Ensure system instruction content has system role

firebase-vertexai/src/main/kotlin/com/google/firebase/vertexai/GenerativeModel.kt

@@ -231,7 +231,7 @@ internal constructor(
       generationConfig?.toInternal(),
       tools?.map { it.toInternal() },
       toolConfig?.toInternal(),
-      systemInstruction?.toInternal()
+      systemInstruction?.copy(role = "system")?.toInternal()
     )
 
   private fun constructCountTokensRequest(vararg prompt: Content) =

firebase-vertexai/src/main/kotlin/com/google/firebase/vertexai/type/Content.kt

@@ -30,6 +30,10 @@ public class Content
 @JvmOverloads
 constructor(public val role: String? = "user", public val parts: List<Part>) {
 
+  public fun copy(role: String? = this.role, parts: List<Part> = this.parts): Content {
+    return Content(role, parts)
+  }
+
   /** Builder class to facilitate constructing complex [Content] objects. */
   public class Builder {
 

firebase-vertexai/src/test/java/com/google/firebase/vertexai/GenerativeModelTesting.kt

@@ -0,0 +1,87 @@
+/*
+ * Copyright 2024 Google LLC
+ *
+ * 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.
+ */
+
+package com.google.firebase.vertexai
+
+import com.google.firebase.vertexai.common.APIController
+import com.google.firebase.vertexai.common.GenerateContentResponse
+import com.google.firebase.vertexai.common.JSON
+import com.google.firebase.vertexai.common.server.Candidate
+import com.google.firebase.vertexai.common.shared.Content
+import com.google.firebase.vertexai.common.shared.TextPart
+import com.google.firebase.vertexai.common.util.doBlocking
+import com.google.firebase.vertexai.type.RequestOptions
+import com.google.firebase.vertexai.type.content
+import io.kotest.assertions.json.shouldContainJsonKey
+import io.kotest.assertions.json.shouldContainJsonKeyValue
+import io.ktor.client.engine.mock.MockEngine
+import io.ktor.client.engine.mock.respond
+import io.ktor.http.HttpHeaders
+import io.ktor.http.HttpStatusCode
+import io.ktor.http.content.TextContent
+import io.ktor.http.headersOf
+import kotlin.time.Duration.Companion.seconds
+import kotlinx.coroutines.withTimeout
+import kotlinx.serialization.encodeToString
+import org.junit.Test
+
+internal class GenerativeModelTesting {
+  private val TEST_CLIENT_ID = "test"
+
+  @Test
+  fun addition() = doBlocking {
+    val mockEngine = MockEngine {
+      respond(
+        generateContentResponseAsJsonString("text response"),
+        HttpStatusCode.OK,
+        headersOf(HttpHeaders.ContentType, "application/json")
+      )
+    }
+
+    val apiController =
+      APIController(
+        "super_cool_test_key",
+        "gemini-1.5-flash",
+        RequestOptions(timeout = 5.seconds, endpoint = "https://my.custom.endpoint"),
+        mockEngine,
+        TEST_CLIENT_ID,
+        null,
+      )
+
+    val generativeModel =
+      GenerativeModel(
+        "gemini-1.5-flash",
+        systemInstruction = content { text("system instruction") },
+        controller = apiController
+      )
+
+    withTimeout(5.seconds) { generativeModel.generateContent("my test prompt") }
+
+    val requestBodyAsText = (mockEngine.requestHistory.first().body as TextContent).text
+
+    requestBodyAsText.let {
+      it shouldContainJsonKey "system_instruction"
+      it.shouldContainJsonKeyValue("$.system_instruction.role", "system")
+      it.shouldContainJsonKeyValue("$.system_instruction.parts[0].text", "system instruction")
+    }
+  }
+
+  private fun generateContentResponseAsJsonString(text: String): String {
+    return JSON.encodeToString(
+      GenerateContentResponse(listOf(Candidate(Content(parts = listOf(TextPart(text))))))
+    )
+  }
+}