Improve UX querying rpc for blocks at or before the snapshot from boot (#23403)

* Bump first-available block to first complete block

* Remove obsolete purges in tests (PrimaryIndex toggling no longer in use

* Check first-available block in Rpc check_slot_cleaned_up

ledger/src/blockstore.rs

@@ -1944,9 +1944,13 @@ impl Blockstore {
         self.block_height_cf.put(slot, &block_height)
     }
 
+    /// The first complete block that is available in the Blockstore ledger
     pub fn get_first_available_block(&self) -> Result<Slot> {
         let mut root_iterator = self.rooted_slot_iterator(self.lowest_slot())?;
-        Ok(root_iterator.next().unwrap_or_default())
+        // The block at root-index 0 cannot be complete, because it is missing its parent
+        // blockhash. A parent blockhash must be calculated from the entries of the previous block.
+        // Therefore, the first available complete block is that at root-index 1.
+        Ok(root_iterator.nth(1).unwrap_or_default())
     }
 
     pub fn get_rooted_block(
@@ -7361,8 +7365,6 @@ pub mod tests {
                 )
                 .unwrap();
         }
-        // Purge to freeze index 0
-        blockstore.run_purge(0, 1, PurgeType::PrimaryIndex).unwrap();
         let slot1 = 20;
         for x in 5..9 {
             let signature = Signature::new(&[x; 64]);
@@ -7511,8 +7513,6 @@ pub mod tests {
                 )
                 .unwrap();
         }
-        // Purge to freeze index 0
-        blockstore.run_purge(0, 1, PurgeType::PrimaryIndex).unwrap();
         for x in 7..9 {
             let signature = Signature::new(&[x; 64]);
             blockstore
@@ -7570,6 +7570,9 @@ pub mod tests {
         let ledger_path = get_tmp_ledger_path_auto_delete!();
         let blockstore = Blockstore::open(ledger_path.path()).unwrap();
 
+        let (shreds, _) = make_slot_entries(1, 0, 4);
+        blockstore.insert_shreds(shreds, None, false).unwrap();
+
         fn make_slot_entries_with_transaction_addresses(addresses: &[Pubkey]) -> Vec<Entry> {
             let mut entries: Vec<Entry> = Vec::new();
             for address in addresses {
@@ -7597,11 +7600,7 @@ pub mod tests {
             let shreds = entries_to_test_shreds(&entries, slot, slot - 1, true, 0);
             blockstore.insert_shreds(shreds, None, false).unwrap();
 
-            for (i, entry) in entries.into_iter().enumerate() {
-                if slot == 4 && i == 2 {
-                    // Purge to freeze index 0 and write address-signatures in new primary index
-                    blockstore.run_purge(0, 1, PurgeType::PrimaryIndex).unwrap();
-                }
+            for entry in entries.into_iter() {
                 for transaction in entry.transactions {
                     assert_eq!(transaction.signatures.len(), 1);
                     blockstore

rpc/src/rpc.rs

@@ -941,15 +941,20 @@ impl JsonRpcRequestProcessor {
         result: &std::result::Result<T, BlockstoreError>,
         slot: Slot,
     ) -> Result<()> {
+        let first_available_block = self
+            .blockstore
+            .get_first_available_block()
+            .unwrap_or_default();
+        let err: Error = RpcCustomError::BlockCleanedUp {
+            slot,
+            first_available_block,
+        }
+        .into();
         if let Err(BlockstoreError::SlotCleanedUp) = result {
-            return Err(RpcCustomError::BlockCleanedUp {
-                slot,
-                first_available_block: self
-                    .blockstore
-                    .get_first_available_block()
-                    .unwrap_or_default(),
-            }
-            .into());
+            return Err(err);
+        }
+        if slot < first_available_block {
+            return Err(err);
         }
         Ok(())
     }