Refactors DemoMCP tool handler to integrate with DemoGRPC for fact retrieval and updates server instructions.

go.mod

@@ -11,11 +11,13 @@ require (
 	gitea.libretechconsulting.com/rmcguire/go-app v0.11.0
 	github.com/go-resty/resty/v2 v2.16.5
 	github.com/grpc-ecosystem/grpc-gateway/v2 v2.27.1
+	github.com/modelcontextprotocol/go-sdk v0.3.0
 	github.com/rs/zerolog v1.34.0
 	go.opentelemetry.io/otel/trace v1.37.0
 	google.golang.org/genproto/googleapis/api v0.0.0-20250811230008-5f3141c8851a
 	google.golang.org/grpc v1.74.2
 	google.golang.org/protobuf v1.36.7
+	k8s.io/utils v0.0.0-20250820121507-0af2bda4dd1d
 )
 
 require (
@@ -47,6 +49,7 @@ require (
 	github.com/go-logr/logr v1.4.3 // indirect
 	github.com/go-logr/stdr v1.2.2 // indirect
 	github.com/google/cel-go v0.26.0 // indirect
+	github.com/google/jsonschema-go v0.2.0 // indirect
 	github.com/google/uuid v1.6.0 // indirect
 	github.com/grafana/regexp v0.0.0-20240518133315-a468a5bfb3bc // indirect
 	github.com/mattn/go-colorable v0.1.14 // indirect
@@ -58,6 +61,7 @@ require (
 	github.com/prometheus/otlptranslator v0.0.0-20250717125610-8549f4ab4f8f // indirect
 	github.com/prometheus/procfs v0.17.0 // indirect
 	github.com/stoewer/go-strcase v1.3.1 // indirect
+	github.com/yosida95/uritemplate/v3 v3.0.2 // indirect
 	go.opentelemetry.io/auto/sdk v1.1.0 // indirect
 	go.opentelemetry.io/otel/exporters/otlp/otlptrace v1.37.0 // indirect
 	go.opentelemetry.io/otel/metric v1.37.0 // indirect

go.sum

@@ -40,6 +40,8 @@ github.com/google/cel-go v0.26.0 h1:DPGjXackMpJWH680oGY4lZhYjIameYmR+/6RBdDGmaI=
 github.com/google/cel-go v0.26.0/go.mod h1:A9O8OU9rdvrK5MQyrqfIxo1a0u4g3sF8KB6PUIaryMM=
 github.com/google/go-cmp v0.7.0 h1:wk8382ETsv4JYUZwIsn6YpYiWiBsYLSJiTsyBybVuN8=
 github.com/google/go-cmp v0.7.0/go.mod h1:pXiqmnSA92OHEEa9HXL2W4E7lf9JzCmGVUdgjX3N/iU=
+github.com/google/jsonschema-go v0.2.0 h1:Uh19091iHC56//WOsAd1oRg6yy1P9BpSvpjOL6RcjLQ=
+github.com/google/jsonschema-go v0.2.0/go.mod h1:r5quNTdLOYEz95Ru18zA0ydNbBuYoo9tgaYcxEYhJVE=
 github.com/google/uuid v1.6.0 h1:NIvaJDMOsjHA8n1jAhLSgzrAzy1Hgr+hNrb57e+94F0=
 github.com/google/uuid v1.6.0/go.mod h1:TIyPZe4MgqvfeYDBFedMoGGpEw/LqOeaOT+nhxU+yHo=
 github.com/grafana/regexp v0.0.0-20240518133315-a468a5bfb3bc h1:GN2Lv3MGO7AS6PrRoT6yV5+wkrOpcszoIsO4+4ds248=
@@ -65,6 +67,8 @@ github.com/mattn/go-isatty v0.0.16/go.mod h1:kYGgaQfpe5nmfYZH+SKPsOc2e4SrIfOl2e/
 github.com/mattn/go-isatty v0.0.19/go.mod h1:W+V8PltTTMOvKvAeJH7IuucS94S2C6jfK/D7dTCTo3Y=
 github.com/mattn/go-isatty v0.0.20 h1:xfD0iDuEKnDkl03q4limB+vH+GxLEtL/jb4xVJSWWEY=
 github.com/mattn/go-isatty v0.0.20/go.mod h1:W+V8PltTTMOvKvAeJH7IuucS94S2C6jfK/D7dTCTo3Y=
+github.com/modelcontextprotocol/go-sdk v0.3.0 h1:/1XC6+PpdKfE4CuFJz8/goo0An31bu8n8G8d3BkeJoY=
+github.com/modelcontextprotocol/go-sdk v0.3.0/go.mod h1:71VUZVa8LL6WARvSgLJ7DMpDWSeomT4uBv8g97mGBvo=
 github.com/munnerz/goautoneg v0.0.0-20191010083416-a7dc8b61c822 h1:C3w9PqII01/Oq1c1nUAm88MOHcQC9l5mIlSMApZMrHA=
 github.com/munnerz/goautoneg v0.0.0-20191010083416-a7dc8b61c822/go.mod h1:+n7T8mK8HuQTcFwEeznm/DIxMOiR9yIdICNftLE1DvQ=
 github.com/pkg/errors v0.9.1/go.mod h1:bwawxfHBFNV+L2hUp1rHADufV3IMtnDRdf1r5NINEl0=
@@ -103,6 +107,8 @@ github.com/swaggest/jsonschema-go v0.3.78 h1:5+YFQrLxOR8z6CHvgtZc42WRy/Q9zRQQ4Ho
 github.com/swaggest/jsonschema-go v0.3.78/go.mod h1:4nniXBuE+FIGkOGuidjOINMH7OEqZK3HCSbfDuLRI0g=
 github.com/swaggest/refl v1.4.0 h1:CftOSdTqRqs100xpFOT/Rifss5xBV/CT0S/FN60Xe9k=
 github.com/swaggest/refl v1.4.0/go.mod h1:4uUVFVfPJ0NSX9FPwMPspeHos9wPFlCMGoPRllUbpvA=
+github.com/yosida95/uritemplate/v3 v3.0.2 h1:Ed3Oyj9yrmi9087+NczuL5BwkIc4wvTb5zIM+UJPGz4=
+github.com/yosida95/uritemplate/v3 v3.0.2/go.mod h1:ILOh0sOhIJR3+L/8afwt/kE++YT040gmv5BQTMR2HP4=
 github.com/yudai/gojsondiff v1.0.0 h1:27cbfqXLVEJ1o8I6v3y9lg8Ydm53EKqHXAOMxEGlCOA=
 github.com/yudai/gojsondiff v1.0.0/go.mod h1:AY32+k2cwILAkW1fbgxQ5mUmMiZFgLIV+FBNExI05xg=
 github.com/yudai/golcs v0.0.0-20170316035057-ecda9a501e82 h1:BHyfKlQyqbsFN5p3IfnEUduWvb9is428/nNb5L3U01M=
@@ -152,6 +158,8 @@ golang.org/x/text v0.28.0 h1:rhazDwis8INMIwQ4tpjLDzUhx6RlXqZNPEM0huQojng=
 golang.org/x/text v0.28.0/go.mod h1:U8nCwOR8jO/marOQ0QbDiOngZVEBB7MAiitBuMjXiNU=
 golang.org/x/time v0.6.0 h1:eTDhh4ZXt5Qf0augr54TN6suAUudPcawVZeIAPU7D4U=
 golang.org/x/time v0.6.0/go.mod h1:3BpzKBy/shNhVucY/MWOyx10tF3SFh9QdLuxbVysPQM=
+golang.org/x/tools v0.36.0 h1:kWS0uv/zsvHEle1LbV5LE8QujrxB3wfQyxHfhOk0Qkg=
+golang.org/x/tools v0.36.0/go.mod h1:WBDiHKJK8YgLHlcQPYQzNCkUxUypCaa5ZegCVutKm+s=
 google.golang.org/genproto/googleapis/api v0.0.0-20250811230008-5f3141c8851a h1:DMCgtIAIQGZqJXMVzJF4MV8BlWoJh2ZuFiRdAleyr58=
 google.golang.org/genproto/googleapis/api v0.0.0-20250811230008-5f3141c8851a/go.mod h1:y2yVLIE/CSMCPXaHnSKXxu1spLPnglFLegmgdY23uuE=
 google.golang.org/genproto/googleapis/rpc v0.0.0-20250811230008-5f3141c8851a h1:tPE/Kp+x9dMSwUm/uM0JKK0IfdiJkwAbSMSeZBXXJXc=
@@ -168,3 +176,5 @@ gopkg.in/check.v1 v1.0.0-20201130134442-10cb98267c6c/go.mod h1:JHkPIbrfpd72SG/EV
 gopkg.in/yaml.v3 v3.0.0-20200313102051-9f266ea9e77c/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=
 gopkg.in/yaml.v3 v3.0.1 h1:fxVm/GzAzEWqLHuvctI91KS9hhNmmWOoWu0XTYJS7CA=
 gopkg.in/yaml.v3 v3.0.1/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=
+k8s.io/utils v0.0.0-20250820121507-0af2bda4dd1d h1:wAhiDyZ4Tdtt7e46e9M5ZSAJ/MnPGPs+Ki1gHw4w1R0=
+k8s.io/utils v0.0.0-20250820121507-0af2bda4dd1d/go.mod h1:OLgZIPagt7ERELqWJFomSt595RzquPNLL48iOWgYOg0=

pkg/demo/demo.go

@@ -12,6 +12,7 @@ import (
 	"gitea.libretechconsulting.com/rmcguire/go-server-with-otel/pkg/config"
 	"gitea.libretechconsulting.com/rmcguire/go-server-with-otel/pkg/demo/demogrpc"
 	"gitea.libretechconsulting.com/rmcguire/go-server-with-otel/pkg/demo/demohttp"
+	"gitea.libretechconsulting.com/rmcguire/go-server-with-otel/pkg/demo/demomcp"
 	"gitea.libretechconsulting.com/rmcguire/go-server-with-otel/pkg/service"
 )
 
@@ -20,6 +21,7 @@ type DemoService struct {
 	config *config.ServiceConfig
 	http   *demohttp.DemoHTTPServer
 	grpc   *demogrpc.DemoGRPCServer
+	mcp    *demomcp.DemoMCPServer
 }
 
 func (d *DemoService) Init(ctx context.Context, config *config.ServiceConfig,
@@ -31,6 +33,7 @@ func (d *DemoService) Init(ctx context.Context, config *config.ServiceConfig,
 	// This is, after all, a demo app. Just implement the interface.
 	d.http = demohttp.NewDemoHTTPServer(ctx, config)
 	d.grpc = demogrpc.NewDemoGRPCServer(ctx, config)
+	d.mcp = demomcp.NewDemoMCPServer(ctx, config)
 
 	// TODO: This should actually do shutdown stuff
 	return func(_ context.Context) (string, error) {
@@ -49,6 +52,7 @@ func (d *DemoService) GetHTTP() *optshttp.AppHTTP {
 	return &optshttp.AppHTTP{
 		Ctx:          d.ctx,
 		Funcs:        d.http.GetHandleFuncs(),
+		Handlers:     d.mcp.GetHandlers(),
 		HealthChecks: d.http.GetHealthCheckFuncs(),
 	}
 }

pkg/demo/demomcp/server.go

@@ -0,0 +1,65 @@
+/*
+Package demomcp contains a simple reference implementation of returning a
+HTTPHandler for an MCP server with a single tool used to retrieve random facts
+*/
+package demomcp
+
+import (
+	"context"
+	"net/http"
+
+	"gitea.libretechconsulting.com/rmcguire/go-app/pkg/srv/http/opts"
+	"github.com/modelcontextprotocol/go-sdk/mcp"
+
+	"gitea.libretechconsulting.com/rmcguire/go-server-with-otel/pkg/config"
+	"gitea.libretechconsulting.com/rmcguire/go-server-with-otel/pkg/demo/demogrpc"
+)
+
+var DemoMCPImpl = &mcp.Implementation{
+	Name:  "Demo MCP Server",
+	Title: "Demo MCP",
+}
+
+type DemoMCPServer struct {
+	ctx      context.Context
+	cfg      *config.ServiceConfig
+	server   *mcp.Server
+	demoGRPC *demogrpc.DemoGRPCServer
+}
+
+func NewDemoMCPServer(ctx context.Context, cfg *config.ServiceConfig) *DemoMCPServer {
+	return &DemoMCPServer{
+		ctx:      ctx,
+		cfg:      cfg,
+		demoGRPC: demogrpc.NewDemoGRPCServer(ctx, cfg),
+		server: mcp.NewServer(DemoMCPImpl, &mcp.ServerOptions{
+			Instructions: "Call this demo MCP tool if the user asks useless questions or wants a random fact",
+			HasTools:     true,
+		}),
+	}
+}
+
+func (d *DemoMCPServer) GetHandlers() []opts.HTTPHandler {
+	// NOTE: Add other tools here
+	d.addDemoRandomFactTool()
+
+	demoHandler := mcp.NewStreamableHTTPHandler(func(*http.Request) *mcp.Server {
+		return d.server
+	}, &mcp.StreamableHTTPOptions{})
+
+	return []opts.HTTPHandler{
+		{
+			Prefix:  "/api/mcp",
+			Handler: demoHandler,
+		},
+	}
+}
+
+func (d *DemoMCPServer) GetHealthCheckFuncs() []opts.HealthCheckFunc {
+	return []opts.HealthCheckFunc{
+		func(ctx context.Context) error {
+			// TODO: Implement real health checks
+			return nil
+		},
+	}
+}

pkg/demo/demomcp/tool.go

@@ -0,0 +1,58 @@
+package demomcp
+
+import (
+	"context"
+
+	"github.com/modelcontextprotocol/go-sdk/mcp"
+	"k8s.io/utils/ptr"
+
+	demo "gitea.libretechconsulting.com/rmcguire/go-server-with-otel/api/demo/app/v1alpha1"
+)
+
+var DemoTool = &mcp.Tool{
+	Name:        "Demo Tool",
+	Title:       "Demo Random Fact Tool",
+	Description: "Returns a random fact for demo or boredom purposes",
+	Annotations: &mcp.ToolAnnotations{
+		ReadOnlyHint:  true,
+		OpenWorldHint: ptr.To(true),
+	},
+}
+
+type DemoToolParams struct {
+	Language string `json:"language,omitempty" jsonschema:"Random Fact Language Abbreviation (e.g. en)"`
+}
+
+func (d *DemoMCPServer) addDemoRandomFactTool() {
+	d.server.AddTool(
+		mcp.ToolFor(DemoTool, d.demoToolHandler),
+	)
+}
+
+func (d *DemoMCPServer) demoToolHandler(ctx context.Context, req *mcp.CallToolRequest, args *DemoToolParams) (
+	*mcp.CallToolResult, any, error,
+) {
+	fact, err := d.demoGRPC.GetDemo(ctx, &demo.GetDemoRequest{
+		Language: &args.Language,
+	})
+	if err != nil {
+		return &mcp.CallToolResult{
+			IsError: true,
+			Meta: mcp.Meta{
+				"error": err,
+			},
+		}, nil, err
+	}
+
+	return &mcp.CallToolResult{
+		Meta: mcp.Meta{
+			"language": fact.GetLanguage(),
+			"source":   fact.GetSource(),
+		},
+		Content: []mcp.Content{
+			&mcp.TextContent{
+				Text: fact.GetFact(),
+			},
+		},
+	}, nil, nil
+}