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15 Dec 2021 22:57:24 UTC
- Distribution: IO-Async
- Module version: 0.801
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- License: perl_5
- Perl: v5.8.4
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- NAME
- SYNOPSIS
- DESCRIPTION
- EVENTS
- PARAMETERS
- read_handle => IO
- write_handle => IO
- handle => IO
- on_read => CODE
- on_read_error => CODE
- on_outgoing_empty => CODE
- on_write_error => CODE
- on_writeable_start => CODE
- on_writeable_stop => CODE
- autoflush => BOOL
- read_len => INT
- read_all => BOOL
- write_len => INT
- write_all => BOOL
- read_high_watermark => INT
- read_low_watermark => INT
- reader => STRING|CODE
- writer => STRING|CODE
- close_on_read_eof => BOOL
- encoding => STRING
- METHODS
- FUTURE-RETURNING READ METHODS
- UTILITY CONSTRUCTORS
- DEBUGGING FLAGS
- EXAMPLES
- SEE ALSO
- AUTHOR
NAME
IO::Async::Stream
- event callbacks and write bufering for a stream filehandleSYNOPSIS
use IO::Async::Stream; use IO::Async::Loop; my $loop = IO::Async::Loop->new; my $stream = IO::Async::Stream->new( read_handle => \*STDIN, write_handle => \*STDOUT, on_read => sub { my ( $self, $buffref, $eof ) = @_; while( $$buffref =~ s/^(.*\n)// ) { print "Received a line $1"; } if( $eof ) { print "EOF; last partial line is $$buffref\n"; } return 0; } ); $loop->add( $stream ); $stream->write( "An initial line here\n" );
DESCRIPTION
This subclass of IO::Async::Handle contains a filehandle that represents a byte-stream. It provides buffering for both incoming and outgoing data. It invokes the
on_read
handler when new data is read from the filehandle. Data may be written to the filehandle by calling thewrite
method.This class is suitable for any kind of filehandle that provides a possibly-bidirectional reliable byte stream, such as a pipe, TTY, or
SOCK_STREAM
socket (such as TCP or a byte-oriented UNIX local socket). For datagram or raw message-based sockets (such as UDP) see instead IO::Async::Socket.EVENTS
The following events are invoked, either using subclass methods or CODE references in parameters:
$ret = on_read \$buffer, $eof
Invoked when more data is available in the internal receiving buffer.
The first argument is a reference to a plain perl string. The code should inspect and remove any data it likes, but is not required to remove all, or indeed any of the data. Any data remaining in the buffer will be preserved for the next call, the next time more data is received from the handle.
In this way, it is easy to implement code that reads records of some form when completed, but ignores partially-received records, until all the data is present. If the handler wishes to be immediately invoke a second time, to have another attempt at consuming more content, it should return
1
. Otherwise, it should return0
, and the handler will next be invoked when more data has arrived from the underlying read handle and appended to the buffer. This makes it easy to implement code that handles multiple incoming records at the same time. Alternatively, if the handler function already attempts to consume as much as possible from the buffer, it will have no need to return1
at all. See the examples at the end of this documentation for more detail.The second argument is a scalar indicating whether the stream has reported an end-of-file (EOF) condition. A reference to the buffer is passed to the handler in the usual way, so it may inspect data contained in it. Once the handler returns a false value, it will not be called again, as the handle is now at EOF and no more data can arrive.
The
on_read
code may also dynamically replace itself with a new callback by returning a CODE reference instead of0
or1
. The original callback or method that the object first started with may be restored by returningundef
. Whenever the callback is changed in this way, the new code is called again; even if the read buffer is currently empty. See the examples at the end of this documentation for more detail.The
push_on_read
method can be used to insert new, temporary handlers that take precedence over the globalon_read
handler. This event is only used if there are no further pending handlers created bypush_on_read
.on_read_eof
Optional. Invoked when the read handle indicates an end-of-file (EOF) condition. If there is any data in the buffer still to be processed, the
on_read
event will be invoked first, before this one.on_write_eof
Optional. Invoked when the write handle indicates an end-of-file (EOF) condition. Note that this condition can only be detected after a
write
syscall returns theEPIPE
error. If there is no data pending to be written then it will not be detected yet.on_read_error $errno
Optional. Invoked when the
sysread
method on the read handle fails.on_write_error $errno
Optional. Invoked when the
syswrite
method on the write handle fails.The
on_read_error
andon_write_error
handlers are passed the value of$!
at the time the error occurred. (The$!
variable itself, by its nature, may have changed from the original error by the time this handler runs so it should always use the value passed in).If an error occurs when the corresponding error callback is not supplied, and there is not a handler for it, then the
close
method is called instead.on_read_high_watermark $length
on_read_low_watermark $length
Optional. Invoked when the read buffer grows larger than the high watermark or smaller than the low watermark respectively. These are edge-triggered events; they will only be triggered once per crossing, not continuously while the buffer remains above or below the given limit.
If these event handlers are not defined, the default behaviour is to disable read-ready notifications if the read buffer grows larger than the high watermark (so as to avoid it growing arbitrarily if nothing is consuming it), and re-enable notifications again once something has read enough to cause it to drop. If these events are overridden, the overriding code will have to perform this behaviour if required, by using
$self->want_readready_for_read(...)
on_outgoing_empty
Optional. Invoked when the writing data buffer becomes empty.
on_writeable_start
on_writeable_stop
Optional. These two events inform when the filehandle becomes writeable, and when it stops being writeable.
on_writeable_start
is invoked by theon_write_ready
event if previously it was known to be not writeable.on_writeable_stop
is invoked after asyswrite
operation fails withEAGAIN
orEWOULDBLOCK
. These two events track the writeability state, and ensure that only state change cause events to be invoked. A stream starts off being presumed writeable, so the first of these events to be observed will beon_writeable_stop
.PARAMETERS
The following named parameters may be passed to
new
orconfigure
:read_handle => IO
The IO handle to read from. Must implement
fileno
andsysread
methods.write_handle => IO
The IO handle to write to. Must implement
fileno
andsyswrite
methods.handle => IO
Shortcut to specifying the same IO handle for both of the above.
on_read => CODE
on_read_error => CODE
on_outgoing_empty => CODE
on_write_error => CODE
on_writeable_start => CODE
on_writeable_stop => CODE
CODE references for event handlers.
autoflush => BOOL
Optional. If true, the
write
method will attempt to write data to the operating system immediately, without waiting for the loop to indicate the filehandle is write-ready. This is useful, for example, on streams that should contain up-to-date logging or console information.It currently defaults to false for any file handle, but future versions of IO::Async may enable this by default on STDOUT and STDERR.
read_len => INT
Optional. Sets the buffer size for
read
calls. Defaults to 8 KiBytes.read_all => BOOL
Optional. If true, attempt to read as much data from the kernel as possible when the handle becomes readable. By default this is turned off, meaning at most one fixed-size buffer is read. If there is still more data in the kernel's buffer, the handle will still be readable, and will be read from again.
This behaviour allows multiple streams and sockets to be multiplexed simultaneously, meaning that a large bulk transfer on one cannot starve other filehandles of processing time. Turning this option on may improve bulk data transfer rate, at the risk of delaying or stalling processing on other filehandles.
write_len => INT
Optional. Sets the buffer size for
write
calls. Defaults to 8 KiBytes.write_all => BOOL
Optional. Analogous to the
read_all
option, but for writing. Whenautoflush
is enabled, this option only affects deferred writing if the initial attempt failed due to buffer space.read_high_watermark => INT
read_low_watermark => INT
Optional. If defined, gives a way to implement flow control or other behaviours that depend on the size of Stream's read buffer.
If after more data is read from the underlying filehandle the read buffer is now larger than the high watermark, the
on_read_high_watermark
event is triggered (which, by default, will disable read-ready notifications and pause reading from the filehandle).If after data is consumed by an
on_read
handler the read buffer is now smaller than the low watermark, theon_read_low_watermark
event is triggered (which, by default, will re-enable read-ready notifications and resume reading from the filehandle). For to be possible, the read handler would have to be one added by thepush_on_read
method or one of the Future-returningread_*
methods.By default these options are not defined, so this behaviour will not happen.
read_low_watermark
may not be set to a larger value thanread_high_watermark
, but it may be set to a smaller value, creating a hysteresis region. If either option is defined then both must be.If these options are used with the default event handlers, be careful not to cause deadlocks by having a high watermark sufficiently low that a single
on_read
invocation might not consider it finished yet.reader => STRING|CODE
writer => STRING|CODE
Optional. If defined, gives the name of a method or a CODE reference to use to implement the actual reading from or writing to the filehandle. These will be invoked as
$stream->reader( $read_handle, $buffer, $len ) $stream->writer( $write_handle, $buffer, $len )
Each is expected to modify the passed buffer;
reader
by appending to it,writer
by removing a prefix from it. Each is expected to return a true value on success, zero on EOF, orundef
with$!
set for errors. If not provided, they will be substituted by implenentations usingsysread
andsyswrite
on the underlying handle, respectively.close_on_read_eof => BOOL
Optional. Usually true, but if set to a false value then the stream will not be
close
d when an EOF condition occurs on read. This is normally not useful as at that point the underlying stream filehandle is no longer useable, but it may be useful for reading regular files, or interacting with TTY devices.encoding => STRING
If supplied, sets the name of encoding of the underlying stream. If an encoding is set, then the
write
method will expect to receive Unicode strings and encodes them into bytes, and incoming bytes will be decoded into Unicode strings for theon_read
event.If an encoding is not supplied then
write
andon_read
will work in byte strings.IMPORTANT NOTE: in order to handle reads of UTF-8 content or other multibyte encodings, the code implementing the
on_read
event uses a feature of Encode; theSTOP_AT_PARTIAL
flag. While this flag has existed for a while and is used by the:encoding
PerlIO layer itself for similar purposes, the flag is not officially documented by theEncode
module. In principle this undocumented feature could be subject to change, in practice I believe it to be reasonably stable.This note applies only to the
on_read
event; data written using thewrite
method does not rely on any undocumented features ofEncode
.If a read handle is given, it is required that either an
on_read
callback reference is configured, or that the object provides anon_read
method. It is optional whether either is true foron_outgoing_empty
; if neither is supplied then no action will be taken when the writing buffer becomes empty.An
on_read
handler may be supplied even if no read handle is yet given, to be used when a read handle is eventually provided by theset_handles
method.This condition is checked at the time the object is added to a Loop; it is allowed to create a
IO::Async::Stream
object with a read handle but without aon_read
handler, provided that one is later given usingconfigure
before the stream is added to its containing Loop, either directly or by being a child of another Notifier already in a Loop, or added to one.METHODS
The following methods documented with a trailing call to
->get
return Future instances.want_readready_for_read
want_readready_for_write
$stream->want_readready_for_read( $set ) $stream->want_readready_for_write( $set )
Mutators for the
want_readready
property on IO::Async::Handle, which control whether theread
orwrite
behaviour should be continued once the filehandle becomes ready for read.Normally,
want_readready_for_read
is always true (though the read watermark behaviour can modify it), andwant_readready_for_write
is not used. However, if a customwriter
function is provided, it may find this useful for being invoked again if it cannot proceed with a write operation until the filehandle becomes readable (such as during transport negotiation or SSL key management, for example).want_writeready_for_read
want_writeready_for_write
$stream->want_writeready_for_write( $set ) $stream->want_writeready_for_read( $set )
Mutators for the
want_writeready
property on IO::Async::Handle, which control whether thewrite
orread
behaviour should be continued once the filehandle becomes ready for write.Normally,
want_writeready_for_write
is managed by thewrite
method and associated flushing, andwant_writeready_for_read
is not used. However, if a customreader
function is provided, it may find this useful for being invoked again if it cannot proceed with a read operation until the filehandle becomes writable (such as during transport negotiation or SSL key management, for example).close
$stream->close
A synonym for
close_when_empty
. This should not be used when the deferred wait behaviour is required, as the behaviour ofclose
may change in a future version of IO::Async. Instead, callclose_when_empty
directly.close_when_empty
$stream->close_when_empty
If the write buffer is empty, this method calls
close
on the underlying IO handles, and removes the stream from its containing loop. If the write buffer still contains data, then this is deferred until the buffer is empty. This is intended for "write-then-close" one-shot streams.$stream->write( "Here is my final data\n" ); $stream->close_when_empty;
Because of this deferred nature, it may not be suitable for error handling. See instead the
close_now
method.close_now
$stream->close_now
This method immediately closes the underlying IO handles and removes the stream from the containing loop. It will not wait to flush the remaining data in the write buffer.
is_read_eof
is_write_eof
$eof = $stream->is_read_eof $eof = $stream->is_write_eof
Returns true after an EOF condition is reported on either the read or the write handle, respectively.
write
$stream->write( $data, %params )
This method adds data to the outgoing data queue, or writes it immediately, according to the
autoflush
parameter.If the
autoflush
option is set, this method will try immediately to write the data to the underlying filehandle. If this completes successfully then it will have been written by the time this method returns. If it fails to write completely, then the data is queued as ifautoflush
were not set, and will be flushed as normal.$data
can either be a plain string, a Future, or a CODE reference. If it is a plain string it is written immediately. If it is not, its value will be used to generate more$data
values, eventually leading to strings to be written.If
$data
is aFuture
, the Stream will wait until it is ready, and take the single value it yields.If
$data
is a CODE reference, it will be repeatedly invoked to generate new values. Each time the filehandle is ready to write more data to it, the function is invoked. Once the function has finished generating data it should return undef. The function is passed the Stream object as its first argument.It is allowed that
Future
s yield CODE references, or CODE references returnFuture
s, as well as plain strings.For example, to stream the contents of an existing opened filehandle:
open my $fileh, "<", $path or die "Cannot open $path - $!"; $stream->write( sub { my ( $stream ) = @_; sysread $fileh, my $buffer, 8192 or return; return $buffer; } );
Takes the following optional named parameters in
%params
:- write_len => INT
-
Overrides the
write_len
parameter for the data written by this call. - on_write => CODE
-
A CODE reference which will be invoked after every successful
syswrite
operation on the underlying filehandle. It will be passed the number of bytes that were written by this call, which may not be the entire length of the buffer - if it takes more than onesyscall
operation to empty the buffer then this callback will be invoked multiple times.$on_write->( $stream, $len )
- on_flush => CODE
-
A CODE reference which will be invoked once the data queued by this
write
call has been flushed. This will be invoked even if the buffer itself is not yet empty; if more data has been queued since the call.$on_flush->( $stream )
- on_error => CODE
-
A CODE reference which will be invoked if a
syswrite
error happens while performing this write. Invoked as for theStream
'son_write_error
event.$on_error->( $stream, $errno )
If the object is not yet a member of a loop and doesn't yet have a
write_handle
, then calls to thewrite
method will simply queue the data and return. It will be flushed when the object is added to the loop.If
$data
is a defined but empty string, the write is still queued, and theon_flush
continuation will be invoked, if supplied. This can be used to obtain a marker, to invoke some code once the output queue has been flushed up to this point.write (scalar)
$stream->write( ... )->get
If called in non-void context, this method returns a Future which will complete (with no value) when the write operation has been flushed. This may be used as an alternative to, or combined with, the
on_flush
callback.push_on_read
$stream->push_on_read( $on_read )
Pushes a new temporary
on_read
handler to the end of the queue. This queue, if non-empty, is used to provideon_read
event handling code in preference to using the object's main event handler or method. New handlers can be supplied at any time, and they will be used in first-in first-out (FIFO) order.As with the main
on_read
event handler, each can return a (defined) boolean to indicate if they wish to be invoked again or not, anotherCODE
reference to replace themself with, orundef
to indicate it is now complete and should be removed. When a temporary handler returnsundef
it is shifted from the queue and the next one, if present, is invoked instead. If there are no more then the object's main handler is invoked instead.FUTURE-RETURNING READ METHODS
The following methods all return a Future which will become ready when enough data has been read by the Stream into its buffer. At this point, the data is removed from the buffer and given to the
Future
object to complete it.my $f = $stream->read_... my ( $string ) = $f->get;
Unlike the
on_read
event handlers, these methods don't allow for access to "partial" results; they only provide the final result once it is ready.If a
Future
is cancelled before it completes it is removed from the read queue without consuming any data; i.e. eachFuture
atomically either completes or is cancelled.Since it is possible to use a readable
Stream
entirely using theseFuture
-returning methods instead of theon_read
event, it may be useful to configure a trivial return-false event handler to keep it from consuming any input, and to allow it to be added to aLoop
in the first place.my $stream = IO::Async::Stream->new( on_read => sub { 0 }, ... ); $loop->add( $stream ); my $f = $stream->read_...
If a read EOF or error condition happens while there are read
Future
s pending, they are all completed. In the case of a read EOF, they are done withundef
; in the case of a read error they are failed using the$!
error value as the failure.$f->fail( $message, sysread => $! )
If a read EOF condition happens to the currently-processing read
Future
, it will return a partial result. The calling code can detect this by the fact that the returned data is not complete according to the specification (too short inread_exactly
's case, or lacking the ending pattern inread_until
's case). Additionally, eachFuture
will yield the$eof
value in its results.my ( $string, $eof ) = $f->get;
read_atmost
read_exactly
( $string, $eof ) = $stream->read_atmost( $len )->get ( $string, $eof ) = $stream->read_exactly( $len )->get
Completes the
Future
when the read buffer contains$len
or more characters of input.read_atmost
will also complete after the first invocation ofon_read
, even if fewer characters are available, whereasread_exactly
will wait until at least$len
are available.read_until
( $string, $eof ) = $stream->read_until( $end )->get
Completes the
Future
when the read buffer contains a match for$end
, which may either be a plain string or a compiledRegexp
reference. Yields the prefix of the buffer up to and including this match.read_until_eof
( $string, $eof ) = $stream->read_until_eof->get
Completes the
Future
when the stream is eventually closed at EOF, and yields all of the data that was available.UTILITY CONSTRUCTORS
new_for_stdin
new_for_stdout
new_for_stdio
$stream = IO::Async::Stream->new_for_stdin $stream = IO::Async::Stream->new_for_stdout $stream = IO::Async::Stream->new_for_stdio
Return a
IO::Async::Stream
object preconfigured with the correctread_handle
,write_handle
or both.connect
$future = $stream->connect( %args )
A convenient wrapper for calling the
connect
method on the underlying IO::Async::Loop object, passing thesocktype
hint asstream
if not otherwise supplied.DEBUGGING FLAGS
The following flags in
IO_ASYNC_DEBUG_FLAGS
enable extra logging:Sr
-
Log byte buffers as data is read from a Stream
Sw
-
Log byte buffers as data is written to a Stream
EXAMPLES
A line-based
on_read
methodThe following
on_read
method accepts incoming\n
-terminated lines and prints them to the program'sSTDOUT
stream.sub on_read { my $self = shift; my ( $buffref, $eof ) = @_; while( $$buffref =~ s/^(.*\n)// ) { print "Received a line: $1"; } return 0; }
Because a reference to the buffer itself is passed, it is simple to use a
s///
regular expression on the scalar it points at, to both check if data is ready (i.e. a whole line), and to remove it from the buffer. Since it always removes as many complete lines as possible, it doesn't need invoking again when it has finished, so it can return a constant0
.Reading binary data
This
on_read
method accepts incoming records in 16-byte chunks, printing each one.sub on_read { my ( $self, $buffref, $eof ) = @_; if( length $$buffref >= 16 ) { my $record = substr( $$buffref, 0, 16, "" ); print "Received a 16-byte record: $record\n"; return 1; } if( $eof and length $$buffref ) { print "EOF: a partial record still exists\n"; } return 0; }
This time, rather than a
while()
loop we have decided to have the handler just process one record, and use thereturn 1
mechanism to ask that the handler be invoked again if there still remains data that might contain another record; only stopping withreturn 0
when we know we can't find one.The 4-argument form of
substr()
extracts the 16-byte record from the buffer and assigns it to the$record
variable, if there was enough data in the buffer to extract it.A lot of protocols use a fixed-size header, followed by a variable-sized body of data, whose size is given by one of the fields of the header. The following
on_read
method extracts messages in such a protocol.sub on_read { my ( $self, $buffref, $eof ) = @_; return 0 unless length $$buffref >= 8; # "N n n" consumes 8 bytes my ( $len, $x, $y ) = unpack "N n n", $$buffref; return 0 unless length $$buffref >= 8 + $len; substr( $$buffref, 0, 8, "" ); my $data = substr( $$buffref, 0, $len, "" ); print "A record with values x=$x y=$y\n"; return 1; }
In this example, the header is
unpack()
ed first, to extract the body length, and then the body is extracted. If the buffer does not have enough data yet for a complete message then0
is returned, and the buffer is left unmodified for next time. Only when there are enough bytes in total does it usesubstr()
to remove them.Dynamic replacement of
on_read
Consider the following protocol (inspired by IMAP), which consists of
\n
-terminated lines that may have an optional data block attached. The presence of such a data block, as well as its size, is indicated by the line prefix.sub on_read { my $self = shift; my ( $buffref, $eof ) = @_; if( $$buffref =~ s/^DATA (\d+):(.*)\n// ) { my $length = $1; my $line = $2; return sub { my $self = shift; my ( $buffref, $eof ) = @_; return 0 unless length $$buffref >= $length; # Take and remove the data from the buffer my $data = substr( $$buffref, 0, $length, "" ); print "Received a line $line with some data ($data)\n"; return undef; # Restore the original method } } elsif( $$buffref =~ s/^LINE:(.*)\n// ) { my $line = $1; print "Received a line $line with no data\n"; return 1; } else { print STDERR "Unrecognised input\n"; # Handle it somehow } }
In the case where trailing data is supplied, a new temporary
on_read
callback is provided in a closure. This closure captures the$length
variable so it knows how much data to expect. It also captures the$line
variable so it can use it in the event report. When this method has finished reading the data, it reports the event, then restores the original method by returningundef
.SEE ALSO
IO::Handle - Supply object methods for I/O handles
AUTHOR
Paul Evans <leonerd@leonerd.org.uk>
Module Install Instructions
To install IO::Async, copy and paste the appropriate command in to your terminal.
cpanm IO::Async
perl -MCPAN -e shell install IO::Async
For more information on module installation, please visit the detailed CPAN module installation guide.