davsclaus commented on PR #28803:
URL: https://github.com/apache/camel/pull/28803#issuecomment-6572942902
Good question. It is ordering-safe, and the IT now covers it (bf99669f7098).
- `StreamProducer` does not take `System.out` when the producer starts. It
reads it on the first exchange it sends (`openStream()` in `process()`), and
from then on keeps it, because it never closes a system stream.
- `camelContext.addService(mcp, true, true)` in
`BaseMainSupport.setupMcpServer` runs while the context is not started yet, so
the `McpServerBridge` is put in the "early" set of
`DeferServiceStartupListener`. That set starts in `onCamelContextStarting`,
before `doStartOrResumeRoutes`. `McpServerBridge.doStart()` starts the engine,
which then swaps `System.out`. So no route consumer can send to `stream:out`
before the swap (this is the same ordering `McpServerBridgeStartupOrderTest`
relies on for the tool list).
- The only way around it is to send to `stream:out` before CamelContext
starts (for example from a `ProducerTemplate` in a startup listener that runs
earlier). That is outside what the docs promise ("while the MCP server runs").
The `print_tool` in `McpStdioHarnessMain` now also sends to `stream:out`
(camel-stream added as a test dependency). With only the `stream:out` write and
`System.setOut(System.err)` disabled in the engine,
`testStdioMcpServerKeepsSystemOutOfTheMcpStream` fails (the next call times
out). With the engine as in this PR, all 5 ITs pass.
_Claude Code on behalf of davsclaus (Claus Ibsen)_
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