fix: Tighten OM2 summary and start timestamp output

prometheus-metrics-exposition-textformats/src/main/java/io/prometheus/metrics/expositionformats/OpenMetrics2TextFormatWriter.java

@@ -15,6 +15,7 @@
 import io.prometheus.metrics.model.snapshots.CounterSnapshot;
 import io.prometheus.metrics.model.snapshots.DataPointSnapshot;
 import io.prometheus.metrics.model.snapshots.Exemplar;
+import io.prometheus.metrics.model.snapshots.Exemplars;
 import io.prometheus.metrics.model.snapshots.GaugeSnapshot;
 import io.prometheus.metrics.model.snapshots.HistogramSnapshot;
 import io.prometheus.metrics.model.snapshots.InfoSnapshot;
@@ -62,7 +63,7 @@ public Builder setOpenMetrics2Properties(OpenMetrics2Properties openMetrics2Prop
     }
 
     /**
-     * @param createdTimestampsEnabled whether to include the _created timestamp in the output
+     * @param createdTimestampsEnabled whether to include the start timestamp in the output
      */
     public Builder setCreatedTimestampsEnabled(boolean createdTimestampsEnabled) {
       this.createdTimestampsEnabled = createdTimestampsEnabled;
@@ -93,8 +94,7 @@ public OpenMetrics2TextFormatWriter build() {
 
   /**
    * @param openMetrics2Properties OpenMetrics 2.0 feature flags
-   * @param createdTimestampsEnabled whether to include the _created timestamp in the output - This
-   *     will produce an invalid OpenMetrics output, but is kept for backwards compatibility.
+   * @param createdTimestampsEnabled whether to include the start timestamp in the output.
    * @param exemplarsOnAllMetricTypesEnabled whether to include exemplars on all metric types
    */
   public OpenMetrics2TextFormatWriter(
@@ -177,8 +177,16 @@ private void writeCounter(Writer writer, CounterSnapshot snapshot, EscapingSchem
     for (CounterSnapshot.CounterDataPointSnapshot data : snapshot.getDataPoints()) {
       writeNameAndLabels(writer, counterName, null, data.getLabels(), scheme);
       writeDouble(writer, data.getValue());
-      writeScrapeTimestampAndExemplar(writer, data, data.getExemplar(), scheme);
-      writeCreated(writer, counterName, data, scheme);
+      if (data.hasScrapeTimestamp()) {
+        writer.write(' ');
+        writeOpenMetricsTimestamp(writer, data.getScrapeTimestampMillis());
+      }
+      if (createdTimestampsEnabled && data.hasCreatedTimestamp()) {
+        writer.write(" st@");
+        writeOpenMetricsTimestamp(writer, data.getCreatedTimestampMillis());
+      }
+      writeExemplar(writer, data.getExemplar(), scheme);
+      writer.write('\n');
     }
   }
 
@@ -316,22 +324,20 @@ private void writeCompositeSummaryDataPoint(
       writeDouble(writer, data.getSum());
       first = false;
     }
-    if (data.getQuantiles().size() > 0) {
-      if (!first) {
+    if (!first) {
+      writer.write(',');
+    }
+    writer.write("quantile:[");
+    for (int i = 0; i < data.getQuantiles().size(); i++) {
+      if (i > 0) {
         writer.write(',');
       }
-      writer.write("quantile:[");
-      for (int i = 0; i < data.getQuantiles().size(); i++) {
-        if (i > 0) {
-          writer.write(',');
-        }
-        Quantile q = data.getQuantiles().get(i);
-        writeDouble(writer, q.getQuantile());
-        writer.write(':');
-        writeDouble(writer, q.getValue());
-      }
-      writer.write(']');
+      Quantile q = data.getQuantiles().get(i);
+      writeDouble(writer, q.getQuantile());
+      writer.write(':');
+      writeDouble(writer, q.getValue());
     }
+    writer.write(']');
     writer.write('}');
     if (data.hasScrapeTimestamp()) {
       writer.write(' ');
@@ -341,7 +347,7 @@ private void writeCompositeSummaryDataPoint(
       writer.write(" st@");
       writeOpenMetricsTimestamp(writer, data.getCreatedTimestampMillis());
     }
-    writeExemplar(writer, data.getExemplars().getLatest(), scheme);
+    writeExemplars(writer, data.getExemplars(), scheme);
     writer.write('\n');
   }
 
@@ -411,20 +417,6 @@ private void writeUnknown(Writer writer, UnknownSnapshot snapshot, EscapingSchem
     }
   }
 
-  private void writeCreated(
-      Writer writer, String name, DataPointSnapshot data, EscapingScheme scheme)
-      throws IOException {
-    if (createdTimestampsEnabled && data.hasCreatedTimestamp()) {
-      writeNameAndLabels(writer, name, "_created", data.getLabels(), scheme);
-      writeOpenMetricsTimestamp(writer, data.getCreatedTimestampMillis());
-      if (data.hasScrapeTimestamp()) {
-        writer.write(' ');
-        writeOpenMetricsTimestamp(writer, data.getScrapeTimestampMillis());
-      }
-      writer.write('\n');
-    }
-  }
-
   private void writeNameAndLabels(
       Writer writer,
       String name,
@@ -496,6 +488,13 @@ private void writeExemplar(Writer writer, @Nullable Exemplar exemplar, EscapingS
     }
   }
 
+  private void writeExemplars(Writer writer, Exemplars exemplars, EscapingScheme scheme)
+      throws IOException {
+    for (Exemplar exemplar : exemplars) {
+      writeExemplar(writer, exemplar, scheme);
+    }
+  }
+
   private void writeMetadataWithName(
       Writer writer, String name, String typeName, MetricMetadata metadata) throws IOException {
     writer.write("# TYPE ");

prometheus-metrics-exposition-textformats/src/test/java/io/prometheus/metrics/expositionformats/OpenMetrics2TextFormatWriterTest.java

@@ -307,13 +307,12 @@ void testCounterWithCreatedTimestamps() throws IOException {
 
     String om2Output = write(snapshots, om2Writer);
 
-    // OM2: no _total, _created uses the counter name directly
+    // OM2: no _total, start timestamp uses st@ inline.
     assertThat(om2Output)
         .isEqualTo(
             "# TYPE my_counter counter\n"
                 + "# HELP my_counter Test counter\n"
-                + "my_counter 42.0\n"
-                + "my_counter_created 1672850385.800\n"
+                + "my_counter 42.0 st@1672850385.800\n"
                 + "# EOF\n");
   }
 
@@ -479,8 +478,10 @@ void testCompositeSummary() throws IOException {
 
   @Test
   void testCompositeSummaryWithCreatedAndExemplar() throws IOException {
-    Exemplar exemplar =
+    Exemplar exemplar1 =
         Exemplar.builder().value(0.5).traceId("abc123").timestampMillis(1520879607000L).build();
+    Exemplar exemplar2 =
+        Exemplar.builder().value(1.5).traceId("def456").timestampMillis(1520879608000L).build();
 
     MetricSnapshots snapshots =
         MetricSnapshots.of(
@@ -491,7 +492,7 @@ void testCompositeSummaryWithCreatedAndExemplar() throws IOException {
                         .count(10)
                         .sum(100.0)
                         .createdTimestampMillis(1520430000000L)
-                        .exemplars(Exemplars.of(exemplar))
+                        .exemplars(Exemplars.of(exemplar1, exemplar2))
                         .build())
                 .build());
 
@@ -500,8 +501,9 @@ void testCompositeSummaryWithCreatedAndExemplar() throws IOException {
     assertThat(output)
         .isEqualTo(
             "# TYPE rpc_duration_seconds summary\n"
-                + "rpc_duration_seconds {count:10,sum:100.0} st@1520430000.000"
-                + " # {trace_id=\"abc123\"} 0.5 1520879607.000\n"
+                + "rpc_duration_seconds {count:10,sum:100.0,quantile:[]} st@1520430000.000"
+                + " # {trace_id=\"abc123\"} 0.5 1520879607.000"
+                + " # {trace_id=\"def456\"} 1.5 1520879608.000\n"
                 + "# EOF\n");
   }