IO::Async::FileStream(User Contributed Perl DocumentatIO::Async::FileStream(3)NAME
"IO::Async::FileStream" - read the tail of a file
SYNOPSIS
use IO::Async::FileStream;
use IO::Async::Loop;
my $loop = IO::Async::Loop->new;
open my $logh, "<", "var/logs/daemon.log" or
die "Cannot open logfile - $!";
my $filestream = IO::Async::FileStream->new(
read_handle => $logh,
on_initial => sub {
my ( $self ) = @_;
$self->seek_to_last( "\n" );
},
on_read => sub {
my ( $self, $buffref ) = @_;
while( $$buffref =~ s/^(.*\n)// ) {
print "Received a line $1";
}
return 0;
},
);
$loop->add( $filestream );
$loop->run;
DESCRIPTION
This subclass of IO::Async::Stream allows reading the end of a regular
file which is being appended to by some other process. It invokes the
"on_read" event when more data has been added to the file.
This class provides an API identical to "IO::Async::Stream" when given
a "read_handle"; it should be treated similarly. In particular, it can
be given an "on_read" handler, or subclassed to provide an "on_read"
method, or even used as the "transport" for an
"IO::Async::Protocol::Stream" object.
It will not support writing.
To watch a file, directory, or other filesystem entity for updates of
other properties, such as "mtime", see also IO::Async::File.
EVENTS
The following events are invoked, either using subclass methods or CODE
references in parameters.
Because this is a subclass of IO::Async::Stream in read-only mode, all
the events supported by "Stream" relating to the read handle are
supported here. This is not a full list; see also the documentation
relating to "IO::Async::Stream".
$ret = on_read \$buffer, $eof
Invoked when more data is available in the internal receiving buffer.
Note that $eof only indicates that all the data currently available in
the file has now been read; in contrast to a regular
"IO::Async::Stream", this object will not stop watching after this
condition. Instead, it will continue watching the file for updates.
on_truncated
Invoked when the file size shrinks. If this happens, it is presumed
that the file content has been replaced. Reading will then commence
from the start of the file.
on_initial $size
Invoked the first time the file is looked at. It is passed the initial
size of the file. The code implementing this method can use the "seek"
or "seek_to_last" methods to set the initial read position in the file
to skip over some initial content.
This method may be useful to skip initial content in the file, if the
object should only respond to new content added after it was created.
PARAMETERS
The following named parameters may be passed to "new" or "configure",
in addition to the parameters relating to reading supported by
"IO::Async::Stream".
filename => STRING
Optional. If supplied, watches the named file rather than the
filehandle given in "read_handle". The file will be opened by
the constructor, and then watched for renames. If the file is
renamed, the new filename is opened and tracked similarly after
closing the previous file.
interval => NUM
Optional. The interval in seconds to poll the filehandle using
stat(2) looking for size changes. A default of 2 seconds will
be applied if not defined.
METHODS
$filestream->seek( $offset, $whence )
Callable only during the "on_initial" event. Moves the read position in
the filehandle to the given offset. $whence is interpreted as for
"sysseek", should be either "SEEK_SET", "SEEK_CUR" or "SEEK_END". Will
be set to "SEEK_SET" if not provided.
Normally this would be used to seek to the end of the file, for example
on_initial => sub {
my ( $self, $filesize ) = @_;
$self->seek( $filesize );
}
$success = $filestream->seek_to_last( $str_pattern, %opts )
Callable only during the "on_initial" event. Attempts to move the read
position in the filehandle to just after the last occurance of a given
match. $str_pattern may be a literal string or regexp pattern.
Returns a true value if the seek was successful, or false if not. Takes
the following named arguments:
blocksize => INT
Optional. Read the file in blocks of this size. Will take a
default of 8KiB if not defined.
horizon => INT
Optional. Give up looking for a match after this number of
bytes. Will take a default value of 4 times the blocksize if
not defined.
To force it to always search through the entire file contents,
set this explicitly to 0.
Because regular file reading happens synchronously, this entire method
operates entirely synchronously. If the file is very large, it may take
a while to read back through the entire contents. While this is
happening no other events can be invoked in the process.
When looking for a string or regexp match, this method appends the
previously-read buffer to each block read from the file, in case a
match becomes split across two reads. If "blocksize" is reduced to a
very small value, take care to ensure it isn't so small that a match
may not be noticed.
This is most likely useful for seeking after the last complete line in
a line-based log file, to commence reading from the end, while still
managing to capture any partial content that isn't yet a complete line.
on_initial => sub {
my $self = shift;
$self->seek_to_last( "\n" );
}
TODO
· Move the actual file update watching code into "IO::Async::Loop",
possibly as a new watch/unwatch method pair "watch_file".
· Consider if a construction-time parameter of "seek_to_end" or
"seek_to_last" might be neater than a small code block in
"on_initial", if that turns out to be the only or most common form
of use.
AUTHOR
Paul Evans <leonerd@leonerd.org.uk>
perl v5.18.2 2014-05-14 IO::Async::FileStream(3)
