view mercurial/util.py @ 3014:01454af644b8

load extensions only after the ui object has been completely initialized

This fixes a traceback printed when hg tries to print another traceback
after an extension fails to be loaded.  Add a test for that.

"""
util.py - Mercurial utility functions and platform specfic implementations

 Copyright 2005 K. Thananchayan <[e-mail]>
 Copyright 2005, 2006 Matt 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, incorporated herein by reference.

This contains helper routines that are independent of the SCM core and hide
platform-specific details from the core.
"""

from i18n import gettext as _
from demandload import *
demandload(globals(), "cStringIO errno getpass popen2 re shutil sys tempfile")
demandload(globals(), "os threading time pwd grp")

# used by parsedate
defaultdateformats = ('%Y-%m-%d %H:%M:%S', '%Y-%m-%d %H:%M',
                      '%a %b %d %H:%M:%S %Y')

class SignalInterrupt(Exception):
    """Exception raised on SIGTERM and SIGHUP."""

def pipefilter(s, cmd):
    '''filter string S through command CMD, returning its output'''
    (pout, pin) = popen2.popen2(cmd, -1, 'b')
    def writer():
        try:
            pin.write(s)
            pin.close()
        except IOError, inst:
            if inst.errno != errno.EPIPE:
                raise

    # we should use select instead on UNIX, but this will work on most
    # systems, including Windows
    w = threading.Thread(target=writer)
    w.start()
    f = pout.read()
    pout.close()
    w.join()
    return f

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 = tempfile.mkstemp(prefix='hg-filter-in-')
        fp = os.fdopen(infd, 'wb')
        fp.write(s)
        fp.close()
        outfd, outname = tempfile.mkstemp(prefix='hg-filter-out-')
        os.close(outfd)
        cmd = cmd.replace('INFILE', inname)
        cmd = cmd.replace('OUTFILE', outname)
        code = os.system(cmd)
        if code: raise Abort(_("command '%s' failed: %s") %
                             (cmd, explain_exit(code)))
        return open(outname, 'rb').read()
    finally:
        try:
            if inname: os.unlink(inname)
        except: pass
        try:
            if outname: os.unlink(outname)
        except: pass

filtertable = {
    'tempfile:': tempfilter,
    'pipe:': pipefilter,
    }

def filter(s, cmd):
    "filter a string through a command that transforms its input to its output"
    for name, fn in filtertable.iteritems():
        if cmd.startswith(name):
            return fn(s, cmd[len(name):].lstrip())
    return pipefilter(s, cmd)

def find_in_path(name, path, default=None):
    '''find name in search path. path can be string (will be split
    with os.pathsep), or iterable thing that returns strings.  if name
    found, return path to name. else return default.'''
    if isinstance(path, str):
        path = path.split(os.pathsep)
    for p in path:
        p_name = os.path.join(p, name)
        if os.path.exists(p_name):
            return p_name
    return default

def binary(s):
    """return true if a string is binary data using diff's heuristic"""
    if s and '\0' in s[:4096]:
        return True
    return False

def unique(g):
    """return the uniq elements of iterable g"""
    seen = {}
    for f in g:
        if f not in seen:
            seen[f] = 1
            yield f

class Abort(Exception):
    """Raised if a command needs to print an error and exit."""

def always(fn): return True
def never(fn): return False

def patkind(name, dflt_pat='glob'):
    """Split a string into an optional pattern kind prefix and the
    actual pattern."""
    for prefix in 're', 'glob', 'path', 'relglob', 'relpath', 'relre':
        if name.startswith(prefix + ':'): return name.split(':', 1)
    return dflt_pat, name

def globre(pat, head='^', tail='$'):
    "convert a glob pattern into a regexp"
    i, n = 0, len(pat)
    res = ''
    group = False
    def peek(): return i < n and pat[i]
    while i < n:
        c = pat[i]
        i = i+1
        if c == '*':
            if peek() == '*':
                i += 1
                res += '.*'
            else:
                res += '[^/]*'
        elif c == '?':
            res += '.'
        elif c == '[':
            j = i
            if j < n and pat[j] in '!]':
                j += 1
            while j < n and pat[j] != ']':
                j += 1
            if j >= n:
                res += '\\['
            else:
                stuff = pat[i:j].replace('\\','\\\\')
                i = j + 1
                if stuff[0] == '!':
                    stuff = '^' + stuff[1:]
                elif stuff[0] == '^':
                    stuff = '\\' + stuff
                res = '%s[%s]' % (res, stuff)
        elif c == '{':
            group = True
            res += '(?:'
        elif c == '}' and group:
            res += ')'
            group = False
        elif c == ',' and group:
            res += '|'
        elif c == '\\':
            p = peek()
            if p:
                i += 1
                res += re.escape(p)
            else:
                res += re.escape(c)
        else:
            res += re.escape(c)
    return head + res + tail

_globchars = {'[': 1, '{': 1, '*': 1, '?': 1}

def pathto(n1, n2):
    '''return the relative path from one place to another.
    this returns a path in the form used by the local filesystem, not hg.'''
    if not n1: return localpath(n2)
    a, b = n1.split('/'), n2.split('/')
    a.reverse()
    b.reverse()
    while a and b and a[-1] == b[-1]:
        a.pop()
        b.pop()
    b.reverse()
    return os.sep.join((['..'] * len(a)) + b)

def canonpath(root, cwd, myname):
    """return the canonical path of myname, given cwd and root"""
    if root == os.sep:
        rootsep = os.sep
    elif root.endswith(os.sep):
        rootsep = root
    else:
        rootsep = root + os.sep
    name = myname
    if not os.path.isabs(name):
        name = os.path.join(root, cwd, name)
    name = os.path.normpath(name)
    if name != rootsep and name.startswith(rootsep):
        name = name[len(rootsep):]
        audit_path(name)
        return pconvert(name)
    elif name == root:
        return ''
    else:
        # Determine whether `name' is in the hierarchy at or beneath `root',
        # by iterating name=dirname(name) until that causes no change (can't
        # check name == '/', because that doesn't work on windows).  For each
        # `name', compare dev/inode numbers.  If they match, the list `rel'
        # holds the reversed list of components making up the relative file
        # name we want.
        root_st = os.stat(root)
        rel = []
        while True:
            try:
                name_st = os.stat(name)
            except OSError:
                break
            if samestat(name_st, root_st):
                rel.reverse()
                name = os.path.join(*rel)
                audit_path(name)
                return pconvert(name)
            dirname, basename = os.path.split(name)
            rel.append(basename)
            if dirname == name:
                break
            name = dirname

        raise Abort('%s not under root' % myname)

def matcher(canonroot, cwd='', names=['.'], inc=[], exc=[], head='', src=None):
    return _matcher(canonroot, cwd, names, inc, exc, head, 'glob', src)

def cmdmatcher(canonroot, cwd='', names=['.'], inc=[], exc=[], head='', src=None):
    if os.name == 'nt':
        dflt_pat = 'glob'
    else:
        dflt_pat = 'relpath'
    return _matcher(canonroot, cwd, names, inc, exc, head, dflt_pat, src)

def _matcher(canonroot, cwd, names, inc, exc, head, dflt_pat, src):
    """build a function to match a set of file patterns

    arguments:
    canonroot - the canonical root of the tree you're matching against
    cwd - the current working directory, if relevant
    names - patterns to find
    inc - patterns to include
    exc - patterns to exclude
    head - a regex to prepend to patterns to control whether a match is rooted

    a pattern is one of:
    'glob:<rooted glob>'
    're:<rooted regexp>'
    'path:<rooted path>'
    'relglob:<relative glob>'
    'relpath:<relative path>'
    'relre:<relative regexp>'
    '<rooted path or regexp>'

    returns:
    a 3-tuple containing
    - list of explicit non-pattern names passed in
    - a bool match(filename) function
    - a bool indicating if any patterns were passed in

    todo:
    make head regex a rooted bool
    """

    def contains_glob(name):
        for c in name:
            if c in _globchars: return True
        return False

    def regex(kind, name, tail):
        '''convert a pattern into a regular expression'''
        if kind == 're':
            return name
        elif kind == 'path':
            return '^' + re.escape(name) + '(?:/|$)'
        elif kind == 'relglob':
            return head + globre(name, '(?:|.*/)', tail)
        elif kind == 'relpath':
            return head + re.escape(name) + tail
        elif kind == 'relre':
            if name.startswith('^'):
                return name
            return '.*' + name
        return head + globre(name, '', tail)

    def matchfn(pats, tail):
        """build a matching function from a set of patterns"""
        if not pats:
            return
        matches = []
        for k, p in pats:
            try:
                pat = '(?:%s)' % regex(k, p, tail)
                matches.append(re.compile(pat).match)
            except re.error:
                if src: raise Abort("%s: invalid pattern (%s): %s" % (src, k, p))
                else: raise Abort("invalid pattern (%s): %s" % (k, p))

        def buildfn(text):
            for m in matches:
                r = m(text)
                if r:
                    return r

        return buildfn

    def globprefix(pat):
        '''return the non-glob prefix of a path, e.g. foo/* -> foo'''
        root = []
        for p in pat.split(os.sep):
            if contains_glob(p): break
            root.append(p)
        return '/'.join(root)

    pats = []
    files = []
    roots = []
    for kind, name in [patkind(p, dflt_pat) for p in names]:
        if kind in ('glob', 'relpath'):
            name = canonpath(canonroot, cwd, name)
            if name == '':
                kind, name = 'glob', '**'
        if kind in ('glob', 'path', 're'):
            pats.append((kind, name))
        if kind == 'glob':
            root = globprefix(name)
            if root: roots.append(root)
        elif kind == 'relpath':
            files.append((kind, name))
            roots.append(name)

    patmatch = matchfn(pats, '$') or always
    filematch = matchfn(files, '(?:/|$)') or always
    incmatch = always
    if inc:
        inckinds = [patkind(canonpath(canonroot, cwd, i)) for i in inc]
        incmatch = matchfn(inckinds, '(?:/|$)')
    excmatch = lambda fn: False
    if exc:
        exckinds = [patkind(canonpath(canonroot, cwd, x)) for x in exc]
        excmatch = matchfn(exckinds, '(?:/|$)')

    return (roots,
            lambda fn: (incmatch(fn) and not excmatch(fn) and
                        (fn.endswith('/') or
                         (not pats and not files) or
                         (pats and patmatch(fn)) or
                         (files and filematch(fn)))),
            (inc or exc or (pats and pats != [('glob', '**')])) and True)

def system(cmd, environ={}, cwd=None, onerr=None, errprefix=None):
    '''enhanced shell command execution.
    run with environment maybe modified, maybe in different dir.

    if command fails and onerr is None, return status.  if ui object,
    print error message and return status, else raise onerr object as
    exception.'''
    def py2shell(val):
        'convert python object into string that is useful to shell'
        if val in (None, False):
            return '0'
        if val == True:
            return '1'
        return str(val)
    oldenv = {}
    for k in environ:
        oldenv[k] = os.environ.get(k)
    if cwd is not None:
        oldcwd = os.getcwd()
    try:
        for k, v in environ.iteritems():
            os.environ[k] = py2shell(v)
        if cwd is not None and oldcwd != cwd:
            os.chdir(cwd)
        rc = os.system(cmd)
        if rc and onerr:
            errmsg = '%s %s' % (os.path.basename(cmd.split(None, 1)[0]),
                                explain_exit(rc)[0])
            if errprefix:
                errmsg = '%s: %s' % (errprefix, errmsg)
            try:
                onerr.warn(errmsg + '\n')
            except AttributeError:
                raise onerr(errmsg)
        return rc
    finally:
        for k, v in oldenv.iteritems():
            if v is None:
                del os.environ[k]
            else:
                os.environ[k] = v
        if cwd is not None and oldcwd != cwd:
            os.chdir(oldcwd)

def rename(src, dst):
    """forcibly rename a file"""
    try:
        os.rename(src, dst)
    except OSError, err:
        # on windows, rename to existing file is not allowed, so we
        # must delete destination first. but if file is open, unlink
        # schedules it for delete but does not delete it. rename
        # happens immediately even for open files, so we create
        # temporary file, delete it, rename destination to that name,
        # then delete that. then rename is safe to do.
        fd, temp = tempfile.mkstemp(dir=os.path.dirname(dst) or '.')
        os.close(fd)
        os.unlink(temp)
        os.rename(dst, temp)
        os.unlink(temp)
        os.rename(src, dst)

def unlink(f):
    """unlink and remove the directory if it is empty"""
    os.unlink(f)
    # try removing directories that might now be empty
    try:
        os.removedirs(os.path.dirname(f))
    except OSError:
        pass

def copyfiles(src, dst, hardlink=None):
    """Copy a directory tree using hardlinks if possible"""

    if hardlink is None:
        hardlink = (os.stat(src).st_dev ==
                    os.stat(os.path.dirname(dst)).st_dev)

    if os.path.isdir(src):
        os.mkdir(dst)
        for name in os.listdir(src):
            srcname = os.path.join(src, name)
            dstname = os.path.join(dst, name)
            copyfiles(srcname, dstname, hardlink)
    else:
        if hardlink:
            try:
                os_link(src, dst)
            except (IOError, OSError):
                hardlink = False
                shutil.copy(src, dst)
        else:
            shutil.copy(src, dst)

def audit_path(path):
    """Abort if path contains dangerous components"""
    parts = os.path.normcase(path).split(os.sep)
    if (os.path.splitdrive(path)[0] or parts[0] in ('.hg', '')
        or os.pardir in parts):
        raise Abort(_("path contains illegal component: %s\n") % path)

def _makelock_file(info, pathname):
    ld = os.open(pathname, os.O_CREAT | os.O_WRONLY | os.O_EXCL)
    os.write(ld, info)
    os.close(ld)

def _readlock_file(pathname):
    return posixfile(pathname).read()

def nlinks(pathname):
    """Return number of hardlinks for the given file."""
    return os.lstat(pathname).st_nlink

if hasattr(os, 'link'):
    os_link = os.link
else:
    def os_link(src, dst):
        raise OSError(0, _("Hardlinks not supported"))

def fstat(fp):
    '''stat file object that may not have fileno method.'''
    try:
        return os.fstat(fp.fileno())
    except AttributeError:
        return os.stat(fp.name)

posixfile = file

def is_win_9x():
    '''return true if run on windows 95, 98 or me.'''
    try:
        return sys.getwindowsversion()[3] == 1
    except AttributeError:
        return os.name == 'nt' and 'command' in os.environ.get('comspec', '')

getuser_fallback = None

def getuser():
    '''return name of current user'''
    try:
        return getpass.getuser()
    except ImportError:
        # import of pwd will fail on windows - try fallback
        if getuser_fallback:
            return getuser_fallback()
    # raised if win32api not available
    raise Abort(_('user name not available - set USERNAME '
                  'environment variable'))

def username(uid=None):
    """Return the name of the user with the given uid.

    If uid is None, return the name of the current user."""
    try:
        # force an ImportError if there's no module pwd
        getpwuid = pwd.getpwuid
        if uid is None:
            uid = os.getuid()
        try:
            return getpwuid(uid)[0]
        except KeyError:
            return str(uid)
    except ImportError:
        return None

def groupname(gid=None):
    """Return the name of the group with the given gid.

    If gid is None, return the name of the current group."""
    try:
        # force an ImportError if there's no module grp
        getgrgid = grp.getgrgid
        if gid is None:
            gid = os.getgid()
        try:
            return getgrgid(gid)[0]
        except KeyError:
            return str(gid)
    except ImportError:
        return None

# Platform specific variants
if os.name == 'nt':
    demandload(globals(), "msvcrt")
    nulldev = 'NUL:'

    class winstdout:
        '''stdout on windows misbehaves if sent through a pipe'''

        def __init__(self, fp):
            self.fp = fp

        def __getattr__(self, key):
            return getattr(self.fp, key)

        def close(self):
            try:
                self.fp.close()
            except: pass

        def write(self, s):
            try:
                return self.fp.write(s)
            except IOError, inst:
                if inst.errno != 0: raise
                self.close()
                raise IOError(errno.EPIPE, 'Broken pipe')

    sys.stdout = winstdout(sys.stdout)

    def system_rcpath():
        try:
            return system_rcpath_win32()
        except:
            return [r'c:\mercurial\mercurial.ini']

    def os_rcpath():
        '''return default os-specific hgrc search path'''
        path = system_rcpath()
        path.append(user_rcpath())
        userprofile = os.environ.get('USERPROFILE')
        if userprofile:
            path.append(os.path.join(userprofile, 'mercurial.ini'))
        return path

    def user_rcpath():
         '''return os-specific hgrc search path to the user dir'''
         return os.path.join(os.path.expanduser('~'), 'mercurial.ini')

    def parse_patch_output(output_line):
        """parses the output produced by patch and returns the file name"""
        pf = output_line[14:]
        if pf[0] == '`':
            pf = pf[1:-1] # Remove the quotes
        return pf

    def testpid(pid):
        '''return False if pid dead, True if running or not known'''
        return True

    def is_exec(f, last):
        return last

    def set_exec(f, mode):
        pass

    def set_binary(fd):
        msvcrt.setmode(fd.fileno(), os.O_BINARY)

    def pconvert(path):
        return path.replace("\\", "/")

    def localpath(path):
        return path.replace('/', '\\')

    def normpath(path):
        return pconvert(os.path.normpath(path))

    makelock = _makelock_file
    readlock = _readlock_file

    def samestat(s1, s2):
        return False

    def shellquote(s):
        return '"%s"' % s.replace('"', '\\"')

    def explain_exit(code):
        return _("exited with status %d") % code, code

    try:
        # override functions with win32 versions if possible
        from util_win32 import *
        if not is_win_9x():
            posixfile = posixfile_nt
    except ImportError:
        pass

else:
    nulldev = '/dev/null'

    def rcfiles(path):
        rcs = [os.path.join(path, 'hgrc')]
        rcdir = os.path.join(path, 'hgrc.d')
        try:
            rcs.extend([os.path.join(rcdir, f) for f in os.listdir(rcdir)
                        if f.endswith(".rc")])
        except OSError, inst: pass
        return rcs

    def os_rcpath():
        '''return default os-specific hgrc search path'''
        path = []
        # old mod_python does not set sys.argv
        if len(getattr(sys, 'argv', [])) > 0:
            path.extend(rcfiles(os.path.dirname(sys.argv[0]) +
                                  '/../etc/mercurial'))
        path.extend(rcfiles('/etc/mercurial'))
        path.append(os.path.expanduser('~/.hgrc'))
        path = [os.path.normpath(f) for f in path]
        return path

    def parse_patch_output(output_line):
        """parses the output produced by patch and returns the file name"""
        pf = output_line[14:]
        if pf.startswith("'") and pf.endswith("'") and " " in pf:
            pf = pf[1:-1] # Remove the quotes
        return pf

    def is_exec(f, last):
        """check whether a file is executable"""
        return (os.lstat(f).st_mode & 0100 != 0)

    def set_exec(f, mode):
        s = os.lstat(f).st_mode
        if (s & 0100 != 0) == mode:
            return
        if mode:
            # Turn on +x for every +r bit when making a file executable
            # and obey umask.
            umask = os.umask(0)
            os.umask(umask)
            os.chmod(f, s | (s & 0444) >> 2 & ~umask)
        else:
            os.chmod(f, s & 0666)

    def set_binary(fd):
        pass

    def pconvert(path):
        return path

    def localpath(path):
        return path

    normpath = os.path.normpath
    samestat = os.path.samestat

    def makelock(info, pathname):
        try:
            os.symlink(info, pathname)
        except OSError, why:
            if why.errno == errno.EEXIST:
                raise
            else:
                _makelock_file(info, pathname)

    def readlock(pathname):
        try:
            return os.readlink(pathname)
        except OSError, why:
            if why.errno == errno.EINVAL:
                return _readlock_file(pathname)
            else:
                raise

    def shellquote(s):
        return "'%s'" % s.replace("'", "'\\''")

    def testpid(pid):
        '''return False if pid dead, True if running or not sure'''
        try:
            os.kill(pid, 0)
            return True
        except OSError, inst:
            return inst.errno != errno.ESRCH

    def explain_exit(code):
        """return a 2-tuple (desc, code) describing a process's status"""
        if os.WIFEXITED(code):
            val = os.WEXITSTATUS(code)
            return _("exited with status %d") % val, val
        elif os.WIFSIGNALED(code):
            val = os.WTERMSIG(code)
            return _("killed by signal %d") % val, val
        elif os.WIFSTOPPED(code):
            val = os.WSTOPSIG(code)
            return _("stopped by signal %d") % val, val
        raise ValueError(_("invalid exit code"))

def opener(base, audit=True):
    """
    return a function that opens files relative to base

    this function is used to hide the details of COW semantics and
    remote file access from higher level code.
    """
    p = base
    audit_p = audit

    def mktempcopy(name):
        d, fn = os.path.split(name)
        fd, temp = tempfile.mkstemp(prefix='.%s-' % fn, dir=d)
        os.close(fd)
        ofp = posixfile(temp, "wb")
        try:
            try:
                ifp = posixfile(name, "rb")
            except IOError, inst:
                if not getattr(inst, 'filename', None):
                    inst.filename = name
                raise
            for chunk in filechunkiter(ifp):
                ofp.write(chunk)
            ifp.close()
            ofp.close()
        except:
            try: os.unlink(temp)
            except: pass
            raise
        st = os.lstat(name)
        os.chmod(temp, st.st_mode)
        return temp

    class atomictempfile(posixfile):
        """the file will only be copied when rename is called"""
        def __init__(self, name, mode):
            self.__name = name
            self.temp = mktempcopy(name)
            posixfile.__init__(self, self.temp, mode)
        def rename(self):
            if not self.closed:
                posixfile.close(self)
                rename(self.temp, localpath(self.__name))
        def __del__(self):
            if not self.closed:
                try:
                    os.unlink(self.temp)
                except: pass
                posixfile.close(self)

    class atomicfile(atomictempfile):
        """the file will only be copied on close"""
        def __init__(self, name, mode):
            atomictempfile.__init__(self, name, mode)
        def close(self):
            self.rename()
        def __del__(self):
            self.rename()

    def o(path, mode="r", text=False, atomic=False, atomictemp=False):
        if audit_p:
            audit_path(path)
        f = os.path.join(p, path)

        if not text:
            mode += "b" # for that other OS

        if mode[0] != "r":
            try:
                nlink = nlinks(f)
            except OSError:
                d = os.path.dirname(f)
                if not os.path.isdir(d):
                    os.makedirs(d)
            else:
                if atomic:
                    return atomicfile(f, mode)
                elif atomictemp:
                    return atomictempfile(f, mode)
                if nlink > 1:
                    rename(mktempcopy(f), f)
        return posixfile(f, mode)

    return o

class chunkbuffer(object):
    """Allow arbitrary sized chunks of data to be efficiently read from an
    iterator over chunks of arbitrary size."""

    def __init__(self, in_iter, targetsize = 2**16):
        """in_iter is the iterator that's iterating over the input chunks.
        targetsize is how big a buffer to try to maintain."""
        self.in_iter = iter(in_iter)
        self.buf = ''
        self.targetsize = int(targetsize)
        if self.targetsize <= 0:
            raise ValueError(_("targetsize must be greater than 0, was %d") %
                             targetsize)
        self.iterempty = False

    def fillbuf(self):
        """Ignore target size; read every chunk from iterator until empty."""
        if not self.iterempty:
            collector = cStringIO.StringIO()
            collector.write(self.buf)
            for ch in self.in_iter:
                collector.write(ch)
            self.buf = collector.getvalue()
            self.iterempty = True

    def read(self, l):
        """Read L bytes of data from the iterator of chunks of data.
        Returns less than L bytes if the iterator runs dry."""
        if l > len(self.buf) and not self.iterempty:
            # Clamp to a multiple of self.targetsize
            targetsize = self.targetsize * ((l // self.targetsize) + 1)
            collector = cStringIO.StringIO()
            collector.write(self.buf)
            collected = len(self.buf)
            for chunk in self.in_iter:
                collector.write(chunk)
                collected += len(chunk)
                if collected >= targetsize:
                    break
            if collected < targetsize:
                self.iterempty = True
            self.buf = collector.getvalue()
        s, self.buf = self.buf[:l], buffer(self.buf, l)
        return s

def filechunkiter(f, size=65536, limit=None):
    """Create a generator that produces the data in the file size
    (default 65536) bytes at a time, up to optional limit (default is
    to read all data).  Chunks may be less than size bytes if the
    chunk is the last chunk in the file, or the file is a socket or
    some other type of file that sometimes reads less data than is
    requested."""
    assert size >= 0
    assert limit is None or limit >= 0
    while True:
        if limit is None: nbytes = size
        else: nbytes = min(limit, size)
        s = nbytes and f.read(nbytes)
        if not s: break
        if limit: limit -= len(s)
        yield s

def makedate():
    lt = time.localtime()
    if lt[8] == 1 and time.daylight:
        tz = time.altzone
    else:
        tz = time.timezone
    return time.mktime(lt), tz

def datestr(date=None, format='%a %b %d %H:%M:%S %Y', timezone=True):
    """represent a (unixtime, offset) tuple as a localized time.
    unixtime is seconds since the epoch, and offset is the time zone's
    number of seconds away from UTC. if timezone is false, do not
    append time zone to string."""
    t, tz = date or makedate()
    s = time.strftime(format, time.gmtime(float(t) - tz))
    if timezone:
        s += " %+03d%02d" % (-tz / 3600, ((-tz % 3600) / 60))
    return s

def strdate(string, format='%a %b %d %H:%M:%S %Y'):
    """parse a localized time string and return a (unixtime, offset) tuple.
    if the string cannot be parsed, ValueError is raised."""
    def hastimezone(string):
        return (string[-4:].isdigit() and
               (string[-5] == '+' or string[-5] == '-') and
               string[-6].isspace())

    if hastimezone(string):
        date, tz = string[:-6], string[-5:]
        tz = int(tz)
        offset = - 3600 * (tz / 100) - 60 * (tz % 100)
    else:
        date, offset = string, 0
    when = int(time.mktime(time.strptime(date, format))) + offset
    return when, offset

def parsedate(string, formats=None):
    """parse a localized time string and return a (unixtime, offset) tuple.
    The date may be a "unixtime offset" string or in one of the specified
    formats."""
    if not formats:
        formats = defaultdateformats
    try:
        when, offset = map(int, string.split(' '))
    except ValueError:
        for format in formats:
            try:
                when, offset = strdate(string, format)
            except ValueError:
                pass
            else:
                break
        else:
            raise ValueError(_('invalid date: %r') % string)
    # validate explicit (probably user-specified) date and
    # time zone offset. values must fit in signed 32 bits for
    # current 32-bit linux runtimes. timezones go from UTC-12
    # to UTC+14
    if abs(when) > 0x7fffffff:
        raise ValueError(_('date exceeds 32 bits: %d') % when)
    if offset < -50400 or offset > 43200:
        raise ValueError(_('impossible time zone offset: %d') % offset)
    return when, offset

def shortuser(user):
    """Return a short representation of a user name or email address."""
    f = user.find('@')
    if f >= 0:
        user = user[:f]
    f = user.find('<')
    if f >= 0:
        user = user[f+1:]
    return user

def walkrepos(path):
    '''yield every hg repository under path, recursively.'''
    def errhandler(err):
        if err.filename == path:
            raise err

    for root, dirs, files in os.walk(path, onerror=errhandler):
        for d in dirs:
            if d == '.hg':
                yield root
                dirs[:] = []
                break

_rcpath = None

def rcpath():
    '''return hgrc search path. if env var HGRCPATH is set, use it.
    for each item in path, if directory, use files ending in .rc,
    else use item.
    make HGRCPATH empty to only look in .hg/hgrc of current repo.
    if no HGRCPATH, use default os-specific path.'''
    global _rcpath
    if _rcpath is None:
        if 'HGRCPATH' in os.environ:
            _rcpath = []
            for p in os.environ['HGRCPATH'].split(os.pathsep):
                if not p: continue
                if os.path.isdir(p):
                    for f in os.listdir(p):
                        if f.endswith('.rc'):
                            _rcpath.append(os.path.join(p, f))
                else:
                    _rcpath.append(p)
        else:
            _rcpath = os_rcpath()
    return _rcpath

def bytecount(nbytes):
    '''return byte count formatted as readable string, with units'''

    units = (
        (100, 1<<30, _('%.0f GB')),
        (10, 1<<30, _('%.1f GB')),
        (1, 1<<30, _('%.2f GB')),
        (100, 1<<20, _('%.0f MB')),
        (10, 1<<20, _('%.1f MB')),
        (1, 1<<20, _('%.2f MB')),
        (100, 1<<10, _('%.0f KB')),
        (10, 1<<10, _('%.1f KB')),
        (1, 1<<10, _('%.2f KB')),
        (1, 1, _('%.0f bytes')),
        )

    for multiplier, divisor, format in units:
        if nbytes >= divisor * multiplier:
            return format % (nbytes / float(divisor))
    return units[-1][2] % nbytes

def drop_scheme(scheme, path):
    sc = scheme + ':'
    if path.startswith(sc):
        path = path[len(sc):]
        if path.startswith('//'):
            path = path[2:]
    return path