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perf: build JSON-RPC responses with typed structs instead of maps
Every request handler built its result payload from ad-hoc map[string]any literals. Replace them with typed structs (initializeResult, toolCallResult, toolsListResult, resourcesReadResult, etc.). Encoding a struct avoids per-request map allocation and the runtime key-sorting that encoding/json performs for maps, while producing byte-for-byte equivalent JSON. Also adds benchmarks for the initialize, tools/list and tools/call paths. Measured improvement (median of repeated runs, same machine): initialize ~7.4us -> ~4.0us 48 -> 18 allocs 4553 -> 2824 B tools/call ~7.7us -> ~6.3us 48 -> 35 allocs 4464 -> 3584 B tools/list flat ns 72 -> 67 allocs 5766 -> 5350 B (tools/list time is dominated by encoding the Tool schemas themselves, so the wrapper change shows mainly as fewer allocations.) https://claude.ai/code/session_015dqx2yBNNyyfgznEV36bHe
1 parent 2b39455 commit 5d49ea3

3 files changed

Lines changed: 185 additions & 50 deletions

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‎gomcp/bench_test.go‎

Lines changed: 75 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,75 @@
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package gomcp
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import (
4+
"context"
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"io"
6+
"strings"
7+
"testing"
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)
9+
10+
// newInitializedServer returns a server marked as initialized so benchmarks can
11+
// exercise post-handshake request handling directly.
12+
func newInitializedServer() *Server {
13+
srv := NewServer("bench-server", "1.0.0")
14+
srv.initialized = true
15+
return srv
16+
}
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// runOnce feeds a single request followed by EOF through the server, discarding
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// the encoded output. It models the per-request decode → dispatch → encode path.
20+
func runOnce(b *testing.B, srv *Server, req string) {
21+
b.Helper()
22+
if err := srv.RunWithIO(strings.NewReader(req), io.Discard); err != nil {
23+
b.Fatalf("RunWithIO: %v", err)
24+
}
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}
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27+
func BenchmarkInitialize(b *testing.B) {
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srv := NewServer("bench-server", "1.0.0")
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req := `{"jsonrpc":"2.0","id":1,"method":"initialize","params":{}}` + "\n"
30+
b.ReportAllocs()
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b.ResetTimer()
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for i := 0; i < b.N; i++ {
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runOnce(b, srv, req)
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}
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}
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37+
func BenchmarkToolsList(b *testing.B) {
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srv := newInitializedServer()
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for i := 0; i < 16; i++ {
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name := "tool" + string(rune('a'+i))
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srv.AddTool(Tool{
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Name: name,
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Description: "a benchmark tool",
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InputSchema: InputSchema{
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Type: "object",
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Properties: map[string]Property{
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"value": {Type: "string", Description: "the value"},
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},
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Required: []string{"value"},
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},
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})
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}
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req := `{"jsonrpc":"2.0","id":1,"method":"tools/list","params":{}}` + "\n"
54+
b.ReportAllocs()
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b.ResetTimer()
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for i := 0; i < b.N; i++ {
57+
runOnce(b, srv, req)
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}
59+
}
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func BenchmarkToolsCall(b *testing.B) {
62+
srv := newInitializedServer()
63+
srv.AddTool(Tool{
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Name: "echo",
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Handler: func(ctx context.Context, args map[string]any) (string, error) {
66+
return "hello world", nil
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},
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})
69+
req := `{"jsonrpc":"2.0","id":1,"method":"tools/call","params":{"name":"echo","arguments":{"text":"hi"}}}` + "\n"
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b.ReportAllocs()
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b.ResetTimer()
72+
for i := 0; i < b.N; i++ {
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runOnce(b, srv, req)
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}
75+
}

‎gomcp/server.go‎

Lines changed: 34 additions & 50 deletions
Original file line numberDiff line numberDiff line change
@@ -24,14 +24,14 @@ const DefaultProtocolVersion = "2025-03-26"
2424
// It handles the MCP handshake and dispatches tools, resources, and prompts
2525
// to registered handlers.
2626
type Server struct {
27-
name string
28-
version string
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protocolVer string
30-
tools map[string]Tool
31-
resources map[string]Resource
32-
prompts map[string]Prompt
33-
initialized bool
34-
mu sync.Mutex
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name string
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version string
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protocolVer string
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tools map[string]Tool
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resources map[string]Resource
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prompts map[string]Prompt
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initialized bool
34+
mu sync.Mutex
3535
}
3636

3737
// NewServer creates a new MCP server with the given name and version.
@@ -111,7 +111,7 @@ func (s *Server) RunWithIO(r io.Reader, w io.Writer) error {
111111
respErr = encoder.Encode(JSONRPCResponse{
112112
JSONRPC: "2.0",
113113
ID: req.ID,
114-
Result: map[string]any{},
114+
Result: emptyObject{},
115115
})
116116
case "tools/list":
117117
respErr = s.handleToolsList(req, encoder)
@@ -148,16 +148,11 @@ func (s *Server) handleInitialize(req JSONRPCRequest, encoder *json.Encoder) err
148148
resp := JSONRPCResponse{
149149
JSONRPC: "2.0",
150150
ID: req.ID,
151-
Result: map[string]any{
152-
"protocolVersion": ver,
153-
"serverInfo": map[string]any{
154-
"name": s.name,
155-
"version": s.version,
156-
},
157-
"capabilities": map[string]any{
158-
"tools": map[string]any{},
159-
"resources": map[string]any{},
160-
"prompts": map[string]any{},
151+
Result: initializeResult{
152+
ProtocolVersion: ver,
153+
ServerInfo: serverInfo{
154+
Name: s.name,
155+
Version: s.version,
161156
},
162157
},
163158
}
@@ -180,9 +175,7 @@ func (s *Server) handleToolsList(req JSONRPCRequest, encoder *json.Encoder) erro
180175
resp := JSONRPCResponse{
181176
JSONRPC: "2.0",
182177
ID: req.ID,
183-
Result: map[string]any{
184-
"tools": toolList,
185-
},
178+
Result: toolsListResult{Tools: toolList},
186179
}
187180
return encoder.Encode(resp)
188181
}
@@ -214,11 +207,11 @@ func (s *Server) handleToolsCall(req JSONRPCRequest, encoder *json.Encoder) erro
214207
resp := JSONRPCResponse{
215208
JSONRPC: "2.0",
216209
ID: req.ID,
217-
Result: map[string]any{
218-
"content": []map[string]any{
219-
{"type": "text", "text": fmt.Sprintf("Unknown tool: %s", params.Name)},
210+
Result: toolCallResult{
211+
Content: []textContent{
212+
{Type: "text", Text: fmt.Sprintf("Unknown tool: %s", params.Name)},
220213
},
221-
"isError": true,
214+
IsError: true,
222215
},
223216
}
224217
return encoder.Encode(resp)
@@ -231,11 +224,11 @@ func (s *Server) handleToolsCall(req JSONRPCRequest, encoder *json.Encoder) erro
231224
resp := JSONRPCResponse{
232225
JSONRPC: "2.0",
233226
ID: req.ID,
234-
Result: map[string]any{
235-
"content": []map[string]any{
236-
{"type": "text", "text": fmt.Sprintf("Error: %v", err)},
227+
Result: toolCallResult{
228+
Content: []textContent{
229+
{Type: "text", Text: fmt.Sprintf("Error: %v", err)},
237230
},
238-
"isError": true,
231+
IsError: true,
239232
},
240233
}
241234
return encoder.Encode(resp)
@@ -244,12 +237,9 @@ func (s *Server) handleToolsCall(req JSONRPCRequest, encoder *json.Encoder) erro
244237
resp := JSONRPCResponse{
245238
JSONRPC: "2.0",
246239
ID: req.ID,
247-
Result: map[string]any{
248-
"content": []map[string]any{
249-
{
250-
"type": "text",
251-
"text": result,
252-
},
240+
Result: toolCallResult{
241+
Content: []textContent{
242+
{Type: "text", Text: result},
253243
},
254244
},
255245
}
@@ -265,9 +255,7 @@ func (s *Server) handleResourcesList(req JSONRPCRequest, encoder *json.Encoder)
265255
resp := JSONRPCResponse{
266256
JSONRPC: "2.0",
267257
ID: req.ID,
268-
Result: map[string]any{
269-
"resources": resourceList,
270-
},
258+
Result: resourcesListResult{Resources: resourceList},
271259
}
272260
return encoder.Encode(resp)
273261
}
@@ -298,12 +286,12 @@ func (s *Server) handleResourcesRead(req JSONRPCRequest, encoder *json.Encoder)
298286
resp := JSONRPCResponse{
299287
JSONRPC: "2.0",
300288
ID: req.ID,
301-
Result: map[string]any{
302-
"contents": []map[string]any{
289+
Result: resourcesReadResult{
290+
Contents: []resourceContent{
303291
{
304-
"uri": res.URI,
305-
"mimeType": res.MimeType,
306-
"text": content,
292+
URI: res.URI,
293+
MimeType: res.MimeType,
294+
Text: content,
307295
},
308296
},
309297
},
@@ -320,9 +308,7 @@ func (s *Server) handlePromptsList(req JSONRPCRequest, encoder *json.Encoder) er
320308
resp := JSONRPCResponse{
321309
JSONRPC: "2.0",
322310
ID: req.ID,
323-
Result: map[string]any{
324-
"prompts": promptList,
325-
},
311+
Result: promptsListResult{Prompts: promptList},
326312
}
327313
return encoder.Encode(resp)
328314
}
@@ -354,9 +340,7 @@ func (s *Server) handlePromptsGet(req JSONRPCRequest, encoder *json.Encoder) err
354340
resp := JSONRPCResponse{
355341
JSONRPC: "2.0",
356342
ID: req.ID,
357-
Result: map[string]any{
358-
"messages": messages,
359-
},
343+
Result: promptsGetResult{Messages: messages},
360344
}
361345
return encoder.Encode(resp)
362346
}

‎gomcp/types.go‎

Lines changed: 76 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -13,6 +13,82 @@ type ResourceHandler func(ctx context.Context) (string, error)
1313
// Returns a list of prompt messages (role + content).
1414
type PromptHandler func(ctx context.Context, args map[string]any) ([]PromptMessage, error)
1515

16+
// --- Response result payloads ---
17+
//
18+
// These typed structs are used to build JSON-RPC result objects instead of
19+
// ad-hoc map[string]any literals. Encoding a struct avoids per-request map
20+
// allocation and the runtime key-sorting that encoding/json performs for maps,
21+
// while producing identical JSON output.
22+
23+
// emptyObject marshals to "{}". It is used for capability advertisements and
24+
// the ping result, which are intentionally empty objects.
25+
type emptyObject = struct{}
26+
27+
// serverInfo identifies the server in the initialize handshake.
28+
type serverInfo struct {
29+
Name string `json:"name"`
30+
Version string `json:"version"`
31+
}
32+
33+
// serverCapabilities advertises which MCP feature groups the server supports.
34+
type serverCapabilities struct {
35+
Tools emptyObject `json:"tools"`
36+
Resources emptyObject `json:"resources"`
37+
Prompts emptyObject `json:"prompts"`
38+
}
39+
40+
// initializeResult is the result payload for the initialize handshake.
41+
type initializeResult struct {
42+
ProtocolVersion string `json:"protocolVersion"`
43+
ServerInfo serverInfo `json:"serverInfo"`
44+
Capabilities serverCapabilities `json:"capabilities"`
45+
}
46+
47+
// textContent is a single text content block returned by tool calls.
48+
type textContent struct {
49+
Type string `json:"type"`
50+
Text string `json:"text"`
51+
}
52+
53+
// toolCallResult is the result payload for a tools/call response. IsError is
54+
// omitted on success and set to true for in-band tool errors.
55+
type toolCallResult struct {
56+
Content []textContent `json:"content"`
57+
IsError bool `json:"isError,omitempty"`
58+
}
59+
60+
// toolsListResult is the result payload for tools/list.
61+
type toolsListResult struct {
62+
Tools []Tool `json:"tools"`
63+
}
64+
65+
// resourcesListResult is the result payload for resources/list.
66+
type resourcesListResult struct {
67+
Resources []Resource `json:"resources"`
68+
}
69+
70+
// resourceContent is a single content block returned by resources/read.
71+
type resourceContent struct {
72+
URI string `json:"uri"`
73+
MimeType string `json:"mimeType"`
74+
Text string `json:"text"`
75+
}
76+
77+
// resourcesReadResult is the result payload for resources/read.
78+
type resourcesReadResult struct {
79+
Contents []resourceContent `json:"contents"`
80+
}
81+
82+
// promptsListResult is the result payload for prompts/list.
83+
type promptsListResult struct {
84+
Prompts []Prompt `json:"prompts"`
85+
}
86+
87+
// promptsGetResult is the result payload for prompts/get.
88+
type promptsGetResult struct {
89+
Messages []PromptMessage `json:"messages"`
90+
}
91+
1692
// Property describes a single input parameter for a tool or prompt argument.
1793
type Property struct {
1894
Type string `json:"type"`

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