ServerCapabilities builder should not assign logging an initial value

[Randgalt]

Motivation and Context

ServerCapabilities builder should not assign logging an initial value

How Has This Been Tested?

added assertThat(result.capabilities().logging()).isNull(); to testSuccessfulInitialization

Breaking Changes

ServerCapabilities builder no longer has logging enabled by default.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update

Checklist

• I have read the MCP Documentation
• My code follows the repository's style guidelines
• New and existing tests pass locally
• I have added appropriate error handling
• I have added or updated documentation as needed

[tzolov]

Thanks @Randgalt. Could you elaborate on this? Does it break existing clients? I don't see how this could be harmful. Also, some existing (deprecated) code expects the logging to be present:

java-sdk/mcp/src/main/java/io/modelcontextprotocol/server/McpAsyncServer.java

Line 767 in 4532b61

public Mono<Void> loggingNotification(LoggingMessageNotification loggingMessageNotification) {

[tzolov]

I see one issue with logging enabled in the stateless server context: it will falsely claim logging capability but won't actually be able to send logs.

[Randgalt]

I see one issue with logging enabled in the stateless server context: it will falsely claim logging capability but won't actually be able to send logs.

There are two issues:

• The stateless server currently has no way of sending log messages. This would require SSE (BTW, I have some ideas to support this for progress messages)
• The spec for Logging from what I can tell requires sessions. This is because clients can send the server the log level that they will accept. Frankly, it would be better if the spec didn't have this or makes it optional, but it is there.

So, the stateless server advertises that it supports logging but it doesn't.

[tzolov]

@Randgalt , we need to ensure backward compatibility for the non-stateless servers
by ensuring that the logging capabilities is enabled by default for those.

I've just added a ServerCapabilities#mutate() method that should help you do this.
(e.g. capabilities = capabilities.mutate().logging();)

[Randgalt]

OK - I understand. I'll close this.

[tzolov]

I will reopen the PR and apply the missing change while merging it

[tzolov]

Thanks @Randgalt
Rebased, extended and merged at 713ee1a