From 21bf913b4835e93ab154640d4b1ec42b7e66ca4d Mon Sep 17 00:00:00 2001
From: Henry de Valence <hdevalence@hdevalence.ca>
Date: Wed, 24 Jun 2020 12:22:08 -0700
Subject: [PATCH] Revert "correctly trim and download tips (#531)"

This reverts commit e102bd5e3470e2c96e7e9781b90009bd69dee439.
---
 zebrad/src/commands/start.rs      |  2 +-
 zebrad/src/commands/start/sync.rs | 38 +++++++++++--------------------
 2 files changed, 14 insertions(+), 26 deletions(-)

diff --git a/zebrad/src/commands/start.rs b/zebrad/src/commands/start.rs
index ad8f43d31..401558be5 100644
--- a/zebrad/src/commands/start.rs
+++ b/zebrad/src/commands/start.rs
@@ -30,7 +30,7 @@ use zebra_chain::block::BlockHeaderHash;
 mod sync;
 
 // genesis
-const GENESIS: BlockHeaderHash = BlockHeaderHash([
+static GENESIS: BlockHeaderHash = BlockHeaderHash([
     8, 206, 61, 151, 49, 176, 0, 192, 131, 56, 69, 92, 138, 74, 107, 208, 93, 161, 110, 38, 177,
     29, 170, 27, 145, 113, 132, 236, 232, 15, 4, 0,
 ]);
diff --git a/zebrad/src/commands/start/sync.rs b/zebrad/src/commands/start/sync.rs
index a28bf5c35..1ead8f390 100644
--- a/zebrad/src/commands/start/sync.rs
+++ b/zebrad/src/commands/start/sync.rs
@@ -161,13 +161,11 @@ where
                     })
                     .await;
                 match res.map_err::<Report, _>(|e| eyre!(e)) {
-                    Ok(zn::Response::BlockHeaderHashes(mut hashes)) => {
-                        let new_tip = if let Some(tip) = hashes.pop() {
-                            tip
-                        } else {
+                    Ok(zn::Response::BlockHeaderHashes(hashes)) => {
+                        if hashes.is_empty() {
                             tracing::debug!("skipping empty response");
                             continue;
-                        };
+                        }
 
                         // ExtendTips Step 3
                         //
@@ -176,20 +174,22 @@ where
                         // 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() {
-                            Some(&super::GENESIS) => {
-                                tracing::debug!("skipping response that does not extend the tip");
-                                continue;
-                            }
-                            Some(_) | None => {}
+                        if hashes[0] == super::GENESIS {
+                            tracing::debug!("skipping response that does not extend the tip");
+                            continue;
                         }
 
                         // ExtendTips Step 4
                         //
                         // Combine the last elements of the remaining responses into
                         // a set, and add this set to the set of prospective tips.
+                        let new_tip = *hashes.last().expect("already checked is_empty");
                         let _ = self.prospective_tips.insert(new_tip);
 
+                        // ExtendTips Step 5
+                        //
+                        // Combine all elements of the remaining responses into a
+                        // set, and queue download and verification of those blocks
                         download_set.extend(hashes);
                     }
                     Ok(r) => tracing::error!("unexpected response {:?}", r),
@@ -198,20 +198,8 @@ where
             }
         }
 
-        self.prospective_tips
-            .retain(|tip| !download_set.contains(tip));
-
-        // ExtendTips Step 5
-        //
-        // Combine all elements of the remaining responses into a
-        // set, and queue download and verification of those blocks
-        self.request_blocks(
-            download_set
-                .into_iter()
-                .chain(self.prospective_tips.iter().cloned())
-                .collect(),
-        )
-        .await?;
+        self.request_blocks(download_set.into_iter().collect())
+            .await?;
 
         Ok(())
     }