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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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18
mcp/resource.go
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@ -15,6 +15,7 @@ import (
"path/filepath"
"strings"
"github.com/modelcontextprotocol/go-sdk/internal/mcpgodebug"
"github.com/modelcontextprotocol/go-sdk/internal/util"
"github.com/modelcontextprotocol/go-sdk/jsonrpc"
"github.com/yosida95/uritemplate/v3"
@ -37,8 +38,25 @@ type serverResourceTemplate struct {
// If it cannot find the resource, it should return the result of calling [ResourceNotFoundError].
type ResourceHandler func(context.Context, *ReadResourceRequest) (*ReadResourceResult, error)
// customresnotfounderrcode is a compatibility parameter that restores the
// pre-1.7.0 behavior of [ResourceNotFoundError] and [CodeResourceNotFound],
// where the error code was a custom -32002. See the documentation for the mcpgodebug
// package for instructions on how to enable it.
// The option will be removed in the future version of the SDK.
var customresnotfounderrcode = mcpgodebug.Value("customresnotfounderrcode")
func init() {
if customresnotfounderrcode == "1" {
CodeResourceNotFound = -32002
}
}
// ResourceNotFoundError returns an error indicating that a resource being read could
// not be found.
//
// By default, the error code 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.
func ResourceNotFoundError(uri string) error {
return &jsonrpc.Error{
Code: CodeResourceNotFound,