fix: don't set base URL of SSE server #42
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Prior to this we would set the base URL of the SSE server to the address of the HTTP server. This isn't quite right because the address on which the server listens isn't always the same as the one which the client connects to; for example, in Docker we might set the address to 0.0.0.0 but the client will connect to localhost. Since most clients will verify that the endpoint sent by the initial SSE handshake matches the address of the server they connect to, they raise an error when they see that `localhost` doesn't match `0.0.0.0`. This commit fixes that by just not setting the base URL at all. This results in the initial message just looking like this: ``` event: endpoint data: /message?sessionId=c96d5796-92f3-42f3-aa51-555aa21e1c8f ``` which matches what the Python SDK does (see [here][python1], [here][python2], and [here][python3]), and fixes things for me when testing with Cursor. Fixes #40. [python1]: https://github.com/sd2k/python-sdk/blob/400dcda2eba67776f708d3dce6eaac3a9db97b92/src/mcp/server/sse.py#L98 [python2]: https://github.com/sd2k/python-sdk/blob/400dcda2eba67776f708d3dce6eaac3a9db97b92/src/mcp/server/sse.py#L77 [python3]: https://github.com/sd2k/python-sdk/blob/400dcda2eba67776f708d3dce6eaac3a9db97b92/src/mcp/server/fastmcp/server.py#L466
csmarchbanks
approved these changes
Mar 13, 2025
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Prior to this we would set the base URL of the SSE server to the
address of the HTTP server. This isn't quite right because the
address on which the server listens isn't always the same as the
one which the client connects to; for example, in Docker we might
set the address to 0.0.0.0 but the client will connect to localhost.
Since most clients will verify that the endpoint sent by the initial
SSE handshake matches the address of the server they connect to, they
raise an error when they see that
localhostdoesn't match0.0.0.0.This commit fixes that by just not setting the base URL at all. This
results in the initial message just looking like this:
which matches what the Python SDK does (see here, here,
and here), and fixes things for me when testing with Cursor.
Fixes #40.