ReadableStreamInterface
extends
EventEmitterInterface
in
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.
Tags
Table of Contents
Methods
- close() : void
- Closes the stream (forcefully).
- emit() : mixed
- isReadable() : bool
- Checks whether this stream is in a readable state (not closed already).
- listeners() : mixed
- on() : mixed
- once() : mixed
- pause() : void
- Pauses reading incoming data events.
- pipe() : WritableStreamInterface
- Pipes all the data from this readable source into the given writable destination.
- removeAllListeners() : mixed
- removeListener() : mixed
- resume() : void
- Resumes reading incoming data events.
Methods
close()
Closes the stream (forcefully).
public
close() : void
This method can be used to (forcefully) close the stream.
$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.
$stream->close();
assert($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.
Tags
emit()
public
emit(mixed $event[, array<string|int, mixed> $arguments = [] ]) : mixed
Parameters
- $event : mixed
- $arguments : array<string|int, mixed> = []
isReadable()
Checks whether this stream is in a readable state (not closed already).
public
isReadable() : bool
This method can be used to check if the stream still accepts incoming
data events or if it is ended or closed already.
Once the stream is non-readable, no further data or end events SHOULD
be emitted.
assert($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 values
boollisteners()
public
listeners([mixed $event = null ]) : mixed
Parameters
- $event : mixed = null
on()
public
on(mixed $event, callable $listener) : mixed
Parameters
- $event : mixed
- $listener : callable
once()
public
once(mixed $event, callable $listener) : mixed
Parameters
- $event : mixed
- $listener : callable
pause()
Pauses reading incoming data events.
public
pause() : void
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.
$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.
Tags
pipe()
Pipes all the data from this readable source into the given writable destination.
public
pipe(WritableStreamInterface $dest[, array<string|int, mixed> $options = array() ]) : WritableStreamInterface
Automatically sends all incoming data to the destination. Automatically throttles the source based on what the destination can handle.
$source->pipe($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:
$connection->pipe($connection);
This method returns the destination stream as-is, which can be used to set up chains of piped streams:
$source->pipe($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:
$source->pipe($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:
$source->pipe($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.
$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:
$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:
$source->pipe($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.
Parameters
- $dest : WritableStreamInterface
- $options : array<string|int, mixed> = array()
Return values
WritableStreamInterface —$dest stream as-is
removeAllListeners()
public
removeAllListeners([mixed $event = null ]) : mixed
Parameters
- $event : mixed = null
removeListener()
public
removeListener(mixed $event, callable $listener) : mixed
Parameters
- $event : mixed
- $listener : callable
resume()
Resumes reading incoming data events.
public
resume() : void
Re-attach the data source after a previous pause().
$stream->pause();
Loop::addTimer(1.0, function () use ($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.