view tests/test-batching.py @ 46607:e9901d01d135

revlog: add a mechanism to verify expected file position before appending

If someone uses `hg debuglocks`, or some non-hg process writes to the .hg
directory without respecting the locks, or if the repo's on a networked
filesystem, it's possible for the revlog code to write out corrupted data.

The form of this corruption can vary depending on what data was written and how
that happened. We are in the "networked filesystem" case (though I've had users
also do this to themselves with the "`hg debuglocks`" scenario), and most often
see this with the changelog. What ends up happening is we produce two items
(let's call them rev1 and rev2) in the .i file that have the same linkrev,
baserev, and offset into the .d file, while the data in the .d file is appended
properly. rev2's compressed_size is accurate for rev2, but when we go to
decompress the data in the .d file, we use the offset that's recorded in the
index file, which is the same as rev1, and attempt to decompress
rev2.compressed_size bytes of rev1's data. This usually does not succeed. :)

When using inline data, this also fails, though I haven't investigated why too
closely. This shows up as a "patch decode" error. I believe what's happening
there is that we're basically ignoring the offset field, getting the data
properly, but since baserev != rev, it thinks this is a delta based on rev
(instead of a full text) and can't actually apply it as such.

For now, I'm going to make this an optional component and default it to entirely
off. I may increase the default severity of this in the future, once I've
enabled it for my users and we gain more experience with it. Luckily, most of my
users have a versioned filesystem and can roll back to before the corruption has
been written, it's just a hassle to do so and not everyone knows how (so it's a
support burden). Users on other filesystems will not have that luxury, and this
can cause them to have a corrupted repository that they are unlikely to know how
to resolve, and they'll see this as a data-loss event. Refusing to create the
corruption is a much better user experience.

This mechanism is not perfect. There may be false-negatives (racy writes that
are not detected). There should not be any false-positives (non-racy writes that
are detected as such). This is not a mechanism that makes putting a repo on a
networked filesystem "safe" or "supported", just *less* likely to cause
corruption.

Differential Revision: https://phab.mercurial-scm.org/D9952

# test-batching.py - tests for transparent command batching
#
# Copyright 2011 Peter Arrenbrecht <[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, print_function

import contextlib

from mercurial import (
    localrepo,
    pycompat,
    wireprotov1peer,
)


def bprint(*bs):
    print(*[pycompat.sysstr(b) for b in bs])


# equivalent of repo.repository
class thing(object):
    def hello(self):
        return b"Ready."


# equivalent of localrepo.localrepository
class localthing(thing):
    def foo(self, one, two=None):
        if one:
            return b"%s and %s" % (
                one,
                two,
            )
        return b"Nope"

    def bar(self, b, a):
        return b"%s und %s" % (
            b,
            a,
        )

    def greet(self, name=None):
        return b"Hello, %s" % name

    @contextlib.contextmanager
    def commandexecutor(self):
        e = localrepo.localcommandexecutor(self)
        try:
            yield e
        finally:
            e.close()


# usage of "thing" interface
def use(it):

    # Direct call to base method shared between client and server.
    bprint(it.hello())

    # Direct calls to proxied methods. They cause individual roundtrips.
    bprint(it.foo(b"Un", two=b"Deux"))
    bprint(it.bar(b"Eins", b"Zwei"))

    # Batched call to a couple of proxied methods.

    with it.commandexecutor() as e:
        ffoo = e.callcommand(b'foo', {b'one': b'One', b'two': b'Two'})
        fbar = e.callcommand(b'bar', {b'b': b'Eins', b'a': b'Zwei'})
        fbar2 = e.callcommand(b'bar', {b'b': b'Uno', b'a': b'Due'})

    bprint(ffoo.result())
    bprint(fbar.result())
    bprint(fbar2.result())


# local usage
mylocal = localthing()
print()
bprint(b"== Local")
use(mylocal)

# demo remoting; mimicks what wireproto and HTTP/SSH do

# shared


def escapearg(plain):
    return (
        plain.replace(b':', b'::')
        .replace(b',', b':,')
        .replace(b';', b':;')
        .replace(b'=', b':=')
    )


def unescapearg(escaped):
    return (
        escaped.replace(b':=', b'=')
        .replace(b':;', b';')
        .replace(b':,', b',')
        .replace(b'::', b':')
    )


# server side

# equivalent of wireproto's global functions
class server(object):
    def __init__(self, local):
        self.local = local

    def _call(self, name, args):
        args = dict(arg.split(b'=', 1) for arg in args)
        return getattr(self, name)(**args)

    def perform(self, req):
        bprint(b"REQ:", req)
        name, args = req.split(b'?', 1)
        args = args.split(b'&')
        vals = dict(arg.split(b'=', 1) for arg in args)
        res = getattr(self, pycompat.sysstr(name))(**pycompat.strkwargs(vals))
        bprint(b"  ->", res)
        return res

    def batch(self, cmds):
        res = []
        for pair in cmds.split(b';'):
            name, args = pair.split(b':', 1)
            vals = {}
            for a in args.split(b','):
                if a:
                    n, v = a.split(b'=')
                    vals[n] = unescapearg(v)
            res.append(
                escapearg(
                    getattr(self, pycompat.sysstr(name))(
                        **pycompat.strkwargs(vals)
                    )
                )
            )
        return b';'.join(res)

    def foo(self, one, two):
        return mangle(self.local.foo(unmangle(one), unmangle(two)))

    def bar(self, b, a):
        return mangle(self.local.bar(unmangle(b), unmangle(a)))

    def greet(self, name):
        return mangle(self.local.greet(unmangle(name)))


myserver = server(mylocal)

# local side

# equivalent of wireproto.encode/decodelist, that is, type-specific marshalling
# here we just transform the strings a bit to check we're properly en-/decoding
def mangle(s):
    return b''.join(pycompat.bytechr(ord(c) + 1) for c in pycompat.bytestr(s))


def unmangle(s):
    return b''.join(pycompat.bytechr(ord(c) - 1) for c in pycompat.bytestr(s))


# equivalent of wireproto.wirerepository and something like http's wire format
class remotething(thing):
    def __init__(self, server):
        self.server = server

    def _submitone(self, name, args):
        req = name + b'?' + b'&'.join([b'%s=%s' % (n, v) for n, v in args])
        return self.server.perform(req)

    def _submitbatch(self, cmds):
        req = []
        for name, args in cmds:
            args = b','.join(n + b'=' + escapearg(v) for n, v in args)
            req.append(name + b':' + args)
        req = b';'.join(req)
        res = self._submitone(
            b'batch',
            [
                (
                    b'cmds',
                    req,
                )
            ],
        )
        for r in res.split(b';'):
            yield r

    @contextlib.contextmanager
    def commandexecutor(self):
        e = wireprotov1peer.peerexecutor(self)
        try:
            yield e
        finally:
            e.close()

    @wireprotov1peer.batchable
    def foo(self, one, two=None):
        encoded_args = [
            (
                b'one',
                mangle(one),
            ),
            (
                b'two',
                mangle(two),
            ),
        ]
        encoded_res_future = wireprotov1peer.future()
        yield encoded_args, encoded_res_future
        yield unmangle(encoded_res_future.value)

    @wireprotov1peer.batchable
    def bar(self, b, a):
        encresref = wireprotov1peer.future()
        yield [
            (
                b'b',
                mangle(b),
            ),
            (
                b'a',
                mangle(a),
            ),
        ], encresref
        yield unmangle(encresref.value)

    # greet is coded directly. It therefore does not support batching. If it
    # does appear in a batch, the batch is split around greet, and the call to
    # greet is done in its own roundtrip.
    def greet(self, name=None):
        return unmangle(
            self._submitone(
                b'greet',
                [
                    (
                        b'name',
                        mangle(name),
                    )
                ],
            )
        )


# demo remote usage

myproxy = remotething(myserver)
print()
bprint(b"== Remote")
use(myproxy)