AGTMETRICS-489 Make serializer bit more robust

dogstatsd-http-core/src/main/java/com/datadoghq/dogstatsd/http/serializer/PayloadBuilder.java

@@ -12,7 +12,14 @@
 import java.util.Collections;
 import java.util.List;
 
-/** Build metrics payloads in a format accepted by the agent or the intake. */
+/**
+ * Build metrics payloads in a format accepted by the agent or the intake.
+ *
+ * <p>If any {@link Metric} method throws, the in-progress metric is no longer valid; the caller
+ * must call {@link #resetMetric()} to discard the partial state before encoding any further
+ * metrics. Metrics that are ended without any successfully-added points are silently dropped from
+ * the payload.
+ */
 public class PayloadBuilder {
     private static final int DEFAULT_MAX_PAYLOAD_SIZE = 256 * 1024;
     private static final int METRIC_DATA_FIELD_ID = 3;
@@ -205,6 +212,10 @@ void endMetric() {
         }
 
         try {
+            if (timestamps.length() == 0) {
+                return;
+            }
+
             m.encodeIndependentFields();
             m.encodeDependentFields();
 
@@ -221,14 +232,24 @@ void endMetric() {
             }
             payload.put(record);
         } finally {
-            record.clear();
-            timestamps.clear();
-            values.clear();
-            counts.clear();
-            metricInProgress = null;
+            resetMetric();
         }
     }
 
+    /**
+     * Discard the in-progress metric without adding it to the payload.
+     *
+     * <p>Must be called after any {@link Metric} method throws — the metric is no longer valid and
+     * its partial state must be discarded before encoding any further metrics.
+     */
+    public void resetMetric() {
+        record.clear();
+        timestamps.clear();
+        values.clear();
+        counts.clear();
+        metricInProgress = null;
+    }
+
     ColumnarBuffer currentRecord() {
         return record;
     }

dogstatsd-http-core/src/test/java/com/datadoghq/dogstatsd/http/serializer/PayloadBuilderTest.java

@@ -43,6 +43,8 @@ public void handle(byte[] p) {
 
         b.gauge("defgh").addPoint(100, 0).close();
 
+        b.gauge("noop").setTags(Arrays.asList(new String[] {"foo", "bar"})).setInterval(10).close();
+
         Sketch sketch1 = new Sketch();
         sketch1.build(new long[] {1, 2, 2}, 1.0);
         Sketch sketch2 = new Sketch();