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feat: support for setting UA for URL previews #17968

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feat: support for setting UA for URL previews #17968

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5d24654
feat: support for setting UA for URL previews
MomentQYC Nov 27, 2024
e18759a
Create 17968.feature
MomentQYC Nov 27, 2024
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1 change: 1 addition & 0 deletions changelog.d/17968.feature
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Original file line number Diff line number Diff line change
@@ -0,0 +1 @@
Add support for setting User-Agent for URL previewing.
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@MadLittleMods MadLittleMods Dec 4, 2024 •
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The option itself seems relatively straightforward. Our sane default feels like it should be good enough. I'm going to add this to the To-Discuss board to talk with the team on Monday whether we want to introduce this.

The workaround use case seems kinda meh but I appreciate the context. (adding yet another option for a problem that will go away/change in the future)

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Discussed with the team and we're not keen on pretending to be someone else. If someone doesn't want to serve content to Synapse, that's their prerogative.

This might be a XY problem. The goal is make YouTube URL previews work. Do they have some API/flow that they prefer people to use? Should we be using OpenGraph/oEmbed instead of scraping, etc? We'd rather have PR's for that instead of this workaround.

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he goal is make YouTube URL previews work. Do they have some API/flow that they prefer people to use? Should we be using OpenGraph/oEmbed instead of scraping, etc?

See #17462.

11 changes: 11 additions & 0 deletions docs/usage/configuration/config_documentation.md
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Expand Up @@ -774,6 +774,17 @@ Example configuration:
```yaml
max_event_delay_duration: 24h
```
---
### `url_preview_user_agent`

Setting the User-Agent for URL previews.

Defaults to `Synapse (bot; +https://github.com/matrix-org/synapse)`.

Example configuration:
```yaml
url_preview_user_agent: "Hello Matrix"
```
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We should put this next to the other url_preview_xxx options


## Homeserver blocking
Useful options for Synapse admins.
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7 changes: 7 additions & 0 deletions synapse/config/server.py
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Expand Up @@ -788,6 +788,13 @@ def read_config(self, config: JsonDict, **kwargs: Any) -> None:
else:
self.max_event_delay_ms = None

self.url_preview_user_agent: str = (
config.get("url_preview_user_agent")
or "Synapse (bot; +https://github.com/matrix-org/synapse)"
Comment on lines +792 to +793
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Suggested change
config.get("url_preview_user_agent")
or "Synapse (bot; +https://github.com/matrix-org/synapse)"
config.get("url_preview_user_agent", "Synapse (bot; +https://github.com/matrix-org/synapse)")

)
if len(self.url_preview_user_agent.strip()) == 0:
raise ConfigError("The 'url_preview_user_agent' must be a valid User-Agent")
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Suggested change
raise ConfigError("The 'url_preview_user_agent' must be a valid User-Agent")
raise ConfigError(
"Must be a valid User-Agent string",
("url_preview_user_agent",),
)


Comment on lines +791 to +797
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We should do this processing alongside the other url_preview_config in synapse/config/repository.py

def has_tls_listener(self) -> bool:
return any(listener.is_tls() for listener in self.listeners)

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5 changes: 2 additions & 3 deletions synapse/media/url_previewer.py
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Expand Up @@ -168,6 +168,7 @@ def __init__(
):
self.clock = hs.get_clock()
self.filepaths = media_repo.filepaths
self.hs = hs
self.max_spider_size = hs.config.media.max_spider_size
self.server_name = hs.hostname
self.store = hs.get_datastores().main
Expand Down Expand Up @@ -464,9 +465,7 @@ async def _download_url(self, url: str, output_stream: BinaryIO) -> DownloadResu
# Use a custom user agent for the preview because some sites will only return
# Open Graph metadata to crawler user agents. Omit the Synapse version
# string to avoid leaking information.
b"User-Agent": [
"Synapse (bot; +https://github.com/matrix-org/synapse)"
],
b"User-Agent": [self.hs.config.server.url_preview_user_agent],
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Similar to what we do for max_spider_size in __init__, we can do the same for url_preview_user_agent

Suggested change
b"User-Agent": [self.hs.config.server.url_preview_user_agent],
b"User-Agent": [self.url_preview_user_agent],

},
is_allowed_content_type=_is_previewable,
)
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