Add action methods (#2199)

* add action methods

Co-authored-by: teor <teor@riseup.net>
Co-authored-by: Janito Vaqueiro Ferreira Filho <janito.vff@gmail.com>

zebra-chain/src/orchard/shielded_data.rs

@@ -3,7 +3,7 @@
 use crate::{
     amount::Amount,
     block::MAX_BLOCK_BYTES,
-    orchard::{tree, Action},
+    orchard::{tree, Action, Nullifier},
     primitives::{
         redpallas::{Binding, Signature, SpendAuth},
         Halo2Proof,
@@ -38,6 +38,27 @@ pub struct ShieldedData {
     pub binding_sig: Signature<Binding>,
 }
 
+impl ShieldedData {
+    /// Iterate over the [`Action`]s for the [`AuthorizedAction`]s in this transaction.
+    pub fn actions(&self) -> impl Iterator<Item = &Action> {
+        self.actions.actions()
+    }
+
+    /// Collect the [`Nullifier`]s for this transaction, if it contains
+    /// [`Action`]s.
+    pub fn nullifiers(&self) -> impl Iterator<Item = &Nullifier> {
+        self.actions().map(|action| &action.nullifier)
+    }
+}
+
+impl AtLeastOne<AuthorizedAction> {
+    /// Iterate over the [`Action`]s of each [`AuthorizedAction`].
+    pub fn actions(&self) -> impl Iterator<Item = &Action> {
+        self.iter()
+            .map(|authorized_action| &authorized_action.action)
+    }
+}
+
 /// An authorized action description.
 ///
 /// Every authorized Orchard `Action` must have a corresponding `SpendAuth` signature.