<?php
namespace Aws;
/**
* Builds a single handler function from zero or more middleware functions and
* a handler. The handler function is then used to send command objects and
* return a promise that is resolved with an AWS result object.
*
* The "front" of the list is invoked before the "end" of the list. You can add
* middleware to the front of the list using one of the "prepend" method, and
* the end of the list using one of the "append" method. The last function
* invoked in a handler list is the handler (a function that does not accept a
* next handler but rather is responsible for returning a promise that is
* fulfilled with an Aws\ResultInterface object).
*
* Handlers are ordered using a "step" that describes the step at which the
* SDK is when sending a command. The available steps are:
*
* - init: The command is being initialized, allowing you to do things like add
* default options.
* - validate: The command is being validated before it is serialized
* - build: The command is being serialized into an HTTP request. A middleware
* in this step MUST serialize an HTTP request and populate the "@request"
* parameter of a command with the request such that it is available to
* subsequent middleware.
* - sign: The request is being signed and prepared to be sent over the wire.
*
* Middleware can be registered with a name to allow you to easily add a
* middleware before or after another middleware by name. This also allows you
* to remove a middleware by name (in addition to removing by instance).
*/
class HandlerList implements \Countable
{
const INIT = 'init';
const VALIDATE = 'validate';
const BUILD = 'build';
const SIGN = 'sign';
/** @var callable */
private $handler;
/** @var array */
private $named = [];
/** @var array */
private $sorted;
/** @var callable|null */
private $interposeFn;
/** @var array Steps (in reverse order) */
private $steps = [
self::SIGN => [],
self::BUILD => [],
self::VALIDATE => [],
self::INIT => [],
];
/**
* @param callable $handler HTTP handler.
*/
public function __construct(callable $handler = null)
{
$this->handler = $handler;
}
/**
* Dumps a string representation of the list.
*
* @return string
*/
public function __toString()
{
$str = '';
$i = 0;
foreach (array_reverse($this->steps) as $k => $step) {
foreach (array_reverse($step) as $j => $tuple) {
$str .= "{$i}) Step: {$k}, ";
if ($tuple[1]) {
$str .= "Name: {$tuple[1]}, ";
}
$str .= "Function: " . $this->debugCallable($tuple[0]) . "\n";
$i++;
}
}
if ($this->handler) {
$str .= "{$i}) Handler: " . $this->debugCallable($this->handler) . "\n";
}
return $str;
}
/**
* Set the HTTP handler that actually returns a response.
*
* @param callable $handler Function that accepts a request and array of
* options and returns a Promise.
*/
public function setHandler(callable $handler)
{
$this->handler = $handler;
}
/**
* Returns true if the builder has a handler.
*
* @return bool
*/
public function hasHandler()
{
return (bool) $this->handler;
}
/**
* Append a middleware to the init step.
*
* @param callable $middleware Middleware function to add.
* @param string $name Name of the middleware.
*/
public function appendInit(callable $middleware, $name = null)
{
$this->add(self::INIT, $name, $middleware);
}
/**
* Prepend a middleware to the init step.
*
* @param callable $middleware Middleware function to add.
* @param string $name Name of the middleware.
*/
public function prependInit(callable $middleware, $name = null)
{
$this->add(self::INIT, $name, $middleware, true);
}
/**
* Append a middleware to the validate step.
*
* @param callable $middleware Middleware function to add.
* @param string $name Name of the middleware.
*/
public function appendValidate(callable $middleware, $name = null)
{
$this->add(self::VALIDATE, $name, $middleware);
}
/**
* Prepend a middleware to the validate step.
*
* @param callable $middleware Middleware function to add.
* @param string $name Name of the middleware.
*/
public function prependValidate(callable $middleware, $name = null)
{
$this->add(self::VALIDATE, $name, $middleware, true);
}
/**
* Append a middleware to the build step.
*
* @param callable $middleware Middleware function to add.
* @param string $name Name of the middleware.
*/
public function appendBuild(callable $middleware, $name = null)
{
$this->add(self::BUILD, $name, $middleware);
}
/**
* Prepend a middleware to the build step.
*
* @param callable $middleware Middleware function to add.
* @param string $name Name of the middleware.
*/
public function prependBuild(callable $middleware, $name = null)
{
$this->add(self::BUILD, $name, $middleware, true);
}
/**
* Append a middleware to the sign step.
*
* @param callable $middleware Middleware function to add.
* @param string $name Name of the middleware.
*/
public function appendSign(callable $middleware, $name = null)
{
$this->add(self::SIGN, $name, $middleware);
}
/**
* Prepend a middleware to the sign step.
*
* @param callable $middleware Middleware function to add.
* @param string $name Name of the middleware.
*/
public function prependSign(callable $middleware, $name = null)
{
$this->add(self::SIGN, $name, $middleware, true);
}
/**
* Add a middleware before the given middleware by name.
*
* @param string|callable $findName Add before this
* @param string $withName Optional name to give the middleware
* @param callable $middleware Middleware to add.
*/
public function before($findName, $withName, callable $middleware)
{
$this->splice($findName, $withName, $middleware, true);
}
/**
* Add a middleware after the given middleware by name.
*
* @param string|callable $findName Add after this
* @param string $withName Optional name to give the middleware
* @param callable $middleware Middleware to add.
*/
public function after($findName, $withName, callable $middleware)
{
$this->splice($findName, $withName, $middleware, false);
}
/**
* Remove a middleware by name or by instance from the list.
*
* @param string|callable $nameOrInstance Middleware to remove.
*/
public function remove($nameOrInstance)
{
if (is_callable($nameOrInstance)) {
$this->removeByInstance($nameOrInstance);
} elseif (is_string($nameOrInstance)) {
$this->removeByName($nameOrInstance);
}
}
/**
* Interpose a function between each middleware (e.g., allowing for a trace
* through the middleware layers).
*
* The interpose function is a function that accepts a "step" argument as a
* string and a "name" argument string. This function must then return a
* function that accepts the next handler in the list. This function must
* then return a function that accepts a CommandInterface and optional
* RequestInterface and returns a promise that is fulfilled with an
* Aws\ResultInterface or rejected with an Aws\Exception\AwsException
* object.
*
* @param callable|null $fn Pass null to remove any previously set function
*/
public function interpose(callable $fn = null)
{
$this->sorted = null;
$this->interposeFn = $fn;
}
/**
* Compose the middleware and handler into a single callable function.
*
* @return callable
*/
public function resolve()
{
if (!($prev = $this->handler)) {
throw new \LogicException('No handler has been specified');
}
if ($this->sorted === null) {
$this->sortMiddleware();
}
foreach ($this->sorted as $fn) {
$prev = $fn($prev);
}
return $prev;
}
public function count()
{
return count($this->steps[self::INIT])
+ count($this->steps[self::VALIDATE])
+ count($this->steps[self::BUILD])
+ count($this->steps[self::SIGN]);
}
/**
* Splices a function into the middleware list at a specific position.
*
* @param $findName
* @param $withName
* @param callable $middleware
* @param $before
*/
private function splice($findName, $withName, callable $middleware, $before)
{
if (!isset($this->named[$findName])) {
throw new \InvalidArgumentException("$findName not found");
}
$idx = $this->sorted = null;
$step = $this->named[$findName];
if ($withName) {
$this->named[$withName] = $step;
}
foreach ($this->steps[$step] as $i => $tuple) {
if ($tuple[1] === $findName) {
$idx = $i;
break;
}
}
$replacement = $before
? [$this->steps[$step][$idx], [$middleware, $withName]]
: [[$middleware, $withName], $this->steps[$step][$idx]];
array_splice($this->steps[$step], $idx, 1, $replacement);
}
/**
* Provides a debug string for a given callable.
*
* @param array|callable $fn Function to write as a string.
*
* @return string
*/
private function debugCallable($fn)
{
if (is_string($fn)) {
return "callable({$fn})";
} elseif (is_array($fn)) {
$ele = is_string($fn[0]) ? $fn[0] : get_class($fn[0]);
return "callable(['{$ele}', '{$fn[1]}'])";
} else {
return 'callable(' . spl_object_hash($fn) . ')';
}
}
/**
* Sort the middleware, and interpose if needed in the sorted list.
*/
private function sortMiddleware()
{
$this->sorted = [];
if (!$this->interposeFn) {
foreach ($this->steps as $step) {
foreach ($step as $fn) {
$this->sorted[] = $fn[0];
}
}
return;
}
$ifn = $this->interposeFn;
// Interpose the interposeFn into the handler stack.
foreach ($this->steps as $stepName => $step) {
foreach ($step as $fn) {
$this->sorted[] = $ifn($stepName, $fn[1]);
$this->sorted[] = $fn[0];
}
}
}
private function removeByName($name)
{
if (!isset($this->named[$name])) {
return;
}
$this->sorted = null;
$step = $this->named[$name];
$this->steps[$step] = array_values(
array_filter(
$this->steps[$step],
function ($tuple) use ($name) {
return $tuple[1] !== $name;
}
)
);
}
private function removeByInstance(callable $fn)
{
foreach ($this->steps as $k => $step) {
foreach ($step as $j => $tuple) {
if ($tuple[0] === $fn) {
$this->sorted = null;
unset($this->named[$this->steps[$k][$j][1]]);
unset($this->steps[$k][$j]);
}
}
}
}
/**
* Add a middleware to a step.
*
* @param string $step Middleware step.
* @param string $name Middleware name.
* @param callable $middleware Middleware function to add.
* @param bool $prepend Prepend instead of append.
*/
private function add($step, $name, callable $middleware, $prepend = false)
{
$this->sorted = null;
if ($prepend) {
$this->steps[$step][] = [$middleware, $name];
} else {
array_unshift($this->steps[$step], [$middleware, $name]);
}
if ($name) {
$this->named[$name] = $step;
}
}
}
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