ZeroTierOne/ext/prometheus-cpp-lite-1.0/core/include/prometheus/text_serializer.h

#pragma once

#include <iosfwd>
#include <vector>
#include <array>
#include <math.h>
#include <ostream>

#include "prometheus/metric_family.h"

#if __cpp_lib_to_chars >= 201611L
  #include <charconv>
#endif

namespace prometheus {

class TextSerializer {

  // Write a double as a string, with proper formatting for infinity and NaN
  static void WriteValue (std::ostream& out, double value) {
    if (std::isnan(value))
      out << "Nan";
    else if (std::isinf(value))
      out << (value < 0 ? "-Inf" : "+Inf");

    else {

      std::array<char, 128> buffer;

#if __cpp_lib_to_chars >= 201611L
      auto [ptr, ec] = std::to_chars(buffer.data(), buffer.data() + buffer.size(), value);
      if (ec != std::errc()) {
        throw std::runtime_error("Could not convert double to string: " +
          std::make_error_code(ec).message());
      }
      out.write(buffer.data(), ptr - buffer.data());
#else
      int wouldHaveWritten = std::snprintf(buffer.data(), buffer.size(), "%.*g", std::numeric_limits<double>::max_digits10 - 1, value);
      if (wouldHaveWritten <= 0 || static_cast<std::size_t>(wouldHaveWritten) >= buffer.size()) {
        throw std::runtime_error("Could not convert double to string");
      }
      out.write(buffer.data(), wouldHaveWritten);
#endif

    }
  }

  static void WriteValue(std::ostream& out, const std::string& value) {
    for (auto c : value) {
      switch (c) {
        case '\n': out << '\\' << 'n'; break;
        case '\\': out << '\\' << c;   break;
        case '"':  out << '\\' << c;   break;
        default:   out << c;           break;
      }
    }
  }

  // Write a line header: metric name and labels
  template <typename T = std::string>
  static void WriteHead(
    std::ostream& out,
    const MetricFamily& family,
    const ClientMetric& metric,
    const std::string&  suffix = "",
    const std::string&  extraLabelName = "",
    const T&            extraLabelValue = T()) {

    out << family.name << suffix;

    if (!metric.label.empty() || !extraLabelName.empty()) {

      out << "{";
      const char* prefix = "";

      for (auto& lp : metric.label) {
        out << prefix << lp.name << "=\"";
        WriteValue(out, lp.value);
        out << "\"";
        prefix = ",";
      }
      if (!extraLabelName.empty()) {
        out << prefix << extraLabelName << "=\"";
        WriteValue(out, extraLabelValue);
        out << "\"";
      }
      out << "}";
    }
    out << " ";
  }

  // Write a line trailer: timestamp
  static void WriteTail(std::ostream& out, const ClientMetric& metric) {
    if (metric.timestamp_ms != 0) {
      out << " " << metric.timestamp_ms;
    }
    out << "\n";
  }

  static void SerializeCounter(std::ostream& out, const MetricFamily& family, const ClientMetric& metric) {
    WriteHead(out, family, metric);
    WriteValue(out, metric.counter.value);
    WriteTail(out, metric);
  }

  static void SerializeGauge(std::ostream& out, const MetricFamily& family, const ClientMetric& metric) {
    WriteHead(out, family, metric);
    WriteValue(out, metric.gauge.value);
    WriteTail(out, metric);
  }

  static void SerializeSummary(std::ostream& out, const MetricFamily& family, const ClientMetric& metric) {
    auto& sum = metric.summary;
    WriteHead(out, family, metric, "_count");
    out << sum.sample_count;
    WriteTail(out, metric);

    WriteHead(out, family, metric, "_sum");
    WriteValue(out, sum.sample_sum);
    WriteTail(out, metric);

    for (auto& q : sum.quantile) {
      WriteHead(out, family, metric, "", "quantile", q.quantile);
      WriteValue(out, q.value);
      WriteTail(out, metric);
    }
  }

  static void SerializeUntyped(std::ostream& out, const MetricFamily& family, const ClientMetric& metric) {
    WriteHead(out, family, metric);
    WriteValue(out, metric.untyped.value);
    WriteTail(out, metric);
  }

  static void SerializeHistogram(std::ostream& out, const MetricFamily& family, const ClientMetric& metric) {
    auto& hist = metric.histogram;
    WriteHead(out, family, metric, "_count");
    out << hist.sample_count;
    WriteTail(out, metric);

    WriteHead(out, family, metric, "_sum");
    WriteValue(out, hist.sample_sum);
    WriteTail(out, metric);

    double last = -std::numeric_limits<double>::infinity();
    for (auto& b : hist.bucket) {
      WriteHead(out, family, metric, "_bucket", "le", b.upper_bound);
      last = b.upper_bound;
      out << b.cumulative_count;
      WriteTail(out, metric);
    }

    if (last != std::numeric_limits<double>::infinity()) {
      WriteHead(out, family, metric, "_bucket", "le", "+Inf");
      out << hist.sample_count;
      WriteTail(out, metric);
    }
  }

  static void SerializeFamily(std::ostream& out, const MetricFamily& family) {
    if (!family.help.empty()) {
      out << "# HELP " << family.name << " " << family.help << "\n";
    }
    switch (family.type) {
    case Metric::Type::Counter:
      out << "# TYPE " << family.name << " counter\n";
      for (auto& metric : family.metric) {
        SerializeCounter(out, family, metric);
      }
      break;
    case Metric::Type::Gauge:
      out << "# TYPE " << family.name << " gauge\n";
      for (auto& metric : family.metric) {
        SerializeGauge(out, family, metric);
      }
      break;
    case Metric::Type::Summary:
      out << "# TYPE " << family.name << " summary\n";
      for (auto& metric : family.metric) {
        SerializeSummary(out, family, metric);
      }
      break;
    case Metric::Type::Untyped:
      out << "# TYPE " << family.name << " untyped\n";
      for (auto& metric : family.metric) {
        SerializeUntyped(out, family, metric);
      }
      break;
    case Metric::Type::Histogram:
      out << "# TYPE " << family.name << " histogram\n";
      for (auto& metric : family.metric) {
        SerializeHistogram(out, family, metric);
      }
      break;
    }
  }

  public:

  static void Serialize (std::ostream& out, const std::vector<MetricFamily>& metrics) {
    std::locale saved_locale = out.getloc();
    out.imbue(std::locale::classic());
    for (auto& family : metrics) {
      SerializeFamily(out, family);
    }
    out.imbue(saved_locale);
  }

};

}  // namespace prometheus