Serialize genesis block using bincode (#4687)

* use mmap to read the genesis block, and deserialize

sdk/Cargo.toml

@@ -18,6 +18,7 @@ generic-array = { version = "0.13.0", default-features = false, features = ["ser
 hex = "0.3.2"
 itertools = "0.8.0"
 log = "0.4.2"
+memmap = "0.6.2"
 num-derive = "0.2"
 num-traits = "0.2"
 rand = "0.6.5"

sdk/src/genesis_block.rs

@@ -9,7 +9,9 @@ use crate::pubkey::Pubkey;
 use crate::signature::{Keypair, KeypairUtil};
 use crate::system_program;
 use crate::timing::{DEFAULT_SLOTS_PER_EPOCH, DEFAULT_TICKS_PER_SLOT};
-use std::fs::File;
+use bincode::{deserialize, serialize};
+use memmap::Mmap;
+use std::fs::{File, OpenOptions};
 use std::io::Write;
 use std::path::Path;
 
@@ -75,19 +77,27 @@ impl GenesisBlock {
     }
 
     pub fn load(ledger_path: &str) -> Result<Self, std::io::Error> {
-        let file = File::open(&Path::new(ledger_path).join("genesis.json"))?;
-        let genesis_block = serde_json::from_reader(file)?;
+        let file = OpenOptions::new()
+            .read(true)
+            .open(&Path::new(ledger_path).join("genesis.bin"))
+            .expect("Unable to open genesis file");
+
+        //UNSAFE: Required to create a Mmap
+        let mem = unsafe { Mmap::map(&file).expect("failed to map the genesis file") };
+        let genesis_block = deserialize(&mem)
+            .map_err(|err| std::io::Error::new(std::io::ErrorKind::Other, format!("{:?}", err)))?;
         Ok(genesis_block)
     }
 
     pub fn write(&self, ledger_path: &str) -> Result<(), std::io::Error> {
-        let serialized = serde_json::to_string(self)?;
+        let serialized = serialize(&self)
+            .map_err(|err| std::io::Error::new(std::io::ErrorKind::Other, format!("{:?}", err)))?;
 
         let dir = Path::new(ledger_path);
         std::fs::create_dir_all(&dir)?;
 
-        let mut file = File::create(&dir.join("genesis.json"))?;
-        file.write_all(&serialized.into_bytes())
+        let mut file = File::create(&dir.join("genesis.bin"))?;
+        file.write_all(&serialized)
     }
 }