use estimatesmartfee for fee estimation (#300)

* use estimatesmartfee for fee estimation, in case of BitcoinSegwit

* use estimatesmartfee in daemon if available

* daemon._is_rpc_available() now catches DaemonError instead of using HTTP error code

server/daemon.py

@@ -20,6 +20,7 @@ import aiohttp
 
 from lib.util import LoggedClass, int_to_varint, hex_to_bytes
 from lib.hash import hex_str_to_hash
+from lib.jsonrpc import JSONRPC
 
 
 class DaemonError(Exception):
@@ -30,6 +31,7 @@ class Daemon(LoggedClass):
     '''Handles connections to a daemon at the given URL.'''
 
     WARMING_UP = -28
+    RPC_MISC_ERROR = -1
 
     class DaemonWarmingUpError(Exception):
         '''Raised when the daemon returns an error in its results.'''
@@ -54,6 +56,7 @@ class Daemon(LoggedClass):
         else:
             self.ClientHttpProcessingError = asyncio.TimeoutError
             self.ClientPayloadError = aiohttp.ClientPayloadError
+        self._available_rpcs = {}  # caches results for _is_rpc_available()
 
     def next_req_id(self):
         '''Retrns the next request ID.'''
@@ -97,7 +100,7 @@ class Daemon(LoggedClass):
                     # If bitcoind can't find a tx, for some reason
                     # it returns 500 but fills out the JSON.
                     # Should still return 200 IMO.
-                    if resp.status in (200, 500):
+                    if resp.status in (200, 404, 500):
                         return await resp.json()
                     return (resp.status, resp.reason)
 
@@ -194,6 +197,34 @@ class Daemon(LoggedClass):
             return await self._send(payload, processor)
         return []
 
+    async def _is_rpc_available(self, method):
+        '''Return whether given RPC method is available in the daemon.
+
+        Results are cached and the daemon will generally not be queried with
+        the same method more than once.'''
+        available = self._available_rpcs.get(method, None)
+        if available is None:
+            try:
+                await self._send_single(method)
+                available = True
+            except DaemonError as e:
+                err = e.args[0]
+                error_code = err.get("code")
+                if error_code == JSONRPC.METHOD_NOT_FOUND:
+                    available = False
+                elif error_code == self.RPC_MISC_ERROR:
+                    # method found but exception was thrown in command handling
+                    # probably because we did not provide arguments
+                    available = True
+                else:
+                    self.logger.warning('unexpected error (code {:d}: {}) when '
+                                        'testing RPC availability of method {}'
+                                        .format(error_code, err.get("message"),
+                                                method))
+                    available = False
+            self._available_rpcs[method] = available
+        return available
+
     async def block_hex_hashes(self, first, count):
         '''Return the hex hashes of count block starting at height first.'''
         params_iterable = ((h, ) for h in range(first, first + count))
@@ -216,6 +247,9 @@ class Daemon(LoggedClass):
 
     async def estimatefee(self, params):
         '''Return the fee estimate for the given parameters.'''
+        if await self._is_rpc_available('estimatesmartfee'):
+            estimate = await self._send_single('estimatesmartfee', params)
+            return estimate['feerate']
         return await self._send_single('estimatefee', params)
 
     async def getnetworkinfo(self):