--- a/mercurial/configitems.py	Wed Sep 26 23:50:14 2018 +0200
+++ b/mercurial/configitems.py	Thu Oct 04 11:28:48 2018 +0200
@@ -737,6 +737,11 @@
 coreconfigitem('http_proxy', 'user',
     default=None,
 )
+
+coreconfigitem('http', 'timeout',
+    default=None,
+)
+
 coreconfigitem('logtoprocess', 'commandexception',
     default=None,
 )

--- a/mercurial/help/config.txt	Wed Sep 26 23:50:14 2018 +0200
+++ b/mercurial/help/config.txt	Thu Oct 04 11:28:48 2018 +0200
@@ -1322,6 +1322,15 @@
     Optional. Always use the proxy, even for localhost and any entries
     in ``http_proxy.no``. (default: False)
 
+``http``
+----------
+
+Used to configure access to Mercurial repositories via HTTP.
+
+``timeout``
+    If set, blocking operations will timeout after that many seconds.
+    (default: None)
+
 ``merge``
 ---------
 

--- a/mercurial/keepalive.py	Wed Sep 26 23:50:14 2018 +0200
+++ b/mercurial/keepalive.py	Thu Oct 04 11:28:48 2018 +0200
@@ -172,8 +172,9 @@
             return dict(self._hostmap)
 
 class KeepAliveHandler(object):
-    def __init__(self):
+    def __init__(self, timeout=None):
         self._cm = ConnectionManager()
+        self._timeout = timeout
         self.requestscount = 0
         self.sentbytescount = 0
 
@@ -234,7 +235,7 @@
                 h = self._cm.get_ready_conn(host)
             else:
                 # no (working) free connections were found.  Create a new one.
-                h = http_class(host)
+                h = http_class(host, timeout=self._timeout)
                 if DEBUG:
                     DEBUG.info("creating new connection to %s (%d)",
                                host, id(h))

--- a/mercurial/url.py	Wed Sep 26 23:50:14 2018 +0200
+++ b/mercurial/url.py	Thu Oct 04 11:28:48 2018 +0200
@@ -317,8 +317,8 @@
 
 class logginghttphandler(httphandler):
     """HTTP handler that logs socket I/O."""
-    def __init__(self, logfh, name, observeropts):
-        super(logginghttphandler, self).__init__()
+    def __init__(self, logfh, name, observeropts, timeout=None):
+        super(logginghttphandler, self).__init__(timeout=timeout)
 
         self._logfh = logfh
         self._logname = name
@@ -365,8 +365,8 @@
             sslutil.validatesocket(self.sock)
 
     class httpshandler(keepalive.KeepAliveHandler, urlreq.httpshandler):
-        def __init__(self, ui):
-            keepalive.KeepAliveHandler.__init__(self)
+        def __init__(self, ui, timeout=None):
+            keepalive.KeepAliveHandler.__init__(self, timeout=timeout)
             urlreq.httpshandler.__init__(self)
             self.ui = ui
             self.pwmgr = passwordmgr(self.ui,
@@ -525,18 +525,19 @@
     ``sendaccept`` allows controlling whether the ``Accept`` request header
     is sent. The header is sent by default.
     '''
+    timeout = ui.configwith(float, 'http', 'timeout')
     handlers = []
 
     if loggingfh:
         handlers.append(logginghttphandler(loggingfh, loggingname,
-                                           loggingopts or {}))
+                                           loggingopts or {}, timeout=timeout))
         # We don't yet support HTTPS when logging I/O. If we attempt to open
         # an HTTPS URL, we'll likely fail due to unknown protocol.
 
     else:
-        handlers.append(httphandler())
+        handlers.append(httphandler(timeout=timeout))
         if has_https:
-            handlers.append(httpshandler(ui))
+            handlers.append(httpshandler(ui, timeout=timeout))
 
     handlers.append(proxyhandler(ui))