[Geneva] Add SpanLink fields name and extend example to cover it (open-telemetry#481)

Author: ThomsonTan

exporters/geneva-trace/example/main.cc

@@ -2,18 +2,30 @@
 // SPDX-License-Identifier: Apache-2.0
 
 #include "opentelemetry/logs/provider.h"
+#include "opentelemetry/trace/provider.h"
+#include "opentelemetry/trace/span.h"
 #include "opentelemetry/exporters/geneva/geneva_logger_exporter.h"
+#include "opentelemetry/exporters/geneva/geneva_tracer_exporter.h"
 
 #include <string>
 
 const char *kGlobalProviderName = "OpenTelemetry-ETW-TLD-Geneva-Example";
 std::string providerName = kGlobalProviderName;
 
+using L = std::vector<std::pair<trace_api::SpanContext, std::map<std::string, std::string>>>;
+
 namespace
 {
+auto InitTracer()
+{
+  static opentelemetry::exporter::etw::TracerProvider tracer_provider;
+  auto tracer = tracer_provider.GetTracer(providerName, "1.0");
+
+  return tracer;
+}
 auto InitLogger()
 {
-  opentelemetry::exporter::etw::LoggerProvider logger_provider;
+  static opentelemetry::exporter::etw::LoggerProvider logger_provider;
   auto logger = logger_provider.GetLogger(providerName, "1.0");
 
   return logger;
@@ -22,8 +34,35 @@ auto InitLogger()
 
 int main()
 {
+  auto tracer = InitTracer();
   auto logger = InitLogger();
 
+  auto s1 = tracer->StartSpan("main");
+
+  {
+    L link1 = {{s1->GetContext(), {}}};
+
+    // Create Span with 1 SpanLink
+    auto s2 = tracer->StartSpan("child", opentelemetry::common::MakeAttributes({{"key1", "value 1"}, {"key2", 1}}), link1);
+
+    s2->SetAttribute("attr_key1", 123);
+
+    {
+      L link2 = {{s1->GetContext(), {}}, {s2->GetContext(), {}}};
+
+      // Create Span with 2 SpanLinks
+      auto s3 = tracer->StartSpan("grandchild", opentelemetry::common::MakeAttributes({{"key3", "value 3"}, {"key4", 2}}), link2);
+
+      s3->SetAttribute("attr_key2", 456);
+
+      s3->End();
+    }
+
+    s2->End();
+  }
+
+  s1->End();
+
   logger->Info("Hello World!");
 
   return 0;

exporters/geneva-trace/include/opentelemetry/exporters/geneva/geneva_fields.h

@@ -51,6 +51,9 @@
 #  define ETW_FIELD_SPAN_KIND         "kind"                  /* Span Kind               */
 #  define ETW_FIELD_SPAN_LINKS        "links"                 /* Span Links array        */
 
+#  define ETW_FIELD_SPAN_LINKS_TO_SPAN_ID  "toSpanId"         /* Span Links toSpanId     */
+#  define ETW_FIELD_SPAN_LINKS_TO_TRACE_ID "toTraceId"        /* Span Links toTraceId    */
+
 #  define ETW_FIELD_PAYLOAD_NAME      "name"                  /* ETW Payload["name"]     */
 
 /* Span option constants */