Crate msql_srv

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::*;
use mysql::Opts;

struct Backend;
impl<W: io::Read + 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(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(Opts::from_url(&format!("mysql://127.0.0.1:{}", port)).unwrap()).unwrap();
    assert_eq!(db.ping(), true);
    assert_eq!(db.query_iter("SELECT a, b FROM foo").unwrap().count(), 1);
    drop(db);
    jh.join().unwrap();
}

Structs

AuthenticationContext

Information about an authenticated user

Column

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

ColumnFlags

MySql column flags

InitWriter

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

MysqlIntermediary

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

ParamParser

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

ParamValue

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

Params

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

QueryResultWriter

Convenience type for providing query results to clients.

RowWriter

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

StatementMetaWriter

Convenience type for responding to a client PREPARE command.

StatusFlags

MySql server status flags

Value

MySQL value as provided when executing prepared statements.

Enums

ColumnType

Type of MySql column field

ErrorKind

MySQL error type

ValueInner

A representation of a concrete, typed MySQL value.

Traits

MysqlShim

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

ToMysqlValue

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