[8.x] HTTP client: only allow a single User-Agent header (#39085)

Co-authored-by: jules <[email protected]>

Author: julesjanssen

src/Illuminate/Http/Client/PendingRequest.php

@@ -374,7 +374,9 @@ public function withToken($token, $type = 'Bearer')
      */
     public function withUserAgent($userAgent)
     {
-        return $this->withHeaders(['User-Agent' => $userAgent]);
+        return tap($this, function ($request) use ($userAgent) {
+            return $this->options['headers']['User-Agent'] = trim($userAgent);
+        });
     }
 
     /**

tests/Http/HttpClientTest.php

@@ -295,6 +295,23 @@ public function testItCanSendUserAgent()
         });
     }
 
+    public function testItOnlySendsOneUserAgentHeader()
+    {
+        $this->factory->fake();
+
+        $this->factory->withUserAgent('Laravel')
+            ->withUserAgent('FooBar')
+            ->post('http://foo.com/json');
+
+        $this->factory->assertSent(function (Request $request) {
+            $userAgent = $request->header('User-Agent');
+
+            return $request->url() === 'http://foo.com/json' &&
+                count($userAgent) === 1 &&
+                $userAgent[0] === 'FooBar';
+        });
+    }
+
     public function testSequenceBuilder()
     {
         $this->factory->fake([