Download genesis (#731)

* feature: Add more CheckpointVerifier tracing

* fix: Download the genesis block

zebra-consensus/src/checkpoint.rs

@@ -376,7 +376,17 @@ impl CheckpointVerifier {
         qblocks.reserve_exact(1);
         qblocks.push(new_qblock);
 
-        tracing::debug!("queued block");
+        let is_checkpoint = self.checkpoint_list.contains(height);
+        tracing::debug!(?height, ?hash, ?is_checkpoint, "Queued block");
+
+        // TODO(teor):
+        //   - Remove this log once the CheckpointVerifier is working?
+        //   - Modify the default filter or add another log, so users see
+        //     regular download progress info (vs verification info)
+        if is_checkpoint {
+            tracing::info!(?height, ?hash, ?is_checkpoint, "Queued checkpoint block");
+        }
+
         rx
     }
 
@@ -421,12 +431,16 @@ impl CheckpointVerifier {
                     // The first valid block at the current height
                     valid_qblock = Some(qblock);
                 } else {
+                    tracing::info!(?height, ?qblock.hash, ?expected_hash,
+                                   "Duplicate block at height in CheckpointVerifier");
                     // Reject duplicate blocks at the same height
                     let _ = qblock.tx.send(Err(
                         "duplicate valid blocks at this height, only one was chosen".into(),
                     ));
                 }
             } else {
+                tracing::info!(?height, ?qblock.hash, ?expected_hash,
+                               "Bad block hash at height in CheckpointVerifier");
                 // A bad block, that isn't part of the chain.
                 let _ = qblock.tx.send(Err(
                     "the block hash does not match the chained checkpoint hash".into(),
@@ -509,8 +523,11 @@ impl CheckpointVerifier {
             } else {
                 // The last block height we processed did not have any blocks
                 // with a matching hash, so chain verification has failed.
-                //
-                // TODO(teor||jlusby): log an error here?
+                tracing::warn!(
+                    ?current_height,
+                    ?current_range,
+                    "No valid blocks at height in CheckpointVerifier"
+                );
 
                 // We kept all the matching blocks down to this height, in
                 // anticipation of the chain verifying. But the chain is
@@ -554,6 +571,8 @@ impl CheckpointVerifier {
             "the previous checkpoint should match: bad checkpoint list, zebra bug, or bad chain"
         );
 
+        tracing::info!(?current_range, "Verified checkpoint range");
+
         // All the blocks we've kept are valid, so let's verify them
         // in height order.
         for qblock in rev_valid_blocks.drain(..).rev() {

zebrad/src/commands/start/sync.rs

@@ -73,6 +73,10 @@ where
 
     #[instrument(skip(self))]
     pub async fn sync(&mut self) -> Result<(), Report> {
+        // We can't download the genesis block using our normal algorithm,
+        // due to protocol limitations
+        self.request_genesis().await?;
+
         loop {
             self.obtain_tips().await?;
             metrics::gauge!(
@@ -215,8 +219,7 @@ where
                         "found index of first unknown hash in response"
                     );
                     if first_unknown == hashes.len() {
-                        // XXX until we fix the TODO above to construct the locator correctly,
-                        // we might hit this case, but it will be unexpected afterwards.
+                        // We should only stop getting hashes once we've finished the initial sync
                         tracing::debug!("no new hashes, even though we gave our tip?");
                         continue;
                     }
@@ -298,7 +301,6 @@ where
                         // response is the genesis block; if so, discard the response.
                         // It indicates that the remote peer does not have any blocks
                         // following the prospective tip.
-                        // TODO(jlusby): reject both main and test net genesis blocks
                         match (hashes.first(), hashes.len()) {
                             (_, 0) => {
                                 tracing::debug!("skipping empty response");
@@ -355,6 +357,35 @@ where
         Ok(())
     }
 
+    /// Queue a download for the genesis block, if it isn't currently known to
+    /// our node.
+    async fn request_genesis(&mut self) -> Result<(), Report> {
+        // Due to Bitcoin protocol limitations, we can't request the genesis
+        // block using our standard tip-following algorithm:
+        //  - getblocks requires at least one hash
+        //  - responses start with the block *after* the requested block, and
+        //  - the genesis hash is used as a placeholder for "no matches".
+        //
+        // So we just queue the genesis block here.
+
+        let state_has_genesis = self
+            .state
+            .ready_and()
+            .await
+            .map_err(|e| eyre!(e))?
+            .call(zebra_state::Request::GetBlock {
+                hash: self.genesis_hash,
+            })
+            .await
+            .is_ok();
+
+        if !state_has_genesis {
+            self.request_blocks(vec![self.genesis_hash]).await?;
+        }
+
+        Ok(())
+    }
+
     /// Queue downloads for each block that isn't currently known to our node
     async fn request_blocks(&mut self, hashes: Vec<BlockHeaderHash>) -> Result<(), Report> {
         tracing::debug!(hashes.len = hashes.len(), "requesting blocks");