refactor: Consolidate binary detection, response building, and filter string logic

Co-authored-by: aider (openai/andrew/openrouter/deepseek/deepseek-chat-v3.1) <aider@aider.chat>

src/common/binary_detection.rs

@@ -0,0 +1,43 @@
+use crate::services::async_item_service::AsyncItemService;
+use crate::services::error::CoreError;
+use axum::http::StatusCode;
+use std::collections::HashMap;
+
+/// Check if content is binary when allow_binary is false
+pub async fn check_binary_content_allowed(
+    item_service: &AsyncItemService,
+    item_id: i64,
+    metadata: &HashMap<String, String>,
+    allow_binary: bool,
+) -> Result<(), StatusCode> {
+    if !allow_binary {
+        let is_binary = is_content_binary(item_service, item_id, metadata).await?;
+        if is_binary {
+            return Err(StatusCode::BAD_REQUEST);
+        }
+    }
+    Ok(())
+}
+
+/// Helper function to determine if content is binary
+pub async fn is_content_binary(
+    item_service: &AsyncItemService,
+    item_id: i64,
+    metadata: &HashMap<String, String>,
+) -> Result<bool, StatusCode> {
+    if let Some(text_val) = metadata.get("text") {
+        Ok(text_val == "false")
+    } else {
+        // If text metadata isn't set, we need to check the content using streaming approach
+        match item_service.get_item_content_info_streaming(
+            item_id,
+            None
+        ).await {
+            Ok((_, _, is_binary)) => Ok(is_binary),
+            Err(e) => {
+                log::warn!("Failed to get content info for binary check for item {}: {}", item_id, e);
+                Err(StatusCode::INTERNAL_SERVER_ERROR)
+            }
+        }
+    }
+}