HOPSFS-330: Translate raw RPC errors via interpretException for all namenode calls

getBlocks(), StatFs(), fetchDefaults(), and fetchDataEncryptionKey() returned
raw RPC errors without interpretException(), causing Java exceptions like
AccessControlException to propagate as unrecognized errors. The mount then
mapped them to EIO instead of the correct errno (e.g., EPERM).

Generated with Claude Code

Author: smkniazi

client.go

@@ -417,7 +417,7 @@ func (c *Client) fetchDataEncryptionKey() (*hdfs.DataEncryptionKeyProto, error)
 
 	err := c.namenode.Execute("getDataEncryptionKey", req, resp)
 	if err != nil {
-		return nil, err
+		return nil, interpretException(err)
 	}
 
 	c.encryptionKey = resp.GetDataEncryptionKey()

defaults.go

@@ -49,7 +49,7 @@ func (c *Client) fetchDefaults() (*hdfs.FsServerDefaultsProto, error) {
 
 	err := c.namenode.Execute("getServerDefaults", req, resp)
 	if err != nil {
-		return nil, err
+		return nil, interpretException(err)
 	}
 
 	c.defaults = resp.GetServerDefaults()

file_reader.go

@@ -454,7 +454,7 @@ func (f *FileReader) getBlocks() error {
 
 	err := f.client.namenode.Execute("getBlockLocations", req, resp)
 	if err != nil {
-		return err
+		return &os.PathError{"open", f.name, interpretException(err)}
 	}
 
 	f.blocks = resp.GetLocations().GetBlocks()

stat_fs.go

@@ -23,7 +23,7 @@ func (c *Client) StatFs() (FsInfo, error) {
 
 	err := c.namenode.Execute("getFsStats", req, resp)
 	if err != nil {
-		return FsInfo{}, err
+		return FsInfo{}, interpretException(err)
 	}
 
 	var fs FsInfo