markdown: Show thumbnails for uploaded images.

Fixes: #16210.
2024-06-21 19:02:36 +00:00 · 2024-06-21 19:02:36 +00:00 · b42863be4b
parent 71406ac767
commit b42863be4b
11 changed files with 654 additions and 149 deletions
--- a/web/src/lightbox.ts
+++ b/web/src/lightbox.ts
@ -509,6 +509,8 @@ export function parse_media_data(media: HTMLElement): Payload {
        type = "image";
        if ($media.attr("data-src-fullsize")) {
            source = $media.attr("data-src-fullsize");
+        } else if ($media.attr("src")?.startsWith("/user_uploads/thumbnail/")) {
+            source = url;
        } else {
            source = preview_src;
        }
--- a/zerver/actions/message_edit.py
+++ b/zerver/actions/message_edit.py
@ -366,33 +366,30 @@ def update_user_message_flags(
 def do_update_embedded_data(
    user_profile: UserProfile,
    message: Message,
-    content: str | None,
-    rendering_result: MessageRenderingResult,
+    rendered_content: str | MessageRenderingResult,
 ) -> None:
-    timestamp = timezone_now()
+    ums = UserMessage.objects.filter(message=message.id)
+    update_fields = ["rendered_content"]
+    if isinstance(rendered_content, MessageRenderingResult):
+        update_user_message_flags(rendered_content, ums)
+        message.rendered_content = rendered_content.rendered_content
+        message.rendered_content_version = markdown_version
+        update_fields.append("rendered_content_version")
+    else:
+        message.rendered_content = rendered_content
+    message.save(update_fields=update_fields)
+
+    update_message_cache([message])
    event: dict[str, Any] = {
        "type": "update_message",
        "user_id": None,
-        "edit_timestamp": datetime_to_timestamp(timestamp),
+        "edit_timestamp": datetime_to_timestamp(timezone_now()),
        "message_id": message.id,
+        "message_ids": [message.id],
+        "content": message.content,
+        "rendered_content": message.rendered_content,
        "rendering_only": True,
    }
-    changed_messages = [message]
-    rendered_content: str | None = None
-
-    ums = UserMessage.objects.filter(message=message.id)
-
-    if content is not None:
-        update_user_message_flags(rendering_result, ums)
-        rendered_content = rendering_result.rendered_content
-        message.rendered_content = rendered_content
-        message.rendered_content_version = markdown_version
-        event["content"] = content
-        event["rendered_content"] = rendered_content
-
-    message.save(update_fields=["content", "rendered_content"])
-
-    event["message_ids"] = update_message_cache(changed_messages)

    def user_info(um: UserMessage) -> dict[str, Any]:
        return {
--- a/zerver/lib/markdown/init.py
+++ b/zerver/lib/markdown/init.py
@ -13,7 +13,7 @@ from datetime import datetime, timezone
 from functools import lru_cache
 from re import Match, Pattern
 from typing import Any, Generic, Optional, TypeAlias, TypedDict, TypeVar, cast
-from urllib.parse import parse_qs, quote, urlencode, urljoin, urlsplit, urlunsplit
+from urllib.parse import parse_qs, quote, urljoin, urlsplit, urlunsplit
 from xml.etree.ElementTree import Element, SubElement

 import ahocorasick
@ -55,7 +55,7 @@ from zerver.lib.mention import (
 from zerver.lib.outgoing_http import OutgoingSession
 from zerver.lib.subdomains import is_static_or_current_realm_url
 from zerver.lib.tex import render_tex
-from zerver.lib.thumbnail import user_uploads_or_external
+from zerver.lib.thumbnail import get_user_upload_previews, rewrite_thumbnailed_images
 from zerver.lib.timeout import unsafe_timeout
 from zerver.lib.timezone import common_timezones
 from zerver.lib.types import LinkifierDict
@ -125,6 +125,7 @@ class DbData:
    sent_by_bot: bool
    stream_names: dict[str, int]
    translate_emoticons: bool
+    user_upload_previews: dict[str, tuple[str, bool] | None]


 # Format version of the Markdown rendering; stored along with rendered
@ -615,18 +616,21 @@ class InlineInterestingLinkProcessor(markdown.treeprocessors.Treeprocessor):
        if data_id is not None:
            a.set("data-id", data_id)
        img = SubElement(a, "img")
-        if (
-            settings.THUMBNAIL_IMAGES
-            and (not already_thumbnailed)
-            and user_uploads_or_external(image_url)
-        ):
-            # We strip leading '/' from relative URLs here to ensure
-            # consistency in what gets passed to /thumbnail
-            image_url = image_url.lstrip("/")
-            img.set("src", "/thumbnail?" + urlencode({"url": image_url, "size": "thumbnail"}))
-            img.set(
-                "data-src-fullsize", "/thumbnail?" + urlencode({"url": image_url, "size": "full"})
-            )
+        if image_url.startswith("/user_uploads/") and self.zmd.zulip_db_data:
+            path_id = image_url[len("/user_uploads/") :]
+
+            # We should have pulled the preview data for this image
+            # (even if that's "no preview yet") from the database
+            # before rendering; is_image should have enforced that.
+            assert path_id in self.zmd.zulip_db_data.user_upload_previews
+
+            # Insert a placeholder image spinner.  We post-process
+            # this content (see rewrite_thumbnailed_images in
+            # zerver.lib.thumbnail), looking specifically for this
+            # tag, and may re-write it into the thumbnail URL if it
+            # already exists when the message is sent.
+            img.set("class", "image-loading-placeholder")
+            img.set("src", "/static/images/loading/loader-black.svg")
        else:
            img.set("src", image_url)

@ -724,6 +728,13 @@ class InlineInterestingLinkProcessor(markdown.treeprocessors.Treeprocessor):
        if parsed_url.netloc == "pasteboard.co":
            return False

+        # Check against the previews we generated -- if we didn't have
+        # a row for the ImageAttachment, then its header didn't parse
+        # as a valid image type which libvips handles.
+        if url.startswith("/user_uploads/") and self.zmd.zulip_db_data:
+            path_id = url[len("/user_uploads/") :]
+            return path_id in self.zmd.zulip_db_data.user_upload_previews
+
        return any(parsed_url.path.lower().endswith(ext) for ext in IMAGE_EXTENSIONS)

    def corrected_image_source(self, url: str) -> str | None:
@ -2623,6 +2634,7 @@ def do_convert(
    _md_engine.url_embed_data = url_embed_data

    # Pre-fetch data from the DB that is used in the Markdown thread
+    user_upload_previews = None
    if message_realm is not None:
        # Here we fetch the data structures needed to render
        # mentions/stream mentions from the database, but only
@ -2645,6 +2657,7 @@ def do_convert(
        else:
            active_realm_emoji = {}

+        user_upload_previews = get_user_upload_previews(message_realm.id, content)
        _md_engine.zulip_db_data = DbData(
            realm_alert_words_automaton=realm_alert_words_automaton,
            mention_data=mention_data,
@ -2653,6 +2666,7 @@ def do_convert(
            sent_by_bot=sent_by_bot,
            stream_names=stream_name_info,
            translate_emoticons=translate_emoticons,
+            user_upload_previews=user_upload_previews,
        )

    try:
@ -2663,6 +2677,14 @@ def do_convert(
        # infinite-loop).
        rendering_result.rendered_content = unsafe_timeout(5, lambda: _md_engine.convert(content))

+        # Post-process the result with the rendered image previews:
+        if user_upload_previews is not None:
+            content_with_thumbnails = rewrite_thumbnailed_images(
+                rendering_result.rendered_content, user_upload_previews
+            )
+            if content_with_thumbnails is not None:
+                rendering_result.rendered_content = content_with_thumbnails
+
        # Throw an exception if the content is huge; this protects the
        # rest of the codebase from any bugs where we end up rendering
        # something huge.
--- a/zerver/lib/thumbnail.py
+++ b/zerver/lib/thumbnail.py
@ -8,6 +8,7 @@ from typing import TypeVar
 from urllib.parse import urljoin

 import pyvips
+from bs4 import BeautifulSoup
 from django.utils.http import url_has_allowed_host_and_scheme
 from django.utils.translation import gettext as _
 from typing_extensions import override
@ -136,12 +137,6 @@ class BadImageError(JsonableError):
    code = ErrorCode.BAD_IMAGE


-def user_uploads_or_external(url: str) -> bool:
-    return not url_has_allowed_host_and_scheme(url, allowed_hosts=None) or url.startswith(
-        "/user_uploads/"
-    )
-
-
 def generate_thumbnail_url(path: str, size: str = "0x0") -> str:
    path = urljoin("/", path)

@ -324,3 +319,99 @@ def split_thumbnail_path(file_path: str) -> tuple[str, BaseThumbnailFormat]:
    assert thumbnail_format is not None
    path_id = "/".join(path_parts[1:])
    return path_id, thumbnail_format
+
+
+def get_user_upload_previews(realm_id: int, content: str) -> dict[str, tuple[str, bool] | None]:
+    matches = re.findall(r"/user_uploads/(\d+/[/\w.-]+)", content)
+    upload_preview_data: dict[str, tuple[str, bool] | None] = {}
+    for image_attachment in ImageAttachment.objects.filter(realm_id=realm_id, path_id__in=matches):
+        if image_attachment.thumbnail_metadata == []:
+            # Image exists, and header of it parsed as a valid image,
+            # but has not been thumbnailed yet; we will render a
+            # spinner.
+            upload_preview_data[image_attachment.path_id] = None
+        else:
+            upload_preview_data[image_attachment.path_id] = get_default_thumbnail_url(
+                image_attachment
+            )
+    return upload_preview_data
+
+
+def get_default_thumbnail_url(image_attachment: ImageAttachment) -> tuple[str, bool]:
+    # For "dumb" clients which cannot rewrite it into their
+    # preferred format and size, we choose the first one in
+    # THUMBNAIL_OUTPUT_FORMATS which matches the animated/not
+    # nature of the source image.
+    found_format: ThumbnailFormat | None = None
+    for thumbnail_format in THUMBNAIL_OUTPUT_FORMATS:
+        if thumbnail_format.animated == (image_attachment.frames > 1):
+            found_format = thumbnail_format
+            break
+    if found_format is None:
+        # No animated thumbnail formats exist somehow, and the
+        # image is animated?  Just take the first thumbnail
+        # format.
+        found_format = THUMBNAIL_OUTPUT_FORMATS[0]
+    return (
+        "/user_uploads/" + get_image_thumbnail_path(image_attachment, found_format),
+        found_format.animated,
+    )
+
+
+def rewrite_thumbnailed_images(
+    rendered_content: str,
+    images: dict[str, tuple[str, bool] | None],
+    to_delete: set[str] | None = None,
+) -> str | None:
+    if not images and not to_delete:
+        return None
+
+    parsed_message = BeautifulSoup(rendered_content, "html.parser")
+
+    changed = False
+    for inline_image_div in parsed_message.find_all("div", class_="message_inline_image"):
+        image_link = inline_image_div.find("a")
+        if (
+            image_link is None
+            or image_link["href"] is None
+            or not image_link["href"].startswith("/user_uploads/")
+        ):
+            # This is not an inline image generated by the markdown
+            # processor for a locally-uploaded image.
+            continue
+        image_tag = image_link.find("img", class_="image-loading-placeholder")
+        if image_tag is None:
+            # The placeholder was already replaced -- for instance,
+            # this is expected if multiple images are included in the
+            # same message.  The second time this is run, for the
+            # second image, the first image will have no placeholder.
+            continue
+
+        path_id = image_link["href"][len("/user_uploads/") :]
+        if to_delete and path_id in to_delete:
+            # This was not a valid thumbnail target, for some reason.
+            # Trim out the whole "message_inline_image" element, since
+            # it's not going be renderable by clients either.
+            inline_image_div.decompose()
+            changed = True
+            continue
+
+        image_data = images.get(path_id)
+        if image_data is None:
+            # Has not been thumbnailed yet; leave it as a spinner.
+            # This happens routinely when a message contained multiple
+            # unthumbnailed images, and only one of those images just
+            # completed thumbnailing.
+            pass
+        else:
+            changed = True
+            del image_tag["class"]
+            image_tag["src"], is_animated = image_data
+            if is_animated:
+                image_tag["data-animated"] = "true"
+
+    if changed:
+        # The formatter="html5" means we do not produce self-closing tags
+        return parsed_message.encode(formatter="html5").decode().strip()
+    else:
+        return None
--- a/zerver/tests/fixtures/markdown_test_cases.json
+++ b/zerver/tests/fixtures/markdown_test_cases.json
@ -408,7 +408,7 @@
    {
      "name": "inline_image",
      "input": "Google logo today: https://www.google.com/images/srpr/logo4w.png\nKinda boring",
-      "expected_output": "<p>Google logo today: <a href=\"https://www.google.com/images/srpr/logo4w.png\">https://www.google.com/images/srpr/logo4w.png</a><br>\nKinda boring</p>\n<div class=\"message_inline_image\"><a href=\"https://www.google.com/images/srpr/logo4w.png\"><img data-src-fullsize=\"/thumbnail?url=https%3A%2F%2Fwww.google.com%2Fimages%2Fsrpr%2Flogo4w.png&amp;size=full\" src=\"/thumbnail?url=https%3A%2F%2Fwww.google.com%2Fimages%2Fsrpr%2Flogo4w.png&amp;size=thumbnail\"></a></div>",
+      "expected_output": "<p>Google logo today: <a href=\"https://www.google.com/images/srpr/logo4w.png\">https://www.google.com/images/srpr/logo4w.png</a><br>\nKinda boring</p>\n<div class=\"message_inline_image\"><a href=\"https://www.google.com/images/srpr/logo4w.png\"><img src=\"https://external-content.zulipcdn.net/external_content/56c362a24201593891955ff526b3b412c0f9fcd2/68747470733a2f2f7777772e676f6f676c652e636f6d2f696d616765732f737270722f6c6f676f34772e706e67\"></a></div>",
      "backend_only_rendering": true,
      "text_content": "Google logo today: https:\/\/www.google.com\/images\/srpr\/logo4w.png\nKinda boring\n"
    },
@ -422,34 +422,34 @@
    {
      "name": "two_inline_images",
      "input": "Google logo today: https://www.google.com/images/srpr/logo4w.png\nKinda boring\nZulip logo: https://zulip.com/static/images/logo/zulip-icon-128x128.png",
-      "expected_output": "<p>Google logo today: <a href=\"https:\/\/www.google.com\/images\/srpr\/logo4w.png\">https:\/\/www.google.com\/images\/srpr\/logo4w.png<\/a><br>\nKinda boring<br>\nZulip logo: <a href=\"https:\/\/zulip.com\/static\/images\/logo\/zulip-icon-128x128.png\">https:\/\/zulip.com\/static\/images\/logo\/zulip-icon-128x128.png<\/a><\/p>\n<div class=\"message_inline_image\"><a href=\"https:\/\/www.google.com\/images\/srpr\/logo4w.png\"><img data-src-fullsize=\"\/thumbnail?url=https%3A%2F%2Fwww.google.com%2Fimages%2Fsrpr%2Flogo4w.png&amp;size=full\" src=\"\/thumbnail?url=https%3A%2F%2Fwww.google.com%2Fimages%2Fsrpr%2Flogo4w.png&amp;size=thumbnail\"><\/a><\/div><div class=\"message_inline_image\"><a href=\"https:\/\/zulip.com\/static\/images\/logo\/zulip-icon-128x128.png\"><img data-src-fullsize=\"\/thumbnail?url=https%3A%2F%2Fzulip.com%2Fstatic%2Fimages%2Flogo%2Fzulip-icon-128x128.png&amp;size=full\" src=\"\/thumbnail?url=https%3A%2F%2Fzulip.com%2Fstatic%2Fimages%2Flogo%2Fzulip-icon-128x128.png&amp;size=thumbnail\"><\/a><\/div>",
+      "expected_output": "<p>Google logo today: <a href=\"https:\/\/www.google.com\/images\/srpr\/logo4w.png\">https:\/\/www.google.com\/images\/srpr\/logo4w.png<\/a><br>\nKinda boring<br>\nZulip logo: <a href=\"https:\/\/zulip.com\/static\/images\/logo\/zulip-icon-128x128.png\">https:\/\/zulip.com\/static\/images\/logo\/zulip-icon-128x128.png<\/a><\/p>\n<div class=\"message_inline_image\"><a href=\"https:\/\/www.google.com\/images\/srpr\/logo4w.png\"><img src=\"https://external-content.zulipcdn.net/external_content/56c362a24201593891955ff526b3b412c0f9fcd2/68747470733a2f2f7777772e676f6f676c652e636f6d2f696d616765732f737270722f6c6f676f34772e706e67\"><\/a><\/div><div class=\"message_inline_image\"><a href=\"https:\/\/zulip.com\/static\/images\/logo\/zulip-icon-128x128.png\"><img src=\"https://external-content.zulipcdn.net/external_content/213b3c6f660b53018c3cb27d48d34f0940a74954/68747470733a2f2f7a756c69702e636f6d2f7374617469632f696d616765732f6c6f676f2f7a756c69702d69636f6e2d313238783132382e706e67\"><\/a><\/div>",
      "backend_only_rendering": true,
      "text_content": "Google logo today: https:\/\/www.google.com\/images\/srpr\/logo4w.png\nKinda boring\nZulip logo: https:\/\/zulip.com\/static\/images\/logo\/zulip-icon-128x128.png\n"
    },
    {
      "name": "deduplicate_inline_previews",
      "input": "Google logo today: https://www.google.com/images/srpr/logo4w.png\nKinda boringGoogle logo today: https://www.google.com/images/srpr/logo4w.png\nKinda boring",
-      "expected_output": "<p>Google logo today: <a href=\"https://www.google.com/images/srpr/logo4w.png\">https://www.google.com/images/srpr/logo4w.png</a><br>\nKinda boringGoogle logo today: <a href=\"https://www.google.com/images/srpr/logo4w.png\">https://www.google.com/images/srpr/logo4w.png</a><br>\nKinda boring</p>\n<div class=\"message_inline_image\"><a href=\"https://www.google.com/images/srpr/logo4w.png\"><img data-src-fullsize=\"/thumbnail?url=https%3A%2F%2Fwww.google.com%2Fimages%2Fsrpr%2Flogo4w.png&amp;size=full\" src=\"/thumbnail?url=https%3A%2F%2Fwww.google.com%2Fimages%2Fsrpr%2Flogo4w.png&amp;size=thumbnail\"></a></div>",
+      "expected_output": "<p>Google logo today: <a href=\"https://www.google.com/images/srpr/logo4w.png\">https://www.google.com/images/srpr/logo4w.png</a><br>\nKinda boringGoogle logo today: <a href=\"https://www.google.com/images/srpr/logo4w.png\">https://www.google.com/images/srpr/logo4w.png</a><br>\nKinda boring</p>\n<div class=\"message_inline_image\"><a href=\"https://www.google.com/images/srpr/logo4w.png\"><img src=\"https://external-content.zulipcdn.net/external_content/56c362a24201593891955ff526b3b412c0f9fcd2/68747470733a2f2f7777772e676f6f676c652e636f6d2f696d616765732f737270722f6c6f676f34772e706e67\"></a></div>",
      "backend_only_rendering": true,
      "text_content": "Google logo today: https:\/\/www.google.com\/images\/srpr\/logo4w.png\nKinda boringGoogle logo today: https:\/\/www.google.com\/images\/srpr\/logo4w.png\nKinda boring\n"
    },
    {
      "name": "bulleted_list_inlining",
      "input": "* Google?\n* Google. https://www.google.com/images/srpr/logo4w.png\n* Google!",
-      "expected_output": "<ul>\n<li>Google?</li>\n<li>Google. <a href=\"https://www.google.com/images/srpr/logo4w.png\">https://www.google.com/images/srpr/logo4w.png</a><div class=\"message_inline_image\"><a href=\"https://www.google.com/images/srpr/logo4w.png\"><img data-src-fullsize=\"/thumbnail?url=https%3A%2F%2Fwww.google.com%2Fimages%2Fsrpr%2Flogo4w.png&amp;size=full\" src=\"/thumbnail?url=https%3A%2F%2Fwww.google.com%2Fimages%2Fsrpr%2Flogo4w.png&amp;size=thumbnail\"></a></div></li>\n<li>Google!</li>\n</ul>",
+      "expected_output": "<ul>\n<li>Google?</li>\n<li>Google. <a href=\"https://www.google.com/images/srpr/logo4w.png\">https://www.google.com/images/srpr/logo4w.png</a><div class=\"message_inline_image\"><a href=\"https://www.google.com/images/srpr/logo4w.png\"><img src=\"https://external-content.zulipcdn.net/external_content/56c362a24201593891955ff526b3b412c0f9fcd2/68747470733a2f2f7777772e676f6f676c652e636f6d2f696d616765732f737270722f6c6f676f34772e706e67\"></a></div></li>\n<li>Google!</li>\n</ul>",
      "backend_only_rendering": true,
      "text_content": "\nGoogle?\nGoogle. https://www.google.com/images/srpr/logo4w.png\nGoogle!\n"
    },
    {
      "name": "only_inline_image",
      "input": "https://www.google.com/images/srpr/logo4w.png",
-      "expected_output": "<div class=\"message_inline_image\"><a href=\"https://www.google.com/images/srpr/logo4w.png\"><img data-src-fullsize=\"/thumbnail?url=https%3A%2F%2Fwww.google.com%2Fimages%2Fsrpr%2Flogo4w.png&amp;size=full\" src=\"/thumbnail?url=https%3A%2F%2Fwww.google.com%2Fimages%2Fsrpr%2Flogo4w.png&amp;size=thumbnail\"></a></div>",
+      "expected_output": "<div class=\"message_inline_image\"><a href=\"https://www.google.com/images/srpr/logo4w.png\"><img src=\"https://external-content.zulipcdn.net/external_content/56c362a24201593891955ff526b3b412c0f9fcd2/68747470733a2f2f7777772e676f6f676c652e636f6d2f696d616765732f737270722f6c6f676f34772e706e67\"></a></div>",
      "backend_only_rendering": true
    },
    {
      "name": "only_named_inline_image",
      "input": "[Google link](https://www.google.com/images/srpr/logo4w.png)",
-      "expected_output": "<p><a href=\"https://www.google.com/images/srpr/logo4w.png\">Google link</a></p>\n<div class=\"message_inline_image\"><a href=\"https://www.google.com/images/srpr/logo4w.png\" title=\"Google link\"><img data-src-fullsize=\"/thumbnail?url=https%3A%2F%2Fwww.google.com%2Fimages%2Fsrpr%2Flogo4w.png&amp;size=full\" src=\"/thumbnail?url=https%3A%2F%2Fwww.google.com%2Fimages%2Fsrpr%2Flogo4w.png&amp;size=thumbnail\"></a></div>",
+        "expected_output": "<p><a href=\"https://www.google.com/images/srpr/logo4w.png\">Google link</a></p>\n<div class=\"message_inline_image\"><a href=\"https://www.google.com/images/srpr/logo4w.png\" title=\"Google link\"><img src=\"https://external-content.zulipcdn.net/external_content/56c362a24201593891955ff526b3b412c0f9fcd2/68747470733a2f2f7777772e676f6f676c652e636f6d2f696d616765732f737270722f6c6f676f34772e706e67\"></a></div>",
      "backend_only_rendering": true,
      "text_content": "Google link\n"
    },
@ -993,9 +993,9 @@
    {
      "name": "spoiler_with_inline_image",
      "input": "```spoiler header\nContent http://example.com/image.png\n```",
-      "expected_output": "<div class=\"spoiler-block\"><div class=\"spoiler-header\">\n<p>header</p>\n</div><div class=\"spoiler-content\" aria-hidden=\"true\">\n<p>Content <a href=\"http://example.com/image.png\">http://example.com/image.png</a></p>\n<div class=\"message_inline_image\"><a href=\"http://example.com/image.png\"><img data-src-fullsize=\"/thumbnail?url=http%3A%2F%2Fexample.com%2Fimage.png&amp;size=full\" src=\"/thumbnail?url=http%3A%2F%2Fexample.com%2Fimage.png&amp;size=thumbnail\"></a></div></div></div>",
-      "marked_expected_output": "<div class=\"spoiler-block\"><div class=\"spoiler-header\">\n<p>header</p>\n</div><div class=\"spoiler-content\" aria-hidden=\"true\">\n<p>Content <a href=\"http://example.com/image.png\">http://example.com/image.png</a></p>\n</div></div>",
-      "text_content": "header (…)\n"
+        "expected_output": "<div class=\"spoiler-block\"><div class=\"spoiler-header\">\n<p>header</p>\n</div><div class=\"spoiler-content\" aria-hidden=\"true\">\n<p>Content <a href=\"http://example.com/image.png\">http://example.com/image.png</a></p>\n<div class=\"message_inline_image\"><a href=\"http://example.com/image.png\"><img src=\"https://external-content.zulipcdn.net/external_content/25fef3bfd3a93e0266153205ea66a83c53d310b4/687474703a2f2f6578616d706c652e636f6d2f696d6167652e706e67\"></a></div></div></div>",
+        "marked_expected_output": "<div class=\"spoiler-block\"><div class=\"spoiler-header\">\n<p>header</p>\n</div><div class=\"spoiler-content\" aria-hidden=\"true\">\n<p>Content <a href=\"http://example.com/image.png\">http://example.com/image.png</a></p>\n</div></div>",
+        "text_content": "header (…)\n"
    },
    {
      "name": "embedded_link_inside_Bold",
--- a/zerver/tests/test_events.py
+++ b/zerver/tests/test_events.py
@ -211,12 +211,14 @@ from zerver.lib.test_helpers import (
    create_dummy_file,
    get_subscription,
    get_test_image_file,
+    read_test_image_file,
    reset_email_visibility_to_everyone_in_zulip_realm,
    stdout_suppressed,
 )
 from zerver.lib.timestamp import convert_to_UTC, datetime_to_timestamp
 from zerver.lib.topic import TOPIC_NAME
 from zerver.lib.types import ProfileDataElementUpdateDict
+from zerver.lib.upload import upload_message_attachment
 from zerver.lib.user_groups import (
    AnonymousSettingGroupDict,
    get_group_setting_value_for_api,
@ -225,6 +227,7 @@ from zerver.lib.user_groups import (
 from zerver.models import (
    Attachment,
    CustomProfileField,
+    ImageAttachment,
    Message,
    MultiuseInvite,
    NamedUserGroup,
@ -258,6 +261,7 @@ from zerver.tornado.event_queue import (
    send_web_reload_client_events,
 )
 from zerver.views.realm_playgrounds import access_playground_by_id
+from zerver.worker.thumbnail import ensure_thumbnails


 class BaseAction(ZulipTestCase):
@ -935,7 +939,7 @@ class NormalActionsTest(BaseAction):
        content = "embed_content"
        rendering_result = render_message_markdown(message, content)
        with self.verify_action(state_change_expected=False) as events:
-            do_update_embedded_data(self.user_profile, message, content, rendering_result)
+            do_update_embedded_data(self.user_profile, message, rendering_result)
        check_update_message(
            "events[0]",
            events[0],
@ -1028,6 +1032,27 @@ class NormalActionsTest(BaseAction):
            is_embedded_update_only=False,
        )

+    def test_thumbnail_event(self) -> None:
+        iago = self.example_user("iago")
+        url = upload_message_attachment(
+            "img.png", "image/png", read_test_image_file("img.png"), self.example_user("iago")
+        )
+        path_id = url[len("/user_upload/") + 1 :]
+        self.send_stream_message(iago, "Verona", f"[img.png]({url})")
+
+        # Generating a thumbnail for an image sends a message update event
+        with self.verify_action(state_change_expected=False) as events:
+            ensure_thumbnails(ImageAttachment.objects.get(path_id=path_id))
+        check_update_message(
+            "events[0]",
+            events[0],
+            is_stream_message=False,
+            has_content=False,
+            has_topic=False,
+            has_new_stream_id=False,
+            is_embedded_update_only=True,
+        )
+
    def test_update_message_flags(self) -> None:
        # Test message flag update events
        message = self.send_personal_message(
--- a/zerver/tests/test_markdown.py
+++ b/zerver/tests/test_markdown.py
@ -713,51 +713,13 @@ class MarkdownEmbedsTest(ZulipTestCase):
            f"""<p><a href="http://www.youtube.com/watch_videos?video_ids=nOJgD4fcZhI,i96UO8-GFvw">http://www.youtube.com/watch_videos?video_ids=nOJgD4fcZhI,i96UO8-GFvw</a></p>\n<div class="youtube-video message_inline_image"><a data-id="nOJgD4fcZhI" href="http://www.youtube.com/watch_videos?video_ids=nOJgD4fcZhI,i96UO8-GFvw"><img src="{get_camo_url("https://i.ytimg.com/vi/nOJgD4fcZhI/default.jpg")}"></a></div>""",
        )

-    @override_settings(THUMBNAIL_IMAGES=True)
-    def test_inline_image_thumbnail_url(self) -> None:
-        realm = get_realm("zephyr")
-        msg = "[foobar](/user_uploads/{realm_id}/50/w2G6ok9kr8AMCQCTNAUOFMln/IMG_0677.JPG)"
-        msg = msg.format(realm_id=realm.id)
-        thumbnail_img = '<img data-src-fullsize="/thumbnail?url=user_uploads%2F{realm_id}%2F50%2Fw2G6ok9kr8AMCQCTNAUOFMln%2FIMG_0677.JPG&amp;size=full" src="/thumbnail?url=user_uploads%2F{realm_id}%2F50%2Fw2G6ok9kr8AMCQCTNAUOFMln%2FIMG_0677.JPG&amp;size=thumbnail"><'
-        thumbnail_img = thumbnail_img.format(realm_id=realm.id)
-        converted = markdown_convert_wrapper(msg)
-        self.assertIn(thumbnail_img, converted)
-
-        msg = "https://www.google.com/images/srpr/logo4w.png"
-        thumbnail_img = '<img data-src-fullsize="/thumbnail?url=https%3A%2F%2Fwww.google.com%2Fimages%2Fsrpr%2Flogo4w.png&amp;size=full" src="/thumbnail?url=https%3A%2F%2Fwww.google.com%2Fimages%2Fsrpr%2Flogo4w.png&amp;size=thumbnail">'
-        converted = markdown_convert_wrapper(msg)
-        self.assertIn(thumbnail_img, converted)
-
-        msg = "www.google.com/images/srpr/logo4w.png"
-        thumbnail_img = '<img data-src-fullsize="/thumbnail?url=http%3A%2F%2Fwww.google.com%2Fimages%2Fsrpr%2Flogo4w.png&amp;size=full" src="/thumbnail?url=http%3A%2F%2Fwww.google.com%2Fimages%2Fsrpr%2Flogo4w.png&amp;size=thumbnail">'
-        converted = markdown_convert_wrapper(msg)
-        self.assertIn(thumbnail_img, converted)
-
-        msg = "https://www.google.com/images/srpr/logo4w.png"
-        thumbnail_img = f"""<div class="message_inline_image"><a href="https://www.google.com/images/srpr/logo4w.png"><img src="{get_camo_url("https://www.google.com/images/srpr/logo4w.png")}"></a></div>"""
-        with self.settings(THUMBNAIL_IMAGES=False):
-            converted = markdown_convert_wrapper(msg)
-        self.assertIn(thumbnail_img, converted)
-
-        # Any URL which is not an external link and doesn't start with
-        # /user_uploads/ is not thumbnailed
-        msg = "[foobar](/static/images/cute/turtle.png)"
-        thumbnail_img = '<div class="message_inline_image"><a href="/static/images/cute/turtle.png" title="foobar"><img src="/static/images/cute/turtle.png"></a></div>'
-        converted = markdown_convert_wrapper(msg)
-        self.assertIn(thumbnail_img, converted)
-
-        msg = "[foobar](/user_avatars/{realm_id}/emoji/images/50.png)"
-        msg = msg.format(realm_id=realm.id)
-        thumbnail_img = '<div class="message_inline_image"><a href="/user_avatars/{realm_id}/emoji/images/50.png" title="foobar"><img src="/user_avatars/{realm_id}/emoji/images/50.png"></a></div>'
-        thumbnail_img = thumbnail_img.format(realm_id=realm.id)
-        converted = markdown_convert_wrapper(msg)
-        self.assertIn(thumbnail_img, converted)
-
-    @override_settings(THUMBNAIL_IMAGES=True)
    def test_inline_image_preview(self) -> None:
-        with_preview = '<div class="message_inline_image"><a href="http://cdn.wallpapersafari.com/13/6/16eVjx.jpeg"><img data-src-fullsize="/thumbnail?url=http%3A%2F%2Fcdn.wallpapersafari.com%2F13%2F6%2F16eVjx.jpeg&amp;size=full" src="/thumbnail?url=http%3A%2F%2Fcdn.wallpapersafari.com%2F13%2F6%2F16eVjx.jpeg&amp;size=thumbnail"></a></div>'
-        without_preview = '<p><a href="http://cdn.wallpapersafari.com/13/6/16eVjx.jpeg">http://cdn.wallpapersafari.com/13/6/16eVjx.jpeg</a></p>'
-        content = "http://cdn.wallpapersafari.com/13/6/16eVjx.jpeg"
+        url = "http://cdn.wallpapersafari.com/13/6/16eVjx.jpeg"
+        camo_url = get_camo_url(url)
+        with_preview = (
+            f'<div class="message_inline_image"><a href="{url}"><img src="{camo_url}"></a></div>'
+        )
+        without_preview = f'<p><a href="{url}">{url}</a></p>'

        sender_user_profile = self.example_user("othello")
        msg = Message(
@ -765,7 +727,7 @@ class MarkdownEmbedsTest(ZulipTestCase):
            sending_client=get_client("test"),
            realm=sender_user_profile.realm,
        )
-        converted = render_message_markdown(msg, content)
+        converted = render_message_markdown(msg, url)
        self.assertEqual(converted.rendered_content, with_preview)

        realm = msg.get_realm()
@ -778,17 +740,9 @@ class MarkdownEmbedsTest(ZulipTestCase):
            sending_client=get_client("test"),
            realm=sender_user_profile.realm,
        )
-        converted = render_message_markdown(msg, content)
+        converted = render_message_markdown(msg, url)
        self.assertEqual(converted.rendered_content, without_preview)

-    @override_settings(EXTERNAL_URI_SCHEME="https://")
-    def test_external_image_preview_use_camo(self) -> None:
-        content = "https://example.com/thing.jpeg"
-
-        thumbnail_img = f"""<div class="message_inline_image"><a href="{content}"><img src="{get_camo_url(content)}"></a></div>"""
-        converted = markdown_convert_wrapper(content)
-        self.assertIn(converted, thumbnail_img)
-
    @override_settings(EXTERNAL_URI_SCHEME="https://")
    def test_static_image_preview_skip_camo(self) -> None:
        content = f"{ settings.STATIC_URL }/thing.jpeg"
@ -843,10 +797,13 @@ class MarkdownEmbedsTest(ZulipTestCase):
        soup = BeautifulSoup(converted, "html.parser")
        self.assert_length(soup(class_="message_inline_image"), 0)

-    @override_settings(THUMBNAIL_IMAGES=True)
    def test_inline_image_quoted_blocks(self) -> None:
-        content = "http://cdn.wallpapersafari.com/13/6/16eVjx.jpeg"
-        expected = '<div class="message_inline_image"><a href="http://cdn.wallpapersafari.com/13/6/16eVjx.jpeg"><img data-src-fullsize="/thumbnail?url=http%3A%2F%2Fcdn.wallpapersafari.com%2F13%2F6%2F16eVjx.jpeg&amp;size=full" src="/thumbnail?url=http%3A%2F%2Fcdn.wallpapersafari.com%2F13%2F6%2F16eVjx.jpeg&amp;size=thumbnail"></a></div>'
+        url = "http://cdn.wallpapersafari.com/13/6/16eVjx.jpeg"
+        camo_url = get_camo_url(url)
+        content = f"{url}"
+        expected = (
+            f'<div class="message_inline_image"><a href="{url}"><img src="{camo_url}"></a></div>'
+        )
        sender_user_profile = self.example_user("othello")
        msg = Message(
            sender=sender_user_profile,
@ -856,8 +813,8 @@ class MarkdownEmbedsTest(ZulipTestCase):
        converted = render_message_markdown(msg, content)
        self.assertEqual(converted.rendered_content, expected)

-        content = ">http://cdn.wallpapersafari.com/13/6/16eVjx.jpeg\n\nAwesome!"
-        expected = '<blockquote>\n<p><a href="http://cdn.wallpapersafari.com/13/6/16eVjx.jpeg">http://cdn.wallpapersafari.com/13/6/16eVjx.jpeg</a></p>\n</blockquote>\n<p>Awesome!</p>'
+        content = f">{url}\n\nAwesome!"
+        expected = f'<blockquote>\n<p><a href="{url}">{url}</a></p>\n</blockquote>\n<p>Awesome!</p>'
        sender_user_profile = self.example_user("othello")
        msg = Message(
            sender=sender_user_profile,
@ -867,8 +824,8 @@ class MarkdownEmbedsTest(ZulipTestCase):
        converted = render_message_markdown(msg, content)
        self.assertEqual(converted.rendered_content, expected)

-        content = ">* http://cdn.wallpapersafari.com/13/6/16eVjx.jpeg\n\nAwesome!"
-        expected = '<blockquote>\n<ul>\n<li><a href="http://cdn.wallpapersafari.com/13/6/16eVjx.jpeg">http://cdn.wallpapersafari.com/13/6/16eVjx.jpeg</a></li>\n</ul>\n</blockquote>\n<p>Awesome!</p>'
+        content = f">* {url}\n\nAwesome!"
+        expected = f'<blockquote>\n<ul>\n<li><a href="{url}">{url}</a></li>\n</ul>\n</blockquote>\n<p>Awesome!</p>'
        sender_user_profile = self.example_user("othello")
        msg = Message(
            sender=sender_user_profile,
@ -878,12 +835,23 @@ class MarkdownEmbedsTest(ZulipTestCase):
        converted = render_message_markdown(msg, content)
        self.assertEqual(converted.rendered_content, expected)

-    @override_settings(THUMBNAIL_IMAGES=True)
    def test_inline_image_preview_order(self) -> None:
-        realm = get_realm("zulip")
-        content = "http://imaging.nikon.com/lineup/dslr/df/img/sample/img_01.jpg\nhttp://imaging.nikon.com/lineup/dslr/df/img/sample/img_02.jpg\nhttp://imaging.nikon.com/lineup/dslr/df/img/sample/img_03.jpg"
-        expected = '<p><a href="http://imaging.nikon.com/lineup/dslr/df/img/sample/img_01.jpg">http://imaging.nikon.com/lineup/dslr/df/img/sample/img_01.jpg</a><br>\n<a href="http://imaging.nikon.com/lineup/dslr/df/img/sample/img_02.jpg">http://imaging.nikon.com/lineup/dslr/df/img/sample/img_02.jpg</a><br>\n<a href="http://imaging.nikon.com/lineup/dslr/df/img/sample/img_03.jpg">http://imaging.nikon.com/lineup/dslr/df/img/sample/img_03.jpg</a></p>\n<div class="message_inline_image"><a href="http://imaging.nikon.com/lineup/dslr/df/img/sample/img_01.jpg"><img data-src-fullsize="/thumbnail?url=http%3A%2F%2Fimaging.nikon.com%2Flineup%2Fdslr%2Fdf%2Fimg%2Fsample%2Fimg_01.jpg&amp;size=full" src="/thumbnail?url=http%3A%2F%2Fimaging.nikon.com%2Flineup%2Fdslr%2Fdf%2Fimg%2Fsample%2Fimg_01.jpg&amp;size=thumbnail"></a></div><div class="message_inline_image"><a href="http://imaging.nikon.com/lineup/dslr/df/img/sample/img_02.jpg"><img data-src-fullsize="/thumbnail?url=http%3A%2F%2Fimaging.nikon.com%2Flineup%2Fdslr%2Fdf%2Fimg%2Fsample%2Fimg_02.jpg&amp;size=full" src="/thumbnail?url=http%3A%2F%2Fimaging.nikon.com%2Flineup%2Fdslr%2Fdf%2Fimg%2Fsample%2Fimg_02.jpg&amp;size=thumbnail"></a></div><div class="message_inline_image"><a href="http://imaging.nikon.com/lineup/dslr/df/img/sample/img_03.jpg"><img data-src-fullsize="/thumbnail?url=http%3A%2F%2Fimaging.nikon.com%2Flineup%2Fdslr%2Fdf%2Fimg%2Fsample%2Fimg_03.jpg&amp;size=full" src="/thumbnail?url=http%3A%2F%2Fimaging.nikon.com%2Flineup%2Fdslr%2Fdf%2Fimg%2Fsample%2Fimg_03.jpg&amp;size=thumbnail"></a></div>'
-
+        urls = [
+            "http://imaging.nikon.com/lineup/dslr/df/img/sample/img_01.jpg",
+            "http://imaging.nikon.com/lineup/dslr/df/img/sample/img_02.jpg",
+            "http://imaging.nikon.com/lineup/dslr/df/img/sample/img_03.jpg",
+        ]
+        content = "\n".join(urls)
+        expected = (
+            "<p>"
+            f'<a href="{urls[0]}">{urls[0]}</a><br>\n'
+            f'<a href="{urls[1]}">{urls[1]}</a><br>\n'
+            f'<a href="{urls[2]}">{urls[2]}</a>'
+            "</p>\n"
+            f'<div class="message_inline_image"><a href="{urls[0]}"><img src="{get_camo_url(urls[0])}"></a></div>'
+            f'<div class="message_inline_image"><a href="{urls[1]}"><img src="{get_camo_url(urls[1])}"></a></div>'
+            f'<div class="message_inline_image"><a href="{urls[2]}"><img src="{get_camo_url(urls[2])}"></a></div>'
+        )
        sender_user_profile = self.example_user("othello")
        msg = Message(
            sender=sender_user_profile,
@ -893,10 +861,16 @@ class MarkdownEmbedsTest(ZulipTestCase):
        converted = render_message_markdown(msg, content)
        self.assertEqual(converted.rendered_content, expected)

-        content = "http://imaging.nikon.com/lineup/dslr/df/img/sample/img_01.jpg\n\n>http://imaging.nikon.com/lineup/dslr/df/img/sample/img_02.jpg\n\n* http://imaging.nikon.com/lineup/dslr/df/img/sample/img_03.jpg\n* https://www.google.com/images/srpr/logo4w.png"
-        expected = '<div class="message_inline_image"><a href="http://imaging.nikon.com/lineup/dslr/df/img/sample/img_01.jpg"><img data-src-fullsize="/thumbnail?url=http%3A%2F%2Fimaging.nikon.com%2Flineup%2Fdslr%2Fdf%2Fimg%2Fsample%2Fimg_01.jpg&amp;size=full" src="/thumbnail?url=http%3A%2F%2Fimaging.nikon.com%2Flineup%2Fdslr%2Fdf%2Fimg%2Fsample%2Fimg_01.jpg&amp;size=thumbnail"></a></div><blockquote>\n<p><a href="http://imaging.nikon.com/lineup/dslr/df/img/sample/img_02.jpg">http://imaging.nikon.com/lineup/dslr/df/img/sample/img_02.jpg</a></p>\n</blockquote>\n<ul>\n<li><div class="message_inline_image"><a href="http://imaging.nikon.com/lineup/dslr/df/img/sample/img_03.jpg"><img data-src-fullsize="/thumbnail?url=http%3A%2F%2Fimaging.nikon.com%2Flineup%2Fdslr%2Fdf%2Fimg%2Fsample%2Fimg_03.jpg&amp;size=full" src="/thumbnail?url=http%3A%2F%2Fimaging.nikon.com%2Flineup%2Fdslr%2Fdf%2Fimg%2Fsample%2Fimg_03.jpg&amp;size=thumbnail"></a></div></li>\n<li><div class="message_inline_image"><a href="https://www.google.com/images/srpr/logo4w.png"><img data-src-fullsize="/thumbnail?url=https%3A%2F%2Fwww.google.com%2Fimages%2Fsrpr%2Flogo4w.png&amp;size=full" src="/thumbnail?url=https%3A%2F%2Fwww.google.com%2Fimages%2Fsrpr%2Flogo4w.png&amp;size=thumbnail"></a></div></li>\n</ul>'
-
-        sender_user_profile = self.example_user("othello")
+        urls.append("https://www.google.com/images/srpr/logo4w.png")
+        content = f"{urls[0]}\n\n" f">{urls[1]}\n\n" f"* {urls[2]}\n" f"* {urls[3]}"
+        expected = (
+            f'<div class="message_inline_image"><a href="{urls[0]}"><img src="{get_camo_url(urls[0])}"></a></div>'
+            f'<blockquote>\n<p><a href="{urls[1]}">{urls[1]}</a></p>\n</blockquote>\n'
+            "<ul>\n"
+            f'<li><div class="message_inline_image"><a href="{urls[2]}"><img src="{get_camo_url(urls[2])}"></a></div></li>\n'
+            f'<li><div class="message_inline_image"><a href="{urls[3]}"><img src="{get_camo_url(urls[3])}"></a></div></li>\n'
+            "</ul>"
+        )
        msg = Message(
            sender=sender_user_profile,
            sending_client=get_client("test"),
@ -905,24 +879,14 @@ class MarkdownEmbedsTest(ZulipTestCase):
        converted = render_message_markdown(msg, content)
        self.assertEqual(converted.rendered_content, expected)

-        content = "Test 1\n[21136101110_1dde1c1a7e_o.jpg](/user_uploads/{realm_id}/6d/F1PX6u16JA2P-nK45PyxHIYZ/21136101110_1dde1c1a7e_o.jpg) \n\nNext image\n[IMG_20161116_023910.jpg](/user_uploads/{realm_id}/69/sh7L06e7uH7NaX6d5WFfVYQp/IMG_20161116_023910.jpg) \n\nAnother screenshot\n[Screenshot-from-2016-06-01-16-22-42.png](/user_uploads/{realm_id}/70/_aZmIEWaN1iUaxwkDjkO7bpj/Screenshot-from-2016-06-01-16-22-42.png)"
-        content = content.format(realm_id=realm.id)
-        expected = '<p>Test 1<br>\n<a href="/user_uploads/{realm_id}/6d/F1PX6u16JA2P-nK45PyxHIYZ/21136101110_1dde1c1a7e_o.jpg">21136101110_1dde1c1a7e_o.jpg</a> </p>\n<div class="message_inline_image"><a href="/user_uploads/{realm_id}/6d/F1PX6u16JA2P-nK45PyxHIYZ/21136101110_1dde1c1a7e_o.jpg" title="21136101110_1dde1c1a7e_o.jpg"><img data-src-fullsize="/thumbnail?url=user_uploads%2F{realm_id}%2F6d%2FF1PX6u16JA2P-nK45PyxHIYZ%2F21136101110_1dde1c1a7e_o.jpg&amp;size=full" src="/thumbnail?url=user_uploads%2F{realm_id}%2F6d%2FF1PX6u16JA2P-nK45PyxHIYZ%2F21136101110_1dde1c1a7e_o.jpg&amp;size=thumbnail"></a></div><p>Next image<br>\n<a href="/user_uploads/{realm_id}/69/sh7L06e7uH7NaX6d5WFfVYQp/IMG_20161116_023910.jpg">IMG_20161116_023910.jpg</a> </p>\n<div class="message_inline_image"><a href="/user_uploads/{realm_id}/69/sh7L06e7uH7NaX6d5WFfVYQp/IMG_20161116_023910.jpg" title="IMG_20161116_023910.jpg"><img data-src-fullsize="/thumbnail?url=user_uploads%2F{realm_id}%2F69%2Fsh7L06e7uH7NaX6d5WFfVYQp%2FIMG_20161116_023910.jpg&amp;size=full" src="/thumbnail?url=user_uploads%2F{realm_id}%2F69%2Fsh7L06e7uH7NaX6d5WFfVYQp%2FIMG_20161116_023910.jpg&amp;size=thumbnail"></a></div><p>Another screenshot<br>\n<a href="/user_uploads/{realm_id}/70/_aZmIEWaN1iUaxwkDjkO7bpj/Screenshot-from-2016-06-01-16-22-42.png">Screenshot-from-2016-06-01-16-22-42.png</a></p>\n<div class="message_inline_image"><a href="/user_uploads/{realm_id}/70/_aZmIEWaN1iUaxwkDjkO7bpj/Screenshot-from-2016-06-01-16-22-42.png" title="Screenshot-from-2016-06-01-16-22-42.png"><img data-src-fullsize="/thumbnail?url=user_uploads%2F{realm_id}%2F70%2F_aZmIEWaN1iUaxwkDjkO7bpj%2FScreenshot-from-2016-06-01-16-22-42.png&amp;size=full" src="/thumbnail?url=user_uploads%2F{realm_id}%2F70%2F_aZmIEWaN1iUaxwkDjkO7bpj%2FScreenshot-from-2016-06-01-16-22-42.png&amp;size=thumbnail"></a></div>'
-        expected = expected.format(realm_id=realm.id)
-
-        msg = Message(
-            sender=sender_user_profile,
-            sending_client=get_client("test"),
-            realm=sender_user_profile.realm,
-        )
-        converted = render_message_markdown(msg, content)
-        self.assertEqual(converted.rendered_content, expected)
-
-    @override_settings(THUMBNAIL_IMAGES=True)
    def test_corrected_image_source(self) -> None:
        # testing only Wikipedia because linx.li URLs can be expected to expire
        content = "https://en.wikipedia.org/wiki/File:Wright_of_Derby,_The_Orrery.jpg"
-        expected = '<div class="message_inline_image"><a href="https://en.wikipedia.org/wiki/Special:FilePath/File:Wright_of_Derby,_The_Orrery.jpg"><img data-src-fullsize="/thumbnail?url=https%3A%2F%2Fen.wikipedia.org%2Fwiki%2FSpecial%3AFilePath%2FFile%3AWright_of_Derby%2C_The_Orrery.jpg&amp;size=full" src="/thumbnail?url=https%3A%2F%2Fen.wikipedia.org%2Fwiki%2FSpecial%3AFilePath%2FFile%3AWright_of_Derby%2C_The_Orrery.jpg&amp;size=thumbnail"></a></div>'
+        expected_url = (
+            "https://en.wikipedia.org/wiki/Special:FilePath/File:Wright_of_Derby,_The_Orrery.jpg"
+        )
+        camo_url = get_camo_url(expected_url)
+        expected = f'<div class="message_inline_image"><a href="{expected_url}"><img src="{camo_url}"></a></div>'

        sender_user_profile = self.example_user("othello")
        msg = Message(
@ -934,7 +898,8 @@ class MarkdownEmbedsTest(ZulipTestCase):
        self.assertEqual(converted.rendered_content, expected)

        content = "https://en.wikipedia.org/static/images/icons/wikipedia.png"
-        expected = '<div class="message_inline_image"><a href="https://en.wikipedia.org/static/images/icons/wikipedia.png"><img data-src-fullsize="/thumbnail?url=https%3A%2F%2Fen.wikipedia.org%2Fstatic%2Fimages%2Ficons%2Fwikipedia.png&amp;size=full" src="/thumbnail?url=https%3A%2F%2Fen.wikipedia.org%2Fstatic%2Fimages%2Ficons%2Fwikipedia.png&amp;size=thumbnail"></a></div>'
+        camo_url = get_camo_url(content)
+        expected = f'<div class="message_inline_image"><a href="https://en.wikipedia.org/static/images/icons/wikipedia.png"><img src="{camo_url}"></a></div>'
        converted = render_message_markdown(msg, content)
        self.assertEqual(converted.rendered_content, expected)

@ -1042,13 +1007,19 @@ class MarkdownEmbedsTest(ZulipTestCase):
    @override_settings(THUMBNAIL_IMAGES=True)
    def test_inline_dropbox_negative(self) -> None:
        # Make sure we're not overzealous in our conversion:
-        msg = "Look at the new dropbox logo: https://www.dropbox.com/static/images/home_logo.png"
+        url = "https://www.dropbox.com/static/images/home_logo.png"
+        msg = f"Look at the new dropbox logo: {url}"
        with mock.patch("zerver.lib.markdown.fetch_open_graph_image", return_value=None):
            converted = markdown_convert_wrapper(msg)

+        camo_url = get_camo_url(url)
        self.assertEqual(
            converted,
-            '<p>Look at the new dropbox logo: <a href="https://www.dropbox.com/static/images/home_logo.png">https://www.dropbox.com/static/images/home_logo.png</a></p>\n<div class="message_inline_image"><a href="https://www.dropbox.com/static/images/home_logo.png"><img data-src-fullsize="/thumbnail?url=https%3A%2F%2Fwww.dropbox.com%2Fstatic%2Fimages%2Fhome_logo.png&amp;size=full" src="/thumbnail?url=https%3A%2F%2Fwww.dropbox.com%2Fstatic%2Fimages%2Fhome_logo.png&amp;size=thumbnail"></a></div>',
+            (
+                f'<p>Look at the new dropbox logo: <a href="{url}">{url}</a></p>'
+                "\n"
+                f'<div class="message_inline_image"><a href="{url}"><img src="{camo_url}"></a></div>'
+            ),
        )

    def test_inline_dropbox_bad(self) -> None:
@ -1063,21 +1034,35 @@ class MarkdownEmbedsTest(ZulipTestCase):

    @override_settings(THUMBNAIL_IMAGES=True)
    def test_inline_github_preview(self) -> None:
-        # Test photo album previews
-        msg = "Test: https://github.com/zulip/zulip/blob/main/static/images/logo/zulip-icon-128x128.png"
+        # Test github URL translation
+        url = "https://github.com/zulip/zulip/blob/main/static/images/logo/zulip-icon-128x128.png"
+        camo_url = get_camo_url(
+            "https://raw.githubusercontent.com/zulip/zulip/main/static/images/logo/zulip-icon-128x128.png"
+        )
+        msg = f"Test: {url}"
        converted = markdown_convert_wrapper(msg)

        self.assertEqual(
            converted,
-            '<p>Test: <a href="https://github.com/zulip/zulip/blob/main/static/images/logo/zulip-icon-128x128.png">https://github.com/zulip/zulip/blob/main/static/images/logo/zulip-icon-128x128.png</a></p>\n<div class="message_inline_image"><a href="https://github.com/zulip/zulip/blob/main/static/images/logo/zulip-icon-128x128.png"><img data-src-fullsize="/thumbnail?url=https%3A%2F%2Fraw.githubusercontent.com%2Fzulip%2Fzulip%2Fmain%2Fstatic%2Fimages%2Flogo%2Fzulip-icon-128x128.png&amp;size=full" src="/thumbnail?url=https%3A%2F%2Fraw.githubusercontent.com%2Fzulip%2Fzulip%2Fmain%2Fstatic%2Fimages%2Flogo%2Fzulip-icon-128x128.png&amp;size=thumbnail"></a></div>',
+            (
+                f'<p>Test: <a href="{url}">{url}</a></p>'
+                "\n"
+                f'<div class="message_inline_image"><a href="{url}"><img src="{camo_url}"></a></div>'
+            ),
        )

-        msg = "Test: https://developer.github.com/assets/images/hero-circuit-bg.png"
+        url = "https://developer.github.com/assets/images/hero-circuit-bg.png"
+        camo_url = get_camo_url(url)
+        msg = f"Test: {url}"
        converted = markdown_convert_wrapper(msg)

        self.assertEqual(
            converted,
-            '<p>Test: <a href="https://developer.github.com/assets/images/hero-circuit-bg.png">https://developer.github.com/assets/images/hero-circuit-bg.png</a></p>\n<div class="message_inline_image"><a href="https://developer.github.com/assets/images/hero-circuit-bg.png"><img data-src-fullsize="/thumbnail?url=https%3A%2F%2Fdeveloper.github.com%2Fassets%2Fimages%2Fhero-circuit-bg.png&amp;size=full" src="/thumbnail?url=https%3A%2F%2Fdeveloper.github.com%2Fassets%2Fimages%2Fhero-circuit-bg.png&amp;size=thumbnail"></a></div>',
+            (
+                f'<p>Test: <a href="{url}">{url}</a></p>'
+                "\n"
+                f'<div class="message_inline_image"><a href="{url}"><img src="{camo_url}"></a></div>'
+            ),
        )

    def test_inline_youtube_preview(self) -> None:
@ -3168,7 +3153,7 @@ class MarkdownStreamMentionTests(ZulipTestCase):
            "</p>\n"
            '<div class="message_inline_image">'
            '<a href="https://example.com/testimage.png" title="My favorite image">'
-            '<img data-src-fullsize="/thumbnail?url=https%3A%2F%2Fexample.com%2Ftestimage.png&amp;size=full" src="/thumbnail?url=https%3A%2F%2Fexample.com%2Ftestimage.png&amp;size=thumbnail">'
+            '<img src="https://external-content.zulipcdn.net/external_content/5cd6ddfa28639e2e95bb85a7c7910b31f5474e03/68747470733a2f2f6578616d706c652e636f6d2f74657374696d6167652e706e67">'
            "</a>"
            "</div>",
        )
--- a/zerver/tests/test_markdown_thumbnail.py
+++ b/zerver/tests/test_markdown_thumbnail.py
@ -0,0 +1,334 @@
+import re
+from unittest.mock import patch
+
+import pyvips
+
+from zerver.actions.message_delete import do_delete_messages
+from zerver.lib.camo import get_camo_url
+from zerver.lib.markdown import render_message_markdown
+from zerver.lib.test_classes import ZulipTestCase
+from zerver.lib.test_helpers import get_test_image_file, read_test_image_file
+from zerver.lib.thumbnail import ThumbnailFormat
+from zerver.lib.upload import upload_message_attachment
+from zerver.models import ArchivedAttachment, ArchivedMessage, Attachment, ImageAttachment, Message
+from zerver.models.clients import get_client
+from zerver.worker.thumbnail import ensure_thumbnails
+
+
+class MarkdownThumbnailTest(ZulipTestCase):
+    def upload_image(self, image_name: str) -> str:
+        self.login("othello")
+        with get_test_image_file(image_name) as image_file:
+            response = self.assert_json_success(
+                self.client_post("/json/user_uploads", {"file": image_file})
+            )
+            return re.sub(r"/user_uploads/", "", response["url"])
+
+    def upload_and_thumbnail_image(self, image_name: str) -> str:
+        with self.captureOnCommitCallbacks(execute=True):
+            # Running captureOnCommitCallbacks includes inserting into
+            # the Rabbitmq queue, which in testing means we
+            # immediately run the worker for it, producing the thumbnails.
+            return self.upload_image(image_name)
+
+    def assert_message_content_is(
+        self, message_id: int, rendered_content: str, user_name: str = "othello"
+    ) -> None:
+        sender_user_profile = self.example_user(user_name)
+        result = self.assert_json_success(
+            self.api_get(sender_user_profile, f"/api/v1/messages/{message_id}")
+        )
+        self.assertEqual(result["message"]["content"], rendered_content)
+
+    def send_message_content(
+        self, content: str, do_thumbnail: bool = False, user_name: str = "othello"
+    ) -> int:
+        sender_user_profile = self.example_user(user_name)
+        return self.send_stream_message(
+            sender=sender_user_profile,
+            stream_name="Verona",
+            content=content,
+            skip_capture_on_commit_callbacks=not do_thumbnail,
+        )
+
+    def test_uploads_preview_order(self) -> None:
+        image_names = ["img.jpg", "img.png", "img.gif"]
+        path_ids = [self.upload_and_thumbnail_image(image_name) for image_name in image_names]
+        content = (
+            f"Test 1\n[{image_names[0]}](/user_uploads/{path_ids[0]}) \n\n"
+            f"Next image\n[{image_names[1]}](/user_uploads/{path_ids[1]}) \n\n"
+            f"Another screenshot\n[{image_names[2]}](/user_uploads/{path_ids[2]})"
+        )
+
+        sender_user_profile = self.example_user("othello")
+        msg = Message(
+            sender=sender_user_profile,
+            sending_client=get_client("test"),
+            realm=sender_user_profile.realm,
+        )
+        converted = render_message_markdown(msg, content)
+        self.assertEqual(
+            converted.rendered_content,
+            (
+                "<p>Test 1<br>\n"
+                f'<a href="/user_uploads/{path_ids[0]}">{image_names[0]}</a> </p>\n'
+                f'<div class="message_inline_image"><a href="/user_uploads/{path_ids[0]}" title="{image_names[0]}">'
+                f'<img src="/user_uploads/thumbnail/{path_ids[0]}/840x560.webp"></a></div>'
+                "<p>Next image<br>\n"
+                f'<a href="/user_uploads/{path_ids[1]}">{image_names[1]}</a> </p>\n'
+                f'<div class="message_inline_image"><a href="/user_uploads/{path_ids[1]}" title="{image_names[1]}">'
+                f'<img src="/user_uploads/thumbnail/{path_ids[1]}/840x560.webp"></a></div>'
+                "<p>Another screenshot<br>\n"
+                f'<a href="/user_uploads/{path_ids[2]}">{image_names[2]}</a></p>\n'
+                f'<div class="message_inline_image"><a href="/user_uploads/{path_ids[2]}" title="{image_names[2]}">'
+                f'<img src="/user_uploads/thumbnail/{path_ids[2]}/840x560.webp"></a></div>'
+            ),
+        )
+
+    def test_thumbnail_code_block(self) -> None:
+        url = "http://example.com/image.png"
+        path_id = self.upload_and_thumbnail_image("img.png")
+        # We have a path_id of an image in the message content, so we
+        # will prefetch the thumbnail metadata -- but not insert it.
+
+        sender_user_profile = self.example_user("othello")
+        msg = Message(
+            sender=sender_user_profile,
+            sending_client=get_client("test"),
+            realm=sender_user_profile.realm,
+        )
+        converted = render_message_markdown(msg, f"{url}\n```\n/user_uploads/{path_id}\n```")
+        self.assertEqual(
+            converted.rendered_content,
+            (
+                f'<div class="message_inline_image"><a href="{url}"><img src="{get_camo_url(url)}"></a></div>'
+                f'<div class="codehilite"><pre><span></span><code>/user_uploads/{path_id}\n'
+                "</code></pre></div>"
+            ),
+        )
+
+    def test_thumbnail_after_send(self) -> None:
+        with self.captureOnCommitCallbacks(execute=True):
+            path_id = self.upload_image("img.png")
+            content = f"[image](/user_uploads/{path_id})"
+            expected = (
+                f'<p><a href="/user_uploads/{path_id}">image</a></p>\n'
+                f'<div class="message_inline_image"><a href="/user_uploads/{path_id}" title="image">'
+                '<img class="image-loading-placeholder" src="/static/images/loading/loader-black.svg"></a></div>'
+            )
+
+            message_id = self.send_message_content(content)
+            self.assert_message_content_is(message_id, expected)
+
+            # Exit the block and run thumbnailing
+        expected = (
+            f'<p><a href="/user_uploads/{path_id}">image</a></p>\n'
+            f'<div class="message_inline_image"><a href="/user_uploads/{path_id}" title="image">'
+            f'<img src="/user_uploads/thumbnail/{path_id}/840x560.webp"></a></div>'
+        )
+        self.assert_message_content_is(message_id, expected)
+
+    def test_thumbnail_escaping(self) -> None:
+        self.login("othello")
+        with self.captureOnCommitCallbacks(execute=True):
+            url = upload_message_attachment(
+                "I am 95% ± 5% certain!",
+                "image/png",
+                read_test_image_file("img.png"),
+                self.example_user("othello"),
+            )
+            path_id = re.sub(r"/user_uploads/", "", url)
+            self.assertTrue(ImageAttachment.objects.filter(path_id=path_id).exists())
+        message_id = self.send_message_content(f"[I am 95% ± 5% certain!](/user_uploads/{path_id})")
+        expected = (
+            f'<p><a href="/user_uploads/{path_id}">I am 95% &plusmn; 5% certain!</a></p>\n'
+            f'<div class="message_inline_image"><a href="/user_uploads/{path_id}" title="I am 95% &plusmn; 5% certain!"><img src="/user_uploads/thumbnail/{path_id}/840x560.webp"></a></div>'
+        )
+        self.assert_message_content_is(message_id, expected)
+
+    def test_thumbnail_repeated(self) -> None:
+        # We currently have no way to generate a thumbnailing event
+        # for the worker except during upload, meaning that we will
+        # never repeat a ImageAttachment thumbnailing.  However, the
+        # code supports it, so test it.
+
+        # Thumbnail with one set of sizes
+        with self.thumbnail_formats(
+            ThumbnailFormat("webp", 100, 75, animated=True),
+            ThumbnailFormat("webp", 100, 75, animated=False),
+        ):
+            path_id = self.upload_and_thumbnail_image("animated_img.gif")
+            content = f"[animated_img.gif](/user_uploads/{path_id})"
+            expected = (
+                f'<p><a href="/user_uploads/{path_id}">animated_img.gif</a></p>\n'
+                f'<div class="message_inline_image"><a href="/user_uploads/{path_id}" title="animated_img.gif">'
+                f'<img data-animated="true" src="/user_uploads/thumbnail/{path_id}/100x75-anim.webp"></a></div>'
+            )
+            message_id = self.send_message_content(content, do_thumbnail=True)
+        self.assert_message_content_is(message_id, expected)
+        self.assert_length(ImageAttachment.objects.get(path_id=path_id).thumbnail_metadata, 2)
+
+        # Re-thumbnail with a non-overlapping set of sizes
+        with self.thumbnail_formats(ThumbnailFormat("jpg", 100, 75, animated=False)):
+            ensure_thumbnails(ImageAttachment.objects.get(path_id=path_id))
+
+        # We generate a new size but leave the old ones
+        self.assert_length(ImageAttachment.objects.get(path_id=path_id).thumbnail_metadata, 3)
+
+        # And the contents are not updated to the new size
+        self.assert_message_content_is(message_id, expected)
+
+    def test_thumbnail_sequential_edits(self) -> None:
+        first_path_id = self.upload_image("img.png")
+        second_path_id = self.upload_image("img.jpg")
+
+        message_id = self.send_message_content(
+            f"[first image](/user_uploads/{first_path_id})\n[second image](/user_uploads/{second_path_id})",
+            do_thumbnail=False,
+        )
+        self.assert_message_content_is(
+            message_id,
+            (
+                f'<p><a href="/user_uploads/{first_path_id}">first image</a><br>\n'
+                f'<a href="/user_uploads/{second_path_id}">second image</a></p>\n'
+                f'<div class="message_inline_image"><a href="/user_uploads/{first_path_id}" title="first image">'
+                '<img class="image-loading-placeholder" src="/static/images/loading/loader-black.svg"></a></div>'
+                f'<div class="message_inline_image"><a href="/user_uploads/{second_path_id}" title="second image">'
+                '<img class="image-loading-placeholder" src="/static/images/loading/loader-black.svg"></a></div>'
+            ),
+        )
+
+        # Complete thumbnailing the second image first -- replacing only that spinner
+        ensure_thumbnails(ImageAttachment.objects.get(path_id=second_path_id))
+        self.assert_message_content_is(
+            message_id,
+            (
+                f'<p><a href="/user_uploads/{first_path_id}">first image</a><br>\n'
+                f'<a href="/user_uploads/{second_path_id}">second image</a></p>\n'
+                f'<div class="message_inline_image"><a href="/user_uploads/{first_path_id}" title="first image">'
+                '<img class="image-loading-placeholder" src="/static/images/loading/loader-black.svg"></a></div>'
+                f'<div class="message_inline_image"><a href="/user_uploads/{second_path_id}" title="second image">'
+                f'<img src="/user_uploads/thumbnail/{second_path_id}/840x560.webp"></a></div>'
+            ),
+        )
+
+        # Finish the other thumbnail
+        ensure_thumbnails(ImageAttachment.objects.get(path_id=first_path_id))
+        self.assert_message_content_is(
+            message_id,
+            (
+                f'<p><a href="/user_uploads/{first_path_id}">first image</a><br>\n'
+                f'<a href="/user_uploads/{second_path_id}">second image</a></p>\n'
+                f'<div class="message_inline_image"><a href="/user_uploads/{first_path_id}" title="first image">'
+                f'<img src="/user_uploads/thumbnail/{first_path_id}/840x560.webp"></a></div>'
+                f'<div class="message_inline_image"><a href="/user_uploads/{second_path_id}" title="second image">'
+                f'<img src="/user_uploads/thumbnail/{second_path_id}/840x560.webp"></a></div>'
+            ),
+        )
+
+    def test_thumbnail_of_deleted(self) -> None:
+        sender_user_profile = self.example_user("othello")
+        path_id = self.upload_image("img.png")
+        message_id = self.send_message_content(f"[image](/user_uploads/{path_id})")
+
+        # Delete the message
+        do_delete_messages(
+            sender_user_profile.realm, [Message.objects.get(id=message_id)], acting_user=None
+        )
+
+        # There is still an ImageAttachment row
+        self.assertFalse(Attachment.objects.filter(path_id=path_id).exists())
+        self.assertTrue(ArchivedAttachment.objects.filter(path_id=path_id).exists())
+        self.assertTrue(ImageAttachment.objects.filter(path_id=path_id).exists())
+
+        # Completing rendering after it is deleted should work, and
+        # update the rendered content in the archived message
+        ensure_thumbnails(ImageAttachment.objects.get(path_id=path_id))
+        expected = (
+            f'<p><a href="/user_uploads/{path_id}">image</a></p>\n'
+            f'<div class="message_inline_image"><a href="/user_uploads/{path_id}" title="image">'
+            f'<img src="/user_uploads/thumbnail/{path_id}/840x560.webp"></a></div>'
+        )
+        self.assertEqual(
+            ArchivedMessage.objects.get(id=message_id).rendered_content,
+            expected,
+        )
+        # See test_delete_unclaimed_attachments for tests of the
+        # archiving process itself, and how it interacts with
+        # thumbnails.
+
+    def test_thumbnail_bad_image(self) -> None:
+        """Test what happens if the file looks fine, but resizing later fails"""
+        path_id = self.upload_image("img.png")
+        message_id = self.send_message_content(f"[image](/user_uploads/{path_id})")
+        self.assert_length(ImageAttachment.objects.get(path_id=path_id).thumbnail_metadata, 0)
+
+        # If the image is found to be bad, we remove all trace of the preview
+        with (
+            patch.object(
+                pyvips.Image, "thumbnail_buffer", side_effect=pyvips.Error("some bad error")
+            ) as thumb_mock,
+            self.assertLogs("zerver.worker.thumbnail", "ERROR") as thumbnail_logs,
+        ):
+            ensure_thumbnails(ImageAttachment.objects.get(path_id=path_id))
+            thumb_mock.assert_called_once()
+        self.assert_length(thumbnail_logs.output, 1)
+        self.assertTrue(
+            thumbnail_logs.output[0].startswith("ERROR:zerver.worker.thumbnail:some bad error")
+        )
+        self.assertFalse(ImageAttachment.objects.filter(path_id=path_id).exists())
+        self.assert_message_content_is(
+            message_id, f'<p><a href="/user_uploads/{path_id}">image</a></p>'
+        )
+
+    def test_thumbnail_multiple_messages(self) -> None:
+        sender_user_profile = self.example_user("othello")
+        path_id = self.upload_image("img.png")
+        channel_message_id = self.send_message_content(f"A public [image](/user_uploads/{path_id})")
+        private_message_id = self.send_personal_message(
+            from_user=sender_user_profile,
+            to_user=self.example_user("hamlet"),
+            content=f"This [image](/user_uploads/{path_id}) is private",
+        )
+        placeholder = (
+            f'<div class="message_inline_image"><a href="/user_uploads/{path_id}" title="image">'
+            '<img class="image-loading-placeholder" src="/static/images/loading/loader-black.svg"></a></div>'
+        )
+        self.assert_message_content_is(
+            channel_message_id,
+            f'<p>A public <a href="/user_uploads/{path_id}">image</a></p>\n{placeholder}',
+        )
+
+        self.assert_message_content_is(
+            private_message_id,
+            f'<p>This <a href="/user_uploads/{path_id}">image</a> is private</p>\n{placeholder}',
+        )
+
+        with (
+            patch.object(
+                pyvips.Image, "thumbnail_buffer", wraps=pyvips.Image.thumbnail_buffer
+            ) as thumb_mock,
+            self.thumbnail_formats(
+                ThumbnailFormat("webp", 100, 75, animated=False),
+                ThumbnailFormat("webp", 200, 150, animated=False),
+            ),
+        ):
+            ensure_thumbnails(ImageAttachment.objects.get(path_id=path_id))
+
+        # Called once per format
+        self.assertEqual(thumb_mock.call_count, 2)
+
+        rendered_thumb = (
+            f'<div class="message_inline_image"><a href="/user_uploads/{path_id}" title="image">'
+            f'<img src="/user_uploads/thumbnail/{path_id}/100x75.webp"></a></div>'
+        )
+
+        self.assert_message_content_is(
+            channel_message_id,
+            f'<p>A public <a href="/user_uploads/{path_id}">image</a></p>\n{rendered_thumb}',
+        )
+
+        self.assert_message_content_is(
+            private_message_id,
+            f'<p>This <a href="/user_uploads/{path_id}">image</a> is private</p>\n{rendered_thumb}',
+        )
--- a/zerver/worker/embed_links.py
+++ b/zerver/worker/embed_links.py
@ -56,7 +56,7 @@ class FetchLinksEmbedData(QueueProcessingWorker):
                realm,
                url_embed_data=url_embed_data,
            )
-            do_update_embedded_data(message.sender, message, message.content, rendering_result)
+            do_update_embedded_data(message.sender, message, rendering_result)

    @override
    def timer_expired(
--- a/zerver/worker/thumbnail.py
+++ b/zerver/worker/thumbnail.py
@ -8,10 +8,17 @@ import pyvips
 from django.db import transaction
 from typing_extensions import override

+from zerver.actions.message_edit import do_update_embedded_data
 from zerver.lib.mime_types import guess_type
-from zerver.lib.thumbnail import StoredThumbnailFormat, get_image_thumbnail_path, missing_thumbnails
+from zerver.lib.thumbnail import (
+    StoredThumbnailFormat,
+    get_default_thumbnail_url,
+    get_image_thumbnail_path,
+    missing_thumbnails,
+    rewrite_thumbnailed_images,
+)
 from zerver.lib.upload import save_attachment_contents, upload_backend
-from zerver.models import ImageAttachment
+from zerver.models import ArchivedMessage, ImageAttachment, Message
 from zerver.worker.base import QueueProcessingWorker, assign_queue

 logger = logging.getLogger(__name__)
@ -120,9 +127,52 @@ def ensure_thumbnails(image_attachment: ImageAttachment) -> int:
            # We have never thumbnailed this -- it most likely had
            # bad data.  Remove the ImageAttachment row, since it is
            # not valid for thumbnailing.
+            update_message_rendered_content(
+                image_attachment.realm_id, image_attachment.path_id, None
+            )
            image_attachment.delete()
            return 0
+        else:  # nocoverage
+            # TODO: Clean up any dangling thumbnails we may have
+            # produced?  Seems unlikely that we'd fail on one size,
+            # but not another, but anything's possible.
+            pass

    image_attachment.save(update_fields=["thumbnail_metadata"])
-
+    update_message_rendered_content(
+        image_attachment.realm_id,
+        image_attachment.path_id,
+        get_default_thumbnail_url(image_attachment),
+    )
    return written_images
+
+
+def update_message_rendered_content(
+    realm_id: int, path_id: str, image_data: tuple[str, bool] | None
+) -> None:
+    for message_class in [Message, ArchivedMessage]:
+        messages_with_image = (
+            message_class.objects.filter(  # type: ignore[attr-defined]  # TODO: ?
+                realm_id=realm_id, attachment__path_id=path_id
+            )
+            .select_for_update()
+            .order_by("id")
+        )
+        for message in messages_with_image:
+            rendered_content = rewrite_thumbnailed_images(
+                message.rendered_content,
+                {} if image_data is None else {path_id: image_data},
+                {path_id} if image_data is None else set(),
+            )
+            if rendered_content is None:
+                # There were no updates -- for instance, if we re-run
+                # ensure_thumbnails on an ImageAttachment we already
+                # ran it on once.  Do not bother to no-op update
+                # clients.
+                continue
+            if isinstance(message, Message):
+                # Perform a silent update push to the clients
+                do_update_embedded_data(message.sender, message, rendered_content)
+            else:
+                message.rendered_content = rendered_content
+                message.save(update_fields=["rendered_content"])
--- a/zproject/default_settings.py
+++ b/zproject/default_settings.py
@ -203,7 +203,6 @@ REDIS_PORT = 6379
 REMOTE_POSTGRES_HOST = ""
 REMOTE_POSTGRES_PORT = ""
 REMOTE_POSTGRES_SSLMODE = ""
-THUMBNAIL_IMAGES = False

 TORNADO_PORTS: list[int] = []
 USING_TORNADO = True