Merge pull request #780 from evoskuil/master

Emit "stripped" field on native configuration method.

Author: evoskuil

include/bitcoin/server/protocols/protocol_native.hpp

@@ -251,6 +251,9 @@ class BCS_API protocol_native
     // Utilities.
     // ------------------------------------------------------------------------
 
+    size_t get_stripped_height() NOEXCEPT;
+    size_t get_active_height(const system::hash_digest& hash) NOEXCEPT;
+
     void inject(boost::json::value& out, std::optional<uint32_t> height,
         const database::header_link& link) const NOEXCEPT;
 

src/protocols/native/protocol_native_configuration.cpp

@@ -50,6 +50,7 @@ bool protocol_native::handle_get_configuration(const code& ec,
         { "witness", network_settings().witness_node() },
         { "retarget", system_settings().forks.retarget },
         { "difficult", system_settings().forks.difficult },
+        { "stripped", get_stripped_height() },
     };
     BC_POP_WARNING()
 
@@ -101,5 +102,40 @@ bool protocol_native::handle_get_event_subscribe(const code& ec,
     return true;
 }
 
+// utility
+// ----------------------------------------------------------------------------
+
+size_t protocol_native::get_stripped_height() NOEXCEPT
+{
+    if (!network_settings().pruned_node() ||
+        !network_settings().witness_node())
+        return {};
+
+    const auto& system_ = system_settings();
+    const auto milestone = get_active_height(system_.milestone.hash());
+    const auto checkpoint = get_active_height(system_.top_checkpoint().hash());
+    return std::max(milestone, checkpoint);
+}
+
+size_t protocol_native::get_active_height(
+    const system::hash_digest& hash) NOEXCEPT
+{
+    const auto& query = archive();
+    const auto link = query.to_header(hash);
+    system::chain::context ctx{};
+
+    // This uses candidate header vs. confirmed block so that stripping will
+    // show at heights below top checkpoint and milestone while still syncing.
+    // This can result in a weak branch milestone block implying a pruned
+    // height that doesn't confirm (ok), which can't happen for checkpoints.
+    // This can be mitigated by setting stripped on the object when it's a
+    // milestone or checked object and pruning is enabled. Pruning can be
+    // enabled after storage of non-stripped blocks, which does not strip them.
+    // This will return false is bip141 is not active by the milestone.
+    return query.get_context(ctx, link) && 
+        ctx.is_enabled(system::chain::bip141_rule) && 
+        query.is_candidate_header(link) ? ctx.height : zero;
+}
+
 } // namespace server
 } // namespace libbitcoin