<?php
/*
* Copyright 2018 Google LLC
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are
* met:
*
* * Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* * Redistributions in binary form must reproduce the above
* copyright notice, this list of conditions and the following disclaimer
* in the documentation and/or other materials provided with the
* distribution.
* * Neither the name of Google Inc. nor the names of its
* contributors may be used to endorse or promote products derived from
* this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
* A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
* OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
namespace Google\ApiCore;
use Google\ApiCore\LongRunning\OperationsClient;
use Google\ApiCore\Middleware\CredentialsWrapperMiddleware;
use Google\ApiCore\Middleware\FixedHeaderMiddleware;
use Google\ApiCore\Middleware\OperationsMiddleware;
use Google\ApiCore\Middleware\OptionsFilterMiddleware;
use Google\ApiCore\Middleware\PagedMiddleware;
use Google\ApiCore\Middleware\RetryMiddleware;
use Google\ApiCore\Transport\GrpcFallbackTransport;
use Google\ApiCore\Transport\GrpcTransport;
use Google\ApiCore\Transport\RestTransport;
use Google\ApiCore\Transport\TransportInterface;
use Automattic\WooCommerce\GoogleListingsAndAds\Vendor\Google\Auth\CredentialsLoader;
use Automattic\WooCommerce\GoogleListingsAndAds\Vendor\Google\Auth\FetchAuthTokenInterface;
use Google\LongRunning\Operation;
use Google\Protobuf\Internal\Message;
use Grpc\Gcp\ApiConfig;
use Grpc\Gcp\Config;
use Automattic\WooCommerce\GoogleListingsAndAds\Vendor\GuzzleHttp\Promise\PromiseInterface;
use LogicException;
/**
* Common functions used to work with various clients.
*/
trait GapicClientTrait
{
use ArrayTrait;
use ValidationTrait {
ValidationTrait::validate as traitValidate;
}
use GrpcSupportTrait;
/** @var TransportInterface */
private $transport;
private $credentialsWrapper;
private static $gapicVersionFromFile;
/** @var RetrySettings[] $retrySettings */
private $retrySettings;
private $serviceName;
private $agentHeader;
private $descriptors;
private $transportCallMethods = [
Call::UNARY_CALL => 'startUnaryCall',
Call::BIDI_STREAMING_CALL => 'startBidiStreamingCall',
Call::CLIENT_STREAMING_CALL => 'startClientStreamingCall',
Call::SERVER_STREAMING_CALL => 'startServerStreamingCall',
];
/**
* Initiates an orderly shutdown in which preexisting calls continue but new
* calls are immediately cancelled.
*
* @experimental
*/
public function close()
{
$this->transport->close();
}
/**
* Get the transport for the client. This method is protected to support
* use by customized clients.
*
* @access private
* @return TransportInterface
*/
protected function getTransport()
{
return $this->transport;
}
/**
* Get the credentials for the client. This method is protected to support
* use by customized clients.
*
* @access private
* @return CredentialsWrapper
*/
protected function getCredentialsWrapper()
{
return $this->credentialsWrapper;
}
private static function getGapicVersion(array $options)
{
if (isset($options['libVersion'])) {
return $options['libVersion'];
} else {
if (!isset(self::$gapicVersionFromFile)) {
self::$gapicVersionFromFile = AgentHeader::readGapicVersionFromFile(__CLASS__);
}
return self::$gapicVersionFromFile;
}
}
private static function initGrpcGcpConfig($hostName, $confPath)
{
$apiConfig = new ApiConfig();
$apiConfig->mergeFromJsonString(file_get_contents($confPath));
$config = new Config($hostName, $apiConfig);
return $config;
}
/**
* Get default options. This function should be "overridden" by clients using late static
* binding to provide default options to the client.
*
* @return array
* @access private
*/
private static function getClientDefaults()
{
return [];
}
private function buildClientOptions(array $options)
{
// Build $defaultOptions starting from top level
// variables, then going into deeper nesting, so that
// we will not encounter missing keys
$defaultOptions = self::getClientDefaults();
$defaultOptions += [
'disableRetries' => false,
'credentials' => null,
'credentialsConfig' => [],
'transport' => null,
'transportConfig' => [],
'gapicVersion' => self::getGapicVersion($options),
'libName' => null,
'libVersion' => null,
'apiEndpoint' => null,
'clientCertSource' => null,
];
$supportedTransports = $this->supportedTransports();
foreach ($supportedTransports as $transportName) {
if (!array_key_exists($transportName, $defaultOptions['transportConfig'])) {
$defaultOptions['transportConfig'][$transportName] = [];
}
}
if (in_array('grpc', $supportedTransports)) {
$defaultOptions['transportConfig']['grpc'] = [
'stubOpts' => ['grpc.service_config_disable_resolution' => 1]
];
}
// Merge defaults into $options starting from top level
// variables, then going into deeper nesting, so that
// we will not encounter missing keys
$options += $defaultOptions;
$options['credentialsConfig'] += $defaultOptions['credentialsConfig'];
$options['transportConfig'] += $defaultOptions['transportConfig']; // @phpstan-ignore-line
if (isset($options['transportConfig']['grpc'])) {
$options['transportConfig']['grpc'] += $defaultOptions['transportConfig']['grpc'];
$options['transportConfig']['grpc']['stubOpts'] += $defaultOptions['transportConfig']['grpc']['stubOpts'];
}
if (isset($options['transportConfig']['rest'])) {
$options['transportConfig']['rest'] += $defaultOptions['transportConfig']['rest'];
}
$this->modifyClientOptions($options);
// serviceAddress is now deprecated and acts as an alias for apiEndpoint
if (isset($options['serviceAddress'])) {
$options['apiEndpoint'] = $this->pluck('serviceAddress', $options, false);
}
// If an API endpoint is set, ensure the "audience" does not conflict
// with the custom endpoint by setting "user defined" scopes.
if ($options['apiEndpoint'] != $defaultOptions['apiEndpoint']
&& empty($options['credentialsConfig']['scopes'])
&& !empty($options['credentialsConfig']['defaultScopes'])
) {
$options['credentialsConfig']['scopes'] = $options['credentialsConfig']['defaultScopes'];
}
if (extension_loaded('sysvshm')
&& isset($options['gcpApiConfigPath'])
&& file_exists($options['gcpApiConfigPath'])
&& isset($options['apiEndpoint'])) {
$grpcGcpConfig = self::initGrpcGcpConfig(
$options['apiEndpoint'],
$options['gcpApiConfigPath']
);
if (array_key_exists('stubOpts', $options['transportConfig']['grpc'])) {
$options['transportConfig']['grpc']['stubOpts'] += [
'grpc_call_invoker' => $grpcGcpConfig->callInvoker()
];
} else {
$options['transportConfig']['grpc'] += [
'stubOpts' => [
'grpc_call_invoker' => $grpcGcpConfig->callInvoker()
]
];
}
}
// mTLS: detect and load the default clientCertSource if the environment variable
// "GOOGLE_API_USE_CLIENT_CERTIFICATE" is true, and the cert source is available
if (empty($options['clientCertSource']) && CredentialsLoader::shouldLoadClientCertSource()) {
if ($defaultCertSource = CredentialsLoader::getDefaultClientCertSource()) {
$options['clientCertSource'] = function () use ($defaultCertSource) {
$cert = call_user_func($defaultCertSource);
// the key and the cert are returned in one string
return [$cert, $cert];
};
}
}
// mTLS: If no apiEndpoint has been supplied by the user, and either
// GOOGLE_API_USE_MTLS_ENDPOINT tells us to, or mTLS is available, use the mTLS endpoint.
if ($options['apiEndpoint'] === $defaultOptions['apiEndpoint']
&& $this->shouldUseMtlsEndpoint($options)
) {
$options['apiEndpoint'] = self::determineMtlsEndpoint($options['apiEndpoint']);
}
return $options;
}
private function shouldUseMtlsEndpoint($options)
{
$mtlsEndpointEnvVar = getenv('GOOGLE_API_USE_MTLS_ENDPOINT');
if ('always' === $mtlsEndpointEnvVar) {
return true;
}
if ('never' === $mtlsEndpointEnvVar) {
return false;
}
// For all other cases, assume "auto" and return true if clientCertSource exists
return !empty($options['clientCertSource']);
}
private static function determineMtlsEndpoint($apiEndpoint)
{
$parts = explode('.', $apiEndpoint);
if (count($parts) < 3) {
return $apiEndpoint; // invalid endpoint!
}
return sprintf('%s.mtls.%s', array_shift($parts), implode('.', $parts));
}
/**
* Configures the GAPIC client based on an array of options.
*
* @param array $options {
* An array of required and optional arguments.
*
* @type string $apiEndpoint
* The address of the API remote host, for example "example.googleapis.com. May also
* include the port, for example "example.googleapis.com:443"
* @type string $serviceAddress
* **Deprecated**. This option will be removed in the next major release. Please
* utilize the `$apiEndpoint` option instead.
* @type bool $disableRetries
* Determines whether or not retries defined by the client configuration should be
* disabled. Defaults to `false`.
* @type string|array $clientConfig
* Client method configuration, including retry settings. This option can be either a
* path to a JSON file, or a PHP array containing the decoded JSON data.
* By default this settings points to the default client config file, which is provided
* in the resources folder.
* @type string|array|FetchAuthTokenInterface|CredentialsWrapper $credentials
* The credentials to be used by the client to authorize API calls. This option
* accepts either a path to a credentials file, or a decoded credentials file as a
* PHP array.
* *Advanced usage*: In addition, this option can also accept a pre-constructed
* \Google\Auth\FetchAuthTokenInterface object or \Google\ApiCore\CredentialsWrapper
* object. Note that when one of these objects are provided, any settings in
* $authConfig will be ignored.
* @type array $credentialsConfig
* Options used to configure credentials, including auth token caching, for the client.
* For a full list of supporting configuration options, see
* \Google\ApiCore\CredentialsWrapper::build.
* @type string|TransportInterface $transport
* The transport used for executing network requests. May be either the string `rest`,
* `grpc`, or 'grpc-fallback'. Defaults to `grpc` if gRPC support is detected on the system.
* *Advanced usage*: Additionally, it is possible to pass in an already instantiated
* TransportInterface object. Note that when this objects is provided, any settings in
* $transportConfig, and any `$apiEndpoint` setting, will be ignored.
* @type array $transportConfig
* Configuration options that will be used to construct the transport. Options for
* each supported transport type should be passed in a key for that transport. For
* example:
* $transportConfig = [
* 'grpc' => [...],
* 'rest' => [...],
* 'grpc-fallback' => [...],
* ];
* See the GrpcTransport::build and RestTransport::build
* methods for the supported options.
* @type string $versionFile
* The path to a file which contains the current version of the client.
* @type string $descriptorsConfigPath
* The path to a descriptor configuration file.
* @type string $serviceName
* The name of the service.
* @type string $libName
* The name of the client application.
* @type string $libVersion
* The version of the client application.
* @type string $gapicVersion
* The code generator version of the GAPIC library.
* @type callable $clientCertSource
* A callable which returns the client cert as a string.
* }
* @throws ValidationException
*/
private function setClientOptions(array $options)
{
// serviceAddress is now deprecated and acts as an alias for apiEndpoint
if (isset($options['serviceAddress'])) {
$options['apiEndpoint'] = $this->pluck('serviceAddress', $options, false);
}
$this->validateNotNull($options, [
'apiEndpoint',
'serviceName',
'descriptorsConfigPath',
'clientConfig',
'disableRetries',
'credentialsConfig',
'transportConfig',
]);
$this->traitValidate($options, [
'credentials',
'transport',
'gapicVersion',
'libName',
'libVersion',
]);
$clientConfig = $options['clientConfig'];
if (is_string($clientConfig)) {
$clientConfig = json_decode(file_get_contents($clientConfig), true);
}
$this->serviceName = $options['serviceName'];
$this->retrySettings = RetrySettings::load(
$this->serviceName,
$clientConfig,
$options['disableRetries']
);
// Edge case: If the client has the gRPC extension installed, but is
// a REST-only library, then the grpcVersion header should not be set.
if ($this->transport instanceof GrpcTransport) {
$options['grpcVersion'] = phpversion('grpc');
unset($options['restVersion']);
} elseif ($this->transport instanceof RestTransport
|| $this->transport instanceof GrpcFallbackTransport) {
unset($options['grpcVersion']);
$options['restVersion'] = Version::getApiCoreVersion();
}
$this->agentHeader = AgentHeader::buildAgentHeader(
$this->pluckArray([
'libName',
'libVersion',
'gapicVersion'
], $options)
);
self::validateFileExists($options['descriptorsConfigPath']);
$descriptors = require($options['descriptorsConfigPath']);
$this->descriptors = $descriptors['interfaces'][$this->serviceName];
$this->credentialsWrapper = $this->createCredentialsWrapper(
$options['credentials'],
$options['credentialsConfig']
);
$transport = $options['transport'] ?: self::defaultTransport();
$this->transport = $transport instanceof TransportInterface
? $transport
: $this->createTransport(
$options['apiEndpoint'],
$transport,
$options['transportConfig'],
$options['clientCertSource']
);
}
/**
* @param mixed $credentials
* @param array $credentialsConfig
* @return CredentialsWrapper
* @throws ValidationException
*/
private function createCredentialsWrapper($credentials, array $credentialsConfig)
{
if (is_null($credentials)) {
return CredentialsWrapper::build($credentialsConfig);
} elseif (is_string($credentials) || is_array($credentials)) {
return CredentialsWrapper::build(['keyFile' => $credentials] + $credentialsConfig);
} elseif ($credentials instanceof FetchAuthTokenInterface) {
$authHttpHandler = isset($credentialsConfig['authHttpHandler'])
? $credentialsConfig['authHttpHandler']
: null;
return new CredentialsWrapper($credentials, $authHttpHandler);
} elseif ($credentials instanceof CredentialsWrapper) {
return $credentials;
} else {
throw new ValidationException(
'Unexpected value in $auth option, got: ' .
print_r($credentials, true)
);
}
}
/**
* @param string $apiEndpoint
* @param string $transport
* @param array $transportConfig
* @param callable $clientCertSource
* @return TransportInterface
* @throws ValidationException
*/
private function createTransport(
$apiEndpoint,
$transport,
array $transportConfig,
callable $clientCertSource = null
) {
if (!is_string($transport)) {
throw new ValidationException(
"'transport' must be a string, instead got:" .
print_r($transport, true)
);
}
$supportedTransports = self::supportedTransports();
if (!in_array($transport, $supportedTransports)) {
throw new ValidationException(sprintf(
'Unexpected transport option "%s". Supported transports: %s',
$transport,
implode(', ', $supportedTransports)
));
}
$configForSpecifiedTransport = isset($transportConfig[$transport])
? $transportConfig[$transport]
: [];
$configForSpecifiedTransport['clientCertSource'] = $clientCertSource;
switch ($transport) {
case 'grpc':
return GrpcTransport::build($apiEndpoint, $configForSpecifiedTransport);
case 'grpc-fallback':
return GrpcFallbackTransport::build($apiEndpoint, $configForSpecifiedTransport);
case 'rest':
if (!isset($configForSpecifiedTransport['restClientConfigPath'])) {
throw new ValidationException(
"The 'restClientConfigPath' config is required for 'rest' transport."
);
}
$restConfigPath = $configForSpecifiedTransport['restClientConfigPath'];
return RestTransport::build($apiEndpoint, $restConfigPath, $configForSpecifiedTransport);
default:
throw new ValidationException(
"Unexpected 'transport' option: $transport. " .
"Supported values: ['grpc', 'rest', 'grpc-fallback']"
);
}
}
/**
* @param array $options
* @return OperationsClient
*/
private function createOperationsClient(array $options)
{
$this->pluckArray([
'serviceName',
'clientConfig',
'descriptorsConfigPath',
], $options);
// User-supplied operations client
if ($operationsClient = $this->pluck('operationsClient', $options, false)) {
return $operationsClient;
}
// operationsClientClass option
$operationsClientClass = $this->pluck('operationsClientClass', $options, false)
?: OperationsCLient::class;
return new $operationsClientClass($options);
}
/**
* @return string
*/
private static function defaultTransport()
{
return self::getGrpcDependencyStatus()
? 'grpc'
: 'rest';
}
/**
* @param string $methodName
* @param string $decodeType
* @param array $optionalArgs {
* Call Options
*
* @type array $headers [optional] key-value array containing headers
* @type int $timeoutMillis [optional] the timeout in milliseconds for the call
* @type array $transportOptions [optional] transport-specific call options
* @type RetrySettings|array $retrySettings [optional] A retry settings
* override for the call.
* }
* @param Message $request
* @param int $callType
* @param string $interfaceName
*
* @return PromiseInterface|BidiStream|ClientStream|ServerStream
*/
private function startCall(
$methodName,
$decodeType,
array $optionalArgs = [],
Message $request = null,
$callType = Call::UNARY_CALL,
$interfaceName = null
) {
$callStack = $this->createCallStack(
$this->configureCallConstructionOptions($methodName, $optionalArgs)
);
$descriptor = isset($this->descriptors[$methodName]['grpcStreaming'])
? $this->descriptors[$methodName]['grpcStreaming']
: null;
$call = new Call(
$this->buildMethod($interfaceName, $methodName),
$decodeType,
$request,
$descriptor,
$callType
);
switch ($callType) {
case Call::UNARY_CALL:
$this->modifyUnaryCallable($callStack);
break;
case Call::BIDI_STREAMING_CALL:
case Call::CLIENT_STREAMING_CALL:
case Call::SERVER_STREAMING_CALL:
$this->modifyStreamingCallable($callStack);
break;
}
return $callStack($call, $optionalArgs + array_filter([
'audience' => self::getDefaultAudience()
]));
}
/**
* @param array $callConstructionOptions {
* Call Construction Options
*
* @type RetrySettings $retrySettings [optional] A retry settings override
* For the call.
* }
*
* @return callable
*/
private function createCallStack(array $callConstructionOptions)
{
$quotaProject = $this->credentialsWrapper->getQuotaProject();
$fixedHeaders = $this->agentHeader;
if ($quotaProject) {
$fixedHeaders += [
'X-Goog-User-Project' => [$quotaProject]
];
}
$callStack = function (Call $call, array $options) {
$startCallMethod = $this->transportCallMethods[$call->getCallType()];
return $this->transport->$startCallMethod($call, $options);
};
$callStack = new CredentialsWrapperMiddleware($callStack, $this->credentialsWrapper);
$callStack = new FixedHeaderMiddleware($callStack, $fixedHeaders, true);
$callStack = new RetryMiddleware($callStack, $callConstructionOptions['retrySettings']);
$callStack = new OptionsFilterMiddleware($callStack, [
'headers',
'timeoutMillis',
'transportOptions',
'metadataCallback',
'audience',
]);
return $callStack;
}
/**
* @param string $methodName
* @param array $optionalArgs {
* Optional arguments
*
* @type RetrySettings|array $retrySettings [optional] A retry settings
* override for the call.
* }
*
* @return array
*/
private function configureCallConstructionOptions($methodName, array $optionalArgs)
{
$retrySettings = $this->retrySettings[$methodName];
// Allow for retry settings to be changed at call time
if (isset($optionalArgs['retrySettings'])) {
if ($optionalArgs['retrySettings'] instanceof RetrySettings) {
$retrySettings = $optionalArgs['retrySettings'];
} else {
$retrySettings = $retrySettings->with(
$optionalArgs['retrySettings']
);
}
}
return [
'retrySettings' => $retrySettings,
];
}
/**
* @param string $methodName
* @param array $optionalArgs {
* Call Options
*
* @type array $headers [optional] key-value array containing headers
* @type int $timeoutMillis [optional] the timeout in milliseconds for the call
* @type array $transportOptions [optional] transport-specific call options
* }
* @param Message $request
* @param OperationsClient|object $client
* @param string $interfaceName
* @param string $operationClass If provided, will be used instead of the default
* operation response class of {@see Google\LongRunning\Operation}.
*
* @return PromiseInterface
*/
private function startOperationsCall(
$methodName,
array $optionalArgs,
Message $request,
$client,
$interfaceName = null,
$operationClass = null
) {
$callStack = $this->createCallStack(
$this->configureCallConstructionOptions($methodName, $optionalArgs)
);
$descriptor = $this->descriptors[$methodName]['longRunning'];
// Call the methods supplied in "additionalArgumentMethods" on the request Message object
// to build the "additionalOperationArguments" option for the operation response.
if (isset($descriptor['additionalArgumentMethods'])) {
$additionalArgs = [];
foreach ($descriptor['additionalArgumentMethods'] as $additionalArgsMethodName) {
$additionalArgs[] = $request->$additionalArgsMethodName();
}
$descriptor['additionalOperationArguments'] = $additionalArgs;
unset($descriptor['additionalArgumentMethods']);
}
$callStack = new OperationsMiddleware($callStack, $client, $descriptor);
$call = new Call(
$this->buildMethod($interfaceName, $methodName),
$operationClass ?: Operation::class,
$request,
[],
Call::UNARY_CALL
);
$this->modifyUnaryCallable($callStack);
return $callStack($call, $optionalArgs + array_filter([
'audience' => self::getDefaultAudience()
]));
}
/**
* @param string $methodName
* @param array $optionalArgs
* @param string $decodeType
* @param Message $request
* @param string $interfaceName
*
* @return PagedListResponse
*/
private function getPagedListResponse(
$methodName,
array $optionalArgs,
$decodeType,
Message $request,
$interfaceName = null
) {
$callStack = $this->createCallStack(
$this->configureCallConstructionOptions($methodName, $optionalArgs)
);
$descriptor = new PageStreamingDescriptor(
$this->descriptors[$methodName]['pageStreaming']
);
$callStack = new PagedMiddleware($callStack, $descriptor);
$call = new Call(
$this->buildMethod($interfaceName, $methodName),
$decodeType,
$request,
[],
Call::UNARY_CALL
);
$this->modifyUnaryCallable($callStack);
return $callStack($call, $optionalArgs + array_filter([
'audience' => self::getDefaultAudience()
]))->wait();
}
/**
* @param string $interfaceName
* @param string $methodName
*
* @return string
*/
private function buildMethod($interfaceName, $methodName)
{
return sprintf(
'%s/%s',
$interfaceName ?: $this->serviceName,
$methodName
);
}
/**
* The SERVICE_ADDRESS constant is set by GAPIC clients
*/
private static function getDefaultAudience()
{
if (!defined('self::SERVICE_ADDRESS')) {
return null;
}
return 'https://' . self::SERVICE_ADDRESS . '/'; // @phpstan-ignore-line
}
/**
* This defaults to all three transports, which One-Platform supports.
* Discovery clients should define this function and only return ['rest'].
*/
private static function supportedTransports()
{
return ['grpc', 'grpc-fallback', 'rest'];
}
// Gapic Client Extension Points
// The methods below provide extension points that can be used to customize client
// functionality. These extension points are currently considered
// private and may change at any time.
/**
* Modify options passed to the client before calling setClientOptions.
*
* @param array $options
* @access private
*/
protected function modifyClientOptions(array &$options)
{
// Do nothing - this method exists to allow option modification by partial veneers.
}
/**
* Modify the unary callable.
*
* @param callable $callable
* @access private
*/
protected function modifyUnaryCallable(callable &$callable)
{
// Do nothing - this method exists to allow callable modification by partial veneers.
}
/**
* Modify the streaming callable.
*
* @param callable $callable
* @access private
*/
protected function modifyStreamingCallable(callable &$callable)
{
// Do nothing - this method exists to allow callable modification by partial veneers.
}
}