Provided by: libyahc-perl_0.035-3_all 
NAME
YAHC - Yet another HTTP client
SYNOPSIS
use YAHC qw/yahc_reinit_conn/;
my @hosts = ('www.booking.com', 'www.google.com:80');
my ($yahc, $yahc_storage) = YAHC->new({ host => \@hosts });
$yahc->request({ path => '/', host => 'www.reddit.com' });
$yahc->request({ path => '/', host => sub { 'www.reddit.com' } });
$yahc->request({ path => '/', host => \@hosts });
$yahc->request({ path => '/', callback => sub { ... } });
$yahc->request({ path => '/' });
$yahc->request({
path => '/',
callback => sub {
yahc_reinit_conn($_[0], { host => 'www.newtarget.com' })
if $_[0]->{response}{status} == 301;
}
});
$yahc->run;
DESCRIPTION
YAHC is fast & minimal low-level asynchronous HTTP client intended to be used where you
control both the client and the server. Is especially suits cases where set of requests
need to be executed against group of machines.
It is NOT a general HTTP user agent, it doesn't support redirects, proxies and any number
of other advanced HTTP features like (in roughly descending order of feature completeness)
LWP::UserAgent, WWW::Curl, HTTP::Tiny, HTTP::Lite or Furl. This library is basically one
step above manually talking HTTP over sockets.
YAHC supports SSL and socket reuse (latter is in experimental mode).
STATE MACHINE
Each YAHC connection goes through following list of states in its lifetime:
+-----------------+
+<<-| INITIALIZED <-<<+
v +-----------------+ ^
v | ^
v +-------v---------+ ^
+<<-+ RESOLVE DNS +->>+
v +-----------------+ ^
v | ^
v +-------v---------+ ^
+<<-+ CONNECTING +->>+
v +-----------------+ ^
v | ^
Path in v +-------v---------+ ^ Retry
case of +<<-+ CONNECTED +->>+ logic
failure v +-----------------+ ^ path
v | ^
v +-------v---------+ ^
+<<-+ WRITING +->>+
v +-----------------+ ^
v | ^
v +-------v---------+ ^
+<<-+ READING +->>+
v +-----------------+ ^
v | ^
v +-------v---------+ ^
+>>-> USER ACTION +->>+
+-----------------+
|
+-------v---------+
| COMPLETED |
+-----------------+
There are three paths of workflow:
1) Normal execution (central line).
In normal situation a connection after being initialized goes through state:
- RESOLVE DNS (not implemented)
- CONNECTING - wait finishing of handshake
- CONNECTED
- WRITING - sending request body
- READING - awaiting and reading response
- USER ACTION - see below
- COMPLETED - all done, this is terminal state
SSL connection has extra state SSL_HANDSHAKE after CONNECTED state. State 'RESOLVE
DNS' is not implemented yet.
2) Retry path (right line).
In case of IO error during normal execution YAHC retries connection "retries" times.
In practice this means that connection goes back to INITIALIZED state.
3) Failure path (left line).
If all retry attempts did not succeeded a connection goes to state 'USER ACTION' (see
below).
State 'USER ACTION'
'USER ACTION' state is called right before connection if going to enter 'COMPLETED' state
(with either failed or successful results) and is meant to give a chance to user to
interrupt the workflow.
'USER ACTION' state is entered in these circumstances:
• HTTP response received. Note that non-200 responses are NOT treated as error.
• unsupported HTTP response is received (such as response without Content-Length header)
• retries limit reached
• lifetime timeout has expired
• provided callback has thrown exception
• internal error has occurred
When a connection enters this state "callback" CodeRef is called:
$yahc->request({
...
callback => sub {
my (
$conn, # connection 'object'
$error, # one of YAHC::Error::* constants
$strerror # string representation of error
) = @_;
# Note that fields in $conn->{response} are not reliable
# if $error != YAHC::Error::NO_ERROR()
# HTTP response is stored in $conn->{response}.
# It can be also accessed via yahc_conn_response().
my $response = $conn->{response};
my $status = $response->{status};
my $body = $response->{body};
}
});
If there was no IO error "yahc_conn_response" return "HashRef" representing response. It
contains the following key-value pairs.
proto => :Str
status => :StatusCode
body => :Str
head => :HashRef
In case of a error or non-200 HTTP response "yahc_retry_conn" or "yahc_reinit_conn" may be
called to give the request more chances to complete successfully (for example by following
redirects or providing new target hosts). Also, note that in case of a error data returned
by "yahc_conn_response" cannot be trusted. For example, if an IO error happened during
receiving HTTP body headers would state 200 response code.
YAHC lowercases headers names returned in "head". This is done to comply with RFC which
identify HTTP headers as case-insensitive.
In some cases connection cannot be retried anymore and callback is called for information
purposes only. This case can be distinguished by $error having
YAHC::Error::TERMINAL_ERROR() bit set. One can use "yahc_terminal_error" helper to detect
such case.
Note that "callback" should NOT throw exception. If so the connection will be immediately
closed.
METHODS
new
This method creates YAHC object and accompanying storage object:
my ($yahc, $yahc_storage) = YAHC->new();
This is a radical way of solving all possible memleak because of cyclic references in
callbacks. Since all references of callbacks are kept in $yahc_storage object it's fine to
use YAHC object inside request callback:
my $yahc->request({
callback => sub {
$yahc->stop; # this is fine!!!
},
});
However, user has to guarantee that both $yahc and $yahc_storage objects are kept in the
same scope. So, they will be destroyed at the same time.
"new" can be passed with all parameters supported by "request". They will be inherited by
all requests.
Additionally, "new" supports three parameters: "socket_cache", "account_for_signals", and
"loop".
socket_cache
"socket_cache" option controls socket reuse logic. By default socket cache is disabled. If
user wants YAHC reuse sockets he should set "socket_cache" to a HashRef.
my ($yahc, $yahc_storage) = YAHC->new({ socket_cache => {} });
In this case YAHC maintains unused sockets keyed on "join($;, $$, $host, $port, $scheme)".
We use $; so we can use the "$socket_cache->{$$, $host, $port, $scheme}" idiom to access
the cache.
It's up to user to control the cache. It's also up to user to set necessary request
headers for keep-alive. YAHC does not cache socket in cases of an error, HTTP/1.0 and when
server explicitly instructs to close connection (i.e. header 'Connection' = 'close').
loop
By default, each YAHC object will use its own EV eventloop. This is normally preferred
since it allows for more accurate timing metrics.
However, if the process is already using an eventloop, having an inner loop means the
outer one stays waiting until the inner one is done.
To get around this, one can specify the eventloop that YAHC will use:
my ($yahc, $storage) = YAHC->new({
loop => EV::default_loop(), # use the default EV eventloop
});
Using the above, YAHC will be sharing the same eventloop as everyone else, so some
operations are now riskier and should be avoided; For example, in most scenarios
"account_for_signals" should not be used alongside "loop", as only whatever is entering
the eventloop should set the signal handlers.
account_for_signals
Another parameter "account_for_signals" requires special attention! Here is why:
excerpt from EV documentation
<http://search.cpan.org/~mlehmann/EV-4.22/EV.pm#PERL_SIGNALS>
While Perl signal handling (%SIG) is not affected by EV, the behaviour with EV is as
the same as any other C library: Perl-signals will only be handled when Perl runs,
which means your signal handler might be invoked only the next time an event callback
is invoked.
In practise this means that none of set %SIG handlers will be called until EV calls one of
perl callbacks. Which, in some cases, may take a long time. By setting
"account_for_signals" YAHC adds "EV::check" watcher with empty callback effectively making
EV calling the callback on every iteration. The trickery comes at some performance cost.
This is what EV documentation says about it:
... you can also force a watcher to be called on every event loop iteration by
installing a EV::check watcher. This ensures that perl gets into control for a short
time to handle any pending signals, and also ensures (slightly) slower overall
operation.
So, if your code or the codes surrounding your code use %SIG handlers it's wise to set
"account_for_signals".
request
protocol => "HTTP/1.1", # (or "HTTP/1.0")
scheme => "http" or "https"
host => see below,
port => ...,
method => "GET",
path => "/",
query_string => "",
head => [],
body => "",
# timeouts
connect_timeout => undef,
request_timeout => undef,
drain_timeout => undef,
lifetime_timeout => undef,
# burst control
backoff_delay => undef,
# callbacks
init_callback => undef,
connecting_callback => undef,
connected_callback => undef,
writing_callback => undef,
reading_callback => undef,
callback => undef,
# SSL options
ssl_options => {},
Notice how YAHC does not take a full URI string as input, you have to specify the
individual parts of the URL. Users who need to parse an existing URI string to produce a
request should use the URI module to do so.
For example, to send a request to "http://example.com/flower?color=red", pass the
following parameters:
$yach->request({
host => "example.com",
port => "80",
path => "/flower",
query_string => "color=red"
});
request building
YAHC doesn't escape any values for you, it just passes them through as-is. You can easily
produce invalid requests if e.g. any of these strings contain a newline, or aren't
otherwise properly escaped.
Notice that you do not need to put the leading "?" character in the "query_string". You
do, however, need to properly "uri_escape" the content of "query_string".
The value of "head" is an "ArrayRef" of key-value pairs instead of a "HashRef", this way
you can decide in which order the headers are sent, and you can send the same header name
multiple times. For example:
head => [
"Content-Type" => "application/json",
"X-Requested-With" => "YAHC",
]
Will produce these request headers:
Content-Type: application/json
X-Requested-With: YAHC
host
"host" parameter can accept one of following values:
1) string - represents target host. String may have following formats:
hostname:port, ip:port.
2) ArrayRef of strings - YAHC will cycle through items selecting new host
for each attempt.
3) CodeRef. The subroutine is invoked for each attempt and should at least
return a string (hostname or IP address). It can also return array
containing: ($host, $ip, $port, $scheme). This option effectively give a
user control over host selection for retries. The CodeRef is passed with
connection "object" which can be fed to yahc_conn_* family of functions.
timeouts
The value of "connect_timeout", "request_timeout" and "drain_timeout" is in floating point
seconds, and is used as the time limit for connecting to the host (reaching CONNECTED
state), full request time (reaching COMPLETED state) and sending request to remote site
(reaching READING state) respectively.
"lifetime_timeout" has special purpose. Its task is to provide upper bound timeout for a
request lifetime. In other words, if a request comes with multiple retries
"connect_timeout", "request_timeout" and "drain_timeout" are per attempt.
"lifetime_timeout" covers all attempts. If by the time "lifetime_timeout" expires a
connection is not in COMPLETED state a error is generated. Note that after this error the
connection cannot be retried anymore. So, it's forced to go to COMPLETED state.
The default value for all is "undef", meaning no timeout limit.
backoff_delay
"backoff_delay" can be used to introduce delay between retries. This is a great way to
avoid load spikes on server side. Following example creates new request which would be
retried twice doing three attempts in total. Second and third attempts will be delay by
one second each.
$yach->request({
host => "example.com",
retries => 2,
backoff_delay => 1,
});
"backoff_delay" can be set in two ways:
1) floating point seconds - define constant delay between retires.
2) CodeRef. The subroutine is invoked on each retry and should return
floating point seconds. This option is useful for having exponentially
growing delay or, for instance, jitted delays.
The default value is "undef", meaning no delay.
callbacks
The value of "init_callback", "connecting_callback", "connected_callback",
"writing_callback", "reading_callback" is a reference to a subroutine which is called upon
reaching corresponding state. Any exception thrown in the subroutine will be ignored.
The value of "callback" defines main request callback which is called when a connection
enters 'USER ACTION' state (see 'USER ACTION' state above).
Also see LIMITATIONS
ssl_options
Performing HTTPS requires the value of "ssl_options" extended by two parameters set to
current hostname:
SSL_verifycn_name => $hostname,
IO::Socket::SSL->can_client_sni ? ( SSL_hostname => $hostname ) : (),
Apart of this changes, the value is directly passed to "IO::Socket::SSL::start_SSL()". For
more details refer to IO::Socket::SSL documentation
<https://metacpan.org/pod/IO::Socket::SSL>.
drop
Given connection HashRef or conn_id move connection to COMPLETED state (avoiding 'USER
ACTION' state) and drop it from internal pool. The function takes two parameters: first is
either a connection id or connection HashRef. Second one is a boolean flag indicating
whether connection's socket should closed or it might be reused.
run
Start YAHC's loop. The loop stops when all connection complete.
Note that "run" can accept two extra parameters: until_state and list of connections.
These two parameters tell YAHC to break the loop once specified connections reach desired
state.
For example:
$yahc->run(YAHC::State::READING(), $conn_id);
Will loop until connection '$conn_id' move to state READING meaning that the data has been
sent to remote side. In order to gather response one should later call:
$yahc->run(YAHC::State::COMPLETED(), $conn_id);
or simply:
$yahc->run();
Leaving list of connection empty makes YAHC waiting for all connection reaching needed
until_state.
Note that waiting one particular connection to finish doesn't mean that others are not
executed. Instead, all active connections are looped at the same time, but YAHC breaks the
loop once waited connection reaches needed state.
run_once
Same as run but with EV::RUN_ONCE set. For more details check
<https://metacpan.org/pod/EV>
run_tick
Same as run but with EV::RUN_NOWAIT set. For more details check
<https://metacpan.org/pod/EV>
is_running
Return true if YAHC is running, false otherwise.
loop
Return underlying EV loop object.
break
Break running EV loop if any.
EXPORTED FUNCTIONS
yahc_reinit_conn
"yahc_reinit_conn" reinitialize given connection. The attempt counter is reset to 0. The
function accepts HashRef as second argument. By passing it one can change host, port,
scheme, body, head and others parameters. The format and meaning of these parameters is
same as in "request" method.
One of use cases of "yahc_reinit_conn", for example, is to handle redirects:
use YAHC qw/yahc_reinit_conn/;
my ($yahc, $yahc_storage) = YAHC->new();
$yahc->request({
host => 'domain_which_returns_301.com',
callback => sub {
...
my $conn = $_[0];
yahc_reinit_conn($conn, { host => 'www.newtarget.com' })
if $_[0]->{response}{status} == 301;
...
}
});
$yahc->run;
"yahc_reinit_conn" is meant to be called inside "callback" i.e. when connection is in
'USER ACTION' state.
yahc_retry_conn
Retries given connection. "yahc_retry_conn" should be called only if
"yahc_conn_attempts_left" returns positive value. Otherwise, it exits silently. The
function accepts HashRef as second argument. By passing it one can change "backoff_delay"
parameter. See docs for "request" for more details about "backoff_delay".
Intended usage is to retry transient failures or to try different host:
use YAHC qw/
yahc_retry_conn
yahc_conn_attempts_left
/;
my ($yahc, $yahc_storage) = YAHC->new();
$yahc->request({
retries => 2,
host => [ 'host1', 'host2' ],
callback => sub {
...
my $conn = $_[0];
if ($_[0]->{response}{status} == 503 && yahc_conn_attempts_left($conn)) {
yahc_retry_conn($conn);
return;
}
...
}
});
$yahc->run;
"yahc_retry_conn" is meant to be called inside "callback" similarly to "yahc_reinit_conn".
yahc_conn_id
Return id of given connection.
yahc_conn_state
Return state of given connection.
yahc_conn_target
Return selected host and port for current attempt for given connection. Format
"host:port". Default port values are omitted.
yahc_conn_url
Same as "yahc_conn_target" but return full URL
yahc_conn_user_data
Let user associate arbitrary data with a connection. Be aware of not creating cyclic
reference!
yahc_conn_errors
Return errors appeared in given connection. Note that the function returns all errors, not
only ones happened during current attempt. Returned value is ArrayRef of ArrayRefs. Later
one represents a error and contains following items:
error number (see YAHC::Error constants)
error string
ArrayRef of host, ip, port, scheme
time when the error happened
attempt when the error happened
yahc_conn_register_error
"yahc_conn_register_error" adds new record in connection's error list. This functions is
used internally for keeping track of all low-level errors during connection's lifetime. It
can be also used by users for high-level errors such as 50x responses. The function takes
$conn, $error which is one of "YAHC::Error" constants and error description. Error
description can be passed in sprintf manner. For example:
$yahc->request({
...
callback => sub {
...
my $conn = $_[0];
my $status = $conn->{response}{status} || 0;
if ($status == 503 || $status == 504) {
yahc_conn_register_error(
$conn,
YAHC::Error::RESPONSE_ERROR(),
"server returned %d",
$status
);
yahc_retry_conn($conn);
return;
}
...
}
});
yahc_conn_last_error
Return last error appeared in connection. See "yahc_conn_errors".
yahc_terminal_error
Given a error return 1 if the error has YAHC::Error::TERMINAL_ERROR() bit set. Otherwise
return 0.
yahc_conn_timeline
Return timeline of given connection. See more about timeline in description of "new"
method.
yahc_conn_request
Return request of given connection. See "request".
yahc_conn_response
Return response of given connection. See "request".
yahc_conn_attempt
Return current attempt starting from 1. The function can also return 0 if no attempts were
made yet.
yahc_conn_attempts_left
Return number of attempts left.
yahc_conn_socket_cache_id
Return socket_cache id for given connection. Should be used to generate key for
"socket_cache". If connection is not initialized yet "undef" is returned.
ERRORS
YAHC provides set of constants for errors. Each constant returns bitmask which can be used
to detect presence of a particular error, for example, in "callback". There is one
exception: YAHC::Error::NO_ERROR() return 0 indicating no error during request execution.
Error handling code can look like following:
$yahc->request({
...
callback => sub {
my (
$conn, # connection 'object'
$error, # one of YAHC::Error::* constants
$strerror # string representation of error
) = @_;
if ($error & YAHC::Error::TIMEOUT()) {
# A timeout has happened. Use one of YAHC::Error::*_TIMEOUT()
# constants for more clarification
} elsif ($error & YAHC::Error::SSL_ERROR()) {
# We had some issues with SSL. $error might have
# YAHC::Error::READ_ERROR() or YAHC::Error::WRITE_ERROR()
# indicating whether is was read or write error.
} elsif (...) { # etc
}
}
});
The list of error constants. The names are self-explanatory in many cases:
"YAHC::Error::NO_ERROR()"
Return value 0 (not a bitmask)> meaning no error
"YAHC::Error::REQUEST_TIMEOUT()"
"YAHC::Error::CONNECT_TIMEOUT()"
"YAHC::Error::DRAIN_TIMEOUT()"
"YAHC::Error::LIFETIME_TIMEOUT()"
"YAHC::Error::TIMEOUT()"
"YAHC::Error::RETRY_LIMIT()"
The connection has exhausted all available retries. This error is usually returned to
"callback". Check connection's errors via "yahc_conn_errors" to inspect the reasons of
failures for each individual attempt.
"YAHC::Error::CONNECT_ERROR()"
"YAHC::Error::READ_ERROR()"
"YAHC::Error::WRITE_ERROR()"
"YAHC::Error::SSL_ERROR()"
"YAHC::Error::REQUEST_ERROR()"
not used
"YAHC::Error::RESPONSE_ERROR()"
Server returned unparsable response
"YAHC::Error::CALLBACK_ERROR()"
Usually represents exception in one of the callbacks
"YAHC::Error::TERMINAL_ERROR()"
This bit is set when connection cannot be retried anymore and is forced to complete
"YAHC::Error::INTERNAL_ERROR()"
REPOSITORY
<https://github.com/ikruglov/YAHC>
NOTES
UTF8 flag
Note that YAHC has astonishing reduction in performance if any parameters participating in
building HTTP message has UTF8 flag set. Those fields are "protocol", "host", "port",
"method", "path", "query_string", "head", "body" and maybe others.
Just one example (check scripts/utf8_test.pl for code). Simple HTTP request with 10MB of
payload:
elapsed without utf8 flag: 0.039s
elapsed with utf8 flag: 0.540s
Because of this YAHC warns if detected UTF8-flagged payload. The user needs to make sure
that *all* data passed to YAHC is unflagged binary strings.
LIMITATIONS
• State 'RESOLVE DNS' is not implemented yet.
AUTHORS
Ivan Kruglov <ivan.kruglov@yahoo.com>
COPYRIGHT
Copyright (c) 2013-2017 Ivan Kruglov "<ivan.kruglov@yahoo.com>".
ACKNOWLEDGMENT
This module derived lots of ideas, code and docs from Hijk
<https://github.com/gugod/Hijk>. This module was originally developed for Booking.com.
LICENCE
The MIT License
DISCLAIMER OF WARRANTY
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