Reorganize Sapling and Orchard note commitment tree sizes in CompactBlock.

We move thes fields out into a separate BlockMetadata struct to ensure
that future additions to block metadata are structurally separated from
future additions to block data.

zcash_client_backend/proto/compact_formats.proto

@@ -10,20 +10,27 @@ option swift_prefix = "";
 // Remember that proto3 fields are all optional. A field that is not present will be set to its zero value.
 // bytes fields of hashes are in canonical little-endian format.
 
+// BlockMetadata represents information about a block that may not be
+// represented directly in the block data, but is instead derived from chain
+// data or other external sources.
+message BlockMetadata {
+    uint32 saplingCommitmentTreeSize = 1; // the size of the Sapling note commitment tree as of the end of this block
+    uint32 orchardCommitmentTreeSize = 2; // the size of the Orchard note commitment tree as of the end of this block
+}
+
 // CompactBlock is a packaging of ONLY the data from a block that's needed to:
 //   1. Detect a payment to your shielded Sapling address
 //   2. Detect a spend of your shielded Sapling notes
 //   3. Update your witnesses to generate new Sapling spend proofs.
 message CompactBlock {
-    uint32 protoVersion = 1;    // the version of this wire format, for storage
-    uint64 height = 2;          // the height of this block
-    bytes hash = 3;             // the ID (hash) of this block, same as in block explorers
-    bytes prevHash = 4;         // the ID (hash) of this block's predecessor
-    uint32 time = 5;            // Unix epoch time when the block was mined
-    bytes header = 6;           // (hash, prevHash, and time) OR (full header)
-    repeated CompactTx vtx = 7; // zero or more compact transactions from this block
-    uint32 saplingCommitmentTreeSize = 8; // the size of the Sapling note commitment tree as of the end of this block
-    uint32 orchardCommitmentTreeSize = 9; // the size of the Orchard note commitment tree as of the end of this block
+    uint32 protoVersion = 1;         // the version of this wire format, for storage
+    uint64 height = 2;               // the height of this block
+    bytes hash = 3;                  // the ID (hash) of this block, same as in block explorers
+    bytes prevHash = 4;              // the ID (hash) of this block's predecessor
+    uint32 time = 5;                 // Unix epoch time when the block was mined
+    bytes header = 6;                // (hash, prevHash, and time) OR (full header)
+    repeated CompactTx vtx = 7;      // zero or more compact transactions from this block
+    BlockMetadata blockMetadata = 8; // information about this block derived from the chain or other sources
 }
 
 // CompactTx contains the minimum information for a wallet to know if this transaction

zcash_client_backend/src/proto/compact_formats.rs

@@ -1,3 +1,16 @@
+/// BlockMetadata represents information about a block that may not be
+/// represented directly in the block data, but is instead derived from chain
+/// data or other external sources.
+#[allow(clippy::derive_partial_eq_without_eq)]
+#[derive(Clone, PartialEq, ::prost::Message)]
+pub struct BlockMetadata {
+    /// the size of the Sapling note commitment tree as of the end of this block
+    #[prost(uint32, tag = "1")]
+    pub sapling_commitment_tree_size: u32,
+    /// the size of the Orchard note commitment tree as of the end of this block
+    #[prost(uint32, tag = "2")]
+    pub orchard_commitment_tree_size: u32,
+}
 /// CompactBlock is a packaging of ONLY the data from a block that's needed to:
 ///    1. Detect a payment to your shielded Sapling address
 ///    2. Detect a spend of your shielded Sapling notes
@@ -26,12 +39,9 @@ pub struct CompactBlock {
     /// zero or more compact transactions from this block
     #[prost(message, repeated, tag = "7")]
     pub vtx: ::prost::alloc::vec::Vec<CompactTx>,
-    /// the size of the Sapling note commitment tree as of the end of this block
-    #[prost(uint32, tag = "8")]
-    pub sapling_commitment_tree_size: u32,
-    /// the size of the Orchard note commitment tree as of the end of this block
-    #[prost(uint32, tag = "9")]
-    pub orchard_commitment_tree_size: u32,
+    /// information about this block derived from the chain or other sources
+    #[prost(message, optional, tag = "8")]
+    pub block_metadata: ::core::option::Option<BlockMetadata>,
 }
 /// CompactTx contains the minimum information for a wallet to know if this transaction
 /// is relevant to it (either pays to it or spends from it) via shielded elements

zcash_client_backend/src/proto/service.rs

@@ -1,3 +1,16 @@
+/// BlockMetadata represents information about a block that may not be
+/// represented directly in the block data, but is instead derived from chain
+/// data or other external sources.
+#[allow(clippy::derive_partial_eq_without_eq)]
+#[derive(Clone, PartialEq, ::prost::Message)]
+pub struct BlockMetadata {
+    /// the size of the Sapling note commitment tree as of the end of this block
+    #[prost(uint32, tag = "1")]
+    pub sapling_commitment_tree_size: u32,
+    /// the size of the Orchard note commitment tree as of the end of this block
+    #[prost(uint32, tag = "2")]
+    pub orchard_commitment_tree_size: u32,
+}
 /// A BlockID message contains identifiers to select a block: a height or a
 /// hash. Specification by hash is not implemented, but may be in the future.
 #[allow(clippy::derive_partial_eq_without_eq)]

zcash_client_backend/src/welding_rig.rs

@@ -218,16 +218,21 @@ pub(crate) fn scan_block_with_runner<
     // to use it. `block.sapling_commitment_tree_size` is expected to be correct as of the end of
     // the block, and we can't have a note of ours in a block with no outputs so treating the zero
     // default value from the protobuf as `None` is always correct.
-    let mut sapling_tree_position = if block.sapling_commitment_tree_size == 0 {
-        initial_commitment_tree_meta.map(|m| (m.sapling_tree_size() + 1).into())
-    } else {
-        let end_position_exclusive = Position::from(u64::from(block.sapling_commitment_tree_size));
+    let mut sapling_tree_position = if let Some(sapling_tree_size) = block
+        .block_metadata
+        .as_ref()
+        .map(|m| m.sapling_commitment_tree_size)
+        .filter(|s| *s != 0)
+    {
+        let end_position_exclusive = Position::from(u64::from(sapling_tree_size));
         let output_count = block
             .vtx
             .iter()
             .map(|tx| u64::try_from(tx.outputs.len()).unwrap())
             .sum();
         Some(end_position_exclusive - output_count)
+    } else {
+        initial_commitment_tree_meta.map(|m| (m.sapling_tree_size() + 1).into())
     };
 
     for tx in block.vtx.into_iter() {
@@ -404,11 +409,10 @@ pub(crate) fn scan_block_with_runner<
         block_hash,
         block_time: block.time,
         transactions: wtxs,
-        sapling_commitment_tree_size: if block.sapling_commitment_tree_size == 0 {
-            None
-        } else {
-            Some(block.sapling_commitment_tree_size)
-        },
+        sapling_commitment_tree_size: block
+            .block_metadata
+            .map(|m| m.sapling_commitment_tree_size)
+            .filter(|s| *s != 0),
         sapling_commitments: sapling_note_commitments,
     })
 }
@@ -439,7 +443,7 @@ mod tests {
     use crate::{
         data_api::chain::CommitmentTreeMeta,
         proto::compact_formats::{
-            CompactBlock, CompactSaplingOutput, CompactSaplingSpend, CompactTx,
+            BlockMetadata, CompactBlock, CompactSaplingOutput, CompactSaplingSpend, CompactTx,
         },
         scan::BatchRunner,
     };
@@ -547,8 +551,11 @@ mod tests {
             cb.vtx.push(tx);
         }
 
-        cb.sapling_commitment_tree_size = initial_sapling_tree_size
-            + cb.vtx.iter().map(|tx| tx.outputs.len() as u32).sum::<u32>();
+        cb.block_metadata = Some(BlockMetadata {
+            sapling_commitment_tree_size: initial_sapling_tree_size
+                + cb.vtx.iter().map(|tx| tx.outputs.len() as u32).sum::<u32>(),
+            ..Default::default()
+        });
 
         cb
     }

zcash_client_sqlite/src/lib.rs

@@ -964,7 +964,7 @@ mod tests {
         data_api::{WalletRead, WalletWrite},
         keys::{sapling, UnifiedFullViewingKey},
         proto::compact_formats::{
-            CompactBlock, CompactSaplingOutput, CompactSaplingSpend, CompactTx,
+            BlockMetadata, CompactBlock, CompactSaplingOutput, CompactSaplingSpend, CompactTx,
         },
     };
 
@@ -1109,8 +1109,11 @@ mod tests {
         };
         cb.prev_hash.extend_from_slice(&prev_hash.0);
         cb.vtx.push(ctx);
-        cb.sapling_commitment_tree_size = initial_sapling_tree_size
-            + cb.vtx.iter().map(|tx| tx.outputs.len() as u32).sum::<u32>();
+        cb.block_metadata = Some(BlockMetadata {
+            sapling_commitment_tree_size: initial_sapling_tree_size
+                + cb.vtx.iter().map(|tx| tx.outputs.len() as u32).sum::<u32>(),
+            ..Default::default()
+        });
         (cb, note.nf(&dfvk.fvk().vk.nk, 0))
     }
 
@@ -1197,8 +1200,11 @@ mod tests {
         };
         cb.prev_hash.extend_from_slice(&prev_hash.0);
         cb.vtx.push(ctx);
-        cb.sapling_commitment_tree_size = initial_sapling_tree_size
-            + cb.vtx.iter().map(|tx| tx.outputs.len() as u32).sum::<u32>();
+        cb.block_metadata = Some(BlockMetadata {
+            sapling_commitment_tree_size: initial_sapling_tree_size
+                + cb.vtx.iter().map(|tx| tx.outputs.len() as u32).sum::<u32>(),
+            ..Default::default()
+        });
         cb
     }