1IO::Async::Stream(3)  User Contributed Perl Documentation IO::Async::Stream(3)
2
3
4

NAME

6       "IO::Async::Stream" - event callbacks and write bufering for a stream
7       filehandle
8

SYNOPSIS

10        use IO::Async::Stream;
11
12        use IO::Async::Loop;
13        my $loop = IO::Async::Loop->new;
14
15        my $stream = IO::Async::Stream->new(
16           read_handle  => \*STDIN,
17           write_handle => \*STDOUT,
18
19           on_read => sub {
20              my ( $self, $buffref, $eof ) = @_;
21
22              while( $$buffref =~ s/^(.*\n)// ) {
23                 print "Received a line $1";
24              }
25
26              if( $eof ) {
27                 print "EOF; last partial line is $$buffref\n";
28              }
29
30              return 0;
31           }
32        );
33
34        $loop->add( $stream );
35
36        $stream->write( "An initial line here\n" );
37

DESCRIPTION

39       This subclass of IO::Async::Handle contains a filehandle that
40       represents a byte-stream. It provides buffering for both incoming and
41       outgoing data. It invokes the "on_read" handler when new data is read
42       from the filehandle. Data may be written to the filehandle by calling
43       the "write" method.
44
45       This class is suitable for any kind of filehandle that provides a
46       possibly-bidirectional reliable byte stream, such as a pipe, TTY, or
47       "SOCK_STREAM" socket (such as TCP or a byte-oriented UNIX local
48       socket). For datagram or raw message-based sockets (such as UDP) see
49       instead IO::Async::Socket.
50

EVENTS

52       The following events are invoked, either using subclass methods or CODE
53       references in parameters:
54
55   $ret = on_read \$buffer, $eof
56       Invoked when more data is available in the internal receiving buffer.
57
58       The first argument is a reference to a plain perl string. The code
59       should inspect and remove any data it likes, but is not required to
60       remove all, or indeed any of the data. Any data remaining in the buffer
61       will be preserved for the next call, the next time more data is
62       received from the handle.
63
64       In this way, it is easy to implement code that reads records of some
65       form when completed, but ignores partially-received records, until all
66       the data is present. If the handler wishes to be immediately invoke a
67       second time, to have another attempt at consuming more content, it
68       should return 1. Otherwise, it should return 0, and the handler will
69       next be invoked when more data has arrived from the underlying read
70       handle and appended to the buffer. This makes it easy to implement code
71       that handles multiple incoming records at the same time. Alternatively,
72       if the handler function already attempts to consume as much as possible
73       from the buffer, it will have no need to return 1 at all.  See the
74       examples at the end of this documentation for more detail.
75
76       The second argument is a scalar indicating whether the stream has
77       reported an end-of-file (EOF) condition. A reference to the buffer is
78       passed to the handler in the usual way, so it may inspect data
79       contained in it. Once the handler returns a false value, it will not be
80       called again, as the handle is now at EOF and no more data can arrive.
81
82       The "on_read" code may also dynamically replace itself with a new
83       callback by returning a CODE reference instead of 0 or 1. The original
84       callback or method that the object first started with may be restored
85       by returning "undef". Whenever the callback is changed in this way, the
86       new code is called again; even if the read buffer is currently empty.
87       See the examples at the end of this documentation for more detail.
88
89       The "push_on_read" method can be used to insert new, temporary handlers
90       that take precedence over the global "on_read" handler. This event is
91       only used if there are no further pending handlers created by
92       "push_on_read".
93
94   on_read_eof
95       Optional. Invoked when the read handle indicates an end-of-file (EOF)
96       condition. If there is any data in the buffer still to be processed,
97       the "on_read" event will be invoked first, before this one.
98
99   on_write_eof
100       Optional. Invoked when the write handle indicates an end-of-file (EOF)
101       condition. Note that this condition can only be detected after a
102       "write" syscall returns the "EPIPE" error. If there is no data pending
103       to be written then it will not be detected yet.
104
105   on_read_error $errno
106       Optional. Invoked when the "sysread" method on the read handle fails.
107
108   on_write_error $errno
109       Optional. Invoked when the "syswrite" method on the write handle fails.
110
111       The "on_read_error" and "on_write_error" handlers are passed the value
112       of $! at the time the error occurred. (The $! variable itself, by its
113       nature, may have changed from the original error by the time this
114       handler runs so it should always use the value passed in).
115
116       If an error occurs when the corresponding error callback is not
117       supplied, and there is not a handler for it, then the "close" method is
118       called instead.
119
120   on_read_high_watermark $length
121   on_read_low_watermark $length
122       Optional. Invoked when the read buffer grows larger than the high
123       watermark or smaller than the low watermark respectively. These are
124       edge-triggered events; they will only be triggered once per crossing,
125       not continuously while the buffer remains above or below the given
126       limit.
127
128       If these event handlers are not defined, the default behaviour is to
129       disable read-ready notifications if the read buffer grows larger than
130       the high watermark (so as to avoid it growing arbitrarily if nothing is
131       consuming it), and re-enable notifications again once something has
132       read enough to cause it to drop. If these events are overridden, the
133       overriding code will have to perform this behaviour if required, by
134       using
135
136        $self->want_readready_for_read(...)
137
138   on_outgoing_empty
139       Optional. Invoked when the writing data buffer becomes empty.
140
141   on_writeable_start
142   on_writeable_stop
143       Optional. These two events inform when the filehandle becomes
144       writeable, and when it stops being writeable. "on_writeable_start" is
145       invoked by the "on_write_ready" event if previously it was known to be
146       not writeable.  "on_writeable_stop" is invoked after a "syswrite"
147       operation fails with "EAGAIN" or "EWOULDBLOCK". These two events track
148       the writeability state, and ensure that only state change cause events
149       to be invoked. A stream starts off being presumed writeable, so the
150       first of these events to be observed will be "on_writeable_stop".
151

PARAMETERS

153       The following named parameters may be passed to "new" or "configure":
154
155   read_handle => IO
156       The IO handle to read from. Must implement "fileno" and "sysread"
157       methods.
158
159   write_handle => IO
160       The IO handle to write to. Must implement "fileno" and "syswrite"
161       methods.
162
163   handle => IO
164       Shortcut to specifying the same IO handle for both of the above.
165
166   on_read => CODE
167   on_read_error => CODE
168   on_outgoing_empty => CODE
169   on_write_error => CODE
170   on_writeable_start => CODE
171   on_writeable_stop => CODE
172       CODE references for event handlers.
173
174   autoflush => BOOL
175       Optional. If true, the "write" method will attempt to write data to the
176       operating system immediately, without waiting for the loop to indicate
177       the filehandle is write-ready. This is useful, for example, on streams
178       that should contain up-to-date logging or console information.
179
180       It currently defaults to false for any file handle, but future versions
181       of IO::Async may enable this by default on STDOUT and STDERR.
182
183   read_len => INT
184       Optional. Sets the buffer size for "read" calls. Defaults to 8 KiBytes.
185
186   read_all => BOOL
187       Optional. If true, attempt to read as much data from the kernel as
188       possible when the handle becomes readable. By default this is turned
189       off, meaning at most one fixed-size buffer is read. If there is still
190       more data in the kernel's buffer, the handle will still be readable,
191       and will be read from again.
192
193       This behaviour allows multiple streams and sockets to be multiplexed
194       simultaneously, meaning that a large bulk transfer on one cannot starve
195       other filehandles of processing time. Turning this option on may
196       improve bulk data transfer rate, at the risk of delaying or stalling
197       processing on other filehandles.
198
199   write_len => INT
200       Optional. Sets the buffer size for "write" calls. Defaults to 8
201       KiBytes.
202
203   write_all => BOOL
204       Optional. Analogous to the "read_all" option, but for writing. When
205       "autoflush" is enabled, this option only affects deferred writing if
206       the initial attempt failed due to buffer space.
207
208   read_high_watermark => INT
209   read_low_watermark => INT
210       Optional. If defined, gives a way to implement flow control or other
211       behaviours that depend on the size of Stream's read buffer.
212
213       If after more data is read from the underlying filehandle the read
214       buffer is now larger than the high watermark, the
215       "on_read_high_watermark" event is triggered (which, by default, will
216       disable read-ready notifications and pause reading from the
217       filehandle).
218
219       If after data is consumed by an "on_read" handler the read buffer is
220       now smaller than the low watermark, the "on_read_low_watermark" event
221       is triggered (which, by default, will re-enable read-ready
222       notifications and resume reading from the filehandle). For to be
223       possible, the read handler would have to be one added by the
224       "push_on_read" method or one of the Future-returning "read_*" methods.
225
226       By default these options are not defined, so this behaviour will not
227       happen.  "read_low_watermark" may not be set to a larger value than
228       "read_high_watermark", but it may be set to a smaller value, creating a
229       hysteresis region. If either option is defined then both must be.
230
231       If these options are used with the default event handlers, be careful
232       not to cause deadlocks by having a high watermark sufficiently low that
233       a single "on_read" invocation might not consider it finished yet.
234
235   reader => STRING|CODE
236   writer => STRING|CODE
237       Optional. If defined, gives the name of a method or a CODE reference to
238       use to implement the actual reading from or writing to the filehandle.
239       These will be invoked as
240
241        $stream->reader( $read_handle, $buffer, $len )
242        $stream->writer( $write_handle, $buffer, $len )
243
244       Each is expected to modify the passed buffer; "reader" by appending to
245       it, "writer" by removing a prefix from it. Each is expected to return a
246       true value on success, zero on EOF, or "undef" with $! set for errors.
247       If not provided, they will be substituted by implenentations using
248       "sysread" and "syswrite" on the underlying handle, respectively.
249
250   close_on_read_eof => BOOL
251       Optional. Usually true, but if set to a false value then the stream
252       will not be "close"d when an EOF condition occurs on read. This is
253       normally not useful as at that point the underlying stream filehandle
254       is no longer useable, but it may be useful for reading regular files,
255       or interacting with TTY devices.
256
257   encoding => STRING
258       If supplied, sets the name of encoding of the underlying stream. If an
259       encoding is set, then the "write" method will expect to receive Unicode
260       strings and encodes them into bytes, and incoming bytes will be decoded
261       into Unicode strings for the "on_read" event.
262
263       If an encoding is not supplied then "write" and "on_read" will work in
264       byte strings.
265
266       IMPORTANT NOTE: in order to handle reads of UTF-8 content or other
267       multibyte encodings, the code implementing the "on_read" event uses a
268       feature of Encode; the "STOP_AT_PARTIAL" flag. While this flag has
269       existed for a while and is used by the ":encoding" PerlIO layer itself
270       for similar purposes, the flag is not officially documented by the
271       "Encode" module. In principle this undocumented feature could be
272       subject to change, in practice I believe it to be reasonably stable.
273
274       This note applies only to the "on_read" event; data written using the
275       "write" method does not rely on any undocumented features of "Encode".
276
277       If a read handle is given, it is required that either an "on_read"
278       callback reference is configured, or that the object provides an
279       "on_read" method. It is optional whether either is true for
280       "on_outgoing_empty"; if neither is supplied then no action will be
281       taken when the writing buffer becomes empty.
282
283       An "on_read" handler may be supplied even if no read handle is yet
284       given, to be used when a read handle is eventually provided by the
285       "set_handles" method.
286
287       This condition is checked at the time the object is added to a Loop; it
288       is allowed to create a "IO::Async::Stream" object with a read handle
289       but without a "on_read" handler, provided that one is later given using
290       "configure" before the stream is added to its containing Loop, either
291       directly or by being a child of another Notifier already in a Loop, or
292       added to one.
293

METHODS

295       The following methods documented with a trailing call to "->get" return
296       Future instances.
297
298   want_readready_for_read
299   want_readready_for_write
300          $stream->want_readready_for_read( $set )
301
302          $stream->want_readready_for_write( $set )
303
304       Mutators for the "want_readready" property on IO::Async::Handle, which
305       control whether the "read" or "write" behaviour should be continued
306       once the filehandle becomes ready for read.
307
308       Normally, "want_readready_for_read" is always true (though the read
309       watermark behaviour can modify it), and "want_readready_for_write" is
310       not used.  However, if a custom "writer" function is provided, it may
311       find this useful for being invoked again if it cannot proceed with a
312       write operation until the filehandle becomes readable (such as during
313       transport negotiation or SSL key management, for example).
314
315   want_writeready_for_read
316   want_writeready_for_write
317          $stream->want_writeready_for_write( $set )
318
319          $stream->want_writeready_for_read( $set )
320
321       Mutators for the "want_writeready" property on IO::Async::Handle, which
322       control whether the "write" or "read" behaviour should be continued
323       once the filehandle becomes ready for write.
324
325       Normally, "want_writeready_for_write" is managed by the "write" method
326       and associated flushing, and "want_writeready_for_read" is not used.
327       However, if a custom "reader" function is provided, it may find this
328       useful for being invoked again if it cannot proceed with a read
329       operation until the filehandle becomes writable (such as during
330       transport negotiation or SSL key management, for example).
331
332   close
333          $stream->close
334
335       A synonym for "close_when_empty". This should not be used when the
336       deferred wait behaviour is required, as the behaviour of "close" may
337       change in a future version of IO::Async. Instead, call
338       "close_when_empty" directly.
339
340   close_when_empty
341          $stream->close_when_empty
342
343       If the write buffer is empty, this method calls "close" on the
344       underlying IO handles, and removes the stream from its containing loop.
345       If the write buffer still contains data, then this is deferred until
346       the buffer is empty. This is intended for "write-then-close" one-shot
347       streams.
348
349        $stream->write( "Here is my final data\n" );
350        $stream->close_when_empty;
351
352       Because of this deferred nature, it may not be suitable for error
353       handling.  See instead the "close_now" method.
354
355   close_now
356          $stream->close_now
357
358       This method immediately closes the underlying IO handles and removes
359       the stream from the containing loop. It will not wait to flush the
360       remaining data in the write buffer.
361
362   is_read_eof
363   is_write_eof
364          $eof = $stream->is_read_eof
365
366          $eof = $stream->is_write_eof
367
368       Returns true after an EOF condition is reported on either the read or
369       the write handle, respectively.
370
371   write
372          $stream->write( $data, %params )
373
374       This method adds data to the outgoing data queue, or writes it
375       immediately, according to the "autoflush" parameter.
376
377       If the "autoflush" option is set, this method will try immediately to
378       write the data to the underlying filehandle. If this completes
379       successfully then it will have been written by the time this method
380       returns. If it fails to write completely, then the data is queued as if
381       "autoflush" were not set, and will be flushed as normal.
382
383       $data can either be a plain string, a Future, or a CODE reference. If
384       it is a plain string it is written immediately. If it is not, its value
385       will be used to generate more $data values, eventually leading to
386       strings to be written.
387
388       If $data is a "Future", the Stream will wait until it is ready, and
389       take the single value it yields.
390
391       If $data is a CODE reference, it will be repeatedly invoked to generate
392       new values. Each time the filehandle is ready to write more data to it,
393       the function is invoked. Once the function has finished generating data
394       it should return undef. The function is passed the Stream object as its
395       first argument.
396
397       It is allowed that "Future"s yield CODE references, or CODE references
398       return "Future"s, as well as plain strings.
399
400       For example, to stream the contents of an existing opened filehandle:
401
402        open my $fileh, "<", $path or die "Cannot open $path - $!";
403
404        $stream->write( sub {
405           my ( $stream ) = @_;
406
407           sysread $fileh, my $buffer, 8192 or return;
408           return $buffer;
409        } );
410
411       Takes the following optional named parameters in %params:
412
413       write_len => INT
414               Overrides the "write_len" parameter for the data written by
415               this call.
416
417       on_write => CODE
418               A CODE reference which will be invoked after every successful
419               "syswrite" operation on the underlying filehandle. It will be
420               passed the number of bytes that were written by this call,
421               which may not be the entire length of the buffer - if it takes
422               more than one "syscall" operation to empty the buffer then this
423               callback will be invoked multiple times.
424
425                $on_write->( $stream, $len )
426
427       on_flush => CODE
428               A CODE reference which will be invoked once the data queued by
429               this "write" call has been flushed. This will be invoked even
430               if the buffer itself is not yet empty; if more data has been
431               queued since the call.
432
433                $on_flush->( $stream )
434
435       on_error => CODE
436               A CODE reference which will be invoked if a "syswrite" error
437               happens while performing this write. Invoked as for the
438               "Stream"'s "on_write_error" event.
439
440                $on_error->( $stream, $errno )
441
442       If the object is not yet a member of a loop and doesn't yet have a
443       "write_handle", then calls to the "write" method will simply queue the
444       data and return. It will be flushed when the object is added to the
445       loop.
446
447       If $data is a defined but empty string, the write is still queued, and
448       the "on_flush" continuation will be invoked, if supplied. This can be
449       used to obtain a marker, to invoke some code once the output queue has
450       been flushed up to this point.
451
452   write (scalar)
453          $stream->write( ... )->get
454
455       If called in non-void context, this method returns a Future which will
456       complete (with no value) when the write operation has been flushed.
457       This may be used as an alternative to, or combined with, the "on_flush"
458       callback.
459
460   push_on_read
461          $stream->push_on_read( $on_read )
462
463       Pushes a new temporary "on_read" handler to the end of the queue. This
464       queue, if non-empty, is used to provide "on_read" event handling code
465       in preference to using the object's main event handler or method. New
466       handlers can be supplied at any time, and they will be used in first-in
467       first-out (FIFO) order.
468
469       As with the main "on_read" event handler, each can return a (defined)
470       boolean to indicate if they wish to be invoked again or not, another
471       "CODE" reference to replace themself with, or "undef" to indicate it is
472       now complete and should be removed. When a temporary handler returns
473       "undef" it is shifted from the queue and the next one, if present, is
474       invoked instead. If there are no more then the object's main handler is
475       invoked instead.
476

FUTURE-RETURNING READ METHODS

478       The following methods all return a Future which will become ready when
479       enough data has been read by the Stream into its buffer. At this point,
480       the data is removed from the buffer and given to the "Future" object to
481       complete it.
482
483        my $f = $stream->read_...
484
485        my ( $string ) = $f->get;
486
487       Unlike the "on_read" event handlers, these methods don't allow for
488       access to "partial" results; they only provide the final result once it
489       is ready.
490
491       If a "Future" is cancelled before it completes it is removed from the
492       read queue without consuming any data; i.e. each "Future" atomically
493       either completes or is cancelled.
494
495       Since it is possible to use a readable "Stream" entirely using these
496       "Future"-returning methods instead of the "on_read" event, it may be
497       useful to configure a trivial return-false event handler to keep it
498       from consuming any input, and to allow it to be added to a "Loop" in
499       the first place.
500
501        my $stream = IO::Async::Stream->new( on_read => sub { 0 }, ... );
502        $loop->add( $stream );
503
504        my $f = $stream->read_...
505
506       If a read EOF or error condition happens while there are read "Future"s
507       pending, they are all completed. In the case of a read EOF, they are
508       done with "undef"; in the case of a read error they are failed using
509       the $! error value as the failure.
510
511        $f->fail( $message, sysread => $! )
512
513       If a read EOF condition happens to the currently-processing read
514       "Future", it will return a partial result. The calling code can detect
515       this by the fact that the returned data is not complete according to
516       the specification (too short in "read_exactly"'s case, or lacking the
517       ending pattern in "read_until"'s case). Additionally, each "Future"
518       will yield the $eof value in its results.
519
520        my ( $string, $eof ) = $f->get;
521
522   read_atmost
523   read_exactly
524          ( $string, $eof ) = $stream->read_atmost( $len )->get
525
526          ( $string, $eof ) = $stream->read_exactly( $len )->get
527
528       Completes the "Future" when the read buffer contains $len or more
529       characters of input. "read_atmost" will also complete after the first
530       invocation of "on_read", even if fewer characters are available,
531       whereas "read_exactly" will wait until at least $len are available.
532
533   read_until
534          ( $string, $eof ) = $stream->read_until( $end )->get
535
536       Completes the "Future" when the read buffer contains a match for $end,
537       which may either be a plain string or a compiled "Regexp" reference.
538       Yields the prefix of the buffer up to and including this match.
539
540   read_until_eof
541          ( $string, $eof ) = $stream->read_until_eof->get
542
543       Completes the "Future" when the stream is eventually closed at EOF, and
544       yields all of the data that was available.
545

UTILITY CONSTRUCTORS

547   new_for_stdin
548   new_for_stdout
549   new_for_stdio
550          $stream = IO::Async::Stream->new_for_stdin
551
552          $stream = IO::Async::Stream->new_for_stdout
553
554          $stream = IO::Async::Stream->new_for_stdio
555
556       Return a "IO::Async::Stream" object preconfigured with the correct
557       "read_handle", "write_handle" or both.
558
559   connect
560          $future = $stream->connect( %args )
561
562       A convenient wrapper for calling the "connect" method on the underlying
563       IO::Async::Loop object, passing the "socktype" hint as "stream" if not
564       otherwise supplied.
565

DEBUGGING FLAGS

567       The following flags in "IO_ASYNC_DEBUG_FLAGS" enable extra logging:
568
569       "Sr"
570           Log byte buffers as data is read from a Stream
571
572       "Sw"
573           Log byte buffers as data is written to a Stream
574

EXAMPLES

576   A line-based "on_read" method
577       The following "on_read" method accepts incoming "\n"-terminated lines
578       and prints them to the program's "STDOUT" stream.
579
580        sub on_read
581        {
582           my $self = shift;
583           my ( $buffref, $eof ) = @_;
584
585           while( $$buffref =~ s/^(.*\n)// ) {
586              print "Received a line: $1";
587           }
588
589           return 0;
590        }
591
592       Because a reference to the buffer itself is passed, it is simple to use
593       a "s///" regular expression on the scalar it points at, to both check
594       if data is ready (i.e. a whole line), and to remove it from the buffer.
595       Since it always removes as many complete lines as possible, it doesn't
596       need invoking again when it has finished, so it can return a constant
597       0.
598
599   Reading binary data
600       This "on_read" method accepts incoming records in 16-byte chunks,
601       printing each one.
602
603        sub on_read
604        {
605           my ( $self, $buffref, $eof ) = @_;
606
607           if( length $$buffref >= 16 ) {
608              my $record = substr( $$buffref, 0, 16, "" );
609              print "Received a 16-byte record: $record\n";
610
611              return 1;
612           }
613
614           if( $eof and length $$buffref ) {
615              print "EOF: a partial record still exists\n";
616           }
617
618           return 0;
619        }
620
621       This time, rather than a "while()" loop we have decided to have the
622       handler just process one record, and use the "return 1" mechanism to
623       ask that the handler be invoked again if there still remains data that
624       might contain another record; only stopping with "return 0" when we
625       know we can't find one.
626
627       The 4-argument form of "substr()" extracts the 16-byte record from the
628       buffer and assigns it to the $record variable, if there was enough data
629       in the buffer to extract it.
630
631       A lot of protocols use a fixed-size header, followed by a variable-
632       sized body of data, whose size is given by one of the fields of the
633       header. The following "on_read" method extracts messages in such a
634       protocol.
635
636        sub on_read
637        {
638           my ( $self, $buffref, $eof ) = @_;
639
640           return 0 unless length $$buffref >= 8; # "N n n" consumes 8 bytes
641
642           my ( $len, $x, $y ) = unpack "N n n", $$buffref;
643
644           return 0 unless length $$buffref >= 8 + $len;
645
646           substr( $$buffref, 0, 8, "" );
647           my $data = substr( $$buffref, 0, $len, "" );
648
649           print "A record with values x=$x y=$y\n";
650
651           return 1;
652        }
653
654       In this example, the header is "unpack()"ed first, to extract the body
655       length, and then the body is extracted. If the buffer does not have
656       enough data yet for a complete message then 0 is returned, and the
657       buffer is left unmodified for next time. Only when there are enough
658       bytes in total does it use "substr()" to remove them.
659
660   Dynamic replacement of "on_read"
661       Consider the following protocol (inspired by IMAP), which consists of
662       "\n"-terminated lines that may have an optional data block attached.
663       The presence of such a data block, as well as its size, is indicated by
664       the line prefix.
665
666        sub on_read
667        {
668           my $self = shift;
669           my ( $buffref, $eof ) = @_;
670
671           if( $$buffref =~ s/^DATA (\d+):(.*)\n// ) {
672              my $length = $1;
673              my $line   = $2;
674
675              return sub {
676                 my $self = shift;
677                 my ( $buffref, $eof ) = @_;
678
679                 return 0 unless length $$buffref >= $length;
680
681                 # Take and remove the data from the buffer
682                 my $data = substr( $$buffref, 0, $length, "" );
683
684                 print "Received a line $line with some data ($data)\n";
685
686                 return undef; # Restore the original method
687              }
688           }
689           elsif( $$buffref =~ s/^LINE:(.*)\n// ) {
690              my $line = $1;
691
692              print "Received a line $line with no data\n";
693
694              return 1;
695           }
696           else {
697              print STDERR "Unrecognised input\n";
698              # Handle it somehow
699           }
700        }
701
702       In the case where trailing data is supplied, a new temporary "on_read"
703       callback is provided in a closure. This closure captures the $length
704       variable so it knows how much data to expect. It also captures the
705       $line variable so it can use it in the event report. When this method
706       has finished reading the data, it reports the event, then restores the
707       original method by returning "undef".
708

SEE ALSO

710       ยท   IO::Handle - Supply object methods for I/O handles
711

AUTHOR

713       Paul Evans <leonerd@leonerd.org.uk>
714
715
716
717perl v5.30.0                      2019-07-26              IO::Async::Stream(3)
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