Zipkin exporter: Serialize EventData attributes as JSON (#4934)

* serialize EventData attributes to json

* remove import

* fix test

* address code review comments.

* safety first

exporters/zipkin/src/main/java/io/opentelemetry/exporter/zipkin/EventDataToAnnotation.java

@@ -0,0 +1,48 @@
+/*
+ * Copyright The OpenTelemetry Authors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package io.opentelemetry.exporter.zipkin;
+
+import static java.util.stream.Collectors.joining;
+
+import io.opentelemetry.api.common.Attributes;
+import io.opentelemetry.sdk.trace.data.EventData;
+import java.util.List;
+
+/**
+ * Converts an EventData instance to a String representation of that data, with attributes converted
+ * to JSON.
+ *
+ * <p>See <a
+ * href="https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/trace/sdk_exporters/zipkin.md#events">the
+ * zipkin exporter spec</a> for details.
+ */
+final class EventDataToAnnotation {
+
+  private EventDataToAnnotation() {}
+
+  static String apply(EventData eventData) {
+    String name = eventData.getName();
+    String value = toJson(eventData.getAttributes());
+    return "\"" + name + "\":" + value;
+  }
+
+  private static String toJson(Attributes attributes) {
+    return attributes.asMap().entrySet().stream()
+        .map(entry -> "\"" + entry.getKey() + "\":" + toValue(entry.getValue()))
+        .collect(joining(",", "{", "}"));
+  }
+
+  private static String toValue(Object o) {
+    if (o instanceof String) {
+      return "\"" + o + "\"";
+    }
+    if (o instanceof List) {
+      return ((List<?>) o)
+          .stream().map(EventDataToAnnotation::toValue).collect(joining(",", "[", "]"));
+    }
+    return String.valueOf(o);
+  }
+}

exporters/zipkin/src/main/java/io/opentelemetry/exporter/zipkin/OtelToZipkinSpanTransformer.java

@@ -41,7 +41,6 @@ final class OtelToZipkinSpanTransformer {
   static final String OTEL_STATUS_CODE = "otel.status_code";
   static final AttributeKey<String> STATUS_ERROR = stringKey("error");
   private final Supplier<InetAddress> ipAddressSupplier;
-
   /**
    * Creates an instance of an OtelToZipkinSpanTransformer with the given Supplier that can produce
    * an InetAddress, which may be null. This value from this Supplier will be used when creating the
@@ -125,8 +124,9 @@ Span generateSpan(SpanData spanData) {
           KEY_INSTRUMENTATION_LIBRARY_VERSION, instrumentationScopeInfo.getVersion());
     }
 
-    for (EventData annotation : spanData.getEvents()) {
-      spanBuilder.addAnnotation(toEpochMicros(annotation.getEpochNanos()), annotation.getName());
+    for (EventData eventData : spanData.getEvents()) {
+      String annotation = EventDataToAnnotation.apply(eventData);
+      spanBuilder.addAnnotation(toEpochMicros(eventData.getEpochNanos()), annotation);
     }
     int droppedEvents = spanData.getTotalRecordedEvents() - spanData.getEvents().size();
     if (droppedEvents > 0) {
@@ -136,7 +136,7 @@ Span generateSpan(SpanData spanData) {
     return spanBuilder.build();
   }
 
-  private static String nullToEmpty(String value) {
+  private static String nullToEmpty(@Nullable String value) {
     return value != null ? value : "";
   }
 

exporters/zipkin/src/test/java/io/opentelemetry/exporter/zipkin/EventDataToAnnotationTest.java

@@ -0,0 +1,49 @@
+/*
+ * Copyright The OpenTelemetry Authors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package io.opentelemetry.exporter.zipkin;
+
+import static org.assertj.core.api.AssertionsForClassTypes.assertThat;
+
+import io.opentelemetry.api.common.Attributes;
+import io.opentelemetry.sdk.trace.data.EventData;
+import org.junit.jupiter.api.Test;
+
+class EventDataToAnnotationTest {
+
+  @Test
+  void basicConversion() {
+
+    Attributes attrs =
+        Attributes.builder()
+            .put("v1", "v1")
+            .put("v2", 12L)
+            .put("v3", 123.45)
+            .put("v4", false)
+            .put("v5", "foo", "bar", "baz")
+            .put("v6", 1, 2, 3)
+            .put("v7", 1.23, 3.45)
+            .put("v8", true, false, true)
+            .build();
+    String expected =
+        "\"cat\":{\"v1\":\"v1\",\"v2\":12,\"v3\":123.45,\"v4\":false,\"v5\":[\"foo\",\"bar\",\"baz\"],\"v6\":[1,2,3],\"v7\":[1.23,3.45],\"v8\":[true,false,true]}";
+    EventData eventData = EventData.create(0, "cat", attrs);
+
+    String result = EventDataToAnnotation.apply(eventData);
+
+    assertThat(result).isEqualTo(expected);
+  }
+
+  @Test
+  void empty() {
+    Attributes attrs = Attributes.empty();
+    String expected = "\"dog\":{}";
+    EventData eventData = EventData.create(0, "dog", attrs);
+
+    String result = EventDataToAnnotation.apply(eventData);
+
+    assertThat(result).isEqualTo(expected);
+  }
+}

exporters/zipkin/src/test/java/io/opentelemetry/exporter/zipkin/ZipkinSpanExporterEndToEndHttpTest.java

@@ -230,8 +230,8 @@ private static Span buildZipkinSpan(InetAddress localAddress, String traceId) {
         .timestamp(START_EPOCH_NANOS / 1000)
         .duration((END_EPOCH_NANOS / 1000) - (START_EPOCH_NANOS / 1000))
         .localEndpoint(Endpoint.newBuilder().serviceName(SERVICE_NAME).ip(localAddress).build())
-        .addAnnotation(RECEIVED_TIMESTAMP_NANOS / 1000, "RECEIVED")
-        .addAnnotation(SENT_TIMESTAMP_NANOS / 1000, "SENT")
+        .addAnnotation(RECEIVED_TIMESTAMP_NANOS / 1000, "\"RECEIVED\":{}")
+        .addAnnotation(SENT_TIMESTAMP_NANOS / 1000, "\"SENT\":{}")
         .putTag(OtelToZipkinSpanTransformer.OTEL_STATUS_CODE, "OK")
         .build();
   }

exporters/zipkin/src/test/java/io/opentelemetry/exporter/zipkin/ZipkinTestUtil.java

@@ -74,7 +74,7 @@ static Span.Builder zipkinSpanBuilder(Span.Kind kind, InetAddress localIp) {
         .timestamp(1505855794000000L + 194009601L / 1000)
         .duration((1505855799000000L + 465726528L / 1000) - (1505855794000000L + 194009601L / 1000))
         .localEndpoint(Endpoint.newBuilder().ip(localIp).serviceName("tweetiebird").build())
-        .addAnnotation(1505855799000000L + 433901068L / 1000, "RECEIVED")
-        .addAnnotation(1505855799000000L + 459486280L / 1000, "SENT");
+        .addAnnotation(1505855799000000L + 433901068L / 1000, "\"RECEIVED\":{}")
+        .addAnnotation(1505855799000000L + 459486280L / 1000, "\"SENT\":{}");
   }
 }