feat(ai-logic): add automatic function calling to LiveGenerativeModel (#8223)

This PR adds automatic function calling support for
`LiveGenerativeModel`. The behavior should match what we did for
[`GenerativeModel`](https://github.com/firebase/firebase-android-sdk/blob/9b6e08e4d198d4d687a7c87fa44083db47c26cc4/ai-logic/firebase-ai/src/main/kotlin/com/google/firebase/ai/GenerativeModel.kt#L255-L302)
and
[`TemplateGenerativeModel`](https://github.com/firebase/firebase-android-sdk/blob/9b6e08e4d198d4d687a7c87fa44083db47c26cc4/ai-logic/firebase-ai/src/main/kotlin/com/google/firebase/ai/TemplateGenerativeModel.kt#L183-L230).

Author: thatfiredev

ai-logic/firebase-ai/CHANGELOG.md

@@ -1,5 +1,7 @@
 # Unreleased
 
+- [feature] Added automatic function calling support for `LiveGenerativeModel`. (#8223)
+
 # 17.13.0
 
 - [feature] Expanded `SpeechConfig` to support `MultiSpeakerVoiceConfig` and `LanguageCode`.

ai-logic/firebase-ai/src/main/kotlin/com/google/firebase/ai/LiveGenerativeModel.kt

@@ -20,7 +20,11 @@ import com.google.firebase.FirebaseApp
 import com.google.firebase.ai.common.APIController
 import com.google.firebase.ai.common.AppCheckHeaderProvider
 import com.google.firebase.ai.common.JSON
+import com.google.firebase.ai.type.AutoFunctionDeclaration
 import com.google.firebase.ai.type.Content
+import com.google.firebase.ai.type.FirebaseAutoFunctionException
+import com.google.firebase.ai.type.FunctionCallPart
+import com.google.firebase.ai.type.FunctionResponsePart
 import com.google.firebase.ai.type.GenerativeBackend
 import com.google.firebase.ai.type.LiveClientSetupMessage
 import com.google.firebase.ai.type.LiveGenerationConfig
@@ -40,8 +44,11 @@ import io.ktor.websocket.readBytes
 import kotlin.coroutines.CoroutineContext
 import kotlinx.coroutines.channels.ClosedReceiveChannelException
 import kotlinx.serialization.ExperimentalSerializationApi
+import kotlinx.serialization.InternalSerializationApi
 import kotlinx.serialization.encodeToString
 import kotlinx.serialization.json.JsonObject
+import kotlinx.serialization.json.JsonPrimitive
+import kotlinx.serialization.json.jsonObject
 
 /**
  * Represents a multimodal model (like Gemini) capable of real-time content generation based on
@@ -140,7 +147,9 @@ internal constructor(
         session = webSession,
         blockingDispatcher = blockingDispatcher,
         firebaseApp = firebaseApp,
-        connectionFactory = connectFactory
+        connectionFactory = connectFactory,
+        hasFunction = ::hasFunction,
+        executeFunction = ::executeFunction
       )
     } catch (e: ClosedReceiveChannelException) {
       val reason = webSession?.closeReason?.await()
@@ -150,6 +159,55 @@ internal constructor(
     }
   }
 
+  internal fun hasFunction(call: FunctionCallPart): Boolean {
+    return tools
+      .flatMap { it.autoFunctionDeclarations ?: emptyList() }
+      .firstOrNull { it.name == call.name && it.functionReference != null } != null
+  }
+
+  @OptIn(InternalSerializationApi::class)
+  internal suspend fun executeFunction(call: FunctionCallPart): FunctionResponsePart {
+    if (tools.isEmpty()) {
+      throw RuntimeException("No registered tools")
+    }
+    val tool = tools.flatMap { it.autoFunctionDeclarations ?: emptyList() }
+    val declaration =
+      tool.firstOrNull { it.name == call.name }
+        ?: throw RuntimeException("No registered function named ${call.name}")
+    return executeFunction<Any, Any>(
+      call,
+      declaration as AutoFunctionDeclaration<Any, Any>,
+      JsonObject(call.args).toString()
+    )
+  }
+
+  @OptIn(InternalSerializationApi::class)
+  internal suspend fun <I : Any, O : Any> executeFunction(
+    functionCall: FunctionCallPart,
+    functionDeclaration: AutoFunctionDeclaration<I, O>,
+    parameter: String
+  ): FunctionResponsePart {
+    val inputDeserializer = functionDeclaration.inputSchema.getSerializer()
+    val input = JSON.decodeFromString(inputDeserializer, parameter)
+    val functionReference =
+      functionDeclaration.functionReference
+        ?: throw RuntimeException("Function reference for ${functionDeclaration.name} is missing")
+    try {
+      val output = functionReference.invoke(input)
+      val outputSerializer = functionDeclaration.outputSchema?.getSerializer()
+      if (outputSerializer != null) {
+        return FunctionResponsePart.from(
+            JSON.encodeToJsonElement(outputSerializer, output).jsonObject
+          )
+          .normalizeAgainstCall(functionCall)
+      }
+      return (output as FunctionResponsePart).normalizeAgainstCall(functionCall)
+    } catch (e: FirebaseAutoFunctionException) {
+      return FunctionResponsePart.from(JsonObject(mapOf("error" to JsonPrimitive(e.message))))
+        .normalizeAgainstCall(functionCall)
+    }
+  }
+
   private companion object {
     private val TAG = LiveGenerativeModel::class.java.simpleName
   }

ai-logic/firebase-ai/src/main/kotlin/com/google/firebase/ai/type/LiveSession.kt

@@ -75,7 +75,9 @@ internal constructor(
   private val firebaseApp: FirebaseApp,
   private val connectionFactory:
     (suspend (SessionResumptionConfig?) -> DefaultClientWebSocketSession)? =
-    null
+    null,
+  private val hasFunction: ((FunctionCallPart) -> Boolean)? = null,
+  private val executeFunction: (suspend (FunctionCallPart) -> FunctionResponsePart)? = null
 ) {
   /**
    * Coroutine scope that we batch data on for network related behavior.
@@ -580,6 +582,14 @@ internal constructor(
               // It's fine to suspend here since you can't have a function call running concurrently
               // with an audio response
               sendFunctionResponse(it.functionCalls.map(functionCallHandler).toList())
+            } else if (
+              hasFunction != null &&
+                executeFunction != null &&
+                it.functionCalls.all { f -> hasFunction.invoke(f) }
+            ) {
+              sendFunctionResponse(
+                it.functionCalls.map { call -> executeFunction.invoke(call) }.toList()
+              )
             } else {
               Log.w(
                 TAG,