Enhance spender queries.

include/bitcoin/database/impl/query/consensus.ipp

@@ -176,6 +176,13 @@ code CLASS::unspent_duplicates(const header_link& link,
 // unspendable
 // ----------------------------------------------------------------------------
 
+TEMPLATE
+bool CLASS::is_strong(const tx_link& tx) const NOEXCEPT
+{
+    // Try all txs with same hash as self (any instance will suffice).
+    return !to_strong(get_tx_key(tx)).is_terminal();
+}
+
 // protected
 TEMPLATE
 error::error_t CLASS::unspendable(uint32_t sequence, bool coinbase,
@@ -184,14 +191,10 @@ error::error_t CLASS::unspendable(uint32_t sequence, bool coinbase,
     // Ensure prevout tx is in a strong block, first try self link.
     auto strong = to_block(tx);
 
-    // Extremely rare, normally implies a duplicate tx.
-    if (strong.is_terminal())
-    {
-        // Try all txs with same hash as self (any instance will suffice).
-        strong = to_strong(get_tx_key(tx));
-        if (strong.is_terminal())
-            return error::unconfirmed_spend;
-    }
+    // Unassociated to block is rare, generally implies a duplicate tx.
+    // Not strong (in any block) implies the spend is not confirmed.
+    if (strong.is_terminal() && !is_strong(tx))
+        return error::unconfirmed_spend;
 
     const auto relative = ctx.is_enabled(system::chain::flags::bip68_rule) &&
         transaction::is_relative_locktime_applied(coinbase, version, sequence);

include/bitcoin/database/impl/query/objects.ipp

@@ -304,6 +304,17 @@ typename CLASS::output::cptr CLASS::get_output(
     return out.output;
 }
 
+TEMPLATE
+typename CLASS::point CLASS::get_spender(const point_link& link) const NOEXCEPT
+{
+    if (const auto tx = to_spending_tx(link); !tx.is_terminal())
+        if (const auto index = to_input_index(tx, link);
+            index != point::null_index)
+            return { get_tx_key(tx), index };
+
+    return {};
+}
+
 TEMPLATE
 typename CLASS::inputs_ptr CLASS::get_spenders(
     const output_link& link, bool witness) const NOEXCEPT

include/bitcoin/database/impl/query/translate.ipp

@@ -187,7 +187,7 @@ header_link CLASS::to_strong(const hash_digest& tx_hash) const NOEXCEPT
         txs.push_back(*it);
 
     // Find the first strong tx of the set and return its block.
-    for (auto tx: txs)
+    for (const auto& tx: txs)
     {
         const auto block = to_block(tx);
         if (!block.is_terminal())
@@ -222,9 +222,13 @@ header_link CLASS::to_confirmed_block(
 }
 
 TEMPLATE
-point_link CLASS::to_confirmed_spender(const point&) const NOEXCEPT
+point_link CLASS::to_confirmed_spender(const point& prevout) const NOEXCEPT
 {
-    // TODO: implement.
+    // see is_spent_output().
+    for (const auto& in: to_spenders(prevout))
+        if (is_confirmed_input(in))
+            return in;
+
     return {};
 }
 
@@ -261,20 +265,6 @@ uint32_t CLASS::to_output_index(const tx_link& parent_fk,
     return point::null_index;
 }
 
-// Assumes singular which doesn't make sense.
-// protected/to_spenders
-////TEMPLATE
-////spend_link CLASS::to_spender(const tx_link& link,
-////    const spend_key& point) const NOEXCEPT
-////{
-////    table::spend::get_key spend{};
-////    for (const auto& spend_fk: to_spends(link))
-////        if (store_.spend.get(spend_fk, spend) && (spend.key == point))
-////            return spend_fk;
-////
-////    return {};
-////}
-
 TEMPLATE
 point_links CLASS::to_spenders(const output_link& link) const NOEXCEPT
 {
@@ -286,12 +276,6 @@ point_links CLASS::to_spenders(const output_link& link) const NOEXCEPT
     return to_spenders(out.parent_fk, to_output_index(out.parent_fk, link));
 }
 
-TEMPLATE
-point_links CLASS::to_spenders(const point& point) const NOEXCEPT
-{
-    return to_spenders(point.hash(), point.index());
-}
-
 TEMPLATE
 point_links CLASS::to_spenders(const tx_link& output_tx,
     uint32_t output_index) const NOEXCEPT
@@ -302,13 +286,19 @@ point_links CLASS::to_spenders(const tx_link& output_tx,
 TEMPLATE
 point_links CLASS::to_spenders(const hash_digest& point_hash,
     uint32_t output_index) const NOEXCEPT
+{
+    return to_spenders({ point_hash, output_index });
+}
+
+TEMPLATE
+point_links CLASS::to_spenders(const point& point) const NOEXCEPT
 {
     // Avoid returning spend links for coinbase inputs (not spenders).
-    if (output_index == point::null_index)
+    if (point.index() == point::null_index)
         return {};
 
     point_links points{};
-    for (auto it = store_.point.it({ point_hash, output_index }); it; ++it)
+    for (auto it = store_.point.it(point); it; ++it)
         points.push_back(*it);
 
     return points;

include/bitcoin/database/query.hpp

@@ -397,6 +397,7 @@ class query
     script::cptr get_output_script(const output_link& link) const NOEXCEPT;
     output::cptr get_output(const output_link& link) const NOEXCEPT;
     output::cptr get_output(const tx_link& link, uint32_t index) const NOEXCEPT;
+    point get_spender(const point_link& link) const NOEXCEPT;
     inputs_ptr get_spenders(const output_link& link,
         bool witness) const NOEXCEPT;
 
@@ -524,6 +525,7 @@ class query
     code block_confirmable(const header_link& link) const NOEXCEPT;
     bool is_prevouts_cached(const header_link& link) const NOEXCEPT;
 
+    bool is_strong(const tx_link& link) const NOEXCEPT;
     bool set_strong(const header_link& link) NOEXCEPT;
     bool set_unstrong(const header_link& link) NOEXCEPT;
     bool set_prevouts(const header_link& link, const block& block) NOEXCEPT;