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I've spent several hours over the past few weeks investigating networking failures involving hg.mozilla.org. As part of this, it has become clear that the Mercurial client's error handling when it encounters network failures is far from robust. To prove this is true, I've devised a battery of tests simulating various network failures, notably premature connection closes. To achieve this, I've implemented an extension that monkeypatches the built-in HTTP server and hooks in at the socket level and allows various events to occur based on config options. For example, you can refuse to accept() a client socket or you can close() the socket after N bytes have been sent or received. The latter effectively simulates an unexpected connection drop (and these occur all the time in the real world). The new test file launches servers exhibiting various "bad" behaviors and points a client at them. As the many TODO comments in the test call attention to, Mercurial often displays unhelpful errors when network-related failures occur. This makes it difficult for users to understand what's going on and difficult for server administrators to pinpoint root causes without packet tracing. Upcoming patches will attempt to fix these error handling deficiencies.
270 lines
9.6 KiB
Python
270 lines
9.6 KiB
Python
# badserverext.py - Extension making servers behave badly
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#
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# Copyright 2017 Gregory Szorc <gregory.szorc@gmail.com>
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#
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# This software may be used and distributed according to the terms of the
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# GNU General Public License version 2 or any later version.
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# no-check-code
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"""Extension to make servers behave badly.
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This extension is useful for testing Mercurial behavior when various network
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events occur.
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Various config options in the [badserver] section influence behavior:
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closebeforeaccept
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If true, close() the server socket when a new connection arrives before
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accept() is called. The server will then exit.
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closeafteraccept
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If true, the server will close() the client socket immediately after
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accept().
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closeafterrecvbytes
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If defined, close the client socket after receiving this many bytes.
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closeaftersendbytes
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If defined, close the client socket after sending this many bytes.
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"""
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from __future__ import absolute_import
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import socket
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from mercurial.hgweb import (
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server,
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)
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# We can't adjust __class__ on a socket instance. So we define a proxy type.
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class socketproxy(object):
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__slots__ = (
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'_orig',
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'_logfp',
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'_closeafterrecvbytes',
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'_closeaftersendbytes',
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)
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def __init__(self, obj, logfp, closeafterrecvbytes=0,
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closeaftersendbytes=0):
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object.__setattr__(self, '_orig', obj)
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object.__setattr__(self, '_logfp', logfp)
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object.__setattr__(self, '_closeafterrecvbytes', closeafterrecvbytes)
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object.__setattr__(self, '_closeaftersendbytes', closeaftersendbytes)
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def __getattribute__(self, name):
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if name in ('makefile',):
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return object.__getattribute__(self, name)
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return getattr(object.__getattribute__(self, '_orig'), name)
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def __delattr__(self, name):
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delattr(object.__getattribute__(self, '_orig'), name)
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def __setattr__(self, name, value):
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setattr(object.__getattribute__(self, '_orig'), name, value)
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def makefile(self, mode, bufsize):
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f = object.__getattribute__(self, '_orig').makefile(mode, bufsize)
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logfp = object.__getattribute__(self, '_logfp')
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closeafterrecvbytes = object.__getattribute__(self,
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'_closeafterrecvbytes')
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closeaftersendbytes = object.__getattribute__(self,
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'_closeaftersendbytes')
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return fileobjectproxy(f, logfp,
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closeafterrecvbytes=closeafterrecvbytes,
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closeaftersendbytes=closeaftersendbytes)
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# We can't adjust __class__ on socket._fileobject, so define a proxy.
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class fileobjectproxy(object):
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__slots__ = (
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'_orig',
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'_logfp',
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'_closeafterrecvbytes',
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'_closeaftersendbytes',
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)
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def __init__(self, obj, logfp, closeafterrecvbytes=0,
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closeaftersendbytes=0):
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object.__setattr__(self, '_orig', obj)
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object.__setattr__(self, '_logfp', logfp)
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object.__setattr__(self, '_closeafterrecvbytes', closeafterrecvbytes)
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object.__setattr__(self, '_closeaftersendbytes', closeaftersendbytes)
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def __getattribute__(self, name):
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if name in ('read', 'readline', 'write', '_writelog'):
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return object.__getattribute__(self, name)
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return getattr(object.__getattribute__(self, '_orig'), name)
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def __delattr__(self, name):
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delattr(object.__getattribute__(self, '_orig'), name)
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def __setattr__(self, name, value):
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setattr(object.__getattribute__(self, '_orig'), name, value)
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def _writelog(self, msg):
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msg = msg.replace('\r', '\\r').replace('\n', '\\n')
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object.__getattribute__(self, '_logfp').write(msg)
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object.__getattribute__(self, '_logfp').write('\n')
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def read(self, size=-1):
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remaining = object.__getattribute__(self, '_closeafterrecvbytes')
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# No read limit. Call original function.
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if not remaining:
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result = object.__getattribute__(self, '_orig').read(size)
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self._writelog('read(%d) -> (%d) (%s) %s' % (size,
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len(result),
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result))
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return result
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origsize = size
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if size < 0:
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size = remaining
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else:
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size = min(remaining, size)
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result = object.__getattribute__(self, '_orig').read(size)
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remaining -= len(result)
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self._writelog('read(%d from %d) -> (%d) %s' % (
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size, origsize, len(result), result))
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object.__setattr__(self, '_closeafterrecvbytes', remaining)
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if remaining <= 0:
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self._writelog('read limit reached, closing socket')
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self._sock.close()
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# This is the easiest way to abort the current request.
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raise Exception('connection closed after receiving N bytes')
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return result
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def readline(self, size=-1):
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remaining = object.__getattribute__(self, '_closeafterrecvbytes')
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# No read limit. Call original function.
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if not remaining:
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result = object.__getattribute__(self, '_orig').readline(size)
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self._writelog('readline(%d) -> (%d) %s' % (
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size, len(result), result))
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return result
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origsize = size
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if size < 0:
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size = remaining
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else:
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size = min(remaining, size)
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result = object.__getattribute__(self, '_orig').readline(size)
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remaining -= len(result)
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self._writelog('readline(%d from %d) -> (%d) %s' % (
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size, origsize, len(result), result))
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object.__setattr__(self, '_closeafterrecvbytes', remaining)
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if remaining <= 0:
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self._writelog('read limit reached; closing socket')
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self._sock.close()
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# This is the easiest way to abort the current request.
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raise Exception('connection closed after receiving N bytes')
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return result
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def write(self, data):
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remaining = object.__getattribute__(self, '_closeaftersendbytes')
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# No byte limit on this operation. Call original function.
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if not remaining:
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self._writelog('write(%d) -> %s' % (len(data), data))
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result = object.__getattribute__(self, '_orig').write(data)
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return result
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if len(data) > remaining:
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newdata = data[0:remaining]
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else:
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newdata = data
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remaining -= len(newdata)
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self._writelog('write(%d from %d) -> (%d) %s' % (
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len(newdata), len(data), remaining, newdata))
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result = object.__getattribute__(self, '_orig').write(newdata)
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object.__setattr__(self, '_closeaftersendbytes', remaining)
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if remaining <= 0:
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self._writelog('write limit reached; closing socket')
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self._sock.close()
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raise Exception('connection closed after sending N bytes')
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return result
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def extsetup(ui):
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# Change the base HTTP server class so various events can be performed.
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# See SocketServer.BaseServer for how the specially named methods work.
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class badserver(server.MercurialHTTPServer):
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def __init__(self, ui, *args, **kwargs):
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self._ui = ui
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super(badserver, self).__init__(ui, *args, **kwargs)
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# Need to inherit object so super() works.
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class badrequesthandler(self.RequestHandlerClass, object):
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def send_header(self, name, value):
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# Make headers deterministic to facilitate testing.
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if name.lower() == 'date':
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value = 'Fri, 14 Apr 2017 00:00:00 GMT'
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elif name.lower() == 'server':
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value = 'badhttpserver'
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return super(badrequesthandler, self).send_header(name,
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value)
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self.RequestHandlerClass = badrequesthandler
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# Called to accept() a pending socket.
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def get_request(self):
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if self._ui.configbool('badserver', 'closebeforeaccept'):
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self.socket.close()
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# Tells the server to stop processing more requests.
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self.__shutdown_request = True
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# Simulate failure to stop processing this request.
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raise socket.error('close before accept')
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if self._ui.configbool('badserver', 'closeafteraccept'):
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request, client_address = super(badserver, self).get_request()
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request.close()
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raise socket.error('close after accept')
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return super(badserver, self).get_request()
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# Does heavy lifting of processing a request. Invokes
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# self.finish_request() which calls self.RequestHandlerClass() which
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# is a hgweb.server._httprequesthandler.
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def process_request(self, socket, address):
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# Wrap socket in a proxy if we need to count bytes.
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closeafterrecvbytes = self._ui.configint('badserver',
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'closeafterrecvbytes', 0)
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closeaftersendbytes = self._ui.configint('badserver',
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'closeaftersendbytes', 0)
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if closeafterrecvbytes or closeaftersendbytes:
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socket = socketproxy(socket, self.errorlog,
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closeafterrecvbytes=closeafterrecvbytes,
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closeaftersendbytes=closeaftersendbytes)
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return super(badserver, self).process_request(socket, address)
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server.MercurialHTTPServer = badserver
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