Adds cli interface to allow reseting chain to a particular block (#9782)

* added BlockChainReset trait, client impl, and cli interface

* show block hashes to be deleted and new best block, update best block in db, better cli interface

* delete BlockNumber from COL_EXTRA

* add TODO comment

* add BlockReciepts to imports

* refactor block_headers_from_best_block, better cli documentation

* exit gracefully if reset arg isn't supplied

* fix cli usage macro

* removed stray int literals

* use Vec::with_capacity

Co-Authored-By: seunlanlege <seunlanlege@gmail.com>

* cast n to usize

* correct imports

* make db reset arg required

ethcore/blockchain/src/blockchain.rs

@@ -668,6 +668,21 @@ impl BlockChain {
 		self.db.key_value().read_with_cache(db::COL_EXTRA, &self.block_details, parent).map_or(false, |d| d.children.contains(hash))
 	}
 
+	/// fetches the list of blocks from best block to n, and n's parent hash
+	/// where n > 0
+	pub fn block_headers_from_best_block(&self, n: u32) -> Option<(Vec<encoded::Header>, H256)> {
+		let mut blocks = Vec::with_capacity(n as usize);
+		let mut hash = self.best_block_hash();
+
+		for _ in 0..n {
+			let current_hash = self.block_header_data(&hash)?;
+			hash = current_hash.parent_hash();
+			blocks.push(current_hash);
+		}
+
+		Some((blocks, hash))
+	}
+
 	/// Returns a tree route between `from` and `to`, which is a tuple of:
 	///
 	/// - a vector of hashes of all blocks, ordered from `from` to `to`.

ethcore/blockchain/src/lib.rs

@@ -33,5 +33,5 @@ pub use self::cache::CacheSize;
 pub use self::config::Config;
 pub use self::import_route::ImportRoute;
 pub use self::update::ExtrasInsert;
-pub use ethcore_db::keys::{BlockReceipts, BlockDetails, TransactionAddress};
+pub use ethcore_db::keys::{BlockReceipts, BlockDetails, TransactionAddress, BlockNumberKey};
 pub use common_types::tree_route::TreeRoute;