fix: support loading .nii.gz files from local file system

Browsers provide application/gzip MIME type for .nii.gz files. The
updateFileMimeType handler now checks if the browser-provided type is
in our supported list before skipping. If the type is unsupported
(like application/gzip), it continues to check the filename extension
to correctly identify compound extensions like .nii.gz, .gipl.gz, etc.

Author: PaulHax

src/io/import/processors/importSingleFile.ts

@@ -43,7 +43,9 @@ const importSingleFile: ImportHandler = async (dataSource) => {
     return asLoadableResult(dataID, dataSource, 'model');
   }
 
-  throw new Error('Data reader did not produce a valid dataset');
+  throw new Error(
+    `Failed to import "${dataSource.file.name}". The file may be corrupted or in an unsupported format variant.`
+  );
 };
 
 export default importSingleFile;

src/io/import/processors/updateFileMimeType.ts

@@ -1,17 +1,27 @@
 import { Skip } from '@/src/utils/evaluateChain';
 import { getFileMimeType } from '@/src/io';
 import { ImportHandler, asIntermediateResult } from '@/src/io/import/common';
+import { MIME_TYPES } from '@/src/io/mimeTypes';
 
 /**
  * Transforms a file data source to have a mime type
  * @param dataSource
  */
 const updateFileMimeType: ImportHandler = async (dataSource) => {
-  if (dataSource.type !== 'file' || dataSource.fileType !== '') return Skip;
+  if (dataSource.type !== 'file') return Skip;
+
+  const knownType =
+    dataSource.fileType !== '' && MIME_TYPES.has(dataSource.fileType);
+  if (knownType) {
+    return Skip;
+  }
 
   const mime = await getFileMimeType(dataSource.file);
+
   if (!mime) {
-    throw new Error('File is unsupported');
+    throw new Error(
+      `Unrecognized file type for "${dataSource.file.name}". This file format is not supported.`
+    );
   }
 
   return asIntermediateResult([