From e4273ffd945f16d6f74e9c64431808ea36148880 Mon Sep 17 00:00:00 2001
From: Owen Jacobson <owen@grimoire.ca>
Date: Tue, 6 May 2025 01:07:54 -0400
Subject: Render "ghost" messages for unsent messages.

There is a subtle race conditon in this code, which is likely not fixable without a protocol change:

* Ghost messages can disappear before their "real" message replacement shows up, if the client finishes sending (i.e., receives an HTTP response on the POST) before the server delivers the real message.
* Ghost messages can be duplicated briefly, if the client receives the real message before the client finishes sending.

Both happen in practice; we make no ordering guarantees between requests.

To aviod this, we'd to give clients a way to correlate pending sends with received messages. This would require fundamentally the same capabilities, like per-operation nonces, that preventing duplicate operations will require.
---
 ui/lib/components/Message.svelte          | 11 +++++++++--
 ui/lib/outbox.svelte.js                   | 16 ++++++++++++++++
 ui/lib/runs.js                            | 10 +++++++++-
 ui/lib/state/remote/messages.svelte.js    |  2 +-
 ui/routes/(app)/ch/[channel]/+page.svelte |  6 +++++-
 ui/styles/messages.css                    |  4 ++++
 ui/styles/variables.css                   |  1 +
 7 files changed, 45 insertions(+), 5 deletions(-)

(limited to 'ui')

diff --git a/ui/lib/components/Message.svelte b/ui/lib/components/Message.svelte
index edd9d79..ea90414 100644
--- a/ui/lib/components/Message.svelte
+++ b/ui/lib/components/Message.svelte
@@ -20,10 +20,17 @@
   }
 </script>
 
-<div class="message" class:delete-armed={deleteArmed} role="article" data-at={at} {onmouseleave}>
+<div
+  class="message"
+  class:delete-armed={deleteArmed}
+  class:unsent={id === null}
+  role="article"
+  data-at={at}
+  {onmouseleave}
+>
   <div class="handle">
     {atFormatted}
-    {#if editable}
+    {#if editable && id}
       <button onclick={ondelete}>&#x1F5D1;&#xFE0F;</button>
     {/if}
   </div>
diff --git a/ui/lib/outbox.svelte.js b/ui/lib/outbox.svelte.js
index fd7fdba..0e4cf29 100644
--- a/ui/lib/outbox.svelte.js
+++ b/ui/lib/outbox.svelte.js
@@ -1,3 +1,6 @@
+import { DateTime } from 'luxon';
+import * as msg from './state/remote/messages.svelte.js';
+
 import * as api from './apiServer.js';
 import * as md from './markdown.js';
 
@@ -5,9 +8,21 @@ class PostToChannel {
   constructor(channel, body) {
     this.channel = channel;
     this.body = body;
+    this.at = DateTime.now();
     this.renderedBody = md.render(body);
   }
 
+  toSkeleton(sender) {
+    return {
+      id: null,
+      at: this.at,
+      channel: this.channel,
+      sender,
+      body: this.body,
+      renderedBody: this.renderedBody
+    };
+  }
+
   async send() {
     return await api.retry(() => api.postToChannel(this.channel, this.body));
   }
@@ -35,6 +50,7 @@ class CreateChannel {
 
 export class Outbox {
   pending = $state([]);
+  messages = $derived(this.pending.filter((operation) => operation instanceof PostToChannel));
 
   static empty() {
     return new Outbox([]);
diff --git a/ui/lib/runs.js b/ui/lib/runs.js
index f4e90be..e3d4c20 100644
--- a/ui/lib/runs.js
+++ b/ui/lib/runs.js
@@ -21,5 +21,13 @@ function runKey(message) {
 }
 
 function continueRun([lastSender, lastAt], [newSender, newAt]) {
-  return lastSender === newSender && newAt - lastAt < RUN_COALESCE_MAX_INTERVAL;
+  const { id: lastId, name: lastName } = lastSender;
+  const { id: newId, name: newName } = newSender;
+  if (lastId !== newId) {
+    return false;
+  }
+  if (lastName !== newName) {
+    return false;
+  }
+  return newAt - lastAt < RUN_COALESCE_MAX_INTERVAL;
 }
diff --git a/ui/lib/state/remote/messages.svelte.js b/ui/lib/state/remote/messages.svelte.js
index 576a74e..c6d31f0 100644
--- a/ui/lib/state/remote/messages.svelte.js
+++ b/ui/lib/state/remote/messages.svelte.js
@@ -1,7 +1,7 @@
 import { DateTime } from 'luxon';
 import { render } from '$lib/markdown.js';
 
-class Message {
+export class Message {
   static boot({ id, at, channel, sender, body }) {
     return new Message({
       id,
diff --git a/ui/routes/(app)/ch/[channel]/+page.svelte b/ui/routes/(app)/ch/[channel]/+page.svelte
index ccf455c..50b6a7d 100644
--- a/ui/routes/(app)/ch/[channel]/+page.svelte
+++ b/ui/routes/(app)/ch/[channel]/+page.svelte
@@ -12,7 +12,11 @@
 
   const channel = $derived(page.params.channel);
   const messages = $derived(session.messages.filter((message) => message.channel === channel));
-  const messageRuns = $derived(runs(messages, session.currentUser));
+  const unsent = $derived(outbox.messages.filter((message) => message.channel === channel));
+  const unsentSkeletons = $derived(
+    unsent.map((message) => message.toSkeleton($state.snapshot(session.currentUser)))
+  );
+  const messageRuns = $derived(runs(messages.concat(unsentSkeletons), session.currentUser));
 
   function inView(parentElement, element) {
     const parRect = parentElement.getBoundingClientRect();
diff --git a/ui/styles/messages.css b/ui/styles/messages.css
index 5890c1a..67a9517 100644
--- a/ui/styles/messages.css
+++ b/ui/styles/messages.css
@@ -39,6 +39,10 @@
   position: relative;
 }
 
+.message.unsent {
+  color: var(--colour-message-run-unsent-text);
+}
+
 .message.delete-armed,
 .message.delete-armed:hover {
   background-color: var(--colour-warn);
diff --git a/ui/styles/variables.css b/ui/styles/variables.css
index c43832c..01efc19 100644
--- a/ui/styles/variables.css
+++ b/ui/styles/variables.css
@@ -56,6 +56,7 @@
   );
   --colour-message-run-self-text: var(--dark-text);
   --colour-message-run-other-text: var(--dark-text);
+  --colour-message-run-unsent-text: var(--light-text);
 
   --colour-message-run-username-bg: color-mix(in srgb, var(--colour-base) 70%, white);
   --colour-message-run-username-border: color-mix(in srgb, var(--colour-base) 50%, black);
-- 
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