feat: implement streaming for item content with offset and length support

Co-authored-by: aider (openai/andrew/openrouter/qwen/qwen3-coder) <aider@aider.chat>

src/services/async_item_service.rs

@@ -56,20 +56,47 @@ impl AsyncItemService {
         &self,
         item_id: i64,
         allow_binary: bool,
-        _offset: u64,
+        offset: u64,
         length: u64,
     ) -> Result<(std::pin::Pin<Box<dyn tokio_stream::Stream<Item = Result<tokio_util::bytes::Bytes, std::io::Error>> + Send>>, String), CoreError> {
-        // Get the item content synchronously
-        let item_with_content = self.get_item_content(item_id).await?;
+        let data_dir = self.data_dir.clone();
+        let db = self.db.clone();
+
+        // Get item metadata first to check binary status and get MIME type
+        let item_with_meta = tokio::task::spawn_blocking(move || {
+            let conn = db.blocking_lock();
+            let item_service = ItemService::new(data_dir);
+            item_service.get_item(&conn, item_id)
+        })
+        .await
+        .unwrap()?;
+
+        let metadata = item_with_meta.meta_as_map();
+        let mime_type = metadata
+            .get("mime_type")
+            .map(|s| s.to_string())
+            .unwrap_or_else(|| "application/octet-stream".to_string());
         
         // Check if content is binary when allow_binary is false
-        let metadata = item_with_content.item_with_meta.meta_as_map();
         if !allow_binary {
             let is_content_binary = if let Some(binary_val) = metadata.get("binary") {
                 binary_val == "true"
             } else {
-                // Fallback to checking the actual content
-                crate::common::is_binary::is_binary(&item_with_content.content)
+                // For the binary check, we need to read a sample of the content
+                // We'll read the first 8192 bytes to determine if it's binary
+                let data_dir = self.data_dir.clone();
+                let db = self.db.clone();
+                
+                let sample_content = tokio::task::spawn_blocking(move || {
+                    let conn = db.blocking_lock();
+                    let item_service = ItemService::new(data_dir);
+                    let item_with_content = item_service.get_item_content(&conn, item_id)?;
+                    Ok::<Vec<u8>, CoreError>(item_with_content.content)
+                })
+                .await
+                .unwrap()?;
+                
+                crate::common::is_binary::is_binary(&sample_content)
             };
             
             if is_content_binary {
@@ -77,17 +104,43 @@ impl AsyncItemService {
             }
         }
         
-        let mime_type = metadata
-            .get("mime_type")
-            .map(|s| s.to_string())
-            .unwrap_or_else(|| "application/octet-stream".to_string());
+        // Create a stream that reads only the requested portion
+        let data_dir = self.data_dir.clone();
+        let db = self.db.clone();
         
-        // Convert content to stream with length limit
-        let mut content = item_with_content.content;
-        if length > 0 && length < content.len() as u64 {
-            content.truncate(length as usize);
+        let stream = Box::pin(tokio_stream::wrappers::ReceiverStream::new({
+            let (tx, rx) = tokio::sync::mpsc::channel(1);
+            
+            tokio::task::spawn_blocking(move || {
+                let conn = db.blocking_lock();
+                let item_service = ItemService::new(data_dir);
+                
+                match item_service.get_item_content(&conn, item_id) {
+                    Ok(item_with_content) => {
+                        let content = item_with_content.content;
+                        let content_len = content.len() as u64;
+                        
+                        // Apply offset and length constraints
+                        let start = std::cmp::min(offset, content_len);
+                        let end = if length > 0 {
+                            std::cmp::min(start + length, content_len)
+                        } else {
+                            content_len
+                        };
+                        
+                        if start < content_len {
+                            let chunk = tokio_util::bytes::Bytes::from(content[start as usize..end as usize].to_vec());
+                            let _ = tx.blocking_send(Ok(chunk));
                         }
-        let stream = Box::pin(tokio_stream::iter(vec![Ok(tokio_util::bytes::Bytes::from(content))]));
+                    }
+                    Err(e) => {
+                        let _ = tx.blocking_send(Err(std::io::Error::new(std::io::ErrorKind::Other, e.to_string())));
+                    }
+                }
+            });
+            
+            rx
+        }));
         
         Ok((stream, mime_type))
     }