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internal/mcp: reorganize the tool API, keeping generics

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CallToolParams.Arguments is any.

Clients can send whatever they want.

Tool authors who create their own ToolHandler (bypassing NewTool)
will receive the arguments as a map[string]any which has been
validated against the input schema.

Tool authors who call NewTool can choose the type that the arguments
unmarshal into.

There is no double-unmarshaling and no downcasting.

There is no way for tool authors to avoid the unmarshal, and no way to
avoid the validation unless the omit an input schema, which is probably
bad for LLMs. If tool authors want this optimization, we can provide
it later.

Change-Id: Ieb201e56c7fb8a23bb1a93b27e946630ec9e79ad
Reviewed-on: https://go-review.googlesource.com/c/tools/+/679595
TryBot-Bypass: Jonathan Amsterdam <jba@google.com>
Auto-Submit: Jonathan Amsterdam <jba@google.com>
Reviewed-by: Robert Findley <rfindley@google.com>
This commit is contained in:
Jonathan Amsterdam 2025-06-05 16:17:03 -04:00
commit f211cc8e4a
1 changed files with 328 additions and 228 deletions
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29
mcp/protocol.go
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@ -26,15 +26,25 @@ type Annotations struct {
Priority float64 `json:"priority,omitempty"`
}
type CallToolParams[TArgs any] struct {
type CallToolParams struct {
// This property is reserved by the protocol to allow clients and servers to
// attach additional metadata to their responses.
Meta Meta `json:"_meta,omitempty"`
Arguments TArgs `json:"arguments,omitempty"`
Arguments any `json:"arguments,omitempty"`
Name string `json:"name"`
}
func (x *CallToolParams[TArgs]) GetMeta() *Meta { return &x.Meta }
func (x *CallToolParams) GetMeta() *Meta { return &x.Meta }
type CallToolParamsFor[In any] struct {
// This property is reserved by the protocol to allow clients and servers to
// attach additional metadata to their responses.
Meta Meta `json:"_meta,omitempty"`
Arguments In `json:"arguments,omitempty"`
Name string `json:"name"`
}
func (x *CallToolParamsFor[In]) GetMeta() *Meta { return &x.Meta }
// The server's response to a tool call.
//
@ -59,6 +69,19 @@ type CallToolResult struct {
func (x *CallToolResult) GetMeta() *Meta { return &x.Meta }
type CallToolResultFor[Out any] struct {
// This property is reserved by the protocol to allow clients and servers to
// attach additional metadata to their responses.
Meta Meta `json:"_meta,omitempty"`
Content []*Content `json:"content"`
// Whether the tool call ended in an error.
//
// If not set, this is assumed to be false (the call was successful).
IsError bool `json:"isError,omitempty"`
}
func (x *CallToolResultFor[Out]) GetMeta() *Meta { return &x.Meta }
type CancelledParams struct {
// This property is reserved by the protocol to allow clients and servers to
// attach additional metadata to their responses.