# 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 close(&mut self) -> Poll<(), Self::SinkError> { ... }
        fn wait(self) -> Wait<Self>
        where
            Self: Sized,
        { ... }
        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 with_flat_map<U, F, St>(self, f: F) -> WithFlatMap<Self, U, F, St>
        where
            F: FnMut(U) -> St,
            St: Stream<Item = Self::SinkItem, Error = Self::SinkError>,
            Self: Sized,
        { ... }
        fn sink_map_err<F, E>(self, f: F) -> SinkMapErr<Self, F>
        where
            F: FnOnce(Self::SinkError) -> E,
            Self: Sized,
        { ... }
        fn sink_from_err<E: From<Self::SinkError>>(self) -> SinkFromErr<Self, E>
        where
            Self: Sized,
        { ... }
        fn buffer(self, amt: usize) -> Buffer<Self>
        where
            Self: Sized,
        { ... }
        fn fanout<S>(self, other: S) -> Fanout<Self, S>
        where
            Self: Sized,
            Self::SinkItem: Clone,
            S: Sink<SinkItem = Self::SinkItem, SinkError = Self::SinkError>,
        { ... }
        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.

You can find more information/tutorials about streams online at https://tokio.rs

## Associated Types

### `type SinkItem`

The type of value that the sink accepts.

### `type SinkError`

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

## Required Methods

### `fn start_send(
&mut self,
item: Self::SinkItem
) -> StartSend<Self::SinkItem, Self::SinkError>`

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 an error.

### `fn poll_complete(&mut self) -> Poll<(), Self::SinkError>`

Flush all output from this sink, if necessary.

Some sinks may buffer intermediate data as an optimization to improve throughput. In other words, if a sink has a corresponding receiver then a successful `start_send` above may not guarantee that the value is actually ready to be received by the receiver. This function is intended to be used to ensure that values do indeed make their way to the receiver.

This function will attempt to process any pending requests on behalf of the sink and drive it to completion.

# Return value

Returns `Ok(Async::Ready(()))` when no buffered items remain. If this value is returned then it is guaranteed that all previous values sent via `start_send` will be guaranteed to be available to a listening receiver.

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 an error.

# Compatibility nodes

The name of this method may be slightly misleading as the original intention was to have this method be more general than just flushing requests. Over time though it was decided to trim back the ambitions of this method to what it's always done, just flushing.

In the 0.2 release series of futures this method will be renamed to `poll_flush`. For 0.1, however, the breaking change is not happening yet.

## Provided Methods

### `fn close(&mut self) -> Poll<(), Self::SinkError>`

A method to indicate that no more values will ever be pushed into this sink.

This method is used to indicate that a sink will no longer even be given another value by the caller. That is, the `start_send` method above will be called no longer (nor `poll_complete`). This method is intended to model "graceful shutdown" in various protocols where the intent to shut down is followed by a little more blocking work.

Callers of this function should work it it in a similar fashion to `poll_complete`. Once called it may return `NotReady` which indicates that more external work needs to happen to make progress. The current task will be scheduled to receive a notification in such an event, however.

Note that this function will imply `poll_complete` above. That is, if a sink has buffered data, then it'll be flushed out during a `close` operation. It is not necessary to have `poll_complete` return `Ready` before a `close` is called. Once a `close` is called, though, `poll_complete` cannot be called.

# Return value

This function, like `poll_complete`, returns a `Poll`. The value is `Ready` once the close operation has completed. At that point it should be safe to drop the sink and deallocate associated resources.

If the value returned is `NotReady` then the sink is not yet closed and work needs to be done to close it. The work has been scheduled and the current task will receive a notification when it's next ready to call this method again.

Finally, this function may also return an error.

# Errors

This function will return an `Err` if any operation along the way during the close operation fails. An error typically is fatal for a sink and is unable to be recovered from, but in specific situations this may not always be true.

Note that it's also typically an error to call `start_send` or `poll_complete` after the `close` function is called. This method will initiate a close, and continuing to send values after that (or attempt to flush) may result in strange behavior, panics, errors, etc. Once this method is called, it must be the only method called on this `Sink`.

# Panics

This method may panic or cause panics if:

- It is called outside the context of a future's task
- It is called and then `start_send` or `poll_complete` is called

# Compatibility notes

Note that this function is currently by default a provided function, defaulted to calling `poll_complete` above. This function was added in the 0.1 series of the crate as a backwards-compatible addition. It is intended that in the 0.2 series the method will no longer be a default method.

It is highly recommended to consider this method a required method and to implement it whenever you implement `Sink` locally. It is especially crucial to be sure to close inner sinks, if applicable.

### `fn wait(self) -> Wait<Self> where
Self: Sized,`

Creates a new object which will produce a synchronous sink.

The sink returned does not implement the `Sink` trait, and instead only has two methods: `send` and `flush`. These two methods correspond to `start_send` and `poll_complete` above except are executed in a blocking fashion.

### `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,`

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`.

### `fn with_flat_map<U, F, St>(self, f: F) -> WithFlatMap<Self, U, F, St> where
F: FnMut(U) -> St,
St: Stream<Item = Self::SinkItem, Error = Self::SinkError>,
Self: Sized,`

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 stream, of which each value is passed to the underlying sink. A new value will not be accepted until the stream has been drained

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

# Examples

Using this function with an iterator through use of the `stream::iter_ok()` function

    use futures::prelude::*;
    use futures::stream;
    use futures::sync::mpsc;

    let (tx, rx) = mpsc::channel::<i32>(5);

    let tx = tx.with_flat_map(|x| {
        stream::iter_ok(vec![42; x].into_iter().map(|y| y))
    });
    tx.send(5).wait().unwrap();
    assert_eq!(rx.collect().wait(), Ok(vec![42, 42, 42, 42, 42]))

### `fn sink_map_err<F, E>(self, f: F) -> SinkMapErr<Self, F> where
F: FnOnce(Self::SinkError) -> E,
Self: Sized,`

Transforms the error returned by the sink.

### `fn sink_from_err<E: From<Self::SinkError>>(self) -> SinkFromErr<Self, E> where
Self: Sized,`

Map this sink's error to any error implementing `From` for this sink's `Error`, returning a new sink.

If wanting to map errors of a `Sink + Stream`, use `.sink_from_err().from_err()`.

### `fn buffer(self, amt: usize) -> Buffer<Self> where
Self: Sized,`

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`.

This method is only available when the `use_std` feature of this library is activated, and it is activated by default.

### `fn fanout<S>(self, other: S) -> Fanout<Self, S> where
Self: Sized,
Self::SinkItem: Clone,
S: Sink<SinkItem = Self::SinkItem, SinkError = Self::SinkError>,`

Fanout items to multiple sinks.

This adapter clones each incoming item and forwards it to both this as well as the other sink at the same time.

### `fn flush(self) -> Flush<Self> where
Self: Sized,`

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.

### `fn send(self, item: Self::SinkItem) -> Send<Self> where
Self: Sized,`

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.

### `fn send_all<S>(self, stream: S) -> SendAll<Self, S> where
S: Stream<Item = Self::SinkItem>,
Self::SinkError: From<S::Error>,
Self: Sized,`

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, the sink has received all items, the sink has been flushed, and the sink has been closed.

Doing `sink.send_all(stream)` is roughly equivalent to `stream.forward(sink)`. The returned future will exhaust all items from `stream` and send them to `self`, closing `self` when all items have been received.

On completion, the pair `(sink, source)` is returned.

## Implementations on Foreign Types

### `impl<T> Sink for Vec<T>`
[src]

#### `type SinkItem = T`

#### `type SinkError = ()`

#### `fn start_send(
&mut self,
item: Self::SinkItem
) -> StartSend<Self::SinkItem, Self::SinkError>`
[src]

#### `fn poll_complete(&mut self) -> Poll<(), Self::SinkError>`
[src]

#### `fn close(&mut self) -> Poll<(), Self::SinkError>`
[src]

#### `fn wait(self) -> Wait<Self> where
Self: Sized,`
[src]

#### `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,`
[src]

#### `fn with_flat_map<U, F, St>(self, f: F) -> WithFlatMap<Self, U, F, St> where
F: FnMut(U) -> St,
St: Stream<Item = Self::SinkItem, Error = Self::SinkError>,
Self: Sized,`
[src]

#### `fn sink_map_err<F, E>(self, f: F) -> SinkMapErr<Self, F> where
F: FnOnce(Self::SinkError) -> E,
Self: Sized,`
[src]

#### `fn sink_from_err<E: From<Self::SinkError>>(self) -> SinkFromErr<Self, E> where
Self: Sized,`
[src]

#### `fn buffer(self, amt: usize) -> Buffer<Self> where
Self: Sized,`
[src]

#### `fn fanout<S>(self, other: S) -> Fanout<Self, S> where
Self: Sized,
Self::SinkItem: Clone,
S: Sink<SinkItem = Self::SinkItem, SinkError = Self::SinkError>,`
[src]

#### `fn flush(self) -> Flush<Self> where
Self: Sized,`
[src]

#### `fn send(self, item: Self::SinkItem) -> Send<Self> where
Self: Sized,`
[src]

#### `fn send_all<S>(self, stream: S) -> SendAll<Self, S> where
S: Stream<Item = Self::SinkItem>,
Self::SinkError: From<S::Error>,
Self: Sized,`
[src]

### `impl<S: ?Sized + Sink> Sink for Box<S>`
[src]

#### `type SinkItem = S::SinkItem`

#### `type SinkError = S::SinkError`

#### `fn start_send(
&mut self,
item: Self::SinkItem
) -> StartSend<Self::SinkItem, Self::SinkError>`
[src]

#### `fn poll_complete(&mut self) -> Poll<(), Self::SinkError>`
[src]

#### `fn close(&mut self) -> Poll<(), Self::SinkError>`
[src]

#### `fn wait(self) -> Wait<Self> where
Self: Sized,`
[src]

#### `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,`
[src]

#### `fn with_flat_map<U, F, St>(self, f: F) -> WithFlatMap<Self, U, F, St> where
F: FnMut(U) -> St,
St: Stream<Item = Self::SinkItem, Error = Self::SinkError>,
Self: Sized,`
[src]

#### `fn sink_map_err<F, E>(self, f: F) -> SinkMapErr<Self, F> where
F: FnOnce(Self::SinkError) -> E,
Self: Sized,`
[src]

#### `fn sink_from_err<E: From<Self::SinkError>>(self) -> SinkFromErr<Self, E> where
Self: Sized,`
[src]

#### `fn buffer(self, amt: usize) -> Buffer<Self> where
Self: Sized,`
[src]

#### `fn fanout<S>(self, other: S) -> Fanout<Self, S> where
Self: Sized,
Self::SinkItem: Clone,
S: Sink<SinkItem = Self::SinkItem, SinkError = Self::SinkError>,`
[src]

#### `fn flush(self) -> Flush<Self> where
Self: Sized,`
[src]

#### `fn send(self, item: Self::SinkItem) -> Send<Self> where
Self: Sized,`
[src]

#### `fn send_all<S>(self, stream: S) -> SendAll<Self, S> where
S: Stream<Item = Self::SinkItem>,
Self::SinkError: From<S::Error>,
Self: Sized,`
[src]

### `impl<'a, S: ?Sized + Sink> Sink for &'a mut S`
[src]

#### `type SinkItem = S::SinkItem`

#### `type SinkError = S::SinkError`

#### `fn start_send(
&mut self,
item: Self::SinkItem
) -> StartSend<Self::SinkItem, Self::SinkError>`
[src]

#### `fn poll_complete(&mut self) -> Poll<(), Self::SinkError>`
[src]

#### `fn close(&mut self) -> Poll<(), Self::SinkError>`
[src]

#### `fn wait(self) -> Wait<Self> where
Self: Sized,`
[src]

#### `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,`
[src]

#### `fn with_flat_map<U, F, St>(self, f: F) -> WithFlatMap<Self, U, F, St> where
F: FnMut(U) -> St,
St: Stream<Item = Self::SinkItem, Error = Self::SinkError>,
Self: Sized,`
[src]

#### `fn sink_map_err<F, E>(self, f: F) -> SinkMapErr<Self, F> where
F: FnOnce(Self::SinkError) -> E,
Self: Sized,`
[src]

#### `fn sink_from_err<E: From<Self::SinkError>>(self) -> SinkFromErr<Self, E> where
Self: Sized,`
[src]

#### `fn buffer(self, amt: usize) -> Buffer<Self> where
Self: Sized,`
[src]

#### `fn fanout<S>(self, other: S) -> Fanout<Self, S> where
Self: Sized,
Self::SinkItem: Clone,
S: Sink<SinkItem = Self::SinkItem, SinkError = Self::SinkError>,`
[src]

#### `fn flush(self) -> Flush<Self> where
Self: Sized,`
[src]

#### `fn send(self, item: Self::SinkItem) -> Send<Self> where
Self: Sized,`
[src]

#### `fn send_all<S>(self, stream: S) -> SendAll<Self, S> where
S: Stream<Item = Self::SinkItem>,
Self::SinkError: From<S::Error>,
Self: Sized,`
[src]

## Implementors

- [src]
  `impl<S, F, U: IntoFuture> Sink for AndThen<S, F, U> where
  S: Sink, type SinkItem = S::SinkItem; type SinkError = S::SinkError;`
- [src]
  `impl<S, F> Sink for Filter<S, F> where
  S: Sink, type SinkItem = S::SinkItem; type SinkError = S::SinkError;`
- [src]
  `impl<S, F> Sink for FilterMap<S, F> where
  S: Sink, type SinkItem = S::SinkItem; type SinkError = S::SinkError;`
- [src]
  `impl<S> Sink for Flatten<S> where
  S: Sink + Stream, type SinkItem = S::SinkItem; type SinkError = S::SinkError;`
- [src]
  `impl<S: Stream + Sink, E> Sink for FromErr<S, E> type SinkItem = S::SinkItem; type SinkError = S::SinkError;`
- [src]
  `impl<S> Sink for Fuse<S> where
  S: Sink, type SinkItem = S::SinkItem; type SinkError = S::SinkError;`
- [src]
  `impl<S, F> Sink for Inspect<S, F> where
  S: Sink + Stream, type SinkItem = S::SinkItem; type SinkError = S::SinkError;`
- [src]
  `impl<S, F> Sink for InspectErr<S, F> where
  S: Sink + Stream, type SinkItem = S::SinkItem; type SinkError = S::SinkError;`
- [src]
  `impl<S, F> Sink for Map<S, F> where
  S: Sink, type SinkItem = S::SinkItem; type SinkError = S::SinkError;`
- [src]
  `impl<S, F> Sink for MapErr<S, F> where
  S: Sink, type SinkItem = S::SinkItem; type SinkError = S::SinkError;`
- [src]
  `impl<S, F, U> Sink for OrElse<S, F, U> where
  S: Sink,
  U: IntoFuture, type SinkItem = S::SinkItem; type SinkError = S::SinkError;`
- [src]
  `impl<S> Sink for Peekable<S> where
  S: Sink + Stream, type SinkItem = S::SinkItem; type SinkError = S::SinkError;`
- [src]
  `impl<S> Sink for Skip<S> where
  S: Sink, type SinkItem = S::SinkItem; type SinkError = S::SinkError;`
- [src]
  `impl<S, P, R> Sink for SkipWhile<S, P, R> where
  S: Sink + Stream,
  R: IntoFuture, type SinkItem = S::SinkItem; type SinkError = S::SinkError;`
- [src]
  `impl<S> Sink for Take<S> where
  S: Sink + Stream, type SinkItem = S::SinkItem; type SinkError = S::SinkError;`
- [src]
  `impl<S, P, R> Sink for TakeWhile<S, P, R> where
  S: Sink + Stream,
  R: IntoFuture, type SinkItem = S::SinkItem; type SinkError = S::SinkError;`
- [src]
  `impl<S, F, U> Sink for Then<S, F, U> where
  S: Sink,
  U: IntoFuture, type SinkItem = S::SinkItem; type SinkError = S::SinkError;`
- [src]
  `impl<S> Sink for Buffered<S> where
  S: Sink + Stream,
  S::Item: IntoFuture, type SinkItem = S::SinkItem; type SinkError = S::SinkError;`
- [src]
  `impl<S> Sink for BufferUnordered<S> where
  S: Sink + Stream,
  S::Item: IntoFuture, type SinkItem = S::SinkItem; type SinkError = S::SinkError;`
- [src]
  `impl<S> Sink for Chunks<S> where
  S: Sink + Stream, type SinkItem = S::SinkItem; type SinkError = S::SinkError;`
- [src]
  `impl<S: Sink> Sink for SplitSink<S> type SinkItem = S::SinkItem; type SinkError = S::SinkError;`
- [src]
  `impl<S, U, F, Fut> Sink for With<S, U, F, Fut> where
  S: Sink,
  F: FnMut(U) -> Fut,
  Fut: IntoFuture<Item = S::SinkItem>,
  Fut::Error: From<S::SinkError>, type SinkItem = U; type SinkError = Fut::Error;`
- [src]
  `impl<S, U, F, St> Sink for WithFlatMap<S, U, F, St> where
  S: Sink,
  F: FnMut(U) -> St,
  St: Stream<Item = S::SinkItem, Error = S::SinkError>, type SinkItem = U; type SinkError = S::SinkError;`
- [src]
  `impl<S, E> Sink for SinkFromErr<S, E> where
  S: Sink,
  E: From<S::SinkError>, type SinkItem = S::SinkItem; type SinkError = E;`
- [src]
  `impl<S, F, E> Sink for SinkMapErr<S, F> where
  S: Sink,
  F: FnOnce(S::SinkError) -> E, type SinkItem = S::SinkItem; type SinkError = E;`
- [src]
  `impl<A, B> Sink for Fanout<A, B> where
  A: Sink,
  A::SinkItem: Clone,
  B: Sink<SinkItem = A::SinkItem, SinkError = A::SinkError>, type SinkItem = A::SinkItem; type SinkError = A::SinkError;`
- [src]
  `impl<S: Sink> Sink for Buffer<S> type SinkItem = S::SinkItem; type SinkError = S::SinkError;`
- [src]
  `impl<T> Sink for futures::sync::mpsc::Sender<T> type SinkItem = T; type SinkError = SendError<T>;`
- [src]
  `impl<T> Sink for futures::sync::mpsc::UnboundedSender<T> type SinkItem = T; type SinkError = SendError<T>;`
- [src]
  `impl<'a, T> Sink for &'a futures::sync::mpsc::UnboundedSender<T> type SinkItem = T; type SinkError = SendError<T>;`
- [src]
  `impl<T> Sink for futures::unsync::mpsc::Sender<T> type SinkItem = T; type SinkError = SendError<T>;`
- [src]
  `impl<T> Sink for futures::unsync::mpsc::UnboundedSender<T> type SinkItem = T; type SinkError = SendError<T>;`
- [src]
  `impl<'a, T> Sink for &'a futures::unsync::mpsc::UnboundedSender<T> type SinkItem = T; type SinkError = SendError<T>;`

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