constellation: Re-split structured data types into separate files (#36615)

In #36364 I moved both serializable and transferable implementations
from the `script_traits` crate into a single file called
`message_ports.rs`. Gregory raised the point that this was a bit of a
inaccurate grouping. This change attempts to fix it according to the
division in the specification.

See [the relevant thread on zulip][thread].

[thread]:
https://servo.zulipchat.com/#narrow/channel/263398-general/topic/Organizing.20*_traits.20crates/near/510864104.

Testing: Covered by existing test as this is just code movement.

Signed-off-by: Martin Robinson <mrobinson@igalia.com>

components/shared/constellation/structured_data/transferable.rs

@@ -0,0 +1,172 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
+
+//! This module contains implementations in script that are transferable as per
+//! <https://html.spec.whatwg.org/multipage/#transferable-objects>. The implementations are here
+//! instead of in script as they need to be passed through the Constellation.
+
+use std::collections::VecDeque;
+
+use base::id::MessagePortId;
+use malloc_size_of_derive::MallocSizeOf;
+use serde::{Deserialize, Serialize};
+use strum::EnumIter;
+
+use crate::PortMessageTask;
+
+/// All the DOM interfaces that can be transferred.
+#[derive(Clone, Copy, Debug, EnumIter)]
+pub enum Transferrable {
+    /// The `MessagePort` interface.
+    MessagePort,
+    /// The `ReadableStream` interface.
+    ReadableStream,
+    /// The `WritableStream` interface.
+    WritableStream,
+}
+
+#[derive(Debug, Deserialize, MallocSizeOf, Serialize)]
+enum MessagePortState {
+    /// <https://html.spec.whatwg.org/multipage/#detached>
+    Detached,
+    /// <https://html.spec.whatwg.org/multipage/#port-message-queue>
+    /// The message-queue of this port is enabled,
+    /// the boolean represents awaiting completion of a transfer.
+    Enabled(bool),
+    /// <https://html.spec.whatwg.org/multipage/#port-message-queue>
+    /// The message-queue of this port is disabled,
+    /// the boolean represents awaiting completion of a transfer.
+    Disabled(bool),
+}
+
+#[derive(Debug, Deserialize, MallocSizeOf, Serialize)]
+/// The data and logic backing the DOM managed MessagePort.
+pub struct MessagePortImpl {
+    /// The current state of the port.
+    state: MessagePortState,
+
+    /// <https://html.spec.whatwg.org/multipage/#entangle>
+    entangled_port: Option<MessagePortId>,
+
+    /// <https://html.spec.whatwg.org/multipage/#port-message-queue>
+    message_buffer: Option<VecDeque<PortMessageTask>>,
+
+    /// The UUID of this port.
+    message_port_id: MessagePortId,
+}
+
+impl MessagePortImpl {
+    /// Create a new messageport impl.
+    pub fn new(port_id: MessagePortId) -> MessagePortImpl {
+        MessagePortImpl {
+            state: MessagePortState::Disabled(false),
+            entangled_port: None,
+            message_buffer: None,
+            message_port_id: port_id,
+        }
+    }
+
+    /// Get the Id.
+    pub fn message_port_id(&self) -> &MessagePortId {
+        &self.message_port_id
+    }
+
+    /// Maybe get the Id of the entangled port.
+    pub fn entangled_port_id(&self) -> Option<MessagePortId> {
+        self.entangled_port
+    }
+
+    /// Entanged this port with another.
+    pub fn entangle(&mut self, other_id: MessagePortId) {
+        self.entangled_port = Some(other_id);
+    }
+
+    /// Is this port enabled?
+    pub fn enabled(&self) -> bool {
+        matches!(self.state, MessagePortState::Enabled(_))
+    }
+
+    /// Mark this port as having been shipped.
+    /// <https://html.spec.whatwg.org/multipage/#has-been-shipped>
+    pub fn set_has_been_shipped(&mut self) {
+        match self.state {
+            MessagePortState::Detached => {
+                panic!("Messageport set_has_been_shipped called in detached state")
+            },
+            MessagePortState::Enabled(_) => self.state = MessagePortState::Enabled(true),
+            MessagePortState::Disabled(_) => self.state = MessagePortState::Disabled(true),
+        }
+    }
+
+    /// Handle the completion of the transfer,
+    /// this is data received from the constellation.
+    pub fn complete_transfer(&mut self, mut tasks: VecDeque<PortMessageTask>) {
+        match self.state {
+            MessagePortState::Detached => return,
+            MessagePortState::Enabled(_) => self.state = MessagePortState::Enabled(false),
+            MessagePortState::Disabled(_) => self.state = MessagePortState::Disabled(false),
+        }
+
+        // Note: these are the tasks that were buffered while the transfer was ongoing,
+        // hence they need to execute first.
+        // The global will call `start` if we are enabled,
+        // which will add tasks on the event-loop to dispatch incoming messages.
+        match self.message_buffer {
+            Some(ref mut incoming_buffer) => {
+                while let Some(task) = tasks.pop_back() {
+                    incoming_buffer.push_front(task);
+                }
+            },
+            None => self.message_buffer = Some(tasks),
+        }
+    }
+
+    /// A message was received from our entangled port,
+    /// returns an optional task to be dispatched.
+    pub fn handle_incoming(&mut self, task: PortMessageTask) -> Option<PortMessageTask> {
+        let should_dispatch = match self.state {
+            MessagePortState::Detached => return None,
+            MessagePortState::Enabled(in_transfer) => !in_transfer,
+            MessagePortState::Disabled(_) => false,
+        };
+
+        if should_dispatch {
+            Some(task)
+        } else {
+            match self.message_buffer {
+                Some(ref mut buffer) => {
+                    buffer.push_back(task);
+                },
+                None => {
+                    let mut queue = VecDeque::new();
+                    queue.push_back(task);
+                    self.message_buffer = Some(queue);
+                },
+            }
+            None
+        }
+    }
+
+    /// <https://html.spec.whatwg.org/multipage/#dom-messageport-start>
+    /// returns an optional queue of tasks that were buffered while the port was disabled.
+    pub fn start(&mut self) -> Option<VecDeque<PortMessageTask>> {
+        match self.state {
+            MessagePortState::Detached => return None,
+            MessagePortState::Enabled(_) => {},
+            MessagePortState::Disabled(in_transfer) => {
+                self.state = MessagePortState::Enabled(in_transfer);
+            },
+        }
+        if let MessagePortState::Enabled(true) = self.state {
+            return None;
+        }
+        self.message_buffer.take()
+    }
+
+    /// <https://html.spec.whatwg.org/multipage/#dom-messageport-close>
+    pub fn close(&mut self) {
+        // Step 1
+        self.state = MessagePortState::Detached;
+    }
+}