Bindings for emulating a MySQL/MariaDB server.
When developing new databases or caching layers, it can be immensely useful to test your system using existing applications. However, this often requires significant work modifying applications to use your database over the existing ones. This crate solves that problem by acting as a MySQL server, and delegating operations such as querying and query execution to user-defined logic.
To start, implement MysqlShim for your backend, and create a MysqlIntermediary over an
instance of your backend and a connection stream. The appropriate methods will be called on
your backend whenever a client issues a QUERY, PREPARE, or EXECUTE command, and you will
have a chance to respond appropriately. For example, to write a shim that always responds to
all commands with a "no results" reply:
extern crate mysql;
use msql_srv::*;
use mysql::prelude::*;
struct Backend;
impl<W: io::Write> MysqlShim<W> for Backend {
type Error = io::Error;
fn on_prepare(&mut self, _: &str, info: StatementMetaWriter<W>) -> io::Result<()> {
info.reply(42, &[], &[])
}
fn on_execute(
&mut self,
_: u32,
_: ParamParser,
results: QueryResultWriter<W>,
) -> io::Result<()> {
results.completed(OkResponse::default())
}
fn on_close(&mut self, _: u32) {}
fn on_init(&mut self, _: &str, writer: InitWriter<W>) -> io::Result<()> { Ok(()) }
fn on_query(&mut self, _: &str, results: QueryResultWriter<W>) -> io::Result<()> {
let cols = [
Column {
table: "foo".to_string(),
column: "a".to_string(),
coltype: ColumnType::MYSQL_TYPE_LONGLONG,
colflags: ColumnFlags::empty(),
},
Column {
table: "foo".to_string(),
column: "b".to_string(),
coltype: ColumnType::MYSQL_TYPE_STRING,
colflags: ColumnFlags::empty(),
},
];
let mut rw = results.start(&cols)?;
rw.write_col(42)?;
rw.write_col("b's value")?;
rw.finish()
}
}
fn main() {
let listener = net::TcpListener::bind("127.0.0.1:0").unwrap();
let port = listener.local_addr().unwrap().port();
let jh = thread::spawn(move || {
if let Ok((s, _)) = listener.accept() {
MysqlIntermediary::run_on_tcp(Backend, s).unwrap();
}
});
let mut db = mysql::Conn::new(&format!("mysql:https://127.0.0.1:{}", port)).unwrap();
assert_eq!(db.ping(), true);
assert_eq!(db.query_iter("SELECT a, b FROM foo").unwrap().count(), 1);
drop(db);
jh.join().unwrap();
}