65ece59643## Description This PR introduces support for custom (non-standard) JSON-RPC methods in the MCP Go SDK. This feature enables servers to handle arbitrary JSON-RPC methods and clients to invoke them, all while maintaining full type safety and integrating seamlessly with the SDK's existing middleware and session management. - Server-Side Registration: Added AddReceivingCustomMethod to allow servers to register handlers for custom methods. Incoming requests are automatically unmarshaled into user-defined parameter structs. - Client-Side Calling: Added AddSendingCustomMethod which returns a strongly-typed caller function that clients can use to invoke custom methods and receive strongly-typed results. - Helper Structs: Provided ParamsBase and ResultBase for users to embed in their custom structs. This allows them to easily satisfy the SDK's internal Params and Result interfaces. Fixes #954
110 lines
3.3 KiB
Go
110 lines
3.3 KiB
Go
// Copyright 2025 The Go MCP SDK Authors. All rights reserved.
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// Use of this source code is governed by the license
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// that can be found in the LICENSE file.
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// The custom-method example demonstrates registering and calling a custom
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// JSON-RPC method that is not part of the standard MCP spec.
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//
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// The server registers a "latin/translate" method that translates simple
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// English phrases into Latin. A client connects over an in-memory transport,
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// calls the custom method, and prints the result.
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package main
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import (
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"context"
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"fmt"
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"log"
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"strings"
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"github.com/modelcontextprotocol/go-sdk/mcp"
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)
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type TranslateParams struct {
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mcp.ParamsBase
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Text string `json:"text"`
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}
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type TranslateResult struct {
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mcp.ResultBase
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Latin string `json:"latin"`
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}
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var translations = map[string]string{
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"hello": "salve",
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"goodbye": "vale",
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"thank you": "gratias tibi ago",
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"how are you": "quid agis",
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"good morning": "bonum mane",
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"good night": "bonam noctem",
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"friend": "amicus",
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"water": "aqua",
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"love": "amor",
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"war": "bellum",
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"peace": "pax",
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"truth": "veritas",
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"light": "lux",
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"time": "tempus",
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"life": "vita",
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"death": "mors",
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"star": "stella",
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"earth": "terra",
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"sea": "mare",
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"the die is cast": "alea iacta est",
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"i came i saw i conquered": "veni vidi vici",
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"seize the day": "carpe diem",
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}
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func main() {
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ctx := context.Background()
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server := mcp.NewServer(&mcp.Implementation{Name: "latin-server", Version: "v1.0.0"}, nil)
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if err := mcp.AddReceivingCustomMethod(server, "latin/translate",
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func(ctx context.Context, ss *mcp.ServerSession, params *TranslateParams) (*TranslateResult, error) {
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key := strings.ToLower(strings.TrimSpace(params.Text))
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latin, ok := translations[key]
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if !ok {
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latin = fmt.Sprintf("[unknown: %q — try: %s]", params.Text, knownPhrases())
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}
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return &TranslateResult{Latin: latin}, nil
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}); err != nil {
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log.Fatal(err)
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}
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ct, st := mcp.NewInMemoryTransports()
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ss, err := server.Connect(ctx, st, nil)
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if err != nil {
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log.Fatal(err)
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}
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defer ss.Close()
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client := mcp.NewClient(&mcp.Implementation{Name: "latin-client", Version: "v1.0.0"}, nil)
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if err := mcp.AddSendingCustomMethod[*TranslateParams, *TranslateResult](client, "latin/translate"); err != nil {
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log.Fatal(err)
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}
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cs, err := client.Connect(ctx, ct, nil)
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if err != nil {
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log.Fatal(err)
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}
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defer cs.Close()
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phrases := []string{"Hello", "Seize the day", "Peace", "Truth", "I came I saw I conquered"}
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for _, phrase := range phrases {
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result, err := mcp.CallCustomMethod[*TranslateParams, *TranslateResult](
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ctx, cs, "latin/translate", &TranslateParams{Text: phrase})
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if err != nil {
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log.Fatalf("translate %q: %v", phrase, err)
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}
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fmt.Printf("%-35s → %s\n", phrase, result.Latin)
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}
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}
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func knownPhrases() string {
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phrases := make([]string, 0, len(translations))
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for k := range translations {
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phrases = append(phrases, fmt.Sprintf("%q", k))
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}
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return strings.Join(phrases, ", ")
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}
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