Code review

- update fuzz documentation
- revise the base64 decoder
- move ConfigManager into its own .cpp
- remove namespace httputil::header
- more specific error code
- RuntimeID rc_id_  -->  std::string client_id_
- TracerId  -->  TracerID
- remove disambiguating "template" keyword
- document k_apm_capabilities
- missed a spot when removing namespace httputil::header
- no need to optimize target file lookup
- slightly safer product parsing

Author: dgoffredo

BUILD.bazel

@@ -4,6 +4,7 @@ cc_library(
     "src/datadog/base64.cpp",
     "src/datadog/cerr_logger.cpp",
     "src/datadog/clock.cpp",
+    "src/datadog/config_manager.cpp",
     "src/datadog/collector_response.cpp",
 #     "src/datadog/curl.cpp", no libcurl
     "src/datadog/datadog_agent_config.cpp",

CMakeLists.txt

@@ -104,6 +104,7 @@ target_sources(dd_trace_cpp-objects PRIVATE
     src/datadog/base64.cpp
     src/datadog/cerr_logger.cpp
     src/datadog/clock.cpp
+    src/datadog/config_manager.cpp
     src/datadog/collector_response.cpp
     src/datadog/curl.cpp
     src/datadog/datadog_agent_config.cpp

bin/cmake-build

@@ -6,5 +6,5 @@ cd "$(dirname "$0")"/..
 
 mkdir -p .build
 cd .build
-cmake ..
+cmake .. "$@"
 make -j "$(nproc)"

fuzz/README.md

@@ -3,24 +3,19 @@ Fuzzers
 Each subdirectory here contains the source of an executable that [fuzz tests][1]
 some part of the library using [LLVM's libfuzzer][2].
 
-There is a toplevel CMake boolean option associated with each fuzzer. The naming
-convention is `FUZZ_<SUBDIRECTORY_WITH_UNDERSCORES>`, e.g.
-`FUZZ_W3C_PROPAGATION` for the fuzzer defined in
-[fuzz/w3c-propagation/](./w3c-propagation/). The resulting binary is called
-`fuzz` by convention.
+There is a toplevel CMake boolean option that adds all of the fuzzer
+executables to the build: `BUILD_FUZZERS`.
 
-When building a fuzzer, the toolchain must be clang-based.  For example, this
-is how to build the fuzzer in [fuzz/w3c-propagation](./w3c-propagation/) from
-the root of the repository:
+When building the fuzzers, the toolchain must be clang-based.  For example:
 ```console
-$ rm -rf .build && mkdir .build # if toolchain or test setup need clearing
-$ cd .build
-$ CC=clang CXX=clang++ cmake .. -DFUZZ_W3C_PROPAGATION=ON
-$ make -j $(nproc)
-$ fuzz/w3c-propagation/fuzz
+$ rm -rf .build # if toolchain needs clearing
+$ bin/with-toolchain llvm bin/cmake-build -DBUILD_FUZZERS=1
+$ .build/fuzz/w3c-propagation/w3c-propagation-fuzz
 
 [... fuzzer output ...]
 ```
 
+The fuzzer executables are named `.build/fuzz/*/*-fuzz` by convention.
+
 [1]: https://en.wikipedia.org/wiki/Fuzzing
 [2]: https://llvm.org/docs/LibFuzzer.html

fuzz/base64/main.cpp

@@ -1,9 +1,11 @@
 #include <datadog/base64.h>
 #include <datadog/string_view.h>
 
+#include <cstdint>
+
 namespace dd = datadog::tracing;
 
 extern "C" int LLVMFuzzerTestOneInput(const std::uint8_t* data, size_t size) {
-  dd::base64::decode(dd::StringView{(char*)data, size});
+  dd::base64_decode(dd::StringView{(const char*)data, size});
   return 0;
 }

src/datadog/base64.cpp

@@ -1,109 +1,98 @@
 #include "base64.h"
 
-#include <stdint.h>
+#include <cstddef>
+#include <cstdint>
 
 namespace datadog {
 namespace tracing {
-namespace base64 {
 
-#define _ 255
-#define SENTINEL_VALUE _
-#define EOL 0
+constexpr uint8_t k_sentinel = 255;
+constexpr uint8_t _ = k_sentinel;  // for brevity
+constexpr uint8_t k_eol = 0;
 
-/*
- * Lookup table mapping the base64 table. Invalid inputs are mapped
- * to the value 255.
- * `=` map to 0.
- */
+// Invalid inputs are mapped to the value 255. '=' maps to 0.
 constexpr uint8_t k_base64_table[]{
-    _,  _,  _,  _,  _,   _,  _,  _,  _,  _,  _,  _,  _,  _,  _,  _,  _,  _,  _,
-    _,  _,  _,  _,  _,   _,  _,  _,  _,  _,  _,  _,  _,  _,  _,  _,  _,  _,  _,
-    _,  _,  _,  _,  _,   62, _,  _,  _,  63, 52, 53, 54, 55, 56, 57, 58, 59, 60,
-    61, _,  _,  _,  EOL, _,  _,  _,  0,  1,  2,  3,  4,  5,  6,  7,  8,  9,  10,
-    11, 12, 13, 14, 15,  16, 17, 18, 19, 20, 21, 22, 23, 24, 25, _,  _,  _,  _,
-    _,  _,  26, 27, 28,  29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42,
-    43, 44, 45, 46, 47,  48, 49, 50, 51, _,  _,  _,  _,  _,  _,  _,  _,  _,  _,
-    _,  _,  _,  _,  _,   _,  _,  _,  _,  _,  _,  _,  _,  _,  _,  _,  _,  _,  _,
-    _,  _,  _,  _,  _,   _,  _,  _,  _,  _,  _,  _,  _,  _,  _,  _,  _,  _,  _,
-    _,  _,  _,  _,  _,   _,  _,  _,  _,  _,  _,  _,  _,  _,  _,  _,  _,  _,  _,
-    _,  _,  _,  _,  _,   _,  _,  _,  _,  _,  _,  _,  _,  _,  _,  _,  _,  _,  _,
-    _,  _,  _,  _,  _,   _,  _,  _,  _,  _,  _,  _,  _,  _,  _,  _,  _,  _,  _,
-    _,  _,  _,  _,  _,   _,  _,  _,  _,  _,  _,  _,  _,  _,  _,  _,  _,  _,  _,
-    _,  _,  _,  _,  _,   _,  _,  _,  _};
-
-// TODO: support input without padding?
-std::string decode(StringView in) {
-  const std::size_t in_size = in.size();
-
-  std::string out;
-  out.reserve(in_size);
+    _,  _,  _,  _,  _,  _,  _,  _,     _,  _,  _,  _,  _,  _,  _,  _,  _,  _,
+    _,  _,  _,  _,  _,  _,  _,  _,     _,  _,  _,  _,  _,  _,  _,  _,  _,  _,
+    _,  _,  _,  _,  _,  _,  _,  62,    _,  _,  _,  63, 52, 53, 54, 55, 56, 57,
+    58, 59, 60, 61, _,  _,  _,  k_eol, _,  _,  _,  0,  1,  2,  3,  4,  5,  6,
+    7,  8,  9,  10, 11, 12, 13, 14,    15, 16, 17, 18, 19, 20, 21, 22, 23, 24,
+    25, _,  _,  _,  _,  _,  _,  26,    27, 28, 29, 30, 31, 32, 33, 34, 35, 36,
+    37, 38, 39, 40, 41, 42, 43, 44,    45, 46, 47, 48, 49, 50, 51, _,  _,  _,
+    _,  _,  _,  _,  _,  _,  _,  _,     _,  _,  _,  _,  _,  _,  _,  _,  _,  _,
+    _,  _,  _,  _,  _,  _,  _,  _,     _,  _,  _,  _,  _,  _,  _,  _,  _,  _,
+    _,  _,  _,  _,  _,  _,  _,  _,     _,  _,  _,  _,  _,  _,  _,  _,  _,  _,
+    _,  _,  _,  _,  _,  _,  _,  _,     _,  _,  _,  _,  _,  _,  _,  _,  _,  _,
+    _,  _,  _,  _,  _,  _,  _,  _,     _,  _,  _,  _,  _,  _,  _,  _,  _,  _,
+    _,  _,  _,  _,  _,  _,  _,  _,     _,  _,  _,  _,  _,  _,  _,  _,  _,  _,
+    _,  _,  _,  _,  _,  _,  _,  _,     _,  _,  _,  _,  _,  _,  _,  _,  _,  _,
+    _,  _,  _,  _};
+
+std::string base64_decode(StringView input) {
+  const size_t in_size = input.size();
+
+  std::string output;
+  output.reserve(in_size);
 
   union {
     uint32_t buffer;
     uint8_t bytes[4];
   } decoder;
 
-  std::size_t i = 0;
+  size_t i = 0;
 
   for (; i + 4 < in_size;) {
-    auto c0 = k_base64_table[static_cast<size_t>(in[i++])];
-    auto c1 = k_base64_table[static_cast<size_t>(in[i++])];
-    auto c2 = k_base64_table[static_cast<size_t>(in[i++])];
-    auto c3 = k_base64_table[static_cast<size_t>(in[i++])];
+    uint32_t c0 = k_base64_table[static_cast<size_t>(input[i++])];
+    uint32_t c1 = k_base64_table[static_cast<size_t>(input[i++])];
+    uint32_t c2 = k_base64_table[static_cast<size_t>(input[i++])];
+    uint32_t c3 = k_base64_table[static_cast<size_t>(input[i++])];
 
-    if (c0 == SENTINEL_VALUE || c1 == SENTINEL_VALUE || c2 == SENTINEL_VALUE ||
-        c3 == SENTINEL_VALUE) {
+    if (c0 == k_sentinel || c1 == k_sentinel || c2 == k_sentinel ||
+        c3 == k_sentinel) {
       return "";
     }
 
-    decoder.buffer =
-        static_cast<uint32_t>(0) | static_cast<uint32_t>(c0) << 26 |
-        static_cast<uint32_t>(c1) << 20 | static_cast<uint32_t>(c2) << 14 |
-        static_cast<uint32_t>(c3) << 8;
+    decoder.buffer = 0 | c0 << 26 | c1 << 20 | c2 << 14 | c3 << 8;
 
-    // NOTE(@dmehala): It might seem confusion to read those bytes in reverse
+    // NOTE(@dmehala): It might seem confusing to read those bytes input reverse
     // order. It is related to the architecture endianess. For now the set of
     // architecture we support (x86_64 and arm64) are all little-endian.
-    out.push_back(decoder.bytes[3]);
-    out.push_back(decoder.bytes[2]);
-    out.push_back(decoder.bytes[1]);
+    // TODO(@dgoffredo): I'd prefer an endian-agnostic implementation.
+    // nginx-datadog targets x86_64 and arm64 in its binary releases, but
+    // dd-trace-cpp targets any standard C++17 compiler.
+    output.push_back(decoder.bytes[3]);
+    output.push_back(decoder.bytes[2]);
+    output.push_back(decoder.bytes[1]);
   }
 
-  if ((in_size - i) < 4) return "";  // not padded input is not supported
+  // If padding is missing, return the empty string in lieu of an Error.
+  if ((in_size - i) < 4) return "";
 
-  auto c0 = k_base64_table[static_cast<size_t>(in[i++])];
-  auto c1 = k_base64_table[static_cast<size_t>(in[i++])];
-  auto c2 = k_base64_table[static_cast<size_t>(in[i++])];
-  auto c3 = k_base64_table[static_cast<size_t>(in[i++])];
+  uint32_t c0 = k_base64_table[static_cast<size_t>(input[i++])];
+  uint32_t c1 = k_base64_table[static_cast<size_t>(input[i++])];
+  uint32_t c2 = k_base64_table[static_cast<size_t>(input[i++])];
+  uint32_t c3 = k_base64_table[static_cast<size_t>(input[i++])];
 
-  if (c0 == SENTINEL_VALUE || c1 == SENTINEL_VALUE || c2 == SENTINEL_VALUE ||
-      c3 == SENTINEL_VALUE) {
+  if (c0 == k_sentinel || c1 == k_sentinel || c2 == k_sentinel ||
+      c3 == k_sentinel) {
     return "";
   }
 
-  decoder.buffer = static_cast<uint32_t>(0) | static_cast<uint32_t>(c0) << 26 |
-                   static_cast<uint32_t>(c1) << 20 |
-                   static_cast<uint32_t>(c2) << 14 |
-                   static_cast<uint32_t>(c3) << 8;
+  decoder.buffer = 0 | c0 << 26 | c1 << 20 | c2 << 14 | c3 << 8;
 
-  if (c2 == EOL) {
-    out.push_back(decoder.bytes[3]);
-  } else if (c3 == EOL) {
-    out.push_back(decoder.bytes[3]);
-    out.push_back(decoder.bytes[2]);
+  if (c2 == k_eol) {
+    output.push_back(decoder.bytes[3]);
+  } else if (c3 == k_eol) {
+    output.push_back(decoder.bytes[3]);
+    output.push_back(decoder.bytes[2]);
   } else {
-    out.push_back(decoder.bytes[3]);
-    out.push_back(decoder.bytes[2]);
-    out.push_back(decoder.bytes[1]);
+    output.push_back(decoder.bytes[3]);
+    output.push_back(decoder.bytes[2]);
+    output.push_back(decoder.bytes[1]);
   }
 
-  return out;
+  return output;
 }
 
-#undef EOL
-#undef SENTINEL_VALUE
-#undef _
-
-}  // namespace base64
 }  // namespace tracing
 }  // namespace datadog

src/datadog/base64.h

@@ -1,19 +1,15 @@
 #pragma once
 
+#include <string>
+
 #include "string_view.h"
 
 namespace datadog {
 namespace tracing {
-namespace base64 {
 
-/*
- * Decode a base64-encoded string and returns the decoded data.
- *
- * It only supported padded base64-encoded string. Providing an unpadded
- * input will return an empty string.
- */
-std::string decode(StringView in);
+// Return the result of decoding the specified padded base64-encoded `input`. If
+// `input` is not padded, then return the empty string instead.
+std::string base64_decode(StringView input);
 
-}  // namespace base64
 }  // namespace tracing
 }  // namespace datadog

src/datadog/config_manager.cpp

@@ -0,0 +1,45 @@
+#include "config_manager.h"
+
+namespace datadog {
+namespace tracing {
+
+ConfigManager::ConfigManager(const FinalizedTracerConfig& config)
+    : clock_(config.clock),
+      default_trace_sampler_(
+          std::make_shared<TraceSampler>(config.trace_sampler, clock_)),
+      current_trace_sampler_(default_trace_sampler_) {}
+
+std::shared_ptr<TraceSampler> ConfigManager::get_trace_sampler() {
+  std::lock_guard<std::mutex> lock(mutex_);
+  return current_trace_sampler_;
+}
+
+void ConfigManager::update(const ConfigManager::Update& conf) {
+  std::lock_guard<std::mutex> lock(mutex_);
+
+  if (conf.trace_sampler) {
+    if (auto finalized_trace_sampler_cfg =
+            finalize_config(*conf.trace_sampler)) {
+      current_trace_sampler_ =
+          std::make_shared<TraceSampler>(*finalized_trace_sampler_cfg, clock_);
+    } else {
+      // TODO: report error
+    }
+  } else {
+    current_trace_sampler_ = default_trace_sampler_;
+  }
+}
+
+void ConfigManager::reset() {
+  std::lock_guard<std::mutex> lock(mutex_);
+  current_trace_sampler_ = default_trace_sampler_;
+}
+
+nlohmann::json ConfigManager::config_json() const {
+  std::lock_guard<std::mutex> lock(mutex_);
+  return nlohmann::json{
+      {"trace_sampler", current_trace_sampler_->config_json()}};
+}
+
+}  // namespace tracing
+}  // namespace datadog

src/datadog/config_manager.h

@@ -1,5 +1,7 @@
 #pragma once
 
+// TODO: Document
+
 #include <mutex>
 
 #include "clock.h"
@@ -10,54 +12,32 @@
 namespace datadog {
 namespace tracing {
 
-struct ConfigUpdate {
-  Optional<TraceSamplerConfig> trace_sampler;
-};
-
 class ConfigManager {
   mutable std::mutex mutex_;
   Clock clock_;
   std::shared_ptr<TraceSampler> default_trace_sampler_;
   std::shared_ptr<TraceSampler> current_trace_sampler_;
 
  public:
-  ConfigManager(const FinalizedTracerConfig& config)
-      : clock_(config.clock),
-        default_trace_sampler_(
-            std::make_shared<TraceSampler>(config.trace_sampler, clock_)),
-        current_trace_sampler_(default_trace_sampler_) {}
+  struct Update {
+    Optional<TraceSamplerConfig> trace_sampler;
+  };
 
-  std::shared_ptr<TraceSampler> get_trace_sampler() {
-    std::lock_guard<std::mutex> lock(mutex_);
-    return current_trace_sampler_;
-  }
+  ConfigManager(const FinalizedTracerConfig& config);
 
-  void update(const ConfigUpdate& conf) {
-    std::lock_guard<std::mutex> lock(mutex_);
+  // Return the `TraceSampler` consistent with the most recent configuration.
+  std::shared_ptr<TraceSampler> get_trace_sampler();
 
-    if (conf.trace_sampler) {
-      if (auto finalized_trace_sampler_cfg =
-              finalize_config(*conf.trace_sampler)) {
-        current_trace_sampler_ = std::make_shared<TraceSampler>(
-            *finalized_trace_sampler_cfg, clock_);
-      } else {
-        // TODO: report error
-      }
-    } else {
-      current_trace_sampler_ = default_trace_sampler_;
-    }
-  }
+  // Apply the specified `conf` update.
+  void update(const Update& conf);
 
-  void reset() {
-    std::lock_guard<std::mutex> lock(mutex_);
-    current_trace_sampler_ = default_trace_sampler_;
-  }
+  // Restore the configuration that was passed to this object's constructor,
+  // overriding any previous calls to `update`.
+  void reset();
 
-  nlohmann::json config_json() const {
-    std::lock_guard<std::mutex> lock(mutex_);
-    return nlohmann::json{
-        {"trace_sampler", current_trace_sampler_->config_json()}};
-  }
+  // Return a JSON representation of the current configuration managed by this
+  // object.
+  nlohmann::json config_json() const;
 };
 
 }  // namespace tracing