procutil: make stream detection in make_line_buffered more correct and strict

In make_line_buffered(), we don’t want to wrap the stream if we know that lines
get flushed to the underlying raw stream already.

Previously, the heuristic was too optimistic. It assumed that any stream which
is not an instance of io.BufferedIOBase doesn’t need wrapping. However, there
are buffered streams that aren’t instances of io.BufferedIOBase, like
Mercurial’s own winstdout.

The new logic is different in two ways:

First, only for the check, if unwraps any combination of WriteAllWrapper and
winstdout.

Second, it skips wrapping the stream only if it is an instance of io.RawIOBase
(or already wrapped). If it is an instance of io.BufferedIOBase, it gets
wrapped. In any other case, the function raises an exception. This ensures
that, if an unknown stream is passed or we add another wrapper in the future,
we don’t wrap the stream if it’s already line buffered or not wrap the stream
if it’s not line buffered. In fact, this was already helpful during development
of this change. Without it, I possibly would have forgot that WriteAllWrapper
needs to be ignored for the check, leading to unnecessary wrapping if stdout is
unbuffered.

The alternative would have been to always wrap unknown streams. However, I
don’t think that anyone would benefit from being less strict. We can expect
streams from the standard library to be subclassing either io.RawIOBase or
io.BufferedIOBase, so running Mercurial in the standard way should not regress
by this change. Py2exe might replace sys.stdout and sys.stderr, but that
currently breaks Mercurial anyway and also these streams don’t claim to be
interactive, so this function is not called for them.

mercurial/utils/procutil.py

@@ -1,770 +1,790
 # procutil.py - utility for managing processes and executable environment
 #
 #  Copyright 2005 K. Thananchayan <[e-mail]>
 #  Copyright 2005-2007 Olivia Mackall <[e-mail]>
 #  Copyright 2006 Vadim Gelfer <[e-mail]>
 #
 # This software may be used and distributed according to the terms of the
 # GNU General Public License version 2 or any later version.
 
 
 import contextlib
 import errno
 import io
 import os
 import signal
 import subprocess
 import sys
 import threading
 import time
 
 from ..i18n import _
 from ..pycompat import (
     getattr,
     open,
 )
 
 from .. import (
     encoding,
     error,
     policy,
     pycompat,
 )
 
 # Import like this to keep import-checker happy
 from ..utils import resourceutil
 
 osutil = policy.importmod('osutil')
 
 if pycompat.iswindows:
     from .. import windows as platform
 else:
     from .. import posix as platform
 
 
 def isatty(fp):
     try:
         return fp.isatty()
     except AttributeError:
         return False
 
 
 class BadFile(io.RawIOBase):
     """Dummy file object to simulate closed stdio behavior"""
 
     def readinto(self, b):
         raise IOError(errno.EBADF, 'Bad file descriptor')
 
     def write(self, b):
         raise IOError(errno.EBADF, 'Bad file descriptor')
 
 
 class LineBufferedWrapper:
     def __init__(self, orig):
         self.orig = orig
 
     def __getattr__(self, attr):
         return getattr(self.orig, attr)
 
     def write(self, s):
         orig = self.orig
         res = orig.write(s)
         if s.endswith(b'\n'):
             orig.flush()
         return res
 
 
 # pytype: disable=attribute-error
 io.BufferedIOBase.register(LineBufferedWrapper)
 # pytype: enable=attribute-error
 
 
 def make_line_buffered(stream):
-    if not isinstance(stream, io.BufferedIOBase):
-        # On Python 3, buffered streams can be expected to subclass
-        # BufferedIOBase. This is definitively the case for the streams
-        # initialized by the interpreter. For unbuffered streams, we don't need
-        # to emulate line buffering.
+    # First, check if we need to wrap the stream.
+    check_stream = stream
+    while True:
+        if isinstance(check_stream, WriteAllWrapper):
+            check_stream = check_stream.orig
+        elif pycompat.iswindows and isinstance(
+            check_stream,
+            # pytype: disable=module-attr
+            platform.winstdout
+            # pytype: enable=module-attr
+        ):
+            check_stream = check_stream.fp
+        else:
+            break
+    if isinstance(check_stream, io.RawIOBase):
+        # The stream is unbuffered, we don't need to emulate line buffering.
         return stream
+    elif isinstance(check_stream, io.BufferedIOBase):
+        # The stream supports some kind of buffering. We can't assume that
+        # lines are flushed. Fall back to wrapping the stream.
+        pass
+    else:
+        raise NotImplementedError(
+            "can't determine whether stream is buffered or not"
+        )
+
     if isinstance(stream, LineBufferedWrapper):
         return stream
     return LineBufferedWrapper(stream)
 
 
 def unwrap_line_buffered(stream):
     if isinstance(stream, LineBufferedWrapper):
         assert not isinstance(stream.orig, LineBufferedWrapper)
         return stream.orig
     return stream
 
 
 class WriteAllWrapper:
     def __init__(self, orig):
         self.orig = orig
 
     def __getattr__(self, attr):
         return getattr(self.orig, attr)
 
     def write(self, s):
         write1 = self.orig.write
         m = memoryview(s)
         total_to_write = len(s)
         total_written = 0
         while total_written < total_to_write:
             c = write1(m[total_written:])
             if c:
                 total_written += c
         return total_written
 
 
 # pytype: disable=attribute-error
 io.IOBase.register(WriteAllWrapper)
 # pytype: enable=attribute-error
 
 
 def _make_write_all(stream):
     if isinstance(stream, WriteAllWrapper):
         return stream
     if isinstance(stream, io.BufferedIOBase):
         # The io.BufferedIOBase.write() contract guarantees that all data is
         # written.
         return stream
     # In general, the write() method of streams is free to write only part of
     # the data.
     return WriteAllWrapper(stream)
 
 
 # Python 3 implements its own I/O streams. Unlike stdio of C library,
 # sys.stdin/stdout/stderr may be None if underlying fd is closed.
 
 # TODO: .buffer might not exist if std streams were replaced; we'll need
 # a silly wrapper to make a bytes stream backed by a unicode one.
 
 if sys.stdin is None:
     stdin = BadFile()
 else:
     stdin = sys.stdin.buffer
 if sys.stdout is None:
     stdout = BadFile()
 else:
     stdout = _make_write_all(sys.stdout.buffer)
 if sys.stderr is None:
     stderr = BadFile()
 else:
     stderr = _make_write_all(sys.stderr.buffer)
 
 if pycompat.iswindows:
     # Work around Windows bugs.
     stdout = platform.winstdout(stdout)  # pytype: disable=module-attr
     stderr = platform.winstdout(stderr)  # pytype: disable=module-attr
 if isatty(stdout):
     # The standard library doesn't offer line-buffered binary streams.
     stdout = make_line_buffered(stdout)
 
 findexe = platform.findexe
 _gethgcmd = platform.gethgcmd
 getuser = platform.getuser
 getpid = os.getpid
 hidewindow = platform.hidewindow
 readpipe = platform.readpipe
 setbinary = platform.setbinary
 setsignalhandler = platform.setsignalhandler
 shellquote = platform.shellquote
 shellsplit = platform.shellsplit
 spawndetached = platform.spawndetached
 sshargs = platform.sshargs
 testpid = platform.testpid
 
 try:
     setprocname = osutil.setprocname
 except AttributeError:
     pass
 try:
     unblocksignal = osutil.unblocksignal
 except AttributeError:
     pass
 
 closefds = pycompat.isposix
 
 
 def explainexit(code):
     """return a message describing a subprocess status
     (codes from kill are negative - not os.system/wait encoding)"""
     if code >= 0:
         return _(b"exited with status %d") % code
     return _(b"killed by signal %d") % -code
 
 
 class _pfile:
     """File-like wrapper for a stream opened by subprocess.Popen()"""
 
     def __init__(self, proc, fp):
         self._proc = proc
         self._fp = fp
 
     def close(self):
         # unlike os.popen(), this returns an integer in subprocess coding
         self._fp.close()
         return self._proc.wait()
 
     def __iter__(self):
         return iter(self._fp)
 
     def __getattr__(self, attr):
         return getattr(self._fp, attr)
 
     def __enter__(self):
         return self
 
     def __exit__(self, exc_type, exc_value, exc_tb):
         self.close()
 
 
 def popen(cmd, mode=b'rb', bufsize=-1):
     if mode == b'rb':
         return _popenreader(cmd, bufsize)
     elif mode == b'wb':
         return _popenwriter(cmd, bufsize)
     raise error.ProgrammingError(b'unsupported mode: %r' % mode)
 
 
 def _popenreader(cmd, bufsize):
     p = subprocess.Popen(
         tonativestr(cmd),
         shell=True,
         bufsize=bufsize,
         close_fds=closefds,
         stdout=subprocess.PIPE,
     )
     return _pfile(p, p.stdout)
 
 
 def _popenwriter(cmd, bufsize):
     p = subprocess.Popen(
         tonativestr(cmd),
         shell=True,
         bufsize=bufsize,
         close_fds=closefds,
         stdin=subprocess.PIPE,
     )
     return _pfile(p, p.stdin)
 
 
 def popen2(cmd, env=None):
     # Setting bufsize to -1 lets the system decide the buffer size.
     # The default for bufsize is 0, meaning unbuffered. This leads to
     # poor performance on Mac OS X: http://bugs.python.org/issue4194
     p = subprocess.Popen(
         tonativestr(cmd),
         shell=True,
         bufsize=-1,
         close_fds=closefds,
         stdin=subprocess.PIPE,
         stdout=subprocess.PIPE,
         env=tonativeenv(env),
     )
     return p.stdin, p.stdout
 
 
 def popen3(cmd, env=None):
     stdin, stdout, stderr, p = popen4(cmd, env)
     return stdin, stdout, stderr
 
 
 def popen4(cmd, env=None, bufsize=-1):
     p = subprocess.Popen(
         tonativestr(cmd),
         shell=True,
         bufsize=bufsize,
         close_fds=closefds,
         stdin=subprocess.PIPE,
         stdout=subprocess.PIPE,
         stderr=subprocess.PIPE,
         env=tonativeenv(env),
     )
     return p.stdin, p.stdout, p.stderr, p
 
 
 def pipefilter(s, cmd):
     '''filter string S through command CMD, returning its output'''
     p = subprocess.Popen(
         tonativestr(cmd),
         shell=True,
         close_fds=closefds,
         stdin=subprocess.PIPE,
         stdout=subprocess.PIPE,
     )
     pout, perr = p.communicate(s)
     return pout
 
 
 def tempfilter(s, cmd):
     """filter string S through a pair of temporary files with CMD.
     CMD is used as a template to create the real command to be run,
     with the strings INFILE and OUTFILE replaced by the real names of
     the temporary files generated."""
     inname, outname = None, None
     try:
         infd, inname = pycompat.mkstemp(prefix=b'hg-filter-in-')
         fp = os.fdopen(infd, 'wb')
         fp.write(s)
         fp.close()
         outfd, outname = pycompat.mkstemp(prefix=b'hg-filter-out-')
         os.close(outfd)
         cmd = cmd.replace(b'INFILE', inname)
         cmd = cmd.replace(b'OUTFILE', outname)
         code = system(cmd)
         if pycompat.sysplatform == b'OpenVMS' and code & 1:
             code = 0
         if code:
             raise error.Abort(
                 _(b"command '%s' failed: %s") % (cmd, explainexit(code))
             )
         with open(outname, b'rb') as fp:
             return fp.read()
     finally:
         try:
             if inname:
                 os.unlink(inname)
         except OSError:
             pass
         try:
             if outname:
                 os.unlink(outname)
         except OSError:
             pass
 
 
 _filtertable = {
     b'tempfile:': tempfilter,
     b'pipe:': pipefilter,
 }
 
 
 def filter(s, cmd):
     """filter a string through a command that transforms its input to its
     output"""
     for name, fn in _filtertable.items():
         if cmd.startswith(name):
             return fn(s, cmd[len(name) :].lstrip())
     return pipefilter(s, cmd)
 
 
 _hgexecutable = None
 
 
 def hgexecutable():
     """return location of the 'hg' executable.
 
     Defaults to $HG or 'hg' in the search path.
     """
     if _hgexecutable is None:
         hg = encoding.environ.get(b'HG')
         mainmod = sys.modules['__main__']
         if hg:
             _sethgexecutable(hg)
         elif resourceutil.mainfrozen():
             if getattr(sys, 'frozen', None) == 'macosx_app':
                 # Env variable set by py2app
                 _sethgexecutable(encoding.environ[b'EXECUTABLEPATH'])
             else:
                 _sethgexecutable(pycompat.sysexecutable)
         elif (
             not pycompat.iswindows
             and os.path.basename(getattr(mainmod, '__file__', '')) == 'hg'
         ):
             _sethgexecutable(pycompat.fsencode(mainmod.__file__))
         else:
             _sethgexecutable(
                 findexe(b'hg') or os.path.basename(pycompat.sysargv[0])
             )
     return _hgexecutable
 
 
 def _sethgexecutable(path):
     """set location of the 'hg' executable"""
     global _hgexecutable
     _hgexecutable = path
 
 
 def _testfileno(f, stdf):
     fileno = getattr(f, 'fileno', None)
     try:
         return fileno and fileno() == stdf.fileno()
     except io.UnsupportedOperation:
         return False  # fileno() raised UnsupportedOperation
 
 
 def isstdin(f):
     return _testfileno(f, sys.__stdin__)
 
 
 def isstdout(f):
     return _testfileno(f, sys.__stdout__)
 
 
 def protectstdio(uin, uout):
     """Duplicate streams and redirect original if (uin, uout) are stdio
 
     If uin is stdin, it's redirected to /dev/null. If uout is stdout, it's
     redirected to stderr so the output is still readable.
 
     Returns (fin, fout) which point to the original (uin, uout) fds, but
     may be copy of (uin, uout). The returned streams can be considered
     "owned" in that print(), exec(), etc. never reach to them.
     """
     uout.flush()
     fin, fout = uin, uout
     if _testfileno(uin, stdin):
         newfd = os.dup(uin.fileno())
         nullfd = os.open(os.devnull, os.O_RDONLY)
         os.dup2(nullfd, uin.fileno())
         os.close(nullfd)
         fin = os.fdopen(newfd, 'rb')
     if _testfileno(uout, stdout):
         newfd = os.dup(uout.fileno())
         os.dup2(stderr.fileno(), uout.fileno())
         fout = os.fdopen(newfd, 'wb')
     return fin, fout
 
 
 def restorestdio(uin, uout, fin, fout):
     """Restore (uin, uout) streams from possibly duplicated (fin, fout)"""
     uout.flush()
     for f, uif in [(fin, uin), (fout, uout)]:
         if f is not uif:
             os.dup2(f.fileno(), uif.fileno())
             f.close()
 
 
 def shellenviron(environ=None):
     """return environ with optional override, useful for shelling out"""
 
     def py2shell(val):
         """convert python object into string that is useful to shell"""
         if val is None or val is False:
             return b'0'
         if val is True:
             return b'1'
         return pycompat.bytestr(val)
 
     env = dict(encoding.environ)
     if environ:
         env.update((k, py2shell(v)) for k, v in environ.items())
     env[b'HG'] = hgexecutable()
     return env
 
 
 if pycompat.iswindows:
 
     def shelltonative(cmd, env):
         return platform.shelltocmdexe(  # pytype: disable=module-attr
             cmd, shellenviron(env)
         )
 
     tonativestr = encoding.strfromlocal
 else:
 
     def shelltonative(cmd, env):
         return cmd
 
     tonativestr = pycompat.identity
 
 
 def tonativeenv(env):
     """convert the environment from bytes to strings suitable for Popen(), etc."""
     return pycompat.rapply(tonativestr, env)
 
 
 def system(cmd, environ=None, cwd=None, out=None):
     """enhanced shell command execution.
     run with environment maybe modified, maybe in different dir.
 
     if out is specified, it is assumed to be a file-like object that has a
     write() method. stdout and stderr will be redirected to out."""
     try:
         stdout.flush()
     except Exception:
         pass
     env = shellenviron(environ)
     if out is None or isstdout(out):
         rc = subprocess.call(
             tonativestr(cmd),
             shell=True,
             close_fds=closefds,
             env=tonativeenv(env),
             cwd=pycompat.rapply(tonativestr, cwd),
         )
     else:
         proc = subprocess.Popen(
             tonativestr(cmd),
             shell=True,
             close_fds=closefds,
             env=tonativeenv(env),
             cwd=pycompat.rapply(tonativestr, cwd),
             stdout=subprocess.PIPE,
             stderr=subprocess.STDOUT,
         )
         for line in iter(proc.stdout.readline, b''):
             out.write(line)
         proc.wait()
         rc = proc.returncode
     if pycompat.sysplatform == b'OpenVMS' and rc & 1:
         rc = 0
     return rc
 
 
 _is_gui = None
 
 
 def _gui():
     '''Are we running in a GUI?'''
     if pycompat.isdarwin:
         if b'SSH_CONNECTION' in encoding.environ:
             # handle SSH access to a box where the user is logged in
             return False
         elif getattr(osutil, 'isgui', None):
             # check if a CoreGraphics session is available
             return osutil.isgui()
         else:
             # pure build; use a safe default
             return True
     else:
         return (
             pycompat.iswindows
             or encoding.environ.get(b"DISPLAY")
             or encoding.environ.get(b"WAYLAND_DISPLAY")
         )
 
 
 def gui():
     global _is_gui
     if _is_gui is None:
         _is_gui = _gui()
     return _is_gui
 
 
 def hgcmd():
     """Return the command used to execute current hg
 
     This is different from hgexecutable() because on Windows we want
     to avoid things opening new shell windows like batch files, so we
     get either the python call or current executable.
     """
     if resourceutil.mainfrozen():
         if getattr(sys, 'frozen', None) == 'macosx_app':
             # Env variable set by py2app
             return [encoding.environ[b'EXECUTABLEPATH']]
         else:
             return [pycompat.sysexecutable]
     return _gethgcmd()
 
 
 def rundetached(args, condfn):
     """Execute the argument list in a detached process.
 
     condfn is a callable which is called repeatedly and should return
     True once the child process is known to have started successfully.
     At this point, the child process PID is returned. If the child
     process fails to start or finishes before condfn() evaluates to
     True, return -1.
     """
     # Windows case is easier because the child process is either
     # successfully starting and validating the condition or exiting
     # on failure. We just poll on its PID. On Unix, if the child
     # process fails to start, it will be left in a zombie state until
     # the parent wait on it, which we cannot do since we expect a long
     # running process on success. Instead we listen for SIGCHLD telling
     # us our child process terminated.
     terminated = set()
 
     def handler(signum, frame):
         terminated.add(os.wait())
 
     prevhandler = None
     SIGCHLD = getattr(signal, 'SIGCHLD', None)
     if SIGCHLD is not None:
         prevhandler = signal.signal(SIGCHLD, handler)
     try:
         pid = spawndetached(args)
         while not condfn():
             if (pid in terminated or not testpid(pid)) and not condfn():
                 return -1
             time.sleep(0.1)
         return pid
     finally:
         if prevhandler is not None:
             signal.signal(signal.SIGCHLD, prevhandler)
 
 
 @contextlib.contextmanager
 def uninterruptible(warn):
     """Inhibit SIGINT handling on a region of code.
 
     Note that if this is called in a non-main thread, it turns into a no-op.
 
     Args:
       warn: A callable which takes no arguments, and returns True if the
             previous signal handling should be restored.
     """
 
     oldsiginthandler = [signal.getsignal(signal.SIGINT)]
     shouldbail = []
 
     def disabledsiginthandler(*args):
         if warn():
             signal.signal(signal.SIGINT, oldsiginthandler[0])
             del oldsiginthandler[0]
         shouldbail.append(True)
 
     try:
         try:
             signal.signal(signal.SIGINT, disabledsiginthandler)
         except ValueError:
             # wrong thread, oh well, we tried
             del oldsiginthandler[0]
         yield
     finally:
         if oldsiginthandler:
             signal.signal(signal.SIGINT, oldsiginthandler[0])
         if shouldbail:
             raise KeyboardInterrupt
 
 
 if pycompat.iswindows:
     # no fork on Windows, but we can create a detached process
     # https://msdn.microsoft.com/en-us/library/windows/desktop/ms684863.aspx
     # No stdlib constant exists for this value
     DETACHED_PROCESS = 0x00000008
     # Following creation flags might create a console GUI window.
     # Using subprocess.CREATE_NEW_CONSOLE might helps.
     # See https://phab.mercurial-scm.org/D1701 for discussion
     _creationflags = (
         DETACHED_PROCESS
         | subprocess.CREATE_NEW_PROCESS_GROUP  # pytype: disable=module-attr
     )
 
     def runbgcommand(
         script,
         env,
         shell=False,
         stdout=None,
         stderr=None,
         ensurestart=True,
         record_wait=None,
         stdin_bytes=None,
     ):
         '''Spawn a command without waiting for it to finish.'''
         # we can't use close_fds *and* redirect stdin. I'm not sure that we
         # need to because the detached process has no console connection.
 
         try:
             stdin = None
             if stdin_bytes is not None:
                 stdin = pycompat.unnamedtempfile()
                 stdin.write(stdin_bytes)
                 stdin.flush()
                 stdin.seek(0)
 
             p = subprocess.Popen(
                 pycompat.rapply(tonativestr, script),
                 shell=shell,
                 env=tonativeenv(env),
                 close_fds=True,
                 creationflags=_creationflags,
                 stdin=stdin,
                 stdout=stdout,
                 stderr=stderr,
             )
             if record_wait is not None:
                 record_wait(p.wait)
         finally:
             if stdin is not None:
                 stdin.close()
 
 
 else:
 
     def runbgcommand(
         cmd,
         env,
         shell=False,
         stdout=None,
         stderr=None,
         ensurestart=True,
         record_wait=None,
         stdin_bytes=None,
     ):
         """Spawn a command without waiting for it to finish.
 
 
         When `record_wait` is not None, the spawned process will not be fully
         detached and the `record_wait` argument will be called with a the
         `Subprocess.wait` function for the spawned process.  This is mostly
         useful for developers that need to make sure the spawned process
         finished before a certain point. (eg: writing test)"""
         if pycompat.isdarwin:
             # avoid crash in CoreFoundation in case another thread
             # calls gui() while we're calling fork().
             gui()
 
         if shell:
             script = cmd
         else:
             if isinstance(cmd, bytes):
                 cmd = [cmd]
             script = b' '.join(shellquote(x) for x in cmd)
         if record_wait is None:
             # double-fork to completely detach from the parent process
             script = b'( %s ) &' % script
             start_new_session = True
         else:
             start_new_session = False
             ensurestart = True
 
         stdin = None
 
         try:
             if stdin_bytes is None:
                 stdin = subprocess.DEVNULL
             else:
                 stdin = pycompat.unnamedtempfile()
                 stdin.write(stdin_bytes)
                 stdin.flush()
                 stdin.seek(0)
             if stdout is None:
                 stdout = subprocess.DEVNULL
             if stderr is None:
                 stderr = subprocess.DEVNULL
 
             p = subprocess.Popen(
                 script,
                 shell=True,
                 env=env,
                 close_fds=True,
                 stdin=stdin,
                 stdout=stdout,
                 stderr=stderr,
                 start_new_session=start_new_session,
             )
         except Exception:
             if record_wait is not None:
                 record_wait(255)
             raise
         finally:
             if stdin_bytes is not None and stdin is not None:
                 assert not isinstance(stdin, int)
                 stdin.close()
         if not ensurestart:
             # Even though we're not waiting on the child process,
             # we still must call waitpid() on it at some point so
             # it's not a zombie/defunct. This is especially relevant for
             # chg since the parent process won't die anytime soon.
             # We use a thread to make the overhead tiny.
             t = threading.Thread(target=lambda: p.wait)
             t.daemon = True
             t.start()
         else:
             returncode = p.wait
             if record_wait is not None:
                 record_wait(returncode)