keepalive: don't concatenate strings when reading chunked transfer

Surprisingly, this didn't appear to speed up HTTP-based stream cloning
on my machine. I suspect this has more to do with the fact we're using
small HTTP chunks and string concatenation overhead isn't so bad.
However, the reasons for this change are solid: we know string
concatenation can be a performance sink.

mercurial/keepalive.py

@@ -1,692 +1,690 b''
 #   This library is free software; you can redistribute it and/or
 #   modify it under the terms of the GNU Lesser General Public
 #   License as published by the Free Software Foundation; either
 #   version 2.1 of the License, or (at your option) any later version.
 #
 #   This library is distributed in the hope that it will be useful,
 #   but WITHOUT ANY WARRANTY; without even the implied warranty of
 #   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 #   Lesser General Public License for more details.
 #
 #   You should have received a copy of the GNU Lesser General Public
 #   License along with this library; if not, see
 #   <http://www.gnu.org/licenses/>.
 
 # This file is part of urlgrabber, a high-level cross-protocol url-grabber
 # Copyright 2002-2004 Michael D. Stenner, Ryan Tomayko
 
 # Modified by Benoit Boissinot:
 #  - fix for digest auth (inspired from urllib2.py @ Python v2.4)
 # Modified by Dirkjan Ochtman:
 #  - import md5 function from a local util module
 # Modified by Augie Fackler:
 #  - add safesend method and use it to prevent broken pipe errors
 #    on large POST requests
 
 """An HTTP handler for urllib2 that supports HTTP 1.1 and keepalive.
 
 >>> import urllib2
 >>> from keepalive import HTTPHandler
 >>> keepalive_handler = HTTPHandler()
 >>> opener = urlreq.buildopener(keepalive_handler)
 >>> urlreq.installopener(opener)
 >>>
 >>> fo = urlreq.urlopen('http://www.python.org')
 
 If a connection to a given host is requested, and all of the existing
 connections are still in use, another connection will be opened.  If
 the handler tries to use an existing connection but it fails in some
 way, it will be closed and removed from the pool.
 
 To remove the handler, simply re-run build_opener with no arguments, and
 install that opener.
 
 You can explicitly close connections by using the close_connection()
 method of the returned file-like object (described below) or you can
 use the handler methods:
 
   close_connection(host)
   close_all()
   open_connections()
 
 NOTE: using the close_connection and close_all methods of the handler
 should be done with care when using multiple threads.
   * there is nothing that prevents another thread from creating new
     connections immediately after connections are closed
   * no checks are done to prevent in-use connections from being closed
 
 >>> keepalive_handler.close_all()
 
 EXTRA ATTRIBUTES AND METHODS
 
   Upon a status of 200, the object returned has a few additional
   attributes and methods, which should not be used if you want to
   remain consistent with the normal urllib2-returned objects:
 
     close_connection()  -  close the connection to the host
     readlines()         -  you know, readlines()
     status              -  the return status (i.e. 404)
     reason              -  english translation of status (i.e. 'File not found')
 
   If you want the best of both worlds, use this inside an
   AttributeError-catching try:
 
   >>> try: status = fo.status
   >>> except AttributeError: status = None
 
   Unfortunately, these are ONLY there if status == 200, so it's not
   easy to distinguish between non-200 responses.  The reason is that
   urllib2 tries to do clever things with error codes 301, 302, 401,
   and 407, and it wraps the object upon return.
 """
 
 # $Id: keepalive.py,v 1.14 2006/04/04 21:00:32 mstenner Exp $
 
 from __future__ import absolute_import, print_function
 
 import errno
 import hashlib
 import socket
 import sys
 import threading
 
 from . import (
     util,
 )
 
 httplib = util.httplib
 urlerr = util.urlerr
 urlreq = util.urlreq
 
 DEBUG = None
 
 class ConnectionManager(object):
     """
     The connection manager must be able to:
       * keep track of all existing
       """
     def __init__(self):
         self._lock = threading.Lock()
         self._hostmap = {} # map hosts to a list of connections
         self._connmap = {} # map connections to host
         self._readymap = {} # map connection to ready state
 
     def add(self, host, connection, ready):
         self._lock.acquire()
         try:
             if host not in self._hostmap:
                 self._hostmap[host] = []
             self._hostmap[host].append(connection)
             self._connmap[connection] = host
             self._readymap[connection] = ready
         finally:
             self._lock.release()
 
     def remove(self, connection):
         self._lock.acquire()
         try:
             try:
                 host = self._connmap[connection]
             except KeyError:
                 pass
             else:
                 del self._connmap[connection]
                 del self._readymap[connection]
                 self._hostmap[host].remove(connection)
                 if not self._hostmap[host]: del self._hostmap[host]
         finally:
             self._lock.release()
 
     def set_ready(self, connection, ready):
         try:
             self._readymap[connection] = ready
         except KeyError:
             pass
 
     def get_ready_conn(self, host):
         conn = None
         self._lock.acquire()
         try:
             if host in self._hostmap:
                 for c in self._hostmap[host]:
                     if self._readymap[c]:
                         self._readymap[c] = 0
                         conn = c
                         break
         finally:
             self._lock.release()
         return conn
 
     def get_all(self, host=None):
         if host:
             return list(self._hostmap.get(host, []))
         else:
             return dict(self._hostmap)
 
 class KeepAliveHandler(object):
     def __init__(self):
         self._cm = ConnectionManager()
 
     #### Connection Management
     def open_connections(self):
         """return a list of connected hosts and the number of connections
         to each.  [('foo.com:80', 2), ('bar.org', 1)]"""
         return [(host, len(li)) for (host, li) in self._cm.get_all().items()]
 
     def close_connection(self, host):
         """close connection(s) to <host>
         host is the host:port spec, as in 'www.cnn.com:8080' as passed in.
         no error occurs if there is no connection to that host."""
         for h in self._cm.get_all(host):
             self._cm.remove(h)
             h.close()
 
     def close_all(self):
         """close all open connections"""
         for host, conns in self._cm.get_all().iteritems():
             for h in conns:
                 self._cm.remove(h)
                 h.close()
 
     def _request_closed(self, request, host, connection):
         """tells us that this request is now closed and that the
         connection is ready for another request"""
         self._cm.set_ready(connection, 1)
 
     def _remove_connection(self, host, connection, close=0):
         if close:
             connection.close()
         self._cm.remove(connection)
 
     #### Transaction Execution
     def http_open(self, req):
         return self.do_open(HTTPConnection, req)
 
     def do_open(self, http_class, req):
         host = req.get_host()
         if not host:
             raise urlerr.urlerror('no host given')
 
         try:
             h = self._cm.get_ready_conn(host)
             while h:
                 r = self._reuse_connection(h, req, host)
 
                 # if this response is non-None, then it worked and we're
                 # done.  Break out, skipping the else block.
                 if r:
                     break
 
                 # connection is bad - possibly closed by server
                 # discard it and ask for the next free connection
                 h.close()
                 self._cm.remove(h)
                 h = self._cm.get_ready_conn(host)
             else:
                 # no (working) free connections were found.  Create a new one.
                 h = http_class(host)
                 if DEBUG:
                     DEBUG.info("creating new connection to %s (%d)",
                                host, id(h))
                 self._cm.add(host, h, 0)
                 self._start_transaction(h, req)
                 r = h.getresponse()
         except (socket.error, httplib.HTTPException) as err:
             raise urlerr.urlerror(err)
 
         # if not a persistent connection, don't try to reuse it
         if r.will_close:
             self._cm.remove(h)
 
         if DEBUG:
             DEBUG.info("STATUS: %s, %s", r.status, r.reason)
         r._handler = self
         r._host = host
         r._url = req.get_full_url()
         r._connection = h
         r.code = r.status
         r.headers = r.msg
         r.msg = r.reason
 
         return r
 
     def _reuse_connection(self, h, req, host):
         """start the transaction with a re-used connection
         return a response object (r) upon success or None on failure.
         This DOES not close or remove bad connections in cases where
         it returns.  However, if an unexpected exception occurs, it
         will close and remove the connection before re-raising.
         """
         try:
             self._start_transaction(h, req)
             r = h.getresponse()
             # note: just because we got something back doesn't mean it
             # worked.  We'll check the version below, too.
         except (socket.error, httplib.HTTPException):
             r = None
         except: # re-raises
             # adding this block just in case we've missed
             # something we will still raise the exception, but
             # lets try and close the connection and remove it
             # first.  We previously got into a nasty loop
             # where an exception was uncaught, and so the
             # connection stayed open.  On the next try, the
             # same exception was raised, etc.  The trade-off is
             # that it's now possible this call will raise
             # a DIFFERENT exception
             if DEBUG:
                 DEBUG.error("unexpected exception - closing "
                             "connection to %s (%d)", host, id(h))
             self._cm.remove(h)
             h.close()
             raise
 
         if r is None or r.version == 9:
             # httplib falls back to assuming HTTP 0.9 if it gets a
             # bad header back.  This is most likely to happen if
             # the socket has been closed by the server since we
             # last used the connection.
             if DEBUG:
                 DEBUG.info("failed to re-use connection to %s (%d)",
                            host, id(h))
             r = None
         else:
             if DEBUG:
                 DEBUG.info("re-using connection to %s (%d)", host, id(h))
 
         return r
 
     def _start_transaction(self, h, req):
         # What follows mostly reimplements HTTPConnection.request()
         # except it adds self.parent.addheaders in the mix.
         headers = dict(self.parent.addheaders)
         headers.update(req.headers)
         headers.update(req.unredirected_hdrs)
         headers = dict((n.lower(), v) for n, v in headers.items())
         skipheaders = {}
         for n in ('host', 'accept-encoding'):
             if n in headers:
                 skipheaders['skip_' + n.replace('-', '_')] = 1
         try:
             if req.has_data():
                 data = req.get_data()
                 h.putrequest('POST', req.get_selector(), **skipheaders)
                 if 'content-type' not in headers:
                     h.putheader('Content-type',
                                 'application/x-www-form-urlencoded')
                 if 'content-length' not in headers:
                     h.putheader('Content-length', '%d' % len(data))
             else:
                 h.putrequest('GET', req.get_selector(), **skipheaders)
         except socket.error as err:
             raise urlerr.urlerror(err)
         for k, v in headers.items():
             h.putheader(k, v)
         h.endheaders()
         if req.has_data():
             h.send(data)
 
 class HTTPHandler(KeepAliveHandler, urlreq.httphandler):
     pass
 
 class HTTPResponse(httplib.HTTPResponse):
     # we need to subclass HTTPResponse in order to
     # 1) add readline() and readlines() methods
     # 2) add close_connection() methods
     # 3) add info() and geturl() methods
 
     # in order to add readline(), read must be modified to deal with a
     # buffer.  example: readline must read a buffer and then spit back
     # one line at a time.  The only real alternative is to read one
     # BYTE at a time (ick).  Once something has been read, it can't be
     # put back (ok, maybe it can, but that's even uglier than this),
     # so if you THEN do a normal read, you must first take stuff from
     # the buffer.
 
     # the read method wraps the original to accommodate buffering,
     # although read() never adds to the buffer.
     # Both readline and readlines have been stolen with almost no
     # modification from socket.py
 
 
     def __init__(self, sock, debuglevel=0, strict=0, method=None):
         httplib.HTTPResponse.__init__(self, sock, debuglevel, method)
         self.fileno = sock.fileno
         self.code = None
         self._rbuf = ''
         self._rbufsize = 8096
         self._handler = None # inserted by the handler later
         self._host = None    # (same)
         self._url = None     # (same)
         self._connection = None # (same)
 
     _raw_read = httplib.HTTPResponse.read
 
     def close(self):
         if self.fp:
             self.fp.close()
             self.fp = None
             if self._handler:
                 self._handler._request_closed(self, self._host,
                                               self._connection)
 
     def close_connection(self):
         self._handler._remove_connection(self._host, self._connection, close=1)
         self.close()
 
     def info(self):
         return self.headers
 
     def geturl(self):
         return self._url
 
     def read(self, amt=None):
         # the _rbuf test is only in this first if for speed.  It's not
         # logically necessary
         if self._rbuf and not amt is None:
             L = len(self._rbuf)
             if amt > L:
                 amt -= L
             else:
                 s = self._rbuf[:amt]
                 self._rbuf = self._rbuf[amt:]
                 return s
 
         s = self._rbuf + self._raw_read(amt)
         self._rbuf = ''
         return s
 
     # stolen from Python SVN #68532 to fix issue1088
     def _read_chunked(self, amt):
         chunk_left = self.chunk_left
-        value = ''
+        parts = []
 
-        # XXX This accumulates chunks by repeated string concatenation,
-        # which is not efficient as the number or size of chunks gets big.
         while True:
             if chunk_left is None:
                 line = self.fp.readline()
                 i = line.find(';')
                 if i >= 0:
                     line = line[:i] # strip chunk-extensions
                 try:
                     chunk_left = int(line, 16)
                 except ValueError:
                     # close the connection as protocol synchronization is
                     # probably lost
                     self.close()
-                    raise httplib.IncompleteRead(value)
+                    raise httplib.IncompleteRead(''.join(parts))
                 if chunk_left == 0:
                     break
             if amt is None:
-                value += self._safe_read(chunk_left)
+                parts.append(self._safe_read(chunk_left))
             elif amt < chunk_left:
-                value += self._safe_read(amt)
+                parts.append(self._safe_read(amt))
                 self.chunk_left = chunk_left - amt
-                return value
+                return ''.join(parts)
             elif amt == chunk_left:
-                value += self._safe_read(amt)
+                parts.append(self._safe_read(amt))
                 self._safe_read(2)  # toss the CRLF at the end of the chunk
                 self.chunk_left = None
-                return value
+                return ''.join(parts)
             else:
-                value += self._safe_read(chunk_left)
+                parts.append(self._safe_read(chunk_left))
                 amt -= chunk_left
 
             # we read the whole chunk, get another
             self._safe_read(2)      # toss the CRLF at the end of the chunk
             chunk_left = None
 
         # read and discard trailer up to the CRLF terminator
         ### note: we shouldn't have any trailers!
         while True:
             line = self.fp.readline()
             if not line:
                 # a vanishingly small number of sites EOF without
                 # sending the trailer
                 break
             if line == '\r\n':
                 break
 
         # we read everything; close the "file"
         self.close()
 
-        return value
+        return ''.join(parts)
 
     def readline(self, limit=-1):
         i = self._rbuf.find('\n')
         while i < 0 and not (0 < limit <= len(self._rbuf)):
             new = self._raw_read(self._rbufsize)
             if not new:
                 break
             i = new.find('\n')
             if i >= 0:
                 i = i + len(self._rbuf)
             self._rbuf = self._rbuf + new
         if i < 0:
             i = len(self._rbuf)
         else:
             i = i + 1
         if 0 <= limit < len(self._rbuf):
             i = limit
         data, self._rbuf = self._rbuf[:i], self._rbuf[i:]
         return data
 
     def readlines(self, sizehint=0):
         total = 0
         list = []
         while True:
             line = self.readline()
             if not line:
                 break
             list.append(line)
             total += len(line)
             if sizehint and total >= sizehint:
                 break
         return list
 
 def safesend(self, str):
     """Send `str' to the server.
 
     Shamelessly ripped off from httplib to patch a bad behavior.
     """
     # _broken_pipe_resp is an attribute we set in this function
     # if the socket is closed while we're sending data but
     # the server sent us a response before hanging up.
     # In that case, we want to pretend to send the rest of the
     # outgoing data, and then let the user use getresponse()
     # (which we wrap) to get this last response before
     # opening a new socket.
     if getattr(self, '_broken_pipe_resp', None) is not None:
         return
 
     if self.sock is None:
         if self.auto_open:
             self.connect()
         else:
             raise httplib.NotConnected
 
     # send the data to the server. if we get a broken pipe, then close
     # the socket. we want to reconnect when somebody tries to send again.
     #
     # NOTE: we DO propagate the error, though, because we cannot simply
     #       ignore the error... the caller will know if they can retry.
     if self.debuglevel > 0:
         print("send:", repr(str))
     try:
         blocksize = 8192
         read = getattr(str, 'read', None)
         if read is not None:
             if self.debuglevel > 0:
                 print("sending a read()able")
             data = read(blocksize)
             while data:
                 self.sock.sendall(data)
                 data = read(blocksize)
         else:
             self.sock.sendall(str)
     except socket.error as v:
         reraise = True
         if v[0] == errno.EPIPE:      # Broken pipe
             if self._HTTPConnection__state == httplib._CS_REQ_SENT:
                 self._broken_pipe_resp = None
                 self._broken_pipe_resp = self.getresponse()
                 reraise = False
             self.close()
         if reraise:
             raise
 
 def wrapgetresponse(cls):
     """Wraps getresponse in cls with a broken-pipe sane version.
     """
     def safegetresponse(self):
         # In safesend() we might set the _broken_pipe_resp
         # attribute, in which case the socket has already
         # been closed and we just need to give them the response
         # back. Otherwise, we use the normal response path.
         r = getattr(self, '_broken_pipe_resp', None)
         if r is not None:
             return r
         return cls.getresponse(self)
     safegetresponse.__doc__ = cls.getresponse.__doc__
     return safegetresponse
 
 class HTTPConnection(httplib.HTTPConnection):
     # use the modified response class
     response_class = HTTPResponse
     send = safesend
     getresponse = wrapgetresponse(httplib.HTTPConnection)
 
 
 #########################################################################
 #####   TEST FUNCTIONS
 #########################################################################
 
 
 def continuity(url):
     md5 = hashlib.md5
     format = '%25s: %s'
 
     # first fetch the file with the normal http handler
     opener = urlreq.buildopener()
     urlreq.installopener(opener)
     fo = urlreq.urlopen(url)
     foo = fo.read()
     fo.close()
     m = md5(foo)
     print(format % ('normal urllib', m.hexdigest()))
 
     # now install the keepalive handler and try again
     opener = urlreq.buildopener(HTTPHandler())
     urlreq.installopener(opener)
 
     fo = urlreq.urlopen(url)
     foo = fo.read()
     fo.close()
     m = md5(foo)
     print(format % ('keepalive read', m.hexdigest()))
 
     fo = urlreq.urlopen(url)
     foo = ''
     while True:
         f = fo.readline()
         if f:
             foo = foo + f
         else: break
     fo.close()
     m = md5(foo)
     print(format % ('keepalive readline', m.hexdigest()))
 
 def comp(N, url):
     print('  making %i connections to:\n  %s' % (N, url))
 
     util.stdout.write('  first using the normal urllib handlers')
     # first use normal opener
     opener = urlreq.buildopener()
     urlreq.installopener(opener)
     t1 = fetch(N, url)
     print('  TIME: %.3f s' % t1)
 
     util.stdout.write('  now using the keepalive handler       ')
     # now install the keepalive handler and try again
     opener = urlreq.buildopener(HTTPHandler())
     urlreq.installopener(opener)
     t2 = fetch(N, url)
     print('  TIME: %.3f s' % t2)
     print('  improvement factor: %.2f' % (t1 / t2))
 
 def fetch(N, url, delay=0):
     import time
     lens = []
     starttime = time.time()
     for i in range(N):
         if delay and i > 0:
             time.sleep(delay)
         fo = urlreq.urlopen(url)
         foo = fo.read()
         fo.close()
         lens.append(len(foo))
     diff = time.time() - starttime
 
     j = 0
     for i in lens[1:]:
         j = j + 1
         if not i == lens[0]:
             print("WARNING: inconsistent length on read %i: %i" % (j, i))
 
     return diff
 
 def test_timeout(url):
     global DEBUG
     dbbackup = DEBUG
     class FakeLogger(object):
         def debug(self, msg, *args):
             print(msg % args)
         info = warning = error = debug
     DEBUG = FakeLogger()
     print("  fetching the file to establish a connection")
     fo = urlreq.urlopen(url)
     data1 = fo.read()
     fo.close()
 
     i = 20
     print("  waiting %i seconds for the server to close the connection" % i)
     while i > 0:
         util.stdout.write('\r  %2i' % i)
         util.stdout.flush()
         time.sleep(1)
         i -= 1
     util.stderr.write('\r')
 
     print("  fetching the file a second time")
     fo = urlreq.urlopen(url)
     data2 = fo.read()
     fo.close()
 
     if data1 == data2:
         print('  data are identical')
     else:
         print('  ERROR: DATA DIFFER')
 
     DEBUG = dbbackup
 
 
 def test(url, N=10):
     print("performing continuity test (making sure stuff isn't corrupted)")
     continuity(url)
     print('')
     print("performing speed comparison")
     comp(N, url)
     print('')
     print("performing dropped-connection check")
     test_timeout(url)
 
 if __name__ == '__main__':
     import time
     try:
         N = int(sys.argv[1])
         url = sys.argv[2]
     except (IndexError, ValueError):
         print("%s <integer> <url>" % sys.argv[0])
     else:
         test(url, N)