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mcp: small changes to CallTool structs (#60)

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- Use `any` for CallToolResult.StructuredContent.

- Change the non-generic structs into aliases for the generic ones.
This commit is contained in:
Jonathan Amsterdam 2025-06-30 13:47:24 -04:00 • committed by GitHub
commit beed2f0677
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GPG key ID: B5690EEEBB952194
3 changed files with 10 additions and 61 deletions
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2
mcp/content_test.go
View file

@ -7,7 +7,6 @@ package mcp_test
import (
"encoding/json"
"fmt"
"log"
"testing"
"github.com/google/go-cmp/cmp"
@ -94,7 +93,6 @@ func TestContent(t *testing.T) {
t.Errorf("json.Marshal(%v) mismatch (-want +got):\n%s", test.in, diff)
}
result := fmt.Sprintf(`{"content":[%s]}`, string(got))
log.Println(result)
var out mcp.CallToolResult
if err := json.Unmarshal([]byte(result), &out); err != nil {
t.Fatal(err)

67
mcp/protocol.go
View file

@ -39,70 +39,18 @@ type Annotations struct {
Priority float64 `json:"priority,omitempty"`
}
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"`
Arguments any `json:"arguments,omitempty"`
Name string `json:"name"`
}
func (x *CallToolParams) GetProgressToken() any { return getProgressToken(x) }
func (x *CallToolParams) SetProgressToken(t any) { setProgressToken(x, t) }
type CallToolParams = CallToolParamsFor[any]
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 `json:"_meta,omitempty"`
Arguments In `json:"arguments,omitempty"`
Name string `json:"name"`
Arguments In `json:"arguments,omitempty"`
}
// The server's response to a tool call.
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"`
// A list of content objects that represent the unstructured result of the tool
// call.
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).
//
// Any errors that originate from the tool should be reported inside the result
// object, with isError set to true, not as an MCP protocol-level error
// response. Otherwise, the LLM would not be able to see that an error occurred
// and self-correct.
//
// However, any errors in finding the tool, an error indicating that the
// server does not support tool calls, or any other exceptional conditions,
// should be reported as an MCP error response.
IsError bool `json:"isError,omitempty"`
// An optional JSON object that represents the structured result of the tool
// call.
// TODO(jba,rfindley): should this be any?
StructuredContent map[string]any `json:"structuredContent,omitempty"`
}
// UnmarshalJSON handles the unmarshalling of content into the Content
// interface.
func (x *CallToolResult) UnmarshalJSON(data []byte) error {
type res CallToolResult // avoid recursion
var wire struct {
res
Content []*wireContent `json:"content"`
}
if err := json.Unmarshal(data, &wire); err != nil {
return err
}
var err error
if wire.res.Content, err = contentsFromWire(wire.Content, nil); err != nil {
return err
}
*x = CallToolResult(wire.res)
return nil
}
type CallToolResult = CallToolResultFor[any]
type CallToolResultFor[Out any] struct {
// This property is reserved by the protocol to allow clients and servers to
@ -111,6 +59,9 @@ type CallToolResultFor[Out any] struct {
// A list of content objects that represent the unstructured result of the tool
// call.
Content []Content `json:"content"`
// An optional JSON object that represents the structured result of the tool
// call.
StructuredContent Out `json:"structuredContent,omitempty"`
// Whether the tool call ended in an error.
//
// If not set, this is assumed to be false (the call was successful).
@ -124,9 +75,6 @@ type CallToolResultFor[Out any] struct {
// server does not support tool calls, or any other exceptional conditions,
// should be reported as an MCP error response.
IsError bool `json:"isError,omitempty"`
// An optional JSON object that represents the structured result of the tool
// call.
StructuredContent Out `json:"structuredContent,omitempty"`
}
// UnmarshalJSON handles the unmarshalling of content into the Content
@ -148,6 +96,9 @@ func (x *CallToolResultFor[Out]) UnmarshalJSON(data []byte) error {
return nil
}
func (x *CallToolParamsFor[Out]) GetProgressToken() any { return getProgressToken(x) }
func (x *CallToolParamsFor[Out]) SetProgressToken(t any) { setProgressToken(x, t) }
type CancelledParams struct {
// This property is reserved by the protocol to allow clients and servers to
// attach additional metadata to their responses.

2
mcp/tool.go
View file

@ -17,7 +17,7 @@ import (
// A ToolHandler handles a call to tools/call.
// [CallToolParams.Arguments] will contain a map[string]any that has been validated
// against the input schema.
// Perhaps this should be an alias for ToolHandlerFor[map[string]any, map[string]any].
// TODO: Perhaps this should be an alias for ToolHandlerFor[map[string]any, map[string]any]?
type ToolHandler func(context.Context, *ServerSession, *CallToolParamsFor[map[string]any]) (*CallToolResult, error)
// A ToolHandlerFor handles a call to tools/call with typed arguments and results.