vanilla implementation of sequencer for protocol lib

include/emlabcpp/protocol/sequencer.h

+#include "emlabcpp/assert.h"
+#include "emlabcpp/either.h"
+#include "emlabcpp/static_circular_buffer.h"
+
+#include <array>
+
+#pragma once
+
+namespace emlabcpp
+{
+
+template < typename Def >
+class protocol_sequencer
+{
+public:
+        static constexpr auto        prefix     = Def::prefix;
+        static constexpr std::size_t fixed_size = Def::fixed_size;
+
+private:
+        static_circular_buffer< uint8_t, Def::buffer_size > buffer_;
+
+public:
+        using message_type = typename Def::message_type;
+
+        template < typename Iterator >
+        either< std::size_t, message_type > load_data( view< Iterator > dview )
+        {
+                std::copy( dview.begin(), dview.end(), std::back_inserter( buffer_ ) );
+
+                while ( !buffer_.empty() ) {
+                        auto [piter, biter] = std::mismatch(
+                            prefix.begin(), prefix.end(), buffer_.begin(), buffer_.end() );
+
+                        // not match, remove one byte from buffer
+                        if ( biter == buffer_.begin() ) {
+                                buffer_.pop_front();
+                                continue;
+                        }
+
+                        // partial match - more bytes could be matched
+                        if ( piter != prefix.end() && biter != buffer_.end() ) {
+                                buffer_.pop_front();
+                                continue;
+                        }
+
+                        // partial match - matched maximum bytes available
+                        if ( piter != prefix.end() ) {
+                                return fixed_size - std::distance( prefix.begin(), piter );
+                        }
+
+                        break;
+                }
+
+                if ( buffer_.empty() ) {
+                        return fixed_size;
+                }
+
+                // This is implied by the fact that we should have full match at the start of buffer
+                EMLABCPP_ASSERT( buffer_.size() >= prefix.size() );
+
+                if ( buffer_.size() < fixed_size ) {
+                        return fixed_size - buffer_.size();
+                }
+
+                std::size_t desired_size = Def::get_size( buffer_ );
+                if ( buffer_.size() < desired_size ) {
+                        return desired_size - buffer_.size();
+                }
+
+                auto opt_msg = message_type::make( view_n( buffer_.begin(), desired_size ) );
+                EMLABCPP_ASSERT( opt_msg );
+
+                // clean up only the matched message
+                for ( std::size_t i = desired_size; i > 0; i-- ) {
+                        buffer_.pop_front();
+                }
+
+                return *opt_msg;
+        }
+};
+
+}  // namespace emlabcpp