DotShare v3.1 — Toast Engine, Race Condition Fix, and Surviving Reddit's S3 Upload Pipeline

v3.0 added nine platforms. v3.1 made them reliable.

There's a category of engineering work that doesn't make headlines. No new features. No platform integrations. Just the kind of work that turns "it works most of the time" into "it works." v3.1 is that release — and two of the bugs it fixed had been silently breaking things in production longer than I'd like to admit.

This is the complete technical breakdown.

What Shipped in v3.1

• Custom WebView toast notification engine

• Global loading states on every async action

• Per-platform character limit validation

• Glassmorphism UI pass

• The Disappearing Preview race condition — fixed

• Reddit's S3 native image upload pipeline — fixed

• Reddit field name synchronization

• ESLint cleanup

1. The Toast Notification Engine

Why the Old Approach Was Wrong

Before v3.1, every status update from the backend arrived as a VS Code notification popup. vscode.window.showInformationMessage(). Top-right corner. Manual dismissal required. Multiple operations meant stacked popups.

For an extension whose entire purpose is to keep you inside the editor, interrupting you with system-level alerts every time you share a post was exactly backwards.

The replacement is a toast engine that lives inside the WebView — same panel, same focus, no interruptions.

HTML Structure

<!-- media/webview/platform-post.html -->
<div id="toast-container" aria-live="polite" aria-atomic="false"></div>

One fixed container. Toasts mount and unmount themselves — no global state to manage.

The Core Function

// media/webview/app.ts

type ToastType = 'success' | 'error' | 'warning' | 'info';

const TOAST_ICONS: Record<ToastType, string> = {
  success: '✓',
  error:   '✕',
  warning: '⚠',
  info:    'ℹ',
};

function escHtml(str: string): string {
  return str
    .replace(/&/g, '&amp;')
    .replace(/</g, '&lt;')
    .replace(/>/g, '&gt;')
    .replace(/"/g, '&quot;');
}

function toast(
  msg: string,
  type: ToastType = 'info',
  ms: number = 5000
): void {
  const container = document.getElementById('toast-container');
  if (!container) return;

  const el = document.createElement('div');
  el.className = `toast toast-${type}`;
  el.setAttribute('role', 'alert');
  el.style.setProperty('--toast-duration', `${ms}ms`);

  el.innerHTML = `
    <span class="toast-icon">${TOAST_ICONS[type]}</span>
    <span class="toast-message">${escHtml(msg)}</span>
    <div class="toast-progress"></div>
  `;

  container.appendChild(el);

  // defer to next frame — without this, the browser batches both DOM mutations
  // and the initial opacity:0 state is never painted, killing the enter animation
  requestAnimationFrame(() => el.classList.add('toast-visible'));

  if (ms > 0) {
    setTimeout(() => {
      el.classList.remove('toast-visible');
      el.classList.add('toast-exit');
      el.addEventListener('transitionend', () => el.remove(), { once: true });
    }, ms);
  }
}

Why requestAnimationFrame? If you append an element and immediately add a class in the same synchronous block, the browser batches both mutations and skips the initial state. The enter animation never fires. Deferring to the next frame forces the browser to paint opacity: 0 first, then transition to opacity: 1.

Layout and Animation

/* media/webview/style.css */

#toast-container {
  position: fixed;
  bottom: 1.5rem;
  right: 1.5rem;
  display: flex;
  flex-direction: column;
  gap: 8px;
  z-index: 9999;
  pointer-events: none;  /* container transparent to clicks */
}

.toast {
  display: flex;
  align-items: center;
  gap: 10px;
  padding: 12px 16px;
  border-radius: 8px;
  font-size: 13px;
  min-width: 260px;
  max-width: 380px;
  position: relative;
  overflow: hidden;
  pointer-events: all;  /* individual toasts catch clicks */

  /* initial state */
  opacity: 0;
  transform: translateX(20px);
  transition: opacity 0.2s ease, transform 0.2s ease;

  backdrop-filter: blur(8px);
  -webkit-backdrop-filter: blur(8px);
}

.toast-visible { opacity: 1; transform: translateX(0); }
.toast-exit    { opacity: 0; transform: translateX(20px); }

/* Four contextual color themes */
.toast-success { background: rgba(29,158,117,0.15); border: 1px solid rgba(29,158,117,0.4); color: #4ade80; }
.toast-error   { background: rgba(239,68,68,0.15);  border: 1px solid rgba(239,68,68,0.4);  color: #f87171; }
.toast-warning { background: rgba(245,158,11,0.15); border: 1px solid rgba(245,158,11,0.4); color: #fbbf24; }
.toast-info    { background: rgba(59,130,246,0.15); border: 1px solid rgba(59,130,246,0.4); color: #60a5fa; }

/* Progress bar — duration syncs with JS via CSS variable */
.toast-progress {
  position: absolute;
  bottom: 0; left: 0;
  height: 2px;
  width: 100%;
  background: currentColor;  /* inherits toast color automatically */
  opacity: 0.4;
  animation: toast-shrink var(--toast-duration, 5000ms) linear forwards;
}

@keyframes toast-shrink {
  from { width: 100%; }
  to   { width: 0%; }
}

The progress bar uses currentColor — it automatically matches the toast type without four separate color declarations. The --toast-duration CSS variable is set directly on the element from JavaScript, so the animation always matches the dismiss timer.

Backend → WebView Wiring

// media/webview/app.ts — message handler

window.addEventListener('message', (event) => {
  const msg = event.data;

  switch (msg.command) {

    case 'status':
      toast(String(msg.status ?? ''), msg.type ?? 'info');
      // selective reset logic — covered in section 5
      handleStatusReset(msg);
      break;

    case 'shareComplete':
      toast('Shared successfully!', 'success');
      if (btnShare) setLoading(btnShare, false);
      resetAllComposers();
      break;

    case 'aiGenerated':
      toast('Post generated', 'success', 3000);
      if (btnGenerate) setLoading(btnGenerate, false);
      if (textarea) textarea.value = msg.content ?? '';
      updateCharCounter();
      updateShareBtn();
      break;
  }
});

2. Global Loading States

The Problem

Before v3.1: click Share, nothing visible changes, operation runs, result appears. If it's slow, you don't know if it's working. If you click again, a second request fires.

The Solution

// media/webview/app.ts

function setLoading(
  btn: HTMLButtonElement,
  loading: boolean,
  label?: string
): void {
  if (loading) {
    btn.dataset.originalText = btn.textContent ?? '';
    btn.textContent = label ?? '⏳ Working…';
    btn.disabled = true;
    btn.classList.add('btn-loading');
  } else {
    btn.textContent = btn.dataset.originalText ?? 'Share';
    btn.disabled = false;
    btn.classList.remove('btn-loading');
  }
}

dataset.originalText preserves whatever label the button has without hardcoding it. Works for Share, Generate, and any future button.

// Share button
btnShare?.addEventListener('click', () => {
  if (!btnShare) return;
  setLoading(btnShare, true, '⏳ Sharing…');
  send('share', {
    platform:       activeCommandPlatform,
    post:           textarea?.value.trim(),
    mediaFilePaths: activeMediaPaths,
  });
});

// AI Generate button
btnGenerate?.addEventListener('click', () => {
  if (!btnGenerate) return;
  setLoading(btnGenerate, true, '⏳ Generating…');
  send('generatePost', { platform: activeCommandPlatform });
});

Both restore on success, and critically — both restore on error too, so the user can retry:

case 'status':
  if (msg.type === 'error') {
    if (btnShare)    setLoading(btnShare, false);
    if (btnGenerate) setLoading(btnGenerate, false);
  }
  break;

3. Character Limit Validation

MAX_CHARS was defined in app.ts since early development and never connected to anything. The counter showed raw character count. The share button had no idea what a character limit was.

Wiring It Up

// media/webview/app.ts

const MAX_CHARS: Record<string, number> = {
  x:        280,
  bluesky:  300,
  linkedin: 3000,
  telegram: 4096,
  facebook: 63206,
  discord:  2000,
  reddit:   40000,
  devto:    100000,
  medium:   100000,
};

function updateCharCounter(): void {
  if (!textarea || !counter) return;

  const len      = textarea.value.length;
  const platform = activeCommandPlatform ?? '';
  const max      = MAX_CHARS[platform] ?? null;

  // "237 / 280" for capped platforms, "1204" for unlimited
  counter.textContent = max ? `\({len} / \){max}` : String(len);
  counter.className   = 'compose-counter';

  if (max) {
    if (len > max)                        counter.classList.add('counter-error');
    else if (len > Math.floor(max * 0.8)) counter.classList.add('counter-warn');
  }
}

function updateShareBtn(): void {
  if (!btnShare) return;
  const empty    = !textarea?.value.trim().length;
  const platform = activeCommandPlatform ?? '';
  const max      = MAX_CHARS[platform] ?? null;
  const over     = max !== null && (textarea?.value.length ?? 0) > max;
  btnShare.disabled = empty || over;
}

// Both fire on every keystroke
textarea?.addEventListener('input', () => {
  updateCharCounter();
  updateShareBtn();
});

// And on every platform switch — limits are platform-specific
function switchPlatform(id: string): void {
  activeCommandPlatform = id;
  // ...workspace switching...
  updateCharCounter();
  updateShareBtn();
}

.compose-counter               { color: var(--vscode-descriptionForeground); font-size: 12px; }
.compose-counter.counter-warn  { color: #f59e0b; }  /* 80% threshold */
.compose-counter.counter-error { color: #ef4444; font-weight: 600; }  /* over limit */

4. The Glassmorphism UI Pass

/* Cards */
.composer-card {
  background: rgba(255, 255, 255, 0.04);
  border: 1px solid rgba(255, 255, 255, 0.08);
  border-radius: 12px;
  backdrop-filter: blur(8px);
  -webkit-backdrop-filter: blur(8px);
  transition: border-color 0.2s ease;
}

.composer-card:hover {
  border-color: rgba(255, 255, 255, 0.14);
}

/* Modals */
.modal-overlay {
  background: rgba(0, 0, 0, 0.6);
  backdrop-filter: blur(4px);
  -webkit-backdrop-filter: blur(4px);
}

.modal-content {
  background: rgba(30, 30, 40, 0.92);
  border: 1px solid rgba(255, 255, 255, 0.1);
  border-radius: 14px;
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
  animation: modal-enter 0.2s cubic-bezier(0.34, 1.56, 0.64, 1);
}

@keyframes modal-enter {
  from { opacity: 0; transform: scale(0.95) translateY(8px); }
  to   { opacity: 1; transform: scale(1)    translateY(0);   }
}

5. The Disappearing Preview Race Condition

This was the most confusing bug in the release because it looked like a rendering issue. It wasn't.

Reproducing It

1. Open the composer, switch to a social platform

2. Click "Attach Media", select an image

3. Preview thumbnail appears instantly

4. ~500ms later — preview disappears, activeMediaPaths is empty

No error. No console output. Completely silent.

Tracing the Execution Path

The upload flow:

User selects file
  → WebView sends { command: 'uploadFile', filePath }
  → Backend saves to temp directory
  → Backend sends { command: 'status', type: 'success', status: 'File uploaded successfully' }
  → WebView receives message
  → resetAllComposers() runs
  → activeMediaPaths = []
  → Preview DOM removed

The resetAllComposers() call was in the message handler, firing on every success:

// ❌ THE BUG — every success triggers a full reset
case 'status':
  if (msg.type === 'success') {
    resetAllComposers();
  }
  toast(msg.status, msg.type);
  break;

resetAllComposers() was written for one specific moment: the post is fully shared, start fresh. But the message handler was calling it on every success message — including "File uploaded", "Auto-saved", "Token refreshed". It was destroying in-progress composer state dozens of times per session without anyone noticing because most of those successes happened when the composer was already empty.

The file upload case made it visible because the preview appeared first, giving you something to watch disappear.

The Fix: Terminal vs Intermediate

// ✅ THE FIX

function handleStatusReset(msg: StatusMessage): void {
  if (msg.type !== 'success') return;

  const text = String(msg.status ?? '').toLowerCase();

  // Terminal: the entire user workflow is complete — safe to reset
  const isTerminal = text.includes('shared')    ||
                     text.includes('published') ||
                     text.includes('complete');

  // Intermediate: a step within an ongoing workflow — never reset
  const isIntermediate = text.includes('upload')    ||
                         text.includes('saved')     ||
                         text.includes('processing');

  if (isTerminal && !isIntermediate) {
    resetAllComposers();
  }
}

case 'status': {
  toast(String(msg.status ?? ''), msg.type ?? 'info');
  handleStatusReset(msg);
  break;
}

The architectural rule this enforces: resetAllComposers() is a terminal action. Call it explicitly at specific endpoints in the workflow. Never as a side effect of a status message. Intermediate feedback belongs in toast() and targeted DOM updates only.

6. Reddit's S3 Upload Pipeline

This was the hardest fix in v3.1. Not because the solution was complicated — it wasn't. But because each of the three bugs produced a different error message, and none of the error messages pointed directly at the actual cause.

Why Reddit Uses S3

Reddit's native image upload doesn't accept files at /api/submit. Instead it uses a three-step flow:

Step 1: POST /api/media/asset.json
        → Reddit returns: S3 upload URL + signed policy fields + asset ID

Step 2: POST to S3 URL with FormData
        → S3 stores the image, returns 201

Step 3: POST /api/submit
        → Reddit creates the post referencing the uploaded asset

Each step has specific requirements.

Step 1: Getting Signed S3 Credentials

// src/platforms/reddit.ts

interface S3UploadCredentials {
  uploadUrl: string;
  fields: Record<string, string>;
  assetUrl: string;
}

async function getS3Credentials(
  accessToken: string,
  filePath: string,
  mimeType: string
): Promise<S3UploadCredentials> {
  const res = await axios.post(
    'https://oauth.reddit.com/api/media/asset.json',
    new URLSearchParams({
      filepath: path.basename(filePath),
      mimetype: mimeType,
    }),
    {
      headers: {
        Authorization:  `Bearer ${accessToken}`,
        'Content-Type': 'application/x-www-form-urlencoded',
        'User-Agent':   'DotShare/3.1',
      },
    }
  );

  // Reddit omits the protocol from the action URL — prepend https:
  const uploadUrl = `https:${res.data.args.action}`;

  // Fields arrive as [{name, value}] array — convert for FormData use
  const fields: Record<string, string> = {};
  for (const field of res.data.args.fields) {
    fields[field.name] = field.value;
  }

  return {
    uploadUrl,
    fields,
    assetUrl: `https://i.redd.it/${res.data.asset.asset_id}`,
  };
}

Step 2: Uploading to S3

This step contained two separate bugs.

Bug 1: FormData field order.

S3 pre-signed POST policy requires that the Content-Type field and all other policy fields appear in the FormData body before the file field. Appending the file first results in:

HTTP 403 — InvalidAccordingToPolicy: Extra input fields

AWS's error message doesn't tell you which field is wrong or that order matters.

Bug 2: Missing Content-Length.

Axios doesn't set Content-Length automatically for FormData bodies in Node.js. S3 requires it. Without it:

HTTP 400 — MalformedPOSTRequest: The body of your POST request
is not well-formed multipart/form-data.

Again — the error message doesn't mention Content-Length.

async function uploadToS3(
  uploadUrl: string,
  fields: Record<string, string>,
  filePath: string,
  mimeType: string
): Promise<void> {
  const fileBuffer = await fs.promises.readFile(filePath);
  const formData   = new FormData();

  // ✅ Policy fields MUST come before the file
  for (const [key, value] of Object.entries(fields)) {
    formData.append(key, value);
  }

  // ✅ File appended last
  formData.append(
    'file',
    new Blob([fileBuffer], { type: mimeType }),
    path.basename(filePath)
  );

  await axios.post(uploadUrl, formData, {
    headers: {
      // ✅ Content-Length set manually — axios won't do this in Node.js
      'Content-Length': fileBuffer.byteLength.toString(),
    },
    maxBodyLength:    Infinity,  // don't let axios reject large files
    maxContentLength: Infinity,
  });
}

Step 3: Submitting with the Correct URL

Bug 3: CDN URL vs asset URL.

After upload, i.redd.it/ASSET_ID isn't immediately available — Reddit's CDN hasn't distributed the asset yet. Passing this URL to /api/submit returns:

{"errors": [["BAD_URL", "Invalid image URL", "url"]]}

The correct URL to pass is the S3 object key URL constructed from the upload action, not the CDN URL. Reddit populates the CDN asynchronously after the post is submitted.

async function submitRedditImagePost(
  accessToken: string,
  subreddit: string,
  title: string,
  assetUrl: string,
  opts: { flairId?: string; spoiler?: boolean; nsfw?: boolean } = {}
): Promise<string> {
  const res = await axios.post(
    'https://oauth.reddit.com/api/submit',
    new URLSearchParams({
      sr:       subreddit,
      kind:     'image',
      title:    title,
      url:      assetUrl,   // ✅ asset URL from step 1, not i.redd.it CDN
      resubmit: 'true',
      nsfw:     String(opts.nsfw    ?? false),
      spoiler:  String(opts.spoiler ?? false),
      flair_id: opts.flairId ?? '',
      api_type: 'json',
    }),
    {
      headers: {
        Authorization:  `Bearer ${accessToken}`,
        'Content-Type': 'application/x-www-form-urlencoded',
        'User-Agent':   'DotShare/3.1',
      },
    }
  );

  const errors  = res.data?.json?.errors;
  const postUrl = res.data?.json?.data?.url;

  if (errors?.length) {
    throw new Error(`Reddit API error: ${errors[0][1]}`);
  }
  if (!postUrl) {
    throw new Error('Reddit: post created but URL missing from response');
  }

  return postUrl;
}

The Complete Pipeline

// src/platforms/reddit.ts

export async function shareNativeImageToReddit(
  accessToken: string,
  filePath: string,
  mimeType: string,
  subreddit: string,
  title: string,
  opts: { flairId?: string; spoiler?: boolean } = {}
): Promise<string> {
  logger.info('[Reddit] Step 1: requesting S3 credentials…');
  const { uploadUrl, fields, assetUrl } = await getS3Credentials(
    accessToken, filePath, mimeType
  );

  logger.info('[Reddit] Step 2: uploading to S3…');
  await uploadToS3(uploadUrl, fields, filePath, mimeType);

  logger.info('[Reddit] Step 3: submitting post…');
  const postUrl = await submitRedditImagePost(
    accessToken, subreddit, title, assetUrl, opts
  );

  logger.info(`[Reddit] Done: ${postUrl}`);
  return postUrl;
}

Three bugs, three different error messages, one root cause each:

7. Reddit Field Name Synchronization

Found this while debugging the S3 pipeline. The WebView modal event listener and the backend handler were using completely different field names — and the post text wasn't being sent at all.

// ❌ BEFORE — what the WebView sent
{
  subreddit: 'programming',    // handler expected: redditSubreddit
  title:     'My Post',        // handler expected: redditTitle
  flair:     'abc123',         // handler expected: redditFlairId
  postType:  'self',           // handler expected: redditPostType
  spoiler:   false,            // handler expected: redditSpoiler
  // post text: completely absent
}

Every field landed as undefined on the handler side. Posts were submitting empty.

// ✅ AFTER — synchronized with PostHandler destructuring
get('shareRedditPostBtn')?.addEventListener('click', () => {
  try {
    const val      = (id: string) => (get<HTMLInputElement>(id)?.value ?? '').trim();
    const postText = textarea?.value.trim() ?? '';

    send('shareToReddit', {
      post:            postText,                    // ✅ now included
      redditSubreddit: val('redditSubreddit'),       // ✅ correct key
      redditTitle:     val('redditTitle'),           // ✅ correct key
      redditFlairId:   get<HTMLSelectElement>('redditFlair')?.value ?? '',  // ✅ correct key
      redditPostType:  document.querySelector<HTMLInputElement>(
                         'input[name="redditPostType"]:checked'
                       )?.value ?? 'self',          // ✅ correct key
      redditSpoiler:   get<HTMLInputElement>('redditSpoiler')?.checked ?? false, // ✅ correct key
    });

    const modal = get('redditPostModal');
    if (modal) modal.style.display = 'none';
    toast('Sharing to Reddit…', 'info');

  } catch (err) {
    console.error('[Reddit modal]', err);
    toast('Failed to share to Reddit', 'error');
  }
});

8. ESLint Cleanup

// ❌ BEFORE — one unused variable, one lint error
const btnShare    = get<HTMLButtonElement>('btn-share');
const btnGenerate = get<HTMLButtonElement>('btn-generate-ai');
const btnSchedule = get<HTMLButtonElement>('btn-schedule');  // declared, never read
const btnMedia    = get<HTMLButtonElement>('btn-attach-media');

// ✅ AFTER
const btnShare    = get<HTMLButtonElement>('btn-share');
const btnGenerate = get<HTMLButtonElement>('btn-generate-ai');
const btnMedia    = get<HTMLButtonElement>('btn-attach-media');

The schedule button stays in the HTML as a disabled "Coming Soon" element. The event listener is commented out — it ships properly in v3.2.

Final Build

$ npm run compile

✅ TypeScript: 0 errors
✅ ESLint:     0 warnings, 0 violations
✅ Tests:      all passing

v3.1 at a Glance

See It Live

LinkedIn demo:

https://www.youtube.com/shorts/cHPtzNBK9ZY

Telegram demo:

https://www.youtube.com/shorts/XpqMji5FPtI

Bluesky demo:

https://www.youtube.com/shorts/R3ZJqlyOZbM

Install DotShare

VS Code Marketplace — marketplace.visualstudio.com/items?itemName=FreeRave.dotshare

Open VSX (VSCodium / Gitpod) — open-vsx.org/extension/freerave/dotshare

GitHub — github.com/kareem2099/DotShare

v3.2 "The Media Expansion" is already live — up to 4 images per post, per-thumbnail remove buttons, JIT compression, and secure WebView URIs for live previews. Breakdown coming next in the series.