New UniqueFilter for images associated with compromised accounts. (#3519)

* New UniqueFilter for images associated with compromised accounts.

Currently, the perceptual hashes of known images are hard-coded, but this is a temporary solution.

* Use `asyncio.to_thread` to make expensive actions awaitable.

`Image.open` and `imagehash.phash` are now awaitable.

* Handle case that `attachment.content_type` is None

* Handle (and ignore) exceptions from reading file attachments.

* Only consider attachments less than 30mb

* Add comments describing the image associated with each perceptual hash.

* Use Rhodium API instead of PIL, imagehash to load and hash images, removing them as dependencies.

* Change attachment limit to 5mb

* Store Rhodium API URL in constants.py; use http session from the bot instance.

* refactoring hash matching logic

* Add logging for exceptions

* Add two new perceptual hashes

* Add Rhodium API key to Keys constant

* Misc changes to image filter implementation

- Switch to using Keys constant for Rhodium API
- Increase timeout to 5 seconds
- Implement new RhodiumAPIError
- Switch to sending JSON to the API
- Handle errors more gracefully and return the error detail
- Handle regular ClientErrors
- Handle TimeoutError with the correct exception type

* Use log.exception instead of log.error

---------

Co-authored-by: Joe Banks <joe@jb3.dev>

Author: swfarnsworth

bot/constants.py

@@ -465,6 +465,8 @@ class _URLs(_BaseURLs):
 
     site_logs_view: str = "https://pythondiscord.com/staff/bot/logs"
 
+    rhodium_api: str = "https://rhodium.python-discord.workers.dev/"
+
 
 URLs = _URLs()
 
@@ -593,6 +595,7 @@ class _Keys(EnvConfig, env_prefix="api_keys_"):
 
     github: str = ""
     site_api: str = ""
+    rhodium: str = ""
 
 
 Keys = _Keys()

bot/exts/filtering/_filters/unique/image.py

@@ -0,0 +1,92 @@
+
+import aiohttp
+
+from bot import instance
+from bot.constants import Keys, URLs
+from bot.exts.filtering._filter_context import Event, FilterContext
+from bot.exts.filtering._filters.filter import UniqueFilter
+from bot.log import get_logger
+
+log = get_logger(__name__)
+
+# Maximum perceptual hash difference for positive predictions
+_THRESHOLD = 4
+# Maximum number of seconds to wait for Rhodium API
+_TIMEOUT = 5
+
+_KNOWN_IMAGE_HASHES = [
+    # A camera-taken image of a tweet attributed to @MrBeast about the purported launch of a crypto casino;
+    # there is a URL in the image that varies by instance
+    219481626328303491,
+    # An image saying "Activate Code for Bonus!"
+    6997610946676476306,
+    # An image saying "Withdrawal Success!"
+    -9135984495352994088,
+    # A collage of four images, the first being a purported tweet from Elon Musk about the opening a crypto casino,
+    # and the rest of similar character to the previous two
+    231962884035511073,
+    # Text centered on a background of a field and sky, the text saying "I've helped 15+ people earn ...
+    # in stock market and crypto trading"
+    360569449461317633,
+]
+
+
+def _is_match(image_hash: int) -> bool:
+    return any(
+        int.bit_count(image_hash ^ candidate_hash) <= _THRESHOLD
+        for candidate_hash in _KNOWN_IMAGE_HASHES
+    )
+
+class RhodiumAPIError(Exception):
+    """Exception raised when the Rhodium API returns an error."""
+
+
+async def _get_hash(image_url: str) -> int:
+    async with instance.http_session.post(
+        url=URLs.rhodium_api,
+        headers={"Authorization": f"Bearer {Keys.rhodium}"},
+        json={"url": image_url},
+        timeout=_TIMEOUT,
+    ) as response:
+        if response.status != 200:
+            contents = await response.text()
+
+            raise RhodiumAPIError(f"Rhodium API returned status code {response.status}: {contents}")
+
+        response_data = await response.json()
+        return response_data["i64"]
+
+
+class ImageFilter(UniqueFilter):
+    """Filter messages that contain an image attachment whose perceptual hash matches images associated with scams."""
+
+    name = "image"
+    events = (Event.MESSAGE, )
+
+    async def triggered_on(self, ctx: FilterContext) -> bool:
+        """Return whether the message has an attached image that is known to be posted by compromised accounts."""
+        log.trace("Entering image filter")
+        for attachment in ctx.attachments:
+            if (
+                attachment.content_type is None
+                or not attachment.content_type.startswith("image")
+                or attachment.size > 5e6  # 5mb
+            ):
+                continue
+
+            try:
+                image_hash = await _get_hash(attachment.url)
+            except aiohttp.ClientError:
+                log.exception("Unhandled aiohttp exception while getting image hash")
+                return False
+            except RhodiumAPIError as e:
+                log.exception("Rhodium API error: %s", e)
+                return False
+            except TimeoutError:
+                log.exception("Timed out getting image hash")
+                return False
+
+            if _is_match(image_hash):
+                return True
+
+        return False