3.4.3

Published 22 April 2026

Bugfixes

• KTOR-9451 OpenAPI schema inference not working for custom nested generics
• KTOR-9490 OpenAPI: Self-referential schema $ref uses FQN while schema is registered with a simple name
• KTOR-9463 OpenAPI: schema inference StackOverflow
• KTOR-8938 WebSockets: WebSockets handler does not inherit server coroutine context
• KTOR-8989 Shared engine is closed when a client created with config method is closed
• KTOR-9485 Apache5: FutureCallback never called, breaking Java agent instrumentation
• KTOR-9497 Darwin: SIGABRT crash when close() races with in-flight execute() since 3.4.2
• KTOR-9431 SuspendFunctionGun: ThreadContextElement leaks across requests when interceptor suspends
• KTOR-9423 CannotTransformContentToTypeException leaks internal class names in response body
• KTOR-9461 Incorrect link to the OWASP cheatsheet in the KDoc for CSRF plugin
• KTOR-9476 Unable to update/remove session data if no response content
• KTOR-9343 HttpRequestLifecycle plugin with cancelCallOnClose on, cancels subsequent requests when CallLogging plugin with callIdMdc is installed

3.4.2

Published 27 March 2026

Improvements

• KTOR-9327 Curl: The WebSockets maxFrameSize option does not have an effect
• KTOR-9383 CaseInsensitiveString: reduce allocations
• KTOR-9385 Netty: Allocation micro-optimizations
• KTOR-9403 Darwin: Unnecessary ByteArray copy for each received response chunk
• KTOR-9412 KDoc for formFieldLimit documents incorrect default value (64 KB instead of 50 MiB)

Bugfixes

• KTOR-9351 OpenAPI: Incorrect schema generated for nested classes with lists
• KTOR-9361 WebSockets: JsWebSocketSession._closeReason is completed twice
• KTOR-9437 Fix GraalVM Compatibility
• KTOR-9424 Logging: OkHttp format should log the full requested URL
• KTOR-8540 Logging: IllegalStateException is thrown when response is cached and deserialization fails
• KTOR-9370 OpenAPI: NoSuchMethodError - getLOCAL_FUNCTION_FOR_LAMBDA with Kotlin 2.3.20-*
• KTOR-9421 Netty: active SSE connection blocks HTTP/2 response flushing for other requests
• KTOR-3390 JS browser: "Failed to execute 'digest' on 'SubtleCrypto'" error when using digest auth
• KTOR-5977 Compression: The encoders buffer streaming response
• KTOR-9393 Certificate pinning matches against all pins instead of hostname-scoped pins
• KTOR-8751 DI: AmbiguousDependencyException when named dependency is overridden in testApplication
• KTOR-9039 Bearer Auth: Request body transformed with jsonIO isn't sent over again after refreshToken request
• KTOR-9404 Darwin: Memory leak in KtorNSURLSessionDelegate
• KTOR-9399 LinkageError when running Ktor app with development mode inside Spring Boot / Amper fat-JAR
• KTOR-9402 NoSuchMethodError on RawWebSocket after 3.4.0
• KTOR-9372 Frame.Text.readText() causes infinite loop and 100% CPU on Kotlin/Native when WebSocket frame data is malformed or connection drops unexpectedly
• KTOR-9387 ZstdEncoder decode fails when source data is split into multiple Zstd frames

3.4.1

Published 3 March 2026

Improvements

• KTOR-9382 HttpProtocolVersion.parse: fast path for common versions
• KTOR-9381 GMTDate: reduce allocations
• KTOR-8971 Support "operationId" in Kdoc for OpenAPI spec. gen.
• KTOR-9333 WebSockets: Infinite spin and potential OOM vulnerabilities in the Inflater.inflateFully method
• KTOR-5616 Ktor always adds by default an Accept-Charset header
• KTOR-9291 OpenAPI: handle atypical route functions
• KTOR-9293 OpenAPI describe needs defaults
• KTOR-9304 OpenAPI: Order of path parameters is not preserved in the spec
• KTOR-9353 Routing: TailcardSelector missing toString(), which clutters the logs

Bugfixes

• KTOR-9281 OpenApi code inference misses lambda argument bodies
• KTOR-9273 OpenAPI static content path appears in resulting model
• KTOR-9004 OpenAPI: No respective formats detected for serializable types like UUID or Instant
• KTOR-9305 OpenAPI: "No mapping for symbol: VAR FOR_LOOP_VARIABLE" error with codeInferenceEnabled=true
• KTOR-9279 OpenAPI: UnsupportedOperationException for a function with a reified type parameter codeInferenceEnabled = true
• KTOR-9289 OpenAPI: Resource routes are missing inferred and comment-based documentation
• KTOR-9330 OpenAPI: Cannot override kotlinx.serialization module
• KTOR-9320 OpenAPI: jsonSchema() does not unwrap Kotlin value classes (inline classes)
• KTOR-9352 Authentication: Creating JWT verifier fails for JWK with kty=EC and alg=null
• KTOR-9344 Flow invariant error happens after update to Ktor 3.4.0
• KTOR-9362 testApplication: Race condition in timeout coroutine when response is streaming
• KTOR-9274 Curl: Undefined symbol errors when linking on Linux since 3.4.0
• KTOR-8782 NodeJS CIO: "Module 'os' could not be imported" error on resolving WORKING_DIRECTORY_PATH with es2015 target
• KTOR-9348 String.decodeBase64String fails to decode when the input has no padding since 3.4.0
• KTOR-9318 CIO engine rejects valid certificates with unsupported signature algorithms
• KTOR-9331 Curl: Segfaults when working with WebSockets
• KTOR-9334 Coroutines in route handlers are dispatched with Dispatchers.Unconfined since 3.2.0
• KTOR-9339 StreamResetException is not propagated to the caller of StreamRequestBody.writeTo since 3.4.0
• KTOR-9329 HTMX: "on" attributes extension not working
• KTOR-9316 WasmJS bad get and set implementations for Uint8Array and ArrayLike
• KTOR-9272 JSON schema inference does not recognize unsigned types
• KTOR-9211 SendCountExceedException when request is sent twice with maxRetries = 0 since 3.3.2
• KTOR-9285 RateLimit: Milliseconds in the Retry-After header are truncated
• KTOR-7512 JWT: Docs for validate method claim that it's optional, but it isn't
• KTOR-9269 Incorrect dependency declaration in swagger / openapi
• KTOR-9372 Frame.Text.readText() causes infinite loop and 100% CPU on Kotlin/Native when WebSocket frame data is malformed or connection drops unexpectedly

3.4.0

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

3.3.3

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

3.3.2

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)

3.3.1

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)

3.3.0

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)

3.2.3

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)

3.2.2

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)