c01fd188d2Summary
Builds on the types and architecture from the previous PR to deliver a
working variant-aware MCP
server that routes requests to inner mcp.Server instances based on
per-request _meta variant selection,
enabling a single MCP endpoint to serve multiple tool/resource/prompt
variants simultaneously.
```go
// Create standard mcp.Server instances — one per variant
codeReviewServer := mcp.NewServer(&mcp.Implementation{Name:
"devplatform", Version: "v1.0.0"}, nil)
mcp.AddTool(codeReviewServer, &mcp.Tool{Name: "list_pull_requests",
...}, handler)
mcp.AddTool(codeReviewServer, &mcp.Tool{Name: "get_diff", ...}, handler)
pmServer := mcp.NewServer(&mcp.Implementation{Name: "devplatform",
Version: "v1.0.0"}, nil)
mcp.AddTool(pmServer, &mcp.Tool{Name: "list_issues", ...}, handler)
mcp.AddTool(pmServer, &mcp.Tool{Name: "create_issue", ...}, handler)
// Register them as variants on a single server
vs := variants.NewServer(&mcp.Implementation{Name: "devplatform",
Version: "v1.0.0"}).
WithVariant(variants.ServerVariant{
ID: "code-review",
Description: "PR and code review operations",
Status: variants.Stable,
}, codeReviewServer, 0).
WithVariant(variants.ServerVariant{
ID: "project-management",
Description: "Issue and project tracking operations",
Status: variants.Stable,
}, pmServer, 1)
// Future: register variants backed by remote MCP servers
// WithHTTPVariant(v, mcpServer, priority) — variant backed by an
mcp.Server exposed over HTTP
// WithRemoteVariant(v, "https://...", priority) — variant backed by a
remote MCP endpoint
// Serve over HTTP for multiple concurrent clients
handler := variants.NewStreamableHTTPHandler(vs, nil)
http.ListenAndServe(":8080", handler)
// Or serve over stdio for single-client use:
// vs.Run(ctx, &mcp.StdioTransport{})
```
Key additions
- Backend abstraction (inMemoryBackend) — creates in-memory transport pairs between the variant server and
inner mcp.Server instances, with notification forwarding for progress and logging events.
- Request dispatcher (dispatch.go) — handles routing for tools/list, tools/call, resources/list,
resources/read, resources/subscribe, prompts/list, prompts/get, and completion/complete methods.
Implements variant-scoped cursor wrapping to correctly paginate across multiple inner servers.
- Session middleware (session.go) — manages per-session inner connections in stateful mode and shared
connections in stateless HTTP mode, ensuring proper lifecycle management.
- Initialize enrichment — injects availableVariants into the server's capabilities response so clients can
discover which variants are available.
- Capability discovery — merges inner server capabilities via union to present a unified capability set to
clients.
- NewStreamableHTTPHandler — provides an HTTP handler for multi-client serving over Streamable HTTP
transport.
- Integration tests (server_test.go, 458 lines) — covers end-to-end variant selection, backward
compatibility (no variant specified), HTTP transport, and stateless modes.
- Examples — stdio-based (examples/server/variants/main.go) and HTTP-based
(examples/server/variants-http/main.go) example servers demonstrating the API.
- README — rewritten with API documentation and architecture diagrams.
TODO (subsequent PRs):
- Unit Testing
- More integration tests
Signed-off-by: Kurt Degiorgio <kdegiorgio@bloomberg.net>
41 lines
1.1 KiB
Go
41 lines
1.1 KiB
Go
// Copyright 2025 The MCP Variants Authors. All rights reserved.
|
|
// Use of this source code is governed by a Apache-2.0
|
|
// license that can be found in the LICENSE file.
|
|
|
|
package variants
|
|
|
|
import (
|
|
"context"
|
|
"slices"
|
|
)
|
|
|
|
// defaultRankingFunc is the built-in ranking function used when no custom
|
|
// RankingFunc is provided. It sorts variants by priority (lowest first),
|
|
// using stable-before-experimental-before-deprecated as a tiebreaker.
|
|
//
|
|
// The input slice is already a copy (from RankedVariants), so sorting
|
|
// in place is safe.
|
|
func defaultRankingFunc(_ context.Context, _ VariantHints, vs []ServerVariant) []ServerVariant {
|
|
slices.SortStableFunc(vs, func(a, b ServerVariant) int {
|
|
if a.Priority() != b.Priority() {
|
|
return a.Priority() - b.Priority()
|
|
}
|
|
return statusWeight(a.Status) - statusWeight(b.Status)
|
|
})
|
|
return vs
|
|
}
|
|
|
|
// statusWeight returns a sort weight for a VariantStatus.
|
|
// Lower is better: stable < experimental < deprecated.
|
|
func statusWeight(s VariantStatus) int {
|
|
switch s {
|
|
case Stable, "":
|
|
return 0
|
|
case Experimental:
|
|
return 1
|
|
case Deprecated:
|
|
return 2
|
|
default:
|
|
return 3
|
|
}
|
|
}
|