rpc: Add ParseFeeRate helper

src/rpc/util.cpp

@@ -75,6 +75,13 @@ CAmount AmountFromValue(const UniValue& value, int decimals)
     return amount;
 }
 
+CFeeRate ParseFeeRate(const UniValue& json)
+{
+    CAmount val{AmountFromValue(json)};
+    if (val >= COIN) throw JSONRPCError(RPC_INVALID_PARAMETER, "Fee rates larger than or equal to 1BTC/kvB are not accepted");
+    return CFeeRate{val};
+}
+
 uint256 ParseHashV(const UniValue& v, std::string_view name)
 {
     const std::string& strHex(v.get_str());

src/rpc/util.h

@@ -103,6 +103,11 @@ std::vector<unsigned char> ParseHexO(const UniValue& o, std::string_view strKey)
  * @returns a CAmount if the various checks pass.
  */
 CAmount AmountFromValue(const UniValue& value, int decimals = 8);
+/**
+ * Parse a json number or string, denoting BTC/kvB, into a CFeeRate (sat/kvB).
+ * Reject negative values or rates larger than 1BTC/kvB.
+ */
+CFeeRate ParseFeeRate(const UniValue& json);
 
 using RPCArgList = std::vector<std::pair<std::string, UniValue>>;
 std::string HelpExampleCli(const std::string& methodname, const std::string& args);