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>