If the MCP server defines content path, the client endpoint can pass the first GET request sent to the/se path, but sending a post request with the response/mcp/message is incorrect, resulting in a 404 error

[hbsjz-swl]

Bug description
How does MCP Server define content path and connect to URL: localhost: port sse endpoint:/contentPath/sse using SSE after defining it? This format can be used for the first get request to connect, but for the second post request to access/mcp/message, the contentpath cannot be added, resulting in a 404 error

Environment
springboot:3.4.2 jdk 17 spring-ai 1.0.0-SNAPSHOT

Steps to reproduce
mcp:
client:
enabled: true
name: mock-client
version: 0.0.1
type: SYNC
request-timeout: 20s
sse:
connections:
soldier-server:
url: http://localhost:port
sse-endpoint: /content-path/sse

[quaff]

If #3112 get merged, it should be fixed by set:

spring.ai.mcp.server.base-url: /context-path

[hbsjz-swl]

If #3112 get merged, it should be fixed by set:

spring.ai.mcp.server.base-url: /context-path

The client side configuration is as follows: sse:
connections:
soldier-server:
url: http:localhost:9526/soldier
The server side configuration is as follows:
spring.ai.mcp.server.name=soldier-server
spring.ai.mcp.server.version=0.0.1
spring.ai.mcp.server.type=SYNC
spring.ai.mcp.server.stdio=false
spring.ai.mcp.server.base-url=/soldier
spring.ai.mcp.server.sse-message-endpoint=/mcp/message

The client startup error is as follows:
2025-05-13 08:58:46 [ForkJoinPool.commonPool-worker-1] ERROR i.m.c.t.HttpClientSseClientTransport

• SSE connection error
  java.util.concurrent.CompletionException: java.lang.RuntimeException: Failed to connect to SSE stream. Unexpected status code: 404
  at java.base/java.util.concurrent.CompletableFuture.encodeThrowable(CompletableFuture.java:315)
  at java.base/java.util.concurrent.CompletableFuture.completeThrowable(CompletableFuture.java:320)
  at java.base/java.util.concurrent.CompletableFuture$UniAccept.tryFire(CompletableFuture.java:722)
  at java.base/java.util.concurrent.CompletableFuture.postComplete(CompletableFuture.java:510)
  at java.base/java.util.concurrent.CompletableFuture.postFire(CompletableFuture.java:614)
  at java.base/java.util.concurrent.CompletableFuture$UniWhenComplete.tryFire(CompletableFuture.java:844)
  at java.base/java.util.concurrent.CompletableFuture$Completion.exec(CompletableFuture.java:483)
  at java.base/java.util.concurrent.ForkJoinTask.doExec(ForkJoinTask.java:373)
  at java.base/java.util.concurrent.ForkJoinPool$WorkQueue.topLevelExec(ForkJoinPool.java:1182)
  at java.base/java.util.concurrent.ForkJoinPool.scan(ForkJoinPool.java:1655)
  at java.base/java.util.concurrent.ForkJoinPool.runWorker(ForkJoinPool.java:1622)
  at java.base/java.util.concurrent.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:165)
  Caused by: java.lang.RuntimeException: Failed to connect to SSE stream. Unexpected status code: 404
  at io.modelcontextprotocol.client.transport.FlowSseClient.lambda$subscribe$2(FlowSseClient.java:202)
  at java.base/java.util.concurrent.CompletableFuture$UniAccept.tryFire(CompletableFuture.java:718)
  ... 9 common frames omitted

On the client side HttpClientSseClientTransport (line 417) The pseudo code is as follows:

URI requestUri = Utils.resolveUri(http://localhost:9526/soldier, /mcp/message?sessionId=cb613423-7fd1-413f-a2c0-89949d79f7e7)
requestUri ignores /soldier
http://localhost:9526/mcp/message?sessionId=a20245aa-8271-4c56-8365-d8f5503e4c7e

[quaff]

Please note it's not merged yet, are you testing against that branch?

[hbsjz-swl]

Please note it's not merged yet, are you testing against that branch?

Sorry, I just noticed that the merge request has been approved, I should wait for this fix before trying it again, thank you very much for your help!

[tzolov]

@hbsjz-swl the #3112 has been merged.
Could you please give it a try again

[tzolov]

Closing this issue as resolved by #3112.
Please feel free to re-open if the issue is still present

[hbsjz-swl]

@tzolov @quaff I have verified it locally and this modification is effective. The following configuration is added on the service side: spring.ai.mcp.server.base-url=/soldier The following configuration is added on the client side: sse:
connections:
soldier-server:
url: http://localhost:9526
sse-endpoint: /soldier/sse

Thank you very much for your help