intial

.eslintrc

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+{
+    "env": {
+        "node": true,
+        "es6": true
+    },
+
+    "extends": "eslint:recommended",
+
+    "rules": {
+        "no-cond-assign": 0,
+        "no-constant-condition": 0,
+        "no-empty": 0,
+        "no-fallthrough": 0,
+        "no-unused-vars": 1,
+        "no-console": 1,
+
+        "semi": 2,
+        "curly": 2,
+        "consistent-this": [2, "self"],
+        "indent": [ 2, 4, { "SwitchCase": 1 } ],
+        "linebreak-style": [2, "unix"],
+        "no-nested-ternary": 2,
+
+        "new-parens": 2,
+        "no-dupe-class-members": 2,
+        "require-yield": 2,
+        "arrow-spacing": 1,
+        "no-var": 2,
+
+        "no-multi-spaces": 1,
+        "space-return-throw-case": 0,
+        "space-infix-ops": [1, {"int32Hint": false}],
+        "brace-style": 1,
+        "space-before-blocks": 1,
+        "operator-linebreak": [1, "before"],
+        "no-unneeded-ternary": 1,
+        "no-lonely-if": 1,
+        "key-spacing": 1,
+        "quotes": [1, "double", "avoid-escape"],
+        "no-trailing-spaces": [1, { "skipBlankLines": true }]
+    }
+}

.gitignore

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+node_modules

.npmignore

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+docker-compose.yml
+test
+.travis.yml
+.eslintrc

.travis.yml

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+language: node_js
+node_js:
+    - "5"
+    - "4"

README.md

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+# express prometheus bundle
+
+A bundle of standard metrics for an express application.
+
+Included metrics:
+    
+* **up**: normally is just 1
+* **nodejs_memory_heap_total_bytes** and **nodejs_memory_heap_used_bytes**
+* **http_request_total**: count of http requests labeled with status_code

example.js

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+"use strict";
+
+const express = require("express"),
+    app = express(),
+    promBundle = require(".");
+
+app.use(promBundle({
+    prefix: "demo_app:something"
+}));
+
+app.get("/hello", (req, res) => res.send("ok"));
+
+app.listen(3000);

package.json

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+{
+  "name": "express-prom-bundle",
+  "version": "1.0.0",
+  "description": "express middleware with standard prometheus metrics in one bundle",
+  "main": "src/index.js",
+  "directories": {
+    "test": "test"
+  },
+  "scripts": {
+    "test": "node_modules/jasme/run.js"
+  },
+  "author": "Konstantin Pogorelov <or@pluseq.com> (https://github.com/disjunction)",
+  "license": "ISC",
+  "dependencies": {
+    "on-finished": "^2.3.0",
+    "prom-client": "^3.4.0"
+  },
+  "devDependencies": {
+    "eslint": "^2.8.0"
+  }
+}

src/PrometheusHelper.js

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+"use strict";
+
+const onFinished = require("on-finished");
+
+module.exports = class {
+    constructor(opts, promClient) {
+        this.opts = opts || {};
+        this.promClient = this.opts.promClient || require("prom-client");
+        this.metrics = {};
+    }
+
+    metricExists(name) {
+        return !!this.metrics[name];
+    }
+
+    checkDuplicate(name) {
+        if (this.metricExists(name)) {
+            throw new Error("trying to add already existing metric: " + name);
+        }
+    }
+
+    makeRealName(name) {
+        const prefix = this.opts.prefix ? (this.opts.prefix + ":") : "";
+        return prefix + name;
+    }
+
+    makeMetric(TheClass, name, description, param) {
+        this.checkDuplicate(name);
+        const realName = this.makeRealName(name);
+        this.metrics[name] = new TheClass(
+            realName, description, param
+        );
+        return this.metrics[name];
+    }
+
+    newCounter(name, description, labels) {
+        return this.makeMetric(this.promClient.Counter, name, description, labels);
+    }
+
+    newGauge(name, description, labels) {
+        return this.makeMetric(this.promClient.Gauge, name, description, labels);
+    }
+
+    newHistogram(name, description, options) {
+        return this.makeMetric(this.promClient.Histogram, name, description, options);
+    }
+
+    newSummary(name, description, options) {
+        return this.makeMetric(this.promClient.Histogram, name, description, options);
+    }
+};

src/index.js

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+"use strict";
+
+const
+    PrometheusHelper = require("./PrometheusHelper"),
+    onFinished = require("on-finished");
+
+function filterArrayByRegExps(array, regexps) {
+    let compiled = regexps.map(regexp => new RegExp(regexp));
+    return array.filter(element => {
+        for (let regexp of compiled) {
+            if (element.match(regexp)) {
+                return true;
+            }
+        }
+        return false;
+    });
+}
+
+function main(opts) {
+    if (arguments[2] && arguments[1] && arguments[1].send) {
+        arguments[1].status(500)
+            .send("<h1>500 Error</h1>\n"
+                + "<p>Unexapected 3d param.\n"
+                + "<p>Did you just put express-prom-bundle into app.use "
+                + "without calling it as a function first?");
+        return;
+    }
+
+    let helper = new PrometheusHelper(opts);
+    let metricTemplates = {
+        "up": () => helper.newGauge(
+            "up",
+            "1 = up, 0 = not up"
+        ),
+        "nodejs_memory_heap_total_bytes": () => helper.newGauge(
+            "nodejs_memory_heap_total_bytes",
+            "value of process.memoryUsage().heapTotal"
+        ),
+        "nodejs_memory_heap_used_bytes": () => helper.newGauge(
+            "nodejs_memory_heap_used_bytes",
+            "value of process.memoryUsage().heapUsed"
+        ),
+        "http_request_total": () => helper.newCounter(
+            "http_request_total",
+            "number of http responses labeled with status code",
+            ["status_code"]
+        )
+    };
+
+    const metrics = {};
+
+    for (let name of Object.keys(metricTemplates)) {
+        metrics[name] = metricTemplates[name]();
+    }
+
+    metrics.up.set(1);
+
+    let middleware = function (req, res, next) {
+        if (req.path == "/metrics") {
+            let memoryUsage = process.memoryUsage();
+            metrics["nodejs_memory_heap_total_bytes"].set(memoryUsage.heapTotal);
+            metrics["nodejs_memory_heap_used_bytes"].set(memoryUsage.heapUsed);
+
+            res.contentType("text/plain")
+                .send(helper.promClient.register.metrics());
+            return;
+        }
+
+        onFinished(res, () => {
+            if (res.statusCode) {
+                metrics["http_request_total"].inc({"status_code": res.statusCode});
+            }
+        });
+
+        next();
+    };
+
+    middleware.helper = helper;
+    middleware.metricTemplates = metricTemplates;
+
+    return middleware;
+}
+
+module.exports = main;