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Do not break URL previews if an image is unreachable. (#12950)
Avoid breaking a URL preview completely if the chosen image 404s or is unreachable for some other reason (e.g. DNS).
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changelog.d/12950.bugfix
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1
changelog.d/12950.bugfix
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@ -0,0 +1 @@
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Fix a long-standing bug where a URL preview would break if the image failed to download.
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@ -586,12 +586,16 @@ class PreviewUrlResource(DirectServeJsonResource):
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og: The Open Graph dictionary. This is modified with image information.
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"""
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# If there's no image or it is blank, there's nothing to do.
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if "og:image" not in og or not og["og:image"]:
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if "og:image" not in og:
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return
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# Remove the raw image URL, this will be replaced with an MXC URL, if successful.
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image_url = og.pop("og:image")
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if not image_url:
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return
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# The image URL from the HTML might be relative to the previewed page,
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# convert it to an URL which can be requested directly.
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image_url = og["og:image"]
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url_parts = urlparse(image_url)
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if url_parts.scheme != "data":
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image_url = urljoin(media_info.uri, image_url)
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@ -599,7 +603,16 @@ class PreviewUrlResource(DirectServeJsonResource):
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# FIXME: it might be cleaner to use the same flow as the main /preview_url
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# request itself and benefit from the same caching etc. But for now we
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# just rely on the caching on the master request to speed things up.
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image_info = await self._handle_url(image_url, user, allow_data_urls=True)
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try:
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image_info = await self._handle_url(image_url, user, allow_data_urls=True)
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except Exception as e:
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# Pre-caching the image failed, don't block the entire URL preview.
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logger.warning(
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"Pre-caching image failed during URL preview: %s errored with %s",
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image_url,
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e,
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)
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return
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if _is_media(image_info.media_type):
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# TODO: make sure we don't choke on white-on-transparent images
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@ -611,13 +624,11 @@ class PreviewUrlResource(DirectServeJsonResource):
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og["og:image:width"] = dims["width"]
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og["og:image:height"] = dims["height"]
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else:
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logger.warning("Couldn't get dims for %s", og["og:image"])
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logger.warning("Couldn't get dims for %s", image_url)
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og["og:image"] = f"mxc://{self.server_name}/{image_info.filesystem_id}"
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og["og:image:type"] = image_info.media_type
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og["matrix:image:size"] = image_info.media_length
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else:
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del og["og:image"]
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async def _handle_oembed_response(
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self, url: str, media_info: MediaInfo, expiration_ms: int
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@ -656,6 +656,41 @@ class URLPreviewTests(unittest.HomeserverTestCase):
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server.data,
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)
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def test_nonexistent_image(self) -> None:
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"""If the preview image doesn't exist, ensure some data is returned."""
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self.lookups["matrix.org"] = [(IPv4Address, "10.1.2.3")]
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end_content = (
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b"""<html><body><img src="http://cdn.matrix.org/foo.jpg"></body></html>"""
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)
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channel = self.make_request(
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"GET",
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"preview_url?url=http://matrix.org",
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shorthand=False,
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await_result=False,
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)
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self.pump()
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client = self.reactor.tcpClients[0][2].buildProtocol(None)
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server = AccumulatingProtocol()
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server.makeConnection(FakeTransport(client, self.reactor))
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client.makeConnection(FakeTransport(server, self.reactor))
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client.dataReceived(
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(
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b"HTTP/1.0 200 OK\r\nContent-Length: %d\r\n"
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b'Content-Type: text/html; charset="utf8"\r\n\r\n'
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)
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% (len(end_content),)
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+ end_content
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)
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self.pump()
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self.assertEqual(channel.code, 200)
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# The image should not be in the result.
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self.assertNotIn("og:image", channel.json_body)
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def test_data_url(self) -> None:
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"""
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Requesting to preview a data URL is not supported.
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