ARROW-15044: [C++] Add OpenTelemetry exporters for debugging use

cpp/CMakeLists.txt

@@ -766,9 +766,15 @@ if(ARROW_S3)
 endif()
 
 if(ARROW_WITH_OPENTELEMETRY)
-  list(APPEND ARROW_LINK_LIBS opentelemetry-cpp::trace
+  list(APPEND
+       ARROW_LINK_LIBS
+       opentelemetry-cpp::trace
+       opentelemetry-cpp::ostream_span_exporter
        opentelemetry-cpp::otlp_http_exporter)
-  list(APPEND ARROW_STATIC_LINK_LIBS opentelemetry-cpp::trace
+  list(APPEND
+       ARROW_STATIC_LINK_LIBS
+       opentelemetry-cpp::trace
+       opentelemetry-cpp::ostream_span_exporter
        opentelemetry-cpp::otlp_http_exporter)
 endif()
 

cpp/src/arrow/util/tracing_internal.cc

@@ -25,13 +25,20 @@
 #pragma warning(push)
 #pragma warning(disable : 4522)
 #endif
+#include <google/protobuf/util/json_util.h>
+
+#include <opentelemetry/exporters/ostream/span_exporter.h>
 #include <opentelemetry/exporters/otlp/otlp_http_exporter.h>
+#include <opentelemetry/exporters/otlp/otlp_recordable_utils.h>
 #include <opentelemetry/sdk/trace/batch_span_processor.h>
 #include <opentelemetry/sdk/trace/recordable.h>
 #include <opentelemetry/sdk/trace/span_data.h>
 #include <opentelemetry/sdk/trace/tracer_provider.h>
-#include <opentelemetry/trace/noop.h>
 #include <opentelemetry/trace/provider.h>
+
+#include <opentelemetry/exporters/otlp/protobuf_include_prefix.h>
+#include <opentelemetry/exporters/otlp/protobuf_include_suffix.h>
+#include <opentelemetry/proto/collector/trace/v1/trace_service.pb.h>
 #ifdef _MSC_VER
 #pragma warning(pop)
 #endif
@@ -53,6 +60,46 @@ namespace {
 
 namespace sdktrace = opentelemetry::sdk::trace;
 
+// Custom JSON exporter. Leverages the OTLP HTTP exporter's utilities
+// to log the same format that would be sent to OTLP.
+class OtlpOStreamExporter final : public sdktrace::SpanExporter {
+ public:
+  explicit OtlpOStreamExporter(std::basic_ostream<char>* out) : out_(out) {
+    protobuf_json_options_.add_whitespace = false;
+  }
+
+  std::unique_ptr<sdktrace::Recordable> MakeRecordable() noexcept override {
+    // The header for the Recordable definition is not installed, work around that
+    return exporter_.MakeRecordable();
+  }
+  otel::sdk::common::ExportResult Export(
+      const nostd::span<std::unique_ptr<sdktrace::Recordable>>& spans) noexcept override {
+    opentelemetry::proto::collector::trace::v1::ExportTraceServiceRequest request;
+    otel::exporter::otlp::OtlpRecordableUtils::PopulateRequest(spans, &request);
+
+    for (const auto& spans : request.resource_spans()) {
+      std::string output;
+      auto status = google::protobuf::util::MessageToJsonString(spans, &output,
+                                                                protobuf_json_options_);
+      if (ARROW_PREDICT_FALSE(!status.ok())) {
+        return otel::sdk::common::ExportResult::kFailure;
+      }
+      (*out_) << output << std::endl;
+    }
+
+    return otel::sdk::common::ExportResult::kSuccess;
+  }
+  bool Shutdown(std::chrono::microseconds timeout =
+                    std::chrono::microseconds(0)) noexcept override {
+    return exporter_.Shutdown(timeout);
+  }
+
+ private:
+  std::basic_ostream<char>* out_;
+  opentelemetry::exporter::otlp::OtlpHttpExporter exporter_;
+  google::protobuf::util::JsonPrintOptions protobuf_json_options_;
+};
+
 class ThreadIdSpanProcessor : public sdktrace::BatchSpanProcessor {
  public:
   using sdktrace::BatchSpanProcessor::BatchSpanProcessor;
@@ -68,15 +115,16 @@ std::unique_ptr<sdktrace::SpanExporter> InitializeExporter() {
   auto maybe_env_var = arrow::internal::GetEnvVar(kTracingBackendEnvVar);
   if (maybe_env_var.ok()) {
     auto env_var = maybe_env_var.ValueOrDie();
-    if (env_var == "otlp_http") {
-#ifdef ARROW_WITH_OPENTELEMETRY
+    if (env_var == "ostream") {
+      return arrow::internal::make_unique<otel::exporter::trace::OStreamSpanExporter>();
+    } else if (env_var == "otlp_http") {
       namespace otlp = opentelemetry::exporter::otlp;
       otlp::OtlpHttpExporterOptions opts;
       return arrow::internal::make_unique<otlp::OtlpHttpExporter>(opts);
-#else
-      ARROW_LOG(WARNING) << "Requested " << kTracingBackendEnvVar << "=" < < < < env_var
-          " but Arrow was not built with ARROW_WITH_OPENTELEMETRY";
-#endif
+    } else if (env_var == "arrow_otlp_stdout") {
+      return arrow::internal::make_unique<OtlpOStreamExporter>(&std::cout);
+    } else if (env_var == "arrow_otlp_stderr") {
+      return arrow::internal::make_unique<OtlpOStreamExporter>(&std::cerr);
     } else if (!env_var.empty()) {
       ARROW_LOG(WARNING) << "Requested unknown backend " << kTracingBackendEnvVar << "="
                          << env_var;