From c22c48ddede7ade6330225915c19062d9c01a6ed Mon Sep 17 00:00:00 2001
From: alexander <alexander.ressler@gmail.com>
Date: Wed, 30 Dec 2020 17:16:42 -0500
Subject: [PATCH] Fix defaultMeta override in child logger #1864

---
 lib/winston/logger.js | 18 +++++++++++++++++-
 test/logger.test.js   |  6 +++++-
 2 files changed, 22 insertions(+), 2 deletions(-)

diff --git a/lib/winston/logger.js b/lib/winston/logger.js
index dc7866854..27d357384 100644
--- a/lib/winston/logger.js
+++ b/lib/winston/logger.js
@@ -44,13 +44,29 @@ class Logger extends Transform {
 
   child(defaultRequestMetadata) {
     const logger = this;
+
     return Object.create(logger, {
       write: {
         value: function (info) {
+
+          // Remark: defaultMeta is passed into the info object,
+          // and we need to check if it is there because a user
+          // specified it in a log call or it is there as a result
+          // of being passed to createLogger as defaultMeta.
+          const defaultMetaOverride = {};
+          if (logger.defaultMeta) {
+            for (const key of Object.getOwnPropertyNames(logger.defaultMeta)) {
+              if (info[key] === logger.defaultMeta[key]) {
+                defaultMetaOverride[key] = defaultRequestMetadata[key];
+              }
+            }
+          }
+
           const infoClone = Object.assign(
             {},
             defaultRequestMetadata,
-            info
+            info,
+            defaultMetaOverride
           );
 
           // Object.assign doesn't copy inherited Error
diff --git a/test/logger.test.js b/test/logger.test.js
index 0d21d3fa1..4d154d813 100755
--- a/test/logger.test.js
+++ b/test/logger.test.js
@@ -997,12 +997,16 @@ describe('Should support child loggers & defaultMeta', () => {
     });
 
     const logger = winston.createLogger({
+      defaultMeta: {
+        requestId: '38',
+        service: 'root-service-logger'
+      },
       transports: [
         mockTransport.createMockTransport(assertFn)
       ]
     });
 
-    const childLogger = logger.child({ service: 'user-service' });
+    const childLogger = logger.child({ service: 'user-service', requestId: '154' });
     childLogger.info('dummy message', { requestId: '451' });
   });