From 1dcc549bd5f59290897ce21b40a60c3d7cd4644c Mon Sep 17 00:00:00 2001
From: Rene Vergara <rene@vergara.network>
Date: Wed, 6 Nov 2024 15:48:50 -0600
Subject: [PATCH] feat: add sapling tree anchor function

---
 librustzcash-wrapper/src/lib.rs | 23 +++++++++++++++++++++++
 src/C/Zcash.chs                 |  7 +++++++
 src/ZcashHaskell/Sapling.hs     |  6 ++++++
 3 files changed, 36 insertions(+)

diff --git a/librustzcash-wrapper/src/lib.rs b/librustzcash-wrapper/src/lib.rs
index 903c256..2c1b644 100644
--- a/librustzcash-wrapper/src/lib.rs
+++ b/librustzcash-wrapper/src/lib.rs
@@ -1660,6 +1660,29 @@ pub extern "C" fn rust_wrapper_read_sapling_commitment_tree_parts(
     }
 }
 
+#[no_mangle]
+pub extern "C" fn rust_wrapper_read_sapling_tree_anchor(
+    tree: *const u8,
+    tree_len: usize,
+    out: *mut u8,
+    out_len: &mut usize
+    ){
+    let tree_in: Vec<u8> = marshall_from_haskell_var(tree, tree_len, RW);
+    let tree_reader = Cursor::new(tree_in);
+    let comm_tree = read_commitment_tree(tree_reader);
+    match comm_tree {
+        Ok::<CommitmentTree<Node, 32>, _>(c1) => {
+            let root = c1.root();
+            let h = Hhex { bytes: root.to_bytes().to_vec() };
+            marshall_to_haskell_var(&h, out, out_len, RW);
+        },
+        Err(_) => {
+            let h0 = Hhex { bytes: vec![0] };
+            marshall_to_haskell_var(&h0, out, out_len, RW);
+        }
+    }
+}
+
 #[no_mangle]
 pub extern "C" fn rust_wrapper_read_orchard_frontier(
     tree: *const u8,
diff --git a/src/C/Zcash.chs b/src/C/Zcash.chs
index 0bcdf6d..6d915bb 100644
--- a/src/C/Zcash.chs
+++ b/src/C/Zcash.chs
@@ -276,6 +276,13 @@ import ZcashHaskell.Types
   -> `()'
 #}
 
+{# fun unsafe rust_wrapper_read_sapling_tree_anchor as rustWrapperReadSaplingTreeAnchor
+     { toBorshVar* `BS.ByteString'&
+     , getVarBuffer `Buffer HexString'&
+     }
+  -> `()'
+#}
+
 {# fun unsafe rust_wrapper_read_orchard_node as rustWrapperReadOrchardNode
      { toBorshVar* `BS.ByteString'&
      , getVarBuffer `Buffer HexString'&
diff --git a/src/ZcashHaskell/Sapling.hs b/src/ZcashHaskell/Sapling.hs
index f0b743c..87b21f7 100644
--- a/src/ZcashHaskell/Sapling.hs
+++ b/src/ZcashHaskell/Sapling.hs
@@ -26,6 +26,7 @@ import C.Zcash
   , rustWrapperReadSaplingFrontier
   , rustWrapperReadSaplingNode
   , rustWrapperReadSaplingPosition
+  , rustWrapperReadSaplingTreeAnchor
   , rustWrapperReadSaplingTreeParts
   , rustWrapperReadSaplingWitness
   , rustWrapperSaplingCheck
@@ -231,6 +232,11 @@ getSaplingTreeParts h =
       withPureBorshVarBuffer $
       rustWrapperReadSaplingTreeParts $ toBytes $ sapTree h
 
+getSaplingTreeAnchor :: SaplingCommitmentTree -> HexString
+getSaplingTreeAnchor tree =
+  withPureBorshVarBuffer $
+  rustWrapperReadSaplingTreeAnchor $ toBytes $ sapTree tree
+
 getSaplingFrontier :: SaplingCommitmentTree -> Maybe SaplingFrontier
 getSaplingFrontier tree =
   if sf_pos updatedTree > 1