http_query.h

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// Copyright (c) Microsoft Corporation. All rights reserved.
// Licensed under the Apache 2.0 License.
#pragma once
 
#include "ccf/ds/nonstd.h"
 
#define FMT_HEADER_ONLY
#include <charconv>
#include <fmt/format.h>
#include <map>
#include <optional>
#include <string_view>
 
namespace ccf::http
{
  // Query is parsed into a multimap, so that duplicate keys are retained.
  // Handling of duplicates (or ignoring them entirely) is left to the caller.
  // Keys and values are both string_views, pointing at subranges of original
  // query string.
  using ParsedQuery = std::multimap<std::string_view, std::string_view>;
 
  static ParsedQuery parse_query(const std::string_view& query)
  {
    ParsedQuery parsed;
    const auto params = ccf::nonstd::split(query, "&");
    for (const auto& param : params)
    {
      // NB: This means both `foo=` and `foo` will be accepted and result in a
      // `{"foo": ""}` in the map
      const auto& [key, value] = ccf::nonstd::split_1(param, "=");
      parsed.emplace(key, value);
    }
 
    return parsed;
  }
 
  template <typename T>
  static bool get_query_value(
    const ParsedQuery& pq,
    const std::string_view& param_key,
    T& val,
    std::string& error_reason)
  {
    const auto it = pq.find(param_key);
 
    if (it == pq.end())
    {
      error_reason = fmt::format("Missing query parameter '{}'", param_key);
      return false;
    }
 
    const std::string_view& param_val = it->second;
 
    if constexpr (std::is_same_v<T, std::string>)
    {
      val = T(param_val);
      return true;
    }
    else if constexpr (std::is_integral_v<T>)
    {
      const auto [p, ec] =
        std::from_chars(param_val.begin(), param_val.end(), val);
      if (ec != std::errc() || p != param_val.end())
      {
        error_reason = fmt::format(
          "Unable to parse value '{}' in parameter '{}'", param_val, param_key);
        return false;
      }
 
      return true;
    }
    else
    {
      static_assert(ccf::nonstd::dependent_false<T>::value, "Unsupported type");
      return false;
    }
  }
 
  template <typename T>
  static std::optional<T> get_query_value_opt(
    const ParsedQuery& pq,
    const std::string_view& param_key,
    std::string& error_reason)
  {
    T val;
    if (get_query_value(pq, param_key, val, error_reason))
    {
      return val;
    }
    else
    {
      return std::nullopt;
    }
  }
}