Published 22 January 2026

Features

• KTOR-8316 Support OpenAPI specification for the Ktor Client and Server Application
  • KTOR-9085 Read OpenAPI security details from authentication plugin
  • KTOR-8993 Use runtime-generated spec for OpenAPI / Swagger plugins
  • KTOR-9086 Read OpenAPI default content type information from ContentNegotiation plugin
  • KTOR-8859 Routing documentation compiler plugin
  • KTOR-8936 Routing documentation runtime API
  • KTOR-9087 Generate JSON schema for type references when using Jackson and Gson
• KTOR-7075 Zstd support
• KTOR-9209 Support Jackson 3
• KTOR-9198 Auth/Bearer: Make BearerAuthProvider detect disguised Bearer scheme
• KTOR-8927 Support for respondResource
• KTOR-9162 Auth API key plugin
• KTOR-7882 Support HTTP QUERY method
• KTOR-8195 Partial HTML response
• KTOR-8985 EngineMain: Support reading trust store settings from the configuration
• KTOR-9066 Add duplex streaming for OkHttpClient
• KTOR-8180 Auth: Provide control over tokens to user code
• KTOR-8273 iOS native interop for WebRTC client
• KTOR-8956 DI: Allow file configuration
• KTOR-9157 Support SIGINT on web and SIGTERM on Native

Improvements

• KTOR-8890 Rename target jsAndWasmShared to web
• KTOR-9242 Upgrade to Kotlin 2.3
• KTOR-9243 Update libcurl to 8.18.0
• KTOR-9014 Deprecate DarwinLegacy engine
• KTOR-8931 Test iOS target of the WebRTC Client in Ktor-Chat
• KTOR-9199 Make HttpHeaders strings const
• KTOR-9208 Expose plusIsSpace in parseUrlEncodedParameters
• KTOR-2404 Ktor Oauth2 feature sends 401 response when the client secret is invalid
• KTOR-9097 Java: Use HTTP/2 by default
• KTOR-8740 HTMX: Missing DSL for some attributes
• KTOR-9171 Redesign ByteReadChannel.readUTF8Line API
• KTOR-4219 Make readUTF8LineTo return number of read symbols instead of boolean
• KTOR-6761 Apache5: Simplify configuration of ConnectionManager
• KTOR-9037 Multipart/form-data: Make formData's block inline
• KTOR-9126 Missing function ByteReadChannel.readTo(sink: RawSink, byteCount: Long)
• KTOR-9026 Introduce/reuse interfaces for logging selectors
• KTOR-6766 Deprecate Apache 4 engine
• KTOR-8642 Excessive memory allocations while writing bytes into write channel of TCP/IP socket
• KTOR-9137 ByteReadChannel.readUTF8Line is inefficient for long lines
• KTOR-8657 Remove kotlinx-datetime from ktor-server-default-headers dependencies
• KTOR-8941 Add override DI conflict policy

Bugfixes

• KTOR-9258 headers { } block does not affect the request in defaultRequest due to function name collision with io.ktor.http.headers
• KTOR-9235 HttpCookies: Support parsing non-compilant Expires dates of Set-Cookie header
• KTOR-8945 ByteReadChannel.readUTF8Line doesn't throw TooLongLineException when the limit is reached
• KTOR-8339 Curl: caPath is not set by default in the Curl client on linuxArm64
• KTOR-9188 WebRTC. IceServer.urls should be a list.
• KTOR-9148 Logging: Body logging of multipart/form-data requests hangs when OkHttp format is on
• KTOR-9166 CORS: Excessive logs on INFO level since 3.3.3
• KTOR-9130 Missing implementation of getPluginId method error with Kotlin 2.3.0-RC
• KTOR-9147 OpenAPI: "AssertionError: Cannot add a performance measurements" leading to StackOverflowError within a multimodule project
• KTOR-2162 JettyKtorHandler executor will never grow beyond core size
• KTOR-9201 audio/x-matroska is wrongly recognized as mkv type
• KTOR-9146 Run HttpStatement.execute on the engine's dispatcher
• KTOR-6300 Native engines should use Dispatchers.IO not Dispatchers.Unconfined
• KTOR-9098 Curl: HttpResponse.version always returns HTTP_1_1
• KTOR-9100 Curl always uses HTTP/1.1
• KTOR-7162 DefaultRequest: Configuration applied twice for client created with HttpClient.config
• KTOR-9102 SSE: Java engine does not close the underlying connection when SSE session is canceled
• KTOR-9108 SSE: The handler adds Connection: Keep-Alive header, which is incompatible with HTTP/2
• KTOR-7884 Auth: The MutableList cannot be accessed since 3.0.0
• KTOR-6569 Bearer auth: Don't cache client bearer token (option)
• KTOR-4946 Auth: Bearer authentication - unable to update tokens
• KTOR-4759 Auth: BearerAuthProvider caches result of loadToken until process death
• KTOR-9129 Fix SendCountExceedException when maxRetries = Int.MAX_VALUE
• KTOR-9113 Netty HTTP2 server hangs on the plugin exception
• KTOR-9135 buildOpenApi fails with unknown serializer
• KTOR-8285 Bearer Auth: request cancellation causes refresh token invalidation
• KTOR-5241 The decodeBase64Bytes method doesn't throw an exception on illegal base64 characters
• KTOR-8912 Incorrect KDoc of ApplicationConfig.tryGetStringList
• KTOR-9079 The ktor-server-test-host module, having junit-jupiter runtime dependency, causes conflicts
• KTOR-7713 HttpCallValidatorConfig.handleResponseException() should receive a CallExceptionHandler
• KTOR-7121 testApplication: Test HTTP client does not use specified coroutine dispatcher
• KTOR-8785 DI: JobCancellationException during cleanup
• KTOR-6198 Client/WebSocket/Darwin close code and reason are incorrect
• KTOR-7824 Ktor doesn't parse multiple headers

Published 26 November 2025

Improvements

• KTOR-6837 Discrepancies when parsing URL host with CIO and Darwin engines compared to the rest engines
• KTOR-9050 Logging: SimpleLogger should be an object, not a class
• KTOR-9094 Jetty Client: Support HTTP/2 over cleartext (h2c)
• KTOR-9120 OpenAPI gen: missing operationId for KDoc fields
• KTOR-3019 Improve logging for CORS plugin

Bugfixes

• KTOR-8671 Netty: RejectedExecutionException during shutdown on MacOS when dev mode is enabled
• KTOR-9096 Darwin: New SSE handlers stop responding after canceling few SSE sessions
• KTOR-9125 Double ResponseSent invocation when exception is thrown after respond
• KTOR-8878 OpenAPI: StackOverflowError when a response object has property with @Contextual serializer
• KTOR-8947 Java, ContentEncoding: IllegalHeaderNameException is thrown for ":status" pseudo header with HTTP/2
• KTOR-9092 NettyHttp2Handler throws IllegalArgumentException: 'ktor.ApplicationCall' is already in use
• KTOR-8924 Curl: Client sends both Transfer-Encoding and Content-Length headers for DELETE requests with body
• KTOR-8838 Exception handling issue in client cache

Published 5 November 2025

Improvements

• WebRTC Client. Remove redundant targets (KTOR-9062)
• Add Socks proxy support to Darwin engine (KTOR-8968)
• Java: Improve error message when SOCKS proxy is used (KTOR-2908)

Bugfixes

• HttpRequestRetry: SendCountExceedException when max retries is more than maxSendCount of HttpSend (KTOR-5850)
• Darwin: The maxFrameSize option has no effect (KTOR-6963)
• OpenAPI: StackOverflowError when a response object has property with @Contextual serializer (KTOR-8878)
• OpenAPI gen: missing KDoc fields (KTOR-9021)
• Server call.request.path() returns routing selectors in path (KTOR-7639)
• StaticContent doesn't allow siblings (KTOR-9012)
• HttpCache: FileStorage doesn't use given dispatcher for all file operations (KTOR-8832)
• Curl: SOCKS proxy doesn't work (KTOR-9008)
• Netty: java.lang.VerifyError is thrown on Android since 3.3.0 (KTOR-8916)
• Response body channel is canceled while the body is being saved when having HttpRequestRetry and onDownload (KTOR-8975)
• HttpCache: InvalidCacheStateException when varyKeys stored in files contain uppercase letters since 3.3.0 (KTOR-8970)

Published 8 October 2025

Improvements

• Add a note about SSE session lifetime in KDoc (KTOR-8440)
• Update Kotlin to 2.2.20 (KTOR-8896)

Bugfixes

• NumberFormatException when Content-Length header value contains null bytes (KTOR-4828)
• SerializationException: Serializer for class 'ClientSSESession' is not found when server responds with JSON (KTOR-7631)
• Netty: loadConfiguration missing enableHttp2 and enableH2c properties (KTOR-8898)
• Netty: EmbeddedServer.stop always blocks for twice of shutdownGracePeriod (KTOR-8770)
• shutdownGracePeriod is used instead of shutdownTimeout in EmbeddedServer.stop() (KTOR-8771)
• Support serving static resources within bootJar (KTOR-8592)

Published 11 September 2025

Features

• Support for server side http2 without tls (h2c) (KTOR-4750)
• OpenAPI generation build extension preview (KTOR-8721)
• Serve static resources with caching headers and ETag based on sha256 of content (KTOR-6700)
• Jetty engine: Upgrade Jetty dependencies to the latest version 12 (KTOR-6734)
• Static content: Support a custom respond logic if the file is not found (KTOR-8496)
• Upgrade OkHttp to version 5.0.0 (KTOR-8652)
• WebRTC Client, Android + WASM (KTOR-7958)

Improvements

• SSE: Cannot read response body from SSEClientException (KTOR-8165)
• SSE: "SSEClientException: Content-Length mismatch" on saving response body in DefaultResponseValidation (KTOR-8753)
• var Route.staticRootFolder: File? should be deprecated (KTOR-5836)
• Add image/bmp to the ContentType (KTOR-8735)
• Add some missing image content types (KTOR-8624)
• Upgrade to Kotlin 2.2 (KTOR-8647)
• Bump Kotlin API level to 2.2 (KTOR-8637)
• CIO: The engine ignores system proxy settings (KTOR-5922)

Bugfixes

• Performance regression when using ContentEncoding and HttpRequestRetry since 3.2.0 (KTOR-8820)
• Big number of simultaneous outbound web socket connections leads to a coroutine deadlock (KTOR-8829)
• DI: JobCancellationException during cleanup (KTOR-8785)
• Autoreloading: JobCancellationException when app is reloaded in the debugger since 3.2.0 (KTOR-8810)
• HttpRedirect: The client is redirected when no Location header in response (KTOR-8697)
• SerializationException when Application.propertyOrNull() is called with type Map<String, Any?> (KTOR-8781)
• "Failed resolution of: Ljava/lang/management/ManagementFactory" on Android when JvmGcMetrics are initialized (KTOR-8714)
• HttpCache: all header values but first in HttpResponse.varyKeys() are ignored (KTOR-6402)
• HttpCache: plugin selects wrong cache entry when filtering Vary headers with different case (KTOR-7621)
• CountedByteWriteChannel: autoFlush of the source channel doesn't make the channel auto flushing (KTOR-8411)

Published 29 July 2025

Improvements

• Server only accepts yaml as the configuration file suffix (KTOR-8712)
• JS / WASM error when process global is undefined (KTOR-8686)
• DI async duplicate resolution (KTOR-8681)

Bugfixes

• CIO: Expect 100-continue response is missing a final \r\n (KTOR-8687)
• Intermittent "ParserException: No colon in HTTP header" when parsing multipart request (KTOR-8523)
• Infinite loop in ByteReadChannel.readFully (KTOR-8682)
• ShutDownUrl: The server cannot shut down since 3.2.0 (KTOR-8674)

Published 14 July 2025

Improvements

• SSE: Change the order of SSE field serialization: put event before data (KTOR-8627)

Bugfixes

• CORS: server replies with the 405 status code on a preflight request when the plugin is installed in a route (KTOR-4499)
• Darwin: The Content-Encoding header is removed since 3.0.3 (KTOR-8526)
• JS/WASM: response doesn't contain the Content-Length header in a browser (KTOR-8377)
• StatusPages: response headers of OutgoingContent aren't available in the status handlers (KTOR-8232)
• testApplication: The client.sse() acts like a REST call and not a stream in test environment (KTOR-7910)
• Config deserialization - default properties problem (KTOR-8654)
• kotlinx.datetime is not available transitively in 3.2.1 (KTOR-8656)
• Request builder block overrides HTTP method in specific request builders (get, post, etc) (KTOR-8636)

Improvements

• Replace kotlinx.datetime APIs with kotlin.time (KTOR-8635)
• Thymeleaf: null values in template model (KTOR-8559)
• Publish Javadoc as a maven artifact (KTOR-3962)
• Netty: Invalid hex byte with malformed query string (KTOR-2934)

Bugfixes

• "Space characters in SimpleName" error when executing R8 mergeExtDex task with 3.2.0 (KTOR-8583)
• ForwardedHeaders: the plugin does not handle parameters case-insensitively (KTOR-8622)
• Potential race condition in socket.awaitClosed (hangs indefinitely) since 3.2.0 (KTOR-8618)
• Module parameter type Application.() -> kotlin.Unit is not supported in 3.2.0 (KTOR-8602)
• OkHttp: java.net.ProtocolException when sending MultiPartFormDataContent with onUpload (KTOR-6790)
• OAuth2 authentication provider breaks form-urlencoded POST requests when receiving request body (KTOR-4420)
• 404 for a link in KDoc for io.ktor.server.plugins.contentnegotiation.ContentNegotiation (KTOR-8597)
• Ktor fails to boot with default jvminline argument (KTOR-8608)
• Flow invariant is violated since 3.2.0 (KTOR-8606)
• ResponseSent hook handler of the plugin installed into a route isn't executed when an exception is thrown from the route (KTOR-6794)

Published 12 June 2025

Features

• Dependency injection Ktor extension (KTOR-8267)
• Support Version Catalog (KTOR-8162)
• Unix domain socket support at the Ktor Engine level (KTOR-4766)
• Allow suspend Ktor modules (KTOR-8005)
• Ability to use browser cookie storage (KTOR-539)
• Configuration file deserialization (KTOR-7874)
• HttpCache: Support evicting/clearing cache (KTOR-6653)
• File configuration for dependencies (KTOR-8304)

Improvements

• Excessive allocation of ApplicationConfig when loading multiple files from CLI (KTOR-8563)
• Linux curl engine doesn't work for simultaneous websocket and http request (KTOR-8259)
• ktor-network produces ProGuard warning (KTOR-8525)
• More overloads for StringValuesBuilder.appendAll (KTOR-8573)
• HttpClientCall: Deprecate wrapWithContent and wrap (KTOR-8378)
• Add a way to create an ApplicationCall for testing (KTOR-7607)
• Configuration access API improvements (KTOR-8185)
• Application instance access in testApplication (KTOR-8215)
• The TestApplication client should be configurable and mutable (KTOR-8465)
• Support accessing resolved IP address on an instance of io.ktor.network.sockets.InetSocketAddress (KTOR-8490)
• Deprecate SaveBodyPlugin in favor of HttpClientCall.save (KTOR-8367)
• Obscure log message on server startup (KTOR-8519)
• Routing: accept should return 406 if the Accept header isn't matched (KTOR-8416)
• MicrometerMetrics: the route label can exceed length limit (KTOR-7274)
• Micrometer: Make route label configurable (KTOR-8183)
• Add more common ContentType values (KTOR-7108)

Bugfixes

• Logging/Darwin: IOException is thrown when detecting if body is a binary (KTOR-8581)
• Netty: NoSuchElementException or empty headers when responding with 204 (KTOR-8528)
• YAML configuration: NoSuchElementException when parameter is expanded with curly braces (KTOR-8575)
• ApplicationConfig: Most of the content is absent after merging configs (KTOR-8565)
• Android: "ProtocolException: TRACE does not support writing" when sending TRACE request (KTOR-8352)
• The "Content-Length: 0" header is added for GET requests sent to some servers (KTOR-6508)
• HttpRequestRetry: requests with some IOException's thrown by Java engine aren't retried (KTOR-6770)
• HttpCookies: Encoding of request cookies is not preserved in CookiesStorage (KTOR-8343)
• Url class mangles data URLs (KTOR-5708)
• SaveBodyPlugin: Logging plugin consumes response body (KTOR-6474)
• Config deserialization does not respect testApplication environment (KTOR-8436)
• Resources: Exclude a parent from query params when it is an object (KTOR-8507)
• BearerAuthProvider does not clear token if refreshTokens returns null (KTOR-8470)
• Coroutines launched from RoutingContext are not cancelled upon server shutdown (KTOR-8338)
• Application job is not joined during shutdown (KTOR-8291)
• HttpCache: InvalidCacheStateException thrown when Vary header has different entries is overly severe (KTOR-8345)
• Fix socket channel close handling (KTOR-8201)

Published 5 May 2025

Improvements

• Implement toString for staticContentRoute (KTOR-8451)
• Don't send Authorization header for requests marked with markAsRefreshTokenRequest (KTOR-8107)
• ByteChannel single-byte operations are slow (KTOR-8412)
• Receiving multipart without Content-Length is very slow (KTOR-8407)
• MicrometerMetrics: different path 404s requests can be abused to trigger OOM (KTOR-8276)
• Compression & Static Content: No Vary Header when serving a compressed resource (KTOR-8326)
• HttpTimeout: Reference to nonexistent INFINITE_TIMEOUT_MS in the exception message (KTOR-8358)

Bugfixes

• Websockets: Unable to send a frame when ktor-serialization-kotlinx-json-jvm dependency is defined in Maven build (KTOR-7662)
• OkHttp: Cancelling of SSE request job doesn't cancel the connection (KTOR-8409)
• OkHttp: Exceptions are not propagated to flow collectors (KTOR-7947)
• OOM in CountedByteReadChannel while copying from multipart/form-data part channel (KTOR-8317)
• Apache5: "ProtocolException: OPTIONS request must have Content-Type header" is thrown when body isn't set (KTOR-8318)
• Netty/Websockets: server processes hanging in CLOSE_WAIT state after many concurrent requests (KTOR-7965)
• Update JTE to the version supporting Kotlin 2.1.0 (KTOR-8030)