cloud_api_types: Add types for WebSocket protocol (#35753)

This PR adds types for the Cloud WebSocket protocol to the
`cloud_api_types` crate.

Release Notes:

- N/A

crates/cloud_api_types/Cargo.toml

@@ -12,7 +12,9 @@ workspace = true
 path = "src/cloud_api_types.rs"
 
 [dependencies]
+anyhow.workspace = true
 chrono.workspace = true
+ciborium.workspace = true
 cloud_llm_client.workspace = true
 serde.workspace = true
 workspace-hack.workspace = true

crates/cloud_api_types/src/cloud_api_types.rs

@@ -1,4 +1,5 @@
 mod timestamp;
+pub mod websocket_protocol;
 
 use serde::{Deserialize, Serialize};
 

crates/cloud_api_types/src/websocket_protocol.rs

@@ -0,0 +1,28 @@
+use anyhow::{Context as _, Result};
+use serde::{Deserialize, Serialize};
+
+/// The version of the Cloud WebSocket protocol.
+pub const PROTOCOL_VERSION: u32 = 0;
+
+/// The name of the header used to indicate the protocol version in use.
+pub const PROTOCOL_VERSION_HEADER_NAME: &str = "x-zed-protocol-version";
+
+/// A message from Cloud to the Zed client.
+#[derive(Serialize, Deserialize)]
+pub enum MessageToClient {
+    /// The user was updated and should be refreshed.
+    UserUpdated,
+}
+
+impl MessageToClient {
+    pub fn serialize(&self) -> Result<Vec<u8>> {
+        let mut buffer = Vec::new();
+        ciborium::into_writer(self, &mut buffer).context("failed to serialize message")?;
+
+        Ok(buffer)
+    }
+
+    pub fn deserialize(data: &[u8]) -> Result<Self> {
+        ciborium::from_reader(data).context("failed to deserialize message")
+    }
+}