[Nearby] Support user cancellation before a connection is established

Previously, a user cancellation of an outgoing share from a Chromebook
would have no effect if a connection with the receiving device was
not already established. (The connection is established in roughly
a 3-second window after the share target is selected.) So, an immediate
cancellation previously had no effect, and the transfer proceeded.

In this CL, we support cancellation before a connection is established.
We also bring the Chrome OS cancellation method more in line with the
GmsCore implementation. Notably, we report a cancellation before
disconnecting to provide a more accurate transfer update status of
"cancelled" instead of "failed".

Manually verified cancellation in the following scenarios:
 * sending to and receiving from a phone;
 * cancelling on both the phone and Chromebook;
 * cancelling before a connection was established, after a connection
   was established, and during a payload transfer.

One scenario--cancelling a Chromebook-to-phone share from the phone
while the payload transfer was in progress--resulted in a failure
notification on the Chromebook instead of a cancellation notification.
This seems unrelated to this CL, and it is being tracked in
crbug/1155412.

Fixed: 1154926
Change-Id: I5ac141904af2fc614256b3c14e2ba3a99a984556
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2573884
Auto-Submit: Josh Nohle <nohle@chromium.org>
Commit-Queue: James Vecore <vecore@google.com>
Reviewed-by: James Vecore <vecore@google.com>
Cr-Commit-Position: refs/heads/master@{#833627}

chrome/browser/nearby_sharing/nearby_sharing_service_impl.cc

@@ -767,7 +767,7 @@ void NearbySharingServiceImpl::DoCancel(
     bool write_cancel_frame) {
   ShareTargetInfo* info = GetShareTargetInfo(share_target);
 
-  if (!info || !info->connection() || !info->endpoint_id()) {
+  if (!info || !info->endpoint_id()) {
     NS_LOG(ERROR) << __func__
                   << ": Cancel invoked for unknown share target, returning "
                      "kOutOfOrderApiCall";
@@ -777,20 +777,10 @@ void NearbySharingServiceImpl::DoCancel(
     return;
   }
 
-  base::SequencedTaskRunnerHandle::Get()->PostDelayedTask(
-      FROM_HERE,
-      base::BindOnce(&NearbySharingServiceImpl::CloseConnection,
-                     weak_ptr_factory_.GetWeakPtr(), share_target),
-      kIncomingCancelDelay);
-
-  info->connection()->SetDisconnectionListener(
-      base::BindOnce(&NearbySharingServiceImpl::UnregisterShareTarget,
-                     weak_ptr_factory_.GetWeakPtr(), share_target));
-
-  if (write_cancel_frame) {
-    WriteCancel(*info->connection());
-  }
-
+  // We immediately inform the user that the transfer has been cancelled because
+  // subsequent disconnections might be interpreted as failure. The
+  // TransferUpdateDecorator will ignore subsequent statuses in favor of this
+  // cancelled status.
   if (info->transfer_update_callback()) {
     info->transfer_update_callback()->OnTransferUpdate(
         share_target, TransferMetadataBuilder()
@@ -798,6 +788,36 @@ void NearbySharingServiceImpl::DoCancel(
                           .build());
   }
 
+  // Before disconnecting, cancel all ongoing payloads.
+  for (int64_t attachment_id : share_target.GetAttachmentIds()) {
+    base::Optional<int64_t> payload_id = GetAttachmentPayloadId(attachment_id);
+    if (payload_id) {
+      nearby_connections_manager_->Cancel(*payload_id);
+    }
+  }
+
+  // If a connection exists, close the connection. Otherwise disconnect from
+  // endpoint id directly. Note: A share attempt can be cancelled by the user
+  // before a connection is fully established, so info->connection() might be
+  // null.
+  if (info->connection()) {
+    info->connection()->SetDisconnectionListener(
+        base::BindOnce(&NearbySharingServiceImpl::UnregisterShareTarget,
+                       weak_ptr_factory_.GetWeakPtr(), share_target));
+
+    base::SequencedTaskRunnerHandle::Get()->PostDelayedTask(
+        FROM_HERE,
+        base::BindOnce(&NearbySharingServiceImpl::CloseConnection,
+                       weak_ptr_factory_.GetWeakPtr(), share_target),
+        kIncomingCancelDelay);
+
+    if (write_cancel_frame) {
+      WriteCancel(*info->connection());
+    }
+  } else {
+    nearby_connections_manager_->Disconnect(*info->endpoint_id());
+  }
+
   std::move(status_codes_callback).Run(StatusCodes::kOk);
 }