feat(search): add advanced attachment filters for extension, category and mime type

src/modules/message/attachment.rs

@@ -0,0 +1,19 @@
+use std::collections::HashSet;
+
+use poem_openapi::Object;
+use serde::{Deserialize, Serialize};
+
+#[derive(Clone, Debug, Default, Eq, PartialEq, Deserialize, Serialize, Object)]
+pub struct AttachmentMetadata {
+    /// A collection of unique file extensions found in attachments.
+    /// Example: ["pdf", "docx", "png"]
+    pub extensions: HashSet<String>,
+
+    /// A collection of high-level attachment categories.
+    /// Example: ["document", "image", "archive"]
+    pub categories: HashSet<String>,
+
+    /// A collection of unique MIME types (Content-Type) for the attachments.
+    /// Example: ["application/pdf", "image/jpeg"]
+    pub content_types: HashSet<String>,
+}

src/modules/message/content.rs

@@ -51,7 +51,7 @@ impl AttachmentInfo {
         std::path::Path::new(&self.filename)
             .extension()
             .and_then(|ext| ext.to_str())
-            .map(|ext| ext.to_lowercase())
+            .map(|ext| ext.to_ascii_lowercase())
             .unwrap_or_default()
     }
 

src/modules/message/mod.rs

@@ -17,6 +17,7 @@
 // along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
 pub mod append;
+pub mod attachment;
 pub mod contacts;
 pub mod content;
 pub mod delete;

src/modules/message/search.rs

@@ -50,6 +50,9 @@ pub struct SearchFilter {
     pub has_attachment: Option<bool>,
     pub attachment_name: Option<String>,
     pub tags: Option<HashSet<String>>,
+    pub attachment_extension: Option<String>,
+    pub attachment_category: Option<String>,
+    pub attachment_content_type: Option<String>,
 }
 
 #[derive(Debug, Clone, Default, Eq, PartialEq, Serialize, Deserialize, Enum)]