lib.rs

//! A pure-Rust frontend for the popular PostgreSQL database.
//!
//! ```rust,no_run
//! extern crate postgres;
//!
//! use postgres::{Connection, SslMode};
//!
//! struct Person {
//!     id: i32,
//!     name: String,
//!     data: Option<Vec<u8>>
//! }
//!
//! fn main() {
//!     let conn = Connection::connect("postgresql://postgres@localhost", SslMode::None)
//!             .unwrap();
//!
//!     conn.execute("CREATE TABLE person (
//!                     id              SERIAL PRIMARY KEY,
//!                     name            VARCHAR NOT NULL,
//!                     data            BYTEA
//!                   )", &[]).unwrap();
//!     let me = Person {
//!         id: 0,
//!         name: "Steven".to_owned(),
//!         data: None
//!     };
//!     conn.execute("INSERT INTO person (name, data) VALUES ($1, $2)",
//!                  &[&me.name, &me.data]).unwrap();
//!
//!     for row in &conn.query("SELECT id, name, data FROM person", &[]).unwrap() {
//!         let person = Person {
//!             id: row.get(0),
//!             name: row.get(1),
//!             data: row.get(2)
//!         };
//!         println!("Found person {}", person.name);
//!     }
//! }
//! ```
#![doc(html_root_url="https://sfackler.github.io/rust-postgres/doc/v0.11.7")]
#![warn(missing_docs)]
#![allow(unknown_lints, needless_lifetimes)] // for clippy
#![cfg_attr(all(unix, feature = "nightly"), feature(unix_socket))]
#![cfg_attr(feature = "clippy", feature(plugin))]
#![cfg_attr(feature = "clippy", plugin(clippy))]

extern crate bufstream;
extern crate byteorder;
extern crate hex;
#[macro_use]
extern crate log;
extern crate phf;
#[cfg(feature = "unix_socket")]
extern crate unix_socket;
extern crate net2;

use bufstream::BufStream;
use md5::Md5;
use std::cell::{Cell, RefCell};
use std::collections::{VecDeque, HashMap};
use std::error::Error as StdError;
use std::fmt;
use std::io as std_io;
use std::io::prelude::*;
use std::mem;
use std::result;
use std::sync::Arc;
use std::time::Duration;
#[cfg(any(feature = "unix_socket", all(unix, feature = "nightly")))]
use std::path::PathBuf;

// FIXME remove in 0.12
pub use transaction::{Transaction, IsolationLevel};

use error::{Error, ConnectError, SqlState, DbError};
use io::{StreamWrapper, NegotiateSsl};
use message::{Frontend, Backend, RowDescriptionEntry};
use message::{WriteMessage, ReadMessage};
use notification::{Notifications, Notification};
use rows::{Rows, LazyRows};
use stmt::{Statement, Column};
use types::{IsNull, Kind, Type, SessionInfo, Oid, Other, WrongType, ToSql, FromSql, Field};
use url::Url;

#[macro_use]
mod macros;

mod md5;
mod message;
mod priv_io;
mod url;
pub mod error;
pub mod io;
pub mod notification;
pub mod rows;
pub mod stmt;
pub mod transaction;
pub mod types;

const TYPEINFO_QUERY: &'static str = "__typeinfo";
const TYPEINFO_ENUM_QUERY: &'static str = "__typeinfo_enum";
const TYPEINFO_COMPOSITE_QUERY: &'static str = "__typeinfo_composite";

/// A type alias of the result returned by many methods.
pub type Result<T> = result::Result<T, Error>;

/// Specifies the target server to connect to.
#[derive(Clone, Debug)]
pub enum ConnectTarget {
    /// Connect via TCP to the specified host.
    Tcp(String),
    /// Connect via a Unix domain socket in the specified directory.
    ///
    /// Requires the `unix_socket` or `nightly` feature.
    #[cfg(any(feature = "unix_socket", all(unix, feature = "nightly")))]
    Unix(PathBuf),
}

/// Authentication information.
#[derive(Clone, Debug)]
pub struct UserInfo {
    /// The username.
    pub user: String,
    /// An optional password.
    pub password: Option<String>,
}

/// Information necessary to open a new connection to a Postgres server.
#[derive(Clone, Debug)]
pub struct ConnectParams {
    /// The target server.
    pub target: ConnectTarget,
    /// The target port.
    ///
    /// Defaults to 5432 if not specified.
    pub port: Option<u16>,
    /// The user to login as.
    ///
    /// `Connection::connect` requires a user but `cancel_query` does not.
    pub user: Option<UserInfo>,
    /// The database to connect to.
    ///
    /// Defaults the value of `user`.
    pub database: Option<String>,
    /// Runtime parameters to be passed to the Postgres backend.
    pub options: Vec<(String, String)>,
}

/// A trait implemented by types that can be converted into a `ConnectParams`.
pub trait IntoConnectParams {
    /// Converts the value of `self` into a `ConnectParams`.
    fn into_connect_params(self) -> result::Result<ConnectParams, Box<StdError + Sync + Send>>;
}

impl IntoConnectParams for ConnectParams {
    fn into_connect_params(self) -> result::Result<ConnectParams, Box<StdError + Sync + Send>> {
        Ok(self)
    }
}

impl<'a> IntoConnectParams for &'a str {
    fn into_connect_params(self) -> result::Result<ConnectParams, Box<StdError + Sync + Send>> {
        match Url::parse(self) {
            Ok(url) => url.into_connect_params(),
            Err(err) => Err(err.into()),
        }
    }
}

impl IntoConnectParams for Url {
    fn into_connect_params(self) -> result::Result<ConnectParams, Box<StdError + Sync + Send>> {
        #[cfg(any(feature = "unix_socket", all(unix, feature = "nightly")))]
        fn make_unix(maybe_path: String)
                     -> result::Result<ConnectTarget, Box<StdError + Sync + Send>> {
            Ok(ConnectTarget::Unix(PathBuf::from(maybe_path)))
        }
        #[cfg(not(any(feature = "unix_socket", all(unix, feature = "nightly"))))]
        fn make_unix(_: String) -> result::Result<ConnectTarget, Box<StdError + Sync + Send>> {
            Err("unix socket support requires the `unix_socket` or `nightly` features".into())
        }

        let Url { host, port, user, path: url::Path { mut path, query: options, .. }, .. } = self;

        let maybe_path = try!(url::decode_component(&host));
        let target = if maybe_path.starts_with('/') {
            try!(make_unix(maybe_path))
        } else {
            ConnectTarget::Tcp(host)
        };

        let user = user.map(|url::UserInfo { user, pass }| {
            UserInfo {
                user: user,
                password: pass,
            }
        });

        let database = if path.is_empty() {
            None
        } else {
            // path contains the leading /
            path.remove(0);
            Some(path)
        };

        Ok(ConnectParams {
            target: target,
            port: port,
            user: user,
            database: database,
            options: options,
        })
    }
}

/// Trait for types that can handle Postgres notice messages
///
/// It is implemented for all `Send + FnMut(DbError)` closures.
pub trait HandleNotice: Send {
    /// Handle a Postgres notice message
    fn handle_notice(&mut self, notice: DbError);
}

impl<F: Send + FnMut(DbError)> HandleNotice for F {
    fn handle_notice(&mut self, notice: DbError) {
        self(notice)
    }
}

/// A notice handler which logs at the `info` level.
///
/// This is the default handler used by a `Connection`.
#[derive(Copy, Clone, Debug)]
pub struct LoggingNoticeHandler;

impl HandleNotice for LoggingNoticeHandler {
    fn handle_notice(&mut self, notice: DbError) {
        info!("{}: {}", notice.severity, notice.message);
    }
}

/// Contains information necessary to cancel queries for a session.
#[derive(Copy, Clone, Debug)]
pub struct CancelData {
    /// The process ID of the session.
    pub process_id: u32,
    /// The secret key for the session.
    pub secret_key: u32,
}

/// Attempts to cancel an in-progress query.
///
/// The backend provides no information about whether a cancellation attempt
/// was successful or not. An error will only be returned if the driver was
/// unable to connect to the database.
///
/// A `CancelData` object can be created via `Connection::cancel_data`. The
/// object can cancel any query made on that connection.
///
/// Only the host and port of the connection info are used. See
/// `Connection::connect` for details of the `params` argument.
///
/// # Example
///
/// ```rust,no_run
/// # use postgres::{Connection, SslMode};
/// # use std::thread;
/// # let url = "";
/// let conn = Connection::connect(url, SslMode::None).unwrap();
/// let cancel_data = conn.cancel_data();
/// thread::spawn(move || {
///     conn.execute("SOME EXPENSIVE QUERY", &[]).unwrap();
/// });
/// postgres::cancel_query(url, SslMode::None, &cancel_data).unwrap();
/// ```
pub fn cancel_query<T>(params: T,
                       ssl: SslMode,
                       data: &CancelData)
                       -> result::Result<(), ConnectError>
    where T: IntoConnectParams
{
    let params = try!(params.into_connect_params().map_err(ConnectError::ConnectParams));
    let mut socket = try!(priv_io::initialize_stream(&params, ssl));

    try!(socket.write_message(&Frontend::CancelRequest {
        code: message::CANCEL_CODE,
        process_id: data.process_id,
        secret_key: data.secret_key,
    }));
    try!(socket.flush());

    Ok(())
}

fn bad_response() -> std_io::Error {
    std_io::Error::new(std_io::ErrorKind::InvalidInput,
                       "the server returned an unexpected response")
}

fn desynchronized() -> std_io::Error {
    std_io::Error::new(std_io::ErrorKind::Other,
                       "communication with the server has desynchronized due to an earlier IO \
                        error")
}

/// Specifies the SSL support requested for a new connection.
#[derive(Debug)]
pub enum SslMode<'a> {
    /// The connection will not use SSL.
    None,
    /// The connection will use SSL if the backend supports it.
    Prefer(&'a NegotiateSsl),
    /// The connection must use SSL.
    Require(&'a NegotiateSsl),
}

struct StatementInfo {
    name: String,
    param_types: Vec<Type>,
    columns: Vec<Column>,
}

struct InnerConnection {
    stream: BufStream<Box<StreamWrapper>>,
    notice_handler: Box<HandleNotice>,
    notifications: VecDeque<Notification>,
    cancel_data: CancelData,
    unknown_types: HashMap<Oid, Other>,
    cached_statements: HashMap<String, Arc<StatementInfo>>,
    parameters: HashMap<String, String>,
    next_stmt_id: u32,
    trans_depth: u32,
    desynchronized: bool,
    finished: bool,
}

impl Drop for InnerConnection {
    fn drop(&mut self) {
        if !self.finished {
            let _ = self.finish_inner();
        }
    }
}

impl InnerConnection {
    fn connect<T>(params: T, ssl: SslMode) -> result::Result<InnerConnection, ConnectError>
        where T: IntoConnectParams
    {
        let params = try!(params.into_connect_params().map_err(ConnectError::ConnectParams));
        let stream = try!(priv_io::initialize_stream(&params, ssl));

        let ConnectParams { user, database, mut options, .. } = params;

        let user = match user {
            Some(user) => user,
            None => {
                return Err(ConnectError::ConnectParams("User missing from connection parameters".into()));
            }
        };

        let mut conn = InnerConnection {
            stream: BufStream::new(stream),
            next_stmt_id: 0,
            notice_handler: Box::new(LoggingNoticeHandler),
            notifications: VecDeque::new(),
            cancel_data: CancelData {
                process_id: 0,
                secret_key: 0,
            },
            unknown_types: HashMap::new(),
            cached_statements: HashMap::new(),
            parameters: HashMap::new(),
            desynchronized: false,
            finished: false,
            trans_depth: 0,
        };

        options.push(("client_encoding".to_owned(), "UTF8".to_owned()));
        // Postgres uses the value of TimeZone as the time zone for TIMESTAMP
        // WITH TIME ZONE values. Timespec converts to GMT internally.
        options.push(("timezone".to_owned(), "GMT".to_owned()));
        // We have to clone here since we need the user again for auth
        options.push(("user".to_owned(), user.user.clone()));
        if let Some(database) = database {
            options.push(("database".to_owned(), database));
        }

        try!(conn.write_messages(&[Frontend::StartupMessage {
                                       version: message::PROTOCOL_VERSION,
                                       parameters: &options,
                                   }]));

        try!(conn.handle_auth(user));

        loop {
            match try!(conn.read_message()) {
                Backend::BackendKeyData { process_id, secret_key } => {
                    conn.cancel_data.process_id = process_id;
                    conn.cancel_data.secret_key = secret_key;
                }
                Backend::ReadyForQuery { .. } => break,
                Backend::ErrorResponse { fields } => return DbError::new_connect(fields),
                _ => return Err(ConnectError::Io(bad_response())),
            }
        }

        try!(conn.setup_typeinfo_query());

        Ok(conn)
    }

    #[cfg_attr(rustfmt, rustfmt_skip)]
    fn setup_typeinfo_query(&mut self) -> result::Result<(), ConnectError> {
        match self.raw_prepare(TYPEINFO_ENUM_QUERY,
                               "SELECT enumlabel \
                                FROM pg_catalog.pg_enum \
                                WHERE enumtypid = $1 \
                                ORDER BY enumsortorder") {
            Ok(..) => {}
            Err(Error::Io(e)) => return Err(ConnectError::Io(e)),
            // Old versions of Postgres and things like Redshift don't support enums
            Err(Error::Db(ref e)) if e.code == SqlState::UndefinedTable => {}
            // Some Postgres-like databases are missing a pg_catalog (e.g. Cockroach)
            Err(Error::Db(ref e)) if e.code == SqlState::InvalidCatalogName => return Ok(()),
            Err(Error::Db(e)) => return Err(ConnectError::Db(e)),
            Err(Error::Conversion(_)) => unreachable!(),
        }

        match self.raw_prepare(TYPEINFO_COMPOSITE_QUERY,
                               "SELECT attname, atttypid \
                                FROM pg_catalog.pg_attribute \
                                WHERE attrelid = $1 \
                                    AND NOT attisdropped \
                                    AND attnum > 0 \
                                ORDER BY attnum") {
            Ok(..) => {}
            Err(Error::Io(e)) => return Err(ConnectError::Io(e)),
            // Old versions of Postgres and things like Redshift don't support composites
            Err(Error::Db(ref e)) if e.code == SqlState::UndefinedTable => {}
            Err(Error::Db(e)) => return Err(ConnectError::Db(e)),
            Err(Error::Conversion(_)) => unreachable!(),
        }

        match self.raw_prepare(TYPEINFO_QUERY,
                               "SELECT t.typname, t.typtype, t.typelem, r.rngsubtype, \
                                       t.typbasetype, n.nspname, t.typrelid \
                                FROM pg_catalog.pg_type t \
                                LEFT OUTER JOIN pg_catalog.pg_range r ON \
                                    r.rngtypid = t.oid \
                                INNER JOIN pg_catalog.pg_namespace n ON \
                                    t.typnamespace = n.oid \
                                WHERE t.oid = $1") {
            Ok(..) => return Ok(()),
            Err(Error::Io(e)) => return Err(ConnectError::Io(e)),
            // Range types weren't added until Postgres 9.2, so pg_range may not exist
            Err(Error::Db(ref e)) if e.code == SqlState::UndefinedTable => {}
            Err(Error::Db(e)) => return Err(ConnectError::Db(e)),
            Err(Error::Conversion(_)) => unreachable!(),
        }

        match self.raw_prepare(TYPEINFO_QUERY,
                               "SELECT t.typname, t.typtype, t.typelem, NULL::OID, t.typbasetype, \
                                       n.nspname, t.typrelid \
                                FROM pg_catalog.pg_type t \
                                INNER JOIN pg_catalog.pg_namespace n \
                                    ON t.typnamespace = n.oid \
                                WHERE t.oid = $1") {
            Ok(..) => Ok(()),
            Err(Error::Io(e)) => Err(ConnectError::Io(e)),
            Err(Error::Db(e)) => Err(ConnectError::Db(e)),
            Err(Error::Conversion(_)) => unreachable!(),
        }
    }

    fn write_messages(&mut self, messages: &[Frontend]) -> std_io::Result<()> {
        debug_assert!(!self.desynchronized);
        for message in messages {
            try_desync!(self, self.stream.write_message(message));
        }
        Ok(try_desync!(self, self.stream.flush()))
    }

    fn read_message_with_notification(&mut self) -> std_io::Result<Backend> {
        debug_assert!(!self.desynchronized);
        loop {
            match try_desync!(self, self.stream.read_message()) {
                Backend::NoticeResponse { fields } => {
                    if let Ok(err) = DbError::new_raw(fields) {
                        self.notice_handler.handle_notice(err);
                    }
                }
                Backend::ParameterStatus { parameter, value } => {
                    self.parameters.insert(parameter, value);
                }
                val => return Ok(val),
            }
        }
    }

    fn read_message_with_notification_timeout(&mut self,
                                              timeout: Duration)
                                              -> std::io::Result<Option<Backend>> {
        debug_assert!(!self.desynchronized);
        loop {
            match try_desync!(self, self.stream.read_message_timeout(timeout)) {
                Some(Backend::NoticeResponse { fields }) => {
                    if let Ok(err) = DbError::new_raw(fields) {
                        self.notice_handler.handle_notice(err);
                    }
                }
                Some(Backend::ParameterStatus { parameter, value }) => {
                    self.parameters.insert(parameter, value);
                }
                val => return Ok(val),
            }
        }
    }

    fn read_message_with_notification_nonblocking(&mut self)
                                                  -> std::io::Result<Option<Backend>> {
        debug_assert!(!self.desynchronized);
        loop {
            match try_desync!(self, self.stream.read_message_nonblocking()) {
                Some(Backend::NoticeResponse { fields }) => {
                    if let Ok(err) = DbError::new_raw(fields) {
                        self.notice_handler.handle_notice(err);
                    }
                }
                Some(Backend::ParameterStatus { parameter, value }) => {
                    self.parameters.insert(parameter, value);
                }
                val => return Ok(val),
            }
        }
    }

    fn read_message(&mut self) -> std_io::Result<Backend> {
        loop {
            match try!(self.read_message_with_notification()) {
                Backend::NotificationResponse { pid, channel, payload } => {
                    self.notifications.push_back(Notification {
                        pid: pid,
                        channel: channel,
                        payload: payload,
                    })
                }
                val => return Ok(val),
            }
        }
    }

    fn handle_auth(&mut self, user: UserInfo) -> result::Result<(), ConnectError> {
        match try!(self.read_message()) {
            Backend::AuthenticationOk => return Ok(()),
            Backend::AuthenticationCleartextPassword => {
                let pass = try!(user.password.ok_or_else(|| {
                    ConnectError::ConnectParams("a password was requested but not provided".into())
                }));
                try!(self.write_messages(&[Frontend::PasswordMessage { password: &pass }]));
            }
            Backend::AuthenticationMD5Password { salt } => {
                let pass = try!(user.password.ok_or_else(|| {
                    ConnectError::ConnectParams("a password was requested but not provided".into())
                }));
                let mut hasher = Md5::new();
                hasher.input(pass.as_bytes());
                hasher.input(user.user.as_bytes());
                let output = hasher.result_str();
                hasher.reset();
                hasher.input(output.as_bytes());
                hasher.input(&salt);
                let output = format!("md5{}", hasher.result_str());
                try!(self.write_messages(&[Frontend::PasswordMessage { password: &output }]));
            }
            Backend::AuthenticationKerberosV5 |
            Backend::AuthenticationSCMCredential |
            Backend::AuthenticationGSS |
            Backend::AuthenticationSSPI => {
                return Err(ConnectError::Io(std_io::Error::new(std_io::ErrorKind::Other,
                                                               "unsupported authentication")))
            }
            Backend::ErrorResponse { fields } => return DbError::new_connect(fields),
            _ => return Err(ConnectError::Io(bad_response())),
        }

        match try!(self.read_message()) {
            Backend::AuthenticationOk => Ok(()),
            Backend::ErrorResponse { fields } => DbError::new_connect(fields),
            _ => Err(ConnectError::Io(bad_response())),
        }
    }

    fn set_notice_handler(&mut self, handler: Box<HandleNotice>) -> Box<HandleNotice> {
        mem::replace(&mut self.notice_handler, handler)
    }

    fn raw_prepare(&mut self, stmt_name: &str, query: &str) -> Result<(Vec<Type>, Vec<Column>)> {
        debug!("preparing query with name `{}`: {}", stmt_name, query);

        try!(self.write_messages(&[Frontend::Parse {
                                       name: stmt_name,
                                       query: query,
                                       param_types: &[],
                                   },
                                   Frontend::Describe {
                                       variant: b'S',
                                       name: stmt_name,
                                   },
                                   Frontend::Sync]));

        match try!(self.read_message()) {
            Backend::ParseComplete => {}
            Backend::ErrorResponse { fields } => {
                try!(self.wait_for_ready());
                return DbError::new(fields);
            }
            _ => bad_response!(self),
        }

        let raw_param_types = match try!(self.read_message()) {
            Backend::ParameterDescription { types } => types,
            _ => bad_response!(self),
        };

        let raw_columns = match try!(self.read_message()) {
            Backend::RowDescription { descriptions } => descriptions,
            Backend::NoData => vec![],
            _ => bad_response!(self),
        };

        try!(self.wait_for_ready());

        let mut param_types = vec![];
        for oid in raw_param_types {
            param_types.push(try!(self.get_type(oid)));
        }

        let mut columns = vec![];
        for RowDescriptionEntry { name, type_oid, .. } in raw_columns {
            columns.push(Column::new(name, try!(self.get_type(type_oid))));
        }

        Ok((param_types, columns))
    }

    fn read_rows(&mut self, buf: &mut VecDeque<Vec<Option<Vec<u8>>>>) -> Result<bool> {
        let more_rows;
        loop {
            match try!(self.read_message()) {
                Backend::EmptyQueryResponse | Backend::CommandComplete { .. } => {
                    more_rows = false;
                    break;
                }
                Backend::PortalSuspended => {
                    more_rows = true;
                    break;
                }
                Backend::DataRow { row } => buf.push_back(row),
                Backend::ErrorResponse { fields } => {
                    try!(self.wait_for_ready());
                    return DbError::new(fields);
                }
                Backend::CopyInResponse { .. } => {
                    try!(self.write_messages(&[Frontend::CopyFail {
                                                   message: "COPY queries cannot be directly \
                                                             executed",
                                               },
                                               Frontend::Sync]));
                }
                Backend::CopyOutResponse { .. } => {
                    loop {
                        if let Backend::ReadyForQuery { .. } = try!(self.read_message()) {
                            break;
                        }
                    }
                    return Err(Error::Io(std_io::Error::new(std_io::ErrorKind::InvalidInput,
                                                            "COPY queries cannot be directly \
                                                             executed")));
                }
                _ => {
                    self.desynchronized = true;
                    return Err(Error::Io(bad_response()));
                }
            }
        }
        try!(self.wait_for_ready());
        Ok(more_rows)
    }

    fn raw_execute(&mut self,
                   stmt_name: &str,
                   portal_name: &str,
                   row_limit: i32,
                   param_types: &[Type],
                   params: &[&ToSql])
                   -> Result<()> {
        assert!(param_types.len() == params.len(),
                "expected {} parameters but got {}",
                param_types.len(),
                params.len());
        debug!("executing statement {} with parameters: {:?}",
               stmt_name,
               params);
        let mut values = vec![];
        for (param, ty) in params.iter().zip(param_types) {
            let mut buf = vec![];
            match try!(param.to_sql_checked(ty, &mut buf, &SessionInfo::new(self))) {
                IsNull::Yes => values.push(None),
                IsNull::No => values.push(Some(buf)),
            }
        }

        try!(self.write_messages(&[Frontend::Bind {
                                       portal: portal_name,
                                       statement: &stmt_name,
                                       formats: &[1],
                                       values: &values,
                                       result_formats: &[1],
                                   },
                                   Frontend::Execute {
                                       portal: portal_name,
                                       max_rows: row_limit,
                                   },
                                   Frontend::Sync]));

        match try!(self.read_message()) {
            Backend::BindComplete => Ok(()),
            Backend::ErrorResponse { fields } => {
                try!(self.wait_for_ready());
                DbError::new(fields)
            }
            _ => {
                self.desynchronized = true;
                Err(Error::Io(bad_response()))
            }
        }
    }

    fn make_stmt_name(&mut self) -> String {
        let stmt_name = format!("s{}", self.next_stmt_id);
        self.next_stmt_id += 1;
        stmt_name
    }

    fn prepare<'a>(&mut self, query: &str, conn: &'a Connection) -> Result<Statement<'a>> {
        let stmt_name = self.make_stmt_name();
        let (param_types, columns) = try!(self.raw_prepare(&stmt_name, query));
        let info = Arc::new(StatementInfo {
            name: stmt_name,
            param_types: param_types,
            columns: columns,
        });
        Ok(Statement::new(conn, info, Cell::new(0), false))
    }

    fn prepare_cached<'a>(&mut self, query: &str, conn: &'a Connection) -> Result<Statement<'a>> {
        let info = self.cached_statements.get(query).cloned();

        let info = match info {
            Some(info) => info,
            None => {
                let stmt_name = self.make_stmt_name();
                let (param_types, columns) = try!(self.raw_prepare(&stmt_name, query));
                let info = Arc::new(StatementInfo {
                    name: stmt_name,
                    param_types: param_types,
                    columns: columns,
                });
                self.cached_statements.insert(query.to_owned(), info.clone());
                info
            }
        };

        Ok(Statement::new(conn, info, Cell::new(0), true))
    }

    fn close_statement(&mut self, name: &str, type_: u8) -> Result<()> {
        try!(self.write_messages(&[Frontend::Close {
                                       variant: type_,
                                       name: name,
                                   },
                                   Frontend::Sync]));
        let resp = match try!(self.read_message()) {
            Backend::CloseComplete => Ok(()),
            Backend::ErrorResponse { fields } => DbError::new(fields),
            _ => bad_response!(self),
        };
        try!(self.wait_for_ready());
        resp
    }

    fn get_type(&mut self, oid: Oid) -> Result<Type> {
        if let Some(ty) = Type::from_oid(oid) {
            return Ok(ty);
        }

        if let Some(ty) = self.unknown_types.get(&oid) {
            return Ok(Type::Other(ty.clone()));
        }

        let ty = try!(self.read_type(oid));
        self.unknown_types.insert(oid, ty.clone());
        Ok(Type::Other(ty))
    }

    #[allow(if_not_else)]
    fn read_type(&mut self, oid: Oid) -> Result<Other> {
        try!(self.raw_execute(TYPEINFO_QUERY, "", 0, &[Type::Oid], &[&oid]));
        let mut rows = VecDeque::new();
        try!(self.read_rows(&mut rows));
        let row = rows.pop_front().unwrap();

        let (name, type_, elem_oid, rngsubtype, basetype, schema, relid) = {
            let ctx = SessionInfo::new(self);
            let name = try!(String::from_sql(&Type::Name, &mut &**row[0].as_ref().unwrap(), &ctx));
            let type_ = try!(i8::from_sql(&Type::Char, &mut &**row[1].as_ref().unwrap(), &ctx));
            let elem_oid = try!(Oid::from_sql(&Type::Oid, &mut &**row[2].as_ref().unwrap(), &ctx));
            let rngsubtype = match row[3] {
                Some(ref data) => try!(Option::<Oid>::from_sql(&Type::Oid, &mut &**data, &ctx)),
                None => try!(Option::<Oid>::from_sql_null(&Type::Oid, &ctx)),
            };
            let basetype = try!(Oid::from_sql(&Type::Oid, &mut &**row[4].as_ref().unwrap(), &ctx));
            let schema = try!(String::from_sql(&Type::Name,
                                               &mut &**row[5].as_ref().unwrap(),
                                               &ctx));
            let relid = try!(Oid::from_sql(&Type::Oid, &mut &**row[6].as_ref().unwrap(), &ctx));
            (name, type_, elem_oid, rngsubtype, basetype, schema, relid)
        };

        let kind = if type_ == b'e' as i8 {
            Kind::Enum(try!(self.read_enum_variants(oid)))
        } else if type_ == b'p' as i8 {
            Kind::Pseudo
        } else if basetype != 0 {
            Kind::Domain(try!(self.get_type(basetype)))
        } else if elem_oid != 0 {
            Kind::Array(try!(self.get_type(elem_oid)))
        } else if relid != 0 {
            Kind::Composite(try!(self.read_composite_fields(relid)))
        } else {
            match rngsubtype {
                Some(oid) => Kind::Range(try!(self.get_type(oid))),
                None => Kind::Simple,
            }
        };

        Ok(Other::new(name, oid, kind, schema))
    }

    fn read_enum_variants(&mut self, oid: Oid) -> Result<Vec<String>> {
        try!(self.raw_execute(TYPEINFO_ENUM_QUERY, "", 0, &[Type::Oid], &[&oid]));
        let mut rows = VecDeque::new();
        try!(self.read_rows(&mut rows));

        let ctx = SessionInfo::new(self);
        let mut variants = vec![];
        for row in rows {
            variants.push(try!(String::from_sql(&Type::Name,
                                                &mut &**row[0].as_ref().unwrap(),
                                                &ctx)));
        }

        Ok(variants)
    }

    fn read_composite_fields(&mut self, relid: Oid) -> Result<Vec<Field>> {
        try!(self.raw_execute(TYPEINFO_COMPOSITE_QUERY, "", 0, &[Type::Oid], &[&relid]));
        let mut rows = VecDeque::new();
        try!(self.read_rows(&mut rows));

        let mut fields = vec![];
        for row in rows {
            let (name, type_) = {
                let ctx = SessionInfo::new(self);
                let name = try!(String::from_sql(&Type::Name,
                                                 &mut &**row[0].as_ref().unwrap(),
                                                 &ctx));
                let type_ = try!(Oid::from_sql(&Type::Oid, &mut &**row[1].as_ref().unwrap(), &ctx));
                (name, type_)
            };
            let type_ = try!(self.get_type(type_));
            fields.push(Field::new(name, type_));
        }

        Ok(fields)
    }

    fn is_desynchronized(&self) -> bool {
        self.desynchronized
    }

    #[allow(needless_return)]
    fn wait_for_ready(&mut self) -> Result<()> {
        match try!(self.read_message()) {
            Backend::ReadyForQuery { .. } => Ok(()),
            _ => bad_response!(self),
        }
    }

    fn quick_query(&mut self, query: &str) -> Result<Vec<Vec<Option<String>>>> {
        check_desync!(self);
        debug!("executing query: {}", query);
        try!(self.write_messages(&[Frontend::Query { query: query }]));

        let mut result = vec![];
        loop {
            match try!(self.read_message()) {
                Backend::ReadyForQuery { .. } => break,
                Backend::DataRow { row } => {
                    result.push(row.into_iter()
                                   .map(|opt| {
                                       opt.map(|b| String::from_utf8_lossy(&b).into_owned())
                                   })
                                   .collect());
                }
                Backend::CopyInResponse { .. } => {
                    try!(self.write_messages(&[Frontend::CopyFail {
                                                   message: "COPY queries cannot be directly \
                                                             executed",
                                               },
                                               Frontend::Sync]));
                }
                Backend::ErrorResponse { fields } => {
                    try!(self.wait_for_ready());
                    return DbError::new(fields);
                }
                _ => {}
            }
        }
        Ok(result)
    }

    fn finish_inner(&mut self) -> Result<()> {
        check_desync!(self);
        try!(self.write_messages(&[Frontend::Terminate]));
        Ok(())
    }
}

fn _ensure_send() {
    fn _is_send<T: Send>() {}
    _is_send::<Connection>();
}

/// A connection to a Postgres database.
pub struct Connection {
    conn: RefCell<InnerConnection>,
}

impl fmt::Debug for Connection {
    fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
        let conn = self.conn.borrow();
        fmt.debug_struct("Connection")
           .field("stream", &conn.stream.get_ref())
           .field("cancel_data", &conn.cancel_data)
           .field("notifications", &conn.notifications.len())
           .field("transaction_depth", &conn.trans_depth)
           .field("desynchronized", &conn.desynchronized)
           .field("cached_statements", &conn.cached_statements.len())
           .finish()
    }
}

impl Connection {
    /// Creates a new connection to a Postgres database.
    ///
    /// Most applications can use a URL string in the normal format:
    ///
    /// ```notrust
    /// postgresql://user[:password]@host[:port][/database][?param1=val1[[&param2=val2]...]]
    /// ```
    ///
    /// The password may be omitted if not required. The default Postgres port
    /// (5432) is used if none is specified. The database name defaults to the
    /// username if not specified.
    ///
    /// Connection via Unix sockets is supported with either the `unix_socket`
    /// or `nightly` features. To connect to the server via Unix sockets, `host`
    /// should be set to the absolute path of the directory containing the
    /// socket file.  Since `/` is a reserved character in URLs, the path should
    /// be URL encoded. If the path contains non-UTF 8 characters, a
    /// `ConnectParams` struct should be created manually and passed in. Note
    /// that Postgres does not support SSL over Unix sockets.
    ///
    /// # Examples
    ///
    /// ```rust,no_run
    /// use postgres::{Connection, SslMode};
    ///
    /// let url = "postgresql://postgres:hunter2@localhost:2994/foodb";
    /// let conn = Connection::connect(url, SslMode::None).unwrap();
    /// ```
    ///
    /// ```rust,no_run
    /// use postgres::{Connection, SslMode};
    ///
    /// let url = "postgresql://postgres@%2Frun%2Fpostgres";
    /// let conn = Connection::connect(url, SslMode::None).unwrap();
    /// ```
    ///
    /// ```rust,no_run
    /// use postgres::{Connection, UserInfo, ConnectParams, SslMode, ConnectTarget};
    /// # use std::path::PathBuf;
    ///
    /// # #[cfg(feature = "unix_socket")]
    /// # fn f() {
    /// # let some_crazy_path = PathBuf::new();
    /// let params = ConnectParams {
    ///     target: ConnectTarget::Unix(some_crazy_path),
    ///     port: None,
    ///     user: Some(UserInfo {
    ///         user: "postgres".to_owned(),
    ///         password: None
    ///     }),
    ///     database: None,
    ///     options: vec![],
    /// };
    /// let conn = Connection::connect(params, SslMode::None).unwrap();
    /// # }
    /// ```
    pub fn connect<T>(params: T, ssl: SslMode) -> result::Result<Connection, ConnectError>
        where T: IntoConnectParams
    {
        InnerConnection::connect(params, ssl).map(|conn| Connection { conn: RefCell::new(conn) })
    }

    /// Executes a statement, returning the number of rows modified.
    ///
    /// A statement may contain parameters, specified by `$n` where `n` is the
    /// index of the parameter in the list provided, 1-indexed.
    ///
    /// If the statement does not modify any rows (e.g. SELECT), 0 is returned.
    ///
    /// If the same statement will be repeatedly executed (perhaps with
    /// different query parameters), consider using the `prepare` and
    /// `prepare_cached` methods.
    ///
    /// # Panics
    ///
    /// Panics if the number of parameters provided does not match the number
    /// expected.
    ///
    /// # Example
    ///
    /// ```rust,no_run
    /// # use postgres::{Connection, SslMode};
    /// # let conn = Connection::connect("", SslMode::None).unwrap();
    /// # let bar = 1i32;
    /// # let baz = true;
    /// let rows_updated = conn.execute("UPDATE foo SET bar = $1 WHERE baz = $2", &[&bar, &baz])
    ///                        .unwrap();
    /// println!("{} rows updated", rows_updated);
    /// ```
    pub fn execute(&self, query: &str, params: &[&ToSql]) -> Result<u64> {
        let (param_types, columns) = try!(self.conn.borrow_mut().raw_prepare("", query));
        let info = Arc::new(StatementInfo {
            name: String::new(),
            param_types: param_types,
            columns: columns,
        });
        let stmt = Statement::new(self, info, Cell::new(0), true);
        stmt.execute(params)
    }

    /// Executes a statement, returning the resulting rows.
    ///
    /// A statement may contain parameters, specified by `$n` where `n` is the
    /// index of the parameter in the list provided, 1-indexed.
    ///
    /// If the same statement will be repeatedly executed (perhaps with
    /// different query parameters), consider using the `prepare` and
    /// `prepare_cached` methods.
    ///
    /// # Panics
    ///
    /// Panics if the number of parameters provided does not match the number
    /// expected.
    ///
    /// # Example
    ///
    /// ```rust,no_run
    /// # use postgres::{Connection, SslMode};
    /// # let conn = Connection::connect("", SslMode::None).unwrap();
    /// # let baz = true;
    /// for row in &conn.query("SELECT foo FROM bar WHERE baz = $1", &[&baz]).unwrap() {
    ///     let foo: i32 = row.get("foo");
    ///     println!("foo: {}", foo);
    /// }
    /// ```
    pub fn query<'a>(&'a self, query: &str, params: &[&ToSql]) -> Result<Rows<'a>> {
        let (param_types, columns) = try!(self.conn.borrow_mut().raw_prepare("", query));
        let info = Arc::new(StatementInfo {
            name: String::new(),
            param_types: param_types,
            columns: columns,
        });
        let stmt = Statement::new(self, info, Cell::new(0), true);
        stmt.into_query(params)
    }

    /// Begins a new transaction.
    ///
    /// Returns a `Transaction` object which should be used instead of
    /// the connection for the duration of the transaction. The transaction
    /// is active until the `Transaction` object falls out of scope.
    ///
    /// # Note
    /// A transaction will roll back by default. The `set_commit`,
    /// `set_rollback`, and `commit` methods alter this behavior.
    ///
    /// # Panics
    ///
    /// Panics if a transaction is already active.
    ///
    /// # Example
    ///
    /// ```rust,no_run
    /// # use postgres::{Connection, SslMode};
    /// # let conn = Connection::connect("", SslMode::None).unwrap();
    /// let trans = conn.transaction().unwrap();
    /// trans.execute("UPDATE foo SET bar = 10", &[]).unwrap();
    /// // ...
    ///
    /// trans.commit().unwrap();
    /// ```
    pub fn transaction<'a>(&'a self) -> Result<Transaction<'a>> {
        self.transaction_with(&transaction::Config::new())
    }

    /// Begins a new transaction with the specified configuration.
    pub fn transaction_with<'a>(&'a self, config: &transaction::Config) -> Result<Transaction<'a>> {
        let mut conn = self.conn.borrow_mut();
        check_desync!(conn);
        assert!(conn.trans_depth == 0,
                "`transaction` must be called on the active transaction");
        let mut query = "BEGIN".to_owned();
        config.build_command(&mut query);
        try!(conn.quick_query(&query));
        conn.trans_depth += 1;
        Ok(Transaction::new(self, 1))
    }

    /// Creates a new prepared statement.
    ///
    /// If the same statement will be executed repeatedly, explicitly preparing
    /// it can improve performance.
    ///
    /// The statement is associated with the connection that created it and may
    /// not outlive that connection.
    ///
    /// # Example
    ///
    /// ```rust,no_run
    /// # use postgres::{Connection, SslMode};
    /// # let x = 10i32;
    /// # let conn = Connection::connect("", SslMode::None).unwrap();
    /// # let (a, b) = (0i32, 1i32);
    /// # let updates = vec![(&a, &b)];
    /// let stmt = conn.prepare("UPDATE foo SET bar = $1 WHERE baz = $2").unwrap();
    /// for (bar, baz) in updates {
    ///     stmt.execute(&[bar, baz]).unwrap();
    /// }
    /// ```
    pub fn prepare<'a>(&'a self, query: &str) -> Result<Statement<'a>> {
        self.conn.borrow_mut().prepare(query, self)
    }

    /// Creates a cached prepared statement.
    ///
    /// Like `prepare`, except that the statement is only prepared once over
    /// the lifetime of the connection and then cached. If the same statement
    /// is going to be prepared frequently, caching it can improve performance
    /// by reducing the number of round trips to the Postgres backend.
    ///
    /// # Example
    ///
    /// ```rust,no_run
    /// # use postgres::{Connection, SslMode};
    /// # let x = 10i32;
    /// # let conn = Connection::connect("", SslMode::None).unwrap();
    /// # let (a, b) = (0i32, 1i32);
    /// # let updates = vec![(&a, &b)];
    /// let stmt = conn.prepare_cached("UPDATE foo SET bar = $1 WHERE baz = $2").unwrap();
    /// for (bar, baz) in updates {
    ///     stmt.execute(&[bar, baz]).unwrap();
    /// }
    /// ```
    pub fn prepare_cached<'a>(&'a self, query: &str) -> Result<Statement<'a>> {
        self.conn.borrow_mut().prepare_cached(query, self)
    }

    /// Returns the isolation level which will be used for future transactions.
    ///
    /// This is a simple wrapper around `SHOW TRANSACTION ISOLATION LEVEL`.
    pub fn transaction_isolation(&self) -> Result<IsolationLevel> {
        let mut conn = self.conn.borrow_mut();
        check_desync!(conn);
        let result = try!(conn.quick_query("SHOW TRANSACTION ISOLATION LEVEL"));
        IsolationLevel::new(result[0][0].as_ref().unwrap())
    }

    /// # Deprecated
    ///
    /// Use `Connection::set_transaction_config` instead.
    pub fn set_transaction_isolation(&self, level: IsolationLevel) -> Result<()> {
        self.set_transaction_config(transaction::Config::new().isolation_level(level))
    }

    /// Sets the configuration that will be used for future transactions.
    pub fn set_transaction_config(&self, config: &transaction::Config) -> Result<()> {
        let mut command = "SET SESSION CHARACTERISTICS AS TRANSACTION".to_owned();
        config.build_command(&mut command);
        self.batch_execute(&command)
    }

    /// Execute a sequence of SQL statements.
    ///
    /// Statements should be separated by `;` characters. If an error occurs,
    /// execution of the sequence will stop at that point. This is intended for
    /// execution of batches of non-dynamic statements - for example, creation
    /// of a schema for a fresh database.
    ///
    /// # Warning
    ///
    /// Prepared statements should be used for any SQL statement which contains
    /// user-specified data, as it provides functionality to safely embed that
    /// data in the statement. Do not form statements via string concatenation
    /// and feed them into this method.
    ///
    /// # Example
    ///
    /// ```rust,no_run
    /// # use postgres::{Connection, SslMode, Result};
    /// # let conn = Connection::connect("", SslMode::None).unwrap();
    /// conn.batch_execute("
    ///     CREATE TABLE person (
    ///         id SERIAL PRIMARY KEY,
    ///         name NOT NULL
    ///     );
    ///
    ///     CREATE TABLE purchase (
    ///         id SERIAL PRIMARY KEY,
    ///         person INT NOT NULL REFERENCES person (id),
    ///         time TIMESTAMPTZ NOT NULL,
    ///     );
    ///
    ///     CREATE INDEX ON purchase (time);
    ///     ").unwrap();
    /// ```
    pub fn batch_execute(&self, query: &str) -> Result<()> {
        self.conn.borrow_mut().quick_query(query).map(|_| ())
    }

    /// Returns a structure providing access to asynchronous notifications.
    ///
    /// Use the `LISTEN` command to register this connection for notifications.
    pub fn notifications<'a>(&'a self) -> Notifications<'a> {
        Notifications::new(self)
    }

    /// Returns information used to cancel pending queries.
    ///
    /// Used with the `cancel_query` function. The object returned can be used
    /// to cancel any query executed by the connection it was created from.
    pub fn cancel_data(&self) -> CancelData {
        self.conn.borrow().cancel_data
    }

    /// Returns the value of the specified Postgres backend parameter, such as
    /// `timezone` or `server_version`.
    pub fn parameter(&self, param: &str) -> Option<String> {
        self.conn.borrow().parameters.get(param).cloned()
    }

    /// Sets the notice handler for the connection, returning the old handler.
    pub fn set_notice_handler(&self, handler: Box<HandleNotice>) -> Box<HandleNotice> {
        self.conn.borrow_mut().set_notice_handler(handler)
    }

    /// Returns whether or not the stream has been desynchronized due to an
    /// error in the communication channel with the server.
    ///
    /// If this has occurred, all further queries will immediately return an
    /// error.
    pub fn is_desynchronized(&self) -> bool {
        self.conn.borrow().is_desynchronized()
    }

    /// Determines if the `Connection` is currently "active", that is, if there
    /// are no active transactions.
    ///
    /// The `transaction` method can only be called on the active `Connection`
    /// or `Transaction`.
    pub fn is_active(&self) -> bool {
        self.conn.borrow().trans_depth == 0
    }

    /// Consumes the connection, closing it.
    ///
    /// Functionally equivalent to the `Drop` implementation for `Connection`
    /// except that it returns any error encountered to the caller.
    pub fn finish(self) -> Result<()> {
        let mut conn = self.conn.borrow_mut();
        conn.finished = true;
        conn.finish_inner()
    }
}

/// A trait allowing abstraction over connections and transactions
pub trait GenericConnection {
    /// Like `Connection::execute`.
    fn execute(&self, query: &str, params: &[&ToSql]) -> Result<u64>;

    /// Like `Connection::query`.
    fn query<'a>(&'a self, query: &str, params: &[&ToSql]) -> Result<Rows<'a>>;

    /// Like `Connection::prepare`.
    fn prepare<'a>(&'a self, query: &str) -> Result<Statement<'a>>;

    /// Like `Connection::prepare_cached`.
    fn prepare_cached<'a>(&'a self, query: &str) -> Result<Statement<'a>>;

    /// Like `Connection::transaction`.
    fn transaction<'a>(&'a self) -> Result<Transaction<'a>>;

    /// Like `Connection::batch_execute`.
    fn batch_execute(&self, query: &str) -> Result<()>;

    /// Like `Connection::is_active`.
    fn is_active(&self) -> bool;
}

impl GenericConnection for Connection {
    fn execute(&self, query: &str, params: &[&ToSql]) -> Result<u64> {
        self.execute(query, params)
    }

    fn query<'a>(&'a self, query: &str, params: &[&ToSql]) -> Result<Rows<'a>> {
        self.query(query, params)
    }

    fn prepare<'a>(&'a self, query: &str) -> Result<Statement<'a>> {
        self.prepare(query)
    }

    fn prepare_cached<'a>(&'a self, query: &str) -> Result<Statement<'a>> {
        self.prepare_cached(query)
    }

    fn transaction<'a>(&'a self) -> Result<Transaction<'a>> {
        self.transaction()
    }

    fn batch_execute(&self, query: &str) -> Result<()> {
        self.batch_execute(query)
    }

    fn is_active(&self) -> bool {
        self.is_active()
    }
}

impl<'a> GenericConnection for Transaction<'a> {
    fn execute(&self, query: &str, params: &[&ToSql]) -> Result<u64> {
        self.execute(query, params)
    }

    fn query<'b>(&'b self, query: &str, params: &[&ToSql]) -> Result<Rows<'b>> {
        self.query(query, params)
    }

    fn prepare<'b>(&'b self, query: &str) -> Result<Statement<'b>> {
        self.prepare(query)
    }

    fn prepare_cached<'b>(&'b self, query: &str) -> Result<Statement<'b>> {
        self.prepare_cached(query)
    }

    fn transaction<'b>(&'b self) -> Result<Transaction<'b>> {
        self.transaction()
    }

    fn batch_execute(&self, query: &str) -> Result<()> {
        self.batch_execute(query)
    }

    fn is_active(&self) -> bool {
        self.is_active()
    }
}

trait OtherNew {
    fn new(name: String, oid: Oid, kind: Kind, schema: String) -> Other;
}

trait DbErrorNew {
    fn new_raw(fields: Vec<(u8, String)>) -> result::Result<DbError, ()>;
    fn new_connect<T>(fields: Vec<(u8, String)>) -> result::Result<T, ConnectError>;
    fn new<T>(fields: Vec<(u8, String)>) -> Result<T>;
}

trait RowsNew<'a> {
    fn new(stmt: &'a Statement<'a>, data: Vec<Vec<Option<Vec<u8>>>>) -> Rows<'a>;
    fn new_owned(stmt: Statement<'a>, data: Vec<Vec<Option<Vec<u8>>>>) -> Rows<'a>;
}

trait LazyRowsNew<'trans, 'stmt> {
    fn new(stmt: &'stmt Statement<'stmt>,
           data: VecDeque<Vec<Option<Vec<u8>>>>,
           name: String,
           row_limit: i32,
           more_rows: bool,
           finished: bool,
           trans: &'trans Transaction<'trans>)
           -> LazyRows<'trans, 'stmt>;
}

trait SessionInfoNew<'a> {
    fn new(conn: &'a InnerConnection) -> SessionInfo<'a>;
}

trait StatementInternals<'conn> {
    fn new(conn: &'conn Connection,
           info: Arc<StatementInfo>,
           next_portal_id: Cell<u32>,
           finished: bool)
           -> Statement<'conn>;

    fn conn(&self) -> &'conn Connection;

    fn into_query(self, params: &[&ToSql]) -> Result<Rows<'conn>>;
}

trait ColumnNew {
    fn new(name: String, type_: Type) -> Column;
}

trait NotificationsNew<'conn> {
    fn new(conn: &'conn Connection) -> Notifications<'conn>;
}

trait WrongTypeNew {
    fn new(ty: Type) -> WrongType;
}

trait FieldNew {
    fn new(name: String, type_: Type) -> Field;
}

trait TransactionInternals<'conn> {
    fn new(conn: &'conn Connection, depth: u32) -> Transaction<'conn>;

    fn conn(&self) -> &'conn Connection;

    fn depth(&self) -> u32;
}

trait ConfigInternals {
    fn build_command(&self, s: &mut String);
}

trait IsolationLevelNew {
    fn new(level: &str) -> Result<IsolationLevel>;
}