NMS-19910: Add support for OpenMetrics v1 text format scraping

docs/modules/reference/pages/performance-data-collection/collectors/prometheus.adoc

@@ -3,11 +3,16 @@
 = PrometheusCollector
 :description: Learn how to configure the PrometheusCollector in OpenNMS {page-component-title} to collect performance data via HTTP(S) using the Prometheus Exposition format.
 
-The PrometheusCollector collects performance metrics via HTTP(S) using the text-based https://github.com/prometheus/docs/blob/master/content/docs/instrumenting/exposition_formats.md#text-based-format[Prometheus Exposition format].
-Many applications have adopted it and it is in the process of being standardized in the https://openmetrics.io/[OpenMetrics] project.
+The PrometheusCollector collects performance metrics via HTTP(S), supporting both the classic https://github.com/prometheus/docs/blob/main/docs/instrumenting/exposition_formats.md#prometheus-text-format[Prometheus Text Format] and the newer https://github.com/prometheus/docs/blob/main/docs/specs/om/open_metrics_spec.md[OpenMetrics 1.0 Text Format].
+
+It can scrape endpoints that provide either format or both. When both are available, it automatically prioritizes OpenMetrics. This protocol negotiation is performed via quality/priority values in the HTTP header `Accept`.
 
 This collector provides tools for parsing and mapping the metrics to the collection model used by {page-component-title}.
 
+=== Limitations
+
+The PrometheusCollector only processes a subset of the metric types defined in both formats, namely counters and gauges. Histograms and summaries are *not* supported and will be ignored. Metric timestamps are also ignored.
+
 == Collector facts
 
 [options="autowidth"]

features/prometheus-collector/pom.xml

@@ -142,5 +142,11 @@
       <version>1.57</version>
       <scope>test</scope>
     </dependency>
+	<dependency>
+	    <groupId>javax.persistence</groupId>
+	    <artifactId>javax.persistence-api</artifactId>
+	    <version>2.2</version>
+	    <scope>test</scope>
+	</dependency>
   </dependencies>
 </project>

features/prometheus-collector/src/main/java/org/hawkular/agent/prometheus/PrometheusMetricsProcessor.java

@@ -96,7 +96,7 @@ public void walk() {
                                     ((org.hawkular.agent.prometheus.types.Histogram) metric), metricIndex);
                             break;
 
-                        case UNTYPED:
+                        case UNKNOWN:
                             // if we can't tell what it is, it's a gauge.
                             log.debug("UNtyped metric: '{}'",metric);
                             walker.walkGaugeMetric(convertedMetricFamily, (Gauge) metric, metricIndex);

features/prometheus-collector/src/main/java/org/hawkular/agent/prometheus/Util.java

@@ -16,7 +16,18 @@
  */
 package org.hawkular.agent.prometheus;
 
+import java.time.Instant;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
 public class Util {
+
+    private static final Logger LOGGER = LoggerFactory.getLogger(Util.class);
+
+    private Util() {
+        // prevent instantiation
+    }
 
     public static double convertStringToDouble(String valueString) {
         double doubleValue;
@@ -39,4 +50,19 @@ public static String convertDoubleToString(double value) {
         }
         return String.format("%f", value);
     }
+
+    public static Instant tryConvertTimestamp(CharSequence timestamp) {
+        if (timestamp == null || timestamp.isEmpty()) {
+            return null;
+        }
+        try {
+            double timestampDouble = Double.parseDouble(timestamp.toString());
+            long epochSecond = (long) timestampDouble;
+            return Instant.ofEpochSecond(epochSecond);
+        }
+        catch (NumberFormatException e) {
+            LOGGER.warn("Invalid timestamp: " + timestamp);
+            return null;
+        }
+    }
 }

features/prometheus-collector/src/main/java/org/hawkular/agent/prometheus/text/LineParser.java

@@ -0,0 +1,203 @@
+/*
+ * Licensed to The OpenNMS Group, Inc (TOG) under one or more
+ * contributor license agreements.  See the LICENSE.md file
+ * distributed with this work for additional information
+ * regarding copyright ownership.
+ *
+ * TOG licenses this file to You under the GNU Affero General
+ * Public License Version 3 (the "License") or (at your option)
+ * any later version.  You may not use this file except in
+ * compliance with the License.  You may obtain a copy of the
+ * License at:
+ *
+ *      https://www.gnu.org/licenses/agpl-3.0.txt
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND,
+ * either express or implied.  See the License for the specific
+ * language governing permissions and limitations under the
+ * License.
+ */
+package org.hawkular.agent.prometheus.text;
+
+import java.util.LinkedHashMap;
+import java.util.Map;
+
+import org.hawkular.agent.prometheus.Util;
+
+class LineParser {
+
+    private enum ParseState {
+        NAME,
+        ENDOFNAME,
+        STARTOFLABELNAME,
+        LABELNAME,
+        LABELVALUEEQUALS,
+        LABELVALUEQUOTE,
+        LABELVALUE,
+        LABELVALUESLASH,
+        NEXTLABEL,
+        ENDOFLABELS,
+        VALUE,
+        TIMESTAMP
+    }
+
+    private final StringBuilder name = new StringBuilder();
+    private final StringBuilder labelname = new StringBuilder();
+    private final StringBuilder labelvalue = new StringBuilder();
+    private final StringBuilder value = new StringBuilder();
+    private final StringBuilder timestamp = new StringBuilder();
+    private final Map<String, String> labels = new LinkedHashMap<>();
+    private ParseState state;
+
+    public void reset() {
+        name.setLength(0);
+        labelname.setLength(0);
+        labelvalue.setLength(0);
+        value.setLength(0);
+        timestamp.setLength(0);
+        labels.clear();
+        state = ParseState.NAME;
+    }
+
+    public TextSample parse(String line) {
+        reset();
+
+        for (int c = 0; c < line.length(); c++) {
+            char charAt = line.charAt(c);
+
+            switch (state) {
+                case NAME:
+                    if (charAt == '{') {
+                        state = ParseState.STARTOFLABELNAME;
+                    } else if (charAt == ' ' || charAt == '\t') {
+                        state = ParseState.ENDOFNAME;
+                    } else {
+                        name.append(charAt);
+                    }
+                    break;
+                case ENDOFNAME:
+                    if (charAt == ' ' || charAt == '\t') {
+                        // do nothing
+                    } else if (charAt == '{') {
+                        state = ParseState.STARTOFLABELNAME;
+                    } else {
+                        value.append(charAt);
+                        state = ParseState.VALUE;
+                    }
+                    break;
+                case STARTOFLABELNAME:
+                    if (charAt == ' ' || charAt == '\t') {
+                        // do nothing
+                    } else if (charAt == '}') {
+                        state = ParseState.ENDOFLABELS;
+                    } else {
+                        labelname.append(charAt);
+                        state = ParseState.LABELNAME;
+                    }
+                    break;
+                case LABELNAME:
+                    if (charAt == '=') {
+                        state = ParseState.LABELVALUEQUOTE;
+                    } else if (charAt == '}') {
+                        state = ParseState.ENDOFLABELS;
+                    } else if (charAt == ' ' || charAt == '\t') {
+                        state = ParseState.LABELVALUEEQUALS;
+                    } else {
+                        labelname.append(charAt);
+                    }
+                    break;
+                case LABELVALUEEQUALS:
+                    if (charAt == '=') {
+                        state = ParseState.LABELVALUEQUOTE;
+                    } else if (charAt == ' ' || charAt == '\t') {
+                        // do nothing
+                    } else {
+                        throw new IllegalStateException("Invalid line: " + line);
+                    }
+                    break;
+                case LABELVALUEQUOTE:
+                    if (charAt == '"') {
+                        state = ParseState.LABELVALUE;
+                    } else if (charAt == ' ' || charAt == '\t') {
+                        // do nothing
+                    } else {
+                        throw new IllegalStateException("Invalid line: " + line);
+                    }
+                    break;
+                case LABELVALUE:
+                    if (charAt == '\\') {
+                        state = ParseState.LABELVALUESLASH;
+                    } else if (charAt == '"') {
+                        labels.put(labelname.toString(), labelvalue.toString());
+                        labelname.setLength(0);
+                        labelvalue.setLength(0);
+                        state = ParseState.NEXTLABEL;
+                    } else {
+                        labelvalue.append(charAt);
+                    }
+                    break;
+                case LABELVALUESLASH:
+                    state = ParseState.LABELVALUE;
+                    if (charAt == '\\') {
+                        labelvalue.append('\\');
+                    } else if (charAt == 'n') {
+                        labelvalue.append('\n');
+                    } else if (charAt == '"') {
+                        labelvalue.append('"');
+                    } else {
+                        labelvalue.append('\\').append(charAt);
+                    }
+                    break;
+                case NEXTLABEL:
+                    if (charAt == ',') {
+                        state = ParseState.LABELNAME;
+                    } else if (charAt == '}') {
+                        state = ParseState.ENDOFLABELS;
+                    } else if (charAt == ' ' || charAt == '\t') {
+                        // do nothing
+                    } else {
+                        throw new IllegalStateException("Invalid line: " + line);
+                    }
+                    break;
+                case ENDOFLABELS:
+                    if (charAt == ' ' || charAt == '\t') {
+                        // do nothing
+                    } else {
+                        value.append(charAt);
+                        state = ParseState.VALUE;
+                    }
+                    break;
+                case VALUE:
+                    if (charAt == ' ' || charAt == '\t') {
+                        state = ParseState.TIMESTAMP;                       
+                    } else {
+                        value.append(charAt);
+                    }
+                    break;
+                case TIMESTAMP:
+                    if (charAt == ' ' || charAt == '\t') {
+                        return buildSample(line);
+                    }
+                    else {
+                        timestamp.append(charAt);
+                    }
+                    break;
+            }
+        }
+
+        return buildSample(line);
+    }
+
+    private TextSample buildSample(String line) {
+        return new TextSample.Builder()
+                .setLine(line)
+                .setName(name.toString())
+                .setValue(value.toString())
+                .setTimestamp(Util.tryConvertTimestamp(timestamp))
+                .addLabels(new LinkedHashMap<>(labels))
+                .build();
+    }
+
+}