Implement walk_header()

libimagstore/src/store.rs

@@ -459,6 +459,47 @@ impl EntryHeader {
             .collect()
     }
 
+    fn walk_header(v: &mut Value, tokens: Vec<Token>) -> Result<&mut Value> {
+        use std::vec::IntoIter;
+
+        fn extract_from_table<'a>(v: &'a mut Value, s: &String) -> Result<&'a mut Value> {
+            match v {
+                &mut Value::Table(ref mut t) => {
+                    t.get_mut(&s[..])
+                        .ok_or(StoreError::new(StoreErrorKind::HeaderKeyNotFound, None))
+                },
+                _ => Err(StoreError::new(StoreErrorKind::HeaderPathTypeFailure, None)),
+            }
+        }
+
+        fn extract_from_array(v: &mut Value, i: usize) -> Result<&mut Value> {
+            match v {
+                &mut Value::Array(ref mut a) => Ok(&mut a[i]),
+                _ => Err(StoreError::new(StoreErrorKind::HeaderPathTypeFailure, None)),
+            }
+        }
+
+        fn extract<'a>(v: &'a mut Value, token: &Token) -> Result<&'a mut Value> {
+            match token {
+                &Token::Key(ref s) => extract_from_table(v, s),
+                &Token::Index(i) => extract_from_array(v, i),
+            }
+        }
+
+        fn walk_iter<'a>(v: Result<&'a mut Value>, i: &mut IntoIter<Token>) -> Result<&'a mut Value> {
+            let next = i.next();
+            v.and_then(move |value| {
+                if let Some(token) = next {
+                    walk_iter(extract(value, &token), i)
+                } else {
+                    Ok(value)
+                }
+            })
+        }
+
+        walk_iter(Ok(v), &mut tokens.into_iter())
+    }
+
 }
 
 fn build_default_header() -> BTreeMap<String, Value> {