fix(serve): a paired device opens only folders the window already lists

internal/frontend/serve/hub.go

@@ -583,6 +583,10 @@ func (h *Hub) openRuntime(w http.ResponseWriter, r *http.Request) {
 		badBody(w)
 		return
 	}
+	if !hostReach(r) && !deviceMayOpenRoot(req.Root, h.knownRoots()) {
+		refuse(w, http.StatusNotFound, codeDeviceHostOnly, "a paired device cannot use this", nil)
+		return
+	}
 	rt, err := h.Open(r.Context(), req)
 	if err != nil {
 		// Every refusal Open produces carries its own status; what is left is

internal/frontend/serve/hub_device.go

@@ -0,0 +1,29 @@
+package serve
+
+import "path/filepath"
+
+// deviceMayOpenRoot reports whether a paired device may open a pane on root: the
+// default folder, or one the window already lists. A folder the device names
+// itself would point the agent at whatever directory this machine can read.
+func deviceMayOpenRoot(root string, known []string) bool {
+	if root == "" {
+		return true
+	}
+	want := filepath.Clean(root)
+	for _, k := range known {
+		if filepath.Clean(k) == want {
+			return true
+		}
+	}
+	return false
+}
+
+// knownRoots are the folders open as panes now and the project list the
+// sidebar remembers.
+func (h *Hub) knownRoots() []string {
+	roots := Workspaces()
+	for _, v := range h.List() {
+		roots = append(roots, v.Root)
+	}
+	return roots
+}

internal/frontend/serve/runtime_device_root_test.go

@@ -0,0 +1,59 @@
+package serve
+
+import (
+	"encoding/json"
+	"net/http"
+	"net/http/httptest"
+	"strings"
+	"testing"
+
+	"reasonix/internal/base/testenv"
+	"reasonix/internal/contract/config"
+	"reasonix/internal/session/control"
+)
+
+func TestADeviceOpensOnlyFoldersTheWindowAlreadyListsAsRuntimes(t *testing.T) {
+	t.Setenv("REASONIX_HOME", testenv.TempDir(t))
+	hub := NewHub(HubOptions{Serve: config.ServeConfig{AuthMode: "none"}})
+	defer hub.Shutdown()
+	bc := NewBroadcaster()
+	if _, err := hub.Adopt(New(control.New(control.Options{Sink: bc}), bc, config.ServeConfig{}), bc); err != nil {
+		t.Fatal(err)
+	}
+	before := len(hub.List())
+	elsewhere := testenv.TempDir(t)
+
+	reg := NewDeviceRegistry()
+	code, _ := reg.Offer()
+	cred, _, err := reg.Redeem(code, "phone")
+	if err != nil {
+		t.Fatal(err)
+	}
+	gate := NewDeviceGate(hub.Handler(), DeviceGateOptions{Registry: reg, Origin: "http://192.168.1.5:9000"})
+	req := httptest.NewRequest(http.MethodPost, "http://192.168.1.5:9000/runtimes", strings.NewReader(`{"root":`+quoteJSON(elsewhere)+`}`))
+	req.Header.Set("Origin", "http://192.168.1.5:9000")
+	req.Header.Set("Content-Type", "application/json")
+	req.AddCookie(&http.Cookie{Name: DeviceCookie, Value: cred})
+	rec := httptest.NewRecorder()
+	gate.ServeHTTP(rec, req)
+	if rec.Code != http.StatusNotFound || !strings.Contains(rec.Body.String(), codeDeviceHostOnly) {
+		t.Fatalf("a device opening an unlisted folder: %d %s, want 404 %s", rec.Code, rec.Body.String(), codeDeviceHostOnly)
+	}
+	if after := len(hub.List()); after != before {
+		t.Fatalf("a runtime was opened for the device: %d -> %d", before, after)
+	}
+}
+
+func TestDeviceMayOpenRootNamesOnlyKnownFolders(t *testing.T) {
+	known := []string{"/work/a", "/work/b"}
+	for root, want := range map[string]bool{"": true, "/work/a": true, "/work/a/": true, "/work/b/../b": true, "/work": false, "/etc": false, "/work/a/sub": false} {
+		if got := deviceMayOpenRoot(root, known); got != want {
+			t.Errorf("deviceMayOpenRoot(%q) = %v, want %v", root, got, want)
+		}
+	}
+}
+
+func quoteJSON(s string) string {
+	b, _ := json.Marshal(s)
+	return string(b)
+}