wip

Due to the DefaultFields's design, we setup cyclic references that a managed
language such as Node.JS has no way of solving to release the associated
memory.

As such, this commit provides an helper function that allows breaking the
references and can be called manually, in addition to being called
automatically from the end logger's logging methods.

This choice was pushed by the analysis of the possible alternatives (coming
close to naught), and the context accompanying the feature, such as the fact
the DefaultFields class is aimed at providing relationships management between
various Module loggers and the Request Loggers:
 1. The RequestLogger has a lifetime contained within that of its natural
    parent, the Module Logger
 2. The Module Logger has a lifetime matching that of the program's, since it
    is created once for all at the intialization of the associated module
As such, it was deemed acceptable to never release the Module Logger's memory,
and automate the RequestLogger's memory release through the use of the destroy
function at the end of their lifespan: The call of the endlogger's logging
method (that should be called only once, and called as the last logging entry
of the RequestLogger, thus meaning that the RequestLogger should be released
right after that, and not used anymore).

TL;DR; OOP design is shit in memory-managed languages, so here's our own shit
to work around it, and make the memory leak issue "not that bad".

lib/DefaultFields.js

@@ -0,0 +1,247 @@
+'use strict'; // eslint-disable-line strict
+
+const Utils = require('./Utils.js');
+const objectCopy = Utils.objectCopy;
+
+/**
+ * This class manages the internal `default fields` for logging classes, with a
+ * notion of parent/child relationships and hierarchy.
+ * A Child element will inherit the fields from the Parent element, and
+ * complete (or even override part of it) with its own fields. For instance,
+ * a child can redefine (and thus override in the final result) a field that is
+ * already defined by its parent.
+ *
+ * This class shall be used embedded within loggers, to provide the `Default
+ * fields` and hierarchy logics.
+ *
+ * @private @property {DefaultFields} parent     - The parent node in the
+ *                                                 hierarchy
+ * @private @property {DefaultFields[]} children - The list of children nodes
+ *                                                 in the hierarchy
+ * @private @property {Object} fields            - The dictionary of fields
+ *                                                 defined for this node
+ * @private @property {Object} parentFields      - The dictionary of fields
+ *                                                 inherited by this node from
+ *                                                 its parent node
+ * @private @property {Object} precomputedFields - The prepared dictionary of
+ *                                                 aggregated fields containing
+ *                                                 the parent's fields
+ *                                                 overriden with the node's
+ *                                                 own fields. This is used as
+ *                                                 a trick to reduce the
+ *                                                 computational need.
+ *
+ * @mixin
+ */
+class DefaultFields {
+    constructor() {
+        this.parent = null;
+        this.children = [];
+        this.fields = {};
+        this.parentFields = {};
+        this.precomputedFields = {};
+    }
+
+    /**
+     * This function allows to manually destroy a node, so that all references
+     * to parents or children are released. This helps in avoiding the creation
+     * of memory leaks due to our internal cyclic references that cannot be
+     * automatically released due to the mechanics of GC in Node.JS, and its
+     * shitty prevention of meaningful OOP designs.
+     *
+     * All hail << The Coming of the Great White Handkerchief >> that will
+     * wipe this misery out of our lives !
+     *
+     * @returns {undefined}
+     */
+    _dfDestroy() {
+        this.children.forEach(child => {
+            child.setParent(null);
+        });
+        this.setParent(null);
+        this.children = [];
+    }
+
+    /**
+     * Add a node to the list of children of the current node, effectively
+     * making it one of the node's children.
+     *
+     * @param {DefaultFields} child - The node to add as a child of the current
+     *                                node
+     *
+     * @return {undefined}
+     */
+    _dfRegisterChild(child) {
+        this.children.push(child);
+        this._dfNotifyChild(child);
+    }
+
+    /**
+     * Remove a node from the list of children of the current node, effectively
+     * cutting off the relationship between the two.
+     *
+     * @param {DefaultFields} toRemove - The node to remove from the list of
+     *                                   children of the current node.
+     *
+     * @return {undefined}
+     */
+    _dfUnregisterChild(toRemove) {
+        this.children = this.children.filter(child => child !== toRemove);
+    }
+
+    /**
+     * Utility function to notify one child node of an update of the node's
+     * precomputed fields.
+     *
+     * @param {DefaultField} child - The child node to notify
+     *
+     * @return {undefined}
+     */
+    _dfNotifyChild(child) {
+        child._dfSetParentFields(this.precomputedFields);
+    }
+
+    /**
+     * Utility function to notify every children node of an update of the
+     * node's precomputed fields.
+     *
+     * @return {undefined}
+     */
+    _dfNotifyChildren() {
+        this.children.forEach(child => this._dfNotifyChild(child));
+    }
+
+    /**
+     * This function allows changing the Parent node of the current node,
+     * consequently changing the resulting aggregation of the hierarchy of
+     * fields. This can be used for a temporary switch of parent node.
+     *
+     * @param {DefaultFields} parent - The new parent node to set for the
+     *                                 current node
+     *
+     * @return {DefaultFields|null} The previous parent
+     */
+    setParent(parent) {
+        const oldParent = this.parent;
+        if (parent === oldParent) {
+            return oldParent;
+        }
+        if (oldParent) {
+            oldParent._dfUnregisterChild(this);
+        }
+        this.parent = parent || null;
+        if (this.parent) {
+            this.parent._dfRegisterChild(this);
+        } else {
+            this._dfSetParentFields();
+        }
+        return oldParent;
+    }
+
+    /**
+     * Internal function to partially recompute the precomputedFields through
+     * inclusion of the newly defined fields into the precomputed ones. This
+     * inclusion may override some already defined fields.
+     *
+     * This function shall always be the last one called when updating the
+     * internal fields, as it also triggers the update of the children nodes.
+     *
+     * @param {Object} newFields - The dictionary of newFields to include into
+     *                             the precomputedFields
+     *
+     * @return {undefined}
+     */
+    _dfAugmentPrecomputedFields() {
+        objectCopy(this.precomputedFields, this.fields);
+        this._dfNotifyChildren();
+    }
+
+    /**
+     * Internal function to update the fields provided by the parent node in
+     * the DefaultFields hierarchy. It serves as a notification hook to refresh
+     * the precomputed fields depending on the parent node's fields.
+     * Two situations may lead to calling this function:
+     *  1. The parent node's updated its preComputed fields and notified its
+     *     children, including the current node
+     *  2. The node reset its own fields, and we must re-compute to remove
+     *     obsolete fields previously provided by the current node.
+     *
+     * @param {Object} parentFields - the precomputedFields from the parent node
+     *
+     * @return {undefined}
+     */
+    _dfSetParentFields(parentFields) {
+        this.parentFields = parentFields || {};
+        this.precomputedFields = objectCopy({}, this.parentFields);
+        this._dfAugmentPrecomputedFields();
+    }
+
+    /**
+     * This function allows to reset the fields managed by the DefaultFields
+     * instance. It automatically triggers the re-computation of the
+     * precomputed fields, cascading through the node and its children.
+     *
+     * /!\ This function may lead to an important use of the computational
+     * resources if over-used.
+     *
+     * @return {undefined}
+     */
+    resetDefaultFields() {
+        const oldFields = this.fields;
+        this.fields = {};
+        // Automatically triggers the recomputation of precomputedFields
+        this._dfSetParentFields(this.parentFields);
+        return oldFields;
+    }
+
+    /**
+     * This function allows the user to remove one or more items from the
+     * defaultFields's dict.
+     *
+     * @param {String[]} fields - List of the names of the fields to be removed
+     *                            from the internal dictionary of default
+     *                            fields
+     *
+     * @return {Object}           The previous set of default fields
+     */
+    removeDefaultFields(fields) {
+        const toRemove = {};
+        fields.forEach(key => {
+            toRemove[key] = undefined;
+        });
+        return this.addDefaultFields(toRemove);
+    }
+
+    /**
+     * This function allows the user to add default fields to include into all
+     * JSON log entries generated through this request logger. As this function
+     * attempt not to modify the provided fields object, it copies the field
+     * into a new object for safe keeping.
+     *
+     * @param {Object} fields   The dictionnary of additional fields to include
+     *                          by default for this instance of the
+     *                          RequestLogger.
+     *
+     * @return {Object}        The previous set of default fields (can be
+     *                          safely ignored).
+     */
+    addDefaultFields(fields) {
+        const oldFields = this.fields;
+        this.fields = objectCopy({}, this.fields, fields);
+        this._dfAugmentPrecomputedFields(fields);
+        return oldFields;
+    }
+
+    /**
+     * This function returns the node's precomputed fields, that includes all
+     * of its hierarchy's fields and its own. This is intended to retrieve the
+     * final form of the fields managed by the object.
+     *
+     * @return {Object} The precomputed fields to be added to a log entry
+     */
+    _dfGetFields() {
+        return this.precomputedFields;
+    }
+}
+
+module.exports = DefaultFields;

lib/Logger.js

@@ -2,17 +2,26 @@
 
 const LogLevel = require('./LogLevel.js');
 const RequestLogger = require('./RequestLogger.js');
-const unserializeUids = require('./Utils.js').unserializeUids;
+const Utils = require('./Utils.js');
 const Config = require('./Config.js');
+const DefaultFields = require('./DefaultFields.js');
 
-class Logger {
+const unserializeUids = Utils.unserializeUids;
+const objectCopy = Utils.objectCopy;
+
+class Logger extends DefaultFields {
 
     /**
      * This is the constructor of the Logger class. It takes optional
      * configuration parameters, that allow to modify its behavior.
      *
-     * @param {string} name  - The name of the Logger. It can be found later on
-     *                         in the log entries.
+     * @param {string|Object} fields  - Deprecated: {string}: The name of the
+     *                                  Logger that will be included in the log
+     *                                  entries
+     *                                  Advised: {Object} A set of fields that
+     *                                  will be used as the default fields for
+     *                                  this Logger, and will be included in
+     *                                  all later log entries.
      *
      * @param {object} config         - A configuration object for werelogs.
      * @param {string} config.level   - The string name of the logging level
@@ -23,21 +32,24 @@ class Logger {
      *                                  ('trace', 'debug', 'info', 'warn',
      *                                  'error' and 'fatal' in order of
      *                                  importance.)
-     * @param {object[]} config.streams   - The array of streams into which to
-     *                                      log. Their configuration is directly
-     *                                      related to the expected bunyan
-     *                                      streams array, for compatibility
-     *                                      purposes (except that the 'level'
-     *                                      field is not accounted for)
-     *
-     * @see [Bunyan's documentation]{@link
-     * https://github.com/trentm/node-bunyan/blob/master/README.md#streams} for
-     * a more detailed description of the streams array configuration.
      *
      * @returns {undefined}
      */
-    constructor(name, config) {
-        this.name = name;
+    constructor(fields, config) {
+        super();
+        /* TODO XXX FIXME Remove starting at version 8.0 FIXME XXX TODO
+         * vvvvvvvvvvvvvvvvvvvvvvvv */
+        if (typeof fields === 'string') {
+            this.addDefaultFields({ name: fields });
+        } else if (typeof fields === 'object') {
+            /* ^^^^^^^^^^^^^^^^^^^^^^^
+             * TODO XXX FIXME Remove starting at version 8.0 FIXME XXX TODO */
+            this.addDefaultFields(fields);
+            /* TODO XXX FIXME Remove starting at version 8.0 FIXME XXX TODO
+             * vvvvvvvvvvvvvvvvvvvvvvvv */
+        }
+        /* ^^^^^^^^^^^^^^^^^^^^^^^
+         * TODO XXX FIXME Remove starting at version 8.0 FIXME XXX TODO */
         Config.update(config);
     }
 
@@ -61,7 +73,7 @@ class Logger {
         const rLog = new RequestLogger(Config.logger,
                                        Config.level, Config.dump, Config.end,
                                        uids);
-        rLog.addDefaultFields({ name: this.name });
+        rLog.setParent(this);
         return rLog;
     }
 
@@ -77,13 +89,12 @@ class Logger {
         const rLog = new RequestLogger(Config.logger,
                                        Config.level, Config.dump, Config.end,
                                        unserializeUids(serializedUids));
-        rLog.addDefaultFields({ name: this.name });
+        rLog.setParent(this);
         return rLog;
     }
 
     _doLog(levelName, msg, data) {
         const sLogger = Config.logger;
-        const finalData = { name: this.name, time: Date.now() };
         if (!LogLevel.shouldLog(levelName, Config.level)) {
             return;
         }
@@ -96,6 +107,9 @@ class Logger {
                 + ' This development error should be fixed ASAP.');
             return;
         }
+        const finalData = objectCopy({},
+                                     this._dfGetFields(),
+                                     { time: Date.now() });
         if (data) {
             Object.keys(data).forEach(k => {
                 finalData[k] = data[k];

lib/RequestLogger.js

@@ -4,6 +4,7 @@ const assert = require('assert');
 
 const LogLevel = require('./LogLevel.js');
 const Utils = require('./Utils.js');
+const DefaultFields = require('./DefaultFields.js');
 const serializeUids = Utils.serializeUids;
 const generateUid = Utils.generateUid;
 const objectCopy = Utils.objectCopy;
@@ -16,39 +17,38 @@ function ensureUidValidity(uid) {
     return uid;
 }
 
-class EndLogger {
+/*
+ * @mixes DefaultFields
+ */
+class EndLogger extends DefaultFields {
     constructor(reqLogger) {
+        super();
         this.logger = reqLogger;
-        this.fields = {};
+        this.setParent(reqLogger);
     }
 
     augmentedLog(level, msg, data) {
         assert.strictEqual(this.logger.elapsedTime, null, 'The logger\'s'
                            + 'end() wrapper should not be called more than'
                            + ' once.');
-        // We can alter current instance, as it won't be usable after this
-        // call.
-        this.fields = objectCopy(this.fields, data || {});
-        return this.logger.log(level, msg, this.fields, true);
-    }
-
-    /**
-     * This function allows the user to add default fields to include into all
-     * JSON log entries generated through this request logger. As this function
-     * attempt not to modify the provided fields object, it copies the field
-     * into a new object for safe keeping.
-     *
-     * @param {object} fields   The dictionnary of additional fields to include
-     *                          by default for this instance of the
-     *                          RequestLogger.
-     *
-     * @returns {object}        The previous set of default fields (can be
-     *                          safely ignored).
-     */
-    addDefaultFields(fields) {
-        const oldFields = this.fields;
-        this.fields = objectCopy({}, this.fields, fields);
-        return oldFields;
+        const fields = objectCopy(this.precomputedFields, data || {});
+        const res = this.logger.log(level, msg, fields, true);
+        /* XXX NOTE
+         *
+         * This is our "manual" memory management.
+         * Since child and parent `DefaultFields` are actually refering to each
+         * other, the GC cannot release the child logger.
+         * Also, we have no means to automatically unregister the child from
+         * its parent, nor to have the parent notify the child of its update
+         * without keeping those references. So here we go, manual memory
+         * management in Garbage-collected languages !
+         *
+         * All hail << The Coming of the Great White Handkerchief >> that will
+         * wipe this misery out of our lives !
+         *
+         * XXX NOTE */
+        this._dfDestroy();
+        return res;
     }
 
     /**
@@ -142,7 +142,7 @@ class EndLogger {
  * the global log level; and is used to track the log events for one given
  * request.
  */
-class RequestLogger {
+class RequestLogger extends DefaultFields {
 
     /**
      * Constructor of the WereLogs Request Logger.
@@ -179,6 +179,7 @@ class RequestLogger {
      * @returns {undefined}
      */
     constructor(logger, logLevel, dumpThreshold, endLevel, uids) {
+        super();
         let uidList = undefined;
 
         if (!LogLevel.shouldLog(dumpThreshold, logLevel)) {
@@ -195,7 +196,6 @@ class RequestLogger {
         this.uids = uidList || [generateUid()];
 
         this.entries = [];
-        this.fields = {};
         this.logLevel = logLevel;
         this.dumpThreshold = dumpThreshold;
         this.endLevel = endLevel;
@@ -235,25 +235,6 @@ class RequestLogger {
         return serializeUids(this.uids);
     }
 
-    /**
-     * This function allows the user to add default fields to include into all
-     * JSON log entries generated through this request logger. As this function
-     * attempt not to modify the provided fields object, it copies the field
-     * into a new object for safe keeping.
-     *
-     * @param {object} fields   The dictionnary of additional fields to include
-     *                          by default for this instance of the
-     *                          RequestLogger.
-     *
-     * @returns {object}        The previous set of default fields (can be
-     *                          safely ignored).
-     */
-    addDefaultFields(fields) {
-        const oldFields = this.fields;
-        this.fields = objectCopy({}, this.fields, fields);
-        return oldFields;
-    }
-
     /**
      * Logging function to write a trace-level log entry.
      *
@@ -435,7 +416,7 @@ class RequestLogger {
                 });
             return;
         }
-        const fields = objectCopy({}, this.fields, logFields || {});
+        const fields = objectCopy({}, this._dfGetFields(), logFields || {});
         const endFlag = isEnd || false;
 
         /*
@@ -469,6 +450,10 @@ class RequestLogger {
         } else if (LogLevel.shouldLog(level, this.logLevel)) {
             this.doLogIO(logEntry);
         }
+
+        if (isEnd) {
+            this.setParent(null);
+        }
     }
 
     /**

tests/functional/basic_usage.js

@@ -15,8 +15,9 @@ pass.on('data', data => {
     logBuffer.records.push(data.toString());
 });
 
-function createModuleLogger() {
-    return new Logger('FT-test', {
+function createModuleLogger(fields) {
+    const defaultFields = fields || 'FT-test';
+    return new Logger(defaultFields, {
         level: 'info',
         dump: 'error',
         streams: [{
@@ -105,5 +106,35 @@ describe('Werelogs is usable as a dependency', () => {
             checkFields(fields);
             done();
         });
+
+        it('Should not log a removed field', done => {
+            const logger = createModuleLogger().newRequestLogger();
+            const msg = 'This is a message with no fields(removed)';
+            const fields = { errorCode: 0, description: 'TestNotFailing' };
+            logger.addDefaultFields(fields);
+            logger.removeDefaultFields(['errorCode', 'description']);
+            logger.info(msg);
+            assert.strictEqual(parseLogEntry().message, msg);
+            assert(!parseLogEntry().hasOwnProperty('errorCode'));
+            assert(!parseLogEntry().hasOwnProperty('description'));
+            done();
+        });
+
+        it('Should include the parent Loggers default fields', done => {
+            const mFields = {
+                name: 'TestModule',
+                submodule: 'functional',
+            };
+            const logger = createModuleLogger(mFields);
+            const rLog = logger.newRequestLogger();
+            const msg =
+                "This is a message including the module's default fields";
+            rLog.info(msg);
+            assert.strictEqual(parseLogEntry().message, msg);
+            assert.deepStrictEqual(parseLogEntry().name, mFields.name);
+            assert.deepStrictEqual(parseLogEntry().submodule,
+                                   mFields.submodule);
+            done();
+        });
     });
 });

tests/unit/DefaultFields.js

@@ -0,0 +1,515 @@
+'use strict'; // eslint-disable-line strict
+
+const assert = require('assert');
+
+const DefaultFields = require('../../lib/DefaultFields.js');
+
+describe('class DefaultFields', () => {
+    describe('Basic Fields logic', () => {
+        it('Can get the resulting fields', done => {
+            const df = new DefaultFields();
+            const fields = df._dfGetFields();
+            assert(fields !== null && typeof fields === 'object');
+            done();
+        });
+
+        it('No fields are set by default', done => {
+            const df = new DefaultFields();
+            assert.deepStrictEqual(df._dfGetFields(), {});
+            done();
+        });
+
+        it('Validate defensive coding prevents undefined parentFields',
+            done => {
+                const df = new DefaultFields();
+                df._dfSetParentFields();
+                assert.deepStrictEqual(df._dfGetFields(), {});
+                done();
+            });
+
+        describe('With fields', () => {
+            let df = null;
+            const fields = {
+                name: 'Testing',
+                testing: true,
+                count: 4,
+                data: 'doggy',
+            };
+
+            beforeEach(done => {
+                df = new DefaultFields();
+                df.addDefaultFields(fields);
+                done();
+            });
+
+            it('Can add a dictionary of new fields', done => {
+                assert.deepStrictEqual(df._dfGetFields(), fields);
+                done();
+            });
+
+            it('Can remove a list of invalid fields', done => {
+                df.removeDefaultFields(['invalid', 'notthere']);
+                done();
+            });
+
+            it('Can remove a list of fields', done => {
+                df.removeDefaultFields(['data', 'count']);
+                assert.strictEqual(df._dfGetFields().data, undefined);
+                assert.strictEqual(df._dfGetFields().count, undefined);
+                assert.strictEqual(df._dfGetFields().name, 'Testing');
+                assert.strictEqual(df._dfGetFields().testing, true);
+                done();
+            });
+
+
+            it('Can reset the fields', done => {
+                df.resetDefaultFields();
+                assert.deepStrictEqual(df._dfGetFields(), {});
+                done();
+            });
+        });
+    });
+
+    describe('Basic Parent-Child logic', () => {
+        let parentNode = null;
+
+        beforeEach(done => {
+            parentNode = new DefaultFields();
+            done();
+        });
+
+        function linkedChild(pNode) {
+            const childNode = new DefaultFields();
+            childNode.setParent(pNode);
+            return childNode;
+        }
+
+        it('Can set a parent to a node', done => {
+            const childNode = linkedChild(parentNode);
+            assert.strictEqual(childNode.parent, parentNode);
+            assert.notStrictEqual(parentNode.children.indexOf(childNode), -1);
+            done();
+        });
+
+        it('Can remove a child from a node', done => {
+            const childNode = linkedChild(parentNode);
+            parentNode._dfUnregisterChild(childNode);
+            assert.strictEqual(parentNode.children.indexOf(childNode), -1);
+            done();
+        });
+
+        it('Can reset the parent of a node (w/ undefined)', done => {
+            const childNode = linkedChild(parentNode);
+            childNode.setParent(undefined);
+            assert.strictEqual(childNode.parent, null);
+            assert.strictEqual(parentNode.children.indexOf(childNode), -1);
+            done();
+        });
+
+        it('Can reset the parent of a node (w/ null)', done => {
+            const childNode = linkedChild(parentNode);
+            childNode.setParent(null);
+            assert.strictEqual(childNode.parent, null);
+            assert.strictEqual(parentNode.children.indexOf(childNode), -1);
+            done();
+        });
+    });
+
+    describe('Single parent-child relationship', () => {
+        let parentNode = null;
+        let childNode = null;
+
+        beforeEach(done => {
+            parentNode = new DefaultFields();
+            childNode = new DefaultFields();
+            childNode.setParent(parentNode);
+            done();
+        });
+
+        it('Child can define its own fields', done => {
+            const fields = {
+                child: true,
+                parent: false,
+                test: 1,
+            };
+            childNode.addDefaultFields(fields);
+            assert.deepStrictEqual(childNode._dfGetFields(), fields);
+            done();
+        });
+
+        it('Parent can define its own fields', done => {
+            const fields = {
+                child: false,
+                parent: true,
+                test: 2,
+            };
+            parentNode.addDefaultFields(fields);
+            assert.deepStrictEqual(parentNode._dfGetFields(), fields);
+            done();
+        });
+
+        it('Child inherits parents fields', done => {
+            const fields = {
+                child: true,
+                parent: false,
+                test: 3,
+            };
+            parentNode.addDefaultFields(fields);
+            assert.deepStrictEqual(childNode._dfGetFields(), fields);
+            done();
+        });
+
+        it('Child inherits successive parent field updates', done => {
+            const pFields1 = {
+                parent: true,
+                test: 4,
+            };
+            const rFields1 = {
+                parent: true,
+                test: 4,
+            };
+            const pFields2 = { child: false };
+            const rFields2 = {
+                parent: true,
+                test: 4,
+                child: false,
+            };
+            const pFields3 = {
+                data: 'pouet',
+            };
+            const rFields3 = {
+                parent: true,
+                test: 4,
+                child: false,
+                data: 'pouet',
+            };
+            parentNode.addDefaultFields(pFields1);
+            assert.deepStrictEqual(childNode._dfGetFields(), rFields1);
+            parentNode.addDefaultFields(pFields2);
+            assert.deepStrictEqual(childNode._dfGetFields(), rFields2);
+            parentNode.addDefaultFields(pFields3);
+            assert.deepStrictEqual(childNode._dfGetFields(), rFields3);
+            done();
+        });
+
+        it('Child inherits reset parent fields', done => {
+            const pFields = {
+                parent: true,
+                test: 5,
+            };
+            parentNode.addDefaultFields(pFields);
+            assert.deepStrictEqual(childNode._dfGetFields(), pFields);
+            parentNode.resetDefaultFields();
+            assert.deepStrictEqual(childNode._dfGetFields(), {});
+            done();
+        });
+
+        it('Child mixes parent and own fields', done => {
+            const pFields = { parent: true };
+            const cFields = {
+                child: true,
+                test: 6,
+            };
+            const rFields = {
+                parent: true,
+                child: true,
+                test: 6,
+            };
+            parentNode.addDefaultFields(pFields);
+            childNode.addDefaultFields(cFields);
+            assert.deepStrictEqual(childNode._dfGetFields(), rFields);
+            done();
+        });
+
+        it('Child overrides conflicting parent fields', done => {
+            const pFields = {
+                parent: true,
+                child: false,
+                test: 0,
+            };
+            const cFields = {
+                child: true,
+                test: 7,
+            };
+            const rFields = {
+                parent: true,
+                child: true,
+                test: 7,
+            };
+            parentNode.addDefaultFields(pFields);
+            childNode.addDefaultFields(cFields);
+            assert.deepStrictEqual(childNode._dfGetFields(), rFields);
+            done();
+        });
+    });
+
+    describe('Multiple-level parent-child relationship', () => {
+        let ggpNode = null;
+        let gpNode = null;
+        let pNode = null;
+        let childNode = null;
+
+        beforeEach(done => {
+            ggpNode = new DefaultFields();
+            gpNode = new DefaultFields();
+            gpNode.setParent(ggpNode);
+            pNode = new DefaultFields();
+            pNode.setParent(gpNode);
+            childNode = new DefaultFields();
+            childNode.setParent(pNode);
+            done();
+        });
+
+        it('Child inherits from whole hierarchy (newer -> older)',
+            done => {
+                const ggpFields = { great: true };
+                const gpFields = { grand: true };
+                const pFields = { parent: true };
+                const rFields = {
+                    great: true,
+                    grand: true,
+                    parent: true,
+                };
+                pNode.addDefaultFields(pFields);
+                gpNode.addDefaultFields(gpFields);
+                ggpNode.addDefaultFields(ggpFields);
+                assert.deepStrictEqual(childNode._dfGetFields(), rFields);
+                done();
+            });
+
+        it('Child inherits from whole hierarchy (older -> newer)',
+            done => {
+                const ggpFields = { great: true };
+                const gpFields = { grand: true };
+                const pFields = { parent: true };
+                const rFields = {
+                    great: true,
+                    grand: true,
+                    parent: true,
+                };
+                ggpNode.addDefaultFields(ggpFields);
+                gpNode.addDefaultFields(gpFields);
+                pNode.addDefaultFields(pFields);
+                assert.deepStrictEqual(childNode._dfGetFields(), rFields);
+                done();
+            });
+
+        it('Nodes inherit in-hierarchy fields reset', done => {
+            const ggpFields = { great: true };
+            const gpFields = { grand: true };
+            const pFields = { parent: true };
+            const rFields = {
+                great: true,
+                // grand: true, // Part 'reset'
+                parent: true,
+            };
+            ggpNode.addDefaultFields(ggpFields);
+            gpNode.addDefaultFields(gpFields);
+            pNode.addDefaultFields(pFields);
+            gpNode.resetDefaultFields();
+            assert.deepStrictEqual(childNode._dfGetFields(), rFields);
+            done();
+        });
+
+        it('Field overriding is cascading through generations (newer -> older)',
+            done => {
+                const ggpFields = { generation: 0 };
+                const gpFields = { generation: 1 };
+                const pFields = { generation: 2 };
+                const cFields = { generation: 3 };
+                childNode.addDefaultFields(cFields);
+                pNode.addDefaultFields(pFields);
+                gpNode.addDefaultFields(gpFields);
+                ggpNode.addDefaultFields(ggpFields);
+                assert.deepStrictEqual(childNode._dfGetFields(), cFields);
+                assert.deepStrictEqual(pNode._dfGetFields(), pFields);
+                assert.deepStrictEqual(gpNode._dfGetFields(), gpFields);
+                assert.deepStrictEqual(ggpNode._dfGetFields(), ggpFields);
+                done();
+            });
+
+        it('Field overriding is cascading through generations (older -> newer)',
+            done => {
+                const ggpFields = { generation: 0 };
+                const gpFields = { generation: 1 };
+                const pFields = { generation: 2 };
+                const cFields = { generation: 3 };
+                ggpNode.addDefaultFields(ggpFields);
+                gpNode.addDefaultFields(gpFields);
+                pNode.addDefaultFields(pFields);
+                childNode.addDefaultFields(cFields);
+                assert.deepStrictEqual(childNode._dfGetFields(), cFields);
+                assert.deepStrictEqual(pNode._dfGetFields(), pFields);
+                assert.deepStrictEqual(gpNode._dfGetFields(), gpFields);
+                assert.deepStrictEqual(ggpNode._dfGetFields(), ggpFields);
+                done();
+            });
+
+        it('Destroying intermediate level breaks relationships', done => {
+            const ggpFields = { ggp: 1 };
+            const gpFields = { gp: 1 };
+            const pFields = { p: 1 };
+            const cFields = { c: 1 };
+            ggpNode.addDefaultFields(ggpFields);
+            gpNode.addDefaultFields(gpFields);
+            pNode.addDefaultFields(pFields);
+            childNode.addDefaultFields(cFields);
+            pNode._dfDestroy();
+            assert.strictEqual(gpNode.children.indexOf(pNode), -1);
+            assert.strictEqual(pNode.parent, null);
+            assert.strictEqual(pNode.children.indexOf(childNode), -1);
+            assert.strictEqual(childNode.parent, null);
+            assert.deepStrictEqual(pNode._dfGetFields(), pFields);
+            assert.deepStrictEqual(childNode._dfGetFields(), cFields);
+            done();
+        });
+
+        it('Destroying intermediate level(2) breaks relationships', done => {
+            const ggpFields = { ggp: 1 };
+            const gpFields = { gp: 1 };
+            const pFields = { p: 1 };
+            const cFields = { c: 1 };
+            const rCFields = { p: 1, c: 1 };
+            ggpNode.addDefaultFields(ggpFields);
+            gpNode.addDefaultFields(gpFields);
+            pNode.addDefaultFields(pFields);
+            childNode.addDefaultFields(cFields);
+            gpNode._dfDestroy();
+            assert.strictEqual(ggpNode.children.indexOf(gpNode), -1);
+            assert.strictEqual(gpNode.parent, null);
+            assert.strictEqual(gpNode.children.indexOf(pNode), -1);
+            assert.strictEqual(pNode.parent, null);
+            assert.deepStrictEqual(gpNode._dfGetFields(), gpFields);
+            assert.deepStrictEqual(childNode._dfGetFields(), rCFields);
+            done();
+        });
+    });
+
+    describe('Topology changes', () => {
+        let ggpNode1 = null;
+        let ggpNode2 = null;
+        let gpNode1 = null;
+        let gpNode2 = null;
+        let pNode1 = null;
+        let pNode2 = null;
+        let cNode = null;
+
+        const ggp1Fields = { ggp1: true, generation: 0 };
+        const ggp2Fields = { ggp2: true, generation: 0 };
+        const gp1Fields = { gp1: true, generation: 1 };
+        const gp2Fields = { gp2: true, generation: 1 };
+        const p1Fields = { p1: true, generation: 2 };
+        const p2Fields = { p2: true, generation: 2 };
+        const cFields = { c: true, generation: 3 };
+
+        const startFields = {
+            ggp1: true,
+            gp1: true,
+            p1: true,
+            c: true,
+            generation: 3,
+        };
+
+        beforeEach(done => {
+            ggpNode1 = new DefaultFields();
+            gpNode1 = new DefaultFields();
+            gpNode1.setParent(ggpNode1);
+            pNode1 = new DefaultFields();
+            pNode1.setParent(gpNode1);
+
+            ggpNode2 = new DefaultFields();
+            gpNode2 = new DefaultFields();
+            gpNode2.setParent(ggpNode2);
+            pNode2 = new DefaultFields();
+            pNode2.setParent(gpNode2);
+
+            cNode = new DefaultFields();
+            cNode.setParent(pNode1);
+
+            ggpNode1.addDefaultFields(ggp1Fields);
+            ggpNode2.addDefaultFields(ggp2Fields);
+            gpNode1.addDefaultFields(gp1Fields);
+            gpNode2.addDefaultFields(gp2Fields);
+            pNode1.addDefaultFields(p1Fields);
+            pNode2.addDefaultFields(p2Fields);
+            cNode.addDefaultFields(cFields);
+
+            done();
+        });
+
+        it('Nodes are updated accordingly when a parent changes '
+           + '(change whole upper hierarchy)',
+            done => {
+                const rFields = {
+                    ggp2: true,
+                    gp2: true,
+                    p2: true,
+                    c: true,
+                    generation: 3,
+                };
+                assert.deepStrictEqual(cNode._dfGetFields(), startFields);
+                cNode.setParent(pNode2);
+                assert.deepStrictEqual(cNode._dfGetFields(), rFields);
+                done();
+            });
+
+        it('Nodes are updated accordingly when a parent changes '
+           + '(change part of the upper hierarchy)',
+            done => {
+                const rFields = {
+                    ggp2: true,
+                    gp2: true,
+                    p1: true,
+                    c: true,
+                    generation: 3,
+                };
+                assert.deepStrictEqual(cNode._dfGetFields(), startFields);
+                pNode1.setParent(gpNode2);
+                assert.deepStrictEqual(cNode._dfGetFields(), rFields);
+                done();
+            });
+
+        it('Nodes are updated accordingly when a parent changes '
+           + '(shortcut hierarchy)',
+            done => {
+                const rFields = {
+                    ggp2: true,
+                    c: true,
+                    generation: 3,
+                };
+                assert.deepStrictEqual(cNode._dfGetFields(), startFields);
+                cNode.setParent(ggpNode2);
+                assert.deepStrictEqual(cNode._dfGetFields(), rFields);
+                done();
+            });
+
+        it('Nodes are updated accordingly when a parent is unset '
+           + '(remove whole hierarchy)',
+            done => {
+                const rFields = {
+                    c: true,
+                    generation: 3,
+                };
+                assert.deepStrictEqual(cNode._dfGetFields(), startFields);
+                cNode.setParent(null);
+                assert.deepStrictEqual(cNode._dfGetFields(), rFields);
+                done();
+            });
+
+        it('Nodes are updated accordingly when a parent is unset '
+           + '(remove upper hierarchy)',
+            done => {
+                const rFields = {
+                    gp1: true,
+                    p1: true,
+                    c: true,
+                    generation: 3,
+                };
+                assert.deepStrictEqual(cNode._dfGetFields(), startFields);
+                gpNode1.setParent(null);
+                assert.deepStrictEqual(cNode._dfGetFields(), rFields);
+                done();
+            });
+    });
+});
+

tests/unit/Logger.js

@@ -256,3 +256,85 @@ describe('Werelogs Module-level Logger can log as specified by the log level', (
     it('Fatal level does not filter fatal level out',   filterGenerator('fatal', 'fatal'));
 });
 /* eslint-enable no-multi-spaces, max-len */
+
+describe('Werelogs Module-level Logger provide the DefaultFields logic', () => {
+    const loggerConfig = {
+        level: 'info',
+        dump: 'fatal',
+        end: 'info',
+    };
+
+    it('should not modify the object passed as a parameter', done => {
+        const defaultFields = {
+            name: 'TestDefaultFields1',
+            data: 0,
+        };
+        const add1 = {
+            attr1: 0,
+        };
+        const add2 = {
+            attr2: 'string',
+        };
+        const dummyLogger = new DummyLogger();
+        Config.simpleLogger = dummyLogger;
+        const logger = new Logger(defaultFields, loggerConfig);
+        logger.addDefaultFields(add1);
+        logger.addDefaultFields(add2);
+        assert.deepStrictEqual(add1, { attr1: 0 });
+        assert.deepStrictEqual(add2, { attr2: 'string' });
+        done();
+    });
+
+    it('should add one added default field to the log entries', done => {
+        const defaultFields = {
+            name: 'TestDefaultFields2',
+            data: 0,
+        };
+        const clientInfo = {
+            clientIP: '127.0.0.1',
+        };
+        const dummyLogger = new DummyLogger();
+        Config.simpleLogger = dummyLogger;
+        const logger = new Logger(defaultFields, loggerConfig);
+        logger.addDefaultFields(clientInfo);
+        logger.info('test message');
+        assert.strictEqual(dummyLogger.ops[0][1][0].clientIP,
+                           clientInfo.clientIP);
+        done();
+    });
+
+    it('should add multiple added default fields to the log entries',
+        done => {
+            const defaultFields = {
+                name: 'TestDefaultFields3',
+                data: 0,
+            };
+            const clientInfo = {
+                clientIP: '127.0.0.1',
+                clientPort: '1337',
+            };
+            const requestInfo = {
+                object: '/tata/self.txt',
+                creator: 'Joddy',
+            };
+            const dummyLogger = new DummyLogger();
+            Config.simpleLogger = dummyLogger;
+            const logger = new Logger(defaultFields, loggerConfig);
+            logger.addDefaultFields(clientInfo);
+            logger.addDefaultFields(requestInfo);
+            logger.info('test message');
+            assert.strictEqual(dummyLogger.ops[0][1][0].clientIP,
+                               clientInfo.clientIP);
+            assert.strictEqual(dummyLogger.ops[0][1][0].clientPort,
+                               clientInfo.clientPort);
+            assert.strictEqual(dummyLogger.ops[0][1][0].object,
+                               requestInfo.object);
+            assert.strictEqual(dummyLogger.ops[0][1][0].creator,
+                               requestInfo.creator);
+            assert.strictEqual(dummyLogger.ops[0][1][0].name,
+                               defaultFields.name);
+            assert.strictEqual(dummyLogger.ops[0][1][0].data,
+                               defaultFields.data);
+            done();
+        });
+});