Fix full duplex buffer resize interleaving.

include/bitcoin/network/impl/channels/channel_rpc.ipp

@@ -170,10 +170,10 @@ inline rpc::message_ptr<Message> CLASS::assign_message(Message&& message,
     size_t size_hint) NOEXCEPT
 {
     BC_ASSERT(stranded());
-    response_buffer_->max_size(size_hint);
     const auto ptr = system::to_shared<rpc::message_value<Message>>();
     ptr->message = std::move(message);
     ptr->buffer = response_buffer_;
+    ptr->size_hint = size_hint;
     return ptr;
 }
 

include/bitcoin/network/impl/messages/json_body.ipp

@@ -133,15 +133,20 @@ TEMPLATE
 void CLASS::writer::init(boost_code& ec) NOEXCEPT
 {
     using namespace system;
+    const auto size = is_zero(value_.size_hint) ? default_buffer :
+        value_.size_hint;
+
+    // Reuse is unsafe except for half duplex.
     if (!value_.buffer)
     {
-        // Caller controls max_size and other buffer behavior by assigning it.
-        value_.buffer = emplace_shared<http::flat_buffer>(default_buffer);
+        // Caller controls buffer lifetime by assigning it (less allocation).
+        value_.buffer = emplace_shared<http::flat_buffer>(size);
     }
     else
     {
         // Caller has assigned the buffer (or just reused the response).
         value_.buffer->consume(value_.buffer->size());
+        value_.buffer->max_size(size);
     }
 
     ec.clear();

include/bitcoin/network/messages/peer/enums/level.hpp

@@ -171,12 +171,15 @@ enum level: uint32_t
     /// send_address_v2
     bip155 = 70016,
 
-    /// wtxidrelay
-    bip339 = 70016,
-
     /// erlay [not supported]
     bip330 = 70016,
 
+    /// pkgtxns (requires wtxidrelay)
+    bip331 = 70016,
+
+    /// wtxidrelay
+    bip339 = 70016,
+
     /// -----------------------------------------------------------------------
 
     /// We require at least this of peers (for current address structure).