feat: URL preview support

from upstream MR https://gitlab.com/famedly/conduit/-/merge_requests/347
with the following changes (so far):
- remove hardcoded list of allowed hosts (strongly disagree with this,
even if it is desired, it should not be harcoded)
- add more allow config options for granularity via URL contains,
host contains, and domain is (explicit match) for security
- warn if a user is allowing all URLs to be previewed for security reasons
- replace an expect with proper error handling
- bump webpage to 2.0
- improved code style a tad

Co-authored-by: rooot <hey@rooot.gay>
Signed-off-by: rooot <hey@rooot.gay>
Signed-off-by: strawberry <strawberry@puppygock.gay>

src/database/key_value/media.rs

@@ -1,6 +1,10 @@
 use ruma::api::client::error::ErrorKind;
 
-use crate::{database::KeyValueDatabase, service, utils, Error, Result};
+use crate::{
+    database::KeyValueDatabase,
+    service::{self, media::UrlPreviewData},
+    utils, Error, Result,
+};
 
 impl service::media::Data for KeyValueDatabase {
     fn create_file_metadata(
@@ -79,4 +83,112 @@ impl service::media::Data for KeyValueDatabase {
         };
         Ok((content_disposition, content_type, key))
     }
+
+    fn remove_url_preview(&self, url: &str) -> Result<()> {
+        self.url_previews.remove(url.as_bytes())
+    }
+
+    fn set_url_preview(
+        &self,
+        url: &str,
+        data: &UrlPreviewData,
+        timestamp: std::time::Duration,
+    ) -> Result<()> {
+        let mut value = Vec::<u8>::new();
+        value.extend_from_slice(&timestamp.as_secs().to_be_bytes());
+        value.push(0xff);
+        value.extend_from_slice(
+            data.title
+                .as_ref()
+                .map(|t| t.as_bytes())
+                .unwrap_or_default(),
+        );
+        value.push(0xff);
+        value.extend_from_slice(
+            data.description
+                .as_ref()
+                .map(|d| d.as_bytes())
+                .unwrap_or_default(),
+        );
+        value.push(0xff);
+        value.extend_from_slice(
+            data.image
+                .as_ref()
+                .map(|i| i.as_bytes())
+                .unwrap_or_default(),
+        );
+        value.push(0xff);
+        value.extend_from_slice(&data.image_size.unwrap_or(0).to_be_bytes());
+        value.push(0xff);
+        value.extend_from_slice(&data.image_width.unwrap_or(0).to_be_bytes());
+        value.push(0xff);
+        value.extend_from_slice(&data.image_height.unwrap_or(0).to_be_bytes());
+
+        self.url_previews.insert(url.as_bytes(), &value)
+    }
+
+    fn get_url_preview(&self, url: &str) -> Option<UrlPreviewData> {
+        let values = self.url_previews.get(url.as_bytes()).ok()??;
+
+        let mut values = values.split(|&b| b == 0xff);
+
+        let _ts = match values
+            .next()
+            .map(|b| u64::from_be_bytes(b.try_into().expect("valid BE array")))
+        {
+            Some(0) => None,
+            x => x,
+        };
+        let title = match values
+            .next()
+            .and_then(|b| String::from_utf8(b.to_vec()).ok())
+        {
+            Some(s) if s.is_empty() => None,
+            x => x,
+        };
+        let description = match values
+            .next()
+            .and_then(|b| String::from_utf8(b.to_vec()).ok())
+        {
+            Some(s) if s.is_empty() => None,
+            x => x,
+        };
+        let image = match values
+            .next()
+            .and_then(|b| String::from_utf8(b.to_vec()).ok())
+        {
+            Some(s) if s.is_empty() => None,
+            x => x,
+        };
+        let image_size = match values
+            .next()
+            .map(|b| usize::from_be_bytes(b.try_into().expect("valid BE array")))
+        {
+            Some(0) => None,
+            x => x,
+        };
+        let image_width = match values
+            .next()
+            .map(|b| u32::from_be_bytes(b.try_into().expect("valid BE array")))
+        {
+            Some(0) => None,
+            x => x,
+        };
+        let image_height = match values
+            .next()
+            .map(|b| u32::from_be_bytes(b.try_into().expect("valid BE array")))
+        {
+            Some(0) => None,
+            x => x,
+        };
+
+        Some(UrlPreviewData {
+            title,
+            description,
+            image,
+            image_size,
+            image_width,
+            image_height,
+        })
+    }
 }

src/database/mod.rs

@@ -147,6 +147,7 @@ pub struct KeyValueDatabase {
 
     //pub media: media::Media,
     pub(super) mediaid_file: Arc<dyn KvTree>, // MediaId = MXC + WidthHeight + ContentDisposition + ContentType
+    pub(super) url_previews: Arc<dyn KvTree>,
     //pub key_backups: key_backups::KeyBackups,
     pub(super) backupid_algorithm: Arc<dyn KvTree>, // BackupId = UserId + Version(Count)
     pub(super) backupid_etag: Arc<dyn KvTree>,      // BackupId = UserId + Version(Count)
@@ -350,6 +351,7 @@ impl KeyValueDatabase {
             roomuserdataid_accountdata: builder.open_tree("roomuserdataid_accountdata")?,
             roomusertype_roomuserdataid: builder.open_tree("roomusertype_roomuserdataid")?,
             mediaid_file: builder.open_tree("mediaid_file")?,
+            url_previews: builder.open_tree("url_previews")?,
             backupid_algorithm: builder.open_tree("backupid_algorithm")?,
             backupid_etag: builder.open_tree("backupid_etag")?,
             backupkeyid_backup: builder.open_tree("backupkeyid_backup")?,