From 173bf931220cd5867b2c0b3f78b679404c4ce4b2 Mon Sep 17 00:00:00 2001
From: Josh Mock <joshua.mock@elastic.co>
Date: Wed, 2 Jul 2025 16:05:20 -0500
Subject: [PATCH] Deep merge options on client instantiation

---
 src/client.ts            | 13 +++++--------
 test/unit/client.test.ts | 22 ++++++++++++++++++++++
 2 files changed, 27 insertions(+), 8 deletions(-)

diff --git a/src/client.ts b/src/client.ts
index f758553e2..7e303bd52 100644
--- a/src/client.ts
+++ b/src/client.ts
@@ -256,11 +256,13 @@ export default class Client extends API {
       }
     }
 
-    const headers: Record<string, any> = {
+    const headers: Record<string, any> = Object.assign({}, {
       'user-agent': `elasticsearch-js/${clientVersion} (${os.platform()} ${os.release()}-${os.arch()}; Node.js ${nodeVersion}; Transport ${transportVersion})`
-    }
+    }, opts.headers ?? {})
     if (opts.serverMode === 'serverless') headers['elastic-api-version'] = serverlessApiVersion
 
+    const redaction = Object.assign({}, { type: 'replace', additionalKeys: [] }, opts.redaction ?? {})
+
     const options: Required<ClientOptions> = Object.assign({}, {
       Connection: UndiciConnection,
       Transport: opts.serverMode === 'serverless' ? Transport : SniffingTransport,
@@ -277,7 +279,6 @@ export default class Client extends API {
       tls: null,
       caFingerprint: null,
       agent: null,
-      headers,
       nodeFilter: null,
       generateRequestId: null,
       name: 'elasticsearch-js',
@@ -288,12 +289,8 @@ export default class Client extends API {
       enableMetaHeader: true,
       maxResponseSize: null,
       maxCompressedResponseSize: null,
-      redaction: {
-        type: 'replace',
-        additionalKeys: []
-      },
       serverMode: 'stack'
-    }, opts)
+    }, opts, { headers, redaction })
 
     if (options.caFingerprint != null && isHttpConnection(opts.node ?? opts.nodes)) {
       throw new errors.ConfigurationError('You can\'t configure the caFingerprint with a http connection')
diff --git a/test/unit/client.test.ts b/test/unit/client.test.ts
index fc4016a22..feffc373e 100644
--- a/test/unit/client.test.ts
+++ b/test/unit/client.test.ts
@@ -98,6 +98,28 @@ test('Custom headers', t => {
   t.end()
 })
 
+test('Custom headers should merge, not overwrite', t => {
+  const client = new Client({
+    node: 'http://localhost:9200',
+    headers: { foo: 'bar' }
+  })
+  t.ok(client.transport[symbols.kHeaders]['user-agent']?.startsWith('elasticsearch-js/'))
+  t.end()
+})
+
+test('Redaction options should merge, not overwrite', t => {
+  const client = new Client({
+    node: 'http://localhost:9200',
+    // @ts-expect-error
+    redaction: {
+      additionalKeys: ['foo'],
+    }
+  })
+  t.equal(client.transport[symbols.kRedaction].type, 'replace')
+  t.match(client.transport[symbols.kRedaction].additionalKeys, ['foo'])
+  t.end()
+})
+
 test('Basic auth', async t => {
   t.plan(1)