SelectionOwner: add support for TIMESTAMP target

ui/base/x/selection_owner.cc

 // Copyright (c) 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ui/base/x/selection_owner.h"
 
 #include <algorithm>
 #include <X11/Xlib.h>
 #include <X11/Xatom.h>
 
 #include "base/logging.h"
 #include "ui/base/x/selection_utils.h"
 #include "ui/base/x/x11_foreign_window_manager.h"
 #include "ui/base/x/x11_util.h"
 
 namespace ui {
 
 namespace {
 
 const char kAtomPair[] = "ATOM_PAIR";
 const char kIncr[] = "INCR";
 const char kMultiple[] = "MULTIPLE";
 const char kSaveTargets[] = "SAVE_TARGETS";
 const char kTargets[] = "TARGETS";
+const char kTimestamp[] = "TIMESTAMP";
 
-const char* kAtomsToCache[] = {
-  kAtomPair,
-  kIncr,
-  kMultiple,
-  kSaveTargets,
-  kTargets,
-  NULL
-};
+// Used in conjunction with GetCurrentTimeFromX.
+const char kDummyTimestampProperty[] = "CHROMIUM_TIMESTAMP_PROPERTY";
+
+const char* kAtomsToCache[] = {kAtomPair,
+                               kIncr,
+                               kMultiple,
+                               kSaveTargets,
+                               kTargets,
+                               kTimestamp,
+                               kDummyTimestampProperty,
+                               NULL};
 
 // The period of |incremental_transfer_abort_timer_|. Arbitrary but must be <=
 // than kIncrementalTransferTimeoutMs.
 const int kTimerPeriodMs = 1000;
 
 // The amount of time to wait for the selection requestor to process the data
 // sent by the selection owner before aborting an incremental data transfer.
 const int kIncrementalTransferTimeoutMs = 10000;
 
 static_assert(kTimerPeriodMs <= kIncrementalTransferTimeoutMs,
               "timer period must be <= transfer timeout");
 
 // Returns a conservative max size of the data we can pass into
 // XChangeProperty(). Copied from GTK.
 size_t GetMaxRequestSize(XDisplay* display) {
   long extended_max_size = XExtendedMaxRequestSize(display);
   long max_size =
       (extended_max_size ? extended_max_size : XMaxRequestSize(display)) - 100;
   return std::min(static_cast<long>(0x40000),
                   std::max(static_cast<long>(0), max_size));
 }
 
+// Get the value of CurrentTime from X. There's no easy way to do this, so like
+// GTK, we do this by triggering a spurious property change and inspecting the
+// resulting event.
+Time GetCurrentTimeFromX(XDisplay* display, XID window, XAtom property) {
+  unsigned char c = 0;
+  XChangeProperty(display, window, property, property, 8, PropModeReplace, &c,
+                  1);
+  struct ArgData {
+    // Target window and atom to wait for.
+    XID window;
+    XAtom atom;
+  } args = {window, property};
+  auto predicate = [](XDisplay* display, XEvent* event, XPointer arg) -> Bool {
+    ArgData* data = reinterpret_cast<ArgData*>(arg);
+    return (event->type == PropertyNotify &&
+            event->xproperty.window == data->window &&
+            event->xproperty.atom == data->atom)
+               ? True
+               : False;
+
+  };
+  XEvent event;
+  XIfEvent(display, &event, +predicate, reinterpret_cast<XPointer>(&args));

[Elliot Glaysher, 2016/04/15 21:45:31]

"+" predicate? I assume the unary plus is some sort of cast?

[dcheng, 2016/04/15 21:53:47]

I was forcing a decay to function pointer, but it turns out that it's not
necessary.

+  return event.xproperty.time;
+}
+
 // Gets the value of an atom pair array property. On success, true is returned
 // and the value is stored in |value|.
 bool GetAtomPairArrayProperty(XID window,
                               XAtom property,
                               std::vector<std::pair<XAtom,XAtom> >* value) {
   XAtom type = None;
   int format = 0;  // size in bits of each item in 'property'
   unsigned long num_items = 0;
   unsigned char* properties = NULL;
   unsigned long remaining_bytes = 0;
@@ skipping 49 matching lines @@
 
 void SelectionOwner::RetrieveTargets(std::vector<XAtom>* targets) {
   for (SelectionFormatMap::const_iterator it = format_map_.begin();
        it != format_map_.end(); ++it) {
     targets->push_back(it->first);
   }
 }
 
 void SelectionOwner::TakeOwnershipOfSelection(
     const SelectionFormatMap& data) {
-  XSetSelectionOwner(x_display_, selection_name_, x_window_, CurrentTime);
+  // Note that we don't just use CurrentTime, since we need to return an actual
+  // timestamp for the TIMESTAMP target later.
+  acquired_selection_timestamp_ = GetCurrentTimeFromX(
+      x_display_, x_window_, atom_cache_.GetAtom(kDummyTimestampProperty));
+  XSetSelectionOwner(x_display_, selection_name_, x_window_,
+                     acquired_selection_timestamp_);
 
   if (XGetSelectionOwner(x_display_, selection_name_) == x_window_) {
     // The X server agrees that we are the selection owner. Commit our data.
     format_map_ = data;
   }
 }
 
 void SelectionOwner::ClearSelectionOwner() {
   XSetSelectionOwner(x_display_, selection_name_, None, CurrentTime);
   format_map_ = SelectionFormatMap();
@@ skipping 76 matching lines @@
   if (!it->data.get())
     CompleteIncrementalTransfer(it);
 }
 
 bool SelectionOwner::ProcessTarget(XAtom target,
                                    XID requestor,
                                    XAtom property) {
   XAtom multiple_atom = atom_cache_.GetAtom(kMultiple);
   XAtom save_targets_atom = atom_cache_.GetAtom(kSaveTargets);
   XAtom targets_atom = atom_cache_.GetAtom(kTargets);
+  XAtom timestamp_atom = atom_cache_.GetAtom(kTimestamp);
 
   if (target == multiple_atom || target == save_targets_atom)
     return false;
 
-  if (target == targets_atom) {
+  if (target == timestamp_atom) {
+    XChangeProperty(
+        x_display_, requestor, property, XA_INTEGER, 32, PropModeReplace,
+        reinterpret_cast<unsigned char*>(&acquired_selection_timestamp_), 1);
+    return true;
+  } else if (target == targets_atom) {
     // We have been asked for TARGETS. Send an atom array back with the data
     // types we support.
     std::vector<XAtom> targets;
+    targets.push_back(timestamp_atom);
     targets.push_back(targets_atom);
     targets.push_back(save_targets_atom);
     targets.push_back(multiple_atom);
     RetrieveTargets(&targets);
 
     XChangeProperty(x_display_, requestor, property, XA_ATOM, 32,
                     PropModeReplace,
                     reinterpret_cast<unsigned char*>(&targets.front()),
                     targets.size());
     return true;
@@ skipping 136 matching lines @@
       foreign_window_manager_id(foreign_window_manager_id) {
 }
 
 SelectionOwner::IncrementalTransfer::IncrementalTransfer(
     const IncrementalTransfer& other) = default;
 
 SelectionOwner::IncrementalTransfer::~IncrementalTransfer() {
 }
 
 }  // namespace ui