<?php
namespace Aws\Signature;
use Aws\Exception\UnresolvedSignatureException;
/**
* Signature providers.
*
* A signature provider is a function that accepts a version, service, and
* region and returns a {@see SignatureInterface} object on success or NULL if
* no signature can be created from the provided arguments.
*
* You can wrap your calls to a signature provider with the
* {@see SignatureProvider::resolve} function to ensure that a signature object
* is created. If a signature object is not created, then the resolve()
* function will throw a {@see Aws\Exception\UnresolvedSignatureException}.
*
* use Aws\Signature\SignatureProvider;
* $provider = SignatureProvider::defaultProvider();
* // Returns a SignatureInterface or NULL.
* $signer = $provider('v4', 's3', 'us-west-2');
* // Returns a SignatureInterface or throws.
* $signer = SignatureProvider::resolve($provider, 'no', 's3', 'foo');
*
* You can compose multiple providers into a single provider using
* {@see Aws\or_chain}. This function accepts providers as arguments and
* returns a new function that will invoke each provider until a non-null value
* is returned.
*
* $a = SignatureProvider::defaultProvider();
* $b = function ($version, $service, $region) {
* if ($version === 'foo') {
* return new MyFooSignature();
* }
* };
* $c = \Aws\or_chain($a, $b);
* $signer = $c('v4', 'abc', '123'); // $a handles this.
* $signer = $c('foo', 'abc', '123'); // $b handles this.
* $nullValue = $c('???', 'abc', '123'); // Neither can handle this.
*/
class SignatureProvider
{
/**
* Resolves and signature provider and ensures a non-null return value.
*
* @param callable $provider Provider function to invoke.
* @param string $version Signature version.
* @param string $service Service name.
* @param string $region Region name.
*
* @return SignatureInterface
* @throws UnresolvedSignatureException
*/
public static function resolve(callable $provider, $version, $service, $region)
{
$result = $provider($version, $service, $region);
if ($result instanceof SignatureInterface) {
return $result;
}
throw new UnresolvedSignatureException(
"Unable to resolve a signature for $version/$service/$region.\n"
. "Valid signature versions include v4 and anonymous."
);
}
/**
* Default SDK signature provider.
*
* @return callable
*/
public static function defaultProvider()
{
return self::memoize(self::version());
}
/**
* Creates a signature provider that caches previously created signature
* objects. The computed cache key is the concatenation of the version,
* service, and region.
*
* @param callable $provider Signature provider to wrap.
*
* @return callable
*/
public static function memoize(callable $provider)
{
$cache = [];
return function ($version, $service, $region) use (&$cache, $provider) {
$key = "($version)($service)($region)";
if (!isset($cache[$key])) {
$cache[$key] = $provider($version, $service, $region);
}
return $cache[$key];
};
}
/**
* Creates signature objects from known signature versions.
*
* This provider currently recognizes the following signature versions:
*
* - v4: Signature version 4.
* - anonymous: Does not sign requests.
*
* @return callable
*/
public static function version()
{
return function ($version, $service, $region) {
switch ($version) {
case 'v4':
return $service === 's3'
? new S3SignatureV4($service, $region)
: new SignatureV4($service, $region);
case 'anonymous':
return new AnonymousSignature();
default:
return null;
}
};
}
}
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