Provided by: libyahc-perl_0.035-4_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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