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Merged
kpavlov merged 7 commits into from
Dec 5, 2025
+1,024 −3
Merged

[WIP] StreamableHttpServerTransport implementation #449

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d189d4f
Add PrimingEventMessage type and update Protocol to handle it
devcrocod Dec 4, 2025
4667bf0
Add StreamableHttpServerTransport implementation
devcrocod Dec 4, 2025
a40db1d
update api
devcrocod Dec 4, 2025
e593c2e
Add tests for StreamableHttpServerTransport with necessary dependencies
devcrocod Dec 5, 2025
02c3c15
Replace `PrimingEventMessage` with `JSONRPCEmptyMessage` across SDK a…
devcrocod Dec 5, 2025
04956fb
Add JSONRPCEmptyMessage type to the API
devcrocod Dec 5, 2025
600850e
Remove `PrimingEventMessage` type from API
devcrocod Dec 5, 2025
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3 changes: 3 additions & 0 deletions gradle/libs.versions.toml
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Expand Up @@ -44,6 +44,9 @@ kotlinx-serialization-json = { group = "org.jetbrains.kotlinx", name = "kotlinx-
ktor-client-apache5 = { group = "io.ktor", name = "ktor-client-apache5", version.ref = "ktor" }
ktor-client-core = { group = "io.ktor", name = "ktor-client-core", version.ref = "ktor" }
ktor-client-logging = { group = "io.ktor", name = "ktor-client-logging", version.ref = "ktor" }
ktor-server-content-negotiation = { group = "io.ktor", name = "ktor-server-content-negotiation", version.ref = "ktor" }
ktor-client-content-negotiation = { group = "io.ktor", name = "ktor-client-content-negotiation", version.ref = "ktor" }
ktor-serialization = { group = "io.ktor", name = "ktor-serialization-kotlinx-json", version.ref = "ktor" }
ktor-server-core = { group = "io.ktor", name = "ktor-server-core", version.ref = "ktor" }
ktor-server-sse = { group = "io.ktor", name = "ktor-server-sse", version.ref = "ktor" }
ktor-server-websockets = { group = "io.ktor", name = "ktor-server-websockets", version.ref = "ktor" }
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10 changes: 10 additions & 0 deletions kotlin-sdk-core/api/kotlin-sdk-core.api
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Expand Up @@ -988,6 +988,7 @@ public final class io/modelcontextprotocol/kotlin/sdk/types/ClientResult$Default
}

public final class io/modelcontextprotocol/kotlin/sdk/types/CommonKt {
public static final field DEFAULT_NEGOTIATED_PROTOCOL_VERSION Ljava/lang/String;
public static final field LATEST_PROTOCOL_VERSION Ljava/lang/String;
public static final fun ProgressToken (J)Lio/modelcontextprotocol/kotlin/sdk/types/RequestId;
public static final fun ProgressToken (Ljava/lang/String;)Lio/modelcontextprotocol/kotlin/sdk/types/RequestId;
Expand Down Expand Up @@ -2046,6 +2047,15 @@ public final class io/modelcontextprotocol/kotlin/sdk/types/InitializedNotificat
public final fun serializer ()Lkotlinx/serialization/KSerializer;
}

public final class io/modelcontextprotocol/kotlin/sdk/types/JSONRPCEmptyMessage : io/modelcontextprotocol/kotlin/sdk/types/JSONRPCMessage {
public static final field INSTANCE Lio/modelcontextprotocol/kotlin/sdk/types/JSONRPCEmptyMessage;
public fun equals (Ljava/lang/Object;)Z
public fun getJsonrpc ()Ljava/lang/String;
public fun hashCode ()I
public final fun serializer ()Lkotlinx/serialization/KSerializer;
public fun toString ()Ljava/lang/String;
}

public final class io/modelcontextprotocol/kotlin/sdk/types/JSONRPCError : io/modelcontextprotocol/kotlin/sdk/types/JSONRPCMessage {
public static final field Companion Lio/modelcontextprotocol/kotlin/sdk/types/JSONRPCError$Companion;
public fun <init> (Lio/modelcontextprotocol/kotlin/sdk/types/RequestId;Lio/modelcontextprotocol/kotlin/sdk/types/RPCError;)V
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2 changes: 2 additions & 0 deletions kotlin-sdk-core/src/commonMain/kotlin/io/modelcontextprotocol/kotlin/sdk/shared/Protocol.kt
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Expand Up @@ -4,6 +4,7 @@ import io.github.oshai.kotlinlogging.KotlinLogging
import io.modelcontextprotocol.kotlin.sdk.types.CancelledNotification
import io.modelcontextprotocol.kotlin.sdk.types.CancelledNotificationParams
import io.modelcontextprotocol.kotlin.sdk.types.EmptyResult
import io.modelcontextprotocol.kotlin.sdk.types.JSONRPCEmptyMessage
import io.modelcontextprotocol.kotlin.sdk.types.JSONRPCError
import io.modelcontextprotocol.kotlin.sdk.types.JSONRPCNotification
import io.modelcontextprotocol.kotlin.sdk.types.JSONRPCRequest
Expand Down Expand Up @@ -249,6 +250,7 @@ public abstract class Protocol(@PublishedApi internal val options: ProtocolOptio
is JSONRPCRequest -> onRequest(message)
is JSONRPCNotification -> onNotification(message)
is JSONRPCError -> onResponse(null, message)
is JSONRPCEmptyMessage -> Unit
}
}

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4 changes: 2 additions & 2 deletions kotlin-sdk-core/src/commonMain/kotlin/io/modelcontextprotocol/kotlin/sdk/types/common.kt
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@@ -1,7 +1,5 @@
package io.modelcontextprotocol.kotlin.sdk.types

import io.modelcontextprotocol.kotlin.sdk.types.Icon.Theme.Dark
import io.modelcontextprotocol.kotlin.sdk.types.Icon.Theme.Light
import kotlinx.serialization.SerialName
import kotlinx.serialization.Serializable
import kotlinx.serialization.json.JsonObject
Expand All @@ -12,6 +10,8 @@ import kotlinx.serialization.json.JsonObject

public const val LATEST_PROTOCOL_VERSION: String = "2025-06-18"

public const val DEFAULT_NEGOTIATED_PROTOCOL_VERSION: String = "2025-03-26"

public val SUPPORTED_PROTOCOL_VERSIONS: List<String> = listOf(
LATEST_PROTOCOL_VERSION,
"2025-03-26",
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7 changes: 6 additions & 1 deletion kotlin-sdk-core/src/commonMain/kotlin/io/modelcontextprotocol/kotlin/sdk/types/jsonRpc.kt
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Expand Up @@ -85,6 +85,11 @@ public sealed interface JSONRPCMessage {
public val jsonrpc: String
}

@Serializable
public data object JSONRPCEmptyMessage : JSONRPCMessage {
override val jsonrpc: String = JSONRPC_VERSION
}

// ============================================================================
// JSONRPCRequest
// ============================================================================
Expand Down Expand Up @@ -197,7 +202,7 @@ public data class JSONRPCResponse(val id: RequestId, val result: RequestResult =
* @property error Details about the error that occurred, including error code and message.
*/
@Serializable
public data class JSONRPCError(val id: RequestId, val error: RPCError) : JSONRPCMessage {
public data class JSONRPCError(val id: RequestId?, val error: RPCError) : JSONRPCMessage {
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The id field of JSONRPCError is now nullable, but this could be a breaking API change. According to the JSON-RPC 2.0 specification, the id member is required in error responses except when there was an error in detecting the id in the request object (e.g., parse error). Consider documenting when null is appropriate, or ensure this aligns with how the codebase handles error scenarios where the request ID cannot be determined.

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@EncodeDefault
override val jsonrpc: String = JSONRPC_VERSION
}
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1 change: 1 addition & 0 deletions ...in-sdk-core/src/commonMain/kotlin/io/modelcontextprotocol/kotlin/sdk/types/serializers.kt
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Expand Up @@ -384,6 +384,7 @@ internal object JSONRPCMessagePolymorphicSerializer :
"result" in jsonObject -> JSONRPCResponse.serializer()
"method" in jsonObject && "id" in jsonObject -> JSONRPCRequest.serializer()
"method" in jsonObject -> JSONRPCNotification.serializer()
jsonObject.isEmpty() || jsonObject.keys == setOf("jsonrpc") -> JSONRPCEmptyMessage.serializer()
else -> throw SerializationException("Invalid JSONRPCMessage type: ${jsonObject.keys}")
}
}
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12 changes: 12 additions & 0 deletions ...in-sdk-core/src/commonTest/kotlin/io/modelcontextprotocol/kotlin/sdk/types/JsonRpcTest.kt
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Expand Up @@ -430,4 +430,16 @@ class JsonRpcTest {
request.method shouldBe "notifications/log"
request.params shouldBeSameInstanceAs params
}

@Test
fun `should deserialize JSONRPCEmptyMessage`() {
val json = """
{
"jsonrpc": "2.0"
}
""".trimIndent()

val message = McpJson.decodeFromString<JSONRPCMessage>(json)
message shouldBeSameInstanceAs JSONRPCEmptyMessage
}
}
25 changes: 25 additions & 0 deletions kotlin-sdk-server/api/kotlin-sdk-server.api
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@@ -1,3 +1,9 @@
public abstract interface class io/modelcontextprotocol/kotlin/sdk/server/EventStore {
public abstract fun getStreamIdForEventId (Ljava/lang/String;Lkotlin/coroutines/Continuation;)Ljava/lang/Object;
public abstract fun replayEventsAfter (Ljava/lang/String;Lkotlin/jvm/functions/Function3;Lkotlin/coroutines/Continuation;)Ljava/lang/Object;
public abstract fun storeEvent (Ljava/lang/String;Lio/modelcontextprotocol/kotlin/sdk/types/JSONRPCMessage;Lkotlin/coroutines/Continuation;)Ljava/lang/Object;
}

public final class io/modelcontextprotocol/kotlin/sdk/server/KtorServerKt {
public static final fun mcp (Lio/ktor/server/application/Application;Lkotlin/jvm/functions/Function1;)V
public static final fun mcp (Lio/ktor/server/routing/Routing;Ljava/lang/String;Lkotlin/jvm/functions/Function1;)V
Expand Down Expand Up @@ -151,6 +157,25 @@ public final class io/modelcontextprotocol/kotlin/sdk/server/StdioServerTranspor
public fun start (Lkotlin/coroutines/Continuation;)Ljava/lang/Object;
}

public final class io/modelcontextprotocol/kotlin/sdk/server/StreamableHttpServerTransport : io/modelcontextprotocol/kotlin/sdk/shared/AbstractTransport {
public static final field STANDALONE_SSE_STREAM_ID Ljava/lang/String;
public fun <init> ()V
public fun <init> (ZZLjava/util/List;Ljava/util/List;Lio/modelcontextprotocol/kotlin/sdk/server/EventStore;Ljava/lang/Long;)V
public synthetic fun <init> (ZZLjava/util/List;Ljava/util/List;Lio/modelcontextprotocol/kotlin/sdk/server/EventStore;Ljava/lang/Long;ILkotlin/jvm/internal/DefaultConstructorMarker;)V
public fun close (Lkotlin/coroutines/Continuation;)Ljava/lang/Object;
public final fun closeSseStream (Lio/modelcontextprotocol/kotlin/sdk/types/RequestId;Lkotlin/coroutines/Continuation;)Ljava/lang/Object;
public final fun getSessionId ()Ljava/lang/String;
public final fun handleDeleteRequest (Lio/ktor/server/application/ApplicationCall;Lkotlin/coroutines/Continuation;)Ljava/lang/Object;
public final fun handleGetRequest (Lio/ktor/server/sse/ServerSSESession;Lio/ktor/server/application/ApplicationCall;Lkotlin/coroutines/Continuation;)Ljava/lang/Object;
public final fun handlePostRequest (Lio/ktor/server/sse/ServerSSESession;Lio/ktor/server/application/ApplicationCall;Lkotlin/coroutines/Continuation;)Ljava/lang/Object;
public final fun handleRequest (Lio/ktor/server/sse/ServerSSESession;Lio/ktor/server/application/ApplicationCall;Lkotlin/coroutines/Continuation;)Ljava/lang/Object;
public fun send (Lio/modelcontextprotocol/kotlin/sdk/types/JSONRPCMessage;Lio/modelcontextprotocol/kotlin/sdk/shared/TransportSendOptions;Lkotlin/coroutines/Continuation;)Ljava/lang/Object;
public final fun setOnSessionClosed (Lkotlin/jvm/functions/Function1;)V
public final fun setOnSessionInitialized (Lkotlin/jvm/functions/Function1;)V
public final fun setSessionIdGenerator (Lkotlin/jvm/functions/Function0;)V
public fun start (Lkotlin/coroutines/Continuation;)Ljava/lang/Object;
}

public final class io/modelcontextprotocol/kotlin/sdk/server/WebSocketMcpKtorServerExtensionsKt {
public static final fun mcpWebSocket (Lio/ktor/server/application/Application;Ljava/lang/String;Lkotlin/jvm/functions/Function0;)V
public static final fun mcpWebSocket (Lio/ktor/server/application/Application;Lkotlin/jvm/functions/Function0;)V
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7 changes: 7 additions & 0 deletions kotlin-sdk-server/build.gradle.kts
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Expand Up @@ -26,6 +26,13 @@ kotlin {

jvmTest {
dependencies {
implementation(libs.ktor.client.logging)
implementation(libs.ktor.server.content.negotiation)
implementation(libs.ktor.client.content.negotiation)
implementation(libs.ktor.serialization)
implementation(libs.ktor.server.test.host)
implementation(libs.kotest.assertions.core)
implementation(libs.kotest.assertions.json)
runtimeOnly(libs.slf4j.simple)
}
}
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33 changes: 33 additions & 0 deletions ...-sdk-server/src/commonMain/kotlin/io/modelcontextprotocol/kotlin/sdk/server/EventStore.kt
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@@ -0,0 +1,33 @@
package io.modelcontextprotocol.kotlin.sdk.server

import io.modelcontextprotocol.kotlin.sdk.types.JSONRPCMessage

/**
* Interface for resumability support via event storage
*/
public interface EventStore {
/**
* Stores an event for later retrieval
* @param streamId ID of the stream the event belongs to
* @param message The JSON-RPC message to store
* @returns The generated event ID for the stored event
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Copilot AI Dec 5, 2025

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The comment style uses @returns instead of the Kotlin standard @return. KDoc convention uses @return (singular) for documenting return values.

Suggested change
* @returns The generated event ID for the stored event
* @return The generated event ID for the stored event

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*/
public suspend fun storeEvent(streamId: String, message: JSONRPCMessage): String

/**
* Replays events after the specified event ID
* @param lastEventId The last event ID that was received
* @param sender Function to send events
* @return The stream ID for the replayed events
*/
public suspend fun replayEventsAfter(
lastEventId: String,
sender: suspend (eventId: String, message: JSONRPCMessage) -> Unit,
): String

/**
* Returns the stream ID associated with [eventId], or null if the event is unknown.
* Default implementation is a no-op which disables extra validation during replay.
Comment on lines +29 to +30
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Missing KDoc documentation for the getStreamIdForEventId method. The inline comment on line 30 describes it as a "no-op" default implementation, but there's no actual default implementation provided (it's an interface method). Consider either providing a default implementation or clarifying the documentation to explain that implementers may throw NotImplementedError or UnsupportedOperationException to disable this validation.

Suggested change
* Returns the stream ID associated with [eventId], or null if the event is unknown.
* Default implementation is a no-op which disables extra validation during replay.
* Returns the stream ID associated with the given [eventId], or null if the event is unknown.
*
* Implementers may throw [NotImplementedError] or [UnsupportedOperationException] to disable
* extra validation during replay, as there is no default implementation provided.
*
* @param eventId The event ID to look up.
* @return The stream ID associated with the event, or null if unknown.

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*/
public suspend fun getStreamIdForEventId(eventId: String): String?
}
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