From 219aef046afabf361b78e1c5c22430ce37f0e5ec Mon Sep 17 00:00:00 2001
From: Linus Rath <139418639+rathlinus@users.noreply.github.com>
Date: Sat, 31 Oct 2026 04:42:37 +0100
Subject: [PATCH] fix: drop a leading style sheet and padding from message
 previews (bulwarkmail/webmail#1136)

---
 src/components/email/ThreadMessageCard.tsx |  3 +-
 src/lib/__tests__/preview-text.test.ts     | 88 ++++++++++++++++++++++
 src/lib/preview-text.ts                    | 88 ++++++++++++++++++++++
 src/screens/EmailListScreen.tsx            |  3 +-
 src/screens/UnifiedInboxScreen.tsx         |  3 +-
 5 files changed, 182 insertions(+), 3 deletions(-)
 create mode 100644 src/lib/__tests__/preview-text.test.ts
 create mode 100644 src/lib/preview-text.ts

diff --git a/src/components/email/ThreadMessageCard.tsx b/src/components/email/ThreadMessageCard.tsx
index 6fd10d7e..51c822ac 100644
--- a/src/components/email/ThreadMessageCard.tsx
+++ b/src/components/email/ThreadMessageCard.tsx
@@ -10,6 +10,7 @@ import SenderAvatar from '../SenderAvatar';
 import { MessageContent, type MessageContentProps } from './MessageContent';
 import { emailDisplayDate, formatHeaderDate, formatHeaderTime } from '../../lib/email-date';
 import { singleLine } from '../../lib/single-line';
+import { cleanPreview } from '../../lib/preview-text';
 import { useSenderWarning } from './use-sender-warning';
 
 interface Props extends MessageContentProps {
@@ -58,7 +59,7 @@ export function ThreadMessageCard({
             {email.hasAttachment && <Paperclip size={12} color={c.textMuted} />}
             <Text style={styles.collapsedDate}>{formatHeaderDate(date, locale)} {formatHeaderTime(date, timeFormat, locale)}</Text>
           </View>
-          <Text style={styles.collapsedPreview} numberOfLines={1}>{singleLine(email.preview)}</Text>
+          <Text style={styles.collapsedPreview} numberOfLines={1}>{singleLine(cleanPreview(email.preview))}</Text>
         </View>
         {starred && <Star size={14} color={c.starred} fill={c.starred} />}
       </Pressable>
diff --git a/src/lib/__tests__/preview-text.test.ts b/src/lib/__tests__/preview-text.test.ts
new file mode 100644
index 00000000..2acc9fda
--- /dev/null
+++ b/src/lib/__tests__/preview-text.test.ts
@@ -0,0 +1,88 @@
+import { describe, expect, it } from 'vitest';
+import fs from 'node:fs';
+import path from 'node:path';
+import { cleanPreview, stripEmphasisMarkers, stripLeadingCss } from '../preview-text';
+
+// Copied from the webmail (lib/__tests__/preview-leading-css.test.ts), plus
+// the check that the list rows use it (#1136).
+
+// Some servers build a message preview from its HTML without skipping the
+// <style> element, so a marketing mail's preview starts with its style sheet.
+describe('stripLeadingCss', () => {
+  it('drops a leading media query and keeps the text after it', () => {
+    const preview = '@media screen and (min-width:600px){.hide{display:none!important;overflow:hidden!important}.show{display:block!important}} Your parcel is on its way';
+    expect(stripLeadingCss(preview)).toBe('Your parcel is on its way');
+  });
+
+  it('drops several leading rules in a row', () => {
+    expect(stripLeadingCss('.a{color:red} #b p{margin:0} td, th {padding:0}Hello')).toBe('Hello');
+  });
+
+  it('drops a leading @import that ends without a block', () => {
+    expect(stripLeadingCss("@import url('x.css'); Weekly digest")).toBe('Weekly digest');
+  });
+
+  it('empties a preview that ends inside the style sheet', () => {
+    expect(stripLeadingCss('@media screen and (min-width:600px){.hide{display:none!important;max-height:0!import')).toBe('');
+  });
+
+  it('leaves ordinary text alone, braces and all', () => {
+    for (const text of [
+      'Hi Luca, the meeting is at {time} tomorrow',
+      '#1234 has been shipped',
+      '@Luca can you check the figures?',
+      'Order {A-17} confirmed',
+      'Price {EUR}: 10 per box',
+      'Meeting at {room',
+      '@media team, the brief is attached',
+      '@Page can you check?',
+      '@import the CSV, then send it back',
+      'Reminder: your appointment {date: 2026-10-01} is confirmed',
+    ]) expect(stripLeadingCss(text)).toBe(text);
+  });
+});
+
+describe('cleanPreview', () => {
+  it('strips padding and a style sheet together, and treats nothing left as no preview', () => {
+    expect(cleanPreview('\u034f \u200b.x{color:red} Real text')).toBe('Real text');
+    expect(cleanPreview('.x{color:red} ...')).toBe('');
+    expect(cleanPreview(null)).toBe('');
+  });
+});
+
+// The preview comes from the text/plain part, which marks bold with asterisks
+// where the HTML part uses <strong> (#1260).
+describe('stripEmphasisMarkers', () => {
+  it('drops emphasis markers around words', () => {
+    expect(cleanPreview('*@Claude* mentioned you: please review')).toBe('@Claude mentioned you: please review');
+    expect(stripEmphasisMarkers('This is **really** important.')).toBe('This is really important.');
+    expect(stripEmphasisMarkers('See _the docs_ and __this__, (*now*)')).toBe('See the docs and this, (now)');
+  });
+
+  it('leaves asterisks and underscores inside words or between spaces alone', () => {
+    for (const text of [
+      '2 * 3 * 4 = 24',
+      'a*b*c and snake_case_name',
+      'rating: * * *',
+      'my_var_ is set',
+      'footnote* and *',
+      '***',
+      '__init__.py changed',
+    ]) expect(stripEmphasisMarkers(text)).toBe(text);
+  });
+});
+
+describe('stripLeadingCss pseudo-classes', () => {
+  it('still drops a rule whose selector has a pseudo-class', () => {
+    expect(stripLeadingCss('a:hover, a:focus{color:red} Hello')).toBe('Hello');
+  });
+});
+
+describe('list rows', () => {
+  it('show the cleaned preview', () => {
+    const read = (p: string) => fs.readFileSync(path.resolve(__dirname, '../..', p), 'utf8');
+    expect(read('screens/EmailListScreen.tsx')).toMatch(/singleLine\(cleanPreview\(item\.preview\)\)/);
+    expect(read('screens/UnifiedInboxScreen.tsx')).toMatch(/singleLine\(cleanPreview\(item\.preview\)\)/);
+    expect(read('components/email/ThreadMessageCard.tsx')).toMatch(/singleLine\(cleanPreview\(email\.preview\)\)/);
+  });
+});
diff --git a/src/lib/preview-text.ts b/src/lib/preview-text.ts
new file mode 100644
index 00000000..812e0a8b
--- /dev/null
+++ b/src/lib/preview-text.ts
@@ -0,0 +1,88 @@
+// Message previews ready to show (webmail lib/utils.ts cleanPreview, #1136,
+// #1260): some servers build the preview from an HTML body without skipping
+// its <style>, so a marketing mail's preview began with CSS; preheaders pad
+// with invisible characters; text/plain emphasis markers ("*bold*") show.
+// Copied from the webmail as it is.
+
+// Marketing emails pad the preheader with whitespace, format chars (soft
+// hyphens, zero-width chars, BOM, directional marks) and combining marks
+// (e.g. U+034F) to push real content past the preview window. Strip them all.
+// \p{Cf} = Format, \p{Mn} = combining marks; \s covers figure space, NBSP, etc.
+const LEADING_INVISIBLE_RE = /^[\s\p{Cf}\p{Mn}]+/u;
+// After stripping, a server-side truncation indicator like "..." may be all
+// that's left. Treat that as no preview so callers can fall back.
+const ONLY_PUNCTUATION_RE = /^[.\u2026\s]+$/;
+
+export function stripInvisibleLeading(text: string): string {
+  const stripped = text.replace(LEADING_INVISIBLE_RE, '');
+  if (ONLY_PUNCTUATION_RE.test(stripped)) return '';
+  return stripped;
+}
+
+// A style sheet at the start of the text: an at-rule, or a selector opening a
+// rule. Plain prose does not start like this - "@" or "#" followed by a word
+// and then, before any sentence ends, a "{".
+const DECLARATIONS_RE = /^\s*(?:[-\w]+\s*:|[.#@a-z*][^{}]*\{)/i;
+// At-rule names are matched case-sensitively: style sheets write them in lower
+// case, while "@Page …" at the start of a preview is a mention. A selector's
+// colon is a pseudo-class ("a:hover"), never followed by a space as in
+// "Reminder: your appointment {date: …}".
+const AT_RULE_RE = /^@(?:media|font-face|import|supports|keyframes|charset|page)\b/;
+const SELECTOR_RE = /^[.#]?[a-z*](?:[\w\-.#,>~+*\s[\]="']|:(?!\s))*\{/i;
+
+/**
+ * Drops a style sheet from the start of a text preview.
+ *
+ * Some servers build the preview from an HTML body without skipping its
+ * <style> element, so a marketing mail's preview can begin with
+ * "@media screen and (min-width:600px){.hide{display:none!important;…" and
+ * never reach the text. Whole leading rules are removed; a preview that ends
+ * inside one was nothing but CSS and becomes empty, so callers fall back to
+ * their "no preview" text.
+ */
+export function stripLeadingCss(text: string): string {
+  let rest = text.trimStart();
+  for (let guard = 0; guard < 100 && (AT_RULE_RE.test(rest) || SELECTOR_RE.test(rest)); guard++) {
+    const brace = rest.indexOf('{');
+    const semicolon = rest.indexOf(';');
+    // `@import url(...);` and `@charset "x";` end without a block.
+    if (semicolon >= 0 && (brace < 0 || semicolon < brace) && /^@(?:import|charset)\b/.test(rest)) {
+      rest = rest.slice(semicolon + 1).trimStart();
+      continue;
+    }
+    // An at-rule word with no block after it ("@media team, …", "@page 3 …")
+    // starts prose, not a style sheet.
+    if (brace < 0) return rest;
+    let depth = 0;
+    let end = -1;
+    for (let i = brace; i < rest.length; i++) {
+      if (rest[i] === '{') depth++;
+      else if (rest[i] === '}' && --depth === 0) { end = i; break; }
+    }
+    if (end < 0) return rest.startsWith('@') || DECLARATIONS_RE.test(rest.slice(brace + 1)) ? '' : rest;
+    // A rule's block holds declarations ("color: red") or further rules; a
+    // brace in prose ("at {time} tomorrow") holds neither and ends the strip.
+    if (!rest.startsWith('@') && !DECLARATIONS_RE.test(rest.slice(brace + 1, end))) return rest;
+    rest = rest.slice(end + 1).trimStart();
+  }
+  return rest;
+}
+
+// Plain-text emphasis: "*bold*", "**bold**", "_italic_", "__bold__". The
+// markers sit at word edges, so "2 * 3 * 4", "a*b*c", "snake_case_name" and
+// "__init__.py" are left alone.
+const EMPHASIS_RE = /(^|[\s([{"'])(\*\*|__|\*|_)([^\s*_]|[^\s*_].*?[^\s])\2(?=$|[\s)\]}"']|[.,;:!?](?!\w))/g;
+
+/**
+ * Drops plain-text emphasis markers. The server builds the preview from the
+ * text/plain part, where senders like GitHub write "*@user* mentioned you"
+ * while the HTML part shows it in bold.
+ */
+export function stripEmphasisMarkers(text: string): string {
+  return text.replace(EMPHASIS_RE, '$1$3');
+}
+
+/** A message preview ready to show: no leading padding, style sheet or emphasis markers. */
+export function cleanPreview(text: string | null | undefined): string {
+  return stripEmphasisMarkers(stripInvisibleLeading(stripLeadingCss(stripInvisibleLeading(text ?? ''))));
+}
diff --git a/src/screens/EmailListScreen.tsx b/src/screens/EmailListScreen.tsx
index f11c5214..0411ea1d 100644
--- a/src/screens/EmailListScreen.tsx
+++ b/src/screens/EmailListScreen.tsx
@@ -51,6 +51,7 @@ import { toast } from '../stores/toast-store';
 import { getContactDisplayName } from '../lib/contact-utils';
 import { formatListDate } from '../lib/date-format';
 import { singleLine } from '../lib/single-line';
+import { cleanPreview } from '../lib/preview-text';
 import {
   findTrashMailbox, findArchiveMailbox, findJunkMailbox, mailboxesForSiblingOf, ownMailboxes,
 } from '../lib/mailbox-tree';
@@ -304,7 +305,7 @@ const EmailRow = React.memo(function EmailRow({
         {/* Row 3: Preview - hidden in compact density modes regardless of toggle */}
         {showPreview && density.showPreview && (
           <Text style={[styles.emailPreview, dyn.body]} numberOfLines={2}>
-            {singleLine(item.preview)}
+            {singleLine(cleanPreview(item.preview))}
           </Text>
         )}
         {verificationCode && <VerificationCodeChip code={verificationCode} disabled={selectionMode} inList />}
diff --git a/src/screens/UnifiedInboxScreen.tsx b/src/screens/UnifiedInboxScreen.tsx
index a912c350..adf60fec 100644
--- a/src/screens/UnifiedInboxScreen.tsx
+++ b/src/screens/UnifiedInboxScreen.tsx
@@ -23,6 +23,7 @@ import { useSettingsStore, type SwipeAction } from '../stores/settings-store';
 import { useLocaleStore } from '../stores/locale-store';
 import { formatListDate } from '../lib/date-format';
 import { singleLine } from '../lib/single-line';
+import { cleanPreview } from '../lib/preview-text';
 import { prefetchMessage, rememberRows } from '../lib/email-detail-cache';
 import { isPermanentDelete, confirmPermanentDelete } from '../lib/delete-confirm';
 import { confirmMailRemoval } from '../lib/mail-removal-confirm';
@@ -396,7 +397,7 @@ export default function UnifiedInboxScreen({ navigation, route }: Props) {
             </View>
             {/* Same settings as the folder list: preview on/off, density, text size. */}
             {item.preview && showPreview && density.showPreview ? (
-              <Text style={[styles.preview, dyn.body]} numberOfLines={2}>{singleLine(item.preview)}</Text>
+              <Text style={[styles.preview, dyn.body]} numberOfLines={2}>{singleLine(cleanPreview(item.preview))}</Text>
             ) : null}
           </View>
         </Pressable>