annotate mercurial/wireprotoserver.py @ 35987:6010fe1da619

wireprotoserver: document and improve the httplib workaround

This workaround dates all the way back to a42d27bc809d in 2008.
The code is esoteric enough to warrant an inline explanation.
So I've added one.

At the time the code was written, the only wire protocol command
that accepted an HTTP request body was "unbundle." In the years
since, we've grown the ability to accept command arguments via
HTTP POST requests. So, the code has been changed to apply the
httplib workaround to all HTTP POST requests.

While staring at this code, I realized that the HTTP response
body in case of error is always the same. And, it appears to
mimic the behavior of a failed call to the "unbundle" command.
Since we can hit this code path on theoretically any protocol
request (since self.check_perm accepts custom auth checking
functions which may raise), I'm having a hard time believing
that clients react well to an "unbundle" response payload on
any wire protocol command. I wouldn't be surprised if our test
coverage for this feature only covers HTTP POST calls to
"unbundle." In other words, the experimental support for sending
arguments via HTTP POST request bodies may result in badness on
the client. Something to investigate another time perhaps...

Differential Revision: https://phab.mercurial-scm.org/D2064

# Copyright 21 May 2005 - (c) 2005 Jake Edge <[e-mail]>
# Copyright 2005-2007 Matt Mackall <[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 abc
import cgi
import struct
import sys

from .i18n import _
from . import (
    encoding,
    error,
    hook,
    pycompat,
    util,
    wireproto,
)

stringio = util.stringio

urlerr = util.urlerr
urlreq = util.urlreq

HTTP_OK = 200

HGTYPE = 'application/mercurial-0.1'
HGTYPE2 = 'application/mercurial-0.2'
HGERRTYPE = 'application/hg-error'

# Names of the SSH protocol implementations.
SSHV1 = 'ssh-v1'
# This is advertised over the wire. Incremental the counter at the end
# to reflect BC breakages.
SSHV2 = 'exp-ssh-v2-0001'

class abstractserverproto(object):
    """abstract class that summarizes the protocol API

    Used as reference and documentation.
    """

    __metaclass__ = abc.ABCMeta

    @abc.abstractproperty
    def name(self):
        """The name of the protocol implementation.

        Used for uniquely identifying the transport type.
        """

    @abc.abstractmethod
    def getargs(self, args):
        """return the value for arguments in <args>

        returns a list of values (same order as <args>)"""

    @abc.abstractmethod
    def getfile(self, fp):
        """write the whole content of a file into a file like object

        The file is in the form::

            (<chunk-size>\n<chunk>)+0\n

        chunk size is the ascii version of the int.
        """

    @abc.abstractmethod
    def redirect(self):
        """may setup interception for stdout and stderr

        See also the `restore` method."""

    # If the `redirect` function does install interception, the `restore`
    # function MUST be defined. If interception is not used, this function
    # MUST NOT be defined.
    #
    # left commented here on purpose
    #
    #def restore(self):
    #    """reinstall previous stdout and stderr and return intercepted stdout
    #    """
    #    raise NotImplementedError()

def decodevaluefromheaders(req, headerprefix):
    """Decode a long value from multiple HTTP request headers.

    Returns the value as a bytes, not a str.
    """
    chunks = []
    i = 1
    prefix = headerprefix.upper().replace(r'-', r'_')
    while True:
        v = req.env.get(r'HTTP_%s_%d' % (prefix, i))
        if v is None:
            break
        chunks.append(pycompat.bytesurl(v))
        i += 1

    return ''.join(chunks)

class webproto(abstractserverproto):
    def __init__(self, req, ui):
        self._req = req
        self._ui = ui

    @property
    def name(self):
        return 'http'

    def getargs(self, args):
        knownargs = self._args()
        data = {}
        keys = args.split()
        for k in keys:
            if k == '*':
                star = {}
                for key in knownargs.keys():
                    if key != 'cmd' and key not in keys:
                        star[key] = knownargs[key][0]
                data['*'] = star
            else:
                data[k] = knownargs[k][0]
        return [data[k] for k in keys]

    def _args(self):
        args = util.rapply(pycompat.bytesurl, self._req.form.copy())
        postlen = int(self._req.env.get(r'HTTP_X_HGARGS_POST', 0))
        if postlen:
            args.update(cgi.parse_qs(
                self._req.read(postlen), keep_blank_values=True))
            return args

        argvalue = decodevaluefromheaders(self._req, r'X-HgArg')
        args.update(cgi.parse_qs(argvalue, keep_blank_values=True))
        return args

    def getfile(self, fp):
        length = int(self._req.env[r'CONTENT_LENGTH'])
        # If httppostargs is used, we need to read Content-Length
        # minus the amount that was consumed by args.
        length -= int(self._req.env.get(r'HTTP_X_HGARGS_POST', 0))
        for s in util.filechunkiter(self._req, limit=length):
            fp.write(s)

    def redirect(self):
        self._oldio = self._ui.fout, self._ui.ferr
        self._ui.ferr = self._ui.fout = stringio()

    def restore(self):
        val = self._ui.fout.getvalue()
        self._ui.ferr, self._ui.fout = self._oldio
        return val

    def _client(self):
        return 'remote:%s:%s:%s' % (
            self._req.env.get('wsgi.url_scheme') or 'http',
            urlreq.quote(self._req.env.get('REMOTE_HOST', '')),
            urlreq.quote(self._req.env.get('REMOTE_USER', '')))

    def responsetype(self, prefer_uncompressed):
        """Determine the appropriate response type and compression settings.

        Returns a tuple of (mediatype, compengine, engineopts).
        """
        # Determine the response media type and compression engine based
        # on the request parameters.
        protocaps = decodevaluefromheaders(self._req, r'X-HgProto').split(' ')

        if '0.2' in protocaps:
            # All clients are expected to support uncompressed data.
            if prefer_uncompressed:
                return HGTYPE2, util._noopengine(), {}

            # Default as defined by wire protocol spec.
            compformats = ['zlib', 'none']
            for cap in protocaps:
                if cap.startswith('comp='):
                    compformats = cap[5:].split(',')
                    break

            # Now find an agreed upon compression format.
            for engine in wireproto.supportedcompengines(self._ui, self,
                                                         util.SERVERROLE):
                if engine.wireprotosupport().name in compformats:
                    opts = {}
                    level = self._ui.configint('server',
                                              '%slevel' % engine.name())
                    if level is not None:
                        opts['level'] = level

                    return HGTYPE2, engine, opts

            # No mutually supported compression format. Fall back to the
            # legacy protocol.

        # Don't allow untrusted settings because disabling compression or
        # setting a very high compression level could lead to flooding
        # the server's network or CPU.
        opts = {'level': self._ui.configint('server', 'zliblevel')}
        return HGTYPE, util.compengines['zlib'], opts

def iscmd(cmd):
    return cmd in wireproto.commands

def parsehttprequest(repo, req, query):
    """Parse the HTTP request for a wire protocol request.

    If the current request appears to be a wire protocol request, this
    function returns a dict with details about that request, including
    an ``abstractprotocolserver`` instance suitable for handling the
    request. Otherwise, ``None`` is returned.

    ``req`` is a ``wsgirequest`` instance.
    """
    # HTTP version 1 wire protocol requests are denoted by a "cmd" query
    # string parameter. If it isn't present, this isn't a wire protocol
    # request.
    if r'cmd' not in req.form:
        return None

    cmd = pycompat.sysbytes(req.form[r'cmd'][0])

    # The "cmd" request parameter is used by both the wire protocol and hgweb.
    # While not all wire protocol commands are available for all transports,
    # if we see a "cmd" value that resembles a known wire protocol command, we
    # route it to a protocol handler. This is better than routing possible
    # wire protocol requests to hgweb because it prevents hgweb from using
    # known wire protocol commands and it is less confusing for machine
    # clients.
    if cmd not in wireproto.commands:
        return None

    proto = webproto(req, repo.ui)

    return {
        'cmd': cmd,
        'proto': proto,
        'dispatch': lambda: _callhttp(repo, req, proto, cmd),
        'handleerror': lambda ex: _handlehttperror(ex, req, cmd),
    }

def _callhttp(repo, req, proto, cmd):
    def genversion2(gen, engine, engineopts):
        # application/mercurial-0.2 always sends a payload header
        # identifying the compression engine.
        name = engine.wireprotosupport().name
        assert 0 < len(name) < 256
        yield struct.pack('B', len(name))
        yield name

        for chunk in gen:
            yield chunk

    rsp = wireproto.dispatch(repo, proto, cmd)

    if not wireproto.commands.commandavailable(cmd, proto):
        req.respond(HTTP_OK, HGERRTYPE,
                    body=_('requested wire protocol command is not available '
                           'over HTTP'))
        return []

    if isinstance(rsp, bytes):
        req.respond(HTTP_OK, HGTYPE, body=rsp)
        return []
    elif isinstance(rsp, wireproto.streamres_legacy):
        gen = rsp.gen
        req.respond(HTTP_OK, HGTYPE)
        return gen
    elif isinstance(rsp, wireproto.streamres):
        gen = rsp.gen

        # This code for compression should not be streamres specific. It
        # is here because we only compress streamres at the moment.
        mediatype, engine, engineopts = proto.responsetype(
            rsp.prefer_uncompressed)
        gen = engine.compressstream(gen, engineopts)

        if mediatype == HGTYPE2:
            gen = genversion2(gen, engine, engineopts)

        req.respond(HTTP_OK, mediatype)
        return gen
    elif isinstance(rsp, wireproto.pushres):
        val = proto.restore()
        rsp = '%d\n%s' % (rsp.res, val)
        req.respond(HTTP_OK, HGTYPE, body=rsp)
        return []
    elif isinstance(rsp, wireproto.pusherr):
        # This is the httplib workaround documented in _handlehttperror().
        req.drain()

        proto.restore()
        rsp = '0\n%s\n' % rsp.res
        req.respond(HTTP_OK, HGTYPE, body=rsp)
        return []
    elif isinstance(rsp, wireproto.ooberror):
        rsp = rsp.message
        req.respond(HTTP_OK, HGERRTYPE, body=rsp)
        return []
    raise error.ProgrammingError('hgweb.protocol internal failure', rsp)

def _handlehttperror(e, req, cmd):
    """Called when an ErrorResponse is raised during HTTP request processing."""

    # Clients using Python's httplib are stateful: the HTTP client
    # won't process an HTTP response until all request data is
    # sent to the server. The intent of this code is to ensure
    # we always read HTTP request data from the client, thus
    # ensuring httplib transitions to a state that allows it to read
    # the HTTP response. In other words, it helps prevent deadlocks
    # on clients using httplib.

    if (req.env[r'REQUEST_METHOD'] == r'POST' and
        # But not if Expect: 100-continue is being used.
        (req.env.get('HTTP_EXPECT',
                     '').lower() != '100-continue') or
        # Or the non-httplib HTTP library is being advertised by
        # the client.
        req.env.get('X-HgHttp2', '')):
        req.drain()
    else:
        req.headers.append((r'Connection', r'Close'))

    # TODO This response body assumes the failed command was
    # "unbundle." That assumption is not always valid.
    req.respond(e, HGTYPE, body='0\n%s\n' % e)

    return ''

class sshserver(abstractserverproto):
    def __init__(self, ui, repo):
        self._ui = ui
        self._repo = repo
        self._fin = ui.fin
        self._fout = ui.fout

        hook.redirect(True)
        ui.fout = repo.ui.fout = ui.ferr

        # Prevent insertion/deletion of CRs
        util.setbinary(self._fin)
        util.setbinary(self._fout)

    @property
    def name(self):
        return 'ssh'

    def getargs(self, args):
        data = {}
        keys = args.split()
        for n in xrange(len(keys)):
            argline = self._fin.readline()[:-1]
            arg, l = argline.split()
            if arg not in keys:
                raise error.Abort(_("unexpected parameter %r") % arg)
            if arg == '*':
                star = {}
                for k in xrange(int(l)):
                    argline = self._fin.readline()[:-1]
                    arg, l = argline.split()
                    val = self._fin.read(int(l))
                    star[arg] = val
                data['*'] = star
            else:
                val = self._fin.read(int(l))
                data[arg] = val
        return [data[k] for k in keys]

    def getfile(self, fpout):
        self._sendresponse('')
        count = int(self._fin.readline())
        while count:
            fpout.write(self._fin.read(count))
            count = int(self._fin.readline())

    def redirect(self):
        pass

    def _sendresponse(self, v):
        self._fout.write("%d\n" % len(v))
        self._fout.write(v)
        self._fout.flush()

    def _sendstream(self, source):
        write = self._fout.write
        for chunk in source.gen:
            write(chunk)
        self._fout.flush()

    def _sendpushresponse(self, rsp):
        self._sendresponse('')
        self._sendresponse(str(rsp.res))

    def _sendpusherror(self, rsp):
        self._sendresponse(rsp.res)

    def _sendooberror(self, rsp):
        self._ui.ferr.write('%s\n-\n' % rsp.message)
        self._ui.ferr.flush()
        self._fout.write('\n')
        self._fout.flush()

    def serve_forever(self):
        while self.serve_one():
            pass
        sys.exit(0)

    _handlers = {
        str: _sendresponse,
        wireproto.streamres: _sendstream,
        wireproto.streamres_legacy: _sendstream,
        wireproto.pushres: _sendpushresponse,
        wireproto.pusherr: _sendpusherror,
        wireproto.ooberror: _sendooberror,
    }

    def serve_one(self):
        cmd = self._fin.readline()[:-1]
        if cmd and wireproto.commands.commandavailable(cmd, self):
            rsp = wireproto.dispatch(self._repo, self, cmd)
            self._handlers[rsp.__class__](self, rsp)
        elif cmd:
            self._sendresponse("")
        return cmd != ''

    def _client(self):
        client = encoding.environ.get('SSH_CLIENT', '').split(' ', 1)[0]
        return 'remote:ssh:' + client