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mcp: support url mode elicitation (#646)

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Add initial support for URL mode elicitation, by introducing the new
types, as well as both server and client-side validation.

A follow-up CL will add support for ErrURLElicitationRequired.

For #623
This commit is contained in:
Robert Findley 2025-11-23 12:58:28 -05:00 • committed by GitHub
commit 21fb03dd1a
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GPG key ID: B5690EEEBB952194
1 changed files with 398 additions and 60 deletions
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48
examples/server/everything/main.go
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@ -7,6 +7,7 @@ package main
import (
"context"
_ "embed"
"encoding/base64"
"flag"
"fmt"
@ -17,6 +18,7 @@ import (
"os"
"runtime"
"strings"
"sync/atomic"
"github.com/google/jsonschema-go/jsonschema"
"github.com/modelcontextprotocol/go-sdk/mcp"
@ -51,12 +53,8 @@ func main() {
CompletionHandler: complete, // support completions by setting this handler
}
// Optionally add an icon to the server implementation.
icons, err := iconToBase64DataURL("./mcp.png")
if err != nil {
log.Fatalf("failed to read icon: %v", err)
}
// Add an icon to the server implementation.
icons := mcpIcons()
server := mcp.NewServer(&mcp.Implementation{Name: "everything", WebsiteURL: "https://example.com", Icons: icons}, opts)
// Add tools that exercise different features of the protocol.
@ -67,7 +65,8 @@ func main() {
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: "elicit (form)"}, elicitFormTool) // performs form elicitation
mcp.AddTool(server, &mcp.Tool{Name: "elicit (url)"}, elicitURLTool) // performs url elicitation
mcp.AddTool(server, &mcp.Tool{Name: "roots"}, rootsTool) // lists roots
// Add a basic prompt.
@ -235,7 +234,7 @@ func samplingTool(ctx context.Context, req *mcp.CallToolRequest, _ any) (*mcp.Ca
}, nil, nil
}
func elicitingTool(ctx context.Context, req *mcp.CallToolRequest, _ any) (*mcp.CallToolResult, any, error) {
func elicitFormTool(ctx context.Context, req *mcp.CallToolRequest, _ any) (*mcp.CallToolResult, any, error) {
res, err := req.Session.Elicit(ctx, &mcp.ElicitParams{
Message: "provide a random string",
RequestedSchema: &jsonschema.Schema{
@ -255,6 +254,26 @@ func elicitingTool(ctx context.Context, req *mcp.CallToolRequest, _ any) (*mcp.C
}, nil, nil
}
var elicitations atomic.Int32
func elicitURLTool(ctx context.Context, req *mcp.CallToolRequest, _ any) (*mcp.CallToolResult, any, error) {
elicitID := fmt.Sprintf("%d", elicitations.Add(1))
_, err := req.Session.Elicit(ctx, &mcp.ElicitParams{
Message: "submit a string",
URL: fmt.Sprintf("http://localhost:6062?id=%s", elicitID),
ElicitationID: elicitID,
})
if err != nil {
return nil, nil, fmt.Errorf("eliciting failed: %v", err)
}
// TODO: actually wait for the elicitation form to be submitted.
return &mcp.CallToolResult{
Content: []mcp.Content{
&mcp.TextContent{Text: "(elicitation pending)"},
},
}, nil, nil
}
func complete(ctx context.Context, req *mcp.CompleteRequest) (*mcp.CompleteResult, error) {
return &mcp.CompleteResult{
Completion: mcp.CompletionResultDetails{
@ -264,15 +283,14 @@ 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
}
//go:embed mcp.png
var mcpIconData []byte
func mcpIcons() []mcp.Icon {
return []mcp.Icon{{
Source: "data:image/png;base64," + base64.StdEncoding.EncodeToString(data),
Source: "data:image/png;base64," + base64.StdEncoding.EncodeToString(mcpIconData),
MIMEType: "image/png",
Sizes: []string{"48x48"},
Theme: "light", // or "dark" or empty
}}, nil
}}
}