Auto merge of #12309 - szeged:descriptor-functions, r=jdm

Add missing steps to descriptors writeValue function

<!-- Please describe your changes on the following line: -->
Add two missing steps to characteristic's writeValue function. https://webbluetoothcg.github.io/web-bluetooth/#dom-bluetoothremotegattdescriptor-writevalue (Step 4 and 5)
<!-- Thank you for contributing to Servo! Please replace each `[ ]` by `[X]` when the step is complete, and replace `__` with appropriate data: -->
- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [X] These changes do not require tests, because there is no Web Bluetooth test API implementation yet.

<!-- Pull requests that do not address these steps are welcome, but they will require additional verification as part of the review process. -->

<!-- Reviewable:start -->
---
This change is [<img src="https://reviewable.io/review_button.svg" height="35" align="absmiddle" alt="Reviewable"/>](https://reviewable.io/reviews/servo/servo/12309)
<!-- Reviewable:end -->

2 files changed, 9 insertions, 3 deletions

diff --git a/components/script/dom/bluetoothremotegattcharacteristic.rs b/components/script/dom/bluetoothremotegattcharacteristic.rs
index ebdd59ca689..0fc9d7a41f2 100644
--- a/components/script/dom/bluetoothremotegattcharacteristic.rs
+++ b/components/script/dom/bluetoothremotegattcharacteristic.rs
@@ -27,7 +27,7 @@ use net_traits::bluetooth_thread::BluetoothMethodMsg;
 
 // Maximum length of an attribute value.
 // https://www.bluetooth.org/DocMan/handlers/DownloadDoc.ashx?doc_id=286439 (Vol. 3, page 2169)
-const MAXIMUM_ATTRIBUTE_LENGTH: usize = 512;
+pub const MAXIMUM_ATTRIBUTE_LENGTH: usize = 512;
 
 // https://webbluetoothcg.github.io/web-bluetooth/#bluetoothremotegattcharacteristic
 #[dom_struct]
diff --git a/components/script/dom/bluetoothremotegattdescriptor.rs b/components/script/dom/bluetoothremotegattdescriptor.rs
index d2c1de65cb3..035233b01f7 100644
--- a/components/script/dom/bluetoothremotegattdescriptor.rs
+++ b/components/script/dom/bluetoothremotegattdescriptor.rs
@@ -11,13 +11,13 @@ use dom::bindings::codegen::Bindings::BluetoothRemoteGATTDescriptorBinding;
 use dom::bindings::codegen::Bindings::BluetoothRemoteGATTDescriptorBinding::BluetoothRemoteGATTDescriptorMethods;
 use dom::bindings::codegen::Bindings::BluetoothRemoteGATTServerBinding::BluetoothRemoteGATTServerMethods;
 use dom::bindings::codegen::Bindings::BluetoothRemoteGATTServiceBinding::BluetoothRemoteGATTServiceMethods;
-use dom::bindings::error::Error::{Network, Security, Type};
+use dom::bindings::error::Error::{InvalidModification, Network, Security, Type};
 use dom::bindings::error::{Fallible, ErrorResult};
 use dom::bindings::global::GlobalRef;
 use dom::bindings::js::{JS, MutHeap, Root};
 use dom::bindings::reflector::{Reflectable, Reflector, reflect_dom_object};
 use dom::bindings::str::{ByteString, DOMString};
-use dom::bluetoothremotegattcharacteristic::BluetoothRemoteGATTCharacteristic;
+use dom::bluetoothremotegattcharacteristic::{BluetoothRemoteGATTCharacteristic, MAXIMUM_ATTRIBUTE_LENGTH};
 use ipc_channel::ipc::{self, IpcSender};
 use net_traits::bluetooth_thread::BluetoothMethodMsg;
 
@@ -113,6 +113,12 @@ impl BluetoothRemoteGATTDescriptorMethods for BluetoothRemoteGATTDescriptor {
         if uuid_is_blacklisted(self.uuid.as_ref(), Blacklist::Writes) {
             return Err(Security)
         }
+        if value.len() > MAXIMUM_ATTRIBUTE_LENGTH {
+            return Err(InvalidModification)
+        }
+        if !self.Characteristic().Service().Device().Gatt().Connected() {
+            return Err(Network)
+        }
         let (sender, receiver) = ipc::channel().unwrap();
         self.get_bluetooth_thread().send(
             BluetoothMethodMsg::WriteValue(self.get_instance_id(), value, sender)).unwrap();