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ktms mcp: drain on shutdown, clean stop, lenient bearer scheme #111

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Merged
coyl merged 1 commit into from
Oct 24, 2026
Merged

ktms mcp: drain on shutdown, clean stop, lenient bearer scheme #111

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55 changes: 38 additions & 17 deletions cmd/ktms/mcp.go
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Original file line number Diff line number Diff line change
Expand Up @@ -60,6 +60,23 @@ KTMS_MCP_TOKEN or --mcp-token-file. The server speaks plain HTTP: keep it on
localhost, or put a TLS proxy in front of it.`,
Args: cobra.NoArgs,
RunE: func(cmd *cobra.Command, _ []string) error {
var token string
if listen == "" {
if cmd.Flags().Changed("mcp-token-file") {
return usageError{errors.New("--mcp-token-file is for --listen; stdio needs no token")}
}
} else {
token = os.Getenv("KTMS_MCP_TOKEN")
if tokenFile != "" {
var err error
if token, err = readKeyFile(tokenFile); err != nil {
return err
}
}
if len(token) < 16 {
return usageError{errors.New("--listen needs a bearer token of 16 characters or more in KTMS_MCP_TOKEN or --mcp-token-file")}
}
}
// One connection for the server's life: the key is read once, and tool
// calls neither dial nor ask the keychain again.
c, closeConn, err := a.t.admin()
Expand All @@ -71,20 +88,14 @@ localhost, or put a TLS proxy in front of it.`,
srv := a.mcpServer(allowWrite)
ctx, stop := signal.NotifyContext(context.Background(), os.Interrupt, syscall.SIGTERM)
defer stop()
if listen == "" {
return srv.Run(ctx, &mcp.StdioTransport{})
if listen != "" {
return a.serveMCP(ctx, srv, listen, token)
}
token := os.Getenv("KTMS_MCP_TOKEN")
if tokenFile != "" {
var err error
if token, err = readKeyFile(tokenFile); err != nil {
return err
}
}
if len(token) < 16 {
return usageError{errors.New("--listen needs a bearer token of 16 characters or more in KTMS_MCP_TOKEN or --mcp-token-file")}
// A signal is how hosts stop a stdio server: a clean exit, not an error.
if err := srv.Run(ctx, &mcp.StdioTransport{}); err != nil && ctx.Err() == nil {
return err
}
return a.serveMCP(ctx, srv, listen, token)
return nil
},
}
cmd.Flags().BoolVar(&allowWrite, "allow-write", false, "offer the tools that change Keystone")
Expand All @@ -93,16 +104,16 @@ localhost, or put a TLS proxy in front of it.`,
return cmd
}

// serveMCP serves streamable HTTP until ctx ends.
// serveMCP serves streamable HTTP until ctx ends, then lets running calls
// finish before it returns and the caller closes the connection they use.
func (a *app) serveMCP(ctx context.Context, srv *mcp.Server, listen, token string) error {
if !loopback(listen) {
fmt.Fprintf(a.stderr, "ktms: warning: MCP on %s is plain HTTP; put a TLS proxy in front of it\n", listen)
}
h := mcp.NewStreamableHTTPHandler(func(*http.Request) *mcp.Server { return srv }, &mcp.StreamableHTTPOptions{SessionTimeout: 30 * time.Minute})
want := []byte("Bearer " + token)
mux := http.NewServeMux()
mux.Handle("/mcp", http.NewCrossOriginProtection().Handler(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
if subtle.ConstantTimeCompare([]byte(r.Header.Get("Authorization")), want) != 1 {
if !bearerOK(r.Header.Get("Authorization"), token) {
w.Header().Set("WWW-Authenticate", "Bearer")
http.Error(w, "unauthorized", http.StatusUnauthorized)
return
Expand All @@ -115,16 +126,26 @@ func (a *app) serveMCP(ctx context.Context, srv *mcp.Server, listen, token strin
}
hs := &http.Server{Handler: mux, ReadHeaderTimeout: 10 * time.Second}
fmt.Fprintf(a.stderr, "ktms: MCP on http://%s/mcp\n", lis.Addr())
drained := make(chan error, 1)
go func() {
<-ctx.Done()
sctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
defer cancel()
_ = hs.Shutdown(sctx)
drained <- hs.Shutdown(sctx)
}()
if err := hs.Serve(lis); !errors.Is(err, http.ErrServerClosed) {
return err
}
return nil
return <-drained
}

// bearerOK checks an Authorization header; the scheme is case-insensitive.
func bearerOK(header, token string) bool {
scheme, got, ok := strings.Cut(strings.TrimSpace(header), " ")
if !ok || !strings.EqualFold(scheme, "Bearer") {
return false
}
return subtle.ConstantTimeCompare([]byte(strings.TrimSpace(got)), []byte(token)) == 1
}

func (a *app) mcpServer(allowWrite bool) *mcp.Server {
Expand Down
12 changes: 10 additions & 2 deletions cmd/ktms/mcp_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -155,7 +155,7 @@ rules:
t.Fatalf("a refused plan claims partial steps: %s", out)
}

// A new key comes once, for the user.
// A new key comes once, for the user.
res, err := rw.CallTool(context.Background(), &mcp.CallToolParams{Name: "mint_key", Arguments: map[string]any{"name": "bot"}})
if err != nil || res.IsError {
t.Fatalf("mint_key: %v %+v", err, res)
Expand Down Expand Up @@ -287,9 +287,17 @@ func TestMCPOverHTTP(t *testing.T) {

func TestMCPNeedsAToken(t *testing.T) {
isolate(t)
t.Setenv("KTMS_ADMIN_KEY", "ktms_x")
t.Setenv("KTMS_MCP_TOKEN", "short")
// Checked before the admin key or any call to Keystone.
if code, _, errs := call("mcp", "--listen", "127.0.0.1:0"); code != exitUsage || !strings.Contains(errs, "bearer token") {
t.Fatalf("mcp --listen with a short token = %d %q", code, errs)
}
if code, _, _ := call("mcp", "--mcp-token-file", "x"); code != exitUsage {
t.Fatalf("--mcp-token-file without --listen = %d", code)
}
for h, ok := range map[string]bool{"Bearer abc": true, "bearer abc": true, " Bearer abc ": true, "Basic abc": false, "Bearer abd": false, "abc": false} {
if bearerOK(h, "abc") != ok {
t.Errorf("bearerOK(%q) = %v", h, !ok)
}
}
}
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