hgext/fastannotate/protocol.py

encoding: fix trim() to be O(n) instead of O(n^2)

`encoding.trim()` iterated over the possible lengths smaller than the
input and created a slice for each. It then calculated the column
width of the result, which is of course O(n), so the overall algorithm
was O(n). This patch rewrites it to iterate over the unicode
characters, keeping track of the length so far. Also, the old
algorithm started from the end of the string, which made it much worse
when the input is large and the limit is small (such as the typical 72
we pass to it).

You can time it by running something like this:

```
time python3 -c 'from mercurial.utils import stringutil; print(stringutil.ellipsis(b"0123456789" * 1000, 5))'
```

That drops from 4.05 s to 83 ms with this patch (and most of that is
of course startup time).

Differential Revision: https://phab.mercurial-scm.org/D12089

# Copyright 2016-present Facebook. All Rights Reserved.
#
# protocol: logic for a server providing fastannotate support
#
# 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 contextlib
import os

from mercurial.i18n import _
from mercurial.pycompat import open
from mercurial import (
    error,
    extensions,
    hg,
    pycompat,
    util,
    wireprotov1peer,
    wireprotov1server,
)
from mercurial.utils import (
    urlutil,
)
from . import context

# common


def _getmaster(ui):
    """get the mainbranch, and enforce it is set"""
    master = ui.config(b'fastannotate', b'mainbranch')
    if not master:
        raise error.Abort(
            _(
                b'fastannotate.mainbranch is required '
                b'for both the client and the server'
            )
        )
    return master


# server-side


def _capabilities(orig, repo, proto):
    result = orig(repo, proto)
    result.append(b'getannotate')
    return result


def _getannotate(repo, proto, path, lastnode):
    # output:
    #   FILE := vfspath + '\0' + str(size) + '\0' + content
    #   OUTPUT := '' | FILE + OUTPUT
    result = b''
    buildondemand = repo.ui.configbool(
        b'fastannotate', b'serverbuildondemand', True
    )
    with context.annotatecontext(repo, path) as actx:
        if buildondemand:
            # update before responding to the client
            master = _getmaster(repo.ui)
            try:
                if not actx.isuptodate(master):
                    actx.annotate(master, master)
            except Exception:
                # non-fast-forward move or corrupted. rebuild automically.
                actx.rebuild()
                try:
                    actx.annotate(master, master)
                except Exception:
                    actx.rebuild()  # delete files
            finally:
                # although the "with" context will also do a close/flush, we
                # need to do it early so we can send the correct respond to
                # client.
                actx.close()
        # send back the full content of revmap and linelog, in the future we
        # may want to do some rsync-like fancy updating.
        # the lastnode check is not necessary if the client and the server
        # agree where the main branch is.
        if actx.lastnode != lastnode:
            for p in [actx.revmappath, actx.linelogpath]:
                if not os.path.exists(p):
                    continue
                with open(p, b'rb') as f:
                    content = f.read()
                vfsbaselen = len(repo.vfs.base + b'/')
                relpath = p[vfsbaselen:]
                result += b'%s\0%d\0%s' % (relpath, len(content), content)
    return result


def _registerwireprotocommand():
    if b'getannotate' in wireprotov1server.commands:
        return
    wireprotov1server.wireprotocommand(b'getannotate', b'path lastnode')(
        _getannotate
    )


def serveruisetup(ui):
    _registerwireprotocommand()
    extensions.wrapfunction(wireprotov1server, b'_capabilities', _capabilities)


# client-side


def _parseresponse(payload):
    result = {}
    i = 0
    l = len(payload) - 1
    state = 0  # 0: vfspath, 1: size
    vfspath = size = b''
    while i < l:
        ch = payload[i : i + 1]
        if ch == b'\0':
            if state == 1:
                result[vfspath] = payload[i + 1 : i + 1 + int(size)]
                i += int(size)
                state = 0
                vfspath = size = b''
            elif state == 0:
                state = 1
        else:
            if state == 1:
                size += ch
            elif state == 0:
                vfspath += ch
        i += 1
    return result


def peersetup(ui, peer):
    class fastannotatepeer(peer.__class__):
        @wireprotov1peer.batchable
        def getannotate(self, path, lastnode=None):
            if not self.capable(b'getannotate'):
                ui.warn(_(b'remote peer cannot provide annotate cache\n'))
                return None, None
            else:
                args = {b'path': path, b'lastnode': lastnode or b''}
                return args, _parseresponse

    peer.__class__ = fastannotatepeer


@contextlib.contextmanager
def annotatepeer(repo):
    ui = repo.ui

    remotedest = ui.config(b'fastannotate', b'remotepath', b'default')
    r = urlutil.get_unique_pull_path(b'fastannotate', repo, ui, remotedest)
    remotepath = r[0]
    peer = hg.peer(ui, {}, remotepath)

    try:
        yield peer
    finally:
        peer.close()


def clientfetch(repo, paths, lastnodemap=None, peer=None):
    """download annotate cache from the server for paths"""
    if not paths:
        return

    if peer is None:
        with annotatepeer(repo) as peer:
            return clientfetch(repo, paths, lastnodemap, peer)

    if lastnodemap is None:
        lastnodemap = {}

    ui = repo.ui
    results = []
    with peer.commandexecutor() as batcher:
        ui.debug(b'fastannotate: requesting %d files\n' % len(paths))
        for p in paths:
            results.append(
                batcher.callcommand(
                    b'getannotate',
                    {b'path': p, b'lastnode': lastnodemap.get(p)},
                )
            )

        for result in results:
            r = result.result()
            # TODO: pconvert these paths on the server?
            r = {util.pconvert(p): v for p, v in pycompat.iteritems(r)}
            for path in sorted(r):
                # ignore malicious paths
                if not path.startswith(b'fastannotate/') or b'/../' in (
                    path + b'/'
                ):
                    ui.debug(
                        b'fastannotate: ignored malicious path %s\n' % path
                    )
                    continue
                content = r[path]
                if ui.debugflag:
                    ui.debug(
                        b'fastannotate: writing %d bytes to %s\n'
                        % (len(content), path)
                    )
                repo.vfs.makedirs(os.path.dirname(path))
                with repo.vfs(path, b'wb') as f:
                    f.write(content)


def _filterfetchpaths(repo, paths):
    """return a subset of paths whose history is long and need to fetch linelog
    from the server. works with remotefilelog and non-remotefilelog repos.
    """
    threshold = repo.ui.configint(b'fastannotate', b'clientfetchthreshold', 10)
    if threshold <= 0:
        return paths

    result = []
    for path in paths:
        try:
            if len(repo.file(path)) >= threshold:
                result.append(path)
        except Exception:  # file not found etc.
            result.append(path)

    return result


def localreposetup(ui, repo):
    class fastannotaterepo(repo.__class__):
        def prefetchfastannotate(self, paths, peer=None):
            master = _getmaster(self.ui)
            needupdatepaths = []
            lastnodemap = {}
            try:
                for path in _filterfetchpaths(self, paths):
                    with context.annotatecontext(self, path) as actx:
                        if not actx.isuptodate(master, strict=False):
                            needupdatepaths.append(path)
                            lastnodemap[path] = actx.lastnode
                if needupdatepaths:
                    clientfetch(self, needupdatepaths, lastnodemap, peer)
            except Exception as ex:
                # could be directory not writable or so, not fatal
                self.ui.debug(b'fastannotate: prefetch failed: %r\n' % ex)

    repo.__class__ = fastannotaterepo


def clientreposetup(ui, repo):
    _registerwireprotocommand()
    if repo.local():
        localreposetup(ui, repo)
    # TODO: this mutates global state, but only if at least one repo
    # has the extension enabled. This is probably bad for hgweb.
    if peersetup not in hg.wirepeersetupfuncs:
        hg.wirepeersetupfuncs.append(peersetup)