com.amazonaws.services.cognitosync

Interface AmazonCognitoSync

All Known Subinterfaces:

AmazonCognitoSyncAsync

All Known Implementing Classes:

AmazonCognitoSyncAsyncClient, AmazonCognitoSyncClient

public interface AmazonCognitoSync

Interface for accessing AmazonCognitoSync. Amazon Cognito Sync

Amazon Cognito Sync provides an AWS service and client library that enable cross-device syncing of application-related user data. High-level client libraries are available for both iOS and Android. You can use these libraries to persist data locally so that it's available even if the device is offline. Developer credentials don't need to be stored on the mobile device to access the service. You can use Amazon Cognito to obtain a normalized user ID and credentials. User data is persisted in a dataset that can store up to 1 MB of key-value pairs, and you can have up to 20 datasets per user identity.

With Amazon Cognito Sync, the data stored for each identity is accessible only to credentials assigned to that identity. In order to use the Cognito Sync service, you need to make API calls using credentials retrieved with Amazon Cognito Identity service .

If you want to use Cognito Sync in an Android or iOS application, you will probably want to make API calls via the AWS Mobile SDK. To learn more, see the Developer Guide for Android and the Developer Guide for iOS .

Method Summary

Methods

Modifier and Type	Method and Description
BulkPublishResult	bulkPublish(BulkPublishRequest bulkPublishRequest) Initiates a bulk publish of all existing datasets for an Identity Pool to the configured stream.
DeleteDatasetResult	deleteDataset(DeleteDatasetRequest deleteDatasetRequest) Deletes the specific dataset.
DescribeDatasetResult	describeDataset(DescribeDatasetRequest describeDatasetRequest) Gets meta data about a dataset by identity and dataset name.
DescribeIdentityPoolUsageResult	describeIdentityPoolUsage(DescribeIdentityPoolUsageRequest describeIdentityPoolUsageRequest) Gets usage details (for example, data storage) about a particular identity pool.
DescribeIdentityUsageResult	describeIdentityUsage(DescribeIdentityUsageRequest describeIdentityUsageRequest) Gets usage information for an identity, including number of datasets and data usage.
GetBulkPublishDetailsResult	getBulkPublishDetails(GetBulkPublishDetailsRequest getBulkPublishDetailsRequest) Get the status of the last BulkPublish operation for an identity pool.
ResponseMetadata	getCachedResponseMetadata(AmazonWebServiceRequest request) Returns additional metadata for a previously executed successful request, typically used for debugging issues where a service isn't acting as expected.
GetCognitoEventsResult	getCognitoEvents(GetCognitoEventsRequest getCognitoEventsRequest) Gets the events and the corresponding Lambda functions associated with an identity pool.
GetIdentityPoolConfigurationResult	getIdentityPoolConfiguration(GetIdentityPoolConfigurationRequest getIdentityPoolConfigurationRequest) Gets the configuration settings of an identity pool.
ListDatasetsResult	listDatasets(ListDatasetsRequest listDatasetsRequest) Lists datasets for an identity.
ListIdentityPoolUsageResult	listIdentityPoolUsage(ListIdentityPoolUsageRequest listIdentityPoolUsageRequest) Gets a list of identity pools registered with Cognito.
ListRecordsResult	listRecords(ListRecordsRequest listRecordsRequest) Gets paginated records, optionally changed after a particular sync count for a dataset and identity.
RegisterDeviceResult	registerDevice(RegisterDeviceRequest registerDeviceRequest) Registers a device to receive push sync notifications.
void	setCognitoEvents(SetCognitoEventsRequest setCognitoEventsRequest) Sets the AWS Lambda function for a given event type for an identity pool.
void	setEndpoint(String endpoint) Overrides the default endpoint for this client ("https://cognito-sync.us-east-1.amazonaws.com/").
SetIdentityPoolConfigurationResult	setIdentityPoolConfiguration(SetIdentityPoolConfigurationRequest setIdentityPoolConfigurationRequest) Sets the necessary configuration for push sync.
void	setRegion(Region region) An alternative to setEndpoint(String), sets the regional endpoint for this client's service calls.
void	shutdown() Shuts down this client object, releasing any resources that might be held open.
SubscribeToDatasetResult	subscribeToDataset(SubscribeToDatasetRequest subscribeToDatasetRequest) Subscribes to receive notifications when a dataset is modified by another device.
UnsubscribeFromDatasetResult	unsubscribeFromDataset(UnsubscribeFromDatasetRequest unsubscribeFromDatasetRequest) Unsubscribes from receiving notifications when a dataset is modified by another device.
UpdateRecordsResult	updateRecords(UpdateRecordsRequest updateRecordsRequest) Posts updates to records and adds and deletes records for a dataset and user.

Method Detail

setEndpoint

void setEndpoint(String endpoint)
                 throws IllegalArgumentException

Overrides the default endpoint for this client ("https://cognito-sync.us-east-1.amazonaws.com/"). Callers can use this method to control which AWS region they want to work with.

Callers can pass in just the endpoint (ex: "cognito-sync.us-east-1.amazonaws.com/") or a full URL, including the protocol (ex: "https://cognito-sync.us-east-1.amazonaws.com/"). If the protocol is not specified here, the default protocol from this client's ClientConfiguration will be used, which by default is HTTPS.

For more information on using AWS regions with the AWS SDK for Java, and a complete list of all available endpoints for all AWS services, see: http://developer.amazonwebservices.com/connect/entry.jspa?externalID=3912

This method is not threadsafe. An endpoint should be configured when the client is created and before any service requests are made. Changing it afterwards creates inevitable race conditions for any service requests in transit or retrying.

Parameters:

endpoint - The endpoint (ex: "cognito-sync.us-east-1.amazonaws.com/") or a full URL, including the protocol (ex: "https://cognito-sync.us-east-1.amazonaws.com/") of the region specific AWS endpoint this client will communicate with.

Throws:

IllegalArgumentException - If any problems are detected with the specified endpoint.

setRegion

void setRegion(Region region)
               throws IllegalArgumentException

An alternative to setEndpoint(String), sets the regional endpoint for this client's service calls. Callers can use this method to control which AWS region they want to work with.

By default, all service endpoints in all regions use the https protocol. To use http instead, specify it in the ClientConfiguration supplied at construction.

This method is not threadsafe. A region should be configured when the client is created and before any service requests are made. Changing it afterwards creates inevitable race conditions for any service requests in transit or retrying.

Parameters:

region - The region this client will communicate with. See Region.getRegion(com.amazonaws.regions.Regions) for accessing a given region.

Throws:

IllegalArgumentException - If the given region is null, or if this service isn't available in the given region. See Region.isServiceSupported(String)

See Also:

Region.getRegion(com.amazonaws.regions.Regions), Region.createClient(Class, com.amazonaws.auth.AWSCredentialsProvider, ClientConfiguration)

updateRecords

UpdateRecordsResult updateRecords(UpdateRecordsRequest updateRecordsRequest)
                                  throws AmazonServiceException,
                                         AmazonClientException

Posts updates to records and adds and deletes records for a dataset and user.

The sync count in the record patch is your last known sync count for that record. The server will reject an UpdateRecords request with a ResourceConflictException if you try to patch a record with a new value but a stale sync count.

For example, if the sync count on the server is 5 for a key called highScore and you try and submit a new highScore with sync count of 4, the request will be rejected. To obtain the current sync count for a record, call ListRecords. On a successful update of the record, the response returns the new sync count for that record. You should present that sync count the next time you try to update that same record. When the record does not exist, specify the sync count as 0.

This API can be called with temporary user credentials provided by Cognito Identity or with developer credentials.

Parameters:

updateRecordsRequest - Container for the necessary parameters to execute the UpdateRecords service method on AmazonCognitoSync.

Returns:

The response from the UpdateRecords service method, as returned by AmazonCognitoSync.

Throws:

LimitExceededException

TooManyRequestsException

ResourceConflictException

InvalidParameterException

ResourceNotFoundException

InvalidLambdaFunctionOutputException

NotAuthorizedException

LambdaThrottledException

InternalErrorException

AmazonClientException - If any internal errors are encountered inside the client while attempting to make the request or handle the response. For example if a network connection is not available.

AmazonServiceException - If an error response is returned by AmazonCognitoSync indicating either a problem with the data in the request, or a server side issue.

setCognitoEvents

void setCognitoEvents(SetCognitoEventsRequest setCognitoEventsRequest)
                      throws AmazonServiceException,
                             AmazonClientException

Sets the AWS Lambda function for a given event type for an identity pool. This request only updates the key/value pair specified. Other key/values pairs are not updated. To remove a key value pair, pass a empty value for the particular key.

This API can only be called with developer credentials. You cannot call this API with the temporary user credentials provided by Cognito Identity.

Parameters:

setCognitoEventsRequest - Container for the necessary parameters to execute the SetCognitoEvents service method on AmazonCognitoSync.

Throws:

TooManyRequestsException

InvalidParameterException

ResourceNotFoundException

NotAuthorizedException

InternalErrorException

AmazonClientException - If any internal errors are encountered inside the client while attempting to make the request or handle the response. For example if a network connection is not available.

AmazonServiceException - If an error response is returned by AmazonCognitoSync indicating either a problem with the data in the request, or a server side issue.

getCognitoEvents

GetCognitoEventsResult getCognitoEvents(GetCognitoEventsRequest getCognitoEventsRequest)
                                        throws AmazonServiceException,
                                               AmazonClientException

Gets the events and the corresponding Lambda functions associated with an identity pool.

This API can only be called with developer credentials. You cannot call this API with the temporary user credentials provided by Cognito Identity.

Parameters:

getCognitoEventsRequest - Container for the necessary parameters to execute the GetCognitoEvents service method on AmazonCognitoSync.

Returns:

The response from the GetCognitoEvents service method, as returned by AmazonCognitoSync.

Throws:

TooManyRequestsException

InvalidParameterException

ResourceNotFoundException

NotAuthorizedException

InternalErrorException

AmazonClientException - If any internal errors are encountered inside the client while attempting to make the request or handle the response. For example if a network connection is not available.

AmazonServiceException - If an error response is returned by AmazonCognitoSync indicating either a problem with the data in the request, or a server side issue.

describeIdentityUsage

DescribeIdentityUsageResult describeIdentityUsage(DescribeIdentityUsageRequest describeIdentityUsageRequest)
                                                  throws AmazonServiceException,
                                                         AmazonClientException

Gets usage information for an identity, including number of datasets and data usage.

This API can be called with temporary user credentials provided by Cognito Identity or with developer credentials.

Parameters:

describeIdentityUsageRequest - Container for the necessary parameters to execute the DescribeIdentityUsage service method on AmazonCognitoSync.

Returns:

The response from the DescribeIdentityUsage service method, as returned by AmazonCognitoSync.

Throws:

TooManyRequestsException

InvalidParameterException

ResourceNotFoundException

NotAuthorizedException

InternalErrorException

AmazonClientException - If any internal errors are encountered inside the client while attempting to make the request or handle the response. For example if a network connection is not available.

AmazonServiceException - If an error response is returned by AmazonCognitoSync indicating either a problem with the data in the request, or a server side issue.

unsubscribeFromDataset

UnsubscribeFromDatasetResult unsubscribeFromDataset(UnsubscribeFromDatasetRequest unsubscribeFromDatasetRequest)
                                                    throws AmazonServiceException,
                                                           AmazonClientException

Unsubscribes from receiving notifications when a dataset is modified by another device.

This API can only be called with temporary credentials provided by Cognito Identity. You cannot call this API with developer credentials.

Parameters:

unsubscribeFromDatasetRequest - Container for the necessary parameters to execute the UnsubscribeFromDataset service method on AmazonCognitoSync.

Returns:

The response from the UnsubscribeFromDataset service method, as returned by AmazonCognitoSync.

Throws:

TooManyRequestsException

InvalidConfigurationException

InvalidParameterException

ResourceNotFoundException

NotAuthorizedException

InternalErrorException

AmazonClientException - If any internal errors are encountered inside the client while attempting to make the request or handle the response. For example if a network connection is not available.

AmazonServiceException - If an error response is returned by AmazonCognitoSync indicating either a problem with the data in the request, or a server side issue.

setIdentityPoolConfiguration

SetIdentityPoolConfigurationResult setIdentityPoolConfiguration(SetIdentityPoolConfigurationRequest setIdentityPoolConfigurationRequest)
                                                                throws AmazonServiceException,
                                                                       AmazonClientException

Sets the necessary configuration for push sync.

This API can only be called with developer credentials. You cannot call this API with the temporary user credentials provided by Cognito Identity.

Parameters:

setIdentityPoolConfigurationRequest - Container for the necessary parameters to execute the SetIdentityPoolConfiguration service method on AmazonCognitoSync.

Returns:

The response from the SetIdentityPoolConfiguration service method, as returned by AmazonCognitoSync.

Throws:

TooManyRequestsException

InvalidParameterException

ResourceNotFoundException

NotAuthorizedException

InternalErrorException

ConcurrentModificationException

AmazonClientException - If any internal errors are encountered inside the client while attempting to make the request or handle the response. For example if a network connection is not available.

AmazonServiceException - If an error response is returned by AmazonCognitoSync indicating either a problem with the data in the request, or a server side issue.

getIdentityPoolConfiguration

GetIdentityPoolConfigurationResult getIdentityPoolConfiguration(GetIdentityPoolConfigurationRequest getIdentityPoolConfigurationRequest)
                                                                throws AmazonServiceException,
                                                                       AmazonClientException

Gets the configuration settings of an identity pool.

This API can only be called with developer credentials. You cannot call this API with the temporary user credentials provided by Cognito Identity.

Parameters:

getIdentityPoolConfigurationRequest - Container for the necessary parameters to execute the GetIdentityPoolConfiguration service method on AmazonCognitoSync.

Returns:

The response from the GetIdentityPoolConfiguration service method, as returned by AmazonCognitoSync.

Throws:

TooManyRequestsException

InvalidParameterException

ResourceNotFoundException

NotAuthorizedException

InternalErrorException

AmazonClientException - If any internal errors are encountered inside the client while attempting to make the request or handle the response. For example if a network connection is not available.

AmazonServiceException - If an error response is returned by AmazonCognitoSync indicating either a problem with the data in the request, or a server side issue.

subscribeToDataset

SubscribeToDatasetResult subscribeToDataset(SubscribeToDatasetRequest subscribeToDatasetRequest)
                                            throws AmazonServiceException,
                                                   AmazonClientException

Subscribes to receive notifications when a dataset is modified by another device.

This API can only be called with temporary credentials provided by Cognito Identity. You cannot call this API with developer credentials.

Parameters:

subscribeToDatasetRequest - Container for the necessary parameters to execute the SubscribeToDataset service method on AmazonCognitoSync.

Returns:

The response from the SubscribeToDataset service method, as returned by AmazonCognitoSync.

Throws:

TooManyRequestsException

InvalidConfigurationException

InvalidParameterException

ResourceNotFoundException

NotAuthorizedException

InternalErrorException

AmazonClientException - If any internal errors are encountered inside the client while attempting to make the request or handle the response. For example if a network connection is not available.

AmazonServiceException - If an error response is returned by AmazonCognitoSync indicating either a problem with the data in the request, or a server side issue.

describeIdentityPoolUsage

DescribeIdentityPoolUsageResult describeIdentityPoolUsage(DescribeIdentityPoolUsageRequest describeIdentityPoolUsageRequest)
                                                          throws AmazonServiceException,
                                                                 AmazonClientException

Gets usage details (for example, data storage) about a particular identity pool.

This API can only be called with developer credentials. You cannot call this API with the temporary user credentials provided by Cognito Identity.

Parameters:

describeIdentityPoolUsageRequest - Container for the necessary parameters to execute the DescribeIdentityPoolUsage service method on AmazonCognitoSync.

Returns:

The response from the DescribeIdentityPoolUsage service method, as returned by AmazonCognitoSync.

Throws:

TooManyRequestsException

InvalidParameterException

ResourceNotFoundException

NotAuthorizedException

InternalErrorException

AmazonClientException - If any internal errors are encountered inside the client while attempting to make the request or handle the response. For example if a network connection is not available.

AmazonServiceException - If an error response is returned by AmazonCognitoSync indicating either a problem with the data in the request, or a server side issue.

listDatasets

ListDatasetsResult listDatasets(ListDatasetsRequest listDatasetsRequest)
                                throws AmazonServiceException,
                                       AmazonClientException

Lists datasets for an identity. With Amazon Cognito Sync, each identity has access only to its own data. Thus, the credentials used to make this API call need to have access to the identity data.

ListDatasets can be called with temporary user credentials provided by Cognito Identity or with developer credentials. You should use the Cognito Identity credentials to make this API call.

Parameters:

listDatasetsRequest - Container for the necessary parameters to execute the ListDatasets service method on AmazonCognitoSync.

Returns:

The response from the ListDatasets service method, as returned by AmazonCognitoSync.

Throws:

TooManyRequestsException

InvalidParameterException

NotAuthorizedException

InternalErrorException

AmazonClientException - If any internal errors are encountered inside the client while attempting to make the request or handle the response. For example if a network connection is not available.

AmazonServiceException - If an error response is returned by AmazonCognitoSync indicating either a problem with the data in the request, or a server side issue.

listIdentityPoolUsage

ListIdentityPoolUsageResult listIdentityPoolUsage(ListIdentityPoolUsageRequest listIdentityPoolUsageRequest)
                                                  throws AmazonServiceException,
                                                         AmazonClientException

Gets a list of identity pools registered with Cognito.

ListIdentityPoolUsage can only be called with developer credentials. You cannot make this API call with the temporary user credentials provided by Cognito Identity.

Parameters:

listIdentityPoolUsageRequest - Container for the necessary parameters to execute the ListIdentityPoolUsage service method on AmazonCognitoSync.

Returns:

The response from the ListIdentityPoolUsage service method, as returned by AmazonCognitoSync.

Throws:

TooManyRequestsException

InvalidParameterException

NotAuthorizedException

InternalErrorException

AmazonClientException - If any internal errors are encountered inside the client while attempting to make the request or handle the response. For example if a network connection is not available.

AmazonServiceException - If an error response is returned by AmazonCognitoSync indicating either a problem with the data in the request, or a server side issue.

listRecords

ListRecordsResult listRecords(ListRecordsRequest listRecordsRequest)
                              throws AmazonServiceException,
                                     AmazonClientException

Gets paginated records, optionally changed after a particular sync count for a dataset and identity. With Amazon Cognito Sync, each identity has access only to its own data. Thus, the credentials used to make this API call need to have access to the identity data.

ListRecords can be called with temporary user credentials provided by Cognito Identity or with developer credentials. You should use Cognito Identity credentials to make this API call.

Parameters:

listRecordsRequest - Container for the necessary parameters to execute the ListRecords service method on AmazonCognitoSync.

Returns:

The response from the ListRecords service method, as returned by AmazonCognitoSync.

Throws:

TooManyRequestsException

InvalidParameterException

NotAuthorizedException

InternalErrorException

AmazonClientException - If any internal errors are encountered inside the client while attempting to make the request or handle the response. For example if a network connection is not available.

AmazonServiceException - If an error response is returned by AmazonCognitoSync indicating either a problem with the data in the request, or a server side issue.

getBulkPublishDetails

GetBulkPublishDetailsResult getBulkPublishDetails(GetBulkPublishDetailsRequest getBulkPublishDetailsRequest)
                                                  throws AmazonServiceException,
                                                         AmazonClientException

Get the status of the last BulkPublish operation for an identity pool.

This API can only be called with developer credentials. You cannot call this API with the temporary user credentials provided by Cognito Identity.

Parameters:

getBulkPublishDetailsRequest - Container for the necessary parameters to execute the GetBulkPublishDetails service method on AmazonCognitoSync.

Returns:

The response from the GetBulkPublishDetails service method, as returned by AmazonCognitoSync.

Throws:

InvalidParameterException

ResourceNotFoundException

NotAuthorizedException

InternalErrorException

AmazonClientException - If any internal errors are encountered inside the client while attempting to make the request or handle the response. For example if a network connection is not available.

AmazonServiceException - If an error response is returned by AmazonCognitoSync indicating either a problem with the data in the request, or a server side issue.

bulkPublish

BulkPublishResult bulkPublish(BulkPublishRequest bulkPublishRequest)
                              throws AmazonServiceException,
                                     AmazonClientException

Initiates a bulk publish of all existing datasets for an Identity Pool to the configured stream. Customers are limited to one successful bulk publish per 24 hours. Bulk publish is an asynchronous request, customers can see the status of the request via the GetBulkPublishDetails operation.

This API can only be called with developer credentials. You cannot call this API with the temporary user credentials provided by Cognito Identity.

Parameters:

bulkPublishRequest - Container for the necessary parameters to execute the BulkPublish service method on AmazonCognitoSync.

Returns:

The response from the BulkPublish service method, as returned by AmazonCognitoSync.

Throws:

InvalidParameterException

ResourceNotFoundException

NotAuthorizedException

InternalErrorException

DuplicateRequestException

AlreadyStreamedException

AmazonClientException - If any internal errors are encountered inside the client while attempting to make the request or handle the response. For example if a network connection is not available.

AmazonServiceException - If an error response is returned by AmazonCognitoSync indicating either a problem with the data in the request, or a server side issue.

describeDataset

DescribeDatasetResult describeDataset(DescribeDatasetRequest describeDatasetRequest)
                                      throws AmazonServiceException,
                                             AmazonClientException

Gets meta data about a dataset by identity and dataset name. With Amazon Cognito Sync, each identity has access only to its own data. Thus, the credentials used to make this API call need to have access to the identity data.

This API can be called with temporary user credentials provided by Cognito Identity or with developer credentials. You should use Cognito Identity credentials to make this API call.

Parameters:

describeDatasetRequest - Container for the necessary parameters to execute the DescribeDataset service method on AmazonCognitoSync.

Returns:

The response from the DescribeDataset service method, as returned by AmazonCognitoSync.

Throws:

TooManyRequestsException

InvalidParameterException

ResourceNotFoundException

NotAuthorizedException

InternalErrorException

AmazonClientException - If any internal errors are encountered inside the client while attempting to make the request or handle the response. For example if a network connection is not available.

AmazonServiceException - If an error response is returned by AmazonCognitoSync indicating either a problem with the data in the request, or a server side issue.

deleteDataset

DeleteDatasetResult deleteDataset(DeleteDatasetRequest deleteDatasetRequest)
                                  throws AmazonServiceException,
                                         AmazonClientException

Deletes the specific dataset. The dataset will be deleted permanently, and the action can't be undone. Datasets that this dataset was merged with will no longer report the merge. Any subsequent operation on this dataset will result in a ResourceNotFoundException.

This API can be called with temporary user credentials provided by Cognito Identity or with developer credentials.

Parameters:

deleteDatasetRequest - Container for the necessary parameters to execute the DeleteDataset service method on AmazonCognitoSync.

Returns:

The response from the DeleteDataset service method, as returned by AmazonCognitoSync.

Throws:

TooManyRequestsException

ResourceConflictException

InvalidParameterException

ResourceNotFoundException

NotAuthorizedException

InternalErrorException

AmazonClientException - If any internal errors are encountered inside the client while attempting to make the request or handle the response. For example if a network connection is not available.

AmazonServiceException - If an error response is returned by AmazonCognitoSync indicating either a problem with the data in the request, or a server side issue.

registerDevice

RegisterDeviceResult registerDevice(RegisterDeviceRequest registerDeviceRequest)
                                    throws AmazonServiceException,
                                           AmazonClientException

Registers a device to receive push sync notifications.

This API can only be called with temporary credentials provided by Cognito Identity. You cannot call this API with developer credentials.

Parameters:

registerDeviceRequest - Container for the necessary parameters to execute the RegisterDevice service method on AmazonCognitoSync.

Returns:

The response from the RegisterDevice service method, as returned by AmazonCognitoSync.

Throws:

TooManyRequestsException

InvalidConfigurationException

InvalidParameterException

ResourceNotFoundException

NotAuthorizedException

InternalErrorException

AmazonClientException - If any internal errors are encountered inside the client while attempting to make the request or handle the response. For example if a network connection is not available.

AmazonServiceException - If an error response is returned by AmazonCognitoSync indicating either a problem with the data in the request, or a server side issue.

shutdown

void shutdown()

Shuts down this client object, releasing any resources that might be held open. This is an optional method, and callers are not expected to call it, but can if they want to explicitly release any open resources. Once a client has been shutdown, it should not be used to make any more requests.

getCachedResponseMetadata

ResponseMetadata getCachedResponseMetadata(AmazonWebServiceRequest request)

Returns additional metadata for a previously executed successful request, typically used for debugging issues where a service isn't acting as expected. This data isn't considered part of the result data returned by an operation, so it's available through this separate, diagnostic interface.

Response metadata is only cached for a limited period of time, so if you need to access this extra diagnostic information for an executed request, you should use this method to retrieve it as soon as possible after executing a request.

Parameters:

request - The originally executed request.

Returns:

The response metadata for the specified request, or null if none is available.