feat!: default to null logger (#187)

The library now uses a NullLogger by default if no logger is specified.
This means that no logs will be printed unless a customer logger is
provided.

Author: dmehala

BUILD.bazel

@@ -49,7 +49,6 @@ cc_library(
       "src/datadog/version.cpp",
       "src/datadog/w3c_propagation.cpp",
       "src/datadog/base64.h",
-      "src/datadog/cerr_logger.h",
       "src/datadog/config_manager.h",
       "src/datadog/collector_response.h",
       "src/datadog/datadog_agent.h",
@@ -62,6 +61,7 @@ cc_library(
       "src/datadog/json_serializer.h",
       "src/datadog/limiter.h",
       "src/datadog/msgpack.h",
+      "src/datadog/null_logger.h",
       "src/datadog/parse_util.h",
       "src/datadog/platform_util.h",
       "src/datadog/random.h",
@@ -78,6 +78,7 @@ cc_library(
       "src/datadog/w3c_propagation.h",
     ],
     hdrs = [
+      "include/datadog/cerr_logger.h",
       "include/datadog/clock.h",
       "include/datadog/collector.h",
       "include/datadog/config.h",

examples/hasher/hasher.cpp

@@ -10,6 +10,7 @@
 // canonical format.  Produce a trace whose structure reflects the directory
 // structure.
 
+#include <datadog/cerr_logger.h>
 #include <datadog/span_config.h>
 #include <datadog/tracer.h>
 #include <datadog/tracer_config.h>
@@ -133,6 +134,7 @@ int main() {
   dd::TracerConfig config;
   config.service = "dd-trace-cpp-example";
   config.environment = "dev";
+  config.logger = std::make_shared<datadog::tracing::CerrLogger>();
 
   auto validated = dd::finalize_config(config);
   if (auto *error = validated.if_error()) {

examples/http-server/proxy/proxy.cpp

@@ -8,6 +8,7 @@
 #include <optional>
 #include <string_view>
 
+#include "datadog/cerr_logger.h"
 #include "datadog/dict_reader.h"
 #include "datadog/dict_writer.h"
 #include "datadog/span.h"
@@ -27,6 +28,7 @@ int main() {
   dd::TracerConfig config;
   config.service = "dd-trace-cpp-http-server-example-proxy";
   config.service_type = "proxy";
+  config.logger = std::make_shared<datadog::tracing::CerrLogger>();
 
   // `finalize_config` validates `config` and applies any settings from
   // environment variables, such as `DD_AGENT_HOST`.

examples/http-server/server/server.cpp

@@ -21,6 +21,7 @@
 //
 //         will deliver a response after approximately 23 milliseconds.
 
+#include <datadog/cerr_logger.h>
 #include <datadog/clock.h>
 #include <datadog/dict_reader.h>
 #include <datadog/dict_writer.h>
@@ -110,6 +111,7 @@ int main() {
   dd::TracerConfig config;
   config.service = "dd-trace-cpp-http-server-example-server";
   config.service_type = "server";
+  config.logger = std::make_shared<datadog::tracing::CerrLogger>();
 
   // `finalize_config` validates `config` and applies any settings from
   // environment variables, such as `DD_AGENT_HOST`.

src/datadog/cerr_logger.h include/datadog/cerr_logger.hsrc/datadog/cerr_logger.h renamed to include/datadog/cerr_logger.h

@@ -1,4 +1,4 @@
-#include "cerr_logger.h"
+#include <datadog/cerr_logger.h>
 
 #include <iostream>
 

src/datadog/cerr_logger.cpp

@@ -0,0 +1,25 @@
+#pragma once
+
+// This component provides a class, `NullLogger`, that implements the `Logger`
+// interface from `logger.h`.
+// `NullLogger` is a no-op logger, meaning it doesn't log anything.
+//
+// `NullLogger` is the default logger used by `Tracer` unless otherwise
+// configured in `TracerConfig`.
+
+#include <datadog/logger.h>
+
+namespace datadog {
+namespace tracing {
+
+class NullLogger : public Logger {
+ public:
+  void log_error(const LogFunc&) override{};
+  void log_startup(const LogFunc&) override{};
+
+  void log_error(const Error&) override{};
+  void log_error(StringView) override{};
+};
+
+}  // namespace tracing
+}  // namespace datadog

src/datadog/null_logger.h

@@ -8,9 +8,9 @@
 #include <unordered_map>
 #include <vector>
 
-#include "cerr_logger.h"
 #include "datadog_agent.h"
 #include "json.hpp"
+#include "null_logger.h"
 #include "parse_util.h"
 #include "platform_util.h"
 #include "string_util.h"
@@ -240,7 +240,7 @@ Expected<FinalizedTracerConfig> finalize_config(const TracerConfig &config) {
 Expected<FinalizedTracerConfig> finalize_config(const TracerConfig &user_config,
                                                 const Clock &clock) {
   auto logger =
-      user_config.logger ? user_config.logger : std::make_shared<CerrLogger>();
+      user_config.logger ? user_config.logger : std::make_shared<NullLogger>();
 
   Expected<TracerConfig> env_config = load_tracer_env_config(*logger);
   if (auto error = env_config.if_error()) {

src/datadog/tracer_config.cpp

@@ -16,13 +16,6 @@
 
 using namespace datadog::tracing;
 
-struct NullLogger : public Logger {
-  void log_error(const LogFunc&) override {}
-  void log_startup(const LogFunc&) override {}
-  void log_error(const Error&) override {}
-  void log_error(StringView) override {}
-};
-
 struct MockLogger : public Logger {
   struct Entry {
     enum Kind { DD_ERROR, STARTUP } kind;

test/mocks/loggers.h

@@ -3,7 +3,7 @@
 #include "catch.hpp"
 #include "datadog/json.hpp"
 #include "datadog/remote_config/remote_config.h"
-#include "mocks/loggers.h"
+#include "null_logger.h"
 
 namespace rc = datadog::remote_config;
 using namespace datadog::tracing;