http_etag.h

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// Copyright (c) Microsoft Corporation. All rights reserved.
// Licensed under the Apache 2.0 License.
#pragma once
 
#define FMT_HEADER_ONLY
#include <exception>
#include <regex>
#include <set>
#include <string>
 
namespace ccf::http
{
  class MatcherError : public std::exception
  {
  private:
    std::string msg;
 
  public:
    MatcherError(std::string msg_) : msg(std::move(msg_)) {}
 
    [[nodiscard]] const char* what() const noexcept override
    {
      return msg.c_str();
    }
  };
 
  class Matcher
  {
  private:
    bool any_value = false;
    std::set<std::string> if_etags;
 
  public:
    Matcher(const std::string& match_header)
    {
      if (match_header == "*")
      {
        any_value = true;
        return;
      }
 
      std::regex etag_rx(R"(\"([^\"]+)\",?\s*)");
      auto etags_begin =
        std::sregex_iterator(match_header.begin(), match_header.end(), etag_rx);
      auto etags_end = std::sregex_iterator();
      ssize_t last_matched = 0;
 
      for (std::sregex_iterator i = etags_begin; i != etags_end; ++i)
      {
        if (i->position() != last_matched)
        {
          throw MatcherError("Invalid If-Match header");
        }
        const std::smatch& match = *i;
        if_etags.insert(match[1].str());
        last_matched = match.position() + match.length();
      }
 
      ssize_t last_index_in_header = match_header.size();
 
      if (last_matched != last_index_in_header || if_etags.empty())
      {
        throw MatcherError("Invalid If-Match header");
      }
    }
 
    [[nodiscard]] bool matches(const std::string& etag) const
    {
      return any_value || if_etags.contains(etag);
    }
 
    [[nodiscard]] bool is_any() const
    {
      return any_value;
    }
  };
}