Trait futures::sink::Sink [−] [src]

pub trait Sink {
    type SinkItem;
    type SinkError;
    fn start_send(&mut self,
                  item: Self::SinkItem)
                  -> StartSend<Self::SinkItem, Self::SinkError>;
    fn poll_complete(&mut self) -> Poll<(), Self::SinkError>;

    fn with<U, F, Fut>(self, f: F) -> With<Self, U, F, Fut> where F: FnMut(U) -> Fut,
              Fut: IntoFuture<Item=Self::SinkItem>,
              Fut::Error: From<Self::SinkError>,
              Self: Sized { ... }
    fn buffer(self, amt: usize) -> Buffer<Self> where Self: Sized { ... }
    fn flush(self) -> Flush<Self> where Self: Sized { ... }
    fn send(self, item: Self::SinkItem) -> Send<Self> where Self: Sized { ... }
    fn send_all<S>(self, stream: S) -> SendAll<Self, S> where S: Stream<Item=Self::SinkItem>,
              Self::SinkError: From<S::Error>,
              Self: Sized { ... }
}

A Sink is a value into which other values can be sent, asynchronously.

Basic examples of sinks include the sending side of:

  • Channels
  • Sockets
  • Pipes

In addition to such "primitive" sinks, it's typical to layer additional functionality, such as buffering, on top of an existing sink.

Sending to a sink is "asynchronous" in the sense that the value may not be sent in its entirety immediately. Instead, values are sent in a two-phase way: first by initiating a send, and then by polling for completion. This two-phase setup is analogous to buffered writing in synchronous code, where writes often succeed immediately, but internally are buffered and are actually written only upon flushing.

In addition, the Sink may be full, in which case it is not even possible to start the sending process.

As with Future and Stream, the Sink trait is built from a few core required methods, and a host of default methods for working in a higher-level way. The Sink::send_all combinator is of particular importance: you can use it to send an entire stream to a sink, which is the simplest way to ultimately consume a sink.

Associated Types

The type of value that the sink accepts.

The type of value produced by the sink when an error occurs.

Required Methods

Begin the process of sending a value to the sink.

As the name suggests, this method only begins the process of sending the item. If the sink employs buffering, the item isn't fully processed until the buffer is fully flushed. Since sinks are designed to work with asynchronous I/O, the process of actually writing out the data to an underlying object takes place asynchronously. You must use poll_complete in order to drive completion of a send. In particular, start_send does not begin the flushing process

Return value

This method returns AsyncSink::Ready if the sink was able to start sending item. In that case, you must ensure that you call poll_complete to process the sent item to completion. Note, however, that several calls to start_send can be made prior to calling poll_complete, which will work on completing all pending items.

The method returns AsyncSink::NotReady if the sink was unable to begin sending, usually due to being full. The sink must have attempted to complete processing any outstanding requests (equivalent to poll_complete) before yielding this result. The current task will be automatically scheduled for notification when the sink may be ready to receive new values.

Errors

If the sink encounters an error other than being temporarily full, it uses the Err variant to signal that error. In most cases, such errors mean that the sink will permanently be unable to receive items.

Panics

This method may panic in a few situations, depending on the specific sink:

  • It is called outside of the context of a task.
  • A previous call to start_send or poll_complete yielded a permanent error.

Make progress on all pending requests, and determine whether they have completed.

Since sinks are asynchronous, no single method completes all of their work in one shot. Instead, you use poll_complete to repeatedly drive the sink to make progress on requests (such as start_send). As with Future::poll, if the pending requests are not able to complete during this call, the current task is automatically scheduled to be woken up again once more progress is possible.

Return value

Returns Ok(Async::Ready(())) when no unprocessed requests remain.

Returns Ok(Async::NotReady) if there is more work left to do, in which case the current task is scheduled to wake up when more progress may be possible.

Errors

Returns Err if the sink encounters an error while processing one of its pending requests. Due to the buffered nature of requests, it is not generally possible to correlate the error with a particular request. As with start_send, these errors are generally "fatal" for continued use of the sink.

Panics

This method may panic in a few situations, depending on the specific sink:

  • It is called outside of the context of a task.
  • A previous call to start_send or poll_complete yielded a permanent error.

Provided Methods

Composes a function in front of the sink.

This adapter produces a new sink that passes each value through the given function f before sending it to self.

To process each value, f produces a future, which is then polled to completion before passing its result down to the underlying sink. If the future produces an error, that error is returned by the new sink.

Note that this function consumes the given sink, returning a wrapped version, much like Iterator::map.

Adds a fixed-size buffer to the current sink.

The resulting sink will buffer up to amt items when the underlying sink is unwilling to accept additional items. Calling poll_complete on the buffered sink will attempt to both empty the buffer and complete processing on the underlying sink.

Note that this function consumes the given sink, returning a wrapped version, much like Iterator::map.

A future that completes when the sink has finished processing all pending requests.

The sink itself is returned after flushing is complete; this adapter is intended to be used when you want to stop sending to the sink until all current requests are processed.

A future that completes after the given item has been fully processed into the sink, including flushing.

Note that, because of the flushing requirement, it is usually better to batch together items to send via send_all, rather than flushing between each item.

On completion, the sink is returned.

A future that completes after the given stream has been fully processed into the sink, including flushing.

This future will drive the stream to keep producing items until it is exhausted, sending each item to the sink. It will complete once both the stream is exhausted, and the sink has fully processed and flushed all of the items sent to it.

On completion, the sink is returned.

Implementors