From 3422eb65e81394329385a44223638fed5ea23f2a Mon Sep 17 00:00:00 2001
From: Max Brunsfeld <maxbrunsfeld@gmail.com>
Date: Thu, 7 Sep 2023 11:16:51 -0700
Subject: [PATCH] Restore channel chat model and panel view

---
 Cargo.lock                                |   1 +
 crates/channel/src/channel.rs             |   9 +-
 crates/channel/src/channel_buffer.rs      |  14 +-
 crates/channel/src/channel_chat.rs        | 459 ++++++++++++++++++++++
 crates/channel/src/channel_store.rs       |  88 +++--
 crates/channel/src/channel_store_tests.rs | 220 ++++++++++-
 crates/collab/src/tests/test_server.rs    |   2 +-
 crates/collab_ui/Cargo.toml               |   1 +
 crates/collab_ui/src/channel_view.rs      |  11 +-
 crates/collab_ui/src/chat_panel.rs        | 391 ++++++++++++++++++
 crates/collab_ui/src/collab_ui.rs         |   1 +
 crates/rpc/proto/zed.proto                |  57 ++-
 crates/rpc/src/proto.rs                   |  12 +
 crates/theme/src/theme.rs                 |  12 +
 14 files changed, 1227 insertions(+), 51 deletions(-)
 create mode 100644 crates/channel/src/channel_chat.rs
 create mode 100644 crates/collab_ui/src/chat_panel.rs

diff --git a/Cargo.lock b/Cargo.lock
index 121e9a28dd..6b25b47b75 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -1553,6 +1553,7 @@ dependencies = [
  "settings",
  "theme",
  "theme_selector",
+ "time 0.3.27",
  "util",
  "vcs_menu",
  "workspace",
diff --git a/crates/channel/src/channel.rs b/crates/channel/src/channel.rs
index 15631b7dd3..b4acc0c25f 100644
--- a/crates/channel/src/channel.rs
+++ b/crates/channel/src/channel.rs
@@ -1,10 +1,13 @@
+mod channel_buffer;
+mod channel_chat;
 mod channel_store;
 
-pub mod channel_buffer;
-use std::sync::Arc;
+pub use channel_buffer::{ChannelBuffer, ChannelBufferEvent};
+pub use channel_chat::{ChannelChat, ChannelChatEvent, ChannelMessage, ChannelMessageId};
+pub use channel_store::{Channel, ChannelEvent, ChannelId, ChannelMembership, ChannelStore};
 
-pub use channel_store::*;
 use client::Client;
+use std::sync::Arc;
 
 #[cfg(test)]
 mod channel_store_tests;
diff --git a/crates/channel/src/channel_buffer.rs b/crates/channel/src/channel_buffer.rs
index e11282cf79..06f9093fb5 100644
--- a/crates/channel/src/channel_buffer.rs
+++ b/crates/channel/src/channel_buffer.rs
@@ -23,13 +23,13 @@ pub struct ChannelBuffer {
     subscription: Option<client::Subscription>,
 }
 
-pub enum Event {
+pub enum ChannelBufferEvent {
     CollaboratorsChanged,
     Disconnected,
 }
 
 impl Entity for ChannelBuffer {
-    type Event = Event;
+    type Event = ChannelBufferEvent;
 
     fn release(&mut self, _: &mut AppContext) {
         if self.connected {
@@ -101,7 +101,7 @@ impl ChannelBuffer {
             }
         }
         self.collaborators = collaborators;
-        cx.emit(Event::CollaboratorsChanged);
+        cx.emit(ChannelBufferEvent::CollaboratorsChanged);
         cx.notify();
     }
 
@@ -141,7 +141,7 @@ impl ChannelBuffer {
 
         this.update(&mut cx, |this, cx| {
             this.collaborators.push(collaborator);
-            cx.emit(Event::CollaboratorsChanged);
+            cx.emit(ChannelBufferEvent::CollaboratorsChanged);
             cx.notify();
         });
 
@@ -165,7 +165,7 @@ impl ChannelBuffer {
                     true
                 }
             });
-            cx.emit(Event::CollaboratorsChanged);
+            cx.emit(ChannelBufferEvent::CollaboratorsChanged);
             cx.notify();
         });
 
@@ -185,7 +185,7 @@ impl ChannelBuffer {
                     break;
                 }
             }
-            cx.emit(Event::CollaboratorsChanged);
+            cx.emit(ChannelBufferEvent::CollaboratorsChanged);
             cx.notify();
         });
 
@@ -230,7 +230,7 @@ impl ChannelBuffer {
         if self.connected {
             self.connected = false;
             self.subscription.take();
-            cx.emit(Event::Disconnected);
+            cx.emit(ChannelBufferEvent::Disconnected);
             cx.notify()
         }
     }
diff --git a/crates/channel/src/channel_chat.rs b/crates/channel/src/channel_chat.rs
new file mode 100644
index 0000000000..ebe491e5b8
--- /dev/null
+++ b/crates/channel/src/channel_chat.rs
@@ -0,0 +1,459 @@
+use crate::Channel;
+use anyhow::{anyhow, Result};
+use client::{
+    proto,
+    user::{User, UserStore},
+    Client, Subscription, TypedEnvelope,
+};
+use futures::lock::Mutex;
+use gpui::{AppContext, AsyncAppContext, Entity, ModelContext, ModelHandle, Task};
+use rand::prelude::*;
+use std::{collections::HashSet, mem, ops::Range, sync::Arc};
+use sum_tree::{Bias, SumTree};
+use time::OffsetDateTime;
+use util::{post_inc, ResultExt as _, TryFutureExt};
+
+pub struct ChannelChat {
+    channel: Arc<Channel>,
+    messages: SumTree<ChannelMessage>,
+    loaded_all_messages: bool,
+    next_pending_message_id: usize,
+    user_store: ModelHandle<UserStore>,
+    rpc: Arc<Client>,
+    outgoing_messages_lock: Arc<Mutex<()>>,
+    rng: StdRng,
+    _subscription: Subscription,
+}
+
+#[derive(Clone, Debug)]
+pub struct ChannelMessage {
+    pub id: ChannelMessageId,
+    pub body: String,
+    pub timestamp: OffsetDateTime,
+    pub sender: Arc<User>,
+    pub nonce: u128,
+}
+
+#[derive(Copy, Clone, Debug, PartialEq, Eq, PartialOrd, Ord)]
+pub enum ChannelMessageId {
+    Saved(u64),
+    Pending(usize),
+}
+
+#[derive(Clone, Debug, Default)]
+pub struct ChannelMessageSummary {
+    max_id: ChannelMessageId,
+    count: usize,
+}
+
+#[derive(Copy, Clone, Debug, Default, PartialEq, Eq, PartialOrd, Ord)]
+struct Count(usize);
+
+#[derive(Clone, Debug, PartialEq)]
+pub enum ChannelChatEvent {
+    MessagesUpdated {
+        old_range: Range<usize>,
+        new_count: usize,
+    },
+}
+
+impl Entity for ChannelChat {
+    type Event = ChannelChatEvent;
+
+    fn release(&mut self, _: &mut AppContext) {
+        self.rpc
+            .send(proto::LeaveChannelChat {
+                channel_id: self.channel.id,
+            })
+            .log_err();
+    }
+}
+
+impl ChannelChat {
+    pub fn init(rpc: &Arc<Client>) {
+        rpc.add_model_message_handler(Self::handle_message_sent);
+    }
+
+    pub async fn new(
+        channel: Arc<Channel>,
+        user_store: ModelHandle<UserStore>,
+        client: Arc<Client>,
+        mut cx: AsyncAppContext,
+    ) -> Result<ModelHandle<Self>> {
+        let channel_id = channel.id;
+        let subscription = client.subscribe_to_entity(channel_id).unwrap();
+
+        let response = client
+            .request(proto::JoinChannelChat { channel_id })
+            .await?;
+        let messages = messages_from_proto(response.messages, &user_store, &mut cx).await?;
+        let loaded_all_messages = response.done;
+
+        Ok(cx.add_model(|cx| {
+            let mut this = Self {
+                channel,
+                user_store,
+                rpc: client,
+                outgoing_messages_lock: Default::default(),
+                messages: Default::default(),
+                loaded_all_messages,
+                next_pending_message_id: 0,
+                rng: StdRng::from_entropy(),
+                _subscription: subscription.set_model(&cx.handle(), &mut cx.to_async()),
+            };
+            this.insert_messages(messages, cx);
+            this
+        }))
+    }
+
+    pub fn name(&self) -> &str {
+        &self.channel.name
+    }
+
+    pub fn send_message(
+        &mut self,
+        body: String,
+        cx: &mut ModelContext<Self>,
+    ) -> Result<Task<Result<()>>> {
+        if body.is_empty() {
+            Err(anyhow!("message body can't be empty"))?;
+        }
+
+        let current_user = self
+            .user_store
+            .read(cx)
+            .current_user()
+            .ok_or_else(|| anyhow!("current_user is not present"))?;
+
+        let channel_id = self.channel.id;
+        let pending_id = ChannelMessageId::Pending(post_inc(&mut self.next_pending_message_id));
+        let nonce = self.rng.gen();
+        self.insert_messages(
+            SumTree::from_item(
+                ChannelMessage {
+                    id: pending_id,
+                    body: body.clone(),
+                    sender: current_user,
+                    timestamp: OffsetDateTime::now_utc(),
+                    nonce,
+                },
+                &(),
+            ),
+            cx,
+        );
+        let user_store = self.user_store.clone();
+        let rpc = self.rpc.clone();
+        let outgoing_messages_lock = self.outgoing_messages_lock.clone();
+        Ok(cx.spawn(|this, mut cx| async move {
+            let outgoing_message_guard = outgoing_messages_lock.lock().await;
+            let request = rpc.request(proto::SendChannelMessage {
+                channel_id,
+                body,
+                nonce: Some(nonce.into()),
+            });
+            let response = request.await?;
+            drop(outgoing_message_guard);
+            let message = ChannelMessage::from_proto(
+                response.message.ok_or_else(|| anyhow!("invalid message"))?,
+                &user_store,
+                &mut cx,
+            )
+            .await?;
+            this.update(&mut cx, |this, cx| {
+                this.insert_messages(SumTree::from_item(message, &()), cx);
+                Ok(())
+            })
+        }))
+    }
+
+    pub fn load_more_messages(&mut self, cx: &mut ModelContext<Self>) -> bool {
+        if !self.loaded_all_messages {
+            let rpc = self.rpc.clone();
+            let user_store = self.user_store.clone();
+            let channel_id = self.channel.id;
+            if let Some(before_message_id) =
+                self.messages.first().and_then(|message| match message.id {
+                    ChannelMessageId::Saved(id) => Some(id),
+                    ChannelMessageId::Pending(_) => None,
+                })
+            {
+                cx.spawn(|this, mut cx| {
+                    async move {
+                        let response = rpc
+                            .request(proto::GetChannelMessages {
+                                channel_id,
+                                before_message_id,
+                            })
+                            .await?;
+                        let loaded_all_messages = response.done;
+                        let messages =
+                            messages_from_proto(response.messages, &user_store, &mut cx).await?;
+                        this.update(&mut cx, |this, cx| {
+                            this.loaded_all_messages = loaded_all_messages;
+                            this.insert_messages(messages, cx);
+                        });
+                        anyhow::Ok(())
+                    }
+                    .log_err()
+                })
+                .detach();
+                return true;
+            }
+        }
+        false
+    }
+
+    pub fn rejoin(&mut self, cx: &mut ModelContext<Self>) {
+        let user_store = self.user_store.clone();
+        let rpc = self.rpc.clone();
+        let channel_id = self.channel.id;
+        cx.spawn(|this, mut cx| {
+            async move {
+                let response = rpc.request(proto::JoinChannelChat { channel_id }).await?;
+                let messages = messages_from_proto(response.messages, &user_store, &mut cx).await?;
+                let loaded_all_messages = response.done;
+
+                let pending_messages = this.update(&mut cx, |this, cx| {
+                    if let Some((first_new_message, last_old_message)) =
+                        messages.first().zip(this.messages.last())
+                    {
+                        if first_new_message.id > last_old_message.id {
+                            let old_messages = mem::take(&mut this.messages);
+                            cx.emit(ChannelChatEvent::MessagesUpdated {
+                                old_range: 0..old_messages.summary().count,
+                                new_count: 0,
+                            });
+                            this.loaded_all_messages = loaded_all_messages;
+                        }
+                    }
+
+                    this.insert_messages(messages, cx);
+                    if loaded_all_messages {
+                        this.loaded_all_messages = loaded_all_messages;
+                    }
+
+                    this.pending_messages().cloned().collect::<Vec<_>>()
+                });
+
+                for pending_message in pending_messages {
+                    let request = rpc.request(proto::SendChannelMessage {
+                        channel_id,
+                        body: pending_message.body,
+                        nonce: Some(pending_message.nonce.into()),
+                    });
+                    let response = request.await?;
+                    let message = ChannelMessage::from_proto(
+                        response.message.ok_or_else(|| anyhow!("invalid message"))?,
+                        &user_store,
+                        &mut cx,
+                    )
+                    .await?;
+                    this.update(&mut cx, |this, cx| {
+                        this.insert_messages(SumTree::from_item(message, &()), cx);
+                    });
+                }
+
+                anyhow::Ok(())
+            }
+            .log_err()
+        })
+        .detach();
+    }
+
+    pub fn message_count(&self) -> usize {
+        self.messages.summary().count
+    }
+
+    pub fn messages(&self) -> &SumTree<ChannelMessage> {
+        &self.messages
+    }
+
+    pub fn message(&self, ix: usize) -> &ChannelMessage {
+        let mut cursor = self.messages.cursor::<Count>();
+        cursor.seek(&Count(ix), Bias::Right, &());
+        cursor.item().unwrap()
+    }
+
+    pub fn messages_in_range(&self, range: Range<usize>) -> impl Iterator<Item = &ChannelMessage> {
+        let mut cursor = self.messages.cursor::<Count>();
+        cursor.seek(&Count(range.start), Bias::Right, &());
+        cursor.take(range.len())
+    }
+
+    pub fn pending_messages(&self) -> impl Iterator<Item = &ChannelMessage> {
+        let mut cursor = self.messages.cursor::<ChannelMessageId>();
+        cursor.seek(&ChannelMessageId::Pending(0), Bias::Left, &());
+        cursor
+    }
+
+    async fn handle_message_sent(
+        this: ModelHandle<Self>,
+        message: TypedEnvelope<proto::ChannelMessageSent>,
+        _: Arc<Client>,
+        mut cx: AsyncAppContext,
+    ) -> Result<()> {
+        let user_store = this.read_with(&cx, |this, _| this.user_store.clone());
+        let message = message
+            .payload
+            .message
+            .ok_or_else(|| anyhow!("empty message"))?;
+
+        let message = ChannelMessage::from_proto(message, &user_store, &mut cx).await?;
+        this.update(&mut cx, |this, cx| {
+            this.insert_messages(SumTree::from_item(message, &()), cx)
+        });
+
+        Ok(())
+    }
+
+    fn insert_messages(&mut self, messages: SumTree<ChannelMessage>, cx: &mut ModelContext<Self>) {
+        if let Some((first_message, last_message)) = messages.first().zip(messages.last()) {
+            let nonces = messages
+                .cursor::<()>()
+                .map(|m| m.nonce)
+                .collect::<HashSet<_>>();
+
+            let mut old_cursor = self.messages.cursor::<(ChannelMessageId, Count)>();
+            let mut new_messages = old_cursor.slice(&first_message.id, Bias::Left, &());
+            let start_ix = old_cursor.start().1 .0;
+            let removed_messages = old_cursor.slice(&last_message.id, Bias::Right, &());
+            let removed_count = removed_messages.summary().count;
+            let new_count = messages.summary().count;
+            let end_ix = start_ix + removed_count;
+
+            new_messages.append(messages, &());
+
+            let mut ranges = Vec::<Range<usize>>::new();
+            if new_messages.last().unwrap().is_pending() {
+                new_messages.append(old_cursor.suffix(&()), &());
+            } else {
+                new_messages.append(
+                    old_cursor.slice(&ChannelMessageId::Pending(0), Bias::Left, &()),
+                    &(),
+                );
+
+                while let Some(message) = old_cursor.item() {
+                    let message_ix = old_cursor.start().1 .0;
+                    if nonces.contains(&message.nonce) {
+                        if ranges.last().map_or(false, |r| r.end == message_ix) {
+                            ranges.last_mut().unwrap().end += 1;
+                        } else {
+                            ranges.push(message_ix..message_ix + 1);
+                        }
+                    } else {
+                        new_messages.push(message.clone(), &());
+                    }
+                    old_cursor.next(&());
+                }
+            }
+
+            drop(old_cursor);
+            self.messages = new_messages;
+
+            for range in ranges.into_iter().rev() {
+                cx.emit(ChannelChatEvent::MessagesUpdated {
+                    old_range: range,
+                    new_count: 0,
+                });
+            }
+            cx.emit(ChannelChatEvent::MessagesUpdated {
+                old_range: start_ix..end_ix,
+                new_count,
+            });
+            cx.notify();
+        }
+    }
+}
+
+async fn messages_from_proto(
+    proto_messages: Vec<proto::ChannelMessage>,
+    user_store: &ModelHandle<UserStore>,
+    cx: &mut AsyncAppContext,
+) -> Result<SumTree<ChannelMessage>> {
+    let unique_user_ids = proto_messages
+        .iter()
+        .map(|m| m.sender_id)
+        .collect::<HashSet<_>>()
+        .into_iter()
+        .collect();
+    user_store
+        .update(cx, |user_store, cx| {
+            user_store.get_users(unique_user_ids, cx)
+        })
+        .await?;
+
+    let mut messages = Vec::with_capacity(proto_messages.len());
+    for message in proto_messages {
+        messages.push(ChannelMessage::from_proto(message, user_store, cx).await?);
+    }
+    let mut result = SumTree::new();
+    result.extend(messages, &());
+    Ok(result)
+}
+
+impl ChannelMessage {
+    pub async fn from_proto(
+        message: proto::ChannelMessage,
+        user_store: &ModelHandle<UserStore>,
+        cx: &mut AsyncAppContext,
+    ) -> Result<Self> {
+        let sender = user_store
+            .update(cx, |user_store, cx| {
+                user_store.get_user(message.sender_id, cx)
+            })
+            .await?;
+        Ok(ChannelMessage {
+            id: ChannelMessageId::Saved(message.id),
+            body: message.body,
+            timestamp: OffsetDateTime::from_unix_timestamp(message.timestamp as i64)?,
+            sender,
+            nonce: message
+                .nonce
+                .ok_or_else(|| anyhow!("nonce is required"))?
+                .into(),
+        })
+    }
+
+    pub fn is_pending(&self) -> bool {
+        matches!(self.id, ChannelMessageId::Pending(_))
+    }
+}
+
+impl sum_tree::Item for ChannelMessage {
+    type Summary = ChannelMessageSummary;
+
+    fn summary(&self) -> Self::Summary {
+        ChannelMessageSummary {
+            max_id: self.id,
+            count: 1,
+        }
+    }
+}
+
+impl Default for ChannelMessageId {
+    fn default() -> Self {
+        Self::Saved(0)
+    }
+}
+
+impl sum_tree::Summary for ChannelMessageSummary {
+    type Context = ();
+
+    fn add_summary(&mut self, summary: &Self, _: &()) {
+        self.max_id = summary.max_id;
+        self.count += summary.count;
+    }
+}
+
+impl<'a> sum_tree::Dimension<'a, ChannelMessageSummary> for ChannelMessageId {
+    fn add_summary(&mut self, summary: &'a ChannelMessageSummary, _: &()) {
+        debug_assert!(summary.max_id > *self);
+        *self = summary.max_id;
+    }
+}
+
+impl<'a> sum_tree::Dimension<'a, ChannelMessageSummary> for Count {
+    fn add_summary(&mut self, summary: &'a ChannelMessageSummary, _: &()) {
+        self.0 += summary.count;
+    }
+}
diff --git a/crates/channel/src/channel_store.rs b/crates/channel/src/channel_store.rs
index a4c8da6df4..6096692ccb 100644
--- a/crates/channel/src/channel_store.rs
+++ b/crates/channel/src/channel_store.rs
@@ -1,4 +1,4 @@
-use crate::channel_buffer::ChannelBuffer;
+use crate::{channel_buffer::ChannelBuffer, channel_chat::ChannelChat};
 use anyhow::{anyhow, Result};
 use client::{Client, Subscription, User, UserId, UserStore};
 use collections::{hash_map, HashMap, HashSet};
@@ -20,7 +20,8 @@ pub struct ChannelStore {
     channels_with_admin_privileges: HashSet<ChannelId>,
     outgoing_invites: HashSet<(ChannelId, UserId)>,
     update_channels_tx: mpsc::UnboundedSender<proto::UpdateChannels>,
-    opened_buffers: HashMap<ChannelId, OpenedChannelBuffer>,
+    opened_buffers: HashMap<ChannelId, OpenedModelHandle<ChannelBuffer>>,
+    opened_chats: HashMap<ChannelId, OpenedModelHandle<ChannelChat>>,
     client: Arc<Client>,
     user_store: ModelHandle<UserStore>,
     _rpc_subscription: Subscription,
@@ -50,15 +51,9 @@ impl Entity for ChannelStore {
     type Event = ChannelEvent;
 }
 
-pub enum ChannelMemberStatus {
-    Invited,
-    Member,
-    NotMember,
-}
-
-enum OpenedChannelBuffer {
-    Open(WeakModelHandle<ChannelBuffer>),
-    Loading(Shared<Task<Result<ModelHandle<ChannelBuffer>, Arc<anyhow::Error>>>>),
+enum OpenedModelHandle<E: Entity> {
+    Open(WeakModelHandle<E>),
+    Loading(Shared<Task<Result<ModelHandle<E>, Arc<anyhow::Error>>>>),
 }
 
 impl ChannelStore {
@@ -94,6 +89,7 @@ impl ChannelStore {
             channels_with_admin_privileges: Default::default(),
             outgoing_invites: Default::default(),
             opened_buffers: Default::default(),
+            opened_chats: Default::default(),
             update_channels_tx,
             client,
             user_store,
@@ -154,7 +150,7 @@ impl ChannelStore {
 
     pub fn has_open_channel_buffer(&self, channel_id: ChannelId, cx: &AppContext) -> bool {
         if let Some(buffer) = self.opened_buffers.get(&channel_id) {
-            if let OpenedChannelBuffer::Open(buffer) = buffer {
+            if let OpenedModelHandle::Open(buffer) = buffer {
                 return buffer.upgrade(cx).is_some();
             }
         }
@@ -166,24 +162,58 @@ impl ChannelStore {
         channel_id: ChannelId,
         cx: &mut ModelContext<Self>,
     ) -> Task<Result<ModelHandle<ChannelBuffer>>> {
-        // Make sure that a given channel buffer is only opened once per
+        let client = self.client.clone();
+        self.open_channel_resource(
+            channel_id,
+            |this| &mut this.opened_buffers,
+            |channel, cx| ChannelBuffer::new(channel, client, cx),
+            cx,
+        )
+    }
+
+    pub fn open_channel_chat(
+        &mut self,
+        channel_id: ChannelId,
+        cx: &mut ModelContext<Self>,
+    ) -> Task<Result<ModelHandle<ChannelChat>>> {
+        let client = self.client.clone();
+        let user_store = self.user_store.clone();
+        self.open_channel_resource(
+            channel_id,
+            |this| &mut this.opened_chats,
+            |channel, cx| ChannelChat::new(channel, user_store, client, cx),
+            cx,
+        )
+    }
+
+    fn open_channel_resource<T: Entity, F, Fut>(
+        &mut self,
+        channel_id: ChannelId,
+        map: fn(&mut Self) -> &mut HashMap<ChannelId, OpenedModelHandle<T>>,
+        load: F,
+        cx: &mut ModelContext<Self>,
+    ) -> Task<Result<ModelHandle<T>>>
+    where
+        F: 'static + FnOnce(Arc<Channel>, AsyncAppContext) -> Fut,
+        Fut: Future<Output = Result<ModelHandle<T>>>,
+    {
+        // Make sure that a given channel resource is only opened once per
         // app instance, even if this method is called multiple times
         // with the same channel id while the first task is still running.
         let task = loop {
-            match self.opened_buffers.entry(channel_id) {
+            match map(self).entry(channel_id) {
                 hash_map::Entry::Occupied(e) => match e.get() {
-                    OpenedChannelBuffer::Open(buffer) => {
+                    OpenedModelHandle::Open(buffer) => {
                         if let Some(buffer) = buffer.upgrade(cx) {
                             break Task::ready(Ok(buffer)).shared();
                         } else {
-                            self.opened_buffers.remove(&channel_id);
+                            map(self).remove(&channel_id);
                             continue;
                         }
                     }
-                    OpenedChannelBuffer::Loading(task) => break task.clone(),
+                    OpenedModelHandle::Loading(task) => break task.clone(),
                 },
                 hash_map::Entry::Vacant(e) => {
-                    let client = self.client.clone();
                     let task = cx
                         .spawn(|this, cx| async move {
                             let channel = this.read_with(&cx, |this, _| {
@@ -192,12 +222,10 @@ impl ChannelStore {
                                 })
                             })?;
 
-                            ChannelBuffer::new(channel, client, cx)
-                                .await
-                                .map_err(Arc::new)
+                            load(channel, cx).await.map_err(Arc::new)
                         })
                         .shared();
-                    e.insert(OpenedChannelBuffer::Loading(task.clone()));
+                    e.insert(OpenedModelHandle::Loading(task.clone()));
                     cx.spawn({
                         let task = task.clone();
                         |this, mut cx| async move {
@@ -208,14 +236,14 @@ impl ChannelStore {
                                         this.opened_buffers.remove(&channel_id);
                                     })
                                     .detach();
-                                    this.opened_buffers.insert(
+                                    map(this).insert(
                                         channel_id,
-                                        OpenedChannelBuffer::Open(buffer.downgrade()),
+                                        OpenedModelHandle::Open(buffer.downgrade()),
                                     );
                                 }
                                 Err(error) => {
                                     log::error!("failed to open channel buffer {error:?}");
-                                    this.opened_buffers.remove(&channel_id);
+                                    map(this).remove(&channel_id);
                                 }
                             });
                         }
@@ -496,7 +524,7 @@ impl ChannelStore {
 
         let mut buffer_versions = Vec::new();
         for buffer in self.opened_buffers.values() {
-            if let OpenedChannelBuffer::Open(buffer) = buffer {
+            if let OpenedModelHandle::Open(buffer) = buffer {
                 if let Some(buffer) = buffer.upgrade(cx) {
                     let channel_buffer = buffer.read(cx);
                     let buffer = channel_buffer.buffer().read(cx);
@@ -522,7 +550,7 @@ impl ChannelStore {
 
             this.update(&mut cx, |this, cx| {
                 this.opened_buffers.retain(|_, buffer| match buffer {
-                    OpenedChannelBuffer::Open(channel_buffer) => {
+                    OpenedModelHandle::Open(channel_buffer) => {
                         let Some(channel_buffer) = channel_buffer.upgrade(cx) else {
                             return false;
                         };
@@ -583,7 +611,7 @@ impl ChannelStore {
                             false
                         })
                     }
-                    OpenedChannelBuffer::Loading(_) => true,
+                    OpenedModelHandle::Loading(_) => true,
                 });
             });
             anyhow::Ok(())
@@ -605,7 +633,7 @@ impl ChannelStore {
                 if let Some(this) = this.upgrade(&cx) {
                     this.update(&mut cx, |this, cx| {
                         for (_, buffer) in this.opened_buffers.drain() {
-                            if let OpenedChannelBuffer::Open(buffer) = buffer {
+                            if let OpenedModelHandle::Open(buffer) = buffer {
                                 if let Some(buffer) = buffer.upgrade(cx) {
                                     buffer.update(cx, |buffer, cx| buffer.disconnect(cx));
                                 }
@@ -654,7 +682,7 @@ impl ChannelStore {
 
                 for channel_id in &payload.remove_channels {
                     let channel_id = *channel_id;
-                    if let Some(OpenedChannelBuffer::Open(buffer)) =
+                    if let Some(OpenedModelHandle::Open(buffer)) =
                         self.opened_buffers.remove(&channel_id)
                     {
                         if let Some(buffer) = buffer.upgrade(cx) {
diff --git a/crates/channel/src/channel_store_tests.rs b/crates/channel/src/channel_store_tests.rs
index 18894b1f47..3ae899ecde 100644
--- a/crates/channel/src/channel_store_tests.rs
+++ b/crates/channel/src/channel_store_tests.rs
@@ -1,6 +1,8 @@
+use crate::channel_chat::ChannelChatEvent;
+
 use super::*;
-use client::{Client, UserStore};
-use gpui::{AppContext, ModelHandle};
+use client::{test::FakeServer, Client, UserStore};
+use gpui::{AppContext, ModelHandle, TestAppContext};
 use rpc::proto;
 use util::http::FakeHttpClient;
 
@@ -137,6 +139,220 @@ fn test_dangling_channel_paths(cx: &mut AppContext) {
     assert_channels(&channel_store, &[(0, "a".to_string(), true)], cx);
 }
 
+#[gpui::test]
+async fn test_channel_messages(cx: &mut TestAppContext) {
+    cx.foreground().forbid_parking();
+
+    let user_id = 5;
+    let http_client = FakeHttpClient::with_404_response();
+    let client = cx.update(|cx| Client::new(http_client.clone(), cx));
+    let server = FakeServer::for_client(user_id, &client, cx).await;
+    let user_store = cx.add_model(|cx| UserStore::new(client.clone(), http_client, cx));
+    crate::init(&client);
+
+    let channel_store = cx.add_model(|cx| ChannelStore::new(client, user_store, cx));
+
+    let channel_id = 5;
+
+    // Get the available channels.
+    server.send(proto::UpdateChannels {
+        channels: vec![proto::Channel {
+            id: channel_id,
+            name: "the-channel".to_string(),
+            parent_id: None,
+        }],
+        ..Default::default()
+    });
+    channel_store.next_notification(cx).await;
+    cx.read(|cx| {
+        assert_channels(&channel_store, &[(0, "the-channel".to_string(), false)], cx);
+    });
+
+    let get_users = server.receive::<proto::GetUsers>().await.unwrap();
+    assert_eq!(get_users.payload.user_ids, vec![5]);
+    server
+        .respond(
+            get_users.receipt(),
+            proto::UsersResponse {
+                users: vec![proto::User {
+                    id: 5,
+                    github_login: "nathansobo".into(),
+                    avatar_url: "http://avatar.com/nathansobo".into(),
+                }],
+            },
+        )
+        .await;
+
+    // Join a channel and populate its existing messages.
+    let channel = channel_store
+        .update(cx, |store, cx| {
+            let channel_id = store.channels().next().unwrap().1.id;
+            store.open_channel_chat(channel_id, cx)
+        })
+        .await
+        .unwrap();
+    channel.read_with(cx, |channel, _| assert!(channel.messages().is_empty()));
+    let join_channel = server.receive::<proto::JoinChannelChat>().await.unwrap();
+    server
+        .respond(
+            join_channel.receipt(),
+            proto::JoinChannelChatResponse {
+                messages: vec![
+                    proto::ChannelMessage {
+                        id: 10,
+                        body: "a".into(),
+                        timestamp: 1000,
+                        sender_id: 5,
+                        nonce: Some(1.into()),
+                    },
+                    proto::ChannelMessage {
+                        id: 11,
+                        body: "b".into(),
+                        timestamp: 1001,
+                        sender_id: 6,
+                        nonce: Some(2.into()),
+                    },
+                ],
+                done: false,
+            },
+        )
+        .await;
+
+    // Client requests all users for the received messages
+    let mut get_users = server.receive::<proto::GetUsers>().await.unwrap();
+    get_users.payload.user_ids.sort();
+    assert_eq!(get_users.payload.user_ids, vec![6]);
+    server
+        .respond(
+            get_users.receipt(),
+            proto::UsersResponse {
+                users: vec![proto::User {
+                    id: 6,
+                    github_login: "maxbrunsfeld".into(),
+                    avatar_url: "http://avatar.com/maxbrunsfeld".into(),
+                }],
+            },
+        )
+        .await;
+
+    assert_eq!(
+        channel.next_event(cx).await,
+        ChannelChatEvent::MessagesUpdated {
+            old_range: 0..0,
+            new_count: 2,
+        }
+    );
+    channel.read_with(cx, |channel, _| {
+        assert_eq!(
+            channel
+                .messages_in_range(0..2)
+                .map(|message| (message.sender.github_login.clone(), message.body.clone()))
+                .collect::<Vec<_>>(),
+            &[
+                ("nathansobo".into(), "a".into()),
+                ("maxbrunsfeld".into(), "b".into())
+            ]
+        );
+    });
+
+    // Receive a new message.
+    server.send(proto::ChannelMessageSent {
+        channel_id,
+        message: Some(proto::ChannelMessage {
+            id: 12,
+            body: "c".into(),
+            timestamp: 1002,
+            sender_id: 7,
+            nonce: Some(3.into()),
+        }),
+    });
+
+    // Client requests user for message since they haven't seen them yet
+    let get_users = server.receive::<proto::GetUsers>().await.unwrap();
+    assert_eq!(get_users.payload.user_ids, vec![7]);
+    server
+        .respond(
+            get_users.receipt(),
+            proto::UsersResponse {
+                users: vec![proto::User {
+                    id: 7,
+                    github_login: "as-cii".into(),
+                    avatar_url: "http://avatar.com/as-cii".into(),
+                }],
+            },
+        )
+        .await;
+
+    assert_eq!(
+        channel.next_event(cx).await,
+        ChannelChatEvent::MessagesUpdated {
+            old_range: 2..2,
+            new_count: 1,
+        }
+    );
+    channel.read_with(cx, |channel, _| {
+        assert_eq!(
+            channel
+                .messages_in_range(2..3)
+                .map(|message| (message.sender.github_login.clone(), message.body.clone()))
+                .collect::<Vec<_>>(),
+            &[("as-cii".into(), "c".into())]
+        )
+    });
+
+    // Scroll up to view older messages.
+    channel.update(cx, |channel, cx| {
+        assert!(channel.load_more_messages(cx));
+    });
+    let get_messages = server.receive::<proto::GetChannelMessages>().await.unwrap();
+    assert_eq!(get_messages.payload.channel_id, 5);
+    assert_eq!(get_messages.payload.before_message_id, 10);
+    server
+        .respond(
+            get_messages.receipt(),
+            proto::GetChannelMessagesResponse {
+                done: true,
+                messages: vec![
+                    proto::ChannelMessage {
+                        id: 8,
+                        body: "y".into(),
+                        timestamp: 998,
+                        sender_id: 5,
+                        nonce: Some(4.into()),
+                    },
+                    proto::ChannelMessage {
+                        id: 9,
+                        body: "z".into(),
+                        timestamp: 999,
+                        sender_id: 6,
+                        nonce: Some(5.into()),
+                    },
+                ],
+            },
+        )
+        .await;
+
+    assert_eq!(
+        channel.next_event(cx).await,
+        ChannelChatEvent::MessagesUpdated {
+            old_range: 0..0,
+            new_count: 2,
+        }
+    );
+    channel.read_with(cx, |channel, _| {
+        assert_eq!(
+            channel
+                .messages_in_range(0..2)
+                .map(|message| (message.sender.github_login.clone(), message.body.clone()))
+                .collect::<Vec<_>>(),
+            &[
+                ("nathansobo".into(), "y".into()),
+                ("maxbrunsfeld".into(), "z".into())
+            ]
+        );
+    });
+}
+
 fn update_channels(
     channel_store: &ModelHandle<ChannelStore>,
     message: proto::UpdateChannels,
diff --git a/crates/collab/src/tests/test_server.rs b/crates/collab/src/tests/test_server.rs
index eef1dde967..a7dbd97239 100644
--- a/crates/collab/src/tests/test_server.rs
+++ b/crates/collab/src/tests/test_server.rs
@@ -6,7 +6,7 @@ use crate::{
 };
 use anyhow::anyhow;
 use call::ActiveCall;
-use channel::{channel_buffer::ChannelBuffer, ChannelStore};
+use channel::{ChannelBuffer, ChannelStore};
 use client::{
     self, proto::PeerId, Client, Connection, Credentials, EstablishConnectionError, UserStore,
 };
diff --git a/crates/collab_ui/Cargo.toml b/crates/collab_ui/Cargo.toml
index da32308558..0a52b9a19f 100644
--- a/crates/collab_ui/Cargo.toml
+++ b/crates/collab_ui/Cargo.toml
@@ -55,6 +55,7 @@ schemars.workspace = true
 postage.workspace = true
 serde.workspace = true
 serde_derive.workspace = true
+time.workspace = true
 
 [dev-dependencies]
 call = { path = "../call", features = ["test-support"] }
diff --git a/crates/collab_ui/src/channel_view.rs b/crates/collab_ui/src/channel_view.rs
index 5086cc8b37..76b79eaf39 100644
--- a/crates/collab_ui/src/channel_view.rs
+++ b/crates/collab_ui/src/channel_view.rs
@@ -1,8 +1,5 @@
 use anyhow::{anyhow, Result};
-use channel::{
-    channel_buffer::{self, ChannelBuffer},
-    ChannelId,
-};
+use channel::{ChannelBuffer, ChannelBufferEvent, ChannelId};
 use client::proto;
 use clock::ReplicaId;
 use collections::HashMap;
@@ -118,14 +115,14 @@ impl ChannelView {
     fn handle_channel_buffer_event(
         &mut self,
         _: ModelHandle<ChannelBuffer>,
-        event: &channel_buffer::Event,
+        event: &ChannelBufferEvent,
         cx: &mut ViewContext<Self>,
     ) {
         match event {
-            channel_buffer::Event::CollaboratorsChanged => {
+            ChannelBufferEvent::CollaboratorsChanged => {
                 self.refresh_replica_id_map(cx);
             }
-            channel_buffer::Event::Disconnected => self.editor.update(cx, |editor, cx| {
+            ChannelBufferEvent::Disconnected => self.editor.update(cx, |editor, cx| {
                 editor.set_read_only(true);
                 cx.notify();
             }),
diff --git a/crates/collab_ui/src/chat_panel.rs b/crates/collab_ui/src/chat_panel.rs
new file mode 100644
index 0000000000..0105a9d27b
--- /dev/null
+++ b/crates/collab_ui/src/chat_panel.rs
@@ -0,0 +1,391 @@
+use channel::{ChannelChat, ChannelChatEvent, ChannelMessage, ChannelStore};
+use client::Client;
+use editor::Editor;
+use gpui::{
+    actions,
+    elements::*,
+    platform::{CursorStyle, MouseButton},
+    views::{ItemType, Select, SelectStyle},
+    AnyViewHandle, AppContext, Entity, ModelHandle, Subscription, View, ViewContext, ViewHandle,
+};
+use language::language_settings::SoftWrap;
+use menu::Confirm;
+use std::sync::Arc;
+use theme::Theme;
+use time::{OffsetDateTime, UtcOffset};
+use util::{ResultExt, TryFutureExt};
+
+const MESSAGE_LOADING_THRESHOLD: usize = 50;
+
+pub struct ChatPanel {
+    client: Arc<Client>,
+    channel_store: ModelHandle<ChannelStore>,
+    active_channel: Option<(ModelHandle<ChannelChat>, Subscription)>,
+    message_list: ListState<ChatPanel>,
+    input_editor: ViewHandle<Editor>,
+    channel_select: ViewHandle<Select>,
+    local_timezone: UtcOffset,
+}
+
+pub enum Event {}
+
+actions!(chat_panel, [LoadMoreMessages]);
+
+pub fn init(cx: &mut AppContext) {
+    cx.add_action(ChatPanel::send);
+    cx.add_action(ChatPanel::load_more_messages);
+}
+
+impl ChatPanel {
+    pub fn new(
+        rpc: Arc<Client>,
+        channel_list: ModelHandle<ChannelStore>,
+        cx: &mut ViewContext<Self>,
+    ) -> Self {
+        let input_editor = cx.add_view(|cx| {
+            let mut editor = Editor::auto_height(
+                4,
+                Some(Arc::new(|theme| theme.chat_panel.input_editor.clone())),
+                cx,
+            );
+            editor.set_soft_wrap_mode(SoftWrap::EditorWidth, cx);
+            editor
+        });
+        let channel_select = cx.add_view(|cx| {
+            let channel_list = channel_list.clone();
+            Select::new(0, cx, {
+                move |ix, item_type, is_hovered, cx| {
+                    Self::render_channel_name(
+                        &channel_list,
+                        ix,
+                        item_type,
+                        is_hovered,
+                        &theme::current(cx).chat_panel.channel_select,
+                        cx,
+                    )
+                }
+            })
+            .with_style(move |cx| {
+                let style = &theme::current(cx).chat_panel.channel_select;
+                SelectStyle {
+                    header: style.header.container,
+                    menu: style.menu,
+                }
+            })
+        });
+
+        let mut message_list =
+            ListState::<Self>::new(0, Orientation::Bottom, 1000., move |this, ix, cx| {
+                let message = this.active_channel.as_ref().unwrap().0.read(cx).message(ix);
+                this.render_message(message, cx)
+            });
+        message_list.set_scroll_handler(|visible_range, this, cx| {
+            if visible_range.start < MESSAGE_LOADING_THRESHOLD {
+                this.load_more_messages(&LoadMoreMessages, cx);
+            }
+        });
+
+        let mut this = Self {
+            client: rpc,
+            channel_store: channel_list,
+            active_channel: Default::default(),
+            message_list,
+            input_editor,
+            channel_select,
+            local_timezone: cx.platform().local_timezone(),
+        };
+
+        this.init_active_channel(cx);
+        cx.observe(&this.channel_store, |this, _, cx| {
+            this.init_active_channel(cx);
+        })
+        .detach();
+
+        cx.observe(&this.channel_select, |this, channel_select, cx| {
+            let selected_ix = channel_select.read(cx).selected_index();
+            let selected_channel_id = this
+                .channel_store
+                .read(cx)
+                .channel_at_index(selected_ix)
+                .map(|e| e.1.id);
+            if let Some(selected_channel_id) = selected_channel_id {
+                let open_chat = this.channel_store.update(cx, |store, cx| {
+                    store.open_channel_chat(selected_channel_id, cx)
+                });
+                cx.spawn(|this, mut cx| async move {
+                    let chat = open_chat.await?;
+                    this.update(&mut cx, |this, cx| {
+                        this.set_active_channel(chat, cx);
+                    })
+                })
+                .detach_and_log_err(cx);
+            }
+        })
+        .detach();
+
+        this
+    }
+
+    fn init_active_channel(&mut self, cx: &mut ViewContext<Self>) {
+        let channel_count = self.channel_store.read(cx).channel_count();
+        self.message_list.reset(0);
+        self.active_channel = None;
+        self.channel_select.update(cx, |select, cx| {
+            select.set_item_count(channel_count, cx);
+        });
+    }
+
+    fn set_active_channel(
+        &mut self,
+        channel: ModelHandle<ChannelChat>,
+        cx: &mut ViewContext<Self>,
+    ) {
+        if self.active_channel.as_ref().map(|e| &e.0) != Some(&channel) {
+            {
+                let channel = channel.read(cx);
+                self.message_list.reset(channel.message_count());
+                let placeholder = format!("Message #{}", channel.name());
+                self.input_editor.update(cx, move |editor, cx| {
+                    editor.set_placeholder_text(placeholder, cx);
+                });
+            }
+            let subscription = cx.subscribe(&channel, Self::channel_did_change);
+            self.active_channel = Some((channel, subscription));
+        }
+    }
+
+    fn channel_did_change(
+        &mut self,
+        _: ModelHandle<ChannelChat>,
+        event: &ChannelChatEvent,
+        cx: &mut ViewContext<Self>,
+    ) {
+        match event {
+            ChannelChatEvent::MessagesUpdated {
+                old_range,
+                new_count,
+            } => {
+                self.message_list.splice(old_range.clone(), *new_count);
+            }
+        }
+        cx.notify();
+    }
+
+    fn render_channel(&self, cx: &mut ViewContext<Self>) -> AnyElement<Self> {
+        let theme = theme::current(cx);
+        Flex::column()
+            .with_child(
+                ChildView::new(&self.channel_select, cx)
+                    .contained()
+                    .with_style(theme.chat_panel.channel_select.container),
+            )
+            .with_child(self.render_active_channel_messages())
+            .with_child(self.render_input_box(&theme, cx))
+            .into_any()
+    }
+
+    fn render_active_channel_messages(&self) -> AnyElement<Self> {
+        let messages = if self.active_channel.is_some() {
+            List::new(self.message_list.clone()).into_any()
+        } else {
+            Empty::new().into_any()
+        };
+
+        messages.flex(1., true).into_any()
+    }
+
+    fn render_message(&self, message: &ChannelMessage, cx: &AppContext) -> AnyElement<Self> {
+        let now = OffsetDateTime::now_utc();
+        let theme = theme::current(cx);
+        let theme = if message.is_pending() {
+            &theme.chat_panel.pending_message
+        } else {
+            &theme.chat_panel.message
+        };
+
+        Flex::column()
+            .with_child(
+                Flex::row()
+                    .with_child(
+                        Label::new(
+                            message.sender.github_login.clone(),
+                            theme.sender.text.clone(),
+                        )
+                        .contained()
+                        .with_style(theme.sender.container),
+                    )
+                    .with_child(
+                        Label::new(
+                            format_timestamp(message.timestamp, now, self.local_timezone),
+                            theme.timestamp.text.clone(),
+                        )
+                        .contained()
+                        .with_style(theme.timestamp.container),
+                    ),
+            )
+            .with_child(Text::new(message.body.clone(), theme.body.clone()))
+            .contained()
+            .with_style(theme.container)
+            .into_any()
+    }
+
+    fn render_input_box(&self, theme: &Arc<Theme>, cx: &AppContext) -> AnyElement<Self> {
+        ChildView::new(&self.input_editor, cx)
+            .contained()
+            .with_style(theme.chat_panel.input_editor.container)
+            .into_any()
+    }
+
+    fn render_channel_name(
+        channel_store: &ModelHandle<ChannelStore>,
+        ix: usize,
+        item_type: ItemType,
+        is_hovered: bool,
+        theme: &theme::ChannelSelect,
+        cx: &AppContext,
+    ) -> AnyElement<Select> {
+        let channel = &channel_store.read(cx).channel_at_index(ix).unwrap().1;
+        let theme = match (item_type, is_hovered) {
+            (ItemType::Header, _) => &theme.header,
+            (ItemType::Selected, false) => &theme.active_item,
+            (ItemType::Selected, true) => &theme.hovered_active_item,
+            (ItemType::Unselected, false) => &theme.item,
+            (ItemType::Unselected, true) => &theme.hovered_item,
+        };
+        Flex::row()
+            .with_child(
+                Label::new("#".to_string(), theme.hash.text.clone())
+                    .contained()
+                    .with_style(theme.hash.container),
+            )
+            .with_child(Label::new(channel.name.clone(), theme.name.clone()))
+            .contained()
+            .with_style(theme.container)
+            .into_any()
+    }
+
+    fn render_sign_in_prompt(
+        &self,
+        theme: &Arc<Theme>,
+        cx: &mut ViewContext<Self>,
+    ) -> AnyElement<Self> {
+        enum SignInPromptLabel {}
+
+        MouseEventHandler::new::<SignInPromptLabel, _>(0, cx, |mouse_state, _| {
+            Label::new(
+                "Sign in to use chat".to_string(),
+                theme
+                    .chat_panel
+                    .sign_in_prompt
+                    .style_for(mouse_state)
+                    .clone(),
+            )
+        })
+        .with_cursor_style(CursorStyle::PointingHand)
+        .on_click(MouseButton::Left, move |_, this, cx| {
+            let client = this.client.clone();
+            cx.spawn(|this, mut cx| async move {
+                if client
+                    .authenticate_and_connect(true, &cx)
+                    .log_err()
+                    .await
+                    .is_some()
+                {
+                    this.update(&mut cx, |this, cx| {
+                        if cx.handle().is_focused(cx) {
+                            cx.focus(&this.input_editor);
+                        }
+                    })
+                    .ok();
+                }
+            })
+            .detach();
+        })
+        .aligned()
+        .into_any()
+    }
+
+    fn send(&mut self, _: &Confirm, cx: &mut ViewContext<Self>) {
+        if let Some((channel, _)) = self.active_channel.as_ref() {
+            let body = self.input_editor.update(cx, |editor, cx| {
+                let body = editor.text(cx);
+                editor.clear(cx);
+                body
+            });
+
+            if let Some(task) = channel
+                .update(cx, |channel, cx| channel.send_message(body, cx))
+                .log_err()
+            {
+                task.detach();
+            }
+        }
+    }
+
+    fn load_more_messages(&mut self, _: &LoadMoreMessages, cx: &mut ViewContext<Self>) {
+        if let Some((channel, _)) = self.active_channel.as_ref() {
+            channel.update(cx, |channel, cx| {
+                channel.load_more_messages(cx);
+            })
+        }
+    }
+}
+
+impl Entity for ChatPanel {
+    type Event = Event;
+}
+
+impl View for ChatPanel {
+    fn ui_name() -> &'static str {
+        "ChatPanel"
+    }
+
+    fn render(&mut self, cx: &mut ViewContext<Self>) -> AnyElement<Self> {
+        let theme = theme::current(cx);
+        let element = if self.client.user_id().is_some() {
+            self.render_channel(cx)
+        } else {
+            self.render_sign_in_prompt(&theme, cx)
+        };
+        element
+            .contained()
+            .with_style(theme.chat_panel.container)
+            .constrained()
+            .with_min_width(150.)
+            .into_any()
+    }
+
+    fn focus_in(&mut self, _: AnyViewHandle, cx: &mut ViewContext<Self>) {
+        if matches!(
+            *self.client.status().borrow(),
+            client::Status::Connected { .. }
+        ) {
+            cx.focus(&self.input_editor);
+        }
+    }
+}
+
+fn format_timestamp(
+    mut timestamp: OffsetDateTime,
+    mut now: OffsetDateTime,
+    local_timezone: UtcOffset,
+) -> String {
+    timestamp = timestamp.to_offset(local_timezone);
+    now = now.to_offset(local_timezone);
+
+    let today = now.date();
+    let date = timestamp.date();
+    let mut hour = timestamp.hour();
+    let mut part = "am";
+    if hour > 12 {
+        hour -= 12;
+        part = "pm";
+    }
+    if date == today {
+        format!("{:02}:{:02}{}", hour, timestamp.minute(), part)
+    } else if date.next_day() == Some(today) {
+        format!("yesterday at {:02}:{:02}{}", hour, timestamp.minute(), part)
+    } else {
+        format!("{:02}/{}/{}", date.month() as u32, date.day(), date.year())
+    }
+}
diff --git a/crates/collab_ui/src/collab_ui.rs b/crates/collab_ui/src/collab_ui.rs
index ee34f600fa..b40ecc6992 100644
--- a/crates/collab_ui/src/collab_ui.rs
+++ b/crates/collab_ui/src/collab_ui.rs
@@ -1,4 +1,5 @@
 pub mod channel_view;
+pub mod chat_panel;
 pub mod collab_panel;
 mod collab_titlebar_item;
 mod contact_notification;
diff --git a/crates/rpc/proto/zed.proto b/crates/rpc/proto/zed.proto
index 2e96d79f5e..eb26e81b99 100644
--- a/crates/rpc/proto/zed.proto
+++ b/crates/rpc/proto/zed.proto
@@ -155,7 +155,16 @@ message Envelope {
         RemoveChannelBufferCollaborator remove_channel_buffer_collaborator = 136;
         UpdateChannelBufferCollaborator update_channel_buffer_collaborator = 139;
         RejoinChannelBuffers rejoin_channel_buffers = 140;
-        RejoinChannelBuffersResponse rejoin_channel_buffers_response = 141; // Current max
+        RejoinChannelBuffersResponse rejoin_channel_buffers_response = 141;
+
+        JoinChannelChat join_channel_chat = 142;
+        JoinChannelChatResponse join_channel_chat_response = 143;
+        LeaveChannelChat leave_channel_chat = 144;
+        SendChannelMessage send_channel_message = 145;
+        SendChannelMessageResponse send_channel_message_response = 146;
+        ChannelMessageSent channel_message_sent = 147;
+        GetChannelMessages get_channel_messages = 148;
+        GetChannelMessagesResponse get_channel_messages_response = 149; // Current max
     }
 }
 
@@ -1021,10 +1030,56 @@ message RenameChannel {
     string name = 2;
 }
 
+message JoinChannelChat {
+    uint64 channel_id = 1;
+}
+
+message JoinChannelChatResponse {
+    repeated ChannelMessage messages = 1;
+    bool done = 2;
+}
+
+message LeaveChannelChat {
+    uint64 channel_id = 1;
+}
+
+message SendChannelMessage {
+    uint64 channel_id = 1;
+    string body = 2;
+    Nonce nonce = 3;
+}
+
+message SendChannelMessageResponse {
+    ChannelMessage message = 1;
+}
+
+message ChannelMessageSent {
+    uint64 channel_id = 1;
+    ChannelMessage message = 2;
+}
+
+message GetChannelMessages {
+    uint64 channel_id = 1;
+    uint64 before_message_id = 2;
+}
+
+message GetChannelMessagesResponse {
+    repeated ChannelMessage messages = 1;
+    bool done = 2;
+}
+
 message JoinChannelBuffer {
     uint64 channel_id = 1;
 }
 
+message ChannelMessage {
+    uint64 id = 1;
+    string body = 2;
+    uint64 timestamp = 3;
+    uint64 sender_id = 4;
+    Nonce nonce = 5;
+}
+
 message RejoinChannelBuffers {
     repeated ChannelBufferVersion buffers = 1;
 }
diff --git a/crates/rpc/src/proto.rs b/crates/rpc/src/proto.rs
index f643a8c168..7b98f50e75 100644
--- a/crates/rpc/src/proto.rs
+++ b/crates/rpc/src/proto.rs
@@ -147,6 +147,7 @@ messages!(
     (CreateBufferForPeer, Foreground),
     (CreateChannel, Foreground),
     (ChannelResponse, Foreground),
+    (ChannelMessageSent, Foreground),
     (CreateProjectEntry, Foreground),
     (CreateRoom, Foreground),
     (CreateRoomResponse, Foreground),
@@ -163,6 +164,10 @@ messages!(
     (GetCodeActionsResponse, Background),
     (GetHover, Background),
     (GetHoverResponse, Background),
+    (GetChannelMessages, Background),
+    (GetChannelMessagesResponse, Background),
+    (SendChannelMessage, Background),
+    (SendChannelMessageResponse, Background),
     (GetCompletions, Background),
     (GetCompletionsResponse, Background),
     (GetDefinition, Background),
@@ -184,6 +189,9 @@ messages!(
     (JoinProjectResponse, Foreground),
     (JoinRoom, Foreground),
     (JoinRoomResponse, Foreground),
+    (JoinChannelChat, Foreground),
+    (JoinChannelChatResponse, Foreground),
+    (LeaveChannelChat, Foreground),
     (LeaveProject, Foreground),
     (LeaveRoom, Foreground),
     (OpenBufferById, Background),
@@ -293,6 +301,7 @@ request_messages!(
     (InviteChannelMember, Ack),
     (JoinProject, JoinProjectResponse),
     (JoinRoom, JoinRoomResponse),
+    (JoinChannelChat, JoinChannelChatResponse),
     (LeaveRoom, Ack),
     (RejoinRoom, RejoinRoomResponse),
     (IncomingCall, Ack),
@@ -313,6 +322,8 @@ request_messages!(
     (RespondToContactRequest, Ack),
     (RespondToChannelInvite, Ack),
     (SetChannelMemberAdmin, Ack),
+    (SendChannelMessage, SendChannelMessageResponse),
+    (GetChannelMessages, GetChannelMessagesResponse),
     (GetChannelMembers, GetChannelMembersResponse),
     (JoinChannel, JoinRoomResponse),
     (RemoveChannel, Ack),
@@ -388,6 +399,7 @@ entity_messages!(
 
 entity_messages!(
     channel_id,
+    ChannelMessageSent,
     UpdateChannelBuffer,
     RemoveChannelBufferCollaborator,
     AddChannelBufferCollaborator,
diff --git a/crates/theme/src/theme.rs b/crates/theme/src/theme.rs
index a542249788..15d7e1a71f 100644
--- a/crates/theme/src/theme.rs
+++ b/crates/theme/src/theme.rs
@@ -49,6 +49,7 @@ pub struct Theme {
     pub copilot: Copilot,
     pub collab_panel: CollabPanel,
     pub project_panel: ProjectPanel,
+    pub chat_panel: ChatPanel,
     pub command_palette: CommandPalette,
     pub picker: Picker,
     pub editor: Editor,
@@ -611,6 +612,17 @@ pub struct IconButton {
     pub button_width: f32,
 }
 
+#[derive(Deserialize, Default, JsonSchema)]
+pub struct ChatPanel {
+    #[serde(flatten)]
+    pub container: ContainerStyle,
+    pub channel_select: ChannelSelect,
+    pub input_editor: FieldEditor,
+    pub message: ChatMessage,
+    pub pending_message: ChatMessage,
+    pub sign_in_prompt: Interactive<TextStyle>,
+}
+
 #[derive(Deserialize, Default, JsonSchema)]
 pub struct ChatMessage {
     #[serde(flatten)]