fix(transport): fall back after JSON discover rejections - #1288
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| .text() | ||
| .await | ||
| .unwrap_or_else(|_| "<failed to read response body>".to_owned()); | ||
| // A 4xx rejection of `server/discover` is a legacy-server signal even when |
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I don't think this is quite in agreement with https://modelcontextprotocol.io/specification/2026-07-28/basic/versioning#backward-compatibility-with-initialization-based-versions :
a recognized modern JSON-RPC error (such as UnsupportedProtocolVersionError) identifies a modern server: the client retries with a supported version rather than falling back. Anything else identifies a legacy server.
so I think this fixes the generic uncorrelated error case, but may treat recognized modern errors as legacy servers. We need to check the body here too to see if it parses
Check the discover fallback before the JSON-RPC error branch, or middleware rejections with an uncorrelated id abort the handshake instead of falling back to legacy `initialize`.
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Motivation and Context
Check the discover fallback before the JSON-RPC error branch, or middleware rejections with an uncorrelated id abort the handshake instead of falling back to legacy
initialize.How Has This Been Tested?
Unit tests, and tested in a client app (goose)
Breaking Changes
N/A
Types of changes
Checklist
Additional context
Related goose issue aaif-goose/goose#12257