Struct PgListener

pub struct PgListener { /* private fields */ }

Available on crate feature postgres only.

A stream of asynchronous notifications from Postgres.

This listener will auto-reconnect. If the active connection being used ever dies, this listener will detect that event, create a new connection, will re-subscribe to all of the originally specified channels, and will resume operations as normal.

Implementations

impl PgListener

pub async fn connect(url: &str) -> Result<PgListener, Error>

pub async fn connect_with(pool: &Pool<Postgres>) -> Result<PgListener, Error>

pub fn ignore_pool_close_event(&mut self, val: bool)

Set whether or not to ignore Pool::close_event(). Defaults to false.

By default, when Pool::close() is called on the pool this listener is using while Self::recv() or Self::try_recv() are waiting for a message, the wait is cancelled and Err(PoolClosed) is returned.

This is because Pool::close() will wait until all connections are returned and closed, including the one being used by this listener.

Otherwise, pool.close().await would have to wait until PgListener encountered a need to acquire a new connection (timeout, error, etc.) and dropped the one it was currently holding, at which point .recv() or .try_recv() would return Err(PoolClosed) on the attempt to acquire a new connection anyway.

However, if you want PgListener to ignore the close event and continue waiting for a message as long as it can, set this to true.

Does nothing if this was constructed with PgListener::connect(), as that creates an internal pool just for the new instance of PgListener which cannot be closed manually.

pub fn eager_reconnect(&mut self, val: bool)

Set whether a lost connection in try_recv() should be re-established before it returns Ok(None), or on the next call to try_recv().

By default, this is true and the connection is re-established before returning Ok(None).

If this is set to false then notifications will continue to be lost until the next call to try_recv(). If your recovery logic uses a different database connection then notifications that occur after it completes may be lost without any way to tell that they have been.

pub async fn listen(&mut self, channel: &str) -> Result<(), Error>

Starts listening for notifications on a channel. The channel name is quoted here to ensure case sensitivity.

pub async fn listen_all( &mut self, channels: impl IntoIterator<Item = &str>, ) -> Result<(), Error>

Starts listening for notifications on all channels.

pub async fn unlisten(&mut self, channel: &str) -> Result<(), Error>

Stops listening for notifications on a channel. The channel name is quoted here to ensure case sensitivity.

pub async fn unlisten_all(&mut self) -> Result<(), Error>

Stops listening for notifications on all channels.

pub async fn recv(&mut self) -> Result<PgNotification, Error>

Receives the next notification available from any of the subscribed channels.

If the connection to PostgreSQL is lost, it is automatically reconnected on the next call to recv(), and should be entirely transparent (as long as it was just an intermittent network failure or long-lived connection reaper).

As notifications are transient, any received while the connection was lost, will not be returned. If you’d prefer the reconnection to be explicit and have a chance to do something before, please see try_recv.

Example

let mut listener = PgListener::connect("postgres:// ...").await?;
loop {
    // ask for next notification, re-connecting (transparently) if needed
    let notification = listener.recv().await?;

    // handle notification, do something interesting
}

pub async fn try_recv(&mut self) -> Result<Option<PgNotification>, Error>

Receives the next notification available from any of the subscribed channels.

If the connection to PostgreSQL is lost, None is returned, and the connection is reconnected either immediately, or on the next call to try_recv(), depending on the value of eager_reconnect.

Example

loop {
    // start handling notifications, connecting if needed
    while let Some(notification) = listener.try_recv().await? {
        // handle notification
    }

    // connection lost, do something interesting
}

pub fn next_buffered(&mut self) -> Option<PgNotification>

Receives the next notification that already exists in the connection buffer, if any.

This is similar to try_recv, except it will not wait if the connection has not yet received a notification.

This is helpful if you want to retrieve all buffered notifications and process them in batches.

pub fn into_stream( self, ) -> impl Stream<Item = Result<PgNotification, Error>> + Unpin

Consume this listener, returning a Stream of notifications.

The backing connection will be automatically reconnected should it be lost.

This has the same potential drawbacks as recv.

Trait Implementations

impl<'c> Acquire<'c> for &'c mut PgListener

type Database = Postgres

type Connection = &'c mut PgConnection

fn acquire( self, ) -> Pin<Box<dyn Future<Output = Result<<&'c mut PgListener as Acquire<'c>>::Connection, Error>> + Send + 'c>>

fn begin( self, ) -> Pin<Box<dyn Future<Output = Result<Transaction<'c, <&'c mut PgListener as Acquire<'c>>::Database>, Error>> + Send + 'c>>

impl Debug for PgListener

fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), Error>

Formats the value using the given formatter.

impl Drop for PgListener

fn drop(&mut self)

Executes the destructor for this type.

impl<'c> Executor<'c> for &'c mut PgListener

type Database = Postgres

fn fetch_many<'e, 'q, E>( self, query: E, ) -> Pin<Box<dyn Stream<Item = Result<Either<PgQueryResult, PgRow>, Error>> + Send + 'e>>

where 'c: 'e, 'q: 'e, E: Execute<'q, <&'c mut PgListener as Executor<'c>>::Database> + 'q,

Execute multiple queries and return the generated results as a stream from each query, in a stream.

fn fetch_optional<'e, 'q, E>( self, query: E, ) -> Pin<Box<dyn Future<Output = Result<Option<PgRow>, Error>> + Send + 'e>>

where 'c: 'e, 'q: 'e, E: Execute<'q, <&'c mut PgListener as Executor<'c>>::Database> + 'q,

Execute the query and returns at most one row.

fn prepare_with<'e, 'q>( self, query: &'q str, parameters: &'e [PgTypeInfo], ) -> Pin<Box<dyn Future<Output = Result<PgStatement<'q>, Error>> + Send + 'e>>

where 'q: 'e, 'c: 'e,

Prepare the SQL query, with parameter type information, to inspect the type information about its parameters and results.

fn execute<'e, 'q, E>( self, query: E, ) -> Pin<Box<dyn Future<Output = Result<<Self::Database as Database>::QueryResult, Error>> + Send + 'e>>

where 'q: 'e, 'c: 'e, E: 'q + Execute<'q, Self::Database>,

Execute the query and return the total number of rows affected.

fn execute_many<'e, 'q, E>( self, query: E, ) -> Pin<Box<dyn Stream<Item = Result<<Self::Database as Database>::QueryResult, Error>> + Send + 'e>>

where 'q: 'e, 'c: 'e, E: 'q + Execute<'q, Self::Database>,

Execute multiple queries and return the rows affected from each query, in a stream.

fn fetch<'e, 'q, E>( self, query: E, ) -> Pin<Box<dyn Stream<Item = Result<<Self::Database as Database>::Row, Error>> + Send + 'e>>

where 'q: 'e, 'c: 'e, E: 'q + Execute<'q, Self::Database>,

Execute the query and return the generated results as a stream.

fn fetch_all<'e, 'q, E>( self, query: E, ) -> Pin<Box<dyn Future<Output = Result<Vec<<Self::Database as Database>::Row>, Error>> + Send + 'e>>

where 'q: 'e, 'c: 'e, E: 'q + Execute<'q, Self::Database>,

Execute the query and return all the generated results, collected into a Vec.

fn fetch_one<'e, 'q, E>( self, query: E, ) -> Pin<Box<dyn Future<Output = Result<<Self::Database as Database>::Row, Error>> + Send + 'e>>

where 'q: 'e, 'c: 'e, E: 'q + Execute<'q, Self::Database>,

Execute the query and returns exactly one row.

fn prepare<'e, 'q>( self, query: &'q str, ) -> Pin<Box<dyn Future<Output = Result<<Self::Database as Database>::Statement<'q>, Error>> + Send + 'e>>

where 'q: 'e, 'c: 'e,

Prepare the SQL query to inspect the type information of its parameters and results.