[Firebase AI] Add logic for Developer Live API (#1288)

* [Firebase AI] Add logic for Developer Live API

* Update LiveSessionResponse.cs

* Update readme.md

Author: a-maurice

docs/readme.md

@@ -109,6 +109,10 @@ Support
 
 Release Notes
 -------------
+### Upcoming
+-   Changes
+    - Firebase AI: Add support for Developer API backend to LiveSessions.
+
 ### 13.0.0
 -   Changes
     - General: Update to Firebase C++ SDK version 13.0.0.

firebaseai/src/FirebaseAI.cs

@@ -165,8 +165,6 @@ public GenerativeModel GetGenerativeModel(
   /// 
   /// - Note: Refer to [Gemini models](https://firebase.google.com/docs/vertex-ai/gemini-models) for
   /// guidance on choosing an appropriate model for your use case.
-  /// 
-  /// - Note: Currently only supports the VertexAI backend.
   /// </summary>
   /// <param name="modelName">The name of the model to use, for example `"gemini-2.0-flash-live-preview-04-09"`; see
   ///     [available model names
@@ -183,10 +181,6 @@ public LiveGenerativeModel GetLiveModel(
       Tool[] tools = null,
       ModelContent? systemInstruction = null,
       RequestOptions? requestOptions = null) {
-    if (_backend.Provider != Backend.InternalProvider.VertexAI) {
-      throw new NotSupportedException("LiveGenerativeModel is currently only supported with the VertexAI backend.");
-    }
-
     return new LiveGenerativeModel(_firebaseApp, _backend, modelName,
         liveGenerationConfig, tools,
         systemInstruction, requestOptions);

firebaseai/src/LiveGenerativeModel.cs

@@ -70,10 +70,30 @@ internal LiveGenerativeModel(FirebaseApp firebaseApp,
   }
 
   private string GetURL() {
-    return "wss://firebasevertexai.googleapis.com/ws" + 
-           "/google.firebase.vertexai.v1beta.LlmBidiService/BidiGenerateContent" +
-           $"/locations/{_backend.Location}" +
-           $"?key={_firebaseApp.Options.ApiKey}";
+    if (_backend.Provider == FirebaseAI.Backend.InternalProvider.VertexAI) {
+      return "wss://firebasevertexai.googleapis.com/ws" +
+             "/google.firebase.vertexai.v1beta.LlmBidiService/BidiGenerateContent" +
+             $"/locations/{_backend.Location}" +
+             $"?key={_firebaseApp.Options.ApiKey}";
+    } else if (_backend.Provider == FirebaseAI.Backend.InternalProvider.GoogleAI) {
+      return "wss://firebasevertexai.googleapis.com/ws" +
+             "/google.firebase.vertexai.v1beta.GenerativeService/BidiGenerateContent" +
+             $"?key={_firebaseApp.Options.ApiKey}";
+    } else {
+      throw new NotSupportedException($"Missing support for backend: {_backend.Provider}");
+    }
+  }
+  
+  private string GetModelName() {
+    if (_backend.Provider == FirebaseAI.Backend.InternalProvider.VertexAI) {
+      return $"projects/{_firebaseApp.Options.ProjectId}/locations/{_backend.Location}" +
+             $"/publishers/google/models/{_modelName}";
+    } else if (_backend.Provider == FirebaseAI.Backend.InternalProvider.GoogleAI) {
+      return $"projects/{_firebaseApp.Options.ProjectId}" +
+             $"/models/{_modelName}";
+    } else {
+      throw new NotSupportedException($"Missing support for backend: {_backend.Provider}");
+    }
   }
 
   /// <summary>

firebaseai/src/LiveSessionResponse.cs

@@ -58,7 +58,7 @@ public IReadOnlyList<byte[]> Audio {
       if (Message is LiveSessionContent content) {
         return content.Content?.Parts
             .OfType<ModelContent.InlineDataPart>()
-            .Where(part => part.MimeType == "audio/pcm")
+            .Where(part => part.MimeType.StartsWith("audio/pcm"))
             .Select(part => part.Data.ToArray())
             .ToList();
       }

firebaseai/src/ModelContent.cs

@@ -312,9 +312,9 @@ internal Dictionary<string, object> ToJson() {
   /// This method is used for deserializing JSON responses and should not be called directly.
   /// </summary>
   internal static ModelContent FromJson(Dictionary<string, object> jsonDict) {
-    // Both role and parts are required keys
     return new ModelContent(
-      jsonDict.ParseValue<string>("role", JsonParseOptions.ThrowEverything),
+      // If the role is missing, default to model since this is likely coming from the backend.
+      jsonDict.ParseValue("role", defaultValue: "model"),
       // Unknown parts are converted to null, which we then want to filter out here
       jsonDict.ParseObjectList("parts", PartFromJson, JsonParseOptions.ThrowEverything).Where(p => p is not null));
   }