solana/ledger/src/rooted_slot_iterator.rs

use {
    crate::{blockstore::*, blockstore_db::Result, blockstore_meta::SlotMeta},
    log::*,
    solana_sdk::clock::Slot,
};

pub struct RootedSlotIterator<'a> {
    next_slots: Vec<Slot>,
    prev_root: Slot,
    blockstore: &'a Blockstore,
}

impl<'a> RootedSlotIterator<'a> {
    pub fn new(start_slot: Slot, blockstore: &'a Blockstore) -> Result<Self> {
        if blockstore.is_root(start_slot) {
            Ok(Self {
                next_slots: vec![start_slot],
                prev_root: start_slot,
                blockstore,
            })
        } else {
            Err(BlockstoreError::SlotNotRooted)
        }
    }
}
impl<'a> Iterator for RootedSlotIterator<'a> {
    type Item = (Slot, Option<SlotMeta>);

    fn next(&mut self) -> Option<Self::Item> {
        // Clone b/c passing the closure to the map below requires exclusive access to
        // `self`, which is borrowed here if we don't clone.
        let (rooted_slot, slot_skipped) = self
            .next_slots
            .iter()
            .find(|x| self.blockstore.is_root(**x))
            .map(|x| (Some(*x), false))
            .unwrap_or_else(|| {
                let mut iter = self
                    .blockstore
                    .rooted_slot_iterator(
                        // First iteration the root always exists as guaranteed by the constructor,
                        // so this unwrap_or_else cases won't be hit. Every subsequent iteration
                        // of this iterator must thereafter have a valid `prev_root`
                        self.prev_root,
                    )
                    .expect("Database failure, couldn't fetch rooted slots iterator");
                iter.next();
                (iter.next(), true)
            });

        let slot_meta = rooted_slot
            .map(|r| {
                self.blockstore
                    .meta(r)
                    .expect("Database failure, couldn't fetch SlotMeta")
            })
            .unwrap_or(None);

        if let Some(ref slot_meta) = slot_meta {
            self.next_slots = slot_meta.next_slots.clone();
        }

        if slot_meta.is_none() && slot_skipped {
            warn!("Rooted SlotMeta was deleted in between checking is_root and fetch");
        }

        rooted_slot.map(|r| {
            self.prev_root = r;
            if slot_skipped {
                (r, None)
            } else {
                (r, slot_meta)
            }
        })
    }
}

#[cfg(test)]
mod tests {
    use {
        super::*, crate::blockstore_processor::fill_blockstore_slot_with_ticks,
        solana_sdk::hash::Hash,
    };

    #[test]
    fn test_rooted_slot_iterator() {
        let ledger_path = get_tmp_ledger_path_auto_delete!();
        let blockstore = Blockstore::open(ledger_path.path()).unwrap();
        blockstore.set_roots(std::iter::once(&0)).unwrap();
        let ticks_per_slot = 5;
        /*
            Build a blockstore in the ledger with the following fork structure:

                 slot 0
                   |
                 slot 1  <-- set_root
                 /   \
            slot 2   |
               /     |
            slot 3   |
                     |
                   slot 4

        */

        // Fork 1, ending at slot 3
        let last_entry_hash = Hash::default();
        let fork_point = 1;
        let mut fork_hash = Hash::default();
        for slot in 0..=3 {
            let parent = {
                if slot == 0 {
                    0
                } else {
                    slot - 1
                }
            };
            let last_entry_hash = fill_blockstore_slot_with_ticks(
                &blockstore,
                ticks_per_slot,
                slot,
                parent,
                last_entry_hash,
            );

            if slot == fork_point {
                fork_hash = last_entry_hash;
            }
        }

        // Fork 2, ending at slot 4
        let _ =
            fill_blockstore_slot_with_ticks(&blockstore, ticks_per_slot, 4, fork_point, fork_hash);

        // Set a root
        blockstore.set_roots(vec![1, 2, 3].iter()).unwrap();

        // Trying to get an iterator on a different fork will error
        assert!(RootedSlotIterator::new(4, &blockstore).is_err());

        // Trying to get an iterator on any slot on the root fork should succeed
        let result: Vec<_> = RootedSlotIterator::new(3, &blockstore)
            .unwrap()
            .map(|(slot, _)| slot)
            .collect();
        let expected = vec![3];
        assert_eq!(result, expected);

        let result: Vec<_> = RootedSlotIterator::new(0, &blockstore)
            .unwrap()
            .map(|(slot, _)| slot)
            .collect();
        let expected = vec![0, 1, 2, 3];
        assert_eq!(result, expected);
    }

    #[test]
    fn test_skipping_rooted_slot_iterator() {
        let ledger_path = get_tmp_ledger_path_auto_delete!();
        let blockstore = Blockstore::open(ledger_path.path()).unwrap();
        let ticks_per_slot = 5;
        /*
            Build a blockstore in the ledger with the following fork structure:
                 slot 0
                   |
                 slot 1
                   |
                 slot 2
                   |
                 slot 3 <-- set_root
                   |
                 SKIP (caused by a snapshot)
                   |
                 slot 10 <-- set_root
                   |
                 slot 11 <-- set_root
        */

        // Create pre-skip slots
        for slot in 0..=3 {
            let parent = {
                if slot == 0 {
                    0
                } else {
                    slot - 1
                }
            };
            fill_blockstore_slot_with_ticks(
                &blockstore,
                ticks_per_slot,
                slot,
                parent,
                Hash::default(),
            );
        }

        // Set roots
        blockstore.set_roots(vec![0, 1, 2, 3].iter()).unwrap();

        // Create one post-skip slot at 10, simulating starting from a snapshot
        // at 10
        blockstore.set_roots(std::iter::once(&10)).unwrap();
        // Try to get an iterator from before the skip. The post-skip slot
        // should not return a SlotMeta
        let result: Vec<_> = RootedSlotIterator::new(3, &blockstore)
            .unwrap()
            .map(|(slot, meta)| (slot, meta.is_some()))
            .collect();
        let expected = vec![(3, true), (10, false)];
        assert_eq!(result, expected);

        // Create one more post-skip slot at 11 with parent equal to 10
        fill_blockstore_slot_with_ticks(&blockstore, ticks_per_slot, 11, 10, Hash::default());

        // Set roots
        blockstore.set_roots(std::iter::once(&11)).unwrap();

        let result: Vec<_> = RootedSlotIterator::new(0, &blockstore)
            .unwrap()
            .map(|(slot, meta)| (slot, meta.is_some()))
            .collect();
        let expected = vec![
            (0, true),
            (1, true),
            (2, true),
            (3, true),
            (10, false),
            (11, true),
        ];
        assert_eq!(result, expected);
    }
}