From 266e8ad797314c1033d56abb82cc99ce6886f860 Mon Sep 17 00:00:00 2001
From: Will Hunt <willh@matrix.org>
Date: Mon, 25 Jan 2021 12:40:15 +0000
Subject: [PATCH 1/2] Collectors can now be async

---
 changelog.d/304.misc                |  1 +
 src/bridge.ts                       |  6 +++---
 src/components/prometheusmetrics.ts | 29 ++++++++++++++++++-----------
 3 files changed, 22 insertions(+), 14 deletions(-)
 create mode 100644 changelog.d/304.misc

diff --git a/changelog.d/304.misc b/changelog.d/304.misc
new file mode 100644
index 00000000..3d116275
--- /dev/null
+++ b/changelog.d/304.misc
@@ -0,0 +1 @@
+Fetch metrics asynchronously
\ No newline at end of file
diff --git a/src/bridge.ts b/src/bridge.ts
index 62196e28..8bf63f9e 100644
--- a/src/bridge.ts
+++ b/src/bridge.ts
@@ -1404,9 +1404,9 @@ export class Bridge {
      *     }
      * })
      */
-    public registerBridgeGauges(counterFunc: () => BridgeGaugesCounts) {
-        this.getPrometheusMetrics().registerBridgeGauges(() => {
-            const counts = counterFunc();
+    public registerBridgeGauges(counterFunc: () => Promise<BridgeGaugesCounts>|BridgeGaugesCounts) {
+        this.getPrometheusMetrics().registerBridgeGauges(async () => {
+            const counts = await counterFunc();
             if (counts.matrixGhosts !== undefined) {
                 counts.matrixGhosts = Object.keys(this.intents.size).length;
             }
diff --git a/src/components/prometheusmetrics.ts b/src/components/prometheusmetrics.ts
index 04f28744..70ed642a 100644
--- a/src/components/prometheusmetrics.ts
+++ b/src/components/prometheusmetrics.ts
@@ -18,7 +18,8 @@ import { AgeCounters } from "./agecounters";
 import JsSdk from "matrix-js-sdk";
 import { Request, Response } from "express";
 import { Bridge } from "..";
-type CollectorFunction = () => void;
+import Logger from "./logging";
+type CollectorFunction = () => Promise<void>|void;
 
 export interface BridgeGaugesCounts {
     matrixRoomConfigs?: number;
@@ -100,6 +101,9 @@ interface GagueOpts {
  *
  * @constructor
  */
+
+const log = Logger.get('PrometheusMetrics');
+
 export class PrometheusMetrics {
     public static AgeCounters = AgeCounters;
     private timers: {[name: string]: PromClient.Histogram<string>} = {};
@@ -179,7 +183,7 @@ export class PrometheusMetrics {
      * @param {BridgeGaugesCallback} counterFunc A function that when invoked
      * returns the current counts of various items in the bridge.
      */
-    public registerBridgeGauges (counterFunc: () => BridgeGaugesCounts) {
+    public async registerBridgeGauges (counterFunc: () => Promise<BridgeGaugesCounts>|BridgeGaugesCounts) {
         const matrixRoomsGauge = this.addGauge({
             name: "matrix_configured_rooms",
             help: "Current count of configured rooms by matrix room ID",
@@ -220,8 +224,8 @@ export class PrometheusMetrics {
             labels: ["age"],
         });
 
-        this.addCollector(function () {
-            const counts = counterFunc();
+        this.addCollector(async () => {
+            const counts = await counterFunc();
 
             if (counts.matrixRoomConfigs) {matrixRoomsGauge.set(counts.matrixRoomConfigs);}
 
@@ -239,10 +243,6 @@ export class PrometheusMetrics {
         });
     }
 
-    public refresh () {
-        this.collectors.forEach((f) => f());
-    }
-
     /**
      * Adds a new collector function. These collector functions are run whenever
      * the /metrics page is about to be generated, allowing code to update values
@@ -381,9 +381,8 @@ export class PrometheusMetrics {
             // For now, leave this unauthenticated.
             checkToken: false,
             handler: async (_req: Request, res: Response) => {
-                this.refresh();
-
                 try {
+                    await this.refresh();
                     const exposition = await this.register.metrics();
 
                     res.set("Content-Type", "text/plain");
@@ -391,11 +390,19 @@ export class PrometheusMetrics {
                 }
                 catch (e) {
                     res.status(500);
-
                     res.set("Content-Type", "text/plain");
                     res.send(e.toString());
                 }
             },
         });
     }
+
+    private async refresh () {
+        try {
+            await Promise.all(this.collectors.map((f) => f()));
+        }
+        catch (ex) {
+            log.warn(`Failed to refresh metrics:`, ex);
+        }
+    }
 }

From 51846f47973462a5cd2d42858108e4215cb3e358 Mon Sep 17 00:00:00 2001
From: Will Hunt <willh@matrix.org>
Date: Mon, 25 Jan 2021 13:20:00 +0000
Subject: [PATCH 2/2] Reinstate refresh as a public method

---
 src/components/prometheusmetrics.ts | 21 ++++++++++++---------
 1 file changed, 12 insertions(+), 9 deletions(-)

diff --git a/src/components/prometheusmetrics.ts b/src/components/prometheusmetrics.ts
index 70ed642a..61a7c3ea 100644
--- a/src/components/prometheusmetrics.ts
+++ b/src/components/prometheusmetrics.ts
@@ -177,6 +177,18 @@ export class PrometheusMetrics {
         });
     }
 
+    /**
+     * Fetch metrics from all configured collectors
+     */
+    public async refresh () {
+        try {
+            await Promise.all(this.collectors.map((f) => f()));
+        }
+        catch (ex) {
+            log.warn(`Failed to refresh metrics:`, ex);
+        }
+    }
+
     /**
      * Registers some exported metrics that expose counts of various kinds of
      * objects within the bridge.
@@ -396,13 +408,4 @@ export class PrometheusMetrics {
             },
         });
     }
-
-    private async refresh () {
-        try {
-            await Promise.all(this.collectors.map((f) => f()));
-        }
-        catch (ex) {
-            log.warn(`Failed to refresh metrics:`, ex);
-        }
-    }
 }