feat(fcm): Support proxy field in FCM AndroidNotification

FirebaseAdmin/FirebaseAdmin.Tests/Messaging/MessageTest.cs

@@ -293,6 +293,7 @@ public void AndroidConfig()
                         DefaultLightSettings = false,
                         Visibility = NotificationVisibility.PUBLIC,
                         NotificationCount = 10,
+                        Proxy = NotificationProxy.IfPriorityLowered,
                     },
                     FcmOptions = new AndroidFcmOptions()
                     {
@@ -359,6 +360,7 @@ public void AndroidConfig()
                                 { "visibility", "PUBLIC" },
                                 { "vibrate_timings", new JArray() { "1s", "1.001000000s" } },
                                 { "event_time", "2020-06-27T20:29:06.032691000Z" },
+                                { "proxy", "IF_PRIORITY_LOWERED" },
                             }
                         },
                         {
@@ -493,6 +495,7 @@ public void AndroidNotificationDeserialization()
                 DefaultLightSettings = false,
                 Visibility = NotificationVisibility.PUBLIC,
                 NotificationCount = 10,
+                Proxy = NotificationProxy.IfPriorityLowered,
             };
             var json = NewtonsoftJsonSerializer.Instance.Serialize(original);
             var copy = NewtonsoftJsonSerializer.Instance.Deserialize<AndroidNotification>(json);
@@ -523,6 +526,7 @@ public void AndroidNotificationDeserialization()
             Assert.Equal(original.DefaultLightSettings, copy.DefaultLightSettings);
             Assert.Equal(original.Visibility, copy.Visibility);
             Assert.Equal(original.NotificationCount, copy.NotificationCount);
+            Assert.Equal(original.Proxy, copy.Proxy);
         }
 
         [Fact]

FirebaseAdmin/FirebaseAdmin/Messaging/AndroidNotification.cs

@@ -224,6 +224,12 @@ public sealed class AndroidNotification
         [JsonProperty("notification_count")]
         public int? NotificationCount { get; set; }
 
+        /// <summary>
+        /// Gets or sets the proxy behavior of this notification.
+        /// </summary>
+        [JsonIgnore]
+        public NotificationProxy? Proxy { get; set; }
+
         /// <summary>
         /// Gets or sets the string representation of the <see cref="NotificationPriority"/> property.
         /// </summary>
@@ -312,7 +318,7 @@ private string VisibilityString
                         return;
                     default:
                         throw new ArgumentException(
-                            $"Invalid visibility value: {value}. Only 'PUBLIC', 'PRIVATE', ''SECRET' are allowed.");
+                            $"Invalid visibility value: {value}. Only 'PUBLIC', 'PRIVATE', 'SECRET' are allowed.");
                 }
             }
         }
@@ -379,6 +385,47 @@ private string EventTimeString
             }
         }
 
+        /// <summary>
+        /// Gets or sets the string representation of the <see cref="NotificationProxy"/> property.
+        /// </summary>
+        [JsonProperty("proxy")]
+        private string ProxyString
+        {
+            get
+            {
+                switch (this.Proxy)
+                {
+                    case NotificationProxy.Allow:
+                        return "ALLOW";
+                    case NotificationProxy.Deny:
+                        return "DENY";
+                    case NotificationProxy.IfPriorityLowered:
+                        return "IF_PRIORITY_LOWERED";
+                    default:
+                        return null;
+                }
+            }
+
+            set
+            {
+                switch (value)
+                {
+                    case "ALLOW":
+                        this.Proxy = NotificationProxy.Allow;
+                        return;
+                    case "DENY":
+                        this.Proxy = NotificationProxy.Deny;
+                        return;
+                    case "IF_PRIORITY_LOWERED":
+                        this.Proxy = NotificationProxy.IfPriorityLowered;
+                        return;
+                    default:
+                        throw new ArgumentException(
+                            $"Invalid proxy value: {value}. Only 'ALLOW', 'DENY', 'IF_PRIORITY_LOWERED' are allowed.");
+                }
+            }
+        }
+
         /// <summary>
         /// Copies this notification, and validates the content of it to ensure that it can be
         /// serialized into the JSON format expected by the FCM service.
@@ -411,6 +458,7 @@ internal AndroidNotification CopyAndValidate()
                 DefaultLightSettings = this.DefaultLightSettings,
                 Visibility = this.Visibility,
                 NotificationCount = this.NotificationCount,
+                Proxy = this.Proxy,
             };
             if (copy.Color != null && !Regex.Match(copy.Color, "^#[0-9a-fA-F]{6}$").Success)
             {

FirebaseAdmin/FirebaseAdmin/Messaging/NotificationProxy.cs

@@ -0,0 +1,38 @@
+// Copyright 2025, Google Inc. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+namespace FirebaseAdmin.Messaging
+{
+    /// <summary>
+    /// Proxy behavior that can be set on an <see cref="AndroidNotification"/>.
+    /// </summary>
+    public enum NotificationProxy
+    {
+        /// <summary>
+        /// Try to proxy this notification.
+        /// </summary>
+        Allow,
+
+        /// <summary>
+        /// Do not proxy this notification..
+        /// </summary>
+        Deny,
+
+        /// <summary>
+        /// Only try to proxy this notification if its `AndroidMessagePriority`
+        /// was lowered from HIGH to NORMAL on the device.
+        /// </summary>
+        IfPriorityLowered,
+    }
+}