feat: sys::NodeTable::raw_metadata (#628)

* tskit::NodeTable internals use this new fn

Author: molpopgen

src/node_table.rs

@@ -590,7 +590,7 @@ impl NodeTable {
     ///
     /// * `Some(Ok(T))` if `row` is valid and decoding succeeded.
     /// * `Some(Err(_))` if `row` is not valid and decoding failed.
-    /// * `None` if `row` is not valid.
+    /// * `None` if `row` is not valid or the row has no metadata.
     ///
     /// # Errors
     ///
@@ -604,7 +604,7 @@ impl NodeTable {
         &self,
         row: NodeId,
     ) -> Option<Result<T, TskitError>> {
-        let buffer = self.raw_metadata(row)?;
+        let buffer = self.table_.raw_metadata(row).ok()??;
         Some(decode_metadata_row!(T, buffer).map_err(|e| e.into()))
     }
 

src/sys/node_table.rs

@@ -4,6 +4,7 @@ use super::bindings::tsk_node_table_add_row;
 use super::bindings::tsk_node_table_clear;
 use super::bindings::tsk_node_table_init;
 use super::bindings::tsk_node_table_t;
+use super::newtypes::NodeId;
 use super::tskbox::TskBox;
 use super::TskitError;
 
@@ -82,6 +83,20 @@ impl NodeTable {
             code => Err(TskitError::ErrorCode { code }),
         }
     }
+
+    pub fn raw_metadata(&self, row: NodeId) -> Result<Option<&[u8]>, TskitError> {
+        if row.is_null() || row.as_usize() >= self.as_ref().num_rows.try_into().unwrap() {
+            Err(TskitError::IndexError)
+        } else {
+            Ok(super::tsk_ragged_column_access(
+                row,
+                self.as_ref().metadata,
+                self.as_ref().metadata_length,
+                self.as_ref().metadata_offset,
+                self.as_ref().num_rows,
+            ))
+        }
+    }
 }
 
 impl Default for NodeTable {