httppeer: remove support for connecting to <0.9.1 servers (BC)

Previously, HTTP wire protocol clients would attempt a
"capabilities" wire protocol command. If that failed, they would
fall back to issuing a "between" command.

The "capabilities" command was added in Mercurial 0.9.1 (released
July 2006). The "between" command has been present for as long as
the wire protocol has existed. So if the "between" command failed,
it was safe to assume that the remote could not speak any version
of the Mercurial wire protocol.

The "between" fallback was added in 395a84f78736 in 2011. Before that
changeset, Mercurial would *always* issue the "between" command and
would issue "capabilities" if capabilities were requested. At that time,
many connections would issue "capabilities" eventually, so it was
decided to issue "capabilities" by default and fall back to "between"
if that failed. This saved a round trip when connecting to modern
servers while still preserving compatibility with legacy servers.

Fast forward ~7 years. Mercurial servers supporting "capabilities"
have been around for over a decade. If modern clients are
connecting to <0.9.1 servers, they are getting a bad experience.
They may even be getting bad data (an old server is vulnerable to
numerous security issues and could have been p0wned, leading to a
Mercurial repository serving backdoors or other badness).

In addition, the fallback can harm experience for modern servers.
If a client experiences an intermittent HTTP request failure (due to
bad network, etc) and falls back to a "between" that works, it would
assume an empty capability set and would attempt to communicate with
the repository using a very ancient wire protocol. Auditing HTTP logs
for hg.mozilla.org, I did find a handful of requests for the
null range of the "between" command. However, requests can be days
apart. And when I do see requests, they come in batches. Those
batches seem to correlate to spikes of HTTP 500 or other
server/network events. So I think these requests are fallbacks from
failed "capabilities" requests and not from old clients.

If you need even more evidence to discontinue support, apparently
we have no test coverage for communicating with servers not
supporting "capabilities." I know this because all tests pass
with the "between" fallback removed.

Finally, server-side support for <0.9.1 pushing (the "addchangegroup"
wire protocol command along with locking-related commands) was dropped
from the HTTP client in fda0867cfe03 in 2017 and the SSH client in
9f6e0e7ef828 in 2015.

I think this all adds up to enough justification for removing client
support for communicating with servers not supporting "capabilities."
So this commit removes that fallback.

Differential Revision: https://phab.mercurial-scm.org/D2001

mercurial/httppeer.py

@@ -1,508 +1,503 b''
 # httppeer.py - HTTP repository proxy classes for mercurial
 #
 # 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 version 2 or any later version.
 
 from __future__ import absolute_import
 
 import errno
 import io
 import os
 import socket
 import struct
 import tempfile
 
 from .i18n import _
-from .node import nullid
 from . import (
     bundle2,
     error,
     httpconnection,
     pycompat,
     statichttprepo,
     url,
     util,
     wireproto,
 )
 
 httplib = util.httplib
 urlerr = util.urlerr
 urlreq = util.urlreq
 
 def encodevalueinheaders(value, header, limit):
     """Encode a string value into multiple HTTP headers.
 
     ``value`` will be encoded into 1 or more HTTP headers with the names
     ``header-<N>`` where ``<N>`` is an integer starting at 1. Each header
     name + value will be at most ``limit`` bytes long.
 
     Returns an iterable of 2-tuples consisting of header names and
     values as native strings.
     """
     # HTTP Headers are ASCII. Python 3 requires them to be unicodes,
     # not bytes. This function always takes bytes in as arguments.
     fmt = pycompat.strurl(header) + r'-%s'
     # Note: it is *NOT* a bug that the last bit here is a bytestring
     # and not a unicode: we're just getting the encoded length anyway,
     # and using an r-string to make it portable between Python 2 and 3
     # doesn't work because then the \r is a literal backslash-r
     # instead of a carriage return.
     valuelen = limit - len(fmt % r'000') - len(': \r\n')
     result = []
 
     n = 0
     for i in xrange(0, len(value), valuelen):
         n += 1
         result.append((fmt % str(n), pycompat.strurl(value[i:i + valuelen])))
 
     return result
 
 def _wraphttpresponse(resp):
     """Wrap an HTTPResponse with common error handlers.
 
     This ensures that any I/O from any consumer raises the appropriate
     error and messaging.
     """
     origread = resp.read
 
     class readerproxy(resp.__class__):
         def read(self, size=None):
             try:
                 return origread(size)
             except httplib.IncompleteRead as e:
                 # e.expected is an integer if length known or None otherwise.
                 if e.expected:
                     msg = _('HTTP request error (incomplete response; '
                             'expected %d bytes got %d)') % (e.expected,
                                                            len(e.partial))
                 else:
                     msg = _('HTTP request error (incomplete response)')
 
                 raise error.PeerTransportError(
                     msg,
                     hint=_('this may be an intermittent network failure; '
                            'if the error persists, consider contacting the '
                            'network or server operator'))
             except httplib.HTTPException as e:
                 raise error.PeerTransportError(
                     _('HTTP request error (%s)') % e,
                     hint=_('this may be an intermittent network failure; '
                            'if the error persists, consider contacting the '
                            'network or server operator'))
 
     resp.__class__ = readerproxy
 
 class _multifile(object):
     def __init__(self, *fileobjs):
         for f in fileobjs:
             if not util.safehasattr(f, 'length'):
                 raise ValueError(
                     '_multifile only supports file objects that '
                     'have a length but this one does not:', type(f), f)
         self._fileobjs = fileobjs
         self._index = 0
 
     @property
     def length(self):
         return sum(f.length for f in self._fileobjs)
 
     def read(self, amt=None):
         if amt <= 0:
             return ''.join(f.read() for f in self._fileobjs)
         parts = []
         while amt and self._index < len(self._fileobjs):
             parts.append(self._fileobjs[self._index].read(amt))
             got = len(parts[-1])
             if got < amt:
                 self._index += 1
             amt -= got
         return ''.join(parts)
 
     def seek(self, offset, whence=os.SEEK_SET):
         if whence != os.SEEK_SET:
             raise NotImplementedError(
                 '_multifile does not support anything other'
                 ' than os.SEEK_SET for whence on seek()')
         if offset != 0:
             raise NotImplementedError(
                 '_multifile only supports seeking to start, but that '
                 'could be fixed if you need it')
         for f in self._fileobjs:
             f.seek(0)
         self._index = 0
 
 class httppeer(wireproto.wirepeer):
     def __init__(self, ui, path):
         self._path = path
         self._caps = None
         self._urlopener = None
         self._requestbuilder = None
         u = util.url(path)
         if u.query or u.fragment:
             raise error.Abort(_('unsupported URL component: "%s"') %
                              (u.query or u.fragment))
 
         # urllib cannot handle URLs with embedded user or passwd
         self._url, authinfo = u.authinfo()
 
         self._ui = ui
         ui.debug('using %s\n' % self._url)
 
         self._urlopener = url.opener(ui, authinfo)
         self._requestbuilder = urlreq.request
 
     def __del__(self):
         urlopener = getattr(self, '_urlopener', None)
         if urlopener:
             for h in urlopener.handlers:
                 h.close()
                 getattr(h, "close_all", lambda: None)()
 
     def _openurl(self, req):
         if (self._ui.debugflag
             and self._ui.configbool('devel', 'debug.peer-request')):
             dbg = self._ui.debug
             line = 'devel-peer-request: %s\n'
             dbg(line % '%s %s' % (req.get_method(), req.get_full_url()))
             hgargssize = None
 
             for header, value in sorted(req.header_items()):
                 if header.startswith('X-hgarg-'):
                     if hgargssize is None:
                         hgargssize = 0
                     hgargssize += len(value)
                 else:
                     dbg(line % '  %s %s' % (header, value))
 
             if hgargssize is not None:
                 dbg(line % '  %d bytes of commands arguments in headers'
                     % hgargssize)
 
             if req.has_data():
                 data = req.get_data()
                 length = getattr(data, 'length', None)
                 if length is None:
                     length = len(data)
                 dbg(line % '  %d bytes of data' % length)
 
             start = util.timer()
 
         ret = self._urlopener.open(req)
         if self._ui.configbool('devel', 'debug.peer-request'):
             dbg(line % '  finished in %.4f seconds (%s)'
                 % (util.timer() - start, ret.code))
         return ret
 
     # Begin of _basepeer interface.
 
     @util.propertycache
     def ui(self):
         return self._ui
 
     def url(self):
         return self._path
 
     def local(self):
         return None
 
     def peer(self):
         return self
 
     def canpush(self):
         return True
 
     def close(self):
         pass
 
     # End of _basepeer interface.
 
     # Begin of _basewirepeer interface.
 
     def capabilities(self):
         if self._caps is None:
             try:
                 self._fetchcaps()
             except error.RepoError:
                 self._caps = set()
             self.ui.debug('capabilities: %s\n' %
                           (' '.join(self._caps or ['none'])))
         return self._caps
 
     # End of _basewirepeer interface.
 
     # look up capabilities only when needed
 
     def _fetchcaps(self):
         self._caps = set(self._call('capabilities').split())
 
     def _callstream(self, cmd, _compressible=False, **args):
         args = pycompat.byteskwargs(args)
         if cmd == 'pushkey':
             args['data'] = ''
         data = args.pop('data', None)
         headers = args.pop('headers', {})
 
         self.ui.debug("sending %s command\n" % cmd)
         q = [('cmd', cmd)]
         headersize = 0
         varyheaders = []
         # Important: don't use self.capable() here or else you end up
         # with infinite recursion when trying to look up capabilities
         # for the first time.
         postargsok = self._caps is not None and 'httppostargs' in self._caps
         if postargsok and args:
             strargs = urlreq.urlencode(sorted(args.items()))
             if not data:
                 data = strargs
             else:
                 if isinstance(data, bytes):
                     i = io.BytesIO(data)
                     i.length = len(data)
                     data = i
                 argsio = io.BytesIO(strargs)
                 argsio.length = len(strargs)
                 data = _multifile(argsio, data)
             headers[r'X-HgArgs-Post'] = len(strargs)
         else:
             if len(args) > 0:
                 httpheader = self.capable('httpheader')
                 if httpheader:
                     headersize = int(httpheader.split(',', 1)[0])
             if headersize > 0:
                 # The headers can typically carry more data than the URL.
                 encargs = urlreq.urlencode(sorted(args.items()))
                 for header, value in encodevalueinheaders(encargs, 'X-HgArg',
                                                           headersize):
                     headers[header] = value
                     varyheaders.append(header)
             else:
                 q += sorted(args.items())
         qs = '?%s' % urlreq.urlencode(q)
         cu = "%s%s" % (self._url, qs)
         size = 0
         if util.safehasattr(data, 'length'):
             size = data.length
         elif data is not None:
             size = len(data)
         if size and self.ui.configbool('ui', 'usehttp2'):
             headers[r'Expect'] = r'100-Continue'
             headers[r'X-HgHttp2'] = r'1'
         if data is not None and r'Content-Type' not in headers:
             headers[r'Content-Type'] = r'application/mercurial-0.1'
 
         # Tell the server we accept application/mercurial-0.2 and multiple
         # compression formats if the server is capable of emitting those
         # payloads.
         protoparams = []
 
         mediatypes = set()
         if self._caps is not None:
             mt = self.capable('httpmediatype')
             if mt:
                 protoparams.append('0.1')
                 mediatypes = set(mt.split(','))
 
         if '0.2tx' in mediatypes:
             protoparams.append('0.2')
 
         if '0.2tx' in mediatypes and self.capable('compression'):
             # We /could/ compare supported compression formats and prune
             # non-mutually supported or error if nothing is mutually supported.
             # For now, send the full list to the server and have it error.
             comps = [e.wireprotosupport().name for e in
                      util.compengines.supportedwireengines(util.CLIENTROLE)]
             protoparams.append('comp=%s' % ','.join(comps))
 
         if protoparams:
             protoheaders = encodevalueinheaders(' '.join(protoparams),
                                                 'X-HgProto',
                                                 headersize or 1024)
             for header, value in protoheaders:
                 headers[header] = value
                 varyheaders.append(header)
 
         if varyheaders:
             headers[r'Vary'] = r','.join(varyheaders)
 
         req = self._requestbuilder(pycompat.strurl(cu), data, headers)
 
         if data is not None:
             self.ui.debug("sending %s bytes\n" % size)
             req.add_unredirected_header('Content-Length', '%d' % size)
         try:
             resp = self._openurl(req)
         except urlerr.httperror as inst:
             if inst.code == 401:
                 raise error.Abort(_('authorization failed'))
             raise
         except httplib.HTTPException as inst:
             self.ui.debug('http error while sending %s command\n' % cmd)
             self.ui.traceback()
             raise IOError(None, inst)
 
         # Insert error handlers for common I/O failures.
         _wraphttpresponse(resp)
 
         # record the url we got redirected to
         resp_url = pycompat.bytesurl(resp.geturl())
         if resp_url.endswith(qs):
             resp_url = resp_url[:-len(qs)]
         if self._url.rstrip('/') != resp_url.rstrip('/'):
             if not self.ui.quiet:
                 self.ui.warn(_('real URL is %s\n') % resp_url)
         self._url = resp_url
         try:
             proto = pycompat.bytesurl(resp.getheader(r'content-type', r''))
         except AttributeError:
             proto = pycompat.bytesurl(resp.headers.get(r'content-type', r''))
 
         safeurl = util.hidepassword(self._url)
         if proto.startswith('application/hg-error'):
             raise error.OutOfBandError(resp.read())
         # accept old "text/plain" and "application/hg-changegroup" for now
         if not (proto.startswith('application/mercurial-') or
                 (proto.startswith('text/plain')
                  and not resp.headers.get('content-length')) or
                 proto.startswith('application/hg-changegroup')):
             self.ui.debug("requested URL: '%s'\n" % util.hidepassword(cu))
             raise error.RepoError(
                 _("'%s' does not appear to be an hg repository:\n"
                   "---%%<--- (%s)\n%s\n---%%<---\n")
                 % (safeurl, proto or 'no content-type', resp.read(1024)))
 
         if proto.startswith('application/mercurial-'):
             try:
                 version = proto.split('-', 1)[1]
                 version_info = tuple([int(n) for n in version.split('.')])
             except ValueError:
                 raise error.RepoError(_("'%s' sent a broken Content-Type "
                                         "header (%s)") % (safeurl, proto))
 
             # TODO consider switching to a decompression reader that uses
             # generators.
             if version_info == (0, 1):
                 if _compressible:
                     return util.compengines['zlib'].decompressorreader(resp)
                 return resp
             elif version_info == (0, 2):
                 # application/mercurial-0.2 always identifies the compression
                 # engine in the payload header.
                 elen = struct.unpack('B', resp.read(1))[0]
                 ename = resp.read(elen)
                 engine = util.compengines.forwiretype(ename)
                 return engine.decompressorreader(resp)
             else:
                 raise error.RepoError(_("'%s' uses newer protocol %s") %
                                       (safeurl, version))
 
         if _compressible:
             return util.compengines['zlib'].decompressorreader(resp)
 
         return resp
 
     def _call(self, cmd, **args):
         fp = self._callstream(cmd, **args)
         try:
             return fp.read()
         finally:
             # if using keepalive, allow connection to be reused
             fp.close()
 
     def _callpush(self, cmd, cg, **args):
         # have to stream bundle to a temp file because we do not have
         # http 1.1 chunked transfer.
 
         types = self.capable('unbundle')
         try:
             types = types.split(',')
         except AttributeError:
             # servers older than d1b16a746db6 will send 'unbundle' as a
             # boolean capability. They only support headerless/uncompressed
             # bundles.
             types = [""]
         for x in types:
             if x in bundle2.bundletypes:
                 type = x
                 break
 
         tempname = bundle2.writebundle(self.ui, cg, None, type)
         fp = httpconnection.httpsendfile(self.ui, tempname, "rb")
         headers = {'Content-Type': 'application/mercurial-0.1'}
 
         try:
             r = self._call(cmd, data=fp, headers=headers, **args)
             vals = r.split('\n', 1)
             if len(vals) < 2:
                 raise error.ResponseError(_("unexpected response:"), r)
             return vals
         except socket.error as err:
             if err.args[0] in (errno.ECONNRESET, errno.EPIPE):
                 raise error.Abort(_('push failed: %s') % err.args[1])
             raise error.Abort(err.args[1])
         finally:
             fp.close()
             os.unlink(tempname)
 
     def _calltwowaystream(self, cmd, fp, **args):
         fh = None
         fp_ = None
         filename = None
         try:
             # dump bundle to disk
             fd, filename = tempfile.mkstemp(prefix="hg-bundle-", suffix=".hg")
             fh = os.fdopen(fd, pycompat.sysstr("wb"))
             d = fp.read(4096)
             while d:
                 fh.write(d)
                 d = fp.read(4096)
             fh.close()
             # start http push
             fp_ = httpconnection.httpsendfile(self.ui, filename, "rb")
             headers = {'Content-Type': 'application/mercurial-0.1'}
             return self._callstream(cmd, data=fp_, headers=headers, **args)
         finally:
             if fp_ is not None:
                 fp_.close()
             if fh is not None:
                 fh.close()
                 os.unlink(filename)
 
     def _callcompressable(self, cmd, **args):
         return self._callstream(cmd, _compressible=True, **args)
 
     def _abort(self, exception):
         raise exception
 
 class httpspeer(httppeer):
     def __init__(self, ui, path):
         if not url.has_https:
             raise error.Abort(_('Python support for SSL and HTTPS '
                                'is not installed'))
         httppeer.__init__(self, ui, path)
 
 def instance(ui, path, create):
     if create:
         raise error.Abort(_('cannot create new http repository'))
     try:
         if path.startswith('https:'):
             inst = httpspeer(ui, path)
         else:
             inst = httppeer(ui, path)
-        try:
-            # Try to do useful work when checking compatibility.
-            # Usually saves a roundtrip since we want the caps anyway.
-            inst._fetchcaps()
-        except error.RepoError:
-            # No luck, try older compatibility check.
-            inst.between([(nullid, nullid)])
+
+        inst._fetchcaps()
+
         return inst
     except error.RepoError as httpexception:
         try:
             r = statichttprepo.instance(ui, "static-" + path, create)
             ui.note(_('(falling back to static-http)\n'))
             return r
         except error.RepoError:
             raise httpexception # use the original http RepoError instead