Prometheus exporter without external dependencies, exporting histograms directly

common/include/villas/hist.hpp

@@ -7,8 +7,9 @@
 
 #pragma once
 
+#include <string>
 #include <vector>
-
+#include<string>
 #include <jansson.h>
 
 #include <villas/log.hpp>
@@ -49,6 +50,7 @@ class Hist {
   // Print ASCII style plot of histogram.
   void plot(Logger logger) const;
 
+  void test();
   // Dump histogram data in Matlab format.
   //
   // @return The string containing the dump. The caller is responsible to free() the buffer.
@@ -60,6 +62,9 @@ class Hist {
   // Write the histogram in JSON format to file \p f.
   int dumpJson(FILE *f) const;
 
+  std::string toPrometheusText(std::string metric_name,
+                               std::string node_name) const;
+
   // Build a libjansson / JSON object of the histogram.
   json_t *toJson() const;
 

common/lib/hist.cpp

@@ -150,6 +150,31 @@ void Hist::plot(Logger logger) const {
   }
 }
 
+std::string Hist::toPrometheusText(std::string metric_name,
+                             std::string node_name) const {
+  std::stringstream base;
+  base << "#TYPE HISTOGRAM " << metric_name;
+  // Needed because Prometheus understands quantiles.
+  int s = data.size();
+  Hist::cnt_t cumsum = 0;
+  for (int i = 0; i < s; i++) {
+    cumsum += data[i];
+    base << "\n"
+         << metric_name << " {node=\"" << node_name << "\" le=\""
+         << ((double)i + 1) / s << "\"} " << cumsum;
+  }
+
+  base << "\n"
+       << metric_name << " {node=\"" << node_name << "\" le=\"+Inf\"} " << total
+       << "\n"
+       << metric_name << "_count "
+       << " {node=\"" << node_name << "\"} " << total;
+
+  //next line is problematic because buckets have no associated values ?
+  //base +="\n"+metric_name+"_count "+" {node=\""+node_name+"} "+std::to_string(ttl);
+  return base.str();
+}
+
 char *Hist::dump() const {
   char *buf = new char[128];
   if (!buf)

lib/api/CMakeLists.txt

@@ -26,6 +26,7 @@ set(API_SRC
     requests/node_stats.cpp
     requests/node_stats_reset.cpp
     requests/node_file.cpp
+    requests/metrics.cpp
     requests/paths.cpp
     requests/path_info.cpp
     requests/path_action.cpp

lib/api/requests/metrics.cpp

@@ -0,0 +1,65 @@
+/* The metrics API ressource.
+ *
+ * Author: Steffen Vogel <post@steffenvogel.de>
+ * Author: Youssef Nakti <naktiyoussef@proton.me>
+ * SPDX-FileCopyrightText: 2014-2023 Institute for Automation of Complex Power Systems, RWTH Aachen University
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#include <chrono>
+
+#include <jansson.h>
+
+#include <villas/api/request.hpp>
+#include <villas/api/response.hpp>
+#include <villas/api/session.hpp>
+#include <villas/node.hpp>
+#include <villas/stats.hpp>
+#include <villas/super_node.hpp>
+#include <villas/utils.hpp>
+
+namespace villas {
+namespace node {
+namespace api {
+
+class MetricsRequest : public Request {
+public:
+  using Request::Request;
+
+  virtual Response *execute() {
+    if (method != Session::Method::GET)
+      throw InvalidMethod(this);
+
+    if (body != nullptr)
+      throw BadRequest("The metrics endpoint does not accept any body data");
+
+    std::stringstream res_stream;
+    NodeList node_list = session->getSuperNode()->getNodes();
+    for (Node *node : node_list) {
+      auto stats = node->getStats();
+      if (!stats)
+        continue;
+      std::string node_name = node->getNameShort();
+      for (auto &metric : Stats::metrics) {
+        std::string metric_name = metric.second.name;
+        std::replace(metric_name.begin(), metric_name.end(), '.', '_');
+        res_stream << stats->getHistogram(metric.first)
+                          .toPrometheusText(metric_name, node->getNameShort())
+                   << "\n";
+      }
+    }
+    auto text_res = res_stream.str();
+    return new Response(session, HTTP_STATUS_OK, "text/plain; charset=UTF-8",
+                        Buffer(text_res.c_str(), text_res.size()));
+  }
+};
+
+// Register API request
+static char n[] = "metrics";
+static char r[] = "/metrics";
+static char d[] = "Get stats of all nodes in Prometheus metrics format";
+static RequestPlugin<MetricsRequest, n, r, d> p;
+
+} // namespace api
+} // namespace node
+} // namespace villas