Check wallet export file size and determine if it is a symlink vs other special files

src/wallet/rpcdump.cpp

@@ -482,11 +482,19 @@ UniValue importwallet_impl(const UniValue& params, bool fHelp, bool fImportZKeys
     struct stat s;
     if( stat(params[0].get_str(),&s) == 0 ) {
         if( s.st_mode & S_IFDIR ) { // it's a directory
-            throw JSONRPCError(RPC_WALLET_ERROR, "Invalid wallet export file");
+            throw JSONRPCError(RPC_WALLET_ERROR, "Invalid wallet export file (directory)");
         } else if( s.st_mode & S_IFREG ) { // it's a file
-            // TODO: check for a min file size
-        } else { // something else, maybe symlink or special file
-            // TODO: detect difference between symlinks and special files
+            // The absolute smallest valid export file is a single taddr privkey with no
+            // newline and no comments. In practice, autogenerated files will be much larger
+            if(s.st_size < 51) {
+                throw JSONRPCError(RPC_WALLET_ERROR, "Wallet export file is too small to be valid");
+            }
+        } else if( s.st_mode & S_IFLINK ) { // it's a symbolic link
+            // TODO: check filesize of symbolicly linked file
+            // for symlinks, size the length in bytes of the pathname contained in the symbolic link
+            // which is not what we want
+        } else { // something else, either a block/char/FIFO special file or socket, none of which are valid
+            throw JSONRPCError(RPC_WALLET_ERROR, "Invalid wallet export file (special)");
         }
     } else {
          throw JSONRPCError(RPC_WALLET_ERROR, "Wallet export file does not exist");