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feat(cli): migrate exp mcp stdio server to official MCP Go SDK #28057

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Merged
ibetitsmike merged 1 commit into from
Aug 13, 2026
Merged

feat(cli): migrate exp mcp stdio server to official MCP Go SDK #28057

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75 changes: 22 additions & 53 deletions cli/exp_mcp.go
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Original file line number Diff line number Diff line change
@@ -1,10 +1,10 @@
package cli

import (
"bytes"
"context"
"encoding/json"
"errors"
"io"
"net/url"
"os"
"path/filepath"
Expand All @@ -13,8 +13,7 @@ import (
"sync"
"time"

"github.com/mark3labs/mcp-go/mcp"
"github.com/mark3labs/mcp-go/server"
"github.com/modelcontextprotocol/go-sdk/mcp"
"github.com/spf13/afero"
"golang.org/x/xerrors"

Expand All @@ -23,6 +22,7 @@ import (
"github.com/coder/coder/v2/buildinfo"
"github.com/coder/coder/v2/cli/cliui"
"github.com/coder/coder/v2/cli/cliutil"
coderdmcp "github.com/coder/coder/v2/coderd/mcp"
"github.com/coder/coder/v2/codersdk"
"github.com/coder/coder/v2/codersdk/agentsdk"
"github.com/coder/coder/v2/codersdk/toolsdk"
Expand Down Expand Up @@ -692,11 +692,12 @@ func (s *mcpServer) startServer(ctx context.Context, inv *serpent.Invocation, in
cliui.Infof(inv.Stderr, "Allowed Tools : %v", allowedTools)
}

mcpSrv := server.NewMCPServer(
"Coder Agent",
buildinfo.Version(),
server.WithInstructions(instructions),
)
mcpSrv := mcp.NewServer(&mcp.Implementation{
Name: "Coder Agent",
Version: buildinfo.Version(),
}, &mcp.ServerOptions{
Instructions: instructions,
})

// If neither the user client nor the agent socket is available, there
// are no tools we can enable.
Expand Down Expand Up @@ -751,14 +752,16 @@ func (s *mcpServer) startServer(ctx context.Context, inv *serpent.Invocation, in
continue
}

mcpSrv.AddTools(mcpFromSDK(tool, toolDeps))
coderdmcp.RegisterSDKTool(mcpSrv, tool, toolDeps)

@chatgpt-codex-connector chatgpt-codex-connector Bot Aug 13, 2026

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P2 Badge Preserve omitted arguments for no-argument tools

When an MCP client omits the optional arguments field while calling a zero-input tool such as coder_get_authenticated_user or coder_list_templates, RegisterSDKTool forwards the resulting nil json.RawMessage to toolsdk.Generic, whose json.Unmarshal fails with an unexpected end of input. The previous mcpFromSDK adapter encoded the nil arguments map as JSON null, which successfully decoded into NoArgs; normalize missing arguments to {} or null before invoking the shared handler.

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}

srv := server.NewStdioServer(mcpSrv)
done := make(chan error)
go func() {
defer close(done)
srvErr := srv.Listen(ctx, inv.Stdin, inv.Stdout)
srvErr := mcpSrv.Run(ctx, &mcp.IOTransport{
Reader: io.NopCloser(inv.Stdin),
Writer: nopWriteCloser{inv.Stdout},
})
done <- srvErr
}()

Expand All @@ -772,6 +775,14 @@ func (s *mcpServer) startServer(ctx context.Context, inv *serpent.Invocation, in
return nil
}

// nopWriteCloser adapts the invocation's stdout to the WriteCloser
// the SDK transport requires without closing the underlying stream.
type nopWriteCloser struct {
io.Writer
}

func (nopWriteCloser) Close() error { return nil }

type ClaudeConfig struct {
ConfigPath string
ProjectDirectory string
Expand Down Expand Up @@ -984,45 +995,3 @@ func indexOf(s, substr string) int {
}
return -1
}

// mcpFromSDK adapts a toolsdk.Tool to go-mcp's server.ServerTool.
// It assumes that the tool responds with a valid JSON object.
func mcpFromSDK(sdkTool toolsdk.GenericTool, tb toolsdk.Deps) server.ServerTool {
// NOTE: some clients will silently refuse to use tools if there is an issue
// with the tool's schema or configuration.
if sdkTool.Schema.Properties == nil {
panic("developer error: schema properties cannot be nil")
}
return server.ServerTool{
Tool: mcp.Tool{
Name: sdkTool.Tool.Name,
Description: sdkTool.Description,
InputSchema: mcp.ToolInputSchema{
Type: "object", // Default of mcp.NewTool()
Properties: sdkTool.Schema.Properties,
Required: sdkTool.Schema.Required,
},
Annotations: mcp.ToolAnnotation{
ReadOnlyHint: mcp.ToBoolPtr(sdkTool.MCPAnnotations.ReadOnlyHint),
DestructiveHint: mcp.ToBoolPtr(sdkTool.MCPAnnotations.DestructiveHint),
IdempotentHint: mcp.ToBoolPtr(sdkTool.MCPAnnotations.IdempotentHint),
OpenWorldHint: mcp.ToBoolPtr(sdkTool.MCPAnnotations.OpenWorldHint),
},
},
Handler: func(ctx context.Context, request mcp.CallToolRequest) (*mcp.CallToolResult, error) {
var buf bytes.Buffer
if err := json.NewEncoder(&buf).Encode(request.Params.Arguments); err != nil {
return nil, xerrors.Errorf("failed to encode request arguments: %w", err)
}
result, err := sdkTool.Handler(ctx, tb, buf.Bytes())
if err != nil {
return nil, err
}
return &mcp.CallToolResult{
Content: []mcp.Content{
mcp.NewTextContent(string(result)),
},
}, nil
},
}
}
14 changes: 10 additions & 4 deletions cli/exp_mcp_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -63,6 +63,12 @@ func TestExpMcpServer(t *testing.T) {
assert.NoError(t, err)
}()

// The SDK server enforces the MCP lifecycle, so complete the
// initialize handshake before listing tools.
stdin.WriteLine(`{"jsonrpc":"2.0","id":1,"method":"initialize","params":{"protocolVersion":"2025-06-18","capabilities":{},"clientInfo":{"name":"test","version":"1.0"}}}`)
_ = stdout.ReadLine(ctx)
stdin.WriteLine(`{"jsonrpc":"2.0","method":"notifications/initialized"}`)

// When: we send a tools/list request
toolsPayload := `{"jsonrpc":"2.0","id":2,"method":"tools/list"}`
stdin.WriteLine(toolsPayload)
Expand Down Expand Up @@ -140,7 +146,7 @@ func TestExpMcpServer(t *testing.T) {
assert.NoError(t, err)
}()

payload := `{"jsonrpc":"2.0","id":1,"method":"initialize"}`
payload := `{"jsonrpc":"2.0","id":1,"method":"initialize","params":{"protocolVersion":"2025-06-18","capabilities":{},"clientInfo":{"name":"test","version":"1.0"}}}`
stdin.WriteLine(payload)
output := stdout.ReadLine(ctx)
cancel()
Expand Down Expand Up @@ -588,7 +594,7 @@ func TestExpMcpServerOptionalUserToken(t *testing.T) {
}()

// Verify server starts by checking for a successful initialization
payload := `{"jsonrpc":"2.0","id":1,"method":"initialize"}`
payload := `{"jsonrpc":"2.0","id":1,"method":"initialize","params":{"protocolVersion":"2025-06-18","capabilities":{},"clientInfo":{"name":"test","version":"1.0"}}}`
stdin.WriteLine(payload)
output := stdout.ReadLine(ctx)

Expand Down Expand Up @@ -1005,7 +1011,7 @@ func TestExpMcpReporter(t *testing.T) {
}()

// Initialize.
payload := `{"jsonrpc":"2.0","id":1,"method":"initialize"}`
payload := `{"jsonrpc":"2.0","id":1,"method":"initialize","params":{"protocolVersion":"2025-06-18","capabilities":{},"clientInfo":{"name":"test","version":"1.0"}}}`

@chatgpt-codex-connector chatgpt-codex-connector Bot Aug 13, 2026

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P1 Badge Send initialized before reporter tool calls

The official SDK enforces the MCP initialization lifecycle, but both reporter test paths send tools/call immediately after reading the initialize response without sending notifications/initialized. In TestExpMcpReporter, the SDK can reject the call instead of invoking coder_report_task, causing the subsequent wait on the report channel to time out; send the notification here and in the Reconnect path, as the earlier server tests already do.

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stdin.WriteLine(payload)
_ = stdout.ReadLine(ctx) // ignore init response

Expand Down Expand Up @@ -1112,7 +1118,7 @@ func TestExpMcpReporter(t *testing.T) {
clitest.Start(t, inv)

// Initialize.
payload := `{"jsonrpc":"2.0","id":1,"method":"initialize"}`
payload := `{"jsonrpc":"2.0","id":1,"method":"initialize","params":{"protocolVersion":"2025-06-18","capabilities":{},"clientInfo":{"name":"test","version":"1.0"}}}`
stdin.WriteLine(payload)
_ = stdout.ReadLine(ctx) // ignore init response

Expand Down
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