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mcp: introduce Requests (#267)

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Handlers and client/server methods take a single request argument
combining the session and params. This slightly simplifies the signature
for handlers, since there is no longer an often-ignored session
argument.

But more importantly, it opens the door to adding more information in
requests, such as auth info and HTTP request headers.

For #243.
This commit is contained in:
Jonathan Amsterdam 2025-08-12 17:49:50 -04:00 • committed by GitHub
commit 6e03217c83
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1 changed files with 517 additions and 380 deletions
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23
mcp/tool.go
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@ -20,10 +20,12 @@ import (
type ToolHandler = ToolHandlerFor[map[string]any, any]
// A ToolHandlerFor handles a call to tools/call with typed arguments and results.
type ToolHandlerFor[In, Out any] func(context.Context, *ServerSession, *CallToolParamsFor[In]) (*CallToolResultFor[Out], error)
type ToolHandlerFor[In, Out any] func(context.Context, *ServerRequest[*CallToolParamsFor[In]]) (*CallToolResultFor[Out], error)
// A rawToolHandler is like a ToolHandler, but takes the arguments as as json.RawMessage.
type rawToolHandler = func(context.Context, *ServerSession, *CallToolParamsFor[json.RawMessage]) (*CallToolResult, error)
// Second arg is *Request[*ServerSession, *CallToolParamsFor[json.RawMessage]], but that creates
// a cycle.
type rawToolHandler = func(context.Context, any) (*CallToolResult, error)
// A serverTool is a tool definition that is bound to a tool handler.
type serverTool struct {
@ -48,20 +50,25 @@ func newServerTool[In, Out any](t *Tool, h ToolHandlerFor[In, Out]) (*serverTool
}
}
st.handler = func(ctx context.Context, ss *ServerSession, rparams *CallToolParamsFor[json.RawMessage]) (*CallToolResult, error) {
st.handler = func(ctx context.Context, areq any) (*CallToolResult, error) {
req := areq.(*ServerRequest[*CallToolParamsFor[json.RawMessage]])
var args In
if rparams.Arguments != nil {
if err := unmarshalSchema(rparams.Arguments, st.inputResolved, &args); err != nil {
if req.Params.Arguments != nil {
if err := unmarshalSchema(req.Params.Arguments, st.inputResolved, &args); err != nil {
return nil, err
}
}
// TODO(jba): future-proof this copy.
params := &CallToolParamsFor[In]{
Meta: rparams.Meta,
Name: rparams.Name,
Meta: req.Params.Meta,
Name: req.Params.Name,
Arguments: args,
}
res, err := h(ctx, ss, params)
// TODO(jba): improve copy
res, err := h(ctx, &ServerRequest[*CallToolParamsFor[In]]{
Session: req.Session,
Params: params,
})
// TODO(rfindley): investigate why server errors are embedded in this strange way,
// rather than returned as jsonrpc2 server errors.
if err != nil {