8704137635<!-- Provide a brief summary of your changes -->
Update the Go interceptor SDK to use
`github.com/modelcontextprotocol/go-sdk` v1.7.0 custom method APIs and
remove the vendored Go SDK copy. This shouldn't update the behaviours,
but addding following functions.
Changed public/user-facing interfaces:
extension.Extension.Install now returns an error:
```
// before
ext.Install(mcpServer)
// after
if err := ext.Install(mcpServer); err != nil {
return err
}
```
New helper added:
```
extension.RegisterSendingMethods(client *mcp.Client) error
```
## Motivation and Context
<!-- Why is this change needed? What problem does it solve? -->
Pick up MCP Go SDK 1.7.0. This provides upstream custom method support,
so the local vendored SDK copy is no longer needed.
## How Has This Been Tested?
<!-- Have you tested this in a real application? Which scenarios were
tested? -->
- `go test -v ./...`
## Breaking Changes
<!-- Will users need to update their code or configurations? -->
```go
if err := ext.Install(mcpServer); err != nil {
return err
}
```
The Go SDK module now requires Go 1.25 via
github.com/modelcontextprotocol/go-sdk v1.7.0.
## Types of changes
<!-- What types of changes does your code introduce? Put an `x` in all
the boxes that apply: -->
- [ ] Bug fix (non-breaking change which fixes an issue)
- [x] New feature (non-breaking change which adds functionality)
- [x] Breaking change (fix or feature that would cause existing
functionality to change)
- [x] Documentation update
## Checklist
<!-- Go over all the following points, and put an `x` in all the boxes
that apply. -->
- [x] I have read the [MCP
Documentation](https://modelcontextprotocol.io)
- [x] My code follows the repository's style guidelines
- [x] New and existing tests pass locally
- [x] I have added appropriate error handling
- [x] I have added or updated documentation as needed
## Additional context
<!-- Add any other context, implementation notes, or design decisions
-->
LocalChain now registers interceptor custom sending methods internally.
Manual remote chain setup should call
`extension.RegisterSendingMethods(client)` before connecting the MCP
client session used with chain.AddMCPServer.
Signed-off-by: Ukjae Jeong <jeongukjae@gmail.com>
2.9 KiB
Go SDK Interceptors — Performance
Analysis of per-request costs and allocation patterns.
Design Rationale: JSON-RPC Invocation
The interceptor chain follows the SEP execution model: each interceptor
is invoked via interceptor/invoke JSON-RPC calls through an MCP client
session. For in-process interceptors, Extension.LocalChain(ctx, server)
creates an in-memory transport, so there is no network I/O.
Payloads are json.RawMessage at the protocol level. The middleware
marshals request params and response results once per phase, and
interceptor handlers unmarshal the specific fields they need.
Per-Request Cost Model
Every intercepted request passes through gomiddleware.Middleware.
The cost depends on whether interceptors match the event.
Fast Path (skipped methods)
The middleware skips initialize, notifications/*, interceptors/list,
and interceptor/invoke with a map lookup. Zero allocations, zero JSON
operations.
Intercepted Path
With interceptors active, each active phase incurs:
| Step | Operation | Allocations | JSON ops |
|---|---|---|---|
| 1 | Marshal request params / response result | 1 json.RawMessage |
1 marshal |
| 2 | ChainExecutionResult struct (with pre-allocated Results slice) |
1 struct + 1 slice | 0 |
| 3 | Per-interceptor interceptor/invoke RPC |
1 InvokeParams + 1 InvokeResult per interceptor |
1 marshal + 1 unmarshal per interceptor (handled by go-sdk JSON-RPC layer) |
| 4 | Validator execution | 1 goroutine per validator | Handler-specific |
| 5 | Mutator payload threading | 0 | Payload passed as json.RawMessage between mutators |
| 6 | Unmarshal mutated payload back to params/result | 0 | 1 unmarshal (if mutated) |
In-Memory Transport Overhead
When using LocalChain(), the in-memory transport uses newline-delimited
JSON over a net.Pipe(). Each interceptor/invoke call involves:
- JSON marshal of
InvokeParams(client side) - Write to pipe
- JSON unmarshal of
InvokeParams(server side) - Handler execution
- JSON marshal of
InvokeResult(server side) - Write to pipe
- JSON unmarshal of
InvokeResult(client side)
The JSON-RPC overhead is bounded by the payload size and is negligible for typical MCP payloads. The in-memory pipe avoids network I/O entirely.
Audit Mode
Audit-mode mutators run normally but their mutated payload is not
propagated to subsequent interceptors. No deep-copy is needed — the
chain simply skips updating FinalPayload for audit-mode entries.
Optimization Opportunities
- Batch invoke: A future
interceptor/invokeValidatorsmethod could reduce round-trips for validators that run in parallel. - Payload caching: For validators that don't need the full payload, a lightweight invoke variant could skip payload serialization.
- Connection pooling: For remote interceptor servers, reusing client sessions across requests avoids connection setup overhead.