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<?php
namespace React\Stream;
use Evenement\EventEmitterInterface;
/**
* The `ReadableStreamInterface` is responsible for providing an interface for
* read-only streams and the readable side of duplex streams.
*
* Besides defining a few methods, this interface also implements the
* `EventEmitterInterface` which allows you to react to certain events:
*
* data event:
* The `data` event will be emitted whenever some data was read/received
* from this source stream.
* The event receives a single mixed argument for incoming data.
*
* ```php
* $stream->on('data', function ($data) {
* echo $data;
* });
* ```
*
* This event MAY be emitted any number of times, which may be zero times if
* this stream does not send any data at all.
* It SHOULD not be emitted after an `end` or `close` event.
*
* The given `$data` argument may be of mixed type, but it's usually
* recommended it SHOULD be a `string` value or MAY use a type that allows
* representation as a `string` for maximum compatibility.
*
* Many common streams (such as a TCP/IP connection or a file-based stream)
* will emit the raw (binary) payload data that is received over the wire as
* chunks of `string` values.
*
* Due to the stream-based nature of this, the sender may send any number
* of chunks with varying sizes. There are no guarantees that these chunks
* will be received with the exact same framing the sender intended to send.
* In other words, many lower-level protocols (such as TCP/IP) transfer the
* data in chunks that may be anywhere between single-byte values to several
* dozens of kilobytes. You may want to apply a higher-level protocol to
* these low-level data chunks in order to achieve proper message framing.
*
* end event:
* The `end` event will be emitted once the source stream has successfully
* reached the end of the stream (EOF).
*
* ```php
* $stream->on('end', function () {
* echo 'END';
* });
* ```
*
* This event SHOULD be emitted once or never at all, depending on whether
* a successful end was detected.
* It SHOULD NOT be emitted after a previous `end` or `close` event.
* It MUST NOT be emitted if the stream closes due to a non-successful
* end, such as after a previous `error` event.
*
* After the stream is ended, it MUST switch to non-readable mode,
* see also `isReadable()`.
*
* This event will only be emitted if the *end* was reached successfully,
* not if the stream was interrupted by an unrecoverable error or explicitly
* closed. Not all streams know this concept of a "successful end".
* Many use-cases involve detecting when the stream closes (terminates)
* instead, in this case you should use the `close` event.
* After the stream emits an `end` event, it SHOULD usually be followed by a
* `close` event.
*
* Many common streams (such as a TCP/IP connection or a file-based stream)
* will emit this event if either the remote side closes the connection or
* a file handle was successfully read until reaching its end (EOF).
*
* Note that this event should not be confused with the `end()` method.
* This event defines a successful end *reading* from a source stream, while
* the `end()` method defines *writing* a successful end to a destination
* stream.
*
* error event:
* The `error` event will be emitted once a fatal error occurs, usually while
* trying to read from this stream.
* The event receives a single `Exception` argument for the error instance.
*
* ```php
* $stream->on('error', function (Exception $e) {
* echo 'Error: ' . $e->getMessage() . PHP_EOL;
* });
* ```
*
* This event SHOULD be emitted once the stream detects a fatal error, such
* as a fatal transmission error or after an unexpected `data` or premature
* `end` event.
* It SHOULD NOT be emitted after a previous `error`, `end` or `close` event.
* It MUST NOT be emitted if this is not a fatal error condition, such as
* a temporary network issue that did not cause any data to be lost.
*
* After the stream errors, it MUST close the stream and SHOULD thus be
* followed by a `close` event and then switch to non-readable mode, see
* also `close()` and `isReadable()`.
*
* Many common streams (such as a TCP/IP connection or a file-based stream)
* only deal with data transmission and do not make assumption about data
* boundaries (such as unexpected `data` or premature `end` events).
* In other words, many lower-level protocols (such as TCP/IP) may choose
* to only emit this for a fatal transmission error once and will then
* close (terminate) the stream in response.
*
* If this stream is a `DuplexStreamInterface`, you should also notice
* how the writable side of the stream also implements an `error` event.
* In other words, an error may occur while either reading or writing the
* stream which should result in the same error processing.
*
* close event:
* The `close` event will be emitted once the stream closes (terminates).
*
* ```php
* $stream->on('close', function () {
* echo 'CLOSED';
* });
* ```
*
* This event SHOULD be emitted once or never at all, depending on whether
* the stream ever terminates.
* It SHOULD NOT be emitted after a previous `close` event.
*
* After the stream is closed, it MUST switch to non-readable mode,
* see also `isReadable()`.
*
* Unlike the `end` event, this event SHOULD be emitted whenever the stream
* closes, irrespective of whether this happens implicitly due to an
* unrecoverable error or explicitly when either side closes the stream.
* If you only want to detect a *successful* end, you should use the `end`
* event instead.
*
* Many common streams (such as a TCP/IP connection or a file-based stream)
* will likely choose to emit this event after reading a *successful* `end`
* event or after a fatal transmission `error` event.
*
* If this stream is a `DuplexStreamInterface`, you should also notice
* how the writable side of the stream also implements a `close` event.
* In other words, after receiving this event, the stream MUST switch into
* non-writable AND non-readable mode, see also `isWritable()`.
* Note that this event should not be confused with the `end` event.
*
* The event callback functions MUST be a valid `callable` that obeys strict
* parameter definitions and MUST accept event parameters exactly as documented.
* The event callback functions MUST NOT throw an `Exception`.
* The return value of the event callback functions will be ignored and has no
* effect, so for performance reasons you're recommended to not return any
* excessive data structures.
*
* Every implementation of this interface MUST follow these event semantics in
* order to be considered a well-behaving stream.
*
* > Note that higher-level implementations of this interface may choose to
* define additional events with dedicated semantics not defined as part of
* this low-level stream specification. Conformance with these event semantics
* is out of scope for this interface, so you may also have to refer to the
* documentation of such a higher-level implementation.
*
* @see EventEmitterInterface
*/
interface ReadableStreamInterface extends EventEmitterInterface
{
/**
* Checks whether this stream is in a readable state (not closed already).
*
* This method can be used to check if the stream still accepts incoming
* data events or if it is ended or closed already.
* Once the stream is non-readable, no further `data` or `end` events SHOULD
* be emitted.
*
* ```php
* assert($stream->isReadable() === false);
*
* $stream->on('data', assertNeverCalled());
* $stream->on('end', assertNeverCalled());
* ```
*
* A successfully opened stream always MUST start in readable mode.
*
* Once the stream ends or closes, it MUST switch to non-readable mode.
* This can happen any time, explicitly through `close()` or
* implicitly due to a remote close or an unrecoverable transmission error.
* Once a stream has switched to non-readable mode, it MUST NOT transition
* back to readable mode.
*
* If this stream is a `DuplexStreamInterface`, you should also notice
* how the writable side of the stream also implements an `isWritable()`
* method. Unless this is a half-open duplex stream, they SHOULD usually
* have the same return value.
*
* @return bool
*/
public function isReadable();
/**
* Pauses reading incoming data events.
*
* Removes the data source file descriptor from the event loop. This
* allows you to throttle incoming data.
*
* Unless otherwise noted, a successfully opened stream SHOULD NOT start
* in paused state.
*
* Once the stream is paused, no futher `data` or `end` events SHOULD
* be emitted.
*
* ```php
* $stream->pause();
*
* $stream->on('data', assertShouldNeverCalled());
* $stream->on('end', assertShouldNeverCalled());
* ```
*
* This method is advisory-only, though generally not recommended, the
* stream MAY continue emitting `data` events.
*
* You can continue processing events by calling `resume()` again.
*
* Note that both methods can be called any number of times, in particular
* calling `pause()` more than once SHOULD NOT have any effect.
*
* @see self::resume()
* @return void
*/
public function pause();
/**
* Resumes reading incoming data events.
*
* Re-attach the data source after a previous `pause()`.
*
* ```php
* $stream->pause();
*
* Loop::addTimer(1.0, function () use ($stream) {
* $stream->resume();
* });
* ```
*
* Note that both methods can be called any number of times, in particular
* calling `resume()` without a prior `pause()` SHOULD NOT have any effect.
*
* @see self::pause()
* @return void
*/
public function resume();
/**
* Pipes all the data from this readable source into the given writable destination.
*
* Automatically sends all incoming data to the destination.
* Automatically throttles the source based on what the destination can handle.
*
* ```php
* $source->pipe($dest);
* ```
*
* Similarly, you can also pipe an instance implementing `DuplexStreamInterface`
* into itself in order to write back all the data that is received.
* This may be a useful feature for a TCP/IP echo service:
*
* ```php
* $connection->pipe($connection);
* ```
*
* This method returns the destination stream as-is, which can be used to
* set up chains of piped streams:
*
* ```php
* $source->pipe($decodeGzip)->pipe($filterBadWords)->pipe($dest);
* ```
*
* By default, this will call `end()` on the destination stream once the
* source stream emits an `end` event. This can be disabled like this:
*
* ```php
* $source->pipe($dest, array('end' => false));
* ```
*
* Note that this only applies to the `end` event.
* If an `error` or explicit `close` event happens on the source stream,
* you'll have to manually close the destination stream:
*
* ```php
* $source->pipe($dest);
* $source->on('close', function () use ($dest) {
* $dest->end('BYE!');
* });
* ```
*
* If the source stream is not readable (closed state), then this is a NO-OP.
*
* ```php
* $source->close();
* $source->pipe($dest); // NO-OP
* ```
*
* If the destinantion stream is not writable (closed state), then this will simply
* throttle (pause) the source stream:
*
* ```php
* $dest->close();
* $source->pipe($dest); // calls $source->pause()
* ```
*
* Similarly, if the destination stream is closed while the pipe is still
* active, it will also throttle (pause) the source stream:
*
* ```php
* $source->pipe($dest);
* $dest->close(); // calls $source->pause()
* ```
*
* Once the pipe is set up successfully, the destination stream MUST emit
* a `pipe` event with this source stream an event argument.
*
* @param WritableStreamInterface $dest
* @param array $options
* @return WritableStreamInterface $dest stream as-is
*/
public function pipe(WritableStreamInterface $dest, array $options = array());
/**
* Closes the stream (forcefully).
*
* This method can be used to (forcefully) close the stream.
*
* ```php
* $stream->close();
* ```
*
* Once the stream is closed, it SHOULD emit a `close` event.
* Note that this event SHOULD NOT be emitted more than once, in particular
* if this method is called multiple times.
*
* After calling this method, the stream MUST switch into a non-readable
* mode, see also `isReadable()`.
* This means that no further `data` or `end` events SHOULD be emitted.
*
* ```php
* $stream->close();
* assert($stream->isReadable() === false);
*
* $stream->on('data', assertNeverCalled());
* $stream->on('end', assertNeverCalled());
* ```
*
* If this stream is a `DuplexStreamInterface`, you should also notice
* how the writable side of the stream also implements a `close()` method.
* In other words, after calling this method, the stream MUST switch into
* non-writable AND non-readable mode, see also `isWritable()`.
* Note that this method should not be confused with the `end()` method.
*
* @return void
* @see WritableStreamInterface::close()
*/
public function close();
}