feat: add baggage API

BUILD.bazel

@@ -5,6 +5,7 @@ cc_library(
       "src/datadog/telemetry/metrics.cpp",
       "src/datadog/telemetry/log.h",
       "src/datadog/telemetry/telemetry.cpp",
+      "src/datadog/baggage.cpp",
       "src/datadog/base64.cpp",
       "src/datadog/cerr_logger.cpp",
       "src/datadog/clock.cpp",
@@ -78,6 +79,7 @@ cc_library(
       "src/datadog/w3c_propagation.h",
     ],
     hdrs = [
+      "include/datadog/baggage.h",
       "include/datadog/cerr_logger.h",
       "include/datadog/clock.h",
       "include/datadog/collector.h",

CMakeLists.txt

@@ -109,6 +109,7 @@ target_sources(dd_trace_cpp-objects
     src/datadog/telemetry/configuration.cpp
     src/datadog/telemetry/metrics.cpp
     src/datadog/telemetry/telemetry.cpp
+    src/datadog/baggage.cpp
     src/datadog/base64.cpp
     src/datadog/cerr_logger.cpp
     src/datadog/clock.cpp

Dockerfile

@@ -36,3 +36,5 @@ run chmod +x /tmp/install-cmake && /tmp/install-cmake && rm /tmp/install-cmake
 copy bin/install-lcov /tmp/install-lcov
 run chmod +x /tmp/install-lcov && /tmp/install-lcov && rm /tmp/install-lcov
 
+run curl -fLSs https://raw.githubusercontent.com/CircleCI-Public/circleci-cli/main/install.sh | bash
+

examples/CMakeLists.txt

@@ -1,2 +1,3 @@
+add_subdirectory(baggage)
 add_subdirectory(hasher)
 add_subdirectory(http-server)

examples/baggage/CMakeLists.txt

@@ -0,0 +1,2 @@
+add_executable(baggage-example main.cpp)
+target_link_libraries(baggage-example dd_trace_cpp-static)

examples/baggage/main.cpp

@@ -0,0 +1,95 @@
+#include <datadog/dict_reader.h>
+#include <datadog/tracer.h>
+
+#include <iostream>
+
+namespace dd = datadog::tracing;
+
+struct CinReader : public dd::DictReader {
+  std::string input;
+
+  dd::Optional<dd::StringView> lookup(dd::StringView key) const override {
+    return input;
+  }
+
+  void visit(
+      const std::function<void(dd::StringView key, dd::StringView value)>&
+          visitor) const override{};
+};
+
+std::istream& operator>>(std::istream& is, CinReader& reader) {
+  is >> reader.input;
+  return is;
+}
+
+std::ostream& operator<<(std::ostream& os, dd::Baggage::Error error) {
+  using dd::Baggage;
+  switch (error.code) {
+    case Baggage::Error::MISSING_HEADER:
+      os << "missing `baggage` header";
+      break;
+    case Baggage::Error::MALFORMED_BAGGAGE_HEADER: {
+      os << "malformed `baggage` header";
+      if (error.pos) {
+        os << " at position " << *error.pos;
+      }
+    } break;
+    case Baggage::Error::MAXIMUM_CAPACITY_REACHED:
+      os << "maximum number of bagge items reached";
+      break;
+    case Baggage::Error::MAXIMUM_BYTES_REACHED:
+      os << "maximum amount of bytes written";
+      break;
+    default:
+      os << "unknown error code";
+      break;
+  }
+  return os;
+}
+
+int main() {
+  dd::TracerConfig cfg;
+  cfg.log_on_startup = false;
+  cfg.telemetry.enabled = false;
+  cfg.agent.remote_configuration_enabled = false;
+  const auto finalized_cfg = datadog::tracing::finalize_config(cfg);
+  if (auto error = finalized_cfg.if_error()) {
+    std::cerr << "Failed to initialize the tracer: " << error->message
+              << std::endl;
+    return error->code;
+  }
+
+  dd::Tracer tracer(*finalized_cfg);
+
+  std::cout
+      << "This program demonstrates how to use baggage, a feature that allows "
+         "metadata (key-value pairs) to be attached to a request and "
+         "propagated across services.\n"
+         "Baggage can be useful for passing contextual information, such as "
+         "user IDs, session tokens, or request attributes, between different "
+         "components of a distributed system.\n\n"
+         "This example lets you input baggage values, validate them and "
+         "displays the baggage content parsed.\n"
+         "You can enter baggage manually or provide it through a file, try:\n"
+         "- k1=v1,k2=v2\n"
+         "- ,invalid=input\n"
+         "or ./baggage-example < list-of-baggages.txt\n\n";
+
+  CinReader reader;
+  std::cout << "Enter baggage (or 'CTRL+C' to quit): ";
+  while (std::getline(std::cin, reader.input)) {
+    auto baggage = tracer.extract_baggage(reader);
+    if (!baggage) {
+      std::cout << "Error parsing \"" << reader.input
+                << "\": " << baggage.error() << ".\n";
+    } else {
+      std::cout << "Baggage key-value parsed: \n";
+      baggage->visit([](dd::StringView key, dd::StringView value) {
+        std::cout << key << ": " << value << std::endl;
+      });
+    }
+
+    std::cout << "\nEnter baggage (or 'CTRL+C' to quit): ";
+  }
+  return 0;
+}

fuzz/CMakeLists.txt

@@ -1,3 +1,4 @@
 add_subdirectory(base64)
+add_subdirectory(tracing)
 add_subdirectory(w3c-propagation)
 

fuzz/tracing/CMakeLists.txt

@@ -0,0 +1,12 @@
+add_executable(baggage-fuzz baggage.cpp)
+
+add_dependencies(baggage-fuzz dd_trace_cpp-static)
+
+target_include_directories(baggage-fuzz
+  PRIVATE
+    ${CMAKE_SOURCE_DIR}/src
+)
+
+target_link_libraries(baggage-fuzz dd_trace_cpp-static)
+
+add_target_to_group(baggage-fuzz dd_trace_cpp-fuzzers)

fuzz/tracing/baggage.cpp

@@ -0,0 +1,33 @@
+#include <datadog/baggage.h>
+#include <datadog/dict_reader.h>
+#include <datadog/string_view.h>
+
+#include <cstdint>
+
+namespace dd = datadog::tracing;
+
+class MapReader : public dd::DictReader {
+  std::unordered_map<std::string, std::string> map_;
+
+ public:
+  ~MapReader() override = default;
+
+  MapReader(std::unordered_map<std::string, std::string> map)
+      : map_(std::move(map)) {}
+
+  dd::Optional<dd::StringView> lookup(dd::StringView key) const override {
+    auto it = map_.find(std::string(key));
+    if (it == map_.cend()) return dd::nullopt;
+
+    return it->second;
+  }
+
+  void visit(const std::function<void(dd::StringView key,
+                                      dd::StringView value)>&) const override{};
+};
+
+extern "C" int LLVMFuzzerTestOneInput(const std::uint8_t* data, size_t size) {
+  MapReader reader({{"baggage", std::string((const char*)data, size)}});
+  dd::Baggage::extract(reader);
+  return 0;
+}

include/datadog/baggage.h

@@ -0,0 +1,148 @@
+#pragma once
+
+#include <datadog/dict_reader.h>
+#include <datadog/dict_writer.h>
+#include <datadog/expected.h>
+#include <datadog/optional.h>
+#include <datadog/string_view.h>
+
+#include <string>
+#include <unordered_map>
+
+namespace datadog {
+namespace tracing {
+
+/// OpenTelemetry-like implementation of the Baggage concept.
+/// Baggage is a key-value store meant to propagate data across services and
+/// processes boundaries.
+///
+/// Baggage are extracted from any tracing context implementing the `DictReader`
+/// interface using `Baggage::extract`.
+///
+/// Baggages are injected to any tracing context implementing the `DictWriter`
+/// interface using the `inject` method.
+class Baggage {
+ public:
+  struct Error final {
+    enum Code : char {
+      /// Baggage propagation is disabled. This may be due to one of the
+      /// following
+      /// reasons:
+      /// - `baggage` is not set as an extraction or injection propagation
+      /// style.
+      /// - The maximum number of items is less than 0.
+      /// - The number of bytes is less than 3.
+      DISABLED,
+      MISSING_HEADER,
+      MALFORMED_BAGGAGE_HEADER,
+      MAXIMUM_CAPACITY_REACHED,
+      MAXIMUM_BYTES_REACHED,
+    };
+    Code code;
+    Optional<size_t> pos;
+
+    Error(Code in_code) : code(in_code), pos(nullopt) {}
+    Error(Code in_code, size_t position) : code(in_code), pos(position) {}
+  };
+
+  struct Options final {
+    size_t max_bytes;
+    size_t max_items;
+  };
+
+  static constexpr size_t default_max_capacity = 64;
+  static constexpr Options default_options{2048, default_max_capacity};
+
+  /// Extracts a Baggage instance from a `DictReader` and creates a Baggage
+  /// instance if no errors are encounters .
+  ///
+  /// @param `reader` The input `DictReader` from which to extract the data.
+  /// @return A `Baggage` instance or an `Error`.
+  static Expected<Baggage, Error> extract(const DictReader& reader);
+
+  /// Initializes an empty Baggage with the default maximum capacity.
+  Baggage() = default;
+
+  /// Initializes an empty Baggage instance with the given maximum capacity.
+  ///
+  /// @param `max_capacity` The maximum capacity for this Baggage instance.
+  Baggage(size_t max_capacity);
+
+  /// Initializes a Baggage instance using the provided unordered_map of
+  /// key-value pairs. The maximum capacity can also be specified.
+  ///
+  /// @param `baggage_map` The map containing key-value pairs to initialize the
+  /// Baggage.
+  /// @param `max_capacity` The maximum capacity for this Baggage instance.
+  Baggage(std::unordered_map<std::string, std::string>,
+          size_t max_capacity = default_max_capacity);
+
+  /// Checks if the Baggage contains a specified key.
+  ///
+  /// @param `key` The key to check.
+  /// @return `true` if the key exists in the Baggage; otherwise, `false`.
+  bool contains(StringView key) const;
+
+  /// Retrieves the value associated with a specified key.
+  ///
+  /// @param `key` The key to retrieve the value for.
+  /// @return An `Optional<StringView>` containing the value if the key exists,
+  /// or an empty Optional if the key is not found.
+  Optional<StringView> get(StringView key) const;
+
+  /// Adds a key-value pair to the Baggage.
+  ///
+  /// This function will attempt to add the given key-value pair to the Baggage.
+  /// If the maximum capacity has been reached, the insertion will fail.
+  /// If a `key` already exists, its value will be overwritten with `value`.
+  ///
+  /// @param `key` The key to insert.
+  /// @param `value` The value to associate with the key.
+  /// @return `true` if the key-value pair was successfully added; `false` if
+  /// the maximum capacity was reached.
+  bool set(std::string key, std::string value);
+
+  /// Removes the key-value pair corresponding to the specified key.
+  ///
+  /// @param `key` The key to remove from the Baggage.
+  void remove(StringView key);
+
+  /// Removes all key-value pair.
+  void clear();
+
+  /// Retrieves the number of items stored.
+  size_t size() const;
+
+  /// Returns whether any items are stored.
+  bool empty() const;
+
+  /// Visits each key-value pair in the Baggage and invoke the provided
+  /// visitor function for each key-value pair in the Baggage.
+  ///
+  /// @param `visitor` A function object that will be called for each
+  /// key-value pair.
+  void visit(std::function<void(StringView, StringView)>&& visitor);
+
+  /// Injects the Baggage data into a `DictWriter` with the constraint that
+  /// the amount of bytes written does not exceed the specified maximum byte
+  /// limit.
+  ///
+  /// @param `writer` The DictWriter to inject the data into.
+  /// @param `opts` Injection options.
+  /// @return An `Expected<void>`, which may either succeed or contain an
+  /// error.
+  Expected<void> inject(DictWriter& writer,
+                        const Options& opts = default_options) const;
+
+  /// Equality operator for comparing two Baggage instances.
+  inline bool operator==(const Baggage& rhs) const {
+    return baggage_ == rhs.baggage_;
+  }
+
+ private:
+  const size_t max_capacity_ = Baggage::default_max_capacity;
+  std::unordered_map<std::string, std::string> baggage_;
+};
+
+}  // namespace tracing
+}  // namespace datadog

include/datadog/config.h

@@ -25,6 +25,8 @@ enum class ConfigName : char {
   TRACE_SAMPLING_LIMIT,
   TRACE_SAMPLING_RULES,
   SPAN_SAMPLING_RULES,
+  TRACE_BAGGAGE_MAX_BYTES,
+  TRACE_BAGGAGE_MAX_ITEMS,
 };
 
 // Represents metadata for configuration parameters

include/datadog/environment.h

@@ -55,6 +55,8 @@ namespace environment {
   MACRO(DD_TELEMETRY_METRICS_ENABLED)                \
   MACRO(DD_TELEMETRY_METRICS_INTERVAL_SECONDS)       \
   MACRO(DD_TELEMETRY_DEBUG)                          \
+  MACRO(DD_TRACE_BAGGAGE_MAX_ITEMS)                  \
+  MACRO(DD_TRACE_BAGGAGE_MAX_BYTES)                  \
   MACRO(DD_TELEMETRY_LOG_COLLECTION_ENABLED)
 
 #define WITH_COMMA(ARG) ARG,

include/datadog/error.h

@@ -76,6 +76,8 @@ struct Error {
     DATADOG_AGENT_INVALID_REMOTE_CONFIG_POLL_INTERVAL = 51,
     SAMPLING_DELEGATION_RESPONSE_INVALID_JSON = 52,
     REMOTE_CONFIGURATION_INVALID_INPUT = 53,
+    BAGGAGE_MAXIMUM_BYTES_REACHED = 54,
+    BAGGAGE_MAXIMUM_ITEMS_REACHED = 55,
   };
 
   Code code;