1 files changed, 37 insertions, 1 deletions
diff --git a/rustables/src/expr/immediate.rs b/rustables/src/expr/immediate.rs
index 15eb452..e8823b1 100644
--- a/rustables/src/expr/immediate.rs
+++ b/rustables/src/expr/immediate.rs
@@ -18,11 +18,47 @@ impl<T> Immediate<T> {
     }
 }
 
-impl<T> Expression for Immediate<T> {
+// The Copy requirement is present to allow us to dereference the newly created raw pointer in `from_expr`
+impl<T: Copy> Expression for Immediate<T> {
     fn get_raw_name() -> *const c_char {
         b"immediate\0" as *const _ as *const c_char
     }
 
+    fn from_expr(expr: *const sys::nftnl_expr) -> Option<Self>
+    where
+        Self: Sized,
+    {
+        unsafe {
+            let ref_len = std::mem::size_of::<T>() as u32;
+            let mut data_len = 0;
+            let data = sys::nftnl_expr_get(
+                expr,
+                sys::NFTNL_EXPR_IMM_DATA as u16,
+                &mut data_len as *mut u32,
+            );
+
+            if data.is_null() {
+                return None;
+            } else if data_len != ref_len {
+                debug!("Invalid size requested for deserializing an 'immediate' expression: expected {} bytes, got {}", ref_len, data_len);
+                return None;
+            }
+
+            // Warning: this is *very* dangerous safety wise if the user supply us with
+            // a type that have the same size as T but a different memory layout.
+            // Is there a better way? And if there isn't, shouldn't we gate this behind
+            // an "unsafe" boundary?
+            let data = *(data as *const T);
+
+            let register = Register::from_raw(sys::nftnl_expr_get_u32(
+                expr,
+                sys::NFTNL_EXPR_IMM_DREG as u16,
+            ));
+
+            register.map(|register| Immediate { data, register })
+        }
+    }
+
     fn to_expr(&self, _rule: &Rule) -> *mut sys::nftnl_expr {
         unsafe {
             let expr = try_alloc!(sys::nftnl_expr_alloc(Self::get_raw_name()));