Use select.

lib/interface.py

@@ -17,10 +17,14 @@
 # along with this program. If not, see <http://www.gnu.org/licenses/>.
 
 
-import copy, re, errno, os
-import threading, traceback, sys, time, Queue
+import os
+import re
 import socket
 import ssl
+import sys
+import threading
+import time
+import traceback
 
 import requests
 ca_path = requests.certs.where()
@@ -28,49 +32,30 @@ ca_path = requests.certs.where()
 import util
 import x509
 import pem
-from version import ELECTRUM_VERSION, PROTOCOL_VERSION
-from simple_config import SimpleConfig
 
 
-def Interface(server, response_queue, config = None):
-    """Interface factory function.  The returned interface class handles the connection
-    to a single remote electrum server.  The object handles all necessary locking.  It's
-    exposed API is:
+def Connection(server, queue, config_path):
+    """Makes asynchronous connections to a remote remote electrum server.
+    Returns the running thread that is making the connection.
 
-    - Inherits everything from threading.Thread.
-    - Member functions send_request(), stop(), is_connected()
-    - Member variable server.
-    
-    "server" is constant for the object's lifetime and hence synchronization is unnecessary.
+    Once the thread has connected, it finishes, placing a tuple on the
+    queue of the form (server, socket), where socket is None if
+    connection failed.
     """
     host, port, protocol = server.split(':')
-    if protocol in 'st':
-        return TcpInterface(server, response_queue, config)
-    else:
-        raise Exception('Unknown protocol: %s'%protocol)
+    if not protocol in 'st':
+        raise Exception('Unknown protocol: %s' % protocol)
+    c = TcpConnection(server, queue, config_path)
+    c.start()
+    return c
 
-# Connection status
-CS_OPENING, CS_CONNECTED, CS_FAILED = range(3)
+class TcpConnection(threading.Thread):
 
-class TcpInterface(threading.Thread):
-
-    def __init__(self, server, response_queue, config = None):
+    def __init__(self, server, queue, config_path):
         threading.Thread.__init__(self)
         self.daemon = True
-        self.config = config if config is not None else SimpleConfig()
-        # Set by stop(); no more data is exchanged and the thread exits after gracefully
-        # closing the socket
-        self.disconnect = False
-        self._status = CS_OPENING
-        self.debug = False # dump network messages. can be changed at runtime using the console
-        self.message_id = 0
-        self.response_queue = response_queue
-        self.request_queue = Queue.Queue()
-        self.unanswered_requests = {}
-        # request timeouts
-        self.request_time = time.time()
-        self.ping_time = 0
-        # parse server
+        self.config_path = config_path
+        self.queue = queue
         self.server = server
         self.host, self.port, self.protocol = self.server.split(':')
         self.host = str(self.host)
@@ -78,47 +63,31 @@ class TcpInterface(threading.Thread):
         self.use_ssl = (self.protocol == 's')
 
     def print_error(self, *msg):
-        util.print_error("[%s]"%self.host, *msg)
+        util.print_error("[%s]" % self.host, *msg)
 
-    def process_response(self, response):
-        if self.debug:
-            self.print_error("<--", response)
-
-        msg_id = response.get('id')
-        error = response.get('error')
-        result = response.get('result')
-
-        if msg_id is not None:
-            method, params, _id, queue = self.unanswered_requests.pop(msg_id)
-            if queue is None:
-                queue = self.response_queue
+    def check_host_name(self, peercert, name):
+        """Simple certificate/host name checker.  Returns True if the
+        certificate matches, False otherwise.  Does not support
+        wildcards."""
+        # Check that the peer has supplied a certificate.
+        # None/{} is not acceptable.
+        if not peercert:
+            return False
+        if peercert.has_key("subjectAltName"):
+            for typ, val in peercert["subjectAltName"]:
+                if typ == "DNS" and val == name:
+                    return True
         else:
-            # notification
-            method = response.get('method')
-            params = response.get('params')
-            _id = None
-            queue = self.response_queue
-            # restore parameters
-            if method == 'blockchain.numblocks.subscribe':
-                result = params[0]
-                params = []
-            elif method == 'blockchain.headers.subscribe':
-                result = params[0]
-                params = []
-            elif method == 'blockchain.address.subscribe':
-                addr = params[0]
-                result = params[1]
-                params = [addr]
-
-        if method == 'server.version':
-            self.server_version = result
-            return
-
-        if error:
-            queue.put((self, {'method':method, 'params':params, 'error':error, 'id':_id}))
-        else:
-            queue.put((self, {'method':method, 'params':params, 'result':result, 'id':_id}))
-
+            # Only check the subject DN if there is no subject alternative
+            # name.
+            cn = None
+            for attr, val in peercert["subject"]:
+                # Use most-specific (last) commonName attribute.
+                if attr == "commonName":
+                    cn = val
+            if cn is not None:
+                return cn == name
+        return False
 
     def get_simple_socket(self):
         try:
@@ -138,10 +107,9 @@ class TcpInterface(threading.Thread):
         else:
             self.print_error("failed to connect", str(e))
 
-
     def get_socket(self):
         if self.use_ssl:
-            cert_path = os.path.join( self.config.path, 'certs', self.host)
+            cert_path = os.path.join(self.config_path, 'certs', self.host)
             if not os.path.exists(cert_path):
                 is_new = True
                 s = self.get_simple_socket()
@@ -152,7 +120,7 @@ class TcpInterface(threading.Thread):
                     s = ssl.wrap_socket(s, ssl_version=ssl.PROTOCOL_TLSv1, cert_reqs=ssl.CERT_REQUIRED, ca_certs=ca_path, do_handshake_on_connect=True)
                 except ssl.SSLError, e:
                     s = None
-                if s and check_host_name(s.getpeercert(), self.host):
+                if s and self.check_host_name(s.getpeercert(), self.host):
                     self.print_error("SSL certificate signed by CA")
                     return s
 
@@ -229,117 +197,131 @@ class TcpInterface(threading.Thread):
 
         return s
 
-    def send_request(self, request, response_queue = None):
+    def run(self):
+        socket = self.get_socket()
+        if socket:
+            self.print_error("connected")
+        self.queue.put((self.server, socket))
+
+class Interface:
+    """The Interface class handles a socket connected to a single remote
+    electrum server.  It's exposed API is:
+
+    - Member functions close(), fileno(), get_responses(), has_timed_out(),
+      ping_required(), queue_request(), send_requests()
+    - Member variable server.
+    """
+
+    def __init__(self, server, socket):
+        self.server = server
+        self.host, _, _ = server.split(':')
+        self.socket = socket
+
+        self.pipe = util.SocketPipe(socket)
+        self.pipe.set_timeout(0.0)  # Don't wait for data
+        # Dump network messages.  Set at runtime from the console.
+        self.debug = False
+        self.message_id = 0
+        self.unsent_requests = []
+        self.unanswered_requests = {}
+        # Set last ping to zero to ensure immediate ping
+        self.last_request = time.time()
+        self.last_ping = 0
+        self.closed_remotely = False
+
+    def print_error(self, *msg):
+        util.print_error("[%s]" % self.host, *msg)
+
+    def fileno(self):
+        # Needed for select
+        return self.socket.fileno()
+
+    def close(self):
+        if not self.closed_remotely:
+            self.socket.shutdown(socket.SHUT_RDWR)
+        self.socket.close()
+
+    def queue_request(self, request):
         '''Queue a request.'''
         self.request_time = time.time()
-        self.request_queue.put((copy.deepcopy(request), response_queue))
+        self.unsent_requests.append(request)
 
     def send_requests(self):
-        '''Sends all queued requests'''
-        while self.is_connected() and not self.request_queue.empty():
-            request, response_queue = self.request_queue.get()
-            method = request.get('method')
-            params = request.get('params')
-            r = {'id': self.message_id, 'method': method, 'params': params}
-            try:
-                self.pipe.send(r)
-            except socket.error, e:
-                self.print_error("socket error:", e)
-                self.stop()
-                return
-            if self.debug:
-                self.print_error("-->", r)
-            self.unanswered_requests[self.message_id] = method, params, request.get('id'), response_queue
+        '''Sends all queued requests.  Returns False on failure.'''
+        def copy_request(orig):
+            # Replace ID after making copy - mustn't change caller's copy
+            request = orig.copy()
+            request['id'] = self.message_id
             self.message_id += 1
+            if self.debug:
+                self.print_error("-->", request, orig.get('id'))
+            return request
 
-    def is_connected(self):
-        '''True if status is connected'''
-        return self._status == CS_CONNECTED and not self.disconnect
+        requests_as_sent = map(copy_request, self.unsent_requests)
+        try:
+            self.pipe.send_all(requests_as_sent)
+        except socket.error, e:
+            self.print_error("socket error:", e)
+            return False
+        # unanswered_requests stores the original unmodified user
+        # request, keyed by wire ID
+        for n, request in enumerate(self.unsent_requests):
+            self.unanswered_requests[requests_as_sent[n]['id']] = request
+        self.unsent_requests = []
+        return True
 
-    def stop(self):
-        if not self.disconnect:
-            self.disconnect = True
-            self.print_error("disconnecting")
+    def ping_required(self):
+        '''Maintains time since last ping.  Returns True if a ping should
+        be sent.
+        '''
+        now = time.time()
+        if now - self.last_ping > 60:
+            self.last_ping = now
+            return True
+        return False
 
-    def maybe_ping(self):
-        # ping the server with server.version
-        if time.time() - self.ping_time > 60:
-            self.send_request({'method':'server.version', 'params':[ELECTRUM_VERSION, PROTOCOL_VERSION]})
-            self.ping_time = time.time()
-        # stop interface if we have been waiting for more than 10 seconds
-        if self.unanswered_requests and time.time() - self.request_time > 10 and self.pipe.idle_time() > 10:
-            self.print_error("interface timeout", len(self.unanswered_requests))
-            self.stop()
+    def has_timed_out(self):
+        '''Returns True if the interface has timed out.'''
+        if (self.unanswered_requests and time.time() - self.request_time > 10
+            and self.pipe.idle_time() > 10):
+            self.print_error("timeout", len(self.unanswered_requests))
+            return True
 
-    def get_and_process_response(self):
-        if self.is_connected():
+        return False
+
+    def get_responses(self):
+        '''Call if there is data available on the socket.  Returns a list of
+        notifications and a list of responses.  The notifications are
+        singleton unsolicited responses presumably as a result of
+        prior subscriptions.  The responses are (request, response)
+        pairs.  If the connection was closed remotely or the remote
+        server is misbehaving, the last notification will be None.
+        '''
+        notifications, responses = [], []
+        while True:
             try:
                 response = self.pipe.get()
             except util.timeout:
-                return
-            # If remote side closed the socket, SocketPipe closes our socket and returns None
+                break
             if response is None:
-                self.disconnect = True
+                notifications.append(None)
+                self.closed_remotely = True
                 self.print_error("connection closed remotely")
+                break
+            if self.debug:
+                self.print_error("<--", response)
+            wire_id = response.pop('id', None)
+            if wire_id is None:
+                notifications.append(response)
+            elif wire_id in self.unanswered_requests:
+                request = self.unanswered_requests.pop(wire_id)
+                responses.append((request, response))
             else:
-                self.process_response(response)
+                notifications.append(None)
+                self.print_error("unknown wire ID", wire_id)
+                break
 
-    def run(self):
-        s = self.get_socket()
-        if s:
-            self.pipe = util.SocketPipe(s)
-            s.settimeout(0.1)
-            self.print_error("connected")
-            self._status = CS_CONNECTED
-            # Indicate to parent that we've connected
-            self.notify_status()
-            while self.is_connected():
-                self.maybe_ping()
-                self.send_requests()
-                self.get_and_process_response()
-            s.shutdown(socket.SHUT_RDWR)
-            s.close()
-
-        # Also for the s is None case 
-        self._status = CS_FAILED
-        # Indicate to parent that the connection is now down
-        self.notify_status()
-
-    def notify_status(self):
-        '''Notify owner that we have just connected or just failed the connection.
-        Owner determines which through e.g. testing is_connected()'''
-        self.response_queue.put((self, None))
-
-
-def _match_hostname(name, val):
-    if val == name:
-        return True
-
-    return val.startswith('*.') and name.endswith(val[1:])
-
-
-def check_host_name(peercert, name):
-    """Simple certificate/host name checker.  Returns True if the
-    certificate matches, False otherwise."""
-    # Check that the peer has supplied a certificate.
-    # None/{} is not acceptable.
-    if not peercert:
-        return False
-    if peercert.has_key("subjectAltName"):
-        for typ, val in peercert["subjectAltName"]:
-            if typ == "DNS" and _match_hostname(name, val):
-                return True
-    else:
-        # Only check the subject DN if there is no subject alternative
-        # name.
-        cn = None
-        for attr, val in peercert["subject"]:
-            # Use most-specific (last) commonName attribute.
-            if attr == "commonName":
-                cn = val
-        if cn is not None:
-            return _match_hostname(name, cn)
-    return False
+        return notifications, responses
 
 
 def check_cert(host, cert):
@@ -361,7 +343,15 @@ def check_cert(host, cert):
     util.print_msg(m)
 
 
+# Used by tests
+def _match_hostname(name, val):
+    if val == name:
+        return True
+
+    return val.startswith('*.') and name.endswith(val[1:])
+
 def test_certificates():
+    from simple_config import SimpleConfig
     config = SimpleConfig()
     mydir = os.path.join(config.path, "certs")
     certs = os.listdir(mydir)

lib/network.py

@@ -3,7 +3,9 @@ import Queue
 import os
 import sys
 import random
+import select
 import traceback
+from collections import deque
 
 import socks
 import socket
@@ -11,9 +13,9 @@ import json
 
 import util
 from bitcoin import *
-import interface
+from interface import Connection, Interface
 from blockchain import Blockchain
-from collections import deque
+from version import ELECTRUM_VERSION, PROTOCOL_VERSION
 
 DEFAULT_PORTS = {'t':'50001', 's':'50002', 'h':'8081', 'g':'8082'}
 
@@ -119,11 +121,13 @@ def deserialize_server(server_str):
 def serialize_server(host, port, protocol):
     return str(':'.join([host, port, protocol]))
 
-
 class Network(util.DaemonThread):
-    """The Network class manages a set of connections to remote
-    electrum servers, each connection is handled by its own
-    thread object returned from Interface().  Its external API:
+    """The Network class manages a set of connections to remote electrum
+    servers, each connected socket is handled by an Interface() object.
+    Connections are initiated by a Connection() thread which stops once
+    the connection succeeds or fails.
+
+    Our external API:
 
     - Member functions get_header(), get_parameters(), get_status_value(),
                        new_blockchain_height(), set_parameters(), start(),
@@ -137,7 +141,6 @@ class Network(util.DaemonThread):
         self.config = SimpleConfig(config) if type(config) == type({}) else config
         self.num_server = 8 if not self.config.get('oneserver') else 0
         self.blockchain = Blockchain(self.config, self)
-        self.queue = Queue.Queue()
         self.requests_queue = pipe.send_queue
         self.response_queue = pipe.get_queue
         # A deque of interface header requests, processed left-to-right
@@ -169,7 +172,7 @@ class Network(util.DaemonThread):
         self.subscribed_addresses = set()
         # cached address status
         self.addr_responses = {}
-        # unanswered requests
+        # Requests from client we've not seen a response to
         self.unanswered_requests = {}
         # retry times
         self.server_retry_time = time.time()
@@ -180,6 +183,8 @@ class Network(util.DaemonThread):
         self.interface = None
         self.interfaces = {}
         self.auto_connect = self.config.get('auto_connect', False)
+        self.connecting = {}
+        self.socket_queue = Queue.Queue()
         self.start_network(deserialize_server(self.default_server)[2],
                            deserialize_proxy(self.config.get('proxy')))
 
@@ -224,19 +229,22 @@ class Network(util.DaemonThread):
         self.notify('status')
 
     def is_connected(self):
-        return self.interface and self.interface.is_connected()
+        return self.interface is not None
+
+    def queue_request(self, method, params):
+        self.interface.queue_request({'method': method, 'params': params})
 
     def send_subscriptions(self):
         # clear cache
         self.cached_responses = {}
         self.print_error('sending subscriptions to', self.interface.server, len(self.unanswered_requests), len(self.subscribed_addresses))
         for r in self.unanswered_requests.values():
-            self.interface.send_request(r)
+            self.interface.queue_request(r)
         for addr in self.subscribed_addresses:
-            self.interface.send_request({'method':'blockchain.address.subscribe','params':[addr]})
-        self.interface.send_request({'method':'server.banner','params':[]})
-        self.interface.send_request({'method':'server.peers.subscribe','params':[]})
-        self.interface.send_request({'method':'blockchain.estimatefee','params':[2]})
+            self.queue_request('blockchain.address.subscribe', [addr])
+        self.queue_request('server.banner', [])
+        self.queue_request('server.peers.subscribe', [])
+        self.queue_request('blockchain.estimatefee', [2])
 
     def get_status_value(self, key):
         if key == 'status':
@@ -263,7 +271,7 @@ class Network(util.DaemonThread):
 
     def get_interfaces(self):
         '''The interfaces that are in connected state'''
-        return [s for s, i in self.interfaces.items() if i.is_connected()]
+        return self.interfaces.keys()
 
     def get_servers(self):
         if self.irc_servers:
@@ -280,12 +288,11 @@ class Network(util.DaemonThread):
         return out
 
     def start_interface(self, server):
-        if not server in self.interfaces.keys():
+        if (not server in self.interfaces and not server in self.connecting):
             if server == self.default_server:
                 self.set_status('connecting')
-            i = interface.Interface(server, self.queue, self.config)
-            self.interfaces[i.server] = i
-            i.start()
+            c = Connection(server, self.socket_queue, self.config.path)
+            self.connecting[server] = c
 
     def start_random_interface(self):
         exclude_set = self.disconnected_servers.union(set(self.interfaces))
@@ -312,6 +319,7 @@ class Network(util.DaemonThread):
 
     def start_network(self, protocol, proxy):
         assert not self.interface and not self.interfaces
+        assert not self.connecting and self.socket_queue.empty()
         self.print_error('starting network')
         self.disconnected_servers = set([])
         self.protocol = protocol
@@ -320,10 +328,13 @@ class Network(util.DaemonThread):
 
     def stop_network(self):
         self.print_error("stopping network")
-        for i in self.interfaces.values():
-            i.stop()
-        self.interface = None
-        self.interfaces = {}
+        for interface in self.interfaces.values():
+            self.close_interface(interface)
+        assert self.interface is None
+        assert not self.interfaces
+        self.connecting = {}
+        # Get a new queue - no old pending connections thanks!
+        self.socket_queue = Queue.Queue()
 
     def set_parameters(self, host, port, protocol, proxy, auto_connect):
         self.auto_connect = auto_connect
@@ -339,7 +350,10 @@ class Network(util.DaemonThread):
             self.switch_lagging_interface()
 
     def switch_to_random_interface(self):
+        '''Switch to a random connected server other than the current one'''
         servers = self.get_interfaces()    # Those in connected state
+        if self.default_server in servers:
+            servers.remove(self.default_server)
         if servers:
             self.switch_to_interface(random.choice(servers))
 
@@ -362,30 +376,28 @@ class Network(util.DaemonThread):
             self.start_interface(server)
             return
         i = self.interfaces[server]
-        if not i.is_connected():
-            # do nothing; we will switch once connected
-            return
         if self.interface != i:
             self.print_error("switching to", server)
             # stop any current interface in order to terminate subscriptions
-            self.stop_interface()
+            self.close_interface(self.interface)
             self.interface = i
             self.addr_responses = {}
             self.send_subscriptions()
             self.set_status('connected')
             self.notify('updated')
 
-    def stop_interface(self):
-        if self.interface:
-            self.interface.stop()
-            self.interface = None
+    def close_interface(self, interface):
+        if interface:
+            self.interfaces.pop(interface.server)
+            if interface.server == self.default_server:
+                self.interface = None
+            interface.close()
 
-    def add_recent_server(self, i):
+    def add_recent_server(self, server):
         # list is ordered
-        s = i.server
-        if s in self.recent_servers:
-            self.recent_servers.remove(s)
-        self.recent_servers.insert(0,s)
+        if server in self.recent_servers:
+            self.recent_servers.remove(server)
+        self.recent_servers.insert(0, server)
         self.recent_servers = self.recent_servers[0:20]
         self.save_recent_servers()
 
@@ -393,70 +405,75 @@ class Network(util.DaemonThread):
         self.switch_lagging_interface(i.server)
         self.notify('updated')
 
-    def process_if_notification(self, i):
-        '''Handle interface addition and removal through notifications'''
-        if i.is_connected():
-            self.add_recent_server(i)
-            i.send_request({'method':'blockchain.headers.subscribe','params':[]})
-            if i.server == self.default_server:
-                self.switch_to_interface(i.server)
-        else:
-            self.interfaces.pop(i.server, None)
-            self.heights.pop(i.server, None)
-            if i == self.interface:
-                self.interface = None
-                self.addr_responses = {}
-                self.set_status('disconnected')
-            self.disconnected_servers.add(i.server)
-        # Our set of interfaces changed
-        self.notify('interfaces')
-
-    def process_response(self, i, response):
-        # the id comes from the daemon or the network proxy
-        _id = response.get('id')
-        if _id is not None:
-            if i != self.interface:
-                return
-            self.unanswered_requests.pop(_id)
-
-        method = response.get('method')
+    def process_response(self, interface, response):
+        error = response.get('error')
         result = response.get('result')
-        if method == 'blockchain.headers.subscribe':
-            self.on_header(i, response)
+        method = response.get('method')
+
+        # We handle some responses; return the rest to the client.
+        if method == 'server.version':
+            interface.server_version = result
+        elif method == 'blockchain.headers.subscribe':
+            if error is None:
+                self.on_header(interface, result)
         elif method == 'server.peers.subscribe':
-            self.irc_servers = parse_servers(result)
-            self.notify('servers')
+            if error is None:
+                self.irc_servers = parse_servers(result)
+                self.notify('servers')
         elif method == 'server.banner':
-            self.banner = result
-            self.notify('banner')
+            if error is None:
+                self.banner = result
+                self.notify('banner')
         elif method == 'blockchain.estimatefee':
-            from bitcoin import COIN
-            self.fee = int(result * COIN)
-            self.print_error("recommended fee", self.fee)
-            self.notify('fee')
-        elif method == 'blockchain.address.subscribe':
-            addr = response.get('params')[0]
-            self.addr_responses[addr] = result
-            self.response_queue.put(response)
+            if error is None:
+                self.fee = int(result * COIN)
+                self.print_error("recommended fee", self.fee)
+                self.notify('fee')
         elif method == 'blockchain.block.get_chunk':
-            self.on_get_chunk(i, response)
+            self.on_get_chunk(interface, response)
         elif method == 'blockchain.block.get_header':
-            self.on_get_header(i, response)
+            self.on_get_header(interface, response)
         else:
+            # Cache address subscription results
+            if method == 'blockchain.address.subscribe' and error is None:
+                addr = response['params'][0]
+                self.addr_responses[addr] = result
             self.response_queue.put(response)
 
-    def handle_requests(self):
-        '''Some requests require connectivity, others we handle locally in
-        process_request() and must do so in order to e.g. prevent the
-        daemon seeming unresponsive.
-        '''
-        unhandled = []
+    def process_responses(self, interface):
+        notifications, responses = interface.get_responses()
+
+        for request, response in responses:
+            # Client ID was given by the daemon or proxy
+            client_id = request.get('id')
+            if client_id is not None:
+                if interface != self.interface:
+                    continue
+                self.unanswered_requests.pop(client_id)
+            # Copy the request method and params to the response
+            response['method'] = request.get('method')
+            response['params'] = request.get('params')
+            response['id'] = client_id
+            self.process_response(interface, response)
+
+        for response in notifications:
+            if not response:  # Closed remotely
+                self.connection_down(interface.server)
+                break
+            # Rewrite response shape to match subscription request response
+            method = response.get('method')
+            if method == 'blockchain.headers.subscribe':
+                response['result'] = response['params'][0]
+                response['params'] = []
+            elif method == 'blockchain.address.subscribe':
+                params = response['params']
+                response['params'] = [params[0]]  # addr
+                response['result'] = params[1]
+            self.process_response(interface, response)
+
+    def handle_incoming_requests(self):
         while not self.requests_queue.empty():
-            request = self.requests_queue.get()
-            if not self.process_request(request):
-                unhandled.append(request)
-        for request in unhandled:
-            self.requests_queue.put(request)
+            self.process_request(self.requests_queue.get())
 
     def process_request(self, request):
         '''Returns true if the request was processed.'''
@@ -487,22 +504,62 @@ class Network(util.DaemonThread):
 
         # This request needs connectivity.  If we don't have an
         # interface, we cannot process it.
-        if not self.is_connected():
+        if not self.interface:
             return False
 
         self.unanswered_requests[_id] = request
-        self.interface.send_request(request)
+        self.interface.queue_request(request)
         return True
 
-    def check_interfaces(self):
+    def connection_down(self, server):
+        '''A connection to server either went down, or was never made.
+        We distinguish by whether it is in self.interfaces.'''
+        self.disconnected_servers.add(server)
+        if server == self.default_server:
+            self.set_status('disconnected')
+        if server in self.interfaces:
+            self.close_interface(self.interfaces[server])
+            self.heights.pop(server, None)
+            self.notify('interfaces')
+
+    def new_interface(self, server, socket):
+        self.add_recent_server(server)
+        self.interfaces[server] = interface = Interface(server, socket)
+        interface.queue_request({'method': 'blockchain.headers.subscribe',
+                                 'params': []})
+        if server == self.default_server:
+            self.switch_to_interface(server)
+        self.notify('interfaces')
+
+    def maintain_sockets(self):
+        '''Socket maintenance.'''
+        # Responses to connection attempts?
+        while not self.socket_queue.empty():
+            server, socket = self.socket_queue.get()
+            self.connecting.pop(server)
+            if socket:
+                self.new_interface(server, socket)
+            else:
+                self.connection_down(server)
+
+        # Send pings and shut down stale interfaces
+        for interface in self.interfaces.values():
+            if interface.has_timed_out():
+                self.connection_down(interface.server)
+            elif interface.ping_required():
+                version_req = {'method': 'server.version',
+                               'params': [ELECTRUM_VERSION, PROTOCOL_VERSION]}
+                interface.queue_request(version_req)
+
         now = time.time()
         # nodes
-        if len(self.interfaces) < self.num_server:
+        if len(self.interfaces) + len(self.connecting) < self.num_server:
             self.start_random_interface()
             if now - self.nodes_retry_time > NODES_RETRY_INTERVAL:
                 self.print_error('network: retrying connections')
                 self.disconnected_servers = set([])
                 self.nodes_retry_time = now
+
         # main interface
         if not self.is_connected():
             if self.auto_connect:
@@ -517,7 +574,8 @@ class Network(util.DaemonThread):
 
     def request_chunk(self, interface, data, idx):
         interface.print_error("requesting chunk %d" % idx)
-        interface.send_request({'method':'blockchain.block.get_chunk', 'params':[idx]})
+        interface.queue_request({'method':'blockchain.block.get_chunk',
+                                 'params':[idx]})
         data['chunk_idx'] = idx
         data['req_time'] = time.time()
 
@@ -537,7 +595,8 @@ class Network(util.DaemonThread):
 
     def request_header(self, interface, data, height):
         interface.print_error("requesting header %d" % height)
-        interface.send_request({'method':'blockchain.block.get_header', 'params':[height]})
+        interface.queue_request({'method':'blockchain.block.get_header',
+                                 'params':[height]})
         data['header_height'] = height
         data['req_time'] = time.time()
         if not 'chain' in data:
@@ -563,7 +622,9 @@ class Network(util.DaemonThread):
                     self.request_header(interface, data, next_height)
 
     def bc_request_headers(self, interface, data):
-        '''Send a request for the next header, or a chunk of them, if necessary'''
+        '''Send a request for the next header, or a chunk of them,
+        if necessary.
+        '''
         local_height, if_height = self.get_local_height(), data['if_height']
         if if_height <= local_height:
             return False
@@ -575,11 +636,12 @@ class Network(util.DaemonThread):
 
     def handle_bc_requests(self):
         '''Work through each interface that has notified us of a new header.
-        Send it requests if it is ahead of our blockchain object'''
+        Send it requests if it is ahead of our blockchain object.
+        '''
         while self.bc_requests:
             interface, data = self.bc_requests.popleft()
             # If the connection was lost move on
-            if not interface.is_connected():
+            if not interface in self.interfaces.values():
                 continue
 
             req_time = data.get('req_time')
@@ -590,36 +652,39 @@ class Network(util.DaemonThread):
                     continue
             elif time.time() - req_time > 10:
                 interface.print_error("blockchain request timed out")
-                interface.stop()
+                self.connection_down(interface.server)
                 continue
             # Put updated request state back at head of deque
             self.bc_requests.appendleft((interface, data))
             break
 
+    def wait_on_sockets(self):
+        # Python docs say Windows doesn't like empty selects.
+        # Sleep to prevent busy looping
+        if not self.interfaces:
+            time.sleep(0.1)
+            return
+        rin = [i for i in self.interfaces.values()]
+        win = [i for i in self.interfaces.values() if i.unsent_requests]
+        rout, wout, xout = select.select(rin, win, [], 0.1)
+        assert not xout
+        for interface in wout:
+            interface.send_requests()
+        for interface in rout:
+            self.process_responses(interface)
+
     def run(self):
         self.blockchain.init()
         while self.is_running():
-            self.check_interfaces()
-            self.handle_requests()
+            self.maintain_sockets()
+            self.wait_on_sockets()
+            self.handle_incoming_requests()
             self.handle_bc_requests()
-            try:
-                i, response = self.queue.get(timeout=0.1)
-            except Queue.Empty:
-                continue
-
-            # if response is None it is a notification about the interface
-            if response is None:
-                self.process_if_notification(i)
-            else:
-                self.process_response(i, response)
 
         self.stop_network()
         self.print_error("stopped")
 
-    def on_header(self, i, r):
-        header = r.get('result')
-        if not header:
-            return
+    def on_header(self, i, header):
         height = header.get('block_height')
         if not height:
             return