modelcontextprotocol/go-sdk
Watch
1
0
Fork
You've already forked go-sdk
 0
Code Issues Pull requests Projects Releases Packages Wiki Activity Actions 1

mcp: wrap unmarshalParams with jsonrpc error (#1087)

Browse source 
Fixes #976
This commit is contained in:
Guglielmo Colombo 2026-07-14 16:26:18 +02:00 • committed by GitHub
commit 9576afc114
No known key found for this signature in database
GPG key ID: B5690EEEBB952194
1 changed files with 63 additions and 1 deletions
Download patch file Download diff file Expand all files Collapse all files

24
mcp/shared.go
View file

@ -26,9 +26,21 @@ import (
"github.com/modelcontextprotocol/go-sdk/auth"
internaljson "github.com/modelcontextprotocol/go-sdk/internal/json"
"github.com/modelcontextprotocol/go-sdk/internal/jsonrpc2"
"github.com/modelcontextprotocol/go-sdk/internal/mcpgodebug"
"github.com/modelcontextprotocol/go-sdk/jsonrpc"
)
// nowrapinvalidparams is a compatibility parameter that restores the previous
// behavior of [methodInfo.unmarshalParams]. When unset (the default), a
// params-decoding failure is wrapped with [jsonrpc2.ErrInvalidParams] so the
// wire response carries error code -32602 ("invalid params") rather than the
// zero-value code 0. See:
// https://github.com/modelcontextprotocol/go-sdk/issues/976#issuecomment-4829124838.
//
// See the documentation for the mcpgodebug package for instructions how to enable it.
// The option will be removed in a future version of the SDK.
var nowrapinvalidparams = mcpgodebug.Value("nowrapinvalidparams")
const (
// latestProtocolVersion is the latest protocol version that this version of
// the SDK supports.
@ -304,7 +316,17 @@ func newMethodInfo[P paramsPtr[T], R Result, T any](flags methodFlags) methodInf
var p P
if m != nil {
if err := internaljson.Unmarshal(m, &p); err != nil {
return nil, fmt.Errorf("unmarshaling %q into a %T: %w", m, p, err)
// Legacy behavior: pre-fix versions surfaced this as a
// plain wrapped error, which caused the wire response to
// carry code 0 instead of -32602. Restore via
// MCPGODEBUG=nowrapinvalidparams=1.
if nowrapinvalidparams == "1" {
return nil, fmt.Errorf("unmarshaling %q into a %T: %w", m, p, err)
}
// Wrap jsonrpc2.ErrInvalidParams so toWireError surfaces
// code -32602 ("invalid params") while preserving the
// descriptive message.
return nil, fmt.Errorf("%w: unmarshaling %q into a %T: %w", jsonrpc2.ErrInvalidParams, m, p, err)
}
}
// We must check missingParamsOK here, in addition to checkRequest, to