oidc-client-mcp-auth-provider with streamable-http transport type: getAuthorization() tries to block the event-loop thread

[btison]

I am trying to use the oidc-client-mcp-auth-provider in combination with streamable-http transport type.
When the Mcp client is initializing, the getAuthorization() method in OidcClientMcpAuthProvider tries to block the event-loop thread by calling Uni.await().indefinitely().

This happens when the mcp client is trying to send an 'initialized' request to the mcp server, even if the mcp client is called in an worker pool thread

2025-08-28 22:08:55,935 INFO  [io.qua.lan.mcp.run.htt.QuarkusStreamableHttpMcpTransport] (executor-thread-1) Request: {"jsonrpc":"2.0","id":0,"method":"initialize","params":{"protocolVersion":"2024-11-05","capabilities":{"roots":{"listChanged":false}},"clientInfo":{"name":"langchai
n4j","version":"1.0"}}}                                                                                                                                                                                                                                                                   
2025-08-28 22:08:56,012 INFO  [io.qua.lan.mcp.run.htt.QuarkusStreamableHttpMcpTransport] (vert.x-eventloop-thread-3) Response: {"jsonrpc":"2.0","id":0,"result":{"capabilities":{"logging":{},"tools":{}},"serverInfo":{"version":"1.0","name":"Mail MCP"},"protocolVersion":"2024-11-05"}
}                                                                                                                                                                                                                                                                                         
2025-08-28 22:08:56,014 INFO  [io.qua.lan.mcp.run.htt.QuarkusStreamableHttpMcpTransport] (vert.x-eventloop-thread-3) Request: {"jsonrpc":"2.0","method":"notifications/initialized"}

Stack trace:

: jakarta.enterprise.inject.CreationException: Error creating synthetic bean [hsVtFY5C2fd5CgqaJqo8cfZe1YE]: java.lang.RuntimeException: java.util.concurrent.ExecutionException: java.lang.IllegalStateException: The current thread cannot be blocked: vert.x-eventloop-thread-3
        at dev.langchain4j.mcp.client.McpClient_hsVtFY5C2fd5CgqaJqo8cfZe1YE_Synthetic_Bean.doCreate(Unknown Source)
        at dev.langchain4j.mcp.client.McpClient_hsVtFY5C2fd5CgqaJqo8cfZe1YE_Synthetic_Bean.create(Unknown Source)
        at dev.langchain4j.mcp.client.McpClient_hsVtFY5C2fd5CgqaJqo8cfZe1YE_Synthetic_Bean.create(Unknown Source)
        at io.quarkus.arc.impl.AbstractSharedContext.createInstanceHandle(AbstractSharedContext.java:119)
        at io.quarkus.arc.impl.AbstractSharedContext$1.get(AbstractSharedContext.java:38)
        at io.quarkus.arc.impl.AbstractSharedContext$1.get(AbstractSharedContext.java:35)
        at io.quarkus.arc.generator.Default_jakarta_enterprise_context_ApplicationScoped_ContextInstances.c20(Unknown Source)
        at io.quarkus.arc.generator.Default_jakarta_enterprise_context_ApplicationScoped_ContextInstances.computeIfAbsent(Unknown Source)
        at io.quarkus.arc.impl.AbstractSharedContext.get(AbstractSharedContext.java:35)
        at io.quarkus.arc.impl.ClientProxies.getApplicationScopedDelegate(ClientProxies.java:23)
        at dev.langchain4j.mcp.client.McpClient_hsVtFY5C2fd5CgqaJqo8cfZe1YE_Synthetic_ClientProxy.arc$delegate(Unknown Source)
        at dev.langchain4j.mcp.client.McpClient_hsVtFY5C2fd5CgqaJqo8cfZe1YE_Synthetic_ClientProxy.listTools(Unknown Source)
        at dev.langchain4j.mcp.McpToolProvider.provideTools(McpToolProvider.java:112)
        at io.quarkiverse.langchain4j.mcp.runtime.QuarkusMcpToolProvider.provideTools(QuarkusMcpToolProvider.java:38)
        at dev.langchain4j.service.tool.ToolProvider_sL_YcZTZI2rxkspvkYJxQT2XtaU_Synthetic_ClientProxy.provideTools(Unknown Source)
        at io.quarkiverse.langchain4j.runtime.aiservice.AiServiceMethodImplementationSupport.doImplement(AiServiceMethodImplementationSupport.java:207)
        at io.quarkiverse.langchain4j.runtime.aiservice.AiServiceMethodImplementationSupport.implement(AiServiceMethodImplementationSupport.java:154)
        at org.globex.ai.WriteEmailAgent$$QuarkusImpl.writeEmail(Unknown Source)
        at org.globex.ai.MailResource.lambda$sendEmail$0(MailResource.java:22)
        at io.smallrye.context.impl.wrappers.SlowContextualConsumer.accept(SlowContextualConsumer.java:21)
        at io.smallrye.mutiny.operators.uni.UniOnItemConsume$UniOnItemComsumeProcessor.invokeEventHandler(UniOnItemConsume.java:77)
        at io.smallrye.mutiny.operators.uni.UniOnItemConsume$UniOnItemComsumeProcessor.onItem(UniOnItemConsume.java:42)
        at io.smallrye.mutiny.operators.uni.UniEmitOn$UniEmitOnProcessor.lambda$onItem$0(UniEmitOn.java:34)
        at io.quarkus.vertx.core.runtime.VertxCoreRecorder$15.runWith(VertxCoreRecorder.java:645)
        at org.jboss.threads.EnhancedQueueExecutor$Task.doRunWith(EnhancedQueueExecutor.java:2651)
        at org.jboss.threads.EnhancedQueueExecutor$Task.run(EnhancedQueueExecutor.java:2630)
        at org.jboss.threads.EnhancedQueueExecutor.runThreadBody(EnhancedQueueExecutor.java:1622)
        at org.jboss.threads.EnhancedQueueExecutor$ThreadBody.run(EnhancedQueueExecutor.java:1589)
        at org.jboss.threads.DelegatingRunnable.run(DelegatingRunnable.java:11)
        at org.jboss.threads.ThreadLocalResettingRunnable.run(ThreadLocalResettingRunnable.java:11)
        at io.netty.util.concurrent.FastThreadLocalRunnable.run(FastThreadLocalRunnable.java:30)
        at java.base/java.lang.Thread.run(Thread.java:1583)
Caused by: java.lang.RuntimeException: java.util.concurrent.ExecutionException: java.lang.IllegalStateException: The current thread cannot be blocked: vert.x-eventloop-thread-3
        at dev.langchain4j.mcp.client.DefaultMcpClient.initialize(DefaultMcpClient.java:123)
        at dev.langchain4j.mcp.client.DefaultMcpClient.<init>(DefaultMcpClient.java:109)
        at dev.langchain4j.mcp.client.DefaultMcpClient$Builder.build(DefaultMcpClient.java:507)
        at io.quarkiverse.langchain4j.mcp.runtime.McpRecorder$2.get(McpRecorder.java:98)
        at io.quarkiverse.langchain4j.mcp.runtime.McpRecorder$2.get(McpRecorder.java:57)
        at io.quarkus.arc.runtime.ArcRecorder$4.apply(ArcRecorder.java:137)
        at io.quarkus.arc.runtime.ArcRecorder$4.apply(ArcRecorder.java:134)
        at dev.langchain4j.mcp.client.McpClient_hsVtFY5C2fd5CgqaJqo8cfZe1YE_Synthetic_Bean.createSynthetic(Unknown Source)
        ... 32 more
Caused by: java.util.concurrent.ExecutionException: java.lang.IllegalStateException: The current thread cannot be blocked: vert.x-eventloop-thread-3
        at java.base/java.util.concurrent.CompletableFuture.reportGet(CompletableFuture.java:396)
        at java.base/java.util.concurrent.CompletableFuture.get(CompletableFuture.java:2096)
        at io.smallrye.context.CompletableFutureWrapper.get(CompletableFutureWrapper.java:161)
        at dev.langchain4j.mcp.client.DefaultMcpClient.initialize(DefaultMcpClient.java:120)
        ... 39 more
Caused by: java.lang.IllegalStateException: The current thread cannot be blocked: vert.x-eventloop-thread-3
        at io.smallrye.mutiny.operators.uni.UniBlockingAwait.await(UniBlockingAwait.java:30)
        at io.smallrye.mutiny.groups.UniAwait.atMost(UniAwait.java:65)
        at io.smallrye.mutiny.groups.UniAwait.indefinitely(UniAwait.java:46)
        at io.quarkiverse.langchain4j.oidc.client.mcp.runtime.OidcClientMcpAuthProvider.getAuthorization(OidcClientMcpAuthProvider.java:23)
        at io.quarkiverse.langchain4j.mcp.runtime.http.QuarkusStreamableHttpMcpTransport.execute(QuarkusStreamableHttpMcpTransport.java:123)
        at io.quarkiverse.langchain4j.mcp.runtime.http.QuarkusStreamableHttpMcpTransport.lambda$initialize$1(QuarkusStreamableHttpMcpTransport.java:75)
        at io.smallrye.context.impl.wrappers.SlowContextualFunction.apply(SlowContextualFunction.java:21)
        at io.smallrye.mutiny.operators.uni.UniOnItemTransformToUni$UniOnItemTransformToUniProcessor.performInnerSubscription(UniOnItemTransformToUni.java:68)
        at io.smallrye.mutiny.operators.uni.UniOnItemTransformToUni$UniOnItemTransformToUniProcessor.onItem(UniOnItemTransformToUni.java:57)
        at io.smallrye.mutiny.operators.uni.builders.UniCreateFromCompletionStage$CompletionStageUniSubscription.forwardResult(UniCreateFromCompletionStage.java:63)
        at java.base/java.util.concurrent.CompletableFuture.uniWhenComplete(CompletableFuture.java:863)
        at java.base/java.util.concurrent.CompletableFuture$UniWhenComplete.tryFire(CompletableFuture.java:841)
        at java.base/java.util.concurrent.CompletableFuture.postComplete(CompletableFuture.java:510)
        at java.base/java.util.concurrent.CompletableFuture.complete(CompletableFuture.java:2179)
        at dev.langchain4j.mcp.client.transport.McpOperation.handle(McpOperationHandler.java:42)
        at io.quarkiverse.langchain4j.mcp.runtime.http.QuarkusStreamableHttpMcpTransport.lambda$execute$4(QuarkusStreamableHttpMcpTransport.java:172)
        at io.vertx.core.impl.future.FutureImpl$1.onSuccess(FutureImpl.java:91)
        at io.vertx.core.impl.future.FutureBase.lambda$emitSuccess$0(FutureBase.java:60)
        at io.vertx.core.impl.ContextImpl.execute(ContextImpl.java:312)
        at io.vertx.core.impl.DuplicatedContext.execute(DuplicatedContext.java:168)
        at io.vertx.core.impl.future.FutureBase.emitSuccess(FutureBase.java:57)
        at io.vertx.core.impl.future.FutureImpl.tryComplete(FutureImpl.java:259)
        at io.vertx.core.http.impl.HttpEventHandler.handleEnd(HttpEventHandler.java:79)
        at io.vertx.core.http.impl.HttpClientResponseImpl.handleEnd(HttpClientResponseImpl.java:250)
        at io.vertx.core.http.impl.Http1xClientConnection$StreamImpl.lambda$new$0(Http1xClientConnection.java:443)
        at io.vertx.core.streams.impl.InboundBuffer.handleEvent(InboundBuffer.java:279)
        at io.vertx.core.streams.impl.InboundBuffer.write(InboundBuffer.java:157)
        at io.vertx.core.http.impl.Http1xClientConnection$StreamImpl.handleEnd(Http1xClientConnection.java:753)
        at io.vertx.core.impl.ContextImpl.execute(ContextImpl.java:327)
        at io.vertx.core.impl.DuplicatedContext.execute(DuplicatedContext.java:158)
        at io.vertx.core.http.impl.Http1xClientConnection.handleResponseEnd(Http1xClientConnection.java:984)
        at io.vertx.core.http.impl.Http1xClientConnection.handleHttpMessage(Http1xClientConnection.java:856)
        at io.vertx.core.http.impl.Http1xClientConnection.handleMessage(Http1xClientConnection.java:818)
        at io.vertx.core.net.impl.ConnectionBase.read(ConnectionBase.java:159)
        at io.vertx.core.net.impl.VertxHandler.channelRead(VertxHandler.java:153)
        at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:442)
        at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:420)
        at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:412)
        at io.netty.channel.CombinedChannelDuplexHandler$DelegatingChannelHandlerContext.fireChannelRead(CombinedChannelDuplexHandler.java:436)
        at io.netty.handler.codec.ByteToMessageDecoder.fireChannelRead(ByteToMessageDecoder.java:346)
        at io.netty.handler.codec.ByteToMessageDecoder.channelRead(ByteToMessageDecoder.java:318)
        at io.netty.channel.CombinedChannelDuplexHandler.channelRead(CombinedChannelDuplexHandler.java:251)
        at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:442)
        at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:420)
        at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:412)
        at io.netty.handler.ssl.SslHandler.unwrap(SslHandler.java:1519)
        at io.netty.handler.ssl.SslHandler.decodeJdkCompatible(SslHandler.java:1377)
        at io.netty.handler.ssl.SslHandler.decode(SslHandler.java:1428)
        at io.netty.handler.codec.ByteToMessageDecoder.decodeRemovalReentryProtection(ByteToMessageDecoder.java:530)
        at io.netty.handler.codec.ByteToMessageDecoder.callDecode(ByteToMessageDecoder.java:469)
        at io.netty.handler.codec.ByteToMessageDecoder.channelRead(ByteToMessageDecoder.java:290)
        at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:444)
        at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:420)
        at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:412)
        at io.netty.channel.DefaultChannelPipeline$HeadContext.channelRead(DefaultChannelPipeline.java:1357)
        at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:440)
        at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:420)
        at io.netty.channel.DefaultChannelPipeline.fireChannelRead(DefaultChannelPipeline.java:868)
        at io.netty.channel.nio.AbstractNioByteChannel$NioByteUnsafe.read(AbstractNioByteChannel.java:166)
        at io.netty.channel.nio.NioEventLoop.processSelectedKey(NioEventLoop.java:796)
        at io.netty.channel.nio.NioEventLoop.processSelectedKeysOptimized(NioEventLoop.java:732)
        at io.netty.channel.nio.NioEventLoop.processSelectedKeys(NioEventLoop.java:658)
        at io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:562)
        at io.netty.util.concurrent.SingleThreadEventExecutor$4.run(SingleThreadEventExecutor.java:998)
        at io.netty.util.internal.ThreadExecutorMap$2.run(ThreadExecutorMap.java:74)
        ... 2 more

[geoand]

cc @sberyozkin

[sberyozkin]

@btison Thanks, so, when Streamable HTTP transport is used, the initiatized request is sent on the event loop thread, right ?

I tested the shipped demo with the SSE transport and it all worked the last time I tried it, so I'm assuming this sending of the initialized request on the event loop thread is specific to the Streamable HTTP transport.

Jan, @jmartisk, can you comment please ?

If updating the Streamable HTTP transport to use a worker thread to initialize is impossible, then the only other option is to rework the interface to support returning Uni

[jmartisk]

I've submitted #1734, hopefully that fixes it?

[sberyozkin]

@jmartisk, awesome, I may still have to rework both MCP and Model authentication interfaces to support CompletableFuture (as Uni won't work upstream), but for now, even without the authentication, it is probably better to send a remote request on a worker thread as there could be slower non-Quarkus MCP servers around too.

@btison Please test Jan's PR

[btison]

@sberyozkin

Hey Sergey,

Sorry for the delay. I did test my application and it works fine with Jan's fix. Thanks for fixing this.

[geoand]

🎉