Merge branch 'release-0.7.7'

docs/ENV-NOTES

@@ -44,6 +44,17 @@ in ElectrumX are very cheap - they consume about 100 bytes of memory
 each and are processed efficiently.  I feel the defaults are low and
 encourage you to raise them.
 
+MAX_HIST         - maximum number of historical transactions to serve for
+                   a single address.  The current Electrum protocol requires
+                   address histories be served en-masse or not at all,
+                   an obvious avenue for abuse.  This limit is a
+                   stop-gap until the protocol is improved to admit
+                   incremental history requests.  The default value is
+                   2,000 which should be ample for most legitimate
+                   users.  Increasing to around 10,000 is likely fine
+                   but bear in mind one client can request multiple
+                   addresses.  I welcome your experiences and suggestions
+                   for an appropriate value.
 MAX_SUBS         - maximum number of address subscriptions across all
                    sessions.  Defaults to 250,000.
 MAX_SESSION_SUBS - maximum number of address subscriptions permitted to a

docs/RELEASE-NOTES

@@ -1,3 +1,11 @@
+version 0.7.7
+-------------
+
+- add MAX_HIST to throttle history requests; see docs/ENV-NOTES.  One
+  provider of ElectrumX services was attacked by a loser requesting
+  long histories; this environment variable allows you to limit what
+  you attempt to serve.
+
 version 0.7.6
 -------------
 

server/env.py

@@ -44,7 +44,8 @@ class Env(LoggedClass):
         # The electrum client takes the empty string as unspecified
         self.donation_address = self.default('DONATION_ADDRESS', '')
         self.db_engine = self.default('DB_ENGINE', 'leveldb')
-        # Subscription limits
+        # Server limits to help prevent DoS
+        self.max_hist = self.integer('MAX_HIST', 2000)
         self.max_subs = self.integer('MAX_SUBS', 250000)
         self.max_session_subs = self.integer('MAX_SESSION_SUBS', 50000)
         # IRC

server/protocol.py

@@ -674,9 +674,11 @@ class ElectrumX(Session):
         return self.bp.read_headers(start_height, count).hex()
 
     async def async_get_history(self, hash168):
+        # Apply DoS limit
+        limit = self.env.max_hist
         # Python 3.6: use async generators; update callers
         history = []
-        for item in self.bp.get_history(hash168, limit=None):
+        for item in self.bp.get_history(hash168, limit=limit):
             history.append(item)
             if len(history) % 100 == 0:
                 await asyncio.sleep(0)

server/version.py

@@ -1 +1 @@
-VERSION = "ElectrumX 0.7.6"
+VERSION = "ElectrumX 0.7.7"