Chapter 7: Testing, Troubleshooting, and Rough Edges

April 13, 2026 · View on GitHub

Welcome to Chapter 7: Testing, Troubleshooting, and Rough Edges. In this part of MCP Go SDK Tutorial: Building Robust MCP Clients and Servers in Go, you will build an intuitive mental model first, then move into concrete implementation details and practical production tradeoffs.

Operational quality improves when teams treat debugging and known limitations as first-class concerns.

Learning Goals

build a practical troubleshooting loop for MCP transport and handler issues
use inspector and HTTP traffic inspection effectively
account for known v1 rough edges in API usage
reduce recurring production support incidents

Troubleshooting Workflow

reproduce against a minimal example transport path
inspect MCP wire logs and HTTP traces
validate capability advertisement vs actual handlers
cross-check behavior against rough-edge notes before escalating

Rough-Edge Themes to Track

default capabilities behavior can surprise teams expecting empty defaults
some naming and capability field decisions are scheduled for v2 cleanup
event store and stream semantics need careful design in resumable deployments

Source References

Summary

You now have a disciplined debugging approach and awareness of v1 API edges that affect production behavior.

Next: Chapter 8: Conformance, Operations, and Upgrade Strategy

Source Code Walkthrough

`mcp/event.go`

The NewMemoryEventStore function in mcp/event.go handles a key part of this chapter's functionality:

const defaultMaxBytes = 10 << 20 // 10 MiB

// NewMemoryEventStore creates a [MemoryEventStore] with the default value
// for MaxBytes.
func NewMemoryEventStore(opts *MemoryEventStoreOptions) *MemoryEventStore {
	return &MemoryEventStore{
		maxBytes: defaultMaxBytes,
		store:    make(map[string]map[string]*dataList),
	}
}

// Open implements [EventStore.Open]. It ensures that the underlying data
// structures for the given session are initialized and ready for use.
func (s *MemoryEventStore) Open(_ context.Context, sessionID, streamID string) error {
	s.mu.Lock()
	defer s.mu.Unlock()
	s.init(sessionID, streamID)
	return nil
}

// init is an internal helper function that ensures the nested map structure for a
// given sessionID and streamID exists, creating it if necessary. It returns the
// dataList associated with the specified IDs.
// Requires s.mu.
func (s *MemoryEventStore) init(sessionID, streamID string) *dataList {
	streamMap, ok := s.store[sessionID]
	if !ok {
		streamMap = make(map[string]*dataList)
		s.store[sessionID] = streamMap
	}
	dl, ok := streamMap[streamID]
	if !ok {

This function is important because it defines how MCP Go SDK Tutorial: Building Robust MCP Clients and Servers in Go implements the patterns covered in this chapter.

`mcp/event.go`

The Open function in mcp/event.go handles a key part of this chapter's functionality:

// All of an EventStore's methods must be safe for use by multiple goroutines.
type EventStore interface {
	// Open is called when a new stream is created. It may be used to ensure that
	// the underlying data structure for the stream is initialized, making it
	// ready to store and replay event streams.
	Open(_ context.Context, sessionID, streamID string) error

	// Append appends data for an outgoing event to given stream, which is part of the
	// given session.
	Append(_ context.Context, sessionID, streamID string, data []byte) error

	// After returns an iterator over the data for the given session and stream, beginning
	// just after the given index.
	//
	// Once the iterator yields a non-nil error, it will stop.
	// After's iterator must return an error immediately if any data after index was
	// dropped; it must not return partial results.
	// The stream must have been opened previously (see [EventStore.Open]).
	After(_ context.Context, sessionID, streamID string, index int) iter.Seq2[[]byte, error]

	// SessionClosed informs the store that the given session is finished, along
	// with all of its streams.
	//
	// A store cannot rely on this method being called for cleanup. It should institute
	// additional mechanisms, such as timeouts, to reclaim storage.
	SessionClosed(_ context.Context, sessionID string) error

	// There is no StreamClosed method. A server doesn't know when a stream is finished, because
	// the client can always send a GET with a Last-Event-ID referring to the stream.
}

// A dataList is a list of []byte.

This function is important because it defines how MCP Go SDK Tutorial: Building Robust MCP Clients and Servers in Go implements the patterns covered in this chapter.

`mcp/event.go`

The init function in mcp/event.go handles a key part of this chapter's functionality:

type EventStore interface {
	// Open is called when a new stream is created. It may be used to ensure that
	// the underlying data structure for the stream is initialized, making it
	// ready to store and replay event streams.
	Open(_ context.Context, sessionID, streamID string) error

	// Append appends data for an outgoing event to given stream, which is part of the
	// given session.
	Append(_ context.Context, sessionID, streamID string, data []byte) error

	// After returns an iterator over the data for the given session and stream, beginning
	// just after the given index.
	//
	// Once the iterator yields a non-nil error, it will stop.
	// After's iterator must return an error immediately if any data after index was
	// dropped; it must not return partial results.
	// The stream must have been opened previously (see [EventStore.Open]).
	After(_ context.Context, sessionID, streamID string, index int) iter.Seq2[[]byte, error]

	// SessionClosed informs the store that the given session is finished, along
	// with all of its streams.
	//
	// A store cannot rely on this method being called for cleanup. It should institute
	// additional mechanisms, such as timeouts, to reclaim storage.
	SessionClosed(_ context.Context, sessionID string) error

	// There is no StreamClosed method. A server doesn't know when a stream is finished, because
	// the client can always send a GET with a Last-Event-ID referring to the stream.
}

// A dataList is a list of []byte.
// The zero dataList is ready to use.

This function is important because it defines how MCP Go SDK Tutorial: Building Robust MCP Clients and Servers in Go implements the patterns covered in this chapter.

`mcp/event.go`

The Append function in mcp/event.go handles a key part of this chapter's functionality:

	Open(_ context.Context, sessionID, streamID string) error

	// Append appends data for an outgoing event to given stream, which is part of the
	// given session.
	Append(_ context.Context, sessionID, streamID string, data []byte) error

	// After returns an iterator over the data for the given session and stream, beginning
	// just after the given index.
	//
	// Once the iterator yields a non-nil error, it will stop.
	// After's iterator must return an error immediately if any data after index was
	// dropped; it must not return partial results.
	// The stream must have been opened previously (see [EventStore.Open]).
	After(_ context.Context, sessionID, streamID string, index int) iter.Seq2[[]byte, error]

	// SessionClosed informs the store that the given session is finished, along
	// with all of its streams.
	//
	// A store cannot rely on this method being called for cleanup. It should institute
	// additional mechanisms, such as timeouts, to reclaim storage.
	SessionClosed(_ context.Context, sessionID string) error

	// There is no StreamClosed method. A server doesn't know when a stream is finished, because
	// the client can always send a GET with a Last-Event-ID referring to the stream.
}

// A dataList is a list of []byte.
// The zero dataList is ready to use.
type dataList struct {
	size  int // total size of data bytes
	first int // the stream index of the first element in data
	data  [][]byte

This function is important because it defines how MCP Go SDK Tutorial: Building Robust MCP Clients and Servers in Go implements the patterns covered in this chapter.

How These Components Connect

flowchart TD
    A[NewMemoryEventStore]
    B[Open]
    C[init]
    D[Append]
    E[After]
    A --> B
    B --> C
    C --> D
    D --> E