Crate msql_srv[][src]

Expand description

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(0, 0)
    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("b's value")?;

fn main() {
    let listener = net::TcpListener::bind("").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://{}", port)).unwrap();
    assert_eq!(, true);
    assert_eq!(db.query_iter("SELECT a, b FROM foo").unwrap().count(), 1);


Meta-information abot a single column, used either to describe a prepared statement parameter or an output column.

MySql column flags

Convenience type for responding to a client USE <db> command.

A server that speaks the MySQL/MariaDB protocol, and can delegate client commands to a backend that implements MysqlShim.

A ParamParser decodes query parameters included in a client’s EXECUTE command given type information for the expected parameters.

A single parameter value provided by a client when issuing an EXECUTE command.

An iterator over parameters provided by a client in an EXECUTE command.

Convenience type for providing query results to clients.

Convenience type for sending rows of a resultset to a client.

Convenience type for responding to a client PREPARE command.

MySql server status flags

MySQL value as provided when executing prepared statements.


Type of MySql column field

MySQL error type

A representation of a concrete, typed MySQL value.


Implementors of this trait can be used to drive a MySQL-compatible database backend.

Implementors of this trait can be sent as a single resultset value to a MySQL/MariaDB client.