Minor environment variable improvements

- COIN and NET strip surrounding whitespace
- new environment variable RPC_HOST, similar to HOST, but
  for RPC.  Permits fine-grained control of which addresses
  the RPC server listens on.
- HOST and RPC_HOST strip surrounding whitespace from hostnames
  and IP addresses
- tests and documentation updated to match

docs/ENVIRONMENT.rst

@@ -8,6 +8,11 @@ given, the rest will have sensible defaults if not specified.  Many of
 the defaults around resource usage are conservative; I encourage you
 to review them.
 
+Note: by default the server will only serve to connections from the
+same machine.  To be accessible to other users across the internet you
+must set **HOST** appropriately; see below.
+
+
 Required
 --------
 
@@ -53,6 +58,7 @@ The following are required if you use the `run` script:
 
   The username the server will run as.
 
+
 Miscellaneous
 -------------
 
@@ -63,12 +69,6 @@ These environment variables are optional:
   Must be a *NET* from one of the **Coin** classes in `lib/coins.py`_.
   Defaults to `mainnet`.
 
-  Note: if you are using Bitcoin Core post the August 1st fork, you
-  should have NET be `bitcoin-segwit`, and if on the Bitcoin Cash
-  chain NET should be `mainnet`.
-  Note Bitcoin Core >= 0.13.1 requires a special *NET* for testnet:
-  `testnet-segwit`.
-
 * **DB_ENGINE**
 
   Database engine for the UTXO and history database.  The default is
@@ -76,13 +76,6 @@ These environment variables are optional:
   install the appropriate python package for your engine.  The value
   is not case sensitive.
 
-* **REORG_LIMIT**
-
-  The maximum number of blocks to be able to handle in a chain
-  reorganisation.  ElectrumX retains some fairly compact undo
-  information for this many blocks in levelDB.  The default is a
-  function of **COIN** and **NET**; for Bitcoin mainnet it is 200.
-
 * **HOST**
 
   The host or IP address that the TCP and SSL servers will use when
@@ -101,20 +94,25 @@ These environment variables are optional:
   If set then SSL_CERTFILE and SSL_KEYFILE must be defined and be
   filesystem paths to those SSL files.
 
-* **RPC_PORT**
+* **RPC_HOST**
 
-  ElectrumX will listen on this port for local RPC connections.
-  ElectrumX listens for RPC connections unless this is explicitly set
-  to blank.  The default is appropriate for **COIN** and **NET**
-  (e.g., 8000 for Bitcoin mainnet) if not set.
+  The host or IP address that the RPC server will listen on and
+  defaults to `localhost`.  To listen on multiple specific addresses
+  specify a comma-separated list.  Servers with unusual networking
+  setups might want to specify e.g. `::1` or `127.0.0.1` explicitly
+  rather than defaulting to `localhost`.
 
-* **EVENT_LOOP_POLICY**
+  An empty string (normally indicating all interfaces) is interpreted
+  as `localhost`, because allowing access to the server's RPC
+  interface to arbitrary connections aacross the internet is not a
+  good idea.
 
-  The name of an event loop policy to replace the default asyncio
-  policy, if any.  At present only `uvloop` is accepted, in which case
-  you must have installed the `uvloop`_ Python package.
+* **RPC_PORT**
 
-  If you are not sure what this means leave it unset.
+  ElectrumX will listen on this port for local RPC connections.
+  ElectrumX listens for RPC connections unless this is explicitly set
+  to blank.  The default depends on **COIN** and **NET** (e.g., 8000
+  for Bitcoin mainnet) if not set, as indicated in `lib/coins.py`_.
 
 * **DONATION_ADDRESS**
 
@@ -159,6 +157,22 @@ These environment variables are optional:
   that **ANON_LOGS** is honoured.  Defaults to 3600.  Set to zero to
   suppress this logging.
 
+* **REORG_LIMIT**
+
+  The maximum number of blocks to be able to handle in a chain
+  reorganisation.  ElectrumX retains some fairly compact undo
+  information for this many blocks in levelDB.  The default is a
+  function of **COIN** and **NET**; for Bitcoin mainnet it is 200.
+
+* **EVENT_LOOP_POLICY**
+
+  The name of an event loop policy to replace the default asyncio
+  policy, if any.  At present only `uvloop` is accepted, in which case
+  you must have installed the `uvloop`_ Python package.
+
+  If you are not sure what this means leave it unset.
+
+
 Resource Usage Limits
 ---------------------
 

server/controller.py

@@ -204,7 +204,7 @@ class Controller(util.LoggedClass):
     async def main_loop(self):
         '''Controller main loop.'''
         if self.env.rpc_port is not None:
-            await self.start_server('RPC', ('127.0.0.1', '::1'),
+            await self.start_server('RPC', self.env.cs_host(for_rpc=True),
                                     self.env.rpc_port)
         self.ensure_future(self.bp.main_loop())
         self.ensure_future(self.wait_for_bp_catchup())
@@ -292,7 +292,7 @@ class Controller(util.LoggedClass):
         self.state = self.LISTENING
 
         env = self.env
-        host = env.cs_host()
+        host = env.cs_host(for_rpc=False)
         if env.tcp_port is not None:
             await self.start_server('TCP', host, env.tcp_port)
         if env.ssl_port is not None:
@@ -317,7 +317,8 @@ class Controller(util.LoggedClass):
                 self.header_cache.clear()
 
             # Make a copy; self.sessions can change whilst await-ing
-            sessions = [s for s in self.sessions if isinstance(s, self.coin.SESSIONCLS)]
+            sessions = [s for s in self.sessions
+                        if isinstance(s, self.coin.SESSIONCLS)]
             for session in sessions:
                 await session.notify(self.bp.db_height, touched)
 

server/env.py

@@ -31,8 +31,8 @@ class Env(lib_util.LoggedClass):
         self.obsolete(['UTXO_MB', 'HIST_MB', 'NETWORK'])
         self.db_dir = self.required('DB_DIRECTORY')
         self.daemon_url = self.required('DAEMON_URL')
-        coin_name = self.required('COIN')
-        network = self.default('NET', 'mainnet')
+        coin_name = self.required('COIN').strip()
+        network = self.default('NET', 'mainnet').strip()
         self.coin = Coin.lookup_coin_class(coin_name, network)
         self.cache_MB = self.integer('CACHE_MB', 1200)
         self.host = self.default('HOST', 'localhost')
@@ -43,6 +43,7 @@ class Env(lib_util.LoggedClass):
         if self.ssl_port:
             self.ssl_certfile = self.required('SSL_CERTFILE')
             self.ssl_keyfile = self.required('SSL_KEYFILE')
+        self.rpc_host = self.default('RPC_HOST', 'localhost')
         self.rpc_port = self.integer('RPC_PORT', 8000)
         self.max_subscriptions = self.integer('MAX_SUBSCRIPTIONS', 10000)
         self.banner_file = self.default('BANNER_FILE', None)
@@ -184,11 +185,20 @@ class Env(lib_util.LoggedClass):
             return uvloop.EventLoopPolicy()
         raise self.Error('unknown event loop policy "{}"'.format(policy))
 
-    def cs_host(self):
+    def cs_host(self, *, for_rpc):
         '''Returns the 'host' argument to pass to asyncio's create_server
         call.  The result can be a single host name string, a list of
-        host name strings, or an empty string to bind to all interfaces.'''
-        result = self.host.split(',')
+        host name strings, or an empty string to bind to all interfaces.
+
+        If rpc is True the host to use for the RPC server is returned.
+        Otherwise the host to use for SSL/TCP servers is returned.
+        '''
+        host = self.rpc_host if for_rpc else self.host
+        result = [part.strip() for part in host.split(',')]
         if len(result) == 1:
             result = result[0]
+        # An empty result indicates all interfaces, which is not
+        # permitted for the RPC server.
+        if for_rpc and not result:
+            result = 'localhost'
         return result

server/peers.py

@@ -524,7 +524,7 @@ class PeerManager(util.LoggedClass):
 
         # Use our listening Host/IP for outgoing connections so our
         # peers see the correct source.
-        host = self.env.cs_host()
+        host = self.env.cs_host(for_rpc=False)
         if isinstance(host, list):
             host = host[0]
         local_addr = (host, None) if host else None

tests/server/test_env.py

@@ -82,8 +82,11 @@ def test_COIN_NET():
     os.environ['NET'] = 'testnet'
     e = Env()
     assert e.coin == lib_coins.BitcoinCashTestnet
+    os.environ['NET'] = ' testnet '
+    e = Env()
+    assert e.coin == lib_coins.BitcoinCashTestnet
     os.environ.pop('NET')
-    os.environ['COIN'] = 'Litecoin'
+    os.environ['COIN'] = ' Litecoin '
     e = Env()
     assert e.coin == lib_coins.Litecoin
     os.environ['NET'] = 'testnet'
@@ -97,10 +100,23 @@ def test_HOST():
     assert_default('HOST', 'host', 'localhost')
     os.environ['HOST'] = ''
     e = Env()
-    assert e.cs_host() == ''
+    assert e.cs_host(for_rpc=False) == ''
     os.environ['HOST'] = '192.168.0.1,23.45.67.89'
     e = Env()
-    assert e.cs_host() == ['192.168.0.1', '23.45.67.89']
+    assert e.cs_host(for_rpc=False) == ['192.168.0.1', '23.45.67.89']
+    os.environ['HOST'] = '192.168.0.1 , 23.45.67.89 '
+    e = Env()
+    assert e.cs_host(for_rpc=False) == ['192.168.0.1', '23.45.67.89']
+
+def test_RPC_HOST():
+    assert_default('RPC_HOST', 'rpc_host', 'localhost')
+    os.environ['RPC_HOST'] = ''
+    e = Env()
+    # Blank reverts to localhost
+    assert e.cs_host(for_rpc=True) == 'localhost'
+    os.environ['RPC_HOST'] = '127.0.0.1, ::1'
+    e = Env()
+    assert e.cs_host(for_rpc=True) == ['127.0.0.1', '::1']
 
 def test_REORG_LIMIT():
     assert_integer('REORG_LIMIT', 'reorg_limit',