feat: Add audio type according to 2025-03-26 spec

src/commonMain/kotlin/io/modelcontextprotocol/kotlin/sdk/types.kt

@@ -884,10 +884,10 @@ public sealed interface PromptMessageContent {
 }
 
 /**
- * Represents prompt message content that is either text or an image.
+ * Represents prompt message content that is either text, image or audio.
  */
-@Serializable(with = PromptMessageContentTextOrImagePolymorphicSerializer::class)
-public sealed interface PromptMessageContentTextOrImage : PromptMessageContent
+@Serializable(with = PromptMessageContentMultimodalPolymorphicSerializer::class)
+public sealed interface PromptMessageContentMultimodal : PromptMessageContent
 
 /**
  * Text provided to or from an LLM.
@@ -898,7 +898,7 @@ public data class TextContent(
      * The text content of the message.
      */
     val text: String? = null,
-) : PromptMessageContentTextOrImage {
+) : PromptMessageContentMultimodal {
     override val type: String = TYPE
 
     public companion object {
@@ -920,7 +920,7 @@ public data class ImageContent(
      * The MIME type of the image. Different providers may support different image types.
      */
     val mimeType: String,
-) : PromptMessageContentTextOrImage {
+) : PromptMessageContentMultimodal {
     override val type: String = TYPE
 
     public companion object {
@@ -929,12 +929,35 @@ public data class ImageContent(
 }
 
 /**
- * An image provided to or from an LLM.
+ * Audio provided to or from an LLM.
+ */
+@Serializable
+public data class AudioContent(
+    /**
+     * The base64-encoded audio data.
+     */
+    val data: String,
+
+    /**
+     * The MIME type of the audio. Different providers may support different audio types.
+     */
+    val mimeType: String,
+) : PromptMessageContentMultimodal {
+    override val type: String = TYPE
+
+    public companion object {
+        public const val TYPE: String = "audio"
+    }
+}
+
+
+/**
+ * Unknown content provided to or from an LLM.
  */
 @Serializable
 public data class UnknownContent(
     override val type: String,
-) : PromptMessageContentTextOrImage
+) : PromptMessageContentMultimodal
 
 /**
  * The contents of a resource, embedded into a prompt or tool call result.
@@ -1204,7 +1227,7 @@ public class ModelPreferences(
 @Serializable
 public data class SamplingMessage(
     val role: Role,
-    val content: PromptMessageContentTextOrImage,
+    val content: PromptMessageContentMultimodal,
 )
 
 /**
@@ -1286,7 +1309,7 @@ public data class CreateMessageResult(
      */
     val stopReason: StopReason? = null,
     val role: Role,
-    val content: PromptMessageContentTextOrImage,
+    val content: PromptMessageContentMultimodal,
     override val _meta: JsonObject = EmptyJsonObject,
 ) : ClientResult
 

src/commonMain/kotlin/io/modelcontextprotocol/kotlin/sdk/types.util.kt

@@ -80,17 +80,19 @@ internal object PromptMessageContentPolymorphicSerializer :
             ImageContent.TYPE -> ImageContent.serializer()
             TextContent.TYPE -> TextContent.serializer()
             EmbeddedResource.TYPE -> EmbeddedResource.serializer()
+            AudioContent.TYPE -> AudioContent.serializer()
             else -> UnknownContent.serializer()
         }
     }
 }
 
-internal object PromptMessageContentTextOrImagePolymorphicSerializer :
-    JsonContentPolymorphicSerializer<PromptMessageContentTextOrImage>(PromptMessageContentTextOrImage::class) {
-    override fun selectDeserializer(element: JsonElement): DeserializationStrategy<PromptMessageContentTextOrImage> {
+internal object PromptMessageContentMultimodalPolymorphicSerializer :
+    JsonContentPolymorphicSerializer<PromptMessageContentMultimodal>(PromptMessageContentMultimodal::class) {
+    override fun selectDeserializer(element: JsonElement): DeserializationStrategy<PromptMessageContentMultimodal> {
         return when (element.jsonObject.getValue("type").jsonPrimitive.content) {
             ImageContent.TYPE -> ImageContent.serializer()
             TextContent.TYPE -> TextContent.serializer()
+            AudioContent.TYPE -> AudioContent.serializer()
             else -> UnknownContent.serializer()
         }
     }

src/commonTest/kotlin/AudioContentSerializationTest.kt

@@ -0,0 +1,34 @@
+package io.modelcontextprotocol.kotlin.sdk
+
+import io.kotest.assertions.json.shouldEqualJson
+import io.modelcontextprotocol.kotlin.sdk.shared.McpJson
+import kotlinx.serialization.encodeToString
+import kotlin.test.Test
+import kotlin.test.assertEquals
+
+class AudioContentSerializationTest {
+
+    private val audioContentJson = """
+        {
+          "data": "base64-encoded-audio-data",
+           "mimeType": "audio/wav",
+          "type": "audio"
+        }
+    """.trimIndent()
+
+    private val audioContent = AudioContent(
+        data = "base64-encoded-audio-data",
+        mimeType = "audio/wav"
+    )
+
+    @Test
+    fun `should serialize audio content`() {
+        McpJson.encodeToString(audioContent) shouldEqualJson audioContentJson
+    }
+
+    @Test
+    fun `should deserialize audio content`() {
+        val content = McpJson.decodeFromString<AudioContent>(audioContentJson)
+        assertEquals(expected = audioContent, actual = content)
+    }
+}