AnyEvent::Handle(3pm) User Contributed Perl DocumentationAnyEvent::Handle(3pm)
NAME
AnyEvent::Handle - non-blocking I/O on streaming handles via AnyEvent
SYNOPSIS
use AnyEvent;
use AnyEvent::Handle;
my $cv = AnyEvent->condvar;
my $hdl; $hdl = new AnyEvent::Handle
fh => \*STDIN,
on_error => sub {
my ($hdl, $fatal, $msg) = @_;
AE::log error => $msg;
$hdl->destroy;
$cv->send;
};
# send some request line
$hdl->push_write ("getinfo\015\012");
# read the response line
$hdl->push_read (line => sub {
my ($hdl, $line) = @_;
say "got line <$line>";
$cv->send;
});
$cv->recv;
DESCRIPTION
This is a helper module to make it easier to do event-based I/O on
stream-based filehandles (sockets, pipes, and other stream things).
Specifically, it doesn't work as expected on files, packet-based
sockets or similar things.
The AnyEvent::Intro tutorial contains some well-documented
AnyEvent::Handle examples.
In the following, where the documentation refers to "bytes", it means
characters. As sysread and syswrite are used for all I/O, their
treatment of characters applies to this module as well.
At the very minimum, you should specify "fh" or "connect", and the
"on_error" callback.
All callbacks will be invoked with the handle object as their first
argument.
METHODS
$handle = new AnyEvent::Handle fh => $filehandle, key => value...
The constructor supports these arguments (all as "key => value"
pairs).
fh => $filehandle ["fh" or "connect" MANDATORY]
The filehandle this AnyEvent::Handle object will operate on.
NOTE: The filehandle will be set to non-blocking mode (using
"AnyEvent::fh_unblock") by the constructor and needs to stay in
that mode.
connect => [$host, $service] ["fh" or "connect" MANDATORY]
Try to connect to the specified host and service (port), using
"AnyEvent::Socket::tcp_connect". The $host additionally becomes
the default "peername".
You have to specify either this parameter, or "fh", above.
It is possible to push requests on the read and write queues,
and modify properties of the stream, even while
AnyEvent::Handle is connecting.
When this parameter is specified, then the "on_prepare",
"on_connect_error" and "on_connect" callbacks will be called
under the appropriate circumstances:
on_prepare => $cb->($handle)
This (rarely used) callback is called before a new
connection is attempted, but after the file handle has been
created (you can access that file handle via
"$handle->{fh}"). It could be used to prepare the file
handle with parameters required for the actual connect (as
opposed to settings that can be changed when the connection
is already established).
The return value of this callback should be the connect
timeout value in seconds (or 0, or "undef", or the empty
list, to indicate that the default timeout is to be used).
on_connect => $cb->($handle, $host, $port, $retry->())
This callback is called when a connection has been
successfully established.
The peer's numeric host and port (the socket peername) are
passed as parameters, together with a retry callback. At
the time it is called the read and write queues, EOF
status, TLS status and similar properties of the handle
will have been reset.
If, for some reason, the handle is not acceptable, calling
$retry will continue with the next connection target (in
case of multi-homed hosts or SRV records there can be
multiple connection endpoints). The $retry callback can be
invoked after the connect callback returns, i.e. one can
start a handshake and then decide to retry with the next
host if the handshake fails.
In most cases, you should ignore the $retry parameter.
on_connect_error => $cb->($handle, $message)
This callback is called when the connection could not be
established. $! will contain the relevant error code, and
$message a message describing it (usually the same as
"$!").
If this callback isn't specified, then "on_error" will be
called with a fatal error instead.
on_error => $cb->($handle, $fatal, $message)
This is the error callback, which is called when, well, some
error occurred, such as not being able to resolve the hostname,
failure to connect, or a read error.
Some errors are fatal (which is indicated by $fatal being
true). On fatal errors the handle object will be destroyed (by
a call to "-> destroy") after invoking the error callback
(which means you are free to examine the handle object).
Examples of fatal errors are an EOF condition with active (but
unsatisfiable) read watchers ("EPIPE") or I/O errors. In cases
where the other side can close the connection at will, it is
often easiest to not report "EPIPE" errors in this callback.
AnyEvent::Handle tries to find an appropriate error code for
you to check against, but in some cases (TLS errors), this does
not work well.
If you report the error to the user, it is recommended to
always output the $message argument in human-readable error
messages (you don't need to report "$!" if you report
$message).
If you want to react programmatically to the error, then
looking at $! and comparing it against some of the documented
"Errno" values is usually better than looking at the $message.
Non-fatal errors can be retried by returning, but it is
recommended to simply ignore this parameter and instead abondon
the handle object when this callback is invoked. Examples of
non-fatal errors are timeouts "ETIMEDOUT") or badly-formatted
data ("EBADMSG").
On entry to the callback, the value of $! contains the
operating system error code (or "ENOSPC", "EPIPE", "ETIMEDOUT",
"EBADMSG" or "EPROTO").
While not mandatory, it is highly recommended to set this
callback, as you will not be notified of errors otherwise. The
default just calls "croak".
on_read => $cb->($handle)
This sets the default read callback, which is called when data
arrives and no read request is in the queue (unlike read queue
callbacks, this callback will only be called when at least one
octet of data is in the read buffer).
To access (and remove data from) the read buffer, use the
"->rbuf" method or access the "$handle->{rbuf}" member
directly. Note that you must not enlarge or modify the read
buffer, you can only remove data at the beginning from it.
You can also call "->push_read (...)" or any other function
that modifies the read queue. Or do both. Or ...
When an EOF condition is detected, AnyEvent::Handle will first
try to feed all the remaining data to the queued callbacks and
"on_read" before calling the "on_eof" callback. If no progress
can be made, then a fatal error will be raised (with $! set to
"EPIPE").
Note that, unlike requests in the read queue, an "on_read"
callback doesn't mean you require some data: if there is an EOF
and there are outstanding read requests then an error will be
flagged. With an "on_read" callback, the "on_eof" callback will
be invoked.
on_eof => $cb->($handle)
Set the callback to be called when an end-of-file condition is
detected, i.e. in the case of a socket, when the other side has
closed the connection cleanly, and there are no outstanding
read requests in the queue (if there are read requests, then an
EOF counts as an unexpected connection close and will be
flagged as an error).
For sockets, this just means that the other side has stopped
sending data, you can still try to write data, and, in fact,
one can return from the EOF callback and continue writing data,
as only the read part has been shut down.
If an EOF condition has been detected but no "on_eof" callback
has been set, then a fatal error will be raised with $! set to
<0>.
on_drain => $cb->($handle)
This sets the callback that is called once when the write
buffer becomes empty (and immediately when the handle object is
created).
To append to the write buffer, use the "->push_write" method.
This callback is useful when you don't want to put all of your
write data into the queue at once, for example, when you want
to write the contents of some file to the socket you might not
want to read the whole file into memory and push it into the
queue, but instead only read more data from the file when the
write queue becomes empty.
timeout => $fractional_seconds
rtimeout => $fractional_seconds
wtimeout => $fractional_seconds
If non-zero, then these enables an "inactivity" timeout:
whenever this many seconds pass without a successful read or
write on the underlying file handle (or a call to
"timeout_reset"), the "on_timeout" callback will be invoked
(and if that one is missing, a non-fatal "ETIMEDOUT" error will
be raised).
There are three variants of the timeouts that work
independently of each other, for both read and write (triggered
when nothing was read OR written), just read (triggered when
nothing was read), and just write: "timeout", "rtimeout" and
"wtimeout", with corresponding callbacks "on_timeout",
"on_rtimeout" and "on_wtimeout", and reset functions
"timeout_reset", "rtimeout_reset", and "wtimeout_reset".
Note that timeout processing is active even when you do not
have any outstanding read or write requests: If you plan to
keep the connection idle then you should disable the timeout
temporarily or ignore the timeout in the corresponding
"on_timeout" callback, in which case AnyEvent::Handle will
simply restart the timeout.
Zero (the default) disables the corresponding timeout.
on_timeout => $cb->($handle)
on_rtimeout => $cb->($handle)
on_wtimeout => $cb->($handle)
Called whenever the inactivity timeout passes. If you return
from this callback, then the timeout will be reset as if some
activity had happened, so this condition is not fatal in any
way.
rbuf_max => <bytes>
If defined, then a fatal error will be raised (with $! set to
"ENOSPC") when the read buffer ever (strictly) exceeds this
size. This is useful to avoid some forms of denial-of-service
attacks.
For example, a server accepting connections from untrusted
sources should be configured to accept only so-and-so much data
that it cannot act on (for example, when expecting a line, an
attacker could send an unlimited amount of data without a
callback ever being called as long as the line isn't finished).
wbuf_max => <bytes>
If defined, then a fatal error will be raised (with $! set to
"ENOSPC") when the write buffer ever (strictly) exceeds this
size. This is useful to avoid some forms of denial-of-service
attacks.
Although the units of this parameter is bytes, this is the raw
number of bytes not yet accepted by the kernel. This can make a
difference when you e.g. use TLS, as TLS typically makes your
write data larger (but it can also make it smaller due to
compression).
As an example of when this limit is useful, take a chat server
that sends chat messages to a client. If the client does not
read those in a timely manner then the send buffer in the
server would grow unbounded.
autocork => <boolean>
When disabled (the default), "push_write" will try to
immediately write the data to the handle if possible. This
avoids having to register a write watcher and wait for the next
event loop iteration, but can be inefficient if you write
multiple small chunks (on the wire, this disadvantage is
usually avoided by your kernel's nagle algorithm, see
"no_delay", but this option can save costly syscalls).
When enabled, writes will always be queued till the next event
loop iteration. This is efficient when you do many small writes
per iteration, but less efficient when you do a single write
only per iteration (or when the write buffer often is full). It
also increases write latency.
no_delay => <boolean>
When doing small writes on sockets, your operating system
kernel might wait a bit for more data before actually sending
it out. This is called the Nagle algorithm, and usually it is
beneficial.
In some situations you want as low a delay as possible, which
can be accomplishd by setting this option to a true value.
The default is your operating system's default behaviour (most
likely enabled). This option explicitly enables or disables it,
if possible.
keepalive => <boolean>
Enables (default disable) the SO_KEEPALIVE option on the stream
socket: normally, TCP connections have no time-out once
established, so TCP connections, once established, can stay
alive forever even when the other side has long gone. TCP
keepalives are a cheap way to take down long-lived TCP
connections when the other side becomes unreachable. While the
default is OS-dependent, TCP keepalives usually kick in after
around two hours, and, if the other side doesn't reply, take
down the TCP connection some 10 to 15 minutes later.
It is harmless to specify this option for file handles that do
not support keepalives, and enabling it on connections that are
potentially long-lived is usually a good idea.
oobinline => <boolean>
BSD majorly fucked up the implementation of TCP urgent data.
The result is that almost no OS implements TCP according to the
specs, and every OS implements it slightly differently.
If you want to handle TCP urgent data, then setting this flag
(the default is enabled) gives you the most portable way of
getting urgent data, by putting it into the stream.
Since BSD emulation of OOB data on top of TCP's urgent data can
have security implications, AnyEvent::Handle sets this flag
automatically unless explicitly specified. Note that setting
this flag after establishing a connection may be a bit too late
(data loss could already have occurred on BSD systems), but at
least it will protect you from most attacks.
read_size => <bytes>
The initial read block size, the number of bytes this module
will try to read during each loop iteration. Each handle object
will consume at least this amount of memory for the read buffer
as well, so when handling many connections watch out for memory
requirements). See also "max_read_size". Default: 2048.
max_read_size => <bytes>
The maximum read buffer size used by the dynamic adjustment
algorithm: Each time AnyEvent::Handle can read "read_size"
bytes in one go it will double "read_size" up to the maximum
given by this option. Default: 131072 or "read_size", whichever
is higher.
low_water_mark => <bytes>
Sets the number of bytes (default: 0) that make up an "empty"
write buffer: If the buffer reaches this size or gets even
samller it is considered empty.
Sometimes it can be beneficial (for performance reasons) to add
data to the write buffer before it is fully drained, but this
is a rare case, as the operating system kernel usually buffers
data as well, so the default is good in almost all cases.
linger => <seconds>
If this is non-zero (default: 3600), the destructor of the
AnyEvent::Handle object will check whether there is still
outstanding write data and will install a watcher that will
write this data to the socket. No errors will be reported (this
mostly matches how the operating system treats outstanding data
at socket close time).
This will not work for partial TLS data that could not be
encoded yet. This data will be lost. Calling the "stoptls"
method in time might help.
peername => $string
A string used to identify the remote site - usually the DNS
hostname (not IDN!) used to create the connection, rarely the
IP address.
Apart from being useful in error messages, this string is also
used in TLS peername verification (see "verify_peername" in
AnyEvent::TLS). This verification will be skipped when
"peername" is not specified or is "undef".
tls => "accept" | "connect" | Net::SSLeay::SSL object
When this parameter is given, it enables TLS (SSL) mode, that
means AnyEvent will start a TLS handshake as soon as the
connection has been established and will transparently
encrypt/decrypt data afterwards.
All TLS protocol errors will be signalled as "EPROTO", with an
appropriate error message.
TLS mode requires Net::SSLeay to be installed (it will be
loaded automatically when you try to create a TLS handle): this
module doesn't have a dependency on that module, so if your
module requires it, you have to add the dependency yourself. If
Net::SSLeay cannot be loaded or is too old, you get an "EPROTO"
error.
Unlike TCP, TLS has a server and client side: for the TLS
server side, use "accept", and for the TLS client side of a
connection, use "connect" mode.
You can also provide your own TLS connection object, but you
have to make sure that you call either
"Net::SSLeay::set_connect_state" or
"Net::SSLeay::set_accept_state" on it before you pass it to
AnyEvent::Handle. Also, this module will take ownership of this
connection object.
At some future point, AnyEvent::Handle might switch to another
TLS implementation, then the option to use your own session
object will go away.
IMPORTANT: since Net::SSLeay "objects" are really only
integers, passing in the wrong integer will lead to certain
crash. This most often happens when one uses a stylish "tls =>
1" and is surprised about the segmentation fault.
Use the "->starttls" method if you need to start TLS
negotiation later.
tls_ctx => $anyevent_tls
Use the given "AnyEvent::TLS" object to create the new TLS
connection (unless a connection object was specified directly).
If this parameter is missing (or "undef"), then
AnyEvent::Handle will use "AnyEvent::Handle::TLS_CTX".
Instead of an object, you can also specify a hash reference
with "key => value" pairs. Those will be passed to
AnyEvent::TLS to create a new TLS context object.
on_starttls => $cb->($handle, $success[, $error_message])
This callback will be invoked when the TLS/SSL handshake has
finished. If $success is true, then the TLS handshake
succeeded, otherwise it failed ("on_stoptls" will not be called
in this case).
The session in "$handle->{tls}" can still be examined in this
callback, even when the handshake was not successful.
TLS handshake failures will not cause "on_error" to be invoked
when this callback is in effect, instead, the error message
will be passed to "on_starttls".
Without this callback, handshake failures lead to "on_error"
being called as usual.
Note that you cannot just call "starttls" again in this
callback. If you need to do that, start an zero-second timer
instead whose callback can then call "->starttls" again.
on_stoptls => $cb->($handle)
When a SSLv3/TLS shutdown/close notify/EOF is detected and this
callback is set, then it will be invoked after freeing the TLS
session. If it is not, then a TLS shutdown condition will be
treated like a normal EOF condition on the handle.
The session in "$handle->{tls}" can still be examined in this
callback.
This callback will only be called on TLS shutdowns, not when
the underlying handle signals EOF.
json => JSON, JSON::PP or JSON::XS object
This is the json coder object used by the "json" read and write
types.
If you don't supply it, then AnyEvent::Handle will create and
use a suitable one (on demand), which will write and expect
UTF-8 encoded JSON texts (either using JSON::XS or JSON). The
written texts are guaranteed not to contain any newline
character.
For security reasons, this encoder will likely not handle
numbers and strings, only arrays and objects/hashes. The reason
is that originally JSON was self-delimited, but Dougles
Crockford thought it was a splendid idea to redefine JSON
incompatibly, so this is no longer true.
For protocols that used back-to-back JSON texts, this might
lead to run-ins, where two or more JSON texts will be
interpreted as one JSON text.
For this reason, if the default encoder uses JSON::XS, it will
default to not allowing anything but arrays and objects/hashes,
at least for the foreseeable future (it will change at some
point). This might or might not be true for the JSON module, so
this might cause a security issue.
If you depend on either behaviour, you should create your own
json object and pass it in explicitly.
cbor => CBOR::XS object
This is the cbor coder object used by the "cbor" read and write
types.
If you don't supply it, then AnyEvent::Handle will create and
use a suitable one (on demand), which will write CBOR without
using extensions, if possible.
Note that you are responsible to depend on the CBOR::XS module
if you want to use this functionality, as AnyEvent does not
have a dependency on it itself.
$fh = $handle->fh
This method returns the file handle used to create the
AnyEvent::Handle object.
$handle->on_error ($cb)
Replace the current "on_error" callback (see the "on_error"
constructor argument).
$handle->on_eof ($cb)
Replace the current "on_eof" callback (see the "on_eof" constructor
argument).
$handle->on_timeout ($cb)
$handle->on_rtimeout ($cb)
$handle->on_wtimeout ($cb)
Replace the current "on_timeout", "on_rtimeout" or "on_wtimeout"
callback, or disables the callback (but not the timeout) if $cb =
"undef". See the "timeout" constructor argument and method.
$handle->autocork ($boolean)
Enables or disables the current autocork behaviour (see "autocork"
constructor argument). Changes will only take effect on the next
write.
$handle->no_delay ($boolean)
Enables or disables the "no_delay" setting (see constructor
argument of the same name for details).
$handle->keepalive ($boolean)
Enables or disables the "keepalive" setting (see constructor
argument of the same name for details).
$handle->oobinline ($boolean)
Enables or disables the "oobinline" setting (see constructor
argument of the same name for details).
$handle->on_starttls ($cb)
Replace the current "on_starttls" callback (see the "on_starttls"
constructor argument).
$handle->on_stoptls ($cb)
Replace the current "on_stoptls" callback (see the "on_stoptls"
constructor argument).
$handle->rbuf_max ($max_octets)
Configures the "rbuf_max" setting ("undef" disables it).
$handle->wbuf_max ($max_octets)
Configures the "wbuf_max" setting ("undef" disables it).
$handle->timeout ($seconds)
$handle->rtimeout ($seconds)
$handle->wtimeout ($seconds)
Configures (or disables) the inactivity timeout.
The timeout will be checked instantly, so this method might destroy
the handle before it returns.
$handle->timeout_reset
$handle->rtimeout_reset
$handle->wtimeout_reset
Reset the activity timeout, as if data was received or sent.
These methods are cheap to call.
WRITE QUEUE
AnyEvent::Handle manages two queues per handle, one for writing and one
for reading.
The write queue is very simple: you can add data to its end, and
AnyEvent::Handle will automatically try to get rid of it for you.
When data could be written and the write buffer is shorter then the low
water mark, the "on_drain" callback will be invoked once.
$handle->on_drain ($cb)
Sets the "on_drain" callback or clears it (see the description of
"on_drain" in the constructor).
This method may invoke callbacks (and therefore the handle might be
destroyed after it returns).
$handle->push_write ($data)
Queues the given scalar to be written. You can push as much data as
you want (only limited by the available memory and "wbuf_max"), as
"AnyEvent::Handle" buffers it independently of the kernel.
This method may invoke callbacks (and therefore the handle might be
destroyed after it returns).
$handle->push_write (type => @args)
Instead of formatting your data yourself, you can also let this
module do the job by specifying a type and type-specific arguments.
You can also specify the (fully qualified) name of a package, in
which case AnyEvent tries to load the package and then expects to
find the "anyevent_write_type" function inside (see "custom write
types", below).
Predefined types are (if you have ideas for additional types, feel
free to drop by and tell us):
netstring => $string
Formats the given value as netstring
(http://cr.yp.to/proto/netstrings.txt, this is not a
recommendation to use them).
packstring => $format, $data
An octet string prefixed with an encoded length. The encoding
$format uses the same format as a Perl "pack" format, but must
specify a single integer only (only one of "cCsSlLqQiInNvVjJw"
is allowed, plus an optional "!", "<" or ">" modifier).
json => $array_or_hashref
Encodes the given hash or array reference into a JSON object.
Unless you provide your own JSON object, this means it will be
encoded to JSON text in UTF-8.
The default encoder might or might not handle every type of
JSON value - it might be limited to arrays and objects for
security reasons. See the "json" constructor attribute for more
details.
JSON objects (and arrays) are self-delimiting, so if you only
use arrays and hashes, you can write JSON at one end of a
handle and read them at the other end without using any
additional framing.
The JSON text generated by the default encoder is guaranteed
not to contain any newlines: While this module doesn't need
delimiters after or between JSON texts to be able to read them,
many other languages depend on them.
A simple RPC protocol that interoperates easily with other
languages is to send JSON arrays (or objects, although arrays
are usually the better choice as they mimic how function
argument passing works) and a newline after each JSON text:
$handle->push_write (json => ["method", "arg1", "arg2"]); # whatever
$handle->push_write ("\012");
An AnyEvent::Handle receiver would simply use the "json" read
type and rely on the fact that the newline will be skipped as
leading whitespace:
$handle->push_read (json => sub { my $array = $_[1]; ... });
Other languages could read single lines terminated by a newline
and pass this line into their JSON decoder of choice.
cbor => $perl_scalar
Encodes the given scalar into a CBOR value. Unless you provide
your own CBOR::XS object, this means it will be encoded to a
CBOR string not using any extensions, if possible.
CBOR values are self-delimiting, so you can write CBOR at one
end of a handle and read them at the other end without using
any additional framing.
A simple nd very very fast RPC protocol that interoperates with
other languages is to send CBOR and receive CBOR values (arrays
are recommended):
$handle->push_write (cbor => ["method", "arg1", "arg2"]); # whatever
An AnyEvent::Handle receiver would simply use the "cbor" read
type:
$handle->push_read (cbor => sub { my $array = $_[1]; ... });
storable => $reference
Freezes the given reference using Storable and writes it to the
handle. Uses the "nfreeze" format.
$handle->push_shutdown
Sometimes you know you want to close the socket after writing your
data before it was actually written. One way to do that is to
replace your "on_drain" handler by a callback that shuts down the
socket (and set "low_water_mark" to 0). This method is a shorthand
for just that, and replaces the "on_drain" callback with:
sub { shutdown $_[0]{fh}, 1 }
This simply shuts down the write side and signals an EOF condition
to the the peer.
You can rely on the normal read queue and "on_eof" handling
afterwards. This is the cleanest way to close a connection.
This method may invoke callbacks (and therefore the handle might be
destroyed after it returns).
custom write types - Package::anyevent_write_type $handle, @args
Instead of one of the predefined types, you can also specify the
name of a package. AnyEvent will try to load the package and then
expects to find a function named "anyevent_write_type" inside. If
it isn't found, it progressively tries to load the parent package
until it either finds the function (good) or runs out of packages
(bad).
Whenever the given "type" is used, "push_write" will the function
with the handle object and the remaining arguments.
The function is supposed to return a single octet string that will
be appended to the write buffer, so you can mentally treat this
function as a "arguments to on-the-wire-format" converter.
Example: implement a custom write type "join" that joins the
remaining arguments using the first one.
$handle->push_write (My::Type => " ", 1,2,3);
# uses the following package, which can be defined in the "My::Type" or in
# the "My" modules to be auto-loaded, or just about anywhere when the
# My::Type::anyevent_write_type is defined before invoking it.
package My::Type;
sub anyevent_write_type {
my ($handle, $delim, @args) = @_;
join $delim, @args
}
READ QUEUE
AnyEvent::Handle manages two queues per handle, one for writing and one
for reading.
The read queue is more complex than the write queue. It can be used in
two ways, the "simple" way, using only "on_read" and the "complex" way,
using a queue.
In the simple case, you just install an "on_read" callback and whenever
new data arrives, it will be called. You can then remove some data (if
enough is there) from the read buffer ("$handle->rbuf"). Or you can
leave the data there if you want to accumulate more (e.g. when only a
partial message has been received so far), or change the read queue
with e.g. "push_read".
In the more complex case, you want to queue multiple callbacks. In this
case, AnyEvent::Handle will call the first queued callback each time
new data arrives (also the first time it is queued) and remove it when
it has done its job (see "push_read", below).
This way you can, for example, push three line-reads, followed by
reading a chunk of data, and AnyEvent::Handle will execute them in
order.
Example 1: EPP protocol parser. EPP sends 4 byte length info, followed
by the specified number of bytes which give an XML datagram.
# in the default state, expect some header bytes
$handle->on_read (sub {
# some data is here, now queue the length-header-read (4 octets)
shift->unshift_read (chunk => 4, sub {
# header arrived, decode
my $len = unpack "N", $_[1];
# now read the payload
shift->unshift_read (chunk => $len, sub {
my $xml = $_[1];
# handle xml
});
});
});
Example 2: Implement a client for a protocol that replies either with
"OK" and another line or "ERROR" for the first request that is sent,
and 64 bytes for the second request. Due to the availability of a
queue, we can just pipeline sending both requests and manipulate the
queue as necessary in the callbacks.
When the first callback is called and sees an "OK" response, it will
"unshift" another line-read. This line-read will be queued before the
64-byte chunk callback.
# request one, returns either "OK + extra line" or "ERROR"
$handle->push_write ("request 1\015\012");
# we expect "ERROR" or "OK" as response, so push a line read
$handle->push_read (line => sub {
# if we got an "OK", we have to _prepend_ another line,
# so it will be read before the second request reads its 64 bytes
# which are already in the queue when this callback is called
# we don't do this in case we got an error
if ($_[1] eq "OK") {
$_[0]->unshift_read (line => sub {
my $response = $_[1];
...
});
}
});
# request two, simply returns 64 octets
$handle->push_write ("request 2\015\012");
# simply read 64 bytes, always
$handle->push_read (chunk => 64, sub {
my $response = $_[1];
...
});
$handle->on_read ($cb)
This replaces the currently set "on_read" callback, or clears it
(when the new callback is "undef"). See the description of
"on_read" in the constructor.
This method may invoke callbacks (and therefore the handle might be
destroyed after it returns).
$handle->rbuf
Returns the read buffer (as a modifiable lvalue). You can also
access the read buffer directly as the "->{rbuf}" member, if you
want (this is much faster, and no less clean).
The only operation allowed on the read buffer (apart from looking
at it) is removing data from its beginning. Otherwise modifying or
appending to it is not allowed and will lead to hard-to-track-down
bugs.
NOTE: The read buffer should only be used or modified in the
"on_read" callback or when "push_read" or "unshift_read" are used
with a single callback (i.e. untyped). Typed "push_read" and
"unshift_read" methods will manage the read buffer on their own.
$handle->push_read ($cb)
$handle->unshift_read ($cb)
Append the given callback to the end of the queue ("push_read") or
prepend it ("unshift_read").
The callback is called each time some additional read data arrives.
It must check whether enough data is in the read buffer already.
If not enough data is available, it must return the empty list or a
false value, in which case it will be called repeatedly until
enough data is available (or an error condition is detected).
If enough data was available, then the callback must remove all
data it is interested in (which can be none at all) and return a
true value. After returning true, it will be removed from the
queue.
These methods may invoke callbacks (and therefore the handle might
be destroyed after it returns).
$handle->push_read (type => @args, $cb)
$handle->unshift_read (type => @args, $cb)
Instead of providing a callback that parses the data itself you can
chose between a number of predefined parsing formats, for chunks of
data, lines etc. You can also specify the (fully qualified) name of
a package, in which case AnyEvent tries to load the package and
then expects to find the "anyevent_read_type" function inside (see
"custom read types", below).
Predefined types are (if you have ideas for additional types, feel
free to drop by and tell us):
chunk => $octets, $cb->($handle, $data)
Invoke the callback only once $octets bytes have been read.
Pass the data read to the callback. The callback will never be
called with less data.
Example: read 2 bytes.
$handle->push_read (chunk => 2, sub {
say "yay " . unpack "H*", $_[1];
});
line => [$eol, ]$cb->($handle, $line, $eol)
The callback will be called only once a full line (including
the end of line marker, $eol) has been read. This line
(excluding the end of line marker) will be passed to the
callback as second argument ($line), and the end of line marker
as the third argument ($eol).
The end of line marker, $eol, can be either a string, in which
case it will be interpreted as a fixed record end marker, or it
can be a regex object (e.g. created by "qr"), in which case it
is interpreted as a regular expression.
The end of line marker argument $eol is optional, if it is
missing (NOT undef), then "qr|\015?\012|" is used (which is
good for most internet protocols).
Partial lines at the end of the stream will never be returned,
as they are not marked by the end of line marker.
regex => $accept[, $reject[, $skip], $cb->($handle, $data)
Makes a regex match against the regex object $accept and
returns everything up to and including the match. All the usual
regex variables ($1, %+ etc.) from the regex match are
available in the callback.
Example: read a single line terminated by '\n'.
$handle->push_read (regex => qr<\n>, sub { ... });
If $reject is given and not undef, then it determines when the
data is to be rejected: it is matched against the data when the
$accept regex does not match and generates an "EBADMSG" error
when it matches. This is useful to quickly reject wrong data
(to avoid waiting for a timeout or a receive buffer overflow).
Example: expect a single decimal number followed by whitespace,
reject anything else (not the use of an anchor).
$handle->push_read (regex => qr<^[0-9]+\s>, qr<[^0-9]>, sub { ... });
If $skip is given and not "undef", then it will be matched
against the receive buffer when neither $accept nor $reject
match, and everything preceding and including the match will be
accepted unconditionally. This is useful to skip large amounts
of data that you know cannot be matched, so that the $accept or
$reject regex do not have to start matching from the beginning.
This is purely an optimisation and is usually worth it only
when you expect more than a few kilobytes.
Example: expect a http header, which ends at
"\015\012\015\012". Since we expect the header to be very large
(it isn't in practice, but...), we use a skip regex to skip
initial portions. The skip regex is tricky in that it only
accepts something not ending in either \015 or \012, as these
are required for the accept regex.
$handle->push_read (regex =>
qr<\015\012\015\012>,
undef, # no reject
qr<^.*[^\015\012]>,
sub { ... });
netstring => $cb->($handle, $string)
A netstring (http://cr.yp.to/proto/netstrings.txt, this is not
an endorsement).
Throws an error with $! set to EBADMSG on format violations.
packstring => $format, $cb->($handle, $string)
An octet string prefixed with an encoded length. The encoding
$format uses the same format as a Perl "pack" format, but must
specify a single integer only (only one of "cCsSlLqQiInNvVjJw"
is allowed, plus an optional "!", "<" or ">" modifier).
For example, DNS over TCP uses a prefix of "n" (2 octet network
order), EPP uses a prefix of "N" (4 octtes).
Example: read a block of data prefixed by its length in BER-
encoded format (very efficient).
$handle->push_read (packstring => "w", sub {
my ($handle, $data) = @_;
});
json => $cb->($handle, $hash_or_arrayref)
Reads a JSON object or array, decodes it and passes it to the
callback. When a parse error occurs, an "EBADMSG" error will be
raised.
If a "json" object was passed to the constructor, then that
will be used for the final decode, otherwise it will create a
JSON::XS or JSON::PP coder object expecting UTF-8.
This read type uses the incremental parser available with JSON
version 2.09 (and JSON::XS version 2.2) and above.
Since JSON texts are fully self-delimiting, the "json" read and
write types are an ideal simple RPC protocol: just exchange
JSON datagrams. See the "json" write type description, above,
for an actual example.
cbor => $cb->($handle, $scalar)
Reads a CBOR value, decodes it and passes it to the callback.
When a parse error occurs, an "EBADMSG" error will be raised.
If a CBOR::XS object was passed to the constructor, then that
will be used for the final decode, otherwise it will create a
CBOR coder without enabling any options.
You have to provide a dependency to CBOR::XS on your own: this
module will load the CBOR::XS module, but AnyEvent does not
depend on it itself.
Since CBOR values are fully self-delimiting, the "cbor" read
and write types are an ideal simple RPC protocol: just exchange
CBOR datagrams. See the "cbor" write type description, above,
for an actual example.
storable => $cb->($handle, $ref)
Deserialises a Storable frozen representation as written by the
"storable" write type (BER-encoded length prefix followed by
nfreeze'd data).
Raises "EBADMSG" error if the data could not be decoded.
tls_detect => $cb->($handle, $detect, $major, $minor)
Checks the input stream for a valid SSL or TLS handshake
TLSPaintext record without consuming anything. Only SSL version
3 or higher is handled, up to the fictituous protocol 4.x (but
both SSL3+ and SSL2-compatible framing is supported).
If it detects that the input data is likely TLS, it calls the
callback with a true value for $detect and the (on-wire) TLS
version as second and third argument ($major is 3, and $minor
is 0..4 for SSL 3.0, TLS 1.0, 1.1, 1.2 and 1.3, respectively).
If it detects the input to be definitely not TLS, it calls the
callback with a false value for $detect.
The callback could use this information to decide whether or
not to start TLS negotiation.
In all cases the data read so far is passed to the following
read handlers.
Usually you want to use the "tls_autostart" read type instead.
If you want to design a protocol that works in the presence of
TLS dtection, make sure that any non-TLS data doesn't start
with the octet 22 (ASCII SYN, 16 hex) or 128-255 (i.e. highest
bit set). The checks this read type does are a bit more strict,
but might losen in the future to accommodate protocol changes.
This read type does not rely on AnyEvent::TLS (and thus, not on
Net::SSLeay).
tls_autostart => [$tls_ctx, ]$tls
Tries to detect a valid SSL or TLS handshake. If one is
detected, it tries to start tls by calling "starttls" with the
given arguments.
In practise, $tls must be "accept", or a Net::SSLeay context
that has been configured to accept, as servers do not normally
send a handshake on their own and ths cannot be detected in
this way.
See "tls_detect" above for more details.
Example: give the client a chance to start TLS before accepting
a text line.
$hdl->push_read (tls_autostart => "accept");
$hdl->push_read (line => sub {
print "received ", ($_[0]{tls} ? "encrypted" : "cleartext"), " <$_[1]>\n";
});
custom read types - Package::anyevent_read_type $handle, $cb, @args
Instead of one of the predefined types, you can also specify the
name of a package. AnyEvent will try to load the package and then
expects to find a function named "anyevent_read_type" inside. If it
isn't found, it progressively tries to load the parent package
until it either finds the function (good) or runs out of packages
(bad).
Whenever this type is used, "push_read" will invoke the function
with the handle object, the original callback and the remaining
arguments.
The function is supposed to return a callback (usually a closure)
that works as a plain read callback (see "->push_read ($cb)"), so
you can mentally treat the function as a "configurable read type to
read callback" converter.
It should invoke the original callback when it is done reading
(remember to pass $handle as first argument as all other callbacks
do that, although there is no strict requirement on this).
For examples, see the source of this module (perldoc -m
AnyEvent::Handle, search for "register_read_type")).
$handle->stop_read
$handle->start_read
In rare cases you actually do not want to read anything from the
socket. In this case you can call "stop_read". Neither "on_read"
nor any queued callbacks will be executed then. To start reading
again, call "start_read".
Note that AnyEvent::Handle will automatically "start_read" for you
when you change the "on_read" callback or push/unshift a read
callback, and it will automatically "stop_read" for you when
neither "on_read" is set nor there are any read requests in the
queue.
In older versions of this module (<= 5.3), these methods had no
effect, as TLS does not support half-duplex connections. In current
versions they work as expected, as this behaviour is required to
avoid certain resource attacks, where the program would be forced
to read (and buffer) arbitrary amounts of data before being able to
send some data. The drawback is that some readings of the the
SSL/TLS specifications basically require this attack to be working,
as SSL/TLS implementations might stall sending data during a
rehandshake.
As a guideline, during the initial handshake, you should not stop
reading, and as a client, it might cause problems, depending on
your application.
$handle->starttls ($tls[, $tls_ctx])
Instead of starting TLS negotiation immediately when the
AnyEvent::Handle object is created, you can also do that at a later
time by calling "starttls". See the "tls" constructor argument for
general info.
Starting TLS is currently an asynchronous operation - when you push
some write data and then call "->starttls" then TLS negotiation
will start immediately, after which the queued write data is then
sent. This might change in future versions, so best make sure you
have no outstanding write data when calling this method.
The first argument is the same as the "tls" constructor argument
(either "connect", "accept" or an existing Net::SSLeay object).
The second argument is the optional "AnyEvent::TLS" object that is
used when AnyEvent::Handle has to create its own TLS connection
object, or a hash reference with "key => value" pairs that will be
used to construct a new context.
The TLS connection object will end up in "$handle->{tls}", the TLS
context in "$handle->{tls_ctx}" after this call and can be used or
changed to your liking. Note that the handshake might have already
started when this function returns.
Due to bugs in OpenSSL, it might or might not be possible to do
multiple handshakes on the same stream. It is best to not attempt
to use the stream after stopping TLS.
This method may invoke callbacks (and therefore the handle might be
destroyed after it returns).
$handle->stoptls
Shuts down the SSL connection - this makes a proper EOF handshake
by sending a close notify to the other side, but since OpenSSL
doesn't support non-blocking shut downs, it is not guaranteed that
you can re-use the stream afterwards.
This method may invoke callbacks (and therefore the handle might be
destroyed after it returns).
$handle->resettls
This rarely-used method simply resets and TLS state on the handle,
usually causing data loss.
One case where it may be useful is when you want to skip over the
data in the stream but you are not interested in interpreting it,
so data loss is no concern.
$handle->destroy
Shuts down the handle object as much as possible - this call
ensures that no further callbacks will be invoked and as many
resources as possible will be freed. Any method you will call on
the handle object after destroying it in this way will be silently
ignored (and it will return the empty list).
Normally, you can just "forget" any references to an
AnyEvent::Handle object and it will simply shut down. This works in
fatal error and EOF callbacks, as well as code outside. It does NOT
work in a read or write callback, so when you want to destroy the
AnyEvent::Handle object from within such an callback. You MUST call
"->destroy" explicitly in that case.
Destroying the handle object in this way has the advantage that
callbacks will be removed as well, so if those are the only
reference holders (as is common), then one doesn't need to do
anything special to break any reference cycles.
The handle might still linger in the background and write out
remaining data, as specified by the "linger" option, however.
$handle->destroyed
Returns false as long as the handle hasn't been destroyed by a call
to "->destroy", true otherwise.
Can be useful to decide whether the handle is still valid after
some callback possibly destroyed the handle. For example,
"->push_write", "->starttls" and other methods can call user
callbacks, which in turn can destroy the handle, so work can be
avoided by checking sometimes:
$hdl->starttls ("accept");
return if $hdl->destroyed;
$hdl->push_write (...
Note that the call to "push_write" will silently be ignored if the
handle has been destroyed, so often you can just ignore the
possibility of the handle being destroyed.
AnyEvent::Handle::TLS_CTX
This function creates and returns the AnyEvent::TLS object used by
default for TLS mode.
The context is created by calling AnyEvent::TLS without any
arguments.
NONFREQUENTLY ASKED QUESTIONS
I "undef" the AnyEvent::Handle reference inside my callback and still
get further invocations!
That's because AnyEvent::Handle keeps a reference to itself when
handling read or write callbacks.
It is only safe to "forget" the reference inside EOF or error
callbacks, from within all other callbacks, you need to explicitly
call the "->destroy" method.
Why is my "on_eof" callback never called?
Probably because your "on_error" callback is being called instead:
When you have outstanding requests in your read queue, then an EOF
is considered an error as you clearly expected some data.
To avoid this, make sure you have an empty read queue whenever your
handle is supposed to be "idle" (i.e. connection closes are O.K.).
You can set an "on_read" handler that simply pushes the first read
requests in the queue.
See also the next question, which explains this in a bit more
detail.
How can I serve requests in a loop?
Most protocols consist of some setup phase (authentication for
example) followed by a request handling phase, where the server
waits for requests and handles them, in a loop.
There are two important variants: The first (traditional, better)
variant handles requests until the server gets some QUIT command,
causing it to close the connection first (highly desirable for a
busy TCP server). A client dropping the connection is an error,
which means this variant can detect an unexpected detection close.
To handle this case, always make sure you have a non-empty read
queue, by pushing the "read request start" handler on it:
# we assume a request starts with a single line
my @start_request; @start_request = (line => sub {
my ($hdl, $line) = @_;
... handle request
# push next request read, possibly from a nested callback
$hdl->push_read (@start_request);
});
# auth done, now go into request handling loop
# now push the first @start_request
$hdl->push_read (@start_request);
By always having an outstanding "push_read", the handle always
expects some data and raises the "EPIPE" error when the connction
is dropped unexpectedly.
The second variant is a protocol where the client can drop the
connection at any time. For TCP, this means that the server machine
may run out of sockets easier, and in general, it means you cannot
distinguish a protocl failure/client crash from a normal connection
close. Nevertheless, these kinds of protocols are common (and
sometimes even the best solution to the problem).
Having an outstanding read request at all times is possible if you
ignore "EPIPE" errors, but this doesn't help with when the client
drops the connection during a request, which would still be an
error.
A better solution is to push the initial request read in an
"on_read" callback. This avoids an error, as when the server
doesn't expect data (i.e. is idly waiting for the next request, an
EOF will not raise an error, but simply result in an "on_eof"
callback. It is also a bit slower and simpler:
# auth done, now go into request handling loop
$hdl->on_read (sub {
my ($hdl) = @_;
# called each time we receive data but the read queue is empty
# simply start read the request
$hdl->push_read (line => sub {
my ($hdl, $line) = @_;
... handle request
# do nothing special when the request has been handled, just
# let the request queue go empty.
});
});
I get different callback invocations in TLS mode/Why can't I pause
reading?
Unlike, say, TCP, TLS connections do not consist of two independent
communication channels, one for each direction. Or put differently,
the read and write directions are not independent of each other:
you cannot write data unless you are also prepared to read, and
vice versa.
This means that, in TLS mode, you might get "on_error" or "on_eof"
callback invocations when you are not expecting any read data - the
reason is that AnyEvent::Handle always reads in TLS mode.
During the connection, you have to make sure that you always have a
non-empty read-queue, or an "on_read" watcher. At the end of the
connection (or when you no longer want to use it) you can call the
"destroy" method.
How do I read data until the other side closes the connection?
If you just want to read your data into a perl scalar, the easiest
way to achieve this is by setting an "on_read" callback that does
nothing, clearing the "on_eof" callback and in the "on_error"
callback, the data will be in "$_[0]{rbuf}":
$handle->on_read (sub { });
$handle->on_eof (undef);
$handle->on_error (sub {
my $data = delete $_[0]{rbuf};
});
Note that this example removes the "rbuf" member from the handle
object, which is not normally allowed by the API. It is expressly
permitted in this case only, as the handle object needs to be
destroyed afterwards.
The reason to use "on_error" is that TCP connections, due to
latencies and packets loss, might get closed quite violently with
an error, when in fact all data has been received.
It is usually better to use acknowledgements when transferring
data, to make sure the other side hasn't just died and you got the
data intact. This is also one reason why so many internet protocols
have an explicit QUIT command.
I don't want to destroy the handle too early - how do I wait until all
data has been written?
After writing your last bits of data, set the "on_drain" callback
and destroy the handle in there - with the default setting of
"low_water_mark" this will be called precisely when all data has
been written to the socket:
$handle->push_write (...);
$handle->on_drain (sub {
AE::log debug => "All data submitted to the kernel.";
undef $handle;
});
If you just want to queue some data and then signal EOF to the
other side, consider using "->push_shutdown" instead.
I want to contact a TLS/SSL server, I don't care about security.
If your TLS server is a pure TLS server (e.g. HTTPS) that only
speaks TLS, connect to it and then create the AnyEvent::Handle with
the "tls" parameter:
tcp_connect $host, $port, sub {
my ($fh) = @_;
my $handle = new AnyEvent::Handle
fh => $fh,
tls => "connect",
on_error => sub { ... };
$handle->push_write (...);
};
I want to contact a TLS/SSL server, I do care about security.
Then you should additionally enable certificate verification,
including peername verification, if the protocol you use supports
it (see AnyEvent::TLS, "verify_peername").
E.g. for HTTPS:
tcp_connect $host, $port, sub {
my ($fh) = @_;
my $handle = new AnyEvent::Handle
fh => $fh,
peername => $host,
tls => "connect",
tls_ctx => { verify => 1, verify_peername => "https" },
...
Note that you must specify the hostname you connected to (or
whatever "peername" the protocol needs) as the "peername" argument,
otherwise no peername verification will be done.
The above will use the system-dependent default set of trusted CA
certificates. If you want to check against a specific CA, add the
"ca_file" (or "ca_cert") arguments to "tls_ctx":
tls_ctx => {
verify => 1,
verify_peername => "https",
ca_file => "my-ca-cert.pem",
},
I want to create a TLS/SSL server, how do I do that?
Well, you first need to get a server certificate and key. You have
three options: a) ask a CA (buy one, use cacert.org etc.) b) create
a self-signed certificate (cheap. check the search engine of your
choice, there are many tutorials on the net) or c) make your own CA
(tinyca2 is a nice program for that purpose).
Then create a file with your private key (in PEM format, see
AnyEvent::TLS), followed by the certificate (also in PEM format).
The file should then look like this:
-----BEGIN RSA PRIVATE KEY-----
...header data
... lots of base64'y-stuff
-----END RSA PRIVATE KEY-----
-----BEGIN CERTIFICATE-----
... lots of base64'y-stuff
-----END CERTIFICATE-----
The important bits are the "PRIVATE KEY" and "CERTIFICATE" parts.
Then specify this file as "cert_file":
tcp_server undef, $port, sub {
my ($fh) = @_;
my $handle = new AnyEvent::Handle
fh => $fh,
tls => "accept",
tls_ctx => { cert_file => "my-server-keycert.pem" },
...
When you have intermediate CA certificates that your clients might
not know about, just append them to the "cert_file".
SUBCLASSING AnyEvent::Handle
In many cases, you might want to subclass AnyEvent::Handle.
To make this easier, a given version of AnyEvent::Handle uses these
conventions:
• all constructor arguments become object members.
At least initially, when you pass a "tls"-argument to the
constructor it will end up in "$handle->{tls}". Those members might
be changed or mutated later on (for example "tls" will hold the TLS
connection object).
• other object member names are prefixed with an "_".
All object members not explicitly documented (internal use) are
prefixed with an underscore character, so the remaining
non-"_"-namespace is free for use for subclasses.
• all members not documented here and not prefixed with an underscore
are free to use in subclasses.
Of course, new versions of AnyEvent::Handle may introduce more
"public" member variables, but that's just life. At least it is
documented.
AUTHOR
Robin Redeker "<elmex at ta-sa.org>", Marc Lehmann
<schmorp@schmorp.de>.
perl v5.36.0 2022-10-20 AnyEvent::Handle(3pm)
Generated by dwww version 1.15 on Sun Jun 30 10:50:49 CEST 2024.