add blockchain.mempoolminfee, update relayfee comments

Adds the `blockchain.mempoolminfee` rpc to fetch the minimum feerate
required to get into the daemons mempool.
Updates the relayfee comments as the fee returned by
`blockchain.relayfee` doesn't guarantee to get into the mempool.

Author: f321x

docs/rpc-interface.rst

@@ -90,6 +90,7 @@ A typical result is as follows (with annotated comments)::
           "blockchain.estimatefee": 12776,
           "blockchain.headers.subscribe": 2825,
           "blockchain.relayfee": 740,
+          "blockchain.mempoolminfee": 121,
           "blockchain.scripthash.get_history": 196,
           "blockchain.scripthash.subscribe": 184626,
           "blockchain.transaction.broadcast": 19,

src/electrumx/server/daemon.py

@@ -79,6 +79,9 @@ def __init__(
         self._networkinfo_cache = (None, 0)
         self._networkinfo_lock = asyncio.Lock()
 
+        self._mempoolinfo_cache = (None, 0)
+        self._mempoolinfo_lock = asyncio.Lock()
+
     async def __aenter__(self):
         self.session = aiohttp.ClientSession(connector=self.connector())
         return self
@@ -284,12 +287,27 @@ async def getnetworkinfo(self):
             self._networkinfo_cache = (val, time.time())
             return val
 
+    async def getmempoolinfo(self):
+        """Return the result of the 'getmempoolinfo' RPC call."""
+        async with self._mempoolinfo_lock:
+            cache_val, cache_time = self._mempoolinfo_cache
+            if time.time() - cache_time < 60:  # seconds
+                return cache_val
+            val = await self._send_single('getmempoolinfo')
+            self._mempoolinfo_cache = (val, time.time())
+            return val
+
     async def relayfee(self):
-        '''The minimum fee a low-priority tx must pay in order to be accepted
-        to the daemon's memory pool.'''
+        """The minimum feerate required for a transaction to be relayed on by the backend to the
+        bitcoin network. Doesn't guarantee mempool acceptance."""
         network_info = await self.getnetworkinfo()
         return network_info['relayfee']
 
+    async def mempoolminfee(self):
+        """The minimum feerate required for a transaction to get accepted into the backends mempool."""
+        mempool_info = await self.getmempoolinfo()
+        return mempool_info['mempoolminfee']
+
     async def getrawtransaction(self, hex_hash, verbose=False):
         '''Return the serialized raw transaction with the given hash.'''
         # Cast to int because some coin daemons are old and require it
@@ -350,8 +368,8 @@ async def estimatefee(self, block_count):
         return self.coin.ESTIMATE_FEE
 
     async def relayfee(self):
-        '''The minimum fee a low-priority tx must pay in order to be accepted
-        to the daemon's memory pool.'''
+        """The minimum fee required for a transaction to be relayed on by the server to the
+        bitcoin network. Doesn't guarantee mempool acceptance."""
         return self.coin.RELAY_FEE
 
 

src/electrumx/server/session.py

@@ -1387,11 +1387,16 @@ async def banner(self):
         return banner
 
     async def relayfee(self):
-        '''The minimum fee a low-priority tx must pay in order to be accepted
-        to the daemon's memory pool.'''
+        """The minimum fee required for a transaction to be relayed on by the server to the
+        bitcoin network. Doesn't guarantee mempool acceptance."""
         self.bump_cost(1.0)
         return await self.daemon_request('relayfee')
 
+    async def mempoolminfee(self):
+        """The minimum feerate required for a transaction to get accepted into the servers mempool."""
+        self.bump_cost(1.0)
+        return await self.daemon_request('mempoolminfee')
+
     async def estimatefee(self, number, mode=None):
         '''The estimated transaction fee per kilobyte to be paid for a
         transaction to be included within a certain number of blocks.
@@ -1628,6 +1633,7 @@ def set_request_handlers(self, ptuple):
             'blockchain.estimatefee': self.estimatefee,
             'blockchain.headers.subscribe': self.headers_subscribe,
             'blockchain.relayfee': self.relayfee,
+            'blockchain.mempoolminfee': self.mempoolminfee,
             'blockchain.scripthash.get_balance': self.scripthash_get_balance,
             'blockchain.scripthash.get_history': self.scripthash_get_history,
             'blockchain.scripthash.get_mempool': self.scripthash_get_mempool,

tests/server/test_daemon.py

@@ -255,6 +255,14 @@ async def test_relayfee(daemon):
     assert await daemon.relayfee() == sats
 
 
+@pytest.mark.asyncio
+async def test_mempoolminfee(daemon):
+    bitcoin_per_kvb = 0.00002123
+    response = {"mempoolminfee": bitcoin_per_kvb, "other:": "cruft"}
+    daemon.session = ClientSessionGood(('getmempoolinfo', [], response))
+    assert await daemon.mempoolminfee() == bitcoin_per_kvb
+
+
 @pytest.mark.asyncio
 async def test_mempool_hashes(daemon):
     hashes = ['hex_hash1', 'hex_hash2']