Merge pull request rust-bitcoin#616 from sgeisler/2021-06-dust-value-amount

Use `Amount` type for dust value calculation

Author: sgeisler

src/blockdata/script.rs

@@ -411,11 +411,11 @@ impl Script {
 
     /// Gets the minimum value an output with this script should have in order to be
     /// broadcastable on today's bitcoin network.
-    pub fn dust_value(&self) -> u64 {
+    pub fn dust_value(&self) -> ::Amount {
         // This must never be lower than Bitcoin Core's GetDustThreshold() (as of v0.21) as it may
         // otherwise allow users to create transactions which likely can never be
         // broadcasted/confirmed.
-        DUST_RELAY_TX_FEE as u64 / 1000 * // The default dust relay fee is 3000 satoshi/kB (ie 3 sat/vByte)
+        let sats = DUST_RELAY_TX_FEE as u64 / 1000 * // The default dust relay fee is 3000 satoshi/kB (ie 3 sat/vByte)
         if self.is_op_return() {
             0
         } else if self.is_witness_program() {
@@ -426,7 +426,9 @@ impl Script {
             32 + 4 + 1 + 107 + 4 + // The spend cost copied from Core
             8 + // The serialized size of the TxOut's amount field
             self.consensus_encode(&mut ::std::io::sink()).unwrap() as u64 // The serialized size of this script_pubkey
-        }
+        };
+
+        ::Amount::from_sat(sats)
     }
 
     /// Iterate over the script in the form of `Instruction`s, which are an enum covering
@@ -1262,7 +1264,7 @@ mod test {
         // well-known scriptPubKey types.
         let script_p2wpkh = Builder::new().push_int(0).push_slice(&[42; 20]).into_script();
         assert!(script_p2wpkh.is_v0_p2wpkh());
-        assert_eq!(script_p2wpkh.dust_value(), 294);
+        assert_eq!(script_p2wpkh.dust_value(), ::Amount::from_sat(294));
 
         let script_p2pkh = Builder::new()
             .push_opcode(opcodes::all::OP_DUP)
@@ -1272,7 +1274,7 @@ mod test {
             .push_opcode(opcodes::all::OP_CHECKSIG)
             .into_script();
         assert!(script_p2pkh.is_p2pkh());
-        assert_eq!(script_p2pkh.dust_value(), 546);
+        assert_eq!(script_p2pkh.dust_value(), ::Amount::from_sat(546));
     }
 }