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mcp: change tool handler design (#325)

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Change the design of tool handlers by removing genericity from the common path.
- `ToolHandler` gets the args as a `json.RawMessage`. Using Server.AddTool does no unmarshaling or schema validation.
- `ToolHandlerFor`, installed with `AddTool`, are the only generic pieces.

TODO:
uncomment and fix some tests
This commit is contained in:
Jonathan Amsterdam 2025-08-20 19:36:34 -04:00 • committed by GitHub
commit 32cf71de3a
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1 changed files with 789 additions and 966 deletions
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42
mcp/protocol.go
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@ -40,20 +40,32 @@ type Annotations struct {
Priority float64 `json:"priority,omitempty"`
}
type CallToolParams = CallToolParamsFor[any]
type CallToolParamsFor[In 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 `json:"_meta,omitempty"`
Name string `json:"name"`
Arguments In `json:"arguments,omitempty"`
Arguments any `json:"arguments,omitempty"`
}
// When unmarshalling CallToolParams on the server side, we need to delay unmarshaling of the arguments.
func (c *CallToolParams) UnmarshalJSON(data []byte) error {
var raw struct {
Meta `json:"_meta,omitempty"`
Name string `json:"name"`
RawArguments json.RawMessage `json:"arguments,omitempty"`
}
if err := json.Unmarshal(data, &raw); err != nil {
return err
}
c.Meta = raw.Meta
c.Name = raw.Name
c.Arguments = raw.RawArguments
return nil
}
// The server's response to a tool call.
type CallToolResult = CallToolResultFor[any]
type CallToolResultFor[Out any] struct {
type CallToolResult struct {
// This property is reserved by the protocol to allow clients and servers to
// attach additional metadata to their responses.
Meta `json:"_meta,omitempty"`
@ -62,7 +74,7 @@ type CallToolResultFor[Out any] struct {
Content []Content `json:"content"`
// An optional JSON object that represents the structured result of the tool
// call.
StructuredContent Out `json:"structuredContent,omitempty"`
StructuredContent any `json:"structuredContent,omitempty"`
// Whether the tool call ended in an error.
//
// If not set, this is assumed to be false (the call was successful).
@ -78,12 +90,12 @@ type CallToolResultFor[Out any] struct {
IsError bool `json:"isError,omitempty"`
}
func (*CallToolResultFor[Out]) isResult() {}
func (*CallToolResult) isResult() {}
// UnmarshalJSON handles the unmarshalling of content into the Content
// interface.
func (x *CallToolResultFor[Out]) UnmarshalJSON(data []byte) error {
type res CallToolResultFor[Out] // avoid recursion
func (x *CallToolResult) UnmarshalJSON(data []byte) error {
type res CallToolResult // avoid recursion
var wire struct {
res
Content []*wireContent `json:"content"`
@ -95,13 +107,13 @@ func (x *CallToolResultFor[Out]) UnmarshalJSON(data []byte) error {
if wire.res.Content, err = contentsFromWire(wire.Content, nil); err != nil {
return err
}
*x = CallToolResultFor[Out](wire.res)
*x = CallToolResult(wire.res)
return nil
}
func (x *CallToolParamsFor[Out]) isParams() {}
func (x *CallToolParamsFor[Out]) GetProgressToken() any { return getProgressToken(x) }
func (x *CallToolParamsFor[Out]) SetProgressToken(t any) { setProgressToken(x, t) }
func (x *CallToolParams) isParams() {}
func (x *CallToolParams) GetProgressToken() any { return getProgressToken(x) }
func (x *CallToolParams) SetProgressToken(t any) { setProgressToken(x, t) }
type CancelledParams struct {
// This property is reserved by the protocol to allow clients and servers to