From f01568c85a4fb1cb508fb2dae6ccb4fce8f982b0 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Tam=C3=A1s=20Blummer?= <tamas.blummer@gmail.com>
Date: Fri, 23 Aug 2019 18:49:31 +0200
Subject: [PATCH] use lambda instead of a hash map to find spent outputs (#319)

* use lambda instead of a hash map to find spent outputs
* check for double use of an input
---
 src/blockdata/script.rs      | 13 ++++-------
 src/blockdata/transaction.rs | 45 ++++++++++++++++++++++++++----------
 2 files changed, 37 insertions(+), 21 deletions(-)

diff --git a/src/blockdata/script.rs b/src/blockdata/script.rs
index ab688071..11a79e0a 100644
--- a/src/blockdata/script.rs
+++ b/src/blockdata/script.rs
@@ -34,7 +34,7 @@ use consensus::{encode, Decodable, Encodable};
 use hashes::{hash160, sha256, Hash};
 #[cfg(feature="bitcoinconsensus")] use bitcoinconsensus;
 #[cfg(feature="bitcoinconsensus")] use std::convert;
-#[cfg(feature="bitcoinconsensus")] use hashes::sha256d;
+#[cfg(feature="bitcoinconsensus")] use OutPoint;
 
 use util::key::PublicKey;
 
@@ -95,11 +95,8 @@ pub enum Error {
     /// Error validating the script with bitcoinconsensus library
     BitcoinConsensus(bitcoinconsensus::Error),
     #[cfg(feature="bitcoinconsensus")]
-    /// Can not find the spent transaction
-    UnknownSpentTransaction(sha256d::Hash),
-    #[cfg(feature="bitcoinconsensus")]
-    /// The spent transaction does not have the referred output
-    WrongSpentOutputIndex(usize),
+    /// Can not find the spent output
+    UnknownSpentOutput(OutPoint),
     #[cfg(feature="bitcoinconsensus")]
     /// Can not serialize the spending transaction
     SerializationError
@@ -122,9 +119,7 @@ impl error::Error for Error {
             #[cfg(feature="bitcoinconsensus")]
             Error::BitcoinConsensus(ref _n) => "bitcoinconsensus verification failed",
             #[cfg(feature="bitcoinconsensus")]
-            Error::UnknownSpentTransaction (ref _hash) => "unknown transaction referred in Transaction::verify()",
-            #[cfg(feature="bitcoinconsensus")]
-            Error::WrongSpentOutputIndex(ref _ix) => "unknown output index {} referred in Transaction::verify()",
+            Error::UnknownSpentOutput(ref _point) => "unknown spent output Transaction::verify()",
             #[cfg(feature="bitcoinconsensus")]
             Error::SerializationError => "can not serialize the spending transaction in Transaction::verify()",
         }
diff --git a/src/blockdata/transaction.rs b/src/blockdata/transaction.rs
index 19a2124c..f6e759f5 100644
--- a/src/blockdata/transaction.rs
+++ b/src/blockdata/transaction.rs
@@ -26,7 +26,6 @@
 use byteorder::{LittleEndian, WriteBytesExt};
 use std::default::Default;
 use std::{fmt, io};
-#[cfg(feature="bitcoinconsensus")] use std::collections::HashMap;
 
 use hashes::{self, sha256d, Hash};
 use hashes::hex::FromHex;
@@ -406,18 +405,16 @@ impl Transaction {
     }
 
     #[cfg(feature="bitcoinconsensus")]
-    /// Verify that this transaction is able to spend some outputs of spent transactions
-    pub fn verify(&self, spent: &HashMap<sha256d::Hash, Transaction>) -> Result<(), script::Error> {
+    /// Verify that this transaction is able to spend its inputs
+    /// The lambda spent should not return the same TxOut twice!
+    pub fn verify<S>(&self, mut spent: S) -> Result<(), script::Error>
+        where S: FnMut(&OutPoint) -> Option<TxOut> {
         let tx = serialize(&*self);
         for (idx, input) in self.input.iter().enumerate() {
-            if let Some(ref s) = spent.get(&input.previous_output.txid) {
-                if let Some(ref output) = s.output.get(input.previous_output.vout as usize) {
-                    output.script_pubkey.verify(idx, output.value, tx.as_slice())?;
-                } else {
-                    return Err(script::Error::WrongSpentOutputIndex(input.previous_output.vout as usize));
-                }
+            if let Some(output) = spent(&input.previous_output) {
+                output.script_pubkey.verify(idx, output.value, tx.as_slice())?;
             } else {
-                return Err(script::Error::UnknownSpentTransaction(input.previous_output.txid));
+                return Err(script::Error::UnknownSpentOutput(input.previous_output.clone()));
             }
         }
         Ok(())
@@ -1130,12 +1127,36 @@ mod tests {
         spent.insert(spent1.txid(), spent1);
         spent.insert(spent2.txid(), spent2);
         spent.insert(spent3.txid(), spent3);
+        let mut spent2 = spent.clone();
+        let mut spent3 = spent.clone();
 
-        spending.verify(&spent).unwrap();
+        spending.verify(|point: &OutPoint| {
+            if let Some(tx) = spent.remove(&point.txid) {
+                return tx.output.get(point.vout as usize).cloned();
+            }
+            None
+        }).unwrap();
+
+        // test that we fail with repeated use of same input
+        let mut double_spending = spending.clone();
+        let re_use = double_spending.input[0].clone();
+        double_spending.input.push (re_use);
+
+        assert!(double_spending.verify(|point: &OutPoint| {
+            if let Some(tx) = spent2.remove(&point.txid) {
+                return tx.output.get(point.vout as usize).cloned();
+            }
+            None
+        }).is_err());
 
         // test that we get a failure if we corrupt a signature
         spending.input[1].witness[0][10] = 42;
-        match spending.verify(&spent).err().unwrap() {
+        match spending.verify(|point: &OutPoint| {
+            if let Some(tx) = spent3.remove(&point.txid) {
+                return tx.output.get(point.vout as usize).cloned();
+            }
+            None
+        }).err().unwrap() {
             script::Error::BitcoinConsensus(_) => {},
             _ => panic!("Wrong error type"),
         }