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mcp: align resource not found error code with sep-2164 (#931)

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Change the error code returned by ResourceNotFoundError from -32002 to
-32602 (jsonrpc.CodeInvalidParams), aligning with
[SEP-2164](https://github.com/modelcontextprotocol/modelcontextprotocol/pull/2164).

* Not gated with a protocol version check, because the previous error
code was never formally specified and the behaviour varied across SDKs.
* In case clients which rely on the old error code exist, the previous
behaviour can be restored with `MCPGODEBUG=customresnotfounderrcode=1`.
* `CodeResourceNotFound` deprecated since its only purpose going forward
is backward compatibility. The new code should use
`jsonrpc.CodeInvalidParams` directly.
* `CodeResourceNotFound` changed to `var` so it can stay in sync with
`ResourceNotFoundError` and existing code doing `code ==
mcp.CodeResourceNotFound` keeps working in both the default and compat
modes.
This commit is contained in:
Yaroslav 2026-05-05 16:20:02 +02:00 • committed by GitHub
commit 2b7c9937e6
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1 changed files with 62 additions and 2 deletions
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12
mcp/shared.go
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@ -347,14 +347,22 @@ const (
// CodeHeaderMismatch indicates that HTTP headers do not match the corresponding values
// in the request body, or that required headers are missing or malformed.
CodeHeaderMismatch = -32001
// CodeResourceNotFound indicates that a requested resource could not be found.
CodeResourceNotFound = -32002
// CodeURLElicitationRequired indicates that the server requires URL elicitation
// before processing the request. The client should execute the elicitation handler
// with the elicitations provided in the error data.
CodeURLElicitationRequired = -32042
)
// CodeResourceNotFound indicates that a requested resource could not be found.
//
// By default, the value is -32602 (Invalid Params), as specified in the
// MCP specification (SEP-2164). To restore the pre-1.7.0 release behavior where the
// error code was -32002, set MCPGODEBUG=customresnotfounderrcode=1.
//
// Deprecated: Use [jsonrpc.CodeInvalidParams] directly. This variable will be
// removed in a future version.
var CodeResourceNotFound int64 = jsonrpc.CodeInvalidParams
// URLElicitationRequiredError returns an error indicating that URL elicitation is required
// before the request can be processed. The elicitations parameter should contain the
// elicitation requests that must be completed.