text: /*
   * This file is open source software, licensed to you under the terms
   * of the Apache License, Version 2.0 (the "License").  See the NOTICE file
   * distributed with this work for additional information regarding copyright
   * ownership.  You may not use this file except in compliance with the License.
   *
   * You may obtain a copy of the License at
   *
   *   http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing,
   * software distributed under the License is distributed on an
   * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
   * KIND, either express or implied.  See the License for the
   * specific language governing permissions and limitations
   * under the License.
   */
  /*
   * Copyright (C) 2014 Cloudius Systems, Ltd.
   */
  
  #pragma once
  
  #include <seastar/core/sstring.hh>
  #include <seastar/core/temporary_buffer.hh>
  #include <seastar/util/eclipse.hh>
  #include <algorithm>
  #include <memory>
  #include <cassert>
  #include <seastar/util/std-compat.hh>
  #include <seastar/core/future.hh>
  
  namespace seastar {
  
  // Support classes for Ragel parsers
  
  // Builds an sstring that can be scattered across multiple packets.
  //
  // Use a sstring_build::guard variable to designate each scattered
  // char array, and call mark_start() and mark_end() at the start
  // and end points, respectively.  sstring_builder will collect data
  // from intervening segments, if needed.
  //
  // After mark_end() has been called, use the get() method to obtain
  // the built string.
  //
  // FIXME: switch to string_view.
  //
  class sstring_builder {
      sstring _value;
      const char* _start = nullptr;
  public:
      class guard;
  public:
      sstring get() && {
          return std::move(_value);
      }
      void reset() {
          _value = {};
          _start = nullptr;
      }
      friend class guard;
  };
  
  class sstring_builder::guard {
      sstring_builder& _builder;
      const char* _block_end;
  public:
      guard(sstring_builder& builder, const char* block_start, const char* block_end)
          : _builder(builder), _block_end(block_end) {
          if (!_builder._value.empty()) {
              mark_start(block_start);
          }
      }
      ~guard() {
          if (_builder._start) {
              mark_end(_block_end);
          }
      }
      void mark_start(const char* p) {
          _builder._start = p;
      }
      void mark_end(const char* p) {
          if (_builder._value.empty()) {
              // avoid an allocation in the common case
              _builder._value = sstring(_builder._start, p);
          } else {
              _builder._value += sstring(_builder._start, p);
          }
          _builder._start = nullptr;
      }
  };
  
  
  // CRTP
  template <typename ConcreteParser>
  class ragel_parser_base {
  protected:
      int _fsm_cs;
      std::unique_ptr<int[]> _fsm_stack = nullptr;
      int _fsm_stack_size = 0;
      int _fsm_top;
      int _fsm_act;
      char* _fsm_ts;
      char* _fsm_te;
      sstring_builder _builder;
  protected:
      void init_base() {
          _builder.reset();
      }
      void prepush() {
          if (_fsm_top == _fsm_stack_size) {
              auto old = _fsm_stack_size;
              _fsm_stack_size = std::max(_fsm_stack_size * 2, 16);
              assert(_fsm_stack_size > old);
              std::unique_ptr<int[]> new_stack{new int[_fsm_stack_size]};
              std::copy(_fsm_stack.get(), _fsm_stack.get() + _fsm_top, new_stack.get());
              std::swap(_fsm_stack, new_stack);
          }
      }
      void postpop() {}
      sstring get_str() {
          return std::move(_builder).get();
      }
  public:
      using unconsumed_remainder = compat::optional<temporary_buffer<char>>;
      future<unconsumed_remainder> operator()(temporary_buffer<char> buf) {
          char* p = buf.get_write();
          char* pe = p + buf.size();
          char* eof = buf.empty() ? pe : nullptr;
          char* parsed = static_cast<ConcreteParser*>(this)->parse(p, pe, eof);
          if (parsed) {
              buf.trim_front(parsed - p);
              return make_ready_future<unconsumed_remainder>(std::move(buf));
          }
          return make_ready_future<unconsumed_remainder>();
      }
  };
  
  }
  