip return u.encode(_sysstr(encoding), r"replace") except LookupError as k: raise error.Abort(k, hint="please check your locale settings") def fromlocal(s): """ Convert a string from the local character encoding to UTF-8 We attempt to decode strings using the encoding mode set by HGENCODINGMODE, which defaults to 'strict'. In this mode, unknown characters will cause an error message. Other modes include 'replace', which replaces unknown characters with a special Unicode character, and 'ignore', which drops the character. """ # can we do a lossless round-trip? if isinstance(s, localstr): return s._utf8 if isasciistr(s): return s try: u = s.decode(_sysstr(encoding), _sysstr(encodingmode)) return u.encode("utf-8") except UnicodeDecodeError as inst: sub = s[max(0, inst.start - 10):inst.start + 10] raise error.Abort("decoding near '%s': %s!" % (sub, pycompat.bytestr(inst))) except LookupError as k: raise error.Abort(k, hint="please check your locale settings") def unitolocal(u): """Convert a unicode string to a byte string of local encoding""" return tolocal(u.encode('utf-8')) def unifromlocal(s): """Convert a byte string of local encoding to a unicode string""" return fromlocal(s).decode('utf-8') def unimethod(bytesfunc): """Create a proxy method that forwards __unicode__() and __str__() of Python 3 to __bytes__()""" def unifunc(obj): return unifromlocal(bytesfunc(obj)) return unifunc # converter functions between native str and byte string. use these if the # character encoding is not aware (e.g. exception message) or is known to # be locale dependent (e.g. date formatting.) if pycompat.ispy3: strtolocal = unitolocal strfromlocal = unifromlocal strmethod = unimethod else: strtolocal = pycompat.identity strfromlocal = pycompat.identity strmethod = pycompat.identity if not _nativeenviron: # now encoding and helper functions are available, recreate the environ # dict to be exported to other modules environ = dict((tolocal(k.encode(r'utf-8')), tolocal(v.encode(r'utf-8'))) for k, v in os.environ.items()) # re-exports if pycompat.ispy3: # os.getcwd() on Python 3 returns string, but it has os.getcwdb() which # returns bytes. if pycompat.iswindows: # Python 3 on Windows issues a DeprecationWarning about using the bytes # API when os.getcwdb() is called. getcwd = lambda: strtolocal(os.getcwd()) # re-exports else: getcwd = os.getcwdb # re-exports else: getcwd = os.getcwd # re-exports # How to treat ambiguous-width characters. Set to 'wide' to treat as wide. _wide = _sysstr(environ.get("HGENCODINGAMBIGUOUS", "narrow") == "wide" and "WFA" or "WF") def colwidth(s): "Find the column width of a string for display in the local encoding" return ucolwidth(s.decode(_sysstr(encoding), r'replace')) def ucolwidth(d): "Find the column width of a Unicode string for display" eaw = getattr(unicodedata, 'east_asian_width', None) if eaw is not None: return sum([eaw(c) in _wide and 2 or 1 for c in d]) return len(d) def getcols(s, start, c): '''Use colwidth to find a c-column substring of s starting at byte index start''' for x in pycompat.xrange(start + c, len(s)): t = s[start:x] if colwidth(t) == c: return t def trim(s, width, ellipsis='', leftside=False): """Trim string 's' to at most 'width' columns (including 'ellipsis'). If 'leftside' is True, left side of string 's' is trimmed. 'ellipsis' is always placed at trimmed side. >>> from .node import bin >>> def bprint(s): ... print(pycompat.sysstr(s)) >>> ellipsis = b'+++' >>> from . import encoding >>> encoding.encoding = b'utf-8' >>> t = b'1234567890' >>> bprint(trim(t, 12, ellipsis=ellipsis)) 1234567890 >>> bprint(trim(t, 10, ellipsis=ellipsis)) 1234567890 >>> bprint(trim(t, 8, ellipsis=ellipsis)) 12345+++ >>> bprint(trim(t, 8, ellipsis=ellipsis, leftside=True)) +++67890 >>> bprint(trim(t, 8)) 12345678 >>> bprint(trim(t, 8, leftside=True)) 34567890 >>> bprint(trim(t, 3, ellipsis=ellipsis)) +++ >>> bprint(trim(t, 1, ellipsis=ellipsis)) + >>> u = u'\u3042\u3044\u3046\u3048\u304a' # 2 x 5 = 10 columns >>> t = u.encode(pycompat.sysstr(encoding.encoding)) >>> bprint(trim(t, 12, ellipsis=ellipsis)) \xe3\x81\x82\xe3\x81\x84\xe3\x81\x86\xe3\x81\x88\xe3\x81\x8a >>> bprint(trim(t, 10, ellipsis=ellipsis)) \xe3\x81\x82\xe3\x81\x84\xe3\x81\x86\xe3\x81\x88\xe3\x81\x8a >>> bprint(trim(t, 8, ellipsis=ellipsis)) \xe3\x81\x82\xe3\x81\x84+++ >>> bprint(trim(t, 8, ellipsis=ellipsis, leftside=True)) +++\xe3\x81\x88\xe3\x81\x8a >>> bprint(trim(t, 5)) \xe3\x81\x82\xe3\x81\x84 >>> bprint(trim(t, 5, leftside=True)) \xe3\x81\x88\xe3\x81\x8a >>> bprint(trim(t, 4, ellipsis=ellipsis)) +++ >>> bprint(trim(t, 4, ellipsis=ellipsis, leftside=True)) +++ >>> t = bin(b'112233445566778899aa') # invalid byte sequence >>> bprint(trim(t, 12, ellipsis=ellipsis)) \x11\x22\x33\x44\x55\x66\x77\x88\x99\xaa >>> bprint(trim(t, 10, ellipsis=ellipsis)) \x11\x22\x33\x44\x55\x66\x77\x88\x99\xaa >>> bprint(trim(t, 8, ellipsis=ellipsis)) \x11\x22\x33\x44\x55+++ >>> bprint(trim(t, 8, ellipsis=ellipsis, leftside=True)) +++\x66\x77\x88\x99\xaa >>> bprint(trim(t, 8)) \x11\x22\x33\x44\x55\x66\x77\x88 >>> bprint(trim(t, 8, leftside=True)) \x33\x44\x55\x66\x77\x88\x99\xaa >>> bprint(trim(t, 3, ellipsis=ellipsis)) +++ >>> bprint(trim(t, 1, ellipsis=ellipsis)) + """ try: u = s.decode(_sysstr(encoding)) except UnicodeDecodeError: if len(s) <= width: # trimming is not needed return s width -= len(ellipsis) if width <= 0: # no enough room even for ellipsis return ellipsis[:width + len(ellipsis)] if leftside: return ellipsis + s[-width:] return s[:width] + ellipsis if ucolwidth(u) <= width: # trimming is not needed return s width -= len(ellipsis) if width <= 0: # no enough room even for ellipsis return ellipsis[:width + len(ellipsis)] if leftside: uslice = lambda i: u[i:] concat = lambda s: ellipsis + s else: uslice = lambda i: u[:-i] concat = lambda s: s + ellipsis for i in pycompat.xrange(1, len(u)): usub = uslice(i) if ucolwidth(usub) <= width: return concat(usub.encode(_sysstr(encoding))) return ellipsis # no enough room for multi-column characters def lower(s): "best-effort encoding-aware case-folding of local string s" try: return asciilower(s) except UnicodeDecodeError: pass try: if isinstance(s, localstr): u = s._utf8.decode("utf-8") else: u = s.decode(_sysstr(encoding), _sysstr(encodingmode)) lu = u.lower() if u == lu: return s # preserve localstring return lu.encode(_sysstr(encoding)) except UnicodeError: return s.lower() # we don't know how to fold this except in ASCII except LookupError as k: raise error.Abort(k, hint="please check your locale settings") def upper(s): "best-effort encoding-aware case-folding of local string s" try: return asciiupper(s) except UnicodeDecodeError: return upperfallback(s) def upperfallback(s): try: if isinstance(s, localstr): u = s._utf8.decode("utf-8") else: u = s.decode(_sysstr(encoding), _sysstr(encodingmode)) uu = u.upper() if u == uu: return s # preserve localstring return uu.encode(_sysstr(encoding)) except UnicodeError: return s.upper() # we don't know how to fold this except in ASCII except LookupError as k: raise error.Abort(k, hint="please check your locale settings") class normcasespecs(object): '''what a platform's normcase does to ASCII strings This is specified per platform, and should be consistent with what normcase on that platform actually does. lower: normcase lowercases ASCII strings upper: normcase uppercases ASCII strings other: the fallback function should always be called This should be kept in sync with normcase_spec in util.h.''' lower = -1 upper = 1 other = 0 def jsonescape(s, paranoid=False): '''returns a string suitable for JSON JSON is problematic for us because it doesn't support non-Unicode bytes. To deal with this, we take the following approach: - localstr/safelocalstr objects are converted back to UTF-8 - valid UTF-8/ASCII strings are passed as-is - other strings are converted to UTF-8b surrogate encoding - apply JSON-specified string escaping (escapes are doubled in these tests) >>> jsonescape(b'this is a test') 'this is a test' >>> jsonescape(b'escape characters: \\0 \\x0b \\x7f') 'escape characters: \\\\u0000 \\\\u000b \\\\u007f' >>> jsonescape(b'escape characters: \\b \\t \\n \\f \\r \\" \\\\') 'escape characters: \\\\b \\\\t \\\\n \\\\f \\\\r \\\\" \\\\\\\\' >>> jsonescape(b'a weird byte: \\xdd') 'a weird byte: \\xed\\xb3\\x9d' >>> jsonescape(b'utf-8: caf\\xc3\\xa9') 'utf-8: caf\\xc3\\xa9' >>> jsonescape(b'') '' If paranoid, non-ascii and common troublesome characters are also escaped. This is suitable for web output. >>> s = b'escape characters: \\0 \\x0b \\x7f' >>> assert jsonescape(s) == jsonescape(s, paranoid=True) >>> s = b'escape characters: \\b \\t \\n \\f \\r \\" \\\\' >>> assert jsonescape(s) == jsonescape(s, paranoid=True) >>> jsonescape(b'escape boundary: \\x7e \\x7f \\xc2\\x80', paranoid=True) 'escape boundary: ~ \\\\u007f \\\\u0080' >>> jsonescape(b'a weird byte: \\xdd', paranoid=True) 'a weird byte: \\\\udcdd' >>> jsonescape(b'utf-8: caf\\xc3\\xa9', paranoid=True) 'utf-8: caf\\\\u00e9' >>> jsonescape(b'non-BMP: \\xf0\\x9d\\x84\\x9e', paranoid=True) 'non-BMP: \\\\ud834\\\\udd1e' >>> jsonescape(b'<foo@example.org>', paranoid=True) '\\\\u003cfoo@example.org\\\\u003e' ''' u8chars = toutf8b(s) try: return _jsonescapeu8fast(u8chars, paranoid) except ValueError: pass return charencodepure.jsonescapeu8fallback(u8chars, paranoid) # We need to decode/encode U+DCxx codes transparently since invalid UTF-8 # bytes are mapped to that range. if pycompat.ispy3: _utf8strict = r'surrogatepass' else: _utf8strict = r'strict' _utf8len = [0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 2, 2, 3, 4] def getutf8char(s, pos): '''get the next full utf-8 character in the given string, starting at pos Raises a UnicodeError if the given location does not start a valid utf-8 character. ''' # find how many bytes to attempt decoding from first nibble l = _utf8len[ord(s[pos:pos + 1]) >> 4] if not l: # ascii return s[pos:pos + 1] c = s[pos:pos + l] # validate with attempted decode c.decode("utf-8", _utf8strict) return c def toutf8b(s): '''convert a local, possibly-binary string into UTF-8b This is intended as a generic method to preserve data when working with schemes like JSON and XML that have no provision for arbitrary byte strings. As Mercurial often doesn't know what encoding data is in, we use so-called UTF-8b. If a string is already valid UTF-8 (or ASCII), it passes unmodified. Otherwise, unsupported bytes are mapped to UTF-16 surrogate range, uDC00-uDCFF. Principles of operation: - ASCII and UTF-8 data successfully round-trips and is understood by Unicode-oriented clients - filenames and file contents in arbitrary other encodings can have be round-tripped or recovered by clueful clients - local strings that have a cached known UTF-8 encoding (aka localstr) get sent as UTF-8 so Unicode-oriented clients get the Unicode data they want - non-lossy local strings (aka safelocalstr) get sent as UTF-8 as well - because we must preserve UTF-8 bytestring in places such as filenames, metadata can't be roundtripped without help (Note: "UTF-8b" often refers to decoding a mix of valid UTF-8 and arbitrary bytes into an internal Unicode format that can be re-encoded back into the original. Here we are exposing the internal surrogate encoding as a UTF-8 string.) ''' if isinstance(s, localstr): # assume that the original UTF-8 sequence would never contain # invalid characters in U+DCxx range return s._utf8 elif isinstance(s, safelocalstr): # already verified that s is non-lossy in legacy encoding, which # shouldn't contain characters in U+DCxx range return fromlocal(s) elif isasciistr(s): return s if "\xed" not in s: try: s.decode('utf-8', _utf8strict) return s except UnicodeDecodeError: pass s = pycompat.bytestr(s) r = "" pos = 0 l = len(s) while pos < l: try: c = getutf8char(s, pos) if "\xed\xb0\x80" <= c <= "\xed\xb3\xbf": # have to re-escape existing U+DCxx characters c = unichr(0xdc00 + ord(s[pos])).encode('utf-8', _utf8strict) pos += 1 else: pos += len(c) except UnicodeDecodeError: c = unichr(0xdc00 + ord(s[pos])).encode('utf-8', _utf8strict) pos += 1 r += c return r def fromutf8b(s): '''Given a UTF-8b string, return a local, possibly-binary string. return the original binary string. This is a round-trip process for strings like filenames, but metadata that's was passed through tolocal will remain in UTF-8. >>> roundtrip = lambda x: fromutf8b(toutf8b(x)) == x >>> m = b"\\xc3\\xa9\\x99abcd" >>> toutf8b(m) '\\xc3\\xa9\\xed\\xb2\\x99abcd' >>> roundtrip(m) True >>> roundtrip(b"\\xc2\\xc2\\x80") True >>> roundtrip(b"\\xef\\xbf\\xbd") True >>> roundtrip(b"\\xef\\xef\\xbf\\xbd") True >>> roundtrip(b"\\xf1\\x80\\x80\\x80\\x80") True ''' if isasciistr(s): return s # fast path - look for uDxxx prefixes in s if "\xed" not in s: return s # We could do this with the unicode type but some Python builds # use UTF-16 internally (issue5031) which causes non-BMP code # points to be escaped. Instead, we use our handy getutf8char # helper again to walk the string without "decoding" it. s = pycompat.bytestr(s) r = "" pos = 0 l = len(s) while pos < l: c = getutf8char(s, pos) pos += len(c) # unescape U+DCxx characters if "\xed\xb0\x80" <= c <= "\xed\xb3\xbf": c = pycompat.bytechr(ord(c.decode("utf-8", _utf8strict)) & 0xff) r += c return r