1 files changed, 62 insertions, 0 deletions
diff --git a/rustables/src/expr/wrapper.rs b/rustables/src/expr/wrapper.rs
new file mode 100644
index 0000000..5162c21
--- /dev/null
+++ b/rustables/src/expr/wrapper.rs
@@ -0,0 +1,62 @@
+use std::ffi::CStr;
+use std::ffi::CString;
+use std::fmt::Debug;
+use std::rc::Rc;
+
+use super::DeserializationError;
+use super::Expression;
+use crate::Rule;
+use rustables_sys as sys;
+
+pub struct ExpressionWrapper {
+    pub(crate) expr: *const sys::nftnl_expr,
+    // we also need the rule here to ensure that the rule lives as long as the `expr` pointer
+    #[allow(dead_code)]
+    pub(crate) rule: Rc<Rule>,
+}
+
+impl Debug for ExpressionWrapper {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        write!(f, "{:?}", self.get_str())
+    }
+}
+
+impl ExpressionWrapper {
+    /// Retrieves a textual description of the expression.
+    pub fn get_str(&self) -> CString {
+        let mut descr_buf = vec![0i8; 4096];
+        unsafe {
+            sys::nftnl_expr_snprintf(
+                descr_buf.as_mut_ptr(),
+                (descr_buf.len() - 1) as u64,
+                self.expr,
+                sys::NFTNL_OUTPUT_DEFAULT,
+                0,
+            );
+            CStr::from_ptr(descr_buf.as_ptr()).to_owned()
+        }
+    }
+
+    /// Retrieves the type of expression ("log", "counter", ...).
+    pub fn get_kind(&self) -> Option<&CStr> {
+        unsafe {
+            let ptr = sys::nftnl_expr_get_str(self.expr, sys::NFTNL_EXPR_NAME as u16);
+            if !ptr.is_null() {
+                Some(CStr::from_ptr(ptr))
+            } else {
+                None
+            }
+        }
+    }
+
+    /// Attempt to decode the expression as the type T.
+    pub fn decode_expr<T: Expression>(&self) -> Result<T, DeserializationError> {
+        if let Some(kind) = self.get_kind() {
+            let raw_name = unsafe { CStr::from_ptr(T::get_raw_name()) };
+            if kind == raw_name {
+                return T::from_expr(self.expr);
+            }
+        }
+        Err(DeserializationError::InvalidExpressionKind)
+    }
+}