add unit tests for media key parsing

We've had at least a couple media key parsing bugs. Let's get a *little*
more confidence that this code works :)

src/database/key_value/media.rs

@@ -9,6 +9,7 @@ use crate::{
     utils, Error, Result,
 };
 
+#[derive(Debug, Eq, PartialEq)]
 struct MediaFileKeyParts {
     mxc: OwnedMxcUri,
     width: u32,
@@ -218,3 +219,142 @@ impl service::media::Data for KeyValueDatabase {
         )
     }
 }
+
+#[cfg(test)]
+mod test {
+    use super::{FileMeta, MediaFileKey, MediaFileKeyParts};
+
+    #[test]
+    fn parse_key_basic() {
+        let mut key = b"mxc://example.com/someid".to_vec();
+        key.push(0xFF);
+        key.extend_from_slice(&640_u32.to_be_bytes());
+        key.extend_from_slice(&480_u32.to_be_bytes());
+        key.push(0xFF);
+        key.extend_from_slice(b"inline");
+        key.push(0xFF);
+        key.extend_from_slice(b"image/png");
+        let key = MediaFileKey::new(key);
+
+        assert_eq!(
+            MediaFileKeyParts::try_from(&key).unwrap(),
+            MediaFileKeyParts {
+                mxc: "mxc://example.com/someid".into(),
+                width: 640,
+                height: 480,
+                meta: FileMeta {
+                    content_disposition: Some("inline".to_owned()),
+                    content_type: Some("image/png".to_owned()),
+                }
+            }
+        );
+    }
+
+    #[test]
+    fn parse_key_no_content_type() {
+        let mut key = b"mxc://example.com/someid".to_vec();
+        key.push(0xFF);
+        key.extend_from_slice(&640_u32.to_be_bytes());
+        key.extend_from_slice(&480_u32.to_be_bytes());
+        key.push(0xFF);
+        key.extend_from_slice(b"inline");
+        key.push(0xFF);
+        // No content type
+        let key = MediaFileKey::new(key);
+
+        assert_eq!(
+            MediaFileKeyParts::try_from(&key).unwrap(),
+            MediaFileKeyParts {
+                mxc: "mxc://example.com/someid".into(),
+                width: 640,
+                height: 480,
+                meta: FileMeta {
+                    content_disposition: Some("inline".to_owned()),
+                    content_type: None,
+                }
+            }
+        );
+    }
+
+    #[test]
+    fn parse_key_no_content_disposition() {
+        let mut key = b"mxc://example.com/someid".to_vec();
+        key.push(0xFF);
+        key.extend_from_slice(&640_u32.to_be_bytes());
+        key.extend_from_slice(&480_u32.to_be_bytes());
+        key.push(0xFF);
+        // No content disposition
+        key.push(0xFF);
+        key.extend_from_slice(b"image/png");
+        let key = MediaFileKey::new(key);
+
+        assert_eq!(
+            MediaFileKeyParts::try_from(&key).unwrap(),
+            MediaFileKeyParts {
+                mxc: "mxc://example.com/someid".into(),
+                width: 640,
+                height: 480,
+                meta: FileMeta {
+                    content_disposition: None,
+                    content_type: Some("image/png".to_owned()),
+                }
+            }
+        );
+    }
+
+    #[test]
+    fn parse_key_no_content_disposition_or_type() {
+        let mut key = b"mxc://example.com/someid".to_vec();
+        key.push(0xFF);
+        key.extend_from_slice(&640_u32.to_be_bytes());
+        key.extend_from_slice(&480_u32.to_be_bytes());
+        key.push(0xFF);
+        // No content disposition
+        key.push(0xFF);
+        // No content type
+        let key = MediaFileKey::new(key);
+
+        assert_eq!(
+            MediaFileKeyParts::try_from(&key).unwrap(),
+            MediaFileKeyParts {
+                mxc: "mxc://example.com/someid".into(),
+                width: 640,
+                height: 480,
+                meta: FileMeta {
+                    content_disposition: None,
+                    content_type: None,
+                }
+            }
+        );
+    }
+
+    // Our current media service code has an allowlist of thumbnail dimensions,
+    // and so we don't expect to create new thumbnails with dimensions
+    // containing a 0xFF byte. Thumbnails with a 0xFF in the dimensions may
+    // have been created previously, so we need to be able to read them.
+    #[test]
+    fn parse_key_separator_in_thumbnail_dims() {
+        let mut key = b"mxc://example.com/someid".to_vec();
+        key.push(0xFF);
+        key.extend_from_slice(&[0x0, 0x0, 0xFF, 0xFF]);
+        key.extend_from_slice(&[0x0, 0x0, 0x10, 0xFF]);
+        key.push(0xFF);
+        key.extend_from_slice(b"inline");
+        key.push(0xFF);
+        key.extend_from_slice(b"image/png");
+        let key = MediaFileKey::new(key);
+
+        assert_eq!(
+            MediaFileKeyParts::try_from(&key).unwrap(),
+            MediaFileKeyParts {
+                mxc: "mxc://example.com/someid".into(),
+                width: 0xFFFF,
+                height: 0x10FF,
+                meta: FileMeta {
+                    content_disposition: Some("inline".to_owned()),
+                    content_type: Some("image/png".to_owned()),
+                }
+            }
+        );
+    }
+}

src/service/media.rs

@@ -14,6 +14,7 @@ mod data;
 
 pub(crate) use data::Data;
 
+#[derive(Debug, Eq, PartialEq)]
 pub(crate) struct FileMeta {
     // This gets written to the database but we no longer read it
     //