Merge bitcoin/bitcoin#21786: wallet: ensure sat/vB feerates are in range (mantissa of 3)

847288df07b45ca535c849e518b22818ab492896 test: fee rate values that cannot be represented as sat/vB (Jon Atack)
06a90fa0381c790f7bde2ab9bf47d2b22acef4a5 rpc: for sat/vB fee rates, limit ParseFixedPoint decimals to 3 (Jon Atack)
0742c7840f03505597fd2de87db97f12597ef667 rpc: enable passing decimals to AmountFromValue, add doxygen (Jon Atack)
8ce3ef57a3e9ad13c0aaa4648e8584241d53592d test: ParseFixedPoint with 3 decimals for sat/vB fee rates (Jon Atack)
b5033275979a2a495b02b25f70cadbdcc8b6eb6a test: type error and out of range fee rates where missing (Jon Atack)
c5fd4344f7fcc257062a610c8ff26ffcc9b53953 test: explicit fee rates with invalid amounts (Jon Atack)
ea6f76b66ecc52360719053489e0ec9f9a673eab test: improve zero-value explicit fee rate coverage (Jon Atack)

Pull request description:

  - Improve/close gaps in existing test coverage before making the change
  - Enable passing `decimals` to `ParseFixedPoint()` when calling `AmountFromValue()`
  - Limit explicit fee rates in sat/vB passed in by users to 3 decimals, and raise otherwise
  - Add regression test coverage

  Closes #20534.

ACKs for top commit:
  MarcoFalke:
    review ACK 847288df07b45ca535c849e518b22818ab492896 🔷

Tree-SHA512: c539d07ae9b21c0d6c8ea460beb9c8dad5559445518aace560abc3c05c588907bae189b6fd7602b3b397de4a42356136c3ec6f960d3dcf2d5d16377aef4ab5a2

9 files changed, 128 insertions, 40 deletions

diff --git a/src/rpc/util.cpp b/src/rpc/util.cpp
index 069669bb3b..7cf25e0c82 100644
--- a/src/rpc/util.cpp
+++ b/src/rpc/util.cpp
@@ -74,12 +74,12 @@ void RPCTypeCheckObj(const UniValue& o,
     }
 }
 
-CAmount AmountFromValue(const UniValue& value)
+CAmount AmountFromValue(const UniValue& value, int decimals)
 {
     if (!value.isNum() && !value.isStr())
         throw JSONRPCError(RPC_TYPE_ERROR, "Amount is not a number or string");
     CAmount amount;
-    if (!ParseFixedPoint(value.getValStr(), 8, &amount))
+    if (!ParseFixedPoint(value.getValStr(), decimals, &amount))
         throw JSONRPCError(RPC_TYPE_ERROR, "Invalid amount");
     if (!MoneyRange(amount))
         throw JSONRPCError(RPC_TYPE_ERROR, "Amount out of range");
diff --git a/src/rpc/util.h b/src/rpc/util.h
index 06381d504c..0120dbcc98 100644
--- a/src/rpc/util.h
+++ b/src/rpc/util.h
@@ -77,7 +77,14 @@ extern uint256 ParseHashO(const UniValue& o, std::string strKey);
 extern std::vector<unsigned char> ParseHexV(const UniValue& v, std::string strName);
 extern std::vector<unsigned char> ParseHexO(const UniValue& o, std::string strKey);
 
-extern CAmount AmountFromValue(const UniValue& value);
+/**
+ * Validate and return a CAmount from a UniValue number or string.
+ *
+ * @param[in] value     UniValue number or string to parse.
+ * @param[in] decimals  Number of significant digits (default: 8).
+ * @returns a CAmount if the various checks pass.
+ */
+extern CAmount AmountFromValue(const UniValue& value, int decimals = 8);
 
 using RPCArgList = std::vector<std::pair<std::string, UniValue>>;
 extern std::string HelpExampleCli(const std::string& methodname, const std::string& args);
diff --git a/src/test/util_tests.cpp b/src/test/util_tests.cpp
index 04b908829b..534d28e5de 100644
--- a/src/test/util_tests.cpp
+++ b/src/test/util_tests.cpp
@@ -1759,6 +1759,15 @@ BOOST_AUTO_TEST_CASE(test_ParseFixedPoint)
     BOOST_CHECK(!ParseFixedPoint("1.1e", 8, &amount));
     BOOST_CHECK(!ParseFixedPoint("1.1e-", 8, &amount));
     BOOST_CHECK(!ParseFixedPoint("1.", 8, &amount));
+
+    // Test with 3 decimal places for fee rates in sat/vB.
+    BOOST_CHECK(ParseFixedPoint("0.001", 3, &amount));
+    BOOST_CHECK_EQUAL(amount, CAmount{1});
+    BOOST_CHECK(!ParseFixedPoint("0.0009", 3, &amount));
+    BOOST_CHECK(!ParseFixedPoint("31.00100001", 3, &amount));
+    BOOST_CHECK(!ParseFixedPoint("31.0011", 3, &amount));
+    BOOST_CHECK(!ParseFixedPoint("31.99999999", 3, &amount));
+    BOOST_CHECK(!ParseFixedPoint("31.999999999999999999999", 3, &amount));
 }
 
 static void TestOtherThread(fs::path dirname, std::string lockname, bool *result)
diff --git a/src/wallet/rpcwallet.cpp b/src/wallet/rpcwallet.cpp
index ae337055e2..7777543ece 100644
--- a/src/wallet/rpcwallet.cpp
+++ b/src/wallet/rpcwallet.cpp
@@ -216,7 +216,8 @@ static void SetFeeEstimateMode(const CWallet& wallet, CCoinControl& cc, const Un
         if (!estimate_mode.isNull() && estimate_mode.get_str() != "unset") {
             throw JSONRPCError(RPC_INVALID_PARAMETER, "Cannot specify both estimate_mode and fee_rate");
         }
-        cc.m_feerate = CFeeRate(AmountFromValue(fee_rate), COIN);
+        // Fee rates in sat/vB cannot represent more than 3 significant digits.
+        cc.m_feerate = CFeeRate{AmountFromValue(fee_rate, /* decimals */ 3)};
         if (override_min_fee) cc.fOverrideFeeRate = true;
         // Default RBF to true for explicit fee_rate, if unset.
         if (!cc.m_signal_bip125_rbf) cc.m_signal_bip125_rbf = true;
diff --git a/test/functional/rpc_fundrawtransaction.py b/test/functional/rpc_fundrawtransaction.py
index 2e1b1e878f..0cce5493fc 100755
--- a/test/functional/rpc_fundrawtransaction.py
+++ b/test/functional/rpc_fundrawtransaction.py
@@ -5,6 +5,8 @@
 """Test the fundrawtransaction RPC."""
 
 from decimal import Decimal
+from itertools import product
+
 from test_framework.descriptors import descsum_create
 from test_framework.test_framework import BitcoinTestFramework
 from test_framework.util import (
@@ -723,17 +725,16 @@ class RawTransactionsTest(BitcoinTestFramework):
         result2 = node.fundrawtransaction(rawtx, {"feeRate": 2 * self.min_relay_tx_fee})
         result3 = node.fundrawtransaction(rawtx, {"fee_rate": 10 * btc_kvb_to_sat_vb * self.min_relay_tx_fee})
         result4 = node.fundrawtransaction(rawtx, {"feeRate": str(10 * self.min_relay_tx_fee)})
-        # Test that funding non-standard "zero-fee" transactions is valid.
-        result5 = self.nodes[3].fundrawtransaction(rawtx, {"fee_rate": 0})
-        result6 = self.nodes[3].fundrawtransaction(rawtx, {"feeRate": 0})
 
         result_fee_rate = result['fee'] * 1000 / count_bytes(result['hex'])
         assert_fee_amount(result1['fee'], count_bytes(result1['hex']), 2 * result_fee_rate)
         assert_fee_amount(result2['fee'], count_bytes(result2['hex']), 2 * result_fee_rate)
         assert_fee_amount(result3['fee'], count_bytes(result3['hex']), 10 * result_fee_rate)
         assert_fee_amount(result4['fee'], count_bytes(result4['hex']), 10 * result_fee_rate)
-        assert_fee_amount(result5['fee'], count_bytes(result5['hex']), 0)
-        assert_fee_amount(result6['fee'], count_bytes(result6['hex']), 0)
+
+        # Test that funding non-standard "zero-fee" transactions is valid.
+        for param, zero_value in product(["fee_rate", "feeRate"], [0, 0.000, 0.00000000, "0", "0.000", "0.00000000"]):
+            assert_equal(self.nodes[3].fundrawtransaction(rawtx, {param: zero_value})["fee"], 0)
 
         # With no arguments passed, expect fee of 141 satoshis.
         assert_approx(node.fundrawtransaction(rawtx)["fee"], vexp=0.00000141, vspan=0.00000001)
@@ -767,11 +768,16 @@ class RawTransactionsTest(BitcoinTestFramework):
                 node.fundrawtransaction, rawtx, {param: -1, "add_inputs": True})
             assert_raises_rpc_error(-3, "Amount is not a number or string",
                 node.fundrawtransaction, rawtx, {param: {"foo": "bar"}, "add_inputs": True})
+            # Test fee rate values that don't pass fixed-point parsing checks.
+            for invalid_value in ["", 0.000000001, 1e-09, 1.111111111, 1111111111111111, "31.999999999999999999999"]:
+                assert_raises_rpc_error(-3, "Invalid amount", node.fundrawtransaction, rawtx, {param: invalid_value, "add_inputs": True})
+        # Test fee_rate values that cannot be represented in sat/vB.
+        for invalid_value in [0.0001, 0.00000001, 0.00099999, 31.99999999, "0.0001", "0.00000001", "0.00099999", "31.99999999"]:
             assert_raises_rpc_error(-3, "Invalid amount",
-                node.fundrawtransaction, rawtx, {param: "", "add_inputs": True})
+                node.fundrawtransaction, rawtx, {"fee_rate": invalid_value, "add_inputs": True})
 
         self.log.info("Test min fee rate checks are bypassed with fundrawtxn, e.g. a fee_rate under 1 sat/vB is allowed")
-        node.fundrawtransaction(rawtx, {"fee_rate": 0.99999999, "add_inputs": True})
+        node.fundrawtransaction(rawtx, {"fee_rate": 0.999, "add_inputs": True})
         node.fundrawtransaction(rawtx, {"feeRate": 0.00000999, "add_inputs": True})
 
         self.log.info("- raises RPC error if both feeRate and fee_rate are passed")
diff --git a/test/functional/rpc_psbt.py b/test/functional/rpc_psbt.py
index 079a3bd3ba..c6e96e4a92 100755
--- a/test/functional/rpc_psbt.py
+++ b/test/functional/rpc_psbt.py
@@ -6,6 +6,8 @@
 """
 
 from decimal import Decimal
+from itertools import product
+
 from test_framework.test_framework import BitcoinTestFramework
 from test_framework.util import (
     assert_approx,
@@ -193,14 +195,14 @@ class PSBTTest(BitcoinTestFramework):
         assert_approx(res2["fee"], 0.055, 0.005)
 
         self.log.info("Test min fee rate checks with walletcreatefundedpsbt are bypassed, e.g. a fee_rate under 1 sat/vB is allowed")
-        res3 = self.nodes[1].walletcreatefundedpsbt(inputs, outputs, 0, {"fee_rate": "0.99999999", "add_inputs": True})
+        res3 = self.nodes[1].walletcreatefundedpsbt(inputs, outputs, 0, {"fee_rate": "0.999", "add_inputs": True})
         assert_approx(res3["fee"], 0.00000381, 0.0000001)
         res4 = self.nodes[1].walletcreatefundedpsbt(inputs, outputs, 0, {"feeRate": 0.00000999, "add_inputs": True})
         assert_approx(res4["fee"], 0.00000381, 0.0000001)
 
         self.log.info("Test min fee rate checks with walletcreatefundedpsbt are bypassed and that funding non-standard 'zero-fee' transactions is valid")
-        for param in ["fee_rate", "feeRate"]:
-            assert_equal(self.nodes[1].walletcreatefundedpsbt(inputs, outputs, 0, {param: 0, "add_inputs": True})["fee"], 0)
+        for param, zero_value in product(["fee_rate", "feeRate"], [0, 0.000, 0.00000000, "0", "0.000", "0.00000000"]):
+            assert_equal(0, self.nodes[1].walletcreatefundedpsbt(inputs, outputs, 0, {param: zero_value, "add_inputs": True})["fee"])
 
         self.log.info("Test invalid fee rate settings")
         for param, value in {("fee_rate", 100000), ("feeRate", 1)}:
@@ -210,8 +212,14 @@ class PSBTTest(BitcoinTestFramework):
                 self.nodes[1].walletcreatefundedpsbt, inputs, outputs, 0, {param: -1, "add_inputs": True})
             assert_raises_rpc_error(-3, "Amount is not a number or string",
                 self.nodes[1].walletcreatefundedpsbt, inputs, outputs, 0, {param: {"foo": "bar"}, "add_inputs": True})
+            # Test fee rate values that don't pass fixed-point parsing checks.
+            for invalid_value in ["", 0.000000001, 1e-09, 1.111111111, 1111111111111111, "31.999999999999999999999"]:
+                assert_raises_rpc_error(-3, "Invalid amount",
+                    self.nodes[1].walletcreatefundedpsbt, inputs, outputs, 0, {param: invalid_value, "add_inputs": True})
+        # Test fee_rate values that cannot be represented in sat/vB.
+        for invalid_value in [0.0001, 0.00000001, 0.00099999, 31.99999999, "0.0001", "0.00000001", "0.00099999", "31.99999999"]:
             assert_raises_rpc_error(-3, "Invalid amount",
-                self.nodes[1].walletcreatefundedpsbt, inputs, outputs, 0, {param: "", "add_inputs": True})
+                self.nodes[1].walletcreatefundedpsbt, inputs, outputs, 0, {"fee_rate": invalid_value, "add_inputs": True})
 
         self.log.info("- raises RPC error if both feeRate and fee_rate are passed")
         assert_raises_rpc_error(-8, "Cannot specify both fee_rate (sat/vB) and feeRate (BTC/kvB)",
diff --git a/test/functional/wallet_basic.py b/test/functional/wallet_basic.py
index 46eecae611..4a1d25bbc5 100755
--- a/test/functional/wallet_basic.py
+++ b/test/functional/wallet_basic.py
@@ -15,6 +15,7 @@ from test_framework.util import (
 )
 from test_framework.wallet_util import test_address
 
+NOT_A_NUMBER_OR_STRING = "Amount is not a number or string"
 OUT_OF_RANGE = "Amount out of range"
 
 
@@ -264,12 +265,25 @@ class WalletTest(BitcoinTestFramework):
         # Test setting explicit fee rate just below the minimum.
         self.log.info("Test sendmany raises 'fee rate too low' if fee_rate of 0.99999999 is passed")
         assert_raises_rpc_error(-6, "Fee rate (0.999 sat/vB) is lower than the minimum fee rate setting (1.000 sat/vB)",
-            self.nodes[2].sendmany, amounts={address: 10}, fee_rate=0.99999999)
-
-        self.log.info("Test sendmany raises if fee_rate of 0 or -1 is passed")
-        assert_raises_rpc_error(-6, "Fee rate (0.000 sat/vB) is lower than the minimum fee rate setting (1.000 sat/vB)",
-            self.nodes[2].sendmany, amounts={address: 10}, fee_rate=0)
+            self.nodes[2].sendmany, amounts={address: 10}, fee_rate=0.999)
+
+        self.log.info("Test sendmany raises if an invalid fee_rate is passed")
+        # Test fee_rate with zero values.
+        msg = "Fee rate (0.000 sat/vB) is lower than the minimum fee rate setting (1.000 sat/vB)"
+        for zero_value in [0, 0.000, 0.00000000, "0", "0.000", "0.00000000"]:
+            assert_raises_rpc_error(-6, msg, self.nodes[2].sendmany, amounts={address: 1}, fee_rate=zero_value)
+        msg = "Invalid amount"
+        # Test fee_rate values that don't pass fixed-point parsing checks.
+        for invalid_value in ["", 0.000000001, 1e-09, 1.111111111, 1111111111111111, "31.999999999999999999999"]:
+            assert_raises_rpc_error(-3, msg, self.nodes[2].sendmany, amounts={address: 1.0}, fee_rate=invalid_value)
+        # Test fee_rate values that cannot be represented in sat/vB.
+        for invalid_value in [0.0001, 0.00000001, 0.00099999, 31.99999999, "0.0001", "0.00000001", "0.00099999", "31.99999999"]:
+            assert_raises_rpc_error(-3, msg, self.nodes[2].sendmany, amounts={address: 10}, fee_rate=invalid_value)
+        # Test fee_rate out of range (negative number).
         assert_raises_rpc_error(-3, OUT_OF_RANGE, self.nodes[2].sendmany, amounts={address: 10}, fee_rate=-1)
+        # Test type error.
+        for invalid_value in [True, {"foo": "bar"}]:
+            assert_raises_rpc_error(-3, NOT_A_NUMBER_OR_STRING, self.nodes[2].sendmany, amounts={address: 10}, fee_rate=invalid_value)
 
         self.log.info("Test sendmany raises if an invalid conf_target or estimate_mode is passed")
         for target, mode in product([-1, 0, 1009], ["economical", "conservative"]):
@@ -447,12 +461,25 @@ class WalletTest(BitcoinTestFramework):
             # Test setting explicit fee rate just below the minimum.
             self.log.info("Test sendtoaddress raises 'fee rate too low' if fee_rate of 0.99999999 is passed")
             assert_raises_rpc_error(-6, "Fee rate (0.999 sat/vB) is lower than the minimum fee rate setting (1.000 sat/vB)",
-                self.nodes[2].sendtoaddress, address=address, amount=1, fee_rate=0.99999999)
-
-            self.log.info("Test sendtoaddress raises if fee_rate of 0 or -1 is passed")
-            assert_raises_rpc_error(-6, "Fee rate (0.000 sat/vB) is lower than the minimum fee rate setting (1.000 sat/vB)",
-                self.nodes[2].sendtoaddress, address=address, amount=10, fee_rate=0)
+                self.nodes[2].sendtoaddress, address=address, amount=1, fee_rate=0.999)
+
+            self.log.info("Test sendtoaddress raises if an invalid fee_rate is passed")
+            # Test fee_rate with zero values.
+            msg = "Fee rate (0.000 sat/vB) is lower than the minimum fee rate setting (1.000 sat/vB)"
+            for zero_value in [0, 0.000, 0.00000000, "0", "0.000", "0.00000000"]:
+                assert_raises_rpc_error(-6, msg, self.nodes[2].sendtoaddress, address=address, amount=1, fee_rate=zero_value)
+            msg = "Invalid amount"
+            # Test fee_rate values that don't pass fixed-point parsing checks.
+            for invalid_value in ["", 0.000000001, 1e-09, 1.111111111, 1111111111111111, "31.999999999999999999999"]:
+                assert_raises_rpc_error(-3, msg, self.nodes[2].sendtoaddress, address=address, amount=1.0, fee_rate=invalid_value)
+            # Test fee_rate values that cannot be represented in sat/vB.
+            for invalid_value in [0.0001, 0.00000001, 0.00099999, 31.99999999, "0.0001", "0.00000001", "0.00099999", "31.99999999"]:
+                assert_raises_rpc_error(-3, msg, self.nodes[2].sendtoaddress, address=address, amount=10, fee_rate=invalid_value)
+            # Test fee_rate out of range (negative number).
             assert_raises_rpc_error(-3, OUT_OF_RANGE, self.nodes[2].sendtoaddress, address=address, amount=1.0, fee_rate=-1)
+            # Test type error.
+            for invalid_value in [True, {"foo": "bar"}]:
+                assert_raises_rpc_error(-3, NOT_A_NUMBER_OR_STRING, self.nodes[2].sendtoaddress, address=address, amount=1.0, fee_rate=invalid_value)
 
             self.log.info("Test sendtoaddress raises if an invalid conf_target or estimate_mode is passed")
             for target, mode in product([-1, 0, 1009], ["economical", "conservative"]):
diff --git a/test/functional/wallet_bumpfee.py b/test/functional/wallet_bumpfee.py
index 0d1b6c54ce..ff5070c1fa 100755
--- a/test/functional/wallet_bumpfee.py
+++ b/test/functional/wallet_bumpfee.py
@@ -110,13 +110,24 @@ class BumpFeeTest(BitcoinTestFramework):
         assert_raises_rpc_error(-8, "Insufficient total fee 0.00000141", rbf_node.bumpfee, rbfid, {"fee_rate": INSUFFICIENT})
 
         self.log.info("Test invalid fee rate settings")
-        assert_raises_rpc_error(-8, "Insufficient total fee 0.00", rbf_node.bumpfee, rbfid, {"fee_rate": 0})
         assert_raises_rpc_error(-4, "Specified or calculated fee 0.141 is too high (cannot be higher than -maxtxfee 0.10",
             rbf_node.bumpfee, rbfid, {"fee_rate": TOO_HIGH})
+        # Test fee_rate with zero values.
+        msg = "Insufficient total fee 0.00"
+        for zero_value in [0, 0.000, 0.00000000, "0", "0.000", "0.00000000"]:
+            assert_raises_rpc_error(-8, msg, rbf_node.bumpfee, rbfid, {"fee_rate": zero_value})
+        msg = "Invalid amount"
+        # Test fee_rate values that don't pass fixed-point parsing checks.
+        for invalid_value in ["", 0.000000001, 1e-09, 1.111111111, 1111111111111111, "31.999999999999999999999"]:
+            assert_raises_rpc_error(-3, msg, rbf_node.bumpfee, rbfid, {"fee_rate": invalid_value})
+        # Test fee_rate values that cannot be represented in sat/vB.
+        for invalid_value in [0.0001, 0.00000001, 0.00099999, 31.99999999, "0.0001", "0.00000001", "0.00099999", "31.99999999"]:
+            assert_raises_rpc_error(-3, msg, rbf_node.bumpfee, rbfid, {"fee_rate": invalid_value})
+        # Test fee_rate out of range (negative number).
         assert_raises_rpc_error(-3, "Amount out of range", rbf_node.bumpfee, rbfid, {"fee_rate": -1})
+        # Test type error.
         for value in [{"foo": "bar"}, True]:
             assert_raises_rpc_error(-3, "Amount is not a number or string", rbf_node.bumpfee, rbfid, {"fee_rate": value})
-        assert_raises_rpc_error(-3, "Invalid amount", rbf_node.bumpfee, rbfid, {"fee_rate": ""})
 
         self.log.info("Test explicit fee rate raises RPC error if both fee_rate and conf_target are passed")
         assert_raises_rpc_error(-8, "Cannot specify both conf_target and fee_rate. Please provide either a confirmation "
diff --git a/test/functional/wallet_send.py b/test/functional/wallet_send.py
index 53553dcd80..e061fa952c 100755
--- a/test/functional/wallet_send.py
+++ b/test/functional/wallet_send.py
@@ -343,22 +343,41 @@ class WalletSendTest(BitcoinTestFramework):
             self.test_send(from_wallet=w0, to_wallet=w1, amount=1, arg_conf_target=0.1, arg_estimate_mode=mode, expect_error=(-8, msg))
             assert_raises_rpc_error(-8, msg, w0.send, {w1.getnewaddress(): 1}, 0.1, mode)
 
-        for mode in ["economical", "conservative", "btc/kb", "sat/b"]:
-            self.log.debug("{}".format(mode))
-            for k, v in {"string": "true", "object": {"foo": "bar"}}.items():
+        for mode in ["economical", "conservative"]:
+            for k, v in {"string": "true", "bool": True, "object": {"foo": "bar"}}.items():
                 self.test_send(from_wallet=w0, to_wallet=w1, amount=1, conf_target=v, estimate_mode=mode,
-                    expect_error=(-3, "Expected type number for conf_target, got {}".format(k)))
+                    expect_error=(-3, f"Expected type number for conf_target, got {k}"))
 
-        # Test setting explicit fee rate just below the minimum and at zero.
+        # Test setting explicit fee rate just below the minimum of 1 sat/vB.
         self.log.info("Explicit fee rate raises RPC error 'fee rate too low' if fee_rate of 0.99999999 is passed")
-        self.test_send(from_wallet=w0, to_wallet=w1, amount=1, fee_rate=0.99999999,
-            expect_error=(-4, "Fee rate (0.999 sat/vB) is lower than the minimum fee rate setting (1.000 sat/vB)"))
-        self.test_send(from_wallet=w0, to_wallet=w1, amount=1, arg_fee_rate=0.99999999,
-            expect_error=(-4, "Fee rate (0.999 sat/vB) is lower than the minimum fee rate setting (1.000 sat/vB)"))
-        self.test_send(from_wallet=w0, to_wallet=w1, amount=1, fee_rate=0,
-            expect_error=(-4, "Fee rate (0.000 sat/vB) is lower than the minimum fee rate setting (1.000 sat/vB)"))
-        self.test_send(from_wallet=w0, to_wallet=w1, amount=1, arg_fee_rate=0,
-            expect_error=(-4, "Fee rate (0.000 sat/vB) is lower than the minimum fee rate setting (1.000 sat/vB)"))
+        msg = "Fee rate (0.999 sat/vB) is lower than the minimum fee rate setting (1.000 sat/vB)"
+        self.test_send(from_wallet=w0, to_wallet=w1, amount=1, fee_rate=0.999, expect_error=(-4, msg))
+        self.test_send(from_wallet=w0, to_wallet=w1, amount=1, arg_fee_rate=0.999, expect_error=(-4, msg))
+
+        self.log.info("Explicit fee rate raises if invalid fee_rate is passed")
+        # Test fee_rate with zero values.
+        msg = "Fee rate (0.000 sat/vB) is lower than the minimum fee rate setting (1.000 sat/vB)"
+        for zero_value in [0, 0.000, 0.00000000, "0", "0.000", "0.00000000"]:
+            self.test_send(from_wallet=w0, to_wallet=w1, amount=1, fee_rate=zero_value, expect_error=(-4, msg))
+            self.test_send(from_wallet=w0, to_wallet=w1, amount=1, arg_fee_rate=zero_value, expect_error=(-4, msg))
+        msg = "Invalid amount"
+        # Test fee_rate values that don't pass fixed-point parsing checks.
+        for invalid_value in ["", 0.000000001, 1e-09, 1.111111111, 1111111111111111, "31.999999999999999999999"]:
+            self.test_send(from_wallet=w0, to_wallet=w1, amount=1, fee_rate=invalid_value, expect_error=(-3, msg))
+            self.test_send(from_wallet=w0, to_wallet=w1, amount=1, arg_fee_rate=invalid_value, expect_error=(-3, msg))
+        # Test fee_rate values that cannot be represented in sat/vB.
+        for invalid_value in [0.0001, 0.00000001, 0.00099999, 31.99999999, "0.0001", "0.00000001", "0.00099999", "31.99999999"]:
+            self.test_send(from_wallet=w0, to_wallet=w1, amount=1, fee_rate=invalid_value, expect_error=(-3, msg))
+            self.test_send(from_wallet=w0, to_wallet=w1, amount=1, arg_fee_rate=invalid_value, expect_error=(-3, msg))
+        # Test fee_rate out of range (negative number).
+        msg = "Amount out of range"
+        self.test_send(from_wallet=w0, to_wallet=w1, amount=1, fee_rate=-1, expect_error=(-3, msg))
+        self.test_send(from_wallet=w0, to_wallet=w1, amount=1, arg_fee_rate=-1, expect_error=(-3, msg))
+        # Test type error.
+        msg = "Amount is not a number or string"
+        for invalid_value in [True, {"foo": "bar"}]:
+            self.test_send(from_wallet=w0, to_wallet=w1, amount=1, fee_rate=invalid_value, expect_error=(-3, msg))
+            self.test_send(from_wallet=w0, to_wallet=w1, amount=1, arg_fee_rate=invalid_value, expect_error=(-3, msg))
 
         # TODO: Return hex if fee rate is below -maxmempool
         # res = self.test_send(from_wallet=w0, to_wallet=w1, amount=1, conf_target=0.1, estimate_mode="sat/b", add_to_wallet=False)