Update README

server.js

@@ -238,15 +238,43 @@ const upload = multer({
     fileSize: 10 * 1024 * 1024 // 10MB limit
   },
   fileFilter: (req, file, cb) => {
-    // Allow text files, PDFs, and images
-    const allowedTypes = /jpeg|jpg|png|gif|pdf|txt|doc|docx/;
-    const extname = allowedTypes.test(path.extname(file.originalname).toLowerCase());
-    const mimetype = allowedTypes.test(file.mimetype);
+    // Define allowed file types for RAG processing - only text-extractable documents
+    const allowedExtensions = ['.pdf', '.txt', '.doc', '.docx', '.xlsx', '.xls', '.md', '.json', '.csv', '.xml'];
+    const allowedMimeTypes = [
+      'application/pdf',
+      'text/plain',
+      'text/markdown',
+      'text/csv',
+      'text/xml',
+      'application/xml',
+      'application/json',
+      'application/msword',
+      'application/vnd.openxmlformats-officedocument.wordprocessingml.document',
+      'application/vnd.ms-excel',
+      'application/vnd.openxmlformats-officedocument.spreadsheetml.sheet'
+    ];
     
-    if (mimetype && extname) {
+    const fileExtension = path.extname(file.originalname).toLowerCase();
+    const fileMimeType = file.mimetype.toLowerCase();
+    
+    // Check if file extension is allowed
+    const isExtensionAllowed = allowedExtensions.includes(fileExtension);
+    
+    // Check if MIME type is allowed
+    const isMimeTypeAllowed = allowedMimeTypes.includes(fileMimeType);
+    
+    // Additional validation for specific file types
+    if (isExtensionAllowed && isMimeTypeAllowed) {
       return cb(null, true);
     } else {
-      cb(new Error('Only text files, PDFs, and images are allowed!'));
+      // Provide specific error messages for different rejection reasons
+      if (!isExtensionAllowed) {
+        return cb(new Error(`File type "${fileExtension}" is not supported. Only document files (PDF, Word, Excel, text files) are allowed for RAG processing.`));
+      } else if (!isMimeTypeAllowed) {
+        return cb(new Error(`MIME type "${fileMimeType}" is not supported. Please upload valid document files only.`));
+      } else {
+        return cb(new Error('Invalid file type. Only text-extractable documents are allowed to prevent RAG corruption.'));
+      }
     }
   }
 });