Write database version file to disk (#2034)

This will let us make breaking changes to the database format in
the future, without having to write ugly code which has to guess
what version of data it is reading.

zilliqa/src/db.rs

@@ -1,7 +1,7 @@
 use std::{
     collections::BTreeMap,
     fmt::Debug,
-    fs::{self, File},
+    fs::{self, File, OpenOptions},
     io::{BufReader, BufWriter, Read, Write},
     ops::Range,
     path::{Path, PathBuf},
@@ -179,6 +179,11 @@ enum BlockFilter {
 
 const CHECKPOINT_HEADER_BYTES: [u8; 8] = *b"ZILCHKPT";
 
+/// Version string that is written to disk along with the persisted database. This should be bumped whenever we make a
+/// backwards incompatible change to our database format. This should be done rarely, since it forces all node
+/// operators to re-sync.
+const CURRENT_DB_VERSION: &str = "1";
+
 #[derive(Debug)]
 pub struct Db {
     db: Arc<Mutex<Connection>>,
@@ -195,6 +200,22 @@ impl Db {
             Some(path) => {
                 let path = path.as_ref().join(shard_id.to_string());
                 fs::create_dir_all(&path).context(format!("Unable to create {path:?}"))?;
+
+                let mut version_file = OpenOptions::new()
+                    .create(true)
+                    .truncate(false)
+                    .read(true)
+                    .write(true)
+                    .open(path.join("version"))?;
+                let mut version = String::new();
+                version_file.read_to_string(&mut version)?;
+
+                if !version.is_empty() && version != CURRENT_DB_VERSION {
+                    return Err(anyhow!("data is incompatible with this version - please delete the data and re-sync"));
+                }
+
+                version_file.write_all(CURRENT_DB_VERSION.as_bytes())?;
+
                 let db_path = path.join("db.sqlite3");
                 (
                     Connection::open(&db_path)