remove the hackish logic against replay attacks because it stopped to work with new android clients

see https://github.com/alexbers/mtprotoproxy/issues/183

Dockerfile

@@ -7,6 +7,8 @@ RUN apk add --no-cache python3 py3-cryptography ca-certificates libcap
 RUN chown -R tgproxy:tgproxy /home/tgproxy
 RUN setcap cap_net_bind_service=+ep /usr/bin/python3.7
 
+COPY mtprotoproxy.py config.py /home/tgproxy/
+
 USER tgproxy
 
 WORKDIR /home/tgproxy/

README.md

@@ -1,6 +1,6 @@
 # Async MTProto Proxy #
 
-Fast and simple to setup mtproto proxy written on Python.
+Fast and simple to setup MTProto proxy written in Python.
 
 ## Starting Up ##
     
@@ -20,10 +20,15 @@ To advertise a channel get a tag from **@MTProxybot** and put it to *config.py*.
 The proxy performance should be enough to comfortably serve about 4 000 simultaneous users on
 the VDS instance with 1 CPU core and 1024MB RAM.
 
+## More Instructions ##
+
+- [Running without Docker](https://github.com/alexbers/mtprotoproxy/wiki/Running-Without-Docker)
+- [Optimization and fine tuning](https://github.com/alexbers/mtprotoproxy/wiki/Optimization-and-Fine-Tuning)
+
 ## Advanced Usage ##
 
 The proxy can be launched:
 - with a custom config: `python3 mtprotoproxy.py [configfile]`
 - several times, clients will be automaticaly balanced between instances
 - with uvloop module to get an extra speed boost
-- with runtime statistics exported for [Prometheus](https://prometheus.io/): using [prometheus](https://github.com/alexbers/mtprotoproxy/tree/prometheus) branch
+- with runtime statistics exported to [Prometheus](https://prometheus.io/)

config.py

@@ -1,20 +1,25 @@
-PORT = 3256
+PORT = 443
 
 # name -> secret (32 hex chars)
 USERS = {
-    "tg":  "00000000000000000000000000000000",
-    "tg2": "0123456789abcdef0123456789abcdef"
+    "tg":  "00000000000000000000000000000001",
+    # "tg2": "0123456789abcdef0123456789abcdef",
 }
 
-# Makes the proxy harder to detect
-# Can be incompatible with very old clients
-SECURE_ONLY = True
+MODES = {
+    # Classic mode, easy to detect
+    "classic": False,
 
-# Makes the proxy even more hard to detect
-# Compatible only with the recent clients
-# TLS_ONLY = True
+    # Makes the proxy harder to detect
+    # Can be incompatible with very old clients
+    "secure": False,
 
-# The domain for TLS, bad clients are proxied there
+    # Makes the proxy even more hard to detect
+    # Can be incompatible with old clients
+    "tls": True
+}
+
+# The domain for TLS mode, bad clients are proxied there
 # Use random existing domain, proxy checks it on start
 # TLS_DOMAIN = "www.google.com"
 

mtprotoproxy.py

@@ -66,6 +66,8 @@ TLS_HANDSHAKE_LEN = 1 + 2 + 2 + 512
 PROTO_TAG_POS = 56
 DC_IDX_POS = 60
 
+MIN_CERT_LEN = 1024
+
 PROTO_TAG_ABRIDGED = b"\xef\xef\xef\xef"
 PROTO_TAG_INTERMEDIATE = b"\xee\xee\xee\xee"
 PROTO_TAG_SECURE = b"\xdd\xdd\xdd\xdd"
@@ -76,13 +78,20 @@ PADDING_FILLER = b"\x04\x00\x00\x00"
 MIN_MSG_LEN = 12
 MAX_MSG_LEN = 2 ** 24
 
+STAT_DURATION_BUCKETS = [0.1, 0.5, 1, 2, 5, 15, 60, 300, 600, 1800, 2**31 - 1]
 
 my_ip_info = {"ipv4": None, "ipv6": None}
 used_handshakes = collections.OrderedDict()
+client_ips = collections.OrderedDict()
+last_client_ips = {}
 disable_middle_proxy = False
 is_time_skewed = False
 fake_cert_len = random.randrange(1024, 4096)
 mask_host_cached_ip = None
+last_clients_with_time_skew = {}
+last_clients_with_same_handshake = collections.Counter()
+proxy_start_time = 0
+proxy_links = []
 
 config = {}
 
@@ -101,8 +110,12 @@ def init_config():
         conf_dict["PORT"] = int(sys.argv[1])
         secrets = sys.argv[2].split(",")
         conf_dict["USERS"] = {"user%d" % i: secrets[i].zfill(32) for i in range(len(secrets))}
+        conf_dict["MODES"] = {"classic": False, "secure": True, "tls": True}
         if len(sys.argv) > 3:
             conf_dict["AD_TAG"] = sys.argv[3]
+        if len(sys.argv) > 4:
+            conf_dict["TLS_DOMAIN"] = sys.argv[4]
+            conf_dict["MODES"] = {"classic": False, "secure": False, "tls": True}
 
     conf_dict = {k: v for k, v in conf_dict.items() if k.isupper()}
 
@@ -121,11 +134,43 @@ def init_config():
     # disables tg->client trafic reencryption, faster but less secure
     conf_dict.setdefault("FAST_MODE", True)
 
-    # doesn't allow to connect in not-secure mode
-    conf_dict.setdefault("SECURE_ONLY", False)
+    # enables some working modes
+    modes = conf_dict.get("MODES", {})
 
-    # allows to connect in tls mode only
-    conf_dict.setdefault("TLS_ONLY", False)
+    if "MODES" not in conf_dict:
+        modes.setdefault("classic", True)
+        modes.setdefault("secure", True)
+        modes.setdefault("tls", True)
+    else:
+        modes.setdefault("classic", False)
+        modes.setdefault("secure", False)
+        modes.setdefault("tls", False)
+
+    legacy_warning = False
+    if "SECURE_ONLY" in conf_dict:
+        legacy_warning = True
+        modes["classic"] = not bool(conf_dict["SECURE_ONLY"])
+
+    if "TLS_ONLY" in conf_dict:
+        legacy_warning = True
+        if conf_dict["TLS_ONLY"]:
+            modes["classic"] = False
+            modes["secure"] = False
+
+    if not modes["classic"] and not modes["secure"] and not modes["tls"]:
+        print_err("No known modes enabled, enabling tls-only mode")
+        modes["tls"] = True
+
+    if legacy_warning:
+        print_err("Legacy options SECURE_ONLY or TLS_ONLY detected")
+        print_err("Please use MODES in your config instead:")
+        print_err("MODES = {")
+        print_err('    "classic": %s,' % modes["classic"])
+        print_err('    "secure": %s,' % modes["secure"])
+        print_err('    "tls": %s' % modes["tls"])
+        print_err("}")
+
+    conf_dict["MODES"] = modes
 
     # accept incoming connections only with proxy protocol v1/v2, useful for nginx and haproxy
     conf_dict.setdefault("PROXY_PROTOCOL", False)
@@ -142,6 +187,16 @@ def init_config():
     # the next host's port to forward bad clients
     conf_dict.setdefault("MASK_PORT", 443)
 
+    # use upstream SOCKS5 proxy
+    conf_dict.setdefault("SOCKS5_HOST", None)
+    conf_dict.setdefault("SOCKS5_PORT", None)
+    conf_dict.setdefault("SOCKS5_USER", None)
+    conf_dict.setdefault("SOCKS5_PASS", None)
+
+    if conf_dict["SOCKS5_HOST"] and conf_dict["SOCKS5_PORT"]:
+        # Disable the middle proxy if using socks, they are not compatible
+        conf_dict["USE_MIDDLE_PROXY"] = False
+
     # user tcp connection limits, the mapping from name to the integer limit
     # one client can create many tcp connections, up to 8
     conf_dict.setdefault("USER_MAX_TCP_CONNS", {})
@@ -156,10 +211,10 @@ def init_config():
     conf_dict.setdefault("USER_DATA_QUOTA", {})
 
     # length of used handshake randoms for active fingerprinting protection, zero to disable
-    conf_dict.setdefault("REPLAY_CHECK_LEN", 32768)
+    conf_dict.setdefault("REPLAY_CHECK_LEN", 65536)
 
-    # block bad first packets to even more protect against replay-based fingerprinting
-    conf_dict.setdefault("BLOCK_IF_FIRST_PKT_BAD", True)
+    # length of last client ip addresses for logging
+    conf_dict.setdefault("CLIENT_IPS_LEN", 131072)
 
     # delay in seconds between stats printing
     conf_dict.setdefault("STATS_PRINT_PERIOD", 600)
@@ -201,10 +256,43 @@ def init_config():
     # listen unix socket
     conf_dict.setdefault("LISTEN_UNIX_SOCK", "")
 
+    # prometheus exporter listen port, use some random port here
+    conf_dict.setdefault("METRICS_PORT", None)
+
+    # prometheus listen addr ipv4
+    conf_dict.setdefault("METRICS_LISTEN_ADDR_IPV4", "0.0.0.0")
+
+    # prometheus listen addr ipv6
+    conf_dict.setdefault("METRICS_LISTEN_ADDR_IPV6", None)
+
+    # prometheus scrapers whitelist
+    conf_dict.setdefault("METRICS_WHITELIST", ["127.0.0.1", "::1"])
+
+    # export proxy link to prometheus
+    conf_dict.setdefault("METRICS_EXPORT_LINKS", False)
+
+    # default prefix for metrics
+    conf_dict.setdefault("METRICS_PREFIX", "mtprotoproxy_")
+
     # allow access to config by attributes
     config = type("config", (dict,), conf_dict)(conf_dict)
 
 
+def apply_upstream_proxy_settings():
+    # apply socks settings in place
+    if config.SOCKS5_HOST and config.SOCKS5_PORT:
+        import socks
+        print_err("Socket-proxy mode activated, it is incompatible with advertising and uvloop")
+        socks.set_default_proxy(socks.PROXY_TYPE_SOCKS5, config.SOCKS5_HOST, config.SOCKS5_PORT,
+                                username=config.SOCKS5_USER, password=config.SOCKS5_PASS)
+        if not hasattr(socket, "origsocket"):
+            socket.origsocket = socket.socket
+            socket.socket = socks.socksocket
+    elif hasattr(socket, "origsocket"):
+        socket.socket = socket.origsocket
+        del socket.origsocket
+
+
 def try_use_cryptography_module():
     from cryptography.hazmat.primitives.ciphers import Cipher, algorithms, modes
     from cryptography.hazmat.backends import default_backend
@@ -294,24 +382,45 @@ def print_err(*params):
 
 def init_stats():
     global stats
-    stats = {user: collections.Counter() for user in config.USERS}
+    global user_stats
+
+    stats = collections.Counter()
+    user_stats = {user: collections.Counter() for user in config.USERS}
 
 
-def update_stats(user, connects=0, curr_connects=0, octets=0, msgs=0):
+def init_proxy_start_time():
+    global proxy_start_time
+    proxy_start_time = time.time()
+
+
+def update_stats(**kw_stats):
+    global stats
+    stats.update(**kw_stats)
+
+
+def update_user_stats(user, **kw_stats):
+    global user_stats
+
+    if user not in user_stats:
+        user_stats[user] = collections.Counter()
+    user_stats[user].update(**kw_stats)
+
+
+def update_durations(duration):
     global stats
 
-    if user not in stats:
-        stats[user] = collections.Counter()
+    for bucket in STAT_DURATION_BUCKETS:
+        if duration <= bucket:
+            break
 
-    stats[user].update(connects=connects, curr_connects=curr_connects,
-                       octets=octets, msgs=msgs)
+    update_stats(**{"connects_with_duration_le_%s" % str(bucket): 1})
 
 
 def get_curr_connects_count():
-    global stats
+    global user_stats
 
     all_connects = 0
-    for user, stat in stats.items():
+    for user, stat in user_stats.items():
         all_connects += stat["curr_connects"]
     return all_connects
 
@@ -360,6 +469,60 @@ class MyRandom(random.Random):
 myrandom = MyRandom()
 
 
+class TgConnectionPool:
+    MAX_CONNS_IN_POOL = 64
+
+    def __init__(self):
+        self.pools = {}
+
+    async def open_tg_connection(self, host, port, init_func=None):
+        task = asyncio.open_connection(host, port, limit=get_to_clt_bufsize())
+        reader_tgt, writer_tgt = await asyncio.wait_for(task, timeout=config.TG_CONNECT_TIMEOUT)
+
+        set_keepalive(writer_tgt.get_extra_info("socket"))
+        set_bufsizes(writer_tgt.get_extra_info("socket"), get_to_clt_bufsize(), get_to_tg_bufsize())
+
+        if init_func:
+            return await asyncio.wait_for(init_func(host, port, reader_tgt, writer_tgt),
+                                          timeout=config.TG_CONNECT_TIMEOUT)
+        return reader_tgt, writer_tgt
+
+    def register_host_port(self, host, port, init_func):
+        if (host, port, init_func) not in self.pools:
+            self.pools[(host, port, init_func)] = []
+
+        while len(self.pools[(host, port, init_func)]) < TgConnectionPool.MAX_CONNS_IN_POOL:
+            connect_task = asyncio.ensure_future(self.open_tg_connection(host, port, init_func))
+            self.pools[(host, port, init_func)].append(connect_task)
+
+    async def get_connection(self, host, port, init_func=None):
+        self.register_host_port(host, port, init_func)
+
+        ret = None
+        for task in self.pools[(host, port, init_func)][::]:
+            if task.done():
+                if task.exception():
+                    self.pools[(host, port, init_func)].remove(task)
+                    continue
+
+                reader, writer, *other = task.result()
+                if writer.transport.is_closing():
+                    self.pools[(host, port, init_func)].remove(task)
+                    continue
+
+                if not ret:
+                    self.pools[(host, port, init_func)].remove(task)
+                    ret = (reader, writer, *other)
+
+        self.register_host_port(host, port, init_func)
+        if ret:
+            return ret
+        return await self.open_tg_connection(host, port, init_func)
+
+
+tg_connection_pool = TgConnectionPool()
+
+
 class LayeredStreamReaderBase:
     __slots__ = ("upstream", )
 
@@ -825,6 +988,8 @@ async def handle_bad_client(reader_clt, writer_clt, handshake):
 
     global mask_host_cached_ip
 
+    update_stats(connects_bad=1)
+
     if writer_clt.transport.is_closing():
         return
 
@@ -899,6 +1064,10 @@ async def handle_bad_client(reader_clt, writer_clt, handshake):
 
 async def handle_fake_tls_handshake(handshake, reader, writer, peer):
     global used_handshakes
+    global client_ips
+    global last_client_ips
+    global last_clients_with_time_skew
+    global last_clients_with_same_handshake
     global fake_cert_len
 
     TIME_SKEW_MIN = -20 * 60
@@ -910,6 +1079,7 @@ async def handle_fake_tls_handshake(handshake, reader, writer, peer):
     TLS_APP_HTTP2_HDR = b"\x17" + TLS_VERS
 
     DIGEST_LEN = 32
+    DIGEST_HALFLEN = 16
     DIGEST_POS = 11
 
     SESSION_ID_LEN_POS = DIGEST_POS + DIGEST_LEN
@@ -920,8 +1090,8 @@ async def handle_fake_tls_handshake(handshake, reader, writer, peer):
 
     digest = handshake[DIGEST_POS: DIGEST_POS + DIGEST_LEN]
 
-    if digest in used_handshakes:
-        print_err("Active TLS fingerprinting detected from %s, handling it" % peer[0])
+    if digest[:DIGEST_HALFLEN] in used_handshakes:
+        last_clients_with_same_handshake[peer[0]] += 1
         return False
 
     sess_id_len = handshake[SESSION_ID_LEN_POS]
@@ -944,8 +1114,7 @@ async def handle_fake_tls_handshake(handshake, reader, writer, peer):
         # some clients fail to read unix time and send the time since boot instead
         client_time_is_small = timestamp < 60*60*24*1000
         if not client_time_is_ok and not is_time_skewed and not client_time_is_small:
-            print_err("Client with time skew detected from %s, can be a replay-attack" % peer[0])
-            print_err("The clocks were %d minutes behind" % ((time.time() - timestamp) // 60))
+            last_clients_with_time_skew[peer[0]] = (time.time() - timestamp) // 60
             continue
 
         http_data = myrandom.getrandbytes(fake_cert_len)
@@ -967,7 +1136,14 @@ async def handle_fake_tls_handshake(handshake, reader, writer, peer):
         if config.REPLAY_CHECK_LEN > 0:
             while len(used_handshakes) >= config.REPLAY_CHECK_LEN:
                 used_handshakes.popitem(last=False)
-            used_handshakes[digest] = True
+            used_handshakes[digest[:DIGEST_HALFLEN]] = True
+
+        if config.CLIENT_IPS_LEN > 0:
+            while len(client_ips) >= config.CLIENT_IPS_LEN:
+                client_ips.popitem(last=False)
+            if peer[0] not in client_ips:
+                client_ips[peer[0]] = True
+                last_client_ips[peer[0]] = True
 
         reader = FakeTLSStreamReader(reader)
         writer = FakeTLSStreamWriter(writer)
@@ -997,7 +1173,7 @@ async def handle_proxy_protocol(reader, peer=None):
         if proxy_fam in (PROXY_TCP4, PROXY_TCP6):
             if len(proxy_addr) == 4:
                 src_addr = proxy_addr[0].decode('ascii')
-                src_port = proxy_addr[2].decode('ascii')
+                src_port = int(proxy_addr[2].decode('ascii'))
                 return (src_addr, src_port)
         elif proxy_fam == PROXY_UNKNOWN:
             return peer
@@ -1033,6 +1209,9 @@ async def handle_proxy_protocol(reader, peer=None):
 
 async def handle_handshake(reader, writer):
     global used_handshakes
+    global client_ips
+    global last_client_ips
+    global last_clients_with_same_handshake
 
     TLS_START_BYTES = b"\x16\x03\x01\x02\x00\x01\x00\x01\xfc\x03\x03"
 
@@ -1067,7 +1246,7 @@ async def handle_handshake(reader, writer):
         reader, writer = tls_handshake_result
         handshake = await reader.readexactly(HANDSHAKE_LEN)
     else:
-        if config.TLS_ONLY:
+        if not config.MODES["classic"] and not config.MODES["secure"]:
             await handle_bad_client(reader, writer, handshake)
             return False
         handshake += await reader.readexactly(HANDSHAKE_LEN - len(handshake))
@@ -1078,7 +1257,7 @@ async def handle_handshake(reader, writer):
     enc_prekey, enc_iv = enc_prekey_and_iv[:PREKEY_LEN], enc_prekey_and_iv[PREKEY_LEN:]
 
     if dec_prekey_and_iv in used_handshakes:
-        print_err("Active fingerprinting detected from %s, handling it" % peer[0])
+        last_clients_with_same_handshake[peer[0]] += 1
         await handle_bad_client(reader, writer, handshake)
         return False
 
@@ -1097,8 +1276,14 @@ async def handle_handshake(reader, writer):
         if proto_tag not in (PROTO_TAG_ABRIDGED, PROTO_TAG_INTERMEDIATE, PROTO_TAG_SECURE):
             continue
 
-        if config.SECURE_ONLY and proto_tag != PROTO_TAG_SECURE:
-            continue
+        if proto_tag == PROTO_TAG_SECURE:
+            if is_tls_handshake and not config.MODES["tls"]:
+                continue
+            if not is_tls_handshake and not config.MODES["secure"]:
+                continue
+        else:
+            if not config.MODES["classic"]:
+                continue
 
         dc_idx = int.from_bytes(decrypted[DC_IDX_POS:DC_IDX_POS+2], "little", signed=True)
 
@@ -1107,6 +1292,13 @@ async def handle_handshake(reader, writer):
                 used_handshakes.popitem(last=False)
             used_handshakes[dec_prekey_and_iv] = True
 
+        if config.CLIENT_IPS_LEN > 0:
+            while len(client_ips) >= config.CLIENT_IPS_LEN:
+                client_ips.popitem(last=False)
+            if peer[0] not in client_ips:
+                client_ips[peer[0]] = True
+                last_client_ips[peer[0]] = True
+
         reader = CryptoWrappedStreamReader(reader, decryptor)
         writer = CryptoWrappedStreamWriter(writer, encryptor)
         return reader, writer, proto_tag, user, dc_idx, enc_key + enc_iv, peer
@@ -1115,21 +1307,6 @@ async def handle_handshake(reader, writer):
     return False
 
 
-async def open_connection_tryer(addr, port, limit, timeout, max_attempts=3):
-    for attempt in range(max_attempts-1):
-        try:
-            task = asyncio.open_connection(addr, port, limit=limit)
-            reader_tgt, writer_tgt = await asyncio.wait_for(task, timeout=timeout)
-            return reader_tgt, writer_tgt
-        except (OSError, asyncio.TimeoutError):
-            continue
-
-    # the last attempt
-    task = asyncio.open_connection(addr, port, limit=limit)
-    reader_tgt, writer_tgt = await asyncio.wait_for(task, timeout=timeout)
-    return reader_tgt, writer_tgt
-
-
 async def do_direct_handshake(proto_tag, dc_idx, dec_key_and_iv=None):
     RESERVED_NONCE_FIRST_CHARS = [b"\xef"]
     RESERVED_NONCE_BEGININGS = [b"\x48\x45\x41\x44", b"\x50\x4F\x53\x54",
@@ -1138,6 +1315,7 @@ async def do_direct_handshake(proto_tag, dc_idx, dec_key_and_iv=None):
     RESERVED_NONCE_CONTINUES = [b"\x00\x00\x00\x00"]
 
     global my_ip_info
+    global tg_connection_pool
 
     dc_idx = abs(dc_idx) - 1
 
@@ -1151,18 +1329,17 @@ async def do_direct_handshake(proto_tag, dc_idx, dec_key_and_iv=None):
         dc = TG_DATACENTERS_V4[dc_idx]
 
     try:
-        reader_tgt, writer_tgt = await open_connection_tryer(
-            dc, TG_DATACENTER_PORT, limit=get_to_clt_bufsize(), timeout=config.TG_CONNECT_TIMEOUT)
+        reader_tgt, writer_tgt = await tg_connection_pool.get_connection(dc, TG_DATACENTER_PORT)
     except ConnectionRefusedError as E:
         print_err("Got connection refused while trying to connect to", dc, TG_DATACENTER_PORT)
         return False
+    except ConnectionAbortedError as E:
+        print_err("The Telegram server connection is bad: %d (%s %s) %s" % (dc_idx, addr, port, E))
+        return False
     except (OSError, asyncio.TimeoutError) as E:
         print_err("Unable to connect to", dc, TG_DATACENTER_PORT)
         return False
 
-    set_keepalive(writer_tgt.get_extra_info("socket"))
-    set_bufsizes(writer_tgt.get_extra_info("socket"), get_to_clt_bufsize(), get_to_tg_bufsize())
-
     while True:
         rnd = bytearray(myrandom.getrandbytes(HANDSHAKE_LEN))
         if rnd[:1] in RESERVED_NONCE_FIRST_CHARS:
@@ -1225,49 +1402,21 @@ def get_middleproxy_aes_key_and_iv(nonce_srv, nonce_clt, clt_ts, srv_ip, clt_por
     return key, iv
 
 
-async def do_middleproxy_handshake(proto_tag, dc_idx, cl_ip, cl_port):
+async def middleproxy_handshake(host, port, reader_tgt, writer_tgt):
+    """ The most logic of middleproxy handshake, launched in pool """
     START_SEQ_NO = -2
     NONCE_LEN = 16
 
-    RPC_NONCE = b"\xaa\x87\xcb\x7a"
     RPC_HANDSHAKE = b"\xf5\xee\x82\x76"
+    RPC_NONCE = b"\xaa\x87\xcb\x7a"
+    # pass as consts to simplify code
+    RPC_FLAGS = b"\x00\x00\x00\x00"
     CRYPTO_AES = b"\x01\x00\x00\x00"
 
     RPC_NONCE_ANS_LEN = 32
     RPC_HANDSHAKE_ANS_LEN = 32
 
-    # pass as consts to simplify code
-    RPC_FLAGS = b"\x00\x00\x00\x00"
-
-    global my_ip_info
-
-    use_ipv6_tg = (my_ip_info["ipv6"] and (config.PREFER_IPV6 or not my_ip_info["ipv4"]))
-    use_ipv6_clt = (":" in cl_ip)
-
-    if use_ipv6_tg:
-        if dc_idx not in TG_MIDDLE_PROXIES_V6:
-            return False
-        addr, port = myrandom.choice(TG_MIDDLE_PROXIES_V6[dc_idx])
-    else:
-        if dc_idx not in TG_MIDDLE_PROXIES_V4:
-            return False
-        addr, port = myrandom.choice(TG_MIDDLE_PROXIES_V4[dc_idx])
-
-    try:
-        reader_tgt, writer_tgt = await open_connection_tryer(addr, port, limit=get_to_clt_bufsize(),
-                                                             timeout=config.TG_CONNECT_TIMEOUT)
-    except ConnectionRefusedError as E:
-        print_err("The Telegram server %d (%s %s) is refusing connections" % (dc_idx, addr, port))
-        return False
-    except (OSError, asyncio.TimeoutError) as E:
-        print_err("Unable to connect to the Telegram server %d (%s %s)" % (dc_idx, addr, port))
-        return False
-
-    set_keepalive(writer_tgt.get_extra_info("socket"))
-    set_bufsizes(writer_tgt.get_extra_info("socket"), get_to_clt_bufsize(), get_to_tg_bufsize())
-
     writer_tgt = MTProtoFrameStreamWriter(writer_tgt, START_SEQ_NO)
-
     key_selector = PROXY_SECRET[:4]
     crypto_ts = int.to_bytes(int(time.time()) % (256**4), 4, "little")
 
@@ -1278,24 +1427,25 @@ async def do_middleproxy_handshake(proto_tag, dc_idx, cl_ip, cl_port):
     writer_tgt.write(msg)
     await writer_tgt.drain()
 
-    old_reader = reader_tgt
     reader_tgt = MTProtoFrameStreamReader(reader_tgt, START_SEQ_NO)
     ans = await reader_tgt.read(get_to_clt_bufsize())
 
     if len(ans) != RPC_NONCE_ANS_LEN:
-        return False
+        raise ConnectionAbortedError("bad rpc answer length")
 
     rpc_type, rpc_key_selector, rpc_schema, rpc_crypto_ts, rpc_nonce = (
         ans[:4], ans[4:8], ans[8:12], ans[12:16], ans[16:32]
     )
 
     if rpc_type != RPC_NONCE or rpc_key_selector != key_selector or rpc_schema != CRYPTO_AES:
-        return False
+        raise ConnectionAbortedError("bad rpc answer")
 
     # get keys
     tg_ip, tg_port = writer_tgt.upstream.get_extra_info('peername')[:2]
     my_ip, my_port = writer_tgt.upstream.get_extra_info('sockname')[:2]
 
+    use_ipv6_tg = (":" in tg_ip)
+
     if not use_ipv6_tg:
         if my_ip_info["ipv4"]:
             # prefer global ip settings to work behind NAT
@@ -1346,11 +1496,42 @@ async def do_middleproxy_handshake(proto_tag, dc_idx, cl_ip, cl_port):
 
     handshake_ans = await reader_tgt.read(1)
     if len(handshake_ans) != RPC_HANDSHAKE_ANS_LEN:
-        return False
+        raise ConnectionAbortedError("bad rpc handshake answer length")
 
     handshake_type, handshake_flags, handshake_sender_pid, handshake_peer_pid = (
         handshake_ans[:4], handshake_ans[4:8], handshake_ans[8:20], handshake_ans[20:32])
     if handshake_type != RPC_HANDSHAKE or handshake_peer_pid != SENDER_PID:
+        raise ConnectionAbortedError("bad rpc handshake answer")
+
+    return reader_tgt, writer_tgt, my_ip, my_port
+
+
+async def do_middleproxy_handshake(proto_tag, dc_idx, cl_ip, cl_port):
+    global my_ip_info
+    global tg_connection_pool
+
+    use_ipv6_tg = (my_ip_info["ipv6"] and (config.PREFER_IPV6 or not my_ip_info["ipv4"]))
+
+    if use_ipv6_tg:
+        if dc_idx not in TG_MIDDLE_PROXIES_V6:
+            return False
+        addr, port = myrandom.choice(TG_MIDDLE_PROXIES_V6[dc_idx])
+    else:
+        if dc_idx not in TG_MIDDLE_PROXIES_V4:
+            return False
+        addr, port = myrandom.choice(TG_MIDDLE_PROXIES_V4[dc_idx])
+
+    try:
+        ret = await tg_connection_pool.get_connection(addr, port, middleproxy_handshake)
+        reader_tgt, writer_tgt, my_ip, my_port = ret
+    except ConnectionRefusedError as E:
+        print_err("The Telegram server %d (%s %s) is refusing connections" % (dc_idx, addr, port))
+        return False
+    except ConnectionAbortedError as E:
+        print_err("The Telegram server connection is bad: %d (%s %s) %s" % (dc_idx, addr, port, E))
+        return False
+    except (OSError, asyncio.TimeoutError) as E:
+        print_err("Unable to connect to the Telegram server %d (%s %s)" % (dc_idx, addr, port))
         return False
 
     writer_tgt = ProxyReqStreamWriter(writer_tgt, cl_ip, cl_port, my_ip, my_port, proto_tag)
@@ -1364,10 +1545,13 @@ async def handle_client(reader_clt, writer_clt):
     set_ack_timeout(writer_clt.get_extra_info("socket"), config.CLIENT_ACK_TIMEOUT)
     set_bufsizes(writer_clt.get_extra_info("socket"), get_to_tg_bufsize(), get_to_clt_bufsize())
 
+    update_stats(connects_all=1)
+
     try:
         clt_data = await asyncio.wait_for(handle_handshake(reader_clt, writer_clt),
                                           timeout=config.CLIENT_HANDSHAKE_TIMEOUT)
     except asyncio.TimeoutError:
+        update_stats(handshake_timeouts=1)
         return
 
     if not clt_data:
@@ -1376,7 +1560,7 @@ async def handle_client(reader_clt, writer_clt):
     reader_clt, writer_clt, proto_tag, user, dc_idx, enc_key_and_iv, peer = clt_data
     cl_ip, cl_port = peer
 
-    update_stats(user, connects=1)
+    update_user_stats(user, connects=1)
 
     connect_directly = (not config.USE_MIDDLE_PROXY or disable_middle_proxy)
 
@@ -1418,8 +1602,7 @@ async def handle_client(reader_clt, writer_clt):
         else:
             return
 
-    async def connect_reader_to_writer(rd, wr, user, rd_buf_size, block_if_first_pkt_bad=False):
-        is_first_pkt = True
+    async def connect_reader_to_writer(rd, wr, user, rd_buf_size):
         try:
             while True:
                 data = await rd.read(rd_buf_size)
@@ -1428,41 +1611,28 @@ async def handle_client(reader_clt, writer_clt):
                 else:
                     extra = {}
 
-                # protection against replay-based fingerprinting
-                if is_first_pkt:
-                    is_first_pkt = False
-
-                    ERR_PKT_DATA = b'l\xfe\xff\xff'
-                    if block_if_first_pkt_bad and data == ERR_PKT_DATA:
-                        print_err("Active fingerprinting detected from %s, dropping it" % cl_ip)
-
-                        wr.write_eof()
-                        await wr.drain()
-                        return
-
                 if not data:
                     wr.write_eof()
                     await wr.drain()
                     return
                 else:
-                    update_stats(user, octets=len(data), msgs=1)
+                    update_user_stats(user, octets=len(data), msgs=1)
                     wr.write(data, extra)
                     await wr.drain()
-        except (OSError, asyncio.streams.IncompleteReadError) as e:
+        except (OSError, asyncio.IncompleteReadError) as e:
             # print_err(e)
             pass
 
-    tg_to_clt = connect_reader_to_writer(reader_tg, writer_clt, user, get_to_clt_bufsize(),
-                                         block_if_first_pkt_bad=config.BLOCK_IF_FIRST_PKT_BAD)
+    tg_to_clt = connect_reader_to_writer(reader_tg, writer_clt, user, get_to_clt_bufsize())
     clt_to_tg = connect_reader_to_writer(reader_clt, writer_tg, user, get_to_tg_bufsize())
     task_tg_to_clt = asyncio.ensure_future(tg_to_clt)
     task_clt_to_tg = asyncio.ensure_future(clt_to_tg)
 
-    update_stats(user, curr_connects=1)
+    update_user_stats(user, curr_connects=1)
 
     tcp_limit_hit = (
         user in config.USER_MAX_TCP_CONNS and
-        stats[user]["curr_connects"] > config.USER_MAX_TCP_CONNS[user]
+        user_stats[user]["curr_connects"] > config.USER_MAX_TCP_CONNS[user]
     )
 
     user_expired = (
@@ -1472,13 +1642,15 @@ async def handle_client(reader_clt, writer_clt):
 
     user_data_quota_hit = (
         user in config.USER_DATA_QUOTA and
-        stats[user]["octets"] > config.USER_DATA_QUOTA[user]
+        user_stats[user]["octets"] > config.USER_DATA_QUOTA[user]
     )
 
     if (not tcp_limit_hit) and (not user_expired) and (not user_data_quota_hit):
+        start = time.time()
         await asyncio.wait([task_tg_to_clt, task_clt_to_tg], return_when=asyncio.FIRST_COMPLETED)
+        update_durations(time.time() - start)
 
-    update_stats(user, curr_connects=-1)
+    update_user_stats(user, curr_connects=-1)
 
     task_tg_to_clt.cancel()
     task_clt_to_tg.cancel()
@@ -1489,7 +1661,9 @@ async def handle_client(reader_clt, writer_clt):
 async def handle_client_wrapper(reader, writer):
     try:
         await handle_client(reader, writer)
-    except (asyncio.IncompleteReadError, ConnectionResetError, TimeoutError):
+    except (asyncio.IncompleteReadError, asyncio.CancelledError):
+        pass
+    except (ConnectionResetError, TimeoutError):
         pass
     except Exception:
         traceback.print_exc()
@@ -1497,18 +1671,139 @@ async def handle_client_wrapper(reader, writer):
         writer.transport.abort()
 
 
-async def stats_printer():
+def make_metrics_pkt(metrics):
+    pkt_body_list = []
+    used_names = set()
+
+    for name, m_type, desc, val in metrics:
+        name = config.METRICS_PREFIX + name
+        if name not in used_names:
+            pkt_body_list.append("# HELP %s %s" % (name, desc))
+            pkt_body_list.append("# TYPE %s %s" % (name, m_type))
+            used_names.add(name)
+
+        if isinstance(val, dict):
+            tags = []
+            for tag, tag_val in val.items():
+                if tag == "val":
+                    continue
+                tag_val = tag_val.replace('"', r'\"')
+                tags.append('%s="%s"' % (tag, tag_val))
+            pkt_body_list.append("%s{%s} %s" % (name, ",".join(tags), val["val"]))
+        else:
+            pkt_body_list.append("%s %s" % (name, val))
+    pkt_body = "\n".join(pkt_body_list) + "\n"
+
+    pkt_header_list = []
+    pkt_header_list.append("HTTP/1.1 200 OK")
+    pkt_header_list.append("Content-Length: %d" % len(pkt_body))
+    pkt_header_list.append("Content-Type: text/plain; version=0.0.4; charset=utf-8")
+    pkt_header_list.append("Date: %s" % time.strftime("%a, %d %b %Y %H:%M:%S GMT", time.gmtime()))
+
+    pkt_header = "\r\n".join(pkt_header_list)
+
+    pkt = pkt_header + "\r\n\r\n" + pkt_body
+    return pkt
+
+
+async def handle_metrics(reader, writer):
     global stats
+    global user_stats
+    global my_ip_info
+    global proxy_start_time
+    global proxy_links
+    global last_clients_with_time_skew
+    global last_clients_with_same_handshake
+
+    client_ip = writer.get_extra_info("peername")[0]
+    if client_ip not in config.METRICS_WHITELIST:
+        writer.close()
+        return
+
+    try:
+        metrics = []
+        metrics.append(["uptime", "counter", "proxy uptime", time.time() - proxy_start_time])
+        metrics.append(["connects_bad", "counter", "connects with bad secret",
+                       stats["connects_bad"]])
+        metrics.append(["connects_all", "counter", "incoming connects", stats["connects_all"]])
+        metrics.append(["handshake_timeouts", "counter", "number of timed out handshakes",
+                       stats["handshake_timeouts"]])
+
+        if config.METRICS_EXPORT_LINKS:
+            for link in proxy_links:
+                link_as_metric = link.copy()
+                link_as_metric["val"] = 1
+                metrics.append(["proxy_link_info", "counter",
+                                "the proxy link info", link_as_metric])
+
+        bucket_start = 0
+        for bucket in STAT_DURATION_BUCKETS:
+            bucket_end = bucket if bucket != STAT_DURATION_BUCKETS[-1] else "+Inf"
+            metric = {
+                "bucket": "%s-%s" % (bucket_start, bucket_end),
+                "val": stats["connects_with_duration_le_%s" % str(bucket)]
+            }
+            metrics.append(["connects_by_duration", "counter", "connects by duration", metric])
+            bucket_start = bucket_end
+
+        user_metrics_desc = [
+            ["user_connects", "counter", "user connects", "connects"],
+            ["user_connects_curr", "gauge", "current user connects", "curr_connects"],
+            ["user_octets", "counter", "octets proxied for user", "octets"],
+            ["user_msgs", "counter", "msgs proxied for user", "msgs"],
+        ]
+
+        for m_name, m_type, m_desc, stat_key in user_metrics_desc:
+            for user, stat in user_stats.items():
+                metric = {"user": user, "val": stat[stat_key]}
+                metrics.append([m_name, m_type, m_desc, metric])
+
+        pkt = make_metrics_pkt(metrics)
+        writer.write(pkt.encode())
+        await writer.drain()
+
+    except Exception:
+        traceback.print_exc()
+    finally:
+        writer.close()
+
+
+async def stats_printer():
+    global user_stats
+    global last_client_ips
+    global last_clients_with_time_skew
+    global last_clients_with_same_handshake
+
     while True:
         await asyncio.sleep(config.STATS_PRINT_PERIOD)
 
         print("Stats for", time.strftime("%d.%m.%Y %H:%M:%S"))
-        for user, stat in stats.items():
+        for user, stat in user_stats.items():
             print("%s: %d connects (%d current), %.2f MB, %d msgs" % (
                 user, stat["connects"], stat["curr_connects"],
                 stat["octets"] / 1000000, stat["msgs"]))
         print(flush=True)
 
+        if last_client_ips:
+            print("New IPs:")
+            for ip in last_client_ips:
+                print(ip)
+            print(flush=True)
+            last_client_ips.clear()
+
+        if last_clients_with_time_skew:
+            print("Clients with time skew (possible replay-attackers):")
+            for ip, skew_minutes in last_clients_with_time_skew.items():
+                print("%s, clocks were %d minutes behind" % (ip, skew_minutes))
+            print(flush=True)
+            last_clients_with_time_skew.clear()
+        if last_clients_with_same_handshake:
+            print("Clients with duplicate handshake (likely replay-attackers):")
+            for ip, times in last_clients_with_same_handshake.items():
+                print("%s, %d times" % (ip, times))
+            print(flush=True)
+            last_clients_with_same_handshake.clear()
+
 
 async def make_https_req(url, host="core.telegram.org"):
     """ Make request, return resp body and headers. """
@@ -1599,8 +1894,14 @@ async def get_mask_host_cert_len():
             task = get_encrypted_cert(config.MASK_HOST, config.MASK_PORT, config.TLS_DOMAIN)
             cert = await asyncio.wait_for(task, timeout=GET_CERT_TIMEOUT)
             if cert:
-                if len(cert) != fake_cert_len:
+                if len(cert) < MIN_CERT_LEN:
+                    msg = ("The MASK_HOST %s returned several TLS records, this is not supported" %
+                           config.MASK_HOST)
+                    print_err(msg)
+                elif len(cert) != fake_cert_len:
                     fake_cert_len = len(cert)
+                    print_err("Got cert from the MASK_HOST %s, its length is %d" %
+                              (config.MASK_HOST, fake_cert_len))
             else:
                 print_err("The MASK_HOST %s is not TLS 1.3 host, this is not recommended" %
                           config.MASK_HOST)
@@ -1753,12 +2054,13 @@ def init_ip_info():
 
 def print_tg_info():
     global my_ip_info
+    global proxy_links
 
     print_default_warning = False
 
     if config.PORT == 3256:
         print("The default port 3256 is used, this is not recommended", flush=True)
-        if config.TLS_ONLY:
+        if not config.MODES["classic"] and not config.MODES["secure"]:
             print("Since you have TLS only mode enabled the best port is 443", flush=True)
         print_default_warning = True
 
@@ -1766,27 +2068,37 @@ def print_tg_info():
     if not ip_addrs:
         ip_addrs = ["YOUR_IP"]
 
+    proxy_links = []
+
     for user, secret in sorted(config.USERS.items(), key=lambda x: x[0]):
         for ip in ip_addrs:
-            if not config.TLS_ONLY:
-                if not config.SECURE_ONLY:
-                    params = {"server": ip, "port": config.PORT, "secret": secret}
-                    params_encodeded = urllib.parse.urlencode(params, safe=':')
-                    print("{}: tg://proxy?{}".format(user, params_encodeded), flush=True)
+            if config.MODES["classic"]:
+                params = {"server": ip, "port": config.PORT, "secret": secret}
+                params_encodeded = urllib.parse.urlencode(params, safe=':')
+                classic_link = "tg://proxy?{}".format(params_encodeded)
+                proxy_links.append({"user": user, "link": classic_link})
+                print("{}: {}".format(user, classic_link), flush=True)
 
+            if config.MODES["secure"]:
                 params = {"server": ip, "port": config.PORT, "secret": "dd" + secret}
                 params_encodeded = urllib.parse.urlencode(params, safe=':')
-                print("{}: tg://proxy?{}".format(user, params_encodeded), flush=True)
+                dd_link = "tg://proxy?{}".format(params_encodeded)
+                proxy_links.append({"user": user, "link": dd_link})
+                print("{}: {}".format(user, dd_link), flush=True)
 
-            tls_secret = "ee" + secret + config.TLS_DOMAIN.encode().hex()
-            # the base64 links is buggy on ios
-            # tls_secret = bytes.fromhex("ee" + secret) + config.TLS_DOMAIN.encode()
-            # tls_secret_base64 = base64.urlsafe_b64encode(tls_secret)
-            params = {"server": ip, "port": config.PORT, "secret": tls_secret}
-            params_encodeded = urllib.parse.urlencode(params, safe=':')
-            print("{}: tg://proxy?{} (new)".format(user, params_encodeded), flush=True)
+            if config.MODES["tls"]:
+                tls_secret = "ee" + secret + config.TLS_DOMAIN.encode().hex()
+                # the base64 links is buggy on ios
+                # tls_secret = bytes.fromhex("ee" + secret) + config.TLS_DOMAIN.encode()
+                # tls_secret_base64 = base64.urlsafe_b64encode(tls_secret)
+                params = {"server": ip, "port": config.PORT, "secret": tls_secret}
+                params_encodeded = urllib.parse.urlencode(params, safe=':')
+                tls_link = "tg://proxy?{}".format(params_encodeded)
+                proxy_links.append({"user": user, "link": tls_link})
+                print("{}: {}".format(user, tls_link), flush=True)
 
-        if secret in ["00000000000000000000000000000000", "0123456789abcdef0123456789abcdef"]:
+        if secret in ["00000000000000000000000000000000", "0123456789abcdef0123456789abcdef",
+                      "00000000000000000000000000000001"]:
             msg = "The default secret {} is used, this is not recommended".format(secret)
             print(msg, flush=True)
             random_secret = "".join(myrandom.choice("0123456789abcdef") for i in range(32))
@@ -1825,6 +2137,7 @@ def setup_signals():
     if hasattr(signal, 'SIGUSR2'):
         def reload_signal(signum, frame):
             init_config()
+            apply_upstream_proxy_settings()
             print("Config reloaded", flush=True, file=sys.stderr)
             print_tg_info()
 
@@ -1832,9 +2145,13 @@ def setup_signals():
 
 
 def try_setup_uvloop():
+    if config.SOCKS5_HOST and config.SOCKS5_PORT:
+        # socks mode is not compatible with uvloop
+        return
     try:
         import uvloop
         asyncio.set_event_loop_policy(uvloop.EventLoopPolicy())
+        print_err("Found uvloop, using it for optimal performance")
     except ImportError:
         pass
 
@@ -1881,6 +2198,7 @@ def main():
     try_setup_uvloop()
 
     init_stats()
+    init_proxy_start_time()
 
     if sys.platform == "win32":
         loop = asyncio.ProactorEventLoop()
@@ -1912,21 +2230,31 @@ def main():
 
     if config.LISTEN_ADDR_IPV4:
         task = asyncio.start_server(handle_client_wrapper, config.LISTEN_ADDR_IPV4, config.PORT,
-                                    limit=get_to_tg_bufsize(), reuse_port=reuse_port, loop=loop)
+                                    limit=get_to_tg_bufsize(), reuse_port=reuse_port)
         servers.append(loop.run_until_complete(task))
 
     if config.LISTEN_ADDR_IPV6 and socket.has_ipv6:
         task = asyncio.start_server(handle_client_wrapper, config.LISTEN_ADDR_IPV6, config.PORT,
-                                    limit=get_to_tg_bufsize(), reuse_port=reuse_port, loop=loop)
+                                    limit=get_to_tg_bufsize(), reuse_port=reuse_port)
         servers.append(loop.run_until_complete(task))
 
     if config.LISTEN_UNIX_SOCK and has_unix:
         remove_unix_socket(config.LISTEN_UNIX_SOCK)
         task = asyncio.start_unix_server(handle_client_wrapper, config.LISTEN_UNIX_SOCK,
-                                         limit=get_to_tg_bufsize(), loop=loop)
+                                         limit=get_to_tg_bufsize())
         servers.append(loop.run_until_complete(task))
         os.chmod(config.LISTEN_UNIX_SOCK, 0o666)
 
+    if config.METRICS_PORT is not None:
+        if config.METRICS_LISTEN_ADDR_IPV4:
+            task = asyncio.start_server(handle_metrics, config.METRICS_LISTEN_ADDR_IPV4,
+                                        config.METRICS_PORT)
+            servers.append(loop.run_until_complete(task))
+        if config.METRICS_LISTEN_ADDR_IPV6 and socket.has_ipv6:
+            task = asyncio.start_server(handle_metrics, config.METRICS_LISTEN_ADDR_IPV6,
+                                        config.METRICS_PORT)
+            servers.append(loop.run_until_complete(task))
+
     try:
         loop.run_forever()
     except KeyboardInterrupt:
@@ -1947,6 +2275,7 @@ def main():
 
 if __name__ == "__main__":
     init_config()
+    apply_upstream_proxy_settings()
     init_ip_info()
     print_tg_info()
     main()