[rpc] Deprecate estimatefee RPC

Deprecate estimatefee in v0.16, for final removal in v0.17.

This commit introduces a phased removal of RPC methods. RPC method is
disabled by default in version x, but can be enabled by using the
`-deprecatedrpc=<method>` argument. RPC method is removed entirely in
version (x+1).

src/init.cpp

@@ -430,6 +430,7 @@ std::string HelpMessage(HelpMessageMode mode)
         strUsage += HelpMessageOpt("-checkmempool=<n>", strprintf("Run checks every <n> transactions (default: %u)", defaultChainParams->DefaultConsistencyChecks()));
         strUsage += HelpMessageOpt("-checkpoints", strprintf("Disable expensive verification for known chain history (default: %u)", DEFAULT_CHECKPOINTS_ENABLED));
         strUsage += HelpMessageOpt("-disablesafemode", strprintf("Disable safemode, override a real safe mode event (default: %u)", DEFAULT_DISABLE_SAFEMODE));
+        strUsage += HelpMessageOpt("-deprecatedrpc=<method>", "Allows deprecated RPC method(s) to be used");
         strUsage += HelpMessageOpt("-testsafemode", strprintf("Force safe mode (default: %u)", DEFAULT_TESTSAFEMODE));
         strUsage += HelpMessageOpt("-dropmessagestest=<n>", "Randomly drop 1 of every <n> network messages");
         strUsage += HelpMessageOpt("-fuzzmessagestest=<n>", "Randomly fuzz 1 of every <n> network messages");

src/rpc/mining.cpp

@@ -789,6 +789,12 @@ UniValue estimatefee(const JSONRPCRequest& request)
             + HelpExampleCli("estimatefee", "6")
             );
 
+    if (!IsDeprecatedRPCEnabled("estimatefee")) {
+        throw JSONRPCError(RPC_METHOD_DEPRECATED, "estimatefee is deprecated and will be fully removed in v0.17. "
+            "To use estimatefee in v0.16, restart bitcoind with -deprecatedrpc=estimatefee.\n"
+            "Projects should transition to using estimatesmartfee before upgrading to v0.17");
+    }
+
     RPCTypeCheck(request.params, {UniValue::VNUM});
 
     int nBlocks = request.params[0].get_int();

src/rpc/protocol.h

@@ -57,6 +57,7 @@ enum RPCErrorCode
     RPC_VERIFY_REJECTED             = -26, //!< Transaction or block was rejected by network rules
     RPC_VERIFY_ALREADY_IN_CHAIN     = -27, //!< Transaction already in chain
     RPC_IN_WARMUP                   = -28, //!< Client still warming up
+    RPC_METHOD_DEPRECATED           = -32, //!< RPC method is deprecated
 
     //! Aliases for backward compatibility
     RPC_TRANSACTION_ERROR           = RPC_VERIFY_ERROR,

src/rpc/server.cpp

@@ -382,6 +382,13 @@ void JSONRPCRequest::parse(const UniValue& valRequest)
         throw JSONRPCError(RPC_INVALID_REQUEST, "Params must be an array or object");
 }
 
+bool IsDeprecatedRPCEnabled(const std::string& method)
+{
+    const std::vector<std::string> enabled_methods = gArgs.GetArgs("-deprecatedrpc");
+
+    return find(enabled_methods.begin(), enabled_methods.end(), method) != enabled_methods.end();
+}
+
 static UniValue JSONRPCExecOne(const UniValue& req)
 {
     UniValue rpc_result(UniValue::VOBJ);

src/rpc/server.h

@@ -171,6 +171,8 @@ public:
     bool appendCommand(const std::string& name, const CRPCCommand* pcmd);
 };
 
+bool IsDeprecatedRPCEnabled(const std::string& method);
+
 extern CRPCTable tableRPC;
 
 /**

test/functional/smartfees.py

@@ -151,7 +151,7 @@ class EstimateFeeTest(BitcoinTestFramework):
         which we will use to generate our transactions.
         """
         self.add_nodes(3, extra_args=[["-maxorphantx=1000", "-whitelist=127.0.0.1"],
-                                      ["-blockmaxsize=17000", "-maxorphantx=1000"],
+                                      ["-blockmaxsize=17000", "-maxorphantx=1000", "-deprecatedrpc=estimatefee"],
                                       ["-blockmaxsize=8000", "-maxorphantx=1000"]])
         # Use node0 to mine blocks for input splitting
         # Node1 mines small blocks but that are bigger than the expected transaction rate.