Add support for openmetrics 0.0.1 besides 1.0.0

doc/api.md

@@ -2321,8 +2321,8 @@ _**Response body**_
 
 Returns the current value of the server stats,
 
--   If `Accept` header contains `application/openmetrics-text`, the response has content-type
-    `application/openmetrics-text; version=1.0.0; charset=utf-8`
+-   If `Accept` header contains `application/openmetrics-text; version=(1.0.0|0.0.1)`, the response has content-type
+    `application/openmetrics-text; version=<the requested version>; charset=utf-8`
 -   Else, If `Accept` header is missing or supports `text/plain` (explicitly or by `*/*`) , the response has
     content-type `text/plain; version=0.0.4; charset=utf-8` (legacy format for [prometheus](https://prometheus.io))
 -   In any other case, returns an error message with `406` status.

lib/services/stats/statsRegistry.js

@@ -72,6 +72,77 @@ function globalLoad(values, callback) {
     callback(null);
 }
 
+/**
+ * Chooses the appropiate content type and version based on Accept header
+ * 
+ * @param {String} accepts The accepts header
+ */
+function matchContentType(accepts) {
+    const requestedType = [];
+    for (const expression of accepts.split(',')) {
+        const parts = expression.split(';').map((part) => part.trim());
+        const mediaType = parts[0];
+        let version = null;
+        let charset = null;
+        let preference = null;
+        for (let part of parts.slice(1)) {
+            if (part.startsWith('version=')) {
+                version = part.substring(8).trim();
+            } else if (part.startsWith('charset=')) {
+                charset = part.substring(8).trim();
+            } else if (part.startsWith('q=')) {
+                preference = parseFloat(part.substring(2).trim());
+            }
+        }
+        requestedType.push({
+            mediaType: mediaType,
+            version: version,
+            charset: charset,
+            preference: preference || 1
+        });
+    }
+    // If both text/plain and openmetrics are accepted,
+    // prefer openmetrics
+    const mediaTypePref = {
+        'application/openmetrics-text': 1,
+        'text/plain': 0.5
+    }
+    // sort requests by priority descending
+    requestedType.sort(function (a, b) {
+        if (a.preference === b.preference) {
+            // same priority, sort by media type.
+            return (mediaTypePref[b.mediaType] || 0) - (mediaTypePref[a.mediaType] || 0);
+        }
+        return b.preference - a.preference;
+    });
+    for (const req of requestedType) {
+        switch(req.mediaType) {
+            case 'application/openmetrics-text':
+                req.version = req.version || '1.0.0';
+                req.charset = req.charset || 'utf-8';
+                if (
+                    (req.version === '1.0.0' || req.version === '0.0.1') &&
+                    (req.charset === 'utf-8')) {
+                    return req;
+                }
+                break;
+            case 'text/plain':
+            case 'text/*':
+            case '*/*':
+                req.version = req.version || '0.0.4';
+                req.charset = req.charset || 'utf-8';
+                if (
+                    (req.version === '0.0.4') &&
+                    (req.charset === 'utf-8')) {
+                    req.mediaType = 'text/plain';
+                    return req;
+                }
+                break;
+        }
+    }
+    return null;
+}
+
 /**
  * Predefined http handler that returns current openmetrics data
  */
@@ -82,60 +153,26 @@ function openmetricsHandler(req, res) {
     // https://github.com/OpenObservability/OpenMetrics/blob/main/specification/OpenMetrics.md#overall-structure
     // - For prometheus compatible collectors, it SHOULD BE 'text/plain; version=0.0.4; charset=utf-8'. See:
     // https://github.com/prometheus/docs/blob/main/content/docs/instrumenting/exposition_formats.md
-    let contentType = 'application/openmetrics-text; version=1.0.0; charset=utf-8';
-    let version = null;
-    let charset = null;
-    // To identify openmetrics collectors, we need to parse the `Accept` header.
-    // An openmetrics-based collectors SHOULD use an `Accept` header such as:
-    //   `Accept: application/openmetrics-text; version=1.0.0; charset=utf-8'
-    // See: https://github.com/open-telemetry/opentelemetry-collector-contrib/issues/18913
-    //
-    // WORKAROUND: express version 4 does not parse properly the openmetrics Accept header,
-    // it won't match the regular expressions supported by `express.accepts`.
-    // So we must parse these key-value pairs ourselves, and remove them from the
-    // header before handling it to `requests.accept`.
-    if (req.headers.accept) {
-        const parts = req.headers.accept.split(';');
-        let unparsed = [];
-        for (let i = 0; i < parts.length; i++) {
-            const current = parts[i];
-            const trimmed = current.trim();
-            if (trimmed.startsWith('version=')) {
-                version = trimmed.substring(8);
-            } else if (trimmed.startsWith('charset=')) {
-                charset = trimmed.substring(8);
-            } else {
-                unparsed.push(current);
-            }
-        }
-        if (unparsed.length < parts.length) {
-            delete req.headers['accept'];
-            req.headers['accept'] = unparsed.join(';');
-        }
-    }
-    // charset MUST BE utf-8
-    if (charset && charset !== 'utf-8') {
-        logger.error(statsContext, 'Unsupported charset: %s', charset);
-        res.status(406).send('Unsupported charset');
-        return;
+    // - Caveat: Some versions of prometheus have been observed to send multivalued Accept headers such as
+    // Accept: application/openmetrics-text; version=0.0.1,text/plain;version=0.0.4;q=0.5,*/*;q=0.1
+    let reqType = {
+        mediaType: 'application/openmetrics-text',
+        version: '1.0.0',
+        charset: 'utf-8'
     }
-    switch (req.accepts(['text/plain', 'application/openmetrics-text'])) {
-        case 'application/openmetrics-text':
-            // Version MUST BE 1.0.0 for openmetrics
-            if (version && version !== '1.0.0') {
-                logger.error(statsContext, 'Unsupported openmetrics version: %s', version);
-                res.status(406).send('Unsupported openmetrics version');
-                return;
-            }
-            break;
-        case 'text/plain':
-            contentType = 'text/plain; version=0.0.4; charset=utf-8';
-            break;
-        default:
-            logger.error(statsContext, 'Unsupported accept header: %s', req.headers.accept);
-            res.status(406).send('Unsupported accept header');
+    if (req.headers.accept) {
+        // WORKAROUND: express version 4 does not parse properly the openmetrics Accept header,
+        // it won't match the regular expressions supported by `express.accepts`.
+        // So we must parse these key-value pairs ourselves.
+        reqType = matchContentType(req.headers.accept);
+        if (reqType === null) {
+            logger.error(statsContext, 'Unsupported media type: %s', req.headers.accept);
+            res.status(406).send('Not Acceptable');
             return;
+        }
     }
+    const contentType = `${reqType.mediaType};version=${reqType.version};charset=${reqType.charset}`;
+    // The actual payload is the same for all supported content types
     const metrics = [];
     for (const key in globalStats) {
         if (globalStats.hasOwnProperty(key)) {
@@ -180,3 +217,4 @@ exports.getAllGlobal = getAllGlobal;
 exports.globalLoad = globalLoad;
 exports.withStats = withStats;
 exports.openmetricsHandler = openmetricsHandler;
+exports.matchContentType = matchContentType;

test/unit/statsRegistry/openmetrics-test.js

@@ -0,0 +1,167 @@
+/*
+ * Copyright 2024 Telefonica Investigación y Desarrollo, S.A.U
+ *
+ * This file is part of fiware-iotagent-lib
+ *
+ * fiware-iotagent-lib is free software: you can redistribute it and/or
+ * modify it under the terms of the GNU Affero General Public License as
+ * published by the Free Software Foundation, either version 3 of the License,
+ * or (at your option) any later version.
+ *
+ * fiware-iotagent-lib is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+ * See the GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public
+ * License along with fiware-iotagent-lib.
+ * If not, see http://www.gnu.org/licenses/.
+ *
+ * For those usages not covered by the GNU Affero General Public License
+ * please contact with::daniel.moranjimenez@telefonica.com
+ */
+
+/* eslint-disable no-unused-vars */
+
+const statsRegistry = require('../../../lib/services/stats/statsRegistry');
+const should = require('should');
+
+describe('statsRegistry - openmetrics endpoint', function () {
+
+    const testCases = [
+        {
+            description: 'Should accept standard openmetrics 0.0.1 header',
+            accept: 'application/openmetrics-text; version=0.0.1; charset=utf-8',
+            contentType: {
+                mediaType: 'application/openmetrics-text',
+                version: '0.0.1',
+                charset: 'utf-8'
+            }
+        },
+        {
+            description: 'Should accept standard openmetrics 1.0.0 header',
+            accept: 'application/openmetrics-text; version=1.0.0; charset=utf-8',
+            contentType: {
+                mediaType: 'application/openmetrics-text',
+                version: '1.0.0',
+                charset: 'utf-8'
+            }
+        },
+        {
+            description: 'Should accept openmetrics with no version',
+            accept: 'application/openmetrics-text',
+            contentType: {
+                mediaType: 'application/openmetrics-text',
+                version: '1.0.0',
+                charset: 'utf-8'
+            }
+        },
+        {
+            description: 'Should accept text/plain header with version',
+            accept: 'text/plain; version=0.0.4',
+            contentType: {
+                mediaType: 'text/plain',
+                version: '0.0.4',
+                charset: 'utf-8'
+            }
+        },
+        {
+            description: 'Should accept wildcard header',
+            accept: '*/*',
+            contentType: {
+                mediaType: 'text/plain',
+                version: '0.0.4',
+                charset: 'utf-8'
+            }
+        },
+        {
+            description: 'Should accept both openmetrics and text/plain, prefer openmetrics',
+            accept: 'application/openmetrics-text; version=0.0.1; charset=utf-8,text/plain;version=0.0.4',
+            contentType: {
+                mediaType: 'application/openmetrics-text',
+                version: '0.0.1',
+                charset: 'utf-8'
+            }
+        },
+        {
+            description: 'Should accept both text/plain and openmetrics, prefer openmetrics',
+            accept: 'text/plain,application/openmetrics-text; version=0.0.1; charset=utf-8',
+            contentType: {
+                mediaType: 'application/openmetrics-text',
+                version: '0.0.1',
+                charset: 'utf-8'
+            }
+        },
+        {
+            description: 'Should accept both openmetrics and text/plain, prefer text if preference set',
+            accept: 'application/openmetrics-text; version=0.0.1; charset=utf-8;q=0.5,text/plain;q=0.7',
+            contentType: {
+                mediaType: 'text/plain',
+                version: '0.0.4',
+                charset: 'utf-8'
+            }
+        },
+        {
+            description: 'Should match version to content-type',
+            accept: 'application/openmetrics-text; version=0.0.1; charset=utf-8, text/plain;version=1.0.0',
+            contentType: {
+                mediaType: 'application/openmetrics-text',
+                version: '0.0.1',
+                charset: 'utf-8'
+            }
+        },
+        {
+            description: 'Should set default q to 1.0',
+            accept: 'application/openmetrics-text; version=0.0.1; q=0.5,text/plain;version=0.0.4',
+            contentType: {
+                mediaType: 'text/plain',
+                version: '0.0.4',
+                charset: 'utf-8'
+            }
+        },
+        {
+            description: 'Should accept mixture of content-types and q',
+            accept: 'application/openmetrics-text; version=0.0.1,text/plain;version=0.0.4;q=0.5,*/*;q=0.1',
+            contentType: {
+                mediaType: 'application/openmetrics-text',
+                version: '0.0.1',
+                charset: 'utf-8'
+            }
+        },
+        {
+            description: 'Should reject Invalid charset',
+            accept: '*/*; charset=utf-16',
+            contentType: null
+        },
+        {
+            description: 'Should reject Invalid openmetrics version',
+            accept: 'application/openmetrics-text; version=0.0.5',
+            contentType: null
+        },
+        {
+            description: 'Should reject Invalid text/plain',
+            accept: 'text/plain; version=0.0.2',
+            contentType: null
+        }
+    ]
+
+    for (const testCase of testCases) {
+        describe(testCase.description, function () {
+            const result = statsRegistry.matchContentType(testCase.accept);
+            if (testCase.contentType) {
+                it('should match', function (done) {
+                    should.exist(result);
+                    result.mediaType.should.equal(testCase.contentType.mediaType);
+                    result.version.should.equal(testCase.contentType.version);
+                    result.charset.should.equal(testCase.contentType.charset);
+                    done();
+                });
+            } else {
+                it('should not match', function (done) {
+                    should.not.exist(result);
+                    done();
+                });
+            }
+        });
+    }
+});