feat(ffi): do not panic in visit_scan_metadata

Author: aleksandarskrbic

ffi/examples/read-table/read_table.c

@@ -110,7 +110,11 @@ void do_visit_scan_metadata(void* engine_context, HandleSharedScanMetadata scan_
 
   // Ask kernel to iterate each individual file and call us back with extracted metadata
   print_diag("Asking kernel to call us back for each scan row (file to read)\n");
-  visit_scan_metadata(scan_metadata, engine_context, scan_row_callback);
+  ExternResultNullableCvoid result = visit_scan_metadata(scan_metadata, context->engine, engine_context, scan_row_callback);
+  if (result.tag != OkNullableCvoid) {
+    printf("Error visiting scan metadata\n");
+    exit(-1);
+  }
   free_bool_slice(selection_vector);
   free_scan_metadata(scan_metadata);
 }

ffi/src/scan.rs

@@ -499,19 +499,21 @@ struct ContextWrapper {
 #[no_mangle]
 pub unsafe extern "C" fn visit_scan_metadata(
     scan_metadata: Handle<SharedScanMetadata>,
+    engine: Handle<SharedExternEngine>,
     engine_context: NullableCvoid,
     callback: CScanCallback,
-) {
+) -> ExternResult<NullableCvoid> {
+    let engine = unsafe { engine.as_ref() };
     let scan_metadata = unsafe { scan_metadata.as_ref() };
     let context_wrapper = ContextWrapper {
         engine_context,
         callback,
     };
 
-    // TODO: return ExternResult to caller instead of panicking?
     scan_metadata
         .visit_scan_files(context_wrapper, rust_callback)
-        .unwrap();
+        .map(|_| None)
+        .into_extern_result(&engine)
 }
 
 #[cfg(test)]