Further documentation, start shoring up API boundaries of existing crates

coins/monero/src/tests/clsag.rs

@@ -64,11 +64,8 @@ fn clsag() {
         image,
         ClsagInput::new(
           Commitment::new(secrets.1, AMOUNT),
-          Decoys {
-            i: u8::try_from(real).unwrap(),
-            offsets: (1 ..= RING_LEN).collect(),
-            ring: ring.clone(),
-          },
+          Decoys::new((1 ..= RING_LEN).collect(), u8::try_from(real).unwrap(), ring.clone())
+            .unwrap(),
         )
         .unwrap(),
       )],
@@ -115,7 +112,7 @@ fn clsag_multisig() {
     Arc::new(RwLock::new(Some(ClsagDetails::new(
       ClsagInput::new(
         Commitment::new(randomness, AMOUNT),
-        Decoys { i: RING_INDEX, offsets: (1 ..= RING_LEN).collect(), ring: ring.clone() },
+        Decoys::new((1 ..= RING_LEN).collect(), RING_INDEX, ring.clone()).unwrap(),
       )
       .unwrap(),
       mask_sum,

coins/monero/src/wallet/decoys.rs

@@ -260,12 +260,15 @@ async fn select_decoys<R: RngCore + CryptoRng, RPC: RpcConnection>(
       // members
     }
 
-    res.push(Decoys {
-      // Binary searches for the real spend since we don't know where it sorted to
-      i: u8::try_from(ring.partition_point(|x| x.0 < o.0)).unwrap(),
-      offsets: offset(&ring.iter().map(|output| output.0).collect::<Vec<_>>()),
-      ring: ring.iter().map(|output| output.1).collect(),
-    });
+    res.push(
+      Decoys::new(
+        offset(&ring.iter().map(|output| output.0).collect::<Vec<_>>()),
+        // Binary searches for the real spend since we don't know where it sorted to
+        u8::try_from(ring.partition_point(|x| x.0 < o.0)).unwrap(),
+        ring.iter().map(|output| output.1).collect(),
+      )
+      .unwrap(),
+    );
   }
 
   Ok(res)

coins/monero/src/wallet/send/mod.rs

@@ -22,6 +22,8 @@ use dalek_ff_group as dfg;
 #[cfg(feature = "multisig")]
 use frost::FrostError;
 
+use monero_io::varint_len;
+
 use crate::{
   Protocol, Commitment, hash,
   serialize::{
@@ -181,7 +183,7 @@ fn prepare_inputs(
 
     tx.prefix.inputs.push(Input::ToKey {
       amount: None,
-      key_offsets: decoys.offsets.clone(),
+      key_offsets: decoys.offsets().to_vec(),
       key_image: signable[i].1,
     });
   }
@@ -518,8 +520,13 @@ impl SignableTransaction {
     }
 
     // Caclculate weight of decoys
-    let decoy_weights =
-      inputs.iter().map(|(_, decoy)| Decoys::fee_weight(&decoy.offsets)).collect::<Vec<_>>();
+    let decoy_weights = inputs
+      .iter()
+      .map(|(_, decoys)| {
+        let offsets = decoys.offsets();
+        varint_len(offsets.len()) + offsets.iter().map(|offset| varint_len(*offset)).sum::<usize>()
+      })
+      .collect::<Vec<_>>();
 
     // Deterministically calculate tx weight and fee
     let (weight, fee) =

coins/monero/src/wallet/send/multisig.rs

@@ -108,11 +108,11 @@ impl SignableTransaction {
       transcript.append_message(b"input_shared_key", input.key_offset().to_bytes());
 
       // Ensure all signers are signing the same rings
-      transcript.append_message(b"real_spend", [decoys.i]);
-      for (i, ring_member) in decoys.ring.iter().enumerate() {
+      transcript.append_message(b"real_spend", [decoys.signer_index()]);
+      for (i, ring_member) in decoys.ring().iter().enumerate() {
         transcript
           .append_message(b"ring_member", [u8::try_from(i).expect("ring size exceeded 255")]);
-        transcript.append_message(b"ring_member_offset", decoys.offsets[i].to_le_bytes());
+        transcript.append_message(b"ring_member_offset", decoys.offsets()[i].to_le_bytes());
         transcript.append_message(b"ring_member_key", ring_member[0].compress().to_bytes());
         transcript.append_message(b"ring_member_commitment", ring_member[1].compress().to_bytes());
       }
@@ -356,7 +356,7 @@ impl SignMachine<Transaction> for TransactionSignMachine {
 
       tx.prefix.inputs.push(Input::ToKey {
         amount: None,
-        key_offsets: value.2.offsets.clone(),
+        key_offsets: value.2.offsets().to_vec(),
         key_image: value.0,
       });