Support multi-target pattern

docs/content/getting-started/multi-target.md

@@ -0,0 +1,50 @@
+---
+title: Multi-Target Pattern
+weight: 7
+---
+
+To support multi-target pattern you can create a custom collector overriding the purposed internal method in ExtendedCollector
+see SampleExtendedCollector in io.prometheus.metrics.examples.httpserver
+
+```java
+public class SampleExtendedCollector extends ExtendedCollector {
+
+	public SampleExtendedCollector() {
+		super();
+	}
+
+	@Override
+	protected MetricSnapshot collectMetricSnapshot(PrometheusScrapeRequest scrapeRequest) {
+		Counter sampleCounter;
+		sampleCounter = Counter.builder().name("x_counter_total").labelNames("target", "proc").build();
+		String[] targetName = scrapeRequest.getParameterValues("target");
+		String[] procs = scrapeRequest.getParameterValues("proc");
+		if (targetName == null || targetName.length == 0) {
+			sampleCounter.labelValues("defaultTarget", "defaultProc").inc();
+		} else {
+			if (procs == null || procs.length == 0) {
+				sampleCounter.labelValues(targetName[0], "defaultProc").inc(Math.random());
+			} else {
+				for (int i = 0; i < procs.length; i++) {
+					sampleCounter.labelValues(targetName[0], procs[i]).inc(Math.random());
+				}
+
+			}
+		}
+		return sampleCounter.collect();
+	}
+
+}
+
+```
+`PrometheusScrapeRequest` provides methods to access http-related infos from the request originally received by the endpoint
+
+```java
+public interface PrometheusScrapeRequest {
+	String getRequestURI();
+
+	String[] getParameterValues(String name);
+}
+
+```
+

examples/example-exporter-httpserver/src/main/java/io/prometheus/metrics/examples/httpserver/MainMultiTarget.java

@@ -0,0 +1,25 @@
+package io.prometheus.metrics.examples.httpserver;
+
+import java.io.IOException;
+
+import io.prometheus.metrics.exporter.httpserver.HTTPServer;
+import io.prometheus.metrics.model.registry.PrometheusRegistry;
+
+/**
+ * Simple example of an application exposing metrics via Prometheus' built-in HTTPServer.
+ */
+public class MainMultiTarget {
+
+    public static void main(String[] args) throws IOException, InterruptedException {
+
+        SampleExtendedCollector xc = new SampleExtendedCollector();
+        PrometheusRegistry.defaultRegistry.register(xc);
+        SampleExtendedMultiCollector xmc = new SampleExtendedMultiCollector();
+        PrometheusRegistry.defaultRegistry.register(xmc);
+        HTTPServer server = HTTPServer.builder()
+                .port(9400)
+                .buildAndStart();
+
+        System.out.println("HTTPServer listening on port http://localhost:" + server.getPort() + "/metrics");
+    }
+}

examples/example-exporter-httpserver/src/main/java/io/prometheus/metrics/examples/httpserver/SampleExtendedCollector.java

@@ -0,0 +1,35 @@
+package io.prometheus.metrics.examples.httpserver;
+
+import io.prometheus.metrics.core.metrics.Counter;
+import io.prometheus.metrics.model.registry.ExtendedCollector;
+import io.prometheus.metrics.model.registry.PrometheusScrapeRequest;
+import io.prometheus.metrics.model.snapshots.MetricSnapshot;
+
+public class SampleExtendedCollector extends ExtendedCollector {
+
+	public SampleExtendedCollector() {
+		super();
+	}
+
+	@Override
+	protected MetricSnapshot collectMetricSnapshot(PrometheusScrapeRequest scrapeRequest) {
+		Counter sampleCounter;
+		sampleCounter = Counter.builder().name("x_counter_total").labelNames("target", "proc").build();
+		String[] targetName = scrapeRequest.getParameterValues("target");
+		String[] procs = scrapeRequest.getParameterValues("proc");
+		if (targetName == null || targetName.length == 0) {
+			sampleCounter.labelValues("defaultTarget", "defaultProc").inc();
+		} else {
+			if (procs == null || procs.length == 0) {
+				sampleCounter.labelValues(targetName[0], "defaultProc").inc(Math.random());
+			} else {
+				for (int i = 0; i < procs.length; i++) {
+					sampleCounter.labelValues(targetName[0], procs[i]).inc(Math.random());
+				}
+
+			}
+		}
+		return sampleCounter.collect();
+	}
+
+}

examples/example-exporter-httpserver/src/main/java/io/prometheus/metrics/examples/httpserver/SampleExtendedMultiCollector.java

@@ -0,0 +1,56 @@
+package io.prometheus.metrics.examples.httpserver;
+
+import java.util.ArrayList;
+import java.util.Collection;
+import java.util.List;
+
+import io.prometheus.metrics.core.metrics.Counter;
+import io.prometheus.metrics.core.metrics.Gauge;
+import io.prometheus.metrics.model.registry.ExtendedMultiCollector;
+import io.prometheus.metrics.model.registry.PrometheusScrapeRequest;
+import io.prometheus.metrics.model.snapshots.MetricSnapshot;
+import io.prometheus.metrics.model.snapshots.MetricSnapshots;
+
+public class SampleExtendedMultiCollector extends ExtendedMultiCollector {
+
+	public SampleExtendedMultiCollector() {
+		super();
+	}
+
+	@Override
+	protected MetricSnapshots collectMetricSnapshots(PrometheusScrapeRequest scrapeRequest) {
+		Counter sampleCounter;
+		Gauge sampleGauge;
+		sampleCounter = Counter.builder().name("x_calls_total").labelNames("target", "proc").build();
+		sampleGauge = Gauge.builder().name("x_load").labelNames("target", "proc").build();
+		String[] targetName = scrapeRequest.getParameterValues("target");
+		String[] procs = scrapeRequest.getParameterValues("proc");
+		if (targetName == null || targetName.length == 0) {
+			sampleCounter.labelValues("defaultTarget", "defaultProc").inc();
+			sampleGauge.labelValues("defaultTarget", "defaultProc").set(Math.random());
+		} else {
+			if (procs == null || procs.length == 0) {
+				sampleCounter.labelValues(targetName[0], "defaultProc").inc(Math.random());
+				sampleGauge.labelValues(targetName[0], "defaultProc").set(Math.random());
+			} else {
+				for (int i = 0; i < procs.length; i++) {
+					sampleCounter.labelValues(targetName[0], procs[i]).inc(Math.random());
+					sampleGauge.labelValues(targetName[0], procs[i]).set(Math.random());
+				}
+
+			}
+		}
+		Collection<MetricSnapshot> snaps = new ArrayList<MetricSnapshot>();
+		snaps.add(sampleCounter.collect());
+		snaps.add(sampleGauge.collect());
+		MetricSnapshots msnaps = new MetricSnapshots(snaps);
+		return msnaps;
+	}
+
+	public List<String> getPrometheusNames() {
+		List<String> names = new ArrayList<String>();
+		names.add("Multi");
+		return names ;
+	}
+
+}

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

@@ -7,6 +7,11 @@
 
 public interface PrometheusHttpRequest {
 
+    /**
+     * Return the absolute path of a Http Request
+     */
+    String getRequestPath();
+
     /**
      * See {@code jakarta.servlet.http.HttpServletRequest.getQueryString()}
      */

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

@@ -0,0 +1,24 @@
+package io.prometheus.metrics.exporter.common;
+
+import io.prometheus.metrics.model.registry.PrometheusScrapeRequest;
+
+public class PrometheusHttpScrapeRequest implements PrometheusScrapeRequest {
+
+	protected PrometheusHttpRequest prometheusHttpRequest;
+
+	public PrometheusHttpScrapeRequest(PrometheusHttpRequest prometheusHttpRequest) {
+		super();
+		this.prometheusHttpRequest = prometheusHttpRequest;
+	}
+
+	@Override
+	public String getRequestURI() {
+		return prometheusHttpRequest.getRequestPath();
+	}
+
+	@Override
+	public String[] getParameterValues(String name) {
+		return prometheusHttpRequest.getParameterValues(name);
+	}
+
+}

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

@@ -104,11 +104,13 @@ private Predicate<String> makeNameFilter(ExporterFilterProperties props) {
     }
 
     private MetricSnapshots scrape(PrometheusHttpRequest request) {
+        PrometheusHttpScrapeRequest scrapeRequest = new PrometheusHttpScrapeRequest(request);
+
         Predicate<String> filter = makeNameFilter(request.getParameterValues("name[]"));
         if (filter != null) {
-            return registry.scrape(filter);
+            return registry.scrape(filter, scrapeRequest);
         } else {
-            return registry.scrape();
+            return registry.scrape(scrapeRequest);
         }
     }
 

prometheus-metrics-exporter-httpserver/src/main/java/io/prometheus/metrics/exporter/httpserver/HttpExchangeAdapter.java

@@ -9,6 +9,7 @@
 import java.io.OutputStream;
 import java.io.PrintWriter;
 import java.io.StringWriter;
+import java.net.URI;
 import java.nio.charset.StandardCharsets;
 import java.util.Collections;
 import java.util.Enumeration;
@@ -29,7 +30,20 @@ public HttpExchangeAdapter(HttpExchange httpExchange) {
 
     public class HttpRequest implements PrometheusHttpRequest {
 
+
+
         @Override
+		public String getRequestPath() {
+    		URI requestURI = httpExchange.getRequestURI();
+    		String uri = requestURI.toString();
+    		int qx = uri.indexOf('?');
+    		if (qx != -1) {
+    			uri = uri.substring(0, qx);
+    		}
+    		return uri;
+		}
+
+		@Override
         public String getQueryString() {
             return httpExchange.getRequestURI().getRawQuery();
         }

prometheus-metrics-exporter-servlet-jakarta/src/main/java/io/prometheus/metrics/exporter/servlet/jakarta/HttpExchangeAdapter.java

@@ -54,6 +54,24 @@ public Request(HttpServletRequest request) {
         }
 
         @Override
+		public String getRequestPath() {
+        	StringBuffer uri = new StringBuffer();
+			String contextPath = request.getContextPath();
+        	if (contextPath.startsWith("/")) {
+        		uri.append(contextPath);
+        	}
+			String servletPath = request.getServletPath();
+			if (servletPath.startsWith("/")) {
+        		uri.append(servletPath);
+			}
+			String pathInfo = request.getPathInfo();
+			if (pathInfo != null) {
+				uri.append(pathInfo);
+			}
+			return uri.toString();
+		}
+
+		@Override
         public String getQueryString() {
             return request.getQueryString();
         }

prometheus-metrics-model/src/main/java/io/prometheus/metrics/model/registry/Collector.java

@@ -19,6 +19,15 @@ public interface Collector {
      */
     MetricSnapshot collect();
 
+    /**
+     * Provides Collector with the details of the request issued by Prometheus to allow multi-target pattern implementation
+     * Override to implement request dependent logic to provide MetricSnapshot
+     */
+	default MetricSnapshot collect(PrometheusScrapeRequest scrapeRequest) {
+		MetricSnapshot result = collect();
+		return result;
+	}
+
     /**
      * Like {@link #collect()}, but returns {@code null} if {@code includedNames.test(name)} is {@code false}.
      * <p>
@@ -33,6 +42,21 @@ default MetricSnapshot collect(Predicate<String> includedNames) {
         }
     }
 
+    /**
+     * Like {@link #collect(includedNames)}, but with support for multi-target pattern.
+     * <p>
+     * Override this if there is a more efficient way than first collecting the snapshot and then discarding it.
+     */
+    default MetricSnapshot collect(Predicate<String> includedNames, PrometheusScrapeRequest scrapeRequest) {
+        MetricSnapshot result = collect(scrapeRequest);
+        if (includedNames.test(result.getMetadata().getPrometheusName())) {
+            return result;
+        } else {
+            return null;
+        }
+    }
+
+
     /**
      * Override this and return {@code null} if a collector does not have a constant name,
      * or if you don't want this library to call {@link #collect()} during registration of this collector.

prometheus-metrics-model/src/main/java/io/prometheus/metrics/model/registry/ExtendedCollector.java

@@ -0,0 +1,30 @@
+package io.prometheus.metrics.model.registry;
+
+import io.prometheus.metrics.model.snapshots.MetricSnapshot;
+
+public abstract class ExtendedCollector implements Collector {
+
+	@Override
+	public MetricSnapshot collect() {
+		return null;
+	}
+
+	@Override
+	public MetricSnapshot collect(PrometheusScrapeRequest scrapeRequest) {
+		return collectMetricSnapshot(scrapeRequest);
+	}
+
+	/**
+	 * Override to implement multi-target exporter pattern
+	 * @param scrapeRequest
+	 *            the (http) request context triggering metrics collection
+	 */
+	protected abstract MetricSnapshot collectMetricSnapshot(PrometheusScrapeRequest scrapeRequest);
+
+	@Override
+	public String getPrometheusName() {
+		return null;
+	}
+
+
+}

prometheus-metrics-model/src/main/java/io/prometheus/metrics/model/registry/ExtendedMultiCollector.java

@@ -0,0 +1,25 @@
+package io.prometheus.metrics.model.registry;
+
+import io.prometheus.metrics.model.snapshots.MetricSnapshots;
+
+public abstract class ExtendedMultiCollector implements MultiCollector {
+
+	@Override
+	public MetricSnapshots collect() {
+		return new MetricSnapshots();
+	}
+
+	@Override
+	public MetricSnapshots collect(PrometheusScrapeRequest scrapeRequest) {
+		return collectMetricSnapshots(scrapeRequest);
+	}
+
+	/**
+	 * Override to implement multi-target exporter pattern
+	 * @param scrapeRequest
+	 *            the (http) request context triggering metrics collection
+	 */
+	protected abstract MetricSnapshots collectMetricSnapshots(PrometheusScrapeRequest scrapeRequest);
+
+
+}