fix: Make TxidFromString() respect string_view length

Prior to this, passing string_view::data() into uint256S() meant the latter would only receive the a naked char* pointer and potentially scan past the string_view::length() until it found a null terminator (or some other non-hex character).

Appears to have been a fully dormant bug as callers were either passing a string literal or std::string directly to TxidFromFromString(), meaning null terminator always existed at pointer[length()]. Bug existed since original merge of TxidFromString(), discussed in bitcoin#28922 (comment).

Author: hodlinator

src/test/transaction_tests.cpp

@@ -1030,10 +1030,10 @@ BOOST_AUTO_TEST_CASE(test_IsStandard)
 
 BOOST_AUTO_TEST_CASE(test_TxidFromString)
 {
-    // TxidFromString currently ignores string_view length and reads the whole
-    // string, not the specified substring.
+    // Make sure TxidFromString respects string_view length and stops reading at
+    // end of the substring.
     BOOST_CHECK_EQUAL(TxidFromString(std::string_view("ABCD1234", 4)).ToString(),
-        "00000000000000000000000000000000000000000000000000000000abcd1234");
+        "000000000000000000000000000000000000000000000000000000000000abcd");
 }
 
 BOOST_AUTO_TEST_SUITE_END()

src/test/txpackage_tests.cpp

@@ -47,7 +47,7 @@ inline CTransactionRef create_placeholder_tx(size_t num_inputs, size_t num_outpu
 // Create a Wtxid from a hex string
 inline Wtxid WtxidFromString(std::string_view str)
 {
-    return Wtxid::FromUint256(uint256S(str.data()));
+    return Wtxid::FromUint256(uint256S(str));
 }
 
 BOOST_FIXTURE_TEST_CASE(package_hash_tests, TestChain100Setup)

src/util/transaction_identifier.h

@@ -68,7 +68,7 @@ using Wtxid = transaction_identifier<true>;
 
 inline Txid TxidFromString(std::string_view str)
 {
-    return Txid::FromUint256(uint256S(str.data()));
+    return Txid::FromUint256(uint256S(str));
 }
 
 #endif // BITCOIN_UTIL_TRANSACTION_IDENTIFIER_H