Implement SEP-973 (#570)

mcp/protocol: Implement SEP-973

- Define Icon structure, which includes source, mimeType and sizes.
- sizes is any array of strings. refer
https://github.com/modelcontextprotocol/modelcontextprotocol/pull/1531
- Support setting websiteUrl, icons for mcp.Implementation
- Support setting icons for mcp.Prompt
- Support setting icons for mcp.Tool
- Support setting icons for mcp.Resource

Fixes #552

examples/server/everything/main.go

@@ -7,6 +7,7 @@ package main
 
 import (
 	"context"
+	"encoding/base64"
 	"flag"
 	"fmt"
 	"log"
@@ -50,19 +51,28 @@ func main() {
 		CompletionHandler: complete, // support completions by setting this handler
 	}
 
-	server := mcp.NewServer(&mcp.Implementation{Name: "everything"}, opts)
+	// Optionally add an icon to the server implementation.
+	icons, err := iconToBase64DataURL("./mcp.png")
+	if err != nil {
+		log.Fatalf("failed to read icon: %v", err)
+	}
+
+	server := mcp.NewServer(&mcp.Implementation{Name: "everything", WebsiteURL: "https://example.com", Icons: icons}, opts)
 
 	// Add tools that exercise different features of the protocol.
 	mcp.AddTool(server, &mcp.Tool{Name: "greet", Description: "say hi"}, contentTool)
-	mcp.AddTool(server, &mcp.Tool{Name: "greet (structured)"}, structuredTool) // returns structured output
-	mcp.AddTool(server, &mcp.Tool{Name: "ping"}, pingingTool)                  // performs a ping
-	mcp.AddTool(server, &mcp.Tool{Name: "log"}, loggingTool)                   // performs a log
-	mcp.AddTool(server, &mcp.Tool{Name: "sample"}, samplingTool)               // performs sampling
-	mcp.AddTool(server, &mcp.Tool{Name: "elicit"}, elicitingTool)              // performs elicitation
-	mcp.AddTool(server, &mcp.Tool{Name: "roots"}, rootsTool)                   // lists roots
+	mcp.AddTool(server, &mcp.Tool{Name: "greet (structured)"}, structuredTool)                                // returns structured output
+	mcp.AddTool(server, &mcp.Tool{Name: "greet (with Icons)", Icons: icons}, structuredTool)                  // tool with icons
+	mcp.AddTool(server, &mcp.Tool{Name: "greet (content with ResourceLink)"}, resourceLinkContentTool(icons)) // tool that returns content with a resource link
+	mcp.AddTool(server, &mcp.Tool{Name: "ping"}, pingingTool)                                                 // performs a ping
+	mcp.AddTool(server, &mcp.Tool{Name: "log"}, loggingTool)                                                  // performs a log
+	mcp.AddTool(server, &mcp.Tool{Name: "sample"}, samplingTool)                                              // performs sampling
+	mcp.AddTool(server, &mcp.Tool{Name: "elicit"}, elicitingTool)                                             // performs elicitation
+	mcp.AddTool(server, &mcp.Tool{Name: "roots"}, rootsTool)                                                  // lists roots
 
 	// Add a basic prompt.
 	server.AddPrompt(&mcp.Prompt{Name: "greet"}, prompt)
+	server.AddPrompt(&mcp.Prompt{Name: "greet (with Icons)", Icons: icons}, prompt) // greet prompt with icons
 
 	// Add an embedded resource.
 	server.AddResource(&mcp.Resource{
@@ -70,6 +80,20 @@ func main() {
 		MIMEType: "text/plain",
 		URI:      "embedded:info",
 	}, embeddedResource)
+	server.AddResource(&mcp.Resource{ // text resource with icons
+		Name:     "info (with Icons)",
+		MIMEType: "text/plain",
+		URI:      "embedded:info",
+		Icons:    icons,
+	}, embeddedResource)
+
+	// Add a resource template.
+	server.AddResourceTemplate(&mcp.ResourceTemplate{
+		Name:        "Resource template (with Icon)",
+		MIMEType:    "text/plain",
+		URITemplate: "http://example.com/~{resource_name}/",
+		Icons:       icons,
+	}, embeddedResource)
 
 	// Serve over stdio, or streamable HTTP if -http is set.
 	if *httpAddr != "" {
@@ -140,6 +164,23 @@ func contentTool(ctx context.Context, req *mcp.CallToolRequest, args args) (*mcp
 	}, nil, nil
 }
 
+// resourceLinkContentTool returns a ResourceLink content with icons.
+func resourceLinkContentTool(icons []mcp.Icon) func(ctx context.Context, req *mcp.CallToolRequest, args args) (*mcp.CallToolResult, any, error) {
+	return func(ctx context.Context, req *mcp.CallToolRequest, args args) (*mcp.CallToolResult, any, error) {
+		return &mcp.CallToolResult{
+			Content: []mcp.Content{
+				&mcp.ResourceLink{
+					Name:     "greeting",
+					Title:    "A friendly greeting",
+					MIMEType: "text/plain",
+					URI:      "data:text/plain,Hi%20" + url.PathEscape(args.Name),
+					Icons:    icons,
+				},
+			},
+		}, nil, nil
+	}
+}
+
 type result struct {
 	Message string `json:"message" jsonschema:"the message to convey"`
 }
@@ -222,3 +263,16 @@ func complete(ctx context.Context, req *mcp.CompleteRequest) (*mcp.CompleteResul
 		},
 	}, nil
 }
+
+func iconToBase64DataURL(path string) ([]mcp.Icon, error) {
+	data, err := os.ReadFile(path)
+	if err != nil {
+		return nil, err
+	}
+	return []mcp.Icon{{
+		Source:   "data:image/png;base64," + base64.StdEncoding.EncodeToString(data),
+		MIMEType: "image/png",
+		Sizes:    []string{"48x48"},
+		Theme:    "light", // or "dark" or empty
+	}}, nil
+}