Add skeleton OpenMetrics2TextFormatWriter

Signed-off-by: Jay DeLuca <jaydeluca4@gmail.com>

Author: jaydeluca

prometheus-metrics-exporter-common/src/main/java/io/prometheus/metrics/exporter/common/PrometheusScrapeHandler.java

@@ -44,7 +44,7 @@ public PrometheusScrapeHandler(PrometheusProperties config) {
   }
 
   public PrometheusScrapeHandler(PrometheusProperties config, PrometheusRegistry registry) {
-    this.expositionFormats = ExpositionFormats.init(config.getExporterProperties());
+    this.expositionFormats = ExpositionFormats.init(config);
     this.preferUncompressedResponse =
         config.getExporterHttpServerProperties().isPreferUncompressedResponse();
     this.registry = registry;

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

@@ -1,6 +1,7 @@
 package io.prometheus.metrics.expositionformats;
 
 import io.prometheus.metrics.config.ExporterProperties;
+import io.prometheus.metrics.config.OpenMetrics2Properties;
 import io.prometheus.metrics.config.PrometheusProperties;
 import javax.annotation.Nullable;
 
@@ -9,44 +10,79 @@ public class ExpositionFormats {
   private final PrometheusProtobufWriter prometheusProtobufWriter;
   private final PrometheusTextFormatWriter prometheusTextFormatWriter;
   private final OpenMetricsTextFormatWriter openMetricsTextFormatWriter;
+  private final OpenMetrics2TextFormatWriter openMetrics2TextFormatWriter;
 
   private ExpositionFormats(
       PrometheusProtobufWriter prometheusProtobufWriter,
       PrometheusTextFormatWriter prometheusTextFormatWriter,
-      OpenMetricsTextFormatWriter openMetricsTextFormatWriter) {
+      OpenMetricsTextFormatWriter openMetricsTextFormatWriter,
+      OpenMetrics2TextFormatWriter openMetrics2TextFormatWriter) {
     this.prometheusProtobufWriter = prometheusProtobufWriter;
     this.prometheusTextFormatWriter = prometheusTextFormatWriter;
     this.openMetricsTextFormatWriter = openMetricsTextFormatWriter;
+    this.openMetrics2TextFormatWriter = openMetrics2TextFormatWriter;
   }
 
   public static ExpositionFormats init() {
-    return init(PrometheusProperties.get().getExporterProperties());
+    return init(PrometheusProperties.get());
   }
 
   @SuppressWarnings("deprecation")
-  public static ExpositionFormats init(ExporterProperties properties) {
+  public static ExpositionFormats init(PrometheusProperties properties) {
+    ExporterProperties exporterProps = properties.getExporterProperties();
+    OpenMetrics2Properties om2Props = properties.getOpenMetrics2Properties();
+
     return new ExpositionFormats(
         new PrometheusProtobufWriter(),
         PrometheusTextFormatWriter.builder()
-            .setIncludeCreatedTimestamps(properties.getIncludeCreatedTimestamps())
-            .setTimestampsInMs(properties.getPrometheusTimestampsInMs())
+            .setIncludeCreatedTimestamps(exporterProps.getIncludeCreatedTimestamps())
+            .setTimestampsInMs(exporterProps.getPrometheusTimestampsInMs())
             .build(),
         OpenMetricsTextFormatWriter.builder()
-            .setCreatedTimestampsEnabled(properties.getIncludeCreatedTimestamps())
-            .setExemplarsOnAllMetricTypesEnabled(properties.getExemplarsOnAllMetricTypes())
+            .setCreatedTimestampsEnabled(exporterProps.getIncludeCreatedTimestamps())
+            .setExemplarsOnAllMetricTypesEnabled(exporterProps.getExemplarsOnAllMetricTypes())
+            .build(),
+        OpenMetrics2TextFormatWriter.builder()
+            .setOpenMetrics2Properties(om2Props)
+            .setCreatedTimestampsEnabled(exporterProps.getIncludeCreatedTimestamps())
+            .setExemplarsOnAllMetricTypesEnabled(exporterProps.getExemplarsOnAllMetricTypes())
             .build());
   }
 
+  /**
+   * @deprecated Use {@link #init(PrometheusProperties)} instead.
+   */
+  @Deprecated
+  @SuppressWarnings({"InlineMeSuggester"})
+  public static ExpositionFormats init(ExporterProperties properties) {
+    return init(PrometheusProperties.builder().exporterProperties(properties).build());
+  }
+
   public ExpositionFormatWriter findWriter(@Nullable String acceptHeader) {
     if (prometheusProtobufWriter.accepts(acceptHeader)) {
       return prometheusProtobufWriter;
     }
+
+    // Prefer OM2 over OM1 when any OM2 feature is enabled
+    if (isOpenMetrics2Enabled() && openMetrics2TextFormatWriter.accepts(acceptHeader)) {
+      return openMetrics2TextFormatWriter;
+    }
+
     if (openMetricsTextFormatWriter.accepts(acceptHeader)) {
       return openMetricsTextFormatWriter;
     }
+
     return prometheusTextFormatWriter;
   }
 
+  private boolean isOpenMetrics2Enabled() {
+    OpenMetrics2Properties props = openMetrics2TextFormatWriter.getOpenMetrics2Properties();
+    return props.getContentNegotiation()
+        || props.getCompositeValues()
+        || props.getExemplarCompliance()
+        || props.getNativeHistograms();
+  }
+
   public PrometheusProtobufWriter getPrometheusProtobufWriter() {
     return prometheusProtobufWriter;
   }
@@ -58,4 +94,8 @@ public PrometheusTextFormatWriter getPrometheusTextFormatWriter() {
   public OpenMetricsTextFormatWriter getOpenMetricsTextFormatWriter() {
     return openMetricsTextFormatWriter;
   }
+
+  public OpenMetrics2TextFormatWriter getOpenMetrics2TextFormatWriter() {
+    return openMetrics2TextFormatWriter;
+  }
 }