Package pubsublite provides an easy way to publish and receive messages using the Pub/Sub Lite service.
Google Pub/Sub services are designed to provide reliable, many-to-many, asynchronous messaging between applications. Publisher applications can send messages to a topic and other applications can subscribe to that topic to receive the messages. By decoupling senders and receivers, Google Pub/Sub allows developers to communicate between independently written applications.
Compared to Cloud Pub/Sub, Pub/Sub Lite provides partitioned zonal data storage with predefined throughput and storage capacity. Guidance on how to choose between Cloud Pub/Sub and Pub/Sub Lite is available at https://cloud.google.com/pubsub/docs/choosing-pubsub-or-lite .
More information about Pub/Sub Lite is available at https://cloud.google.com/pubsub/lite .
Note: This library is in BETA. Backwards-incompatible changes may be made before stable v1.0.0 is released.
Introduction
See https://pkg.go.dev/cloud.google.com/go for authentication, timeouts, connection pooling and similar aspects of this package.
The following imports are required for code snippets below:
import ( "cloud.google.com/go/pubsub" "cloud.google.com/go/pubsublite" "cloud.google.com/go/pubsublite/pscompat" )
More complete examples can be found at https://pkg.go.dev/cloud.google.com/go/pubsublite#pkg-examples and https://pkg.go.dev/cloud.google.com/go/pubsublite/pscompat#pkg-examples .
Creating Topics
Messages are published to topics. Pub/Sub Lite topics may be created like so:
ctx := context . Background () const topicPath = "projects/my-project/locations/us-central1-c/topics/my-topic" topicConfig := pubsublite . TopicConfig { Name : topicPath , PartitionCount : 1 , PublishCapacityMiBPerSec : 4 , SubscribeCapacityMiBPerSec : 4 , PerPartitionBytes : 30 * 1024 * 1024 * 1024 , // 30 GiB RetentionDuration : pubsublite . InfiniteRetention , } adminClient , err := pubsublite . NewAdminClient ( ctx , "us-central1" ) if err != nil { // TODO: Handle error. } if _ , err = adminClient . CreateTopic ( ctx , topicConfig ); err != nil { // TODO: Handle error. }
See https://cloud.google.com/pubsub/lite/docs/topics for more information about how Pub/Sub Lite topics are configured.
See https://cloud.google.com/pubsub/lite/docs/locations for the list of zones where Pub/Sub Lite is available.
Publishing
The pubsublite/pscompat subpackage contains clients for publishing and receiving messages, which have similar interfaces to their pubsub.Topic and pubsub.Subscription counterparts in the Cloud Pub/Sub library: https://pkg.go.dev/cloud.google.com/go/pubsub .
Pub/Sub Lite uses gRPC streams extensively for high throughput. For more differences, see https://pkg.go.dev/cloud.google.com/go/pubsublite/pscompat .
To publish messages to a topic, first create a PublisherClient:
publisher , err := pscompat . NewPublisherClient ( ctx , topicPath ) if err != nil { // TODO: Handle error. }
Then call Publish:
result := publisher . Publish ( ctx , & pubsub . Message { Data : [] byte ( "payload" )})
Publish queues the message for publishing and returns immediately. When enough messages have accumulated, or enough time has elapsed, the batch of messages is sent to the Pub/Sub Lite service. Thresholds for batching can be configured in PublishSettings.
Publish returns a PublishResult, which behaves like a future; its Get method blocks until the message has been sent (or has failed to be sent) to the service:
id , err := result . Get ( ctx ) if err != nil { // TODO: Handle error. }
Once you've finishing publishing all messages, call Stop to flush all messages to the service and close gRPC streams. The PublisherClient can no longer be used after it has been stopped or has terminated due to a permanent service error.
publisher . Stop ()
See https://cloud.google.com/pubsub/lite/docs/publishing for more information about publishing.
Creating Subscriptions
To receive messages published to a topic, create a subscription to the topic. There may be more than one subscription per topic; each message that is published to the topic will be delivered to all of its subscriptions.
Pub/Sub Lite subscriptions may be created like so:
const subscriptionPath = "projects/my-project/locations/us-central1-c/subscriptions/my-subscription" subscriptionConfig := pubsublite . SubscriptionConfig { Name : subscriptionPath , Topic : topicPath , DeliveryRequirement : pubsublite . DeliverImmediately , } if _ , err = adminClient . CreateSubscription ( ctx , subscriptionConfig ); err != nil { // TODO: Handle error. }
See https://cloud.google.com/pubsub/lite/docs/subscriptions for more information about how subscriptions are configured.
Receiving
To receive messages for a subscription, first create a SubscriberClient:
subscriber , err := pscompat . NewSubscriberClient ( ctx , subscriptionPath )
Messages are then consumed from a subscription via callback. The callback may be invoked concurrently by multiple goroutines (one per partition that the subscriber client is connected to).
cctx , cancel := context . WithCancel ( ctx ) err = subscriber . Receive ( cctx , func ( ctx context . Context , m * pubsub . Message ) { log . Printf ( "Got message: %s" , m . Data ) m . Ack () }) if err != nil { // TODO: Handle error. }
Receive blocks until either the context is canceled or a fatal service error occurs. To terminate a call to Receive, cancel its context:
cancel ()
Clients must call pubsub.Message.Ack() or pubsub.Message.Nack() for every message received. Pub/Sub Lite does not have ACK deadlines. Pub/Sub Lite also does not actually have the concept of NACK. The default behavior terminates the SubscriberClient. In Pub/Sub Lite, only a single subscriber for a given subscription is connected to any partition at a time, and there is no other client that may be able to handle messages.
See https://cloud.google.com/pubsub/lite/docs/subscribing for more information about receiving messages.
Constants
InfiniteRetention
InfiniteRetention is a sentinel used in topic configs to denote an infinite retention duration (i.e. retain messages as long as there is available storage).
AdminClient
type
AdminClient
struct
{
// contains filtered or unexported fields
}
AdminClient provides admin operations for Pub/Sub Lite resources within a Google Cloud region. The zone component of resource paths must be within this region. See https://cloud.google.com/pubsub/lite/docs/locations for the list of zones where Pub/Sub Lite is available.
An AdminClient may be shared by multiple goroutines.
func NewAdminClient
func
NewAdminClient
(
ctx
context
.
Context
,
region
string
,
opts
...
option
.
ClientOption
)
(
*
AdminClient
,
error
)
NewAdminClient creates a new Pub/Sub Lite client to perform admin operations for resources within a given region.
func (*AdminClient) Close
func
(
ac
*
AdminClient
)
Close
()
error
Close releases any resources held by the client when it is no longer required. If the client is available for the lifetime of the program, then Close need not be called at exit.
func (*AdminClient) CreateSubscription
func
(
ac
*
AdminClient
)
CreateSubscription
(
ctx
context
.
Context
,
config
SubscriptionConfig
,
opts
...
CreateSubscriptionOption
)
(
*
SubscriptionConfig
,
error
)
CreateSubscription creates a new subscription from the given config. If the subscription already exists an error will be returned.
By default, a new subscription will only receive messages published after the subscription was created. Use StartingOffset to override.
Example
package
main
import
(
"context"
"cloud.google.com/go/pubsublite"
)
func
main
()
{
ctx
:=
context
.
Background
()
// NOTE: region must correspond to the zone of the topic and subscription.
admin
,
err
:=
pubsublite
.
NewAdminClient
(
ctx
,
"region"
)
if
err
!=
nil
{
// TODO: Handle error.
}
subscriptionConfig
:=
pubsublite
.
SubscriptionConfig
{
Name
:
"projects/my-project/locations/zone/subscriptions/my-subscription"
,
Topic
:
"projects/my-project/locations/zone/topics/my-topic"
,
// Do not wait for a published message to be successfully written to storage
// before delivering it to subscribers.
DeliveryRequirement
:
pubsublite
.
DeliverImmediately
,
}
_
,
err
=
admin
.
CreateSubscription
(
ctx
,
subscriptionConfig
)
if
err
!=
nil
{
// TODO: Handle error.
}
}
func (*AdminClient) CreateTopic
func
(
ac
*
AdminClient
)
CreateTopic
(
ctx
context
.
Context
,
config
TopicConfig
)
(
*
TopicConfig
,
error
)
CreateTopic creates a new topic from the given config. If the topic already exists an error will be returned.
Example
package
main
import
(
"context"
"cloud.google.com/go/pubsublite"
)
func
main
()
{
ctx
:=
context
.
Background
()
// NOTE: region must correspond to the zone of the topic.
admin
,
err
:=
pubsublite
.
NewAdminClient
(
ctx
,
"region"
)
if
err
!=
nil
{
// TODO: Handle error.
}
const
gib
=
1
<<
30
topicConfig
:=
pubsublite
.
TopicConfig
{
Name
:
"projects/my-project/locations/zone/topics/my-topic"
,
PartitionCount
:
2
,
// Must be at least 1.
PublishCapacityMiBPerSec
:
4
,
// Must be 4-16 MiB/s.
SubscribeCapacityMiBPerSec
:
8
,
// Must be 4-32 MiB/s.
PerPartitionBytes
:
30
*
gib
,
// Must be 30 GiB-10 TiB.
// Retain messages indefinitely as long as there is available storage.
RetentionDuration
:
pubsublite
.
InfiniteRetention
,
}
_
,
err
=
admin
.
CreateTopic
(
ctx
,
topicConfig
)
if
err
!=
nil
{
// TODO: Handle error.
}
}
func (*AdminClient) DeleteSubscription
func
(
ac
*
AdminClient
)
DeleteSubscription
(
ctx
context
.
Context
,
subscription
string
)
error
DeleteSubscription deletes a subscription. A valid subscription path has the format: "projects/PROJECT_ID/locations/ZONE/subscriptions/SUBSCRIPTION_ID".
Example
package
main
import
(
"context"
"cloud.google.com/go/pubsublite"
)
func
main
()
{
ctx
:=
context
.
Background
()
// NOTE: region must correspond to the zone of the subscription.
admin
,
err
:=
pubsublite
.
NewAdminClient
(
ctx
,
"region"
)
if
err
!=
nil
{
// TODO: Handle error.
}
const
subscription
=
"projects/my-project/locations/zone/subscriptions/my-subscription"
if
err
:=
admin
.
DeleteSubscription
(
ctx
,
subscription
);
err
!=
nil
{
// TODO: Handle error.
}
}
func (*AdminClient) DeleteTopic
func
(
ac
*
AdminClient
)
DeleteTopic
(
ctx
context
.
Context
,
topic
string
)
error
DeleteTopic deletes a topic. A valid topic path has the format: "projects/PROJECT_ID/locations/ZONE/topics/TOPIC_ID".
Example
package
main
import
(
"context"
"cloud.google.com/go/pubsublite"
)
func
main
()
{
ctx
:=
context
.
Background
()
// NOTE: region must correspond to the zone of the topic.
admin
,
err
:=
pubsublite
.
NewAdminClient
(
ctx
,
"region"
)
if
err
!=
nil
{
// TODO: Handle error.
}
const
topic
=
"projects/my-project/locations/zone/topics/my-topic"
if
err
:=
admin
.
DeleteTopic
(
ctx
,
topic
);
err
!=
nil
{
// TODO: Handle error.
}
}
func (*AdminClient) Subscription
func
(
ac
*
AdminClient
)
Subscription
(
ctx
context
.
Context
,
subscription
string
)
(
*
SubscriptionConfig
,
error
)
Subscription retrieves the configuration of a subscription. A valid subscription name has the format: "projects/PROJECT_ID/locations/ZONE/subscriptions/SUBSCRIPTION_ID".
func (*AdminClient) Subscriptions
func
(
ac
*
AdminClient
)
Subscriptions
(
ctx
context
.
Context
,
parent
string
)
*
SubscriptionIterator
Subscriptions retrieves the list of subscription configs for a given project and zone. A valid parent path has the format: "projects/PROJECT_ID/locations/ZONE".
Example
package
main
import
(
"context"
"fmt"
"cloud.google.com/go/pubsublite"
"google.golang.org/api/iterator"
)
func
main
()
{
ctx
:=
context
.
Background
()
// NOTE: region must correspond to the zone below.
admin
,
err
:=
pubsublite
.
NewAdminClient
(
ctx
,
"region"
)
if
err
!=
nil
{
// TODO: Handle error.
}
// List the configs of all subscriptions in the given zone for the project.
it
:=
admin
.
Subscriptions
(
ctx
,
"projects/my-project/locations/zone"
)
for
{
subscriptionConfig
,
err
:=
it
.
Next
()
if
err
==
iterator
.
Done
{
break
}
if
err
!=
nil
{
// TODO: Handle error.
}
fmt
.
Println
(
subscriptionConfig
)
}
}
func (*AdminClient) Topic
func
(
ac
*
AdminClient
)
Topic
(
ctx
context
.
Context
,
topic
string
)
(
*
TopicConfig
,
error
)
Topic retrieves the configuration of a topic. A valid topic path has the format: "projects/PROJECT_ID/locations/ZONE/topics/TOPIC_ID".
func (*AdminClient) TopicPartitionCount
func
(
ac
*
AdminClient
)
TopicPartitionCount
(
ctx
context
.
Context
,
topic
string
)
(
int
,
error
)
TopicPartitionCount returns the number of partitions for a topic. A valid topic path has the format: "projects/PROJECT_ID/locations/ZONE/topics/TOPIC_ID".
func (*AdminClient) TopicSubscriptions
func
(
ac
*
AdminClient
)
TopicSubscriptions
(
ctx
context
.
Context
,
topic
string
)
*
SubscriptionPathIterator
TopicSubscriptions retrieves the list of subscription paths for a topic. A valid topic path has the format: "projects/PROJECT_ID/locations/ZONE/topics/TOPIC_ID".
Example
package
main
import
(
"context"
"fmt"
"cloud.google.com/go/pubsublite"
"google.golang.org/api/iterator"
)
func
main
()
{
ctx
:=
context
.
Background
()
// NOTE: region must correspond to the zone of the topic.
admin
,
err
:=
pubsublite
.
NewAdminClient
(
ctx
,
"region"
)
if
err
!=
nil
{
// TODO: Handle error.
}
// List the paths of all subscriptions of a topic.
const
topic
=
"projects/my-project/locations/zone/topics/my-topic"
it
:=
admin
.
TopicSubscriptions
(
ctx
,
topic
)
for
{
subscriptionPath
,
err
:=
it
.
Next
()
if
err
==
iterator
.
Done
{
break
}
if
err
!=
nil
{
// TODO: Handle error.
}
fmt
.
Println
(
subscriptionPath
)
}
}
func (*AdminClient) Topics
func
(
ac
*
AdminClient
)
Topics
(
ctx
context
.
Context
,
parent
string
)
*
TopicIterator
Topics retrieves the list of topic configs for a given project and zone. A valid parent path has the format: "projects/PROJECT_ID/locations/ZONE".
Example
package
main
import
(
"context"
"fmt"
"cloud.google.com/go/pubsublite"
"google.golang.org/api/iterator"
)
func
main
()
{
ctx
:=
context
.
Background
()
// NOTE: region must correspond to the zone below.
admin
,
err
:=
pubsublite
.
NewAdminClient
(
ctx
,
"region"
)
if
err
!=
nil
{
// TODO: Handle error.
}
// List the configs of all topics in the given zone for the project.
it
:=
admin
.
Topics
(
ctx
,
"projects/my-project/locations/zone"
)
for
{
topicConfig
,
err
:=
it
.
Next
()
if
err
==
iterator
.
Done
{
break
}
if
err
!=
nil
{
// TODO: Handle error.
}
fmt
.
Println
(
topicConfig
)
}
}
func (*AdminClient) UpdateSubscription
func
(
ac
*
AdminClient
)
UpdateSubscription
(
ctx
context
.
Context
,
config
SubscriptionConfigToUpdate
)
(
*
SubscriptionConfig
,
error
)
UpdateSubscription updates an existing subscription from the given config and returns the new subscription config. UpdateSubscription returns an error if no fields were modified.
Example
package
main
import
(
"context"
"cloud.google.com/go/pubsublite"
)
func
main
()
{
ctx
:=
context
.
Background
()
// NOTE: region must correspond to the zone of the subscription.
admin
,
err
:=
pubsublite
.
NewAdminClient
(
ctx
,
"region"
)
if
err
!=
nil
{
// TODO: Handle error.
}
updateConfig
:=
pubsublite
.
SubscriptionConfigToUpdate
{
Name
:
"projects/my-project/locations/zone/subscriptions/my-subscription"
,
// Deliver a published message to subscribers after it has been successfully
// written to storage.
DeliveryRequirement
:
pubsublite
.
DeliverAfterStored
,
}
_
,
err
=
admin
.
UpdateSubscription
(
ctx
,
updateConfig
)
if
err
!=
nil
{
// TODO: Handle error.
}
}
func (*AdminClient) UpdateTopic
func
(
ac
*
AdminClient
)
UpdateTopic
(
ctx
context
.
Context
,
config
TopicConfigToUpdate
)
(
*
TopicConfig
,
error
)
UpdateTopic updates an existing topic from the given config and returns the new topic config. UpdateTopic returns an error if no fields were modified.
Example
package
main
import
(
"context"
"time"
"cloud.google.com/go/pubsublite"
)
func
main
()
{
ctx
:=
context
.
Background
()
// NOTE: region must correspond to the zone of the topic.
admin
,
err
:=
pubsublite
.
NewAdminClient
(
ctx
,
"region"
)
if
err
!=
nil
{
// TODO: Handle error.
}
updateConfig
:=
pubsublite
.
TopicConfigToUpdate
{
Name
:
"projects/my-project/locations/zone/topics/my-topic"
,
PartitionCount
:
3
,
// Only increases currently supported.
PublishCapacityMiBPerSec
:
8
,
SubscribeCapacityMiBPerSec
:
16
,
RetentionDuration
:
24
*
time
.
Hour
,
// Garbage collect messages older than 24 hours.
}
_
,
err
=
admin
.
UpdateTopic
(
ctx
,
updateConfig
)
if
err
!=
nil
{
// TODO: Handle error.
}
}
BacklogLocation
type
BacklogLocation
int
BacklogLocation refers to a location with respect to the message backlog.
End, Beginning
const
(
// End refers to the location past all currently published messages. End
// skips the entire message backlog.
End
BacklogLocation
=
iota
+
1
// Beginning refers to the location of the oldest retained message.
Beginning
)
CreateSubscriptionOption
type
CreateSubscriptionOption
interface
{
Apply
(
*
createSubscriptionSettings
)
}
CreateSubscriptionOption is an option for AdminClient.CreateSubscription.
func StartingOffset
func
StartingOffset
(
location
BacklogLocation
)
CreateSubscriptionOption
StartingOffset specifies the offset at which a newly created subscription will start receiving messages.
DeliveryRequirement
type
DeliveryRequirement
int
DeliveryRequirement specifies when a subscription should send messages to subscribers relative to persistence in storage.
UnspecifiedDeliveryRequirement, DeliverImmediately, DeliverAfterStored
const
(
// UnspecifiedDeliveryRequirement represents an unset delivery requirement.
UnspecifiedDeliveryRequirement
DeliveryRequirement
=
iota
// DeliverImmediately means the server will not wait for a published message
// to be successfully written to storage before delivering it to subscribers.
DeliverImmediately
// DeliverAfterStored means the server will not deliver a published message to
// subscribers until the message has been successfully written to storage.
// This will result in higher end-to-end latency, but consistent delivery.
DeliverAfterStored
)
SubscriptionConfig
type
SubscriptionConfig
struct
{
// The full path of the subscription, in the format:
// "projects/PROJECT_ID/locations/ZONE/subscriptions/SUBSCRIPTION_ID".
//
// - PROJECT_ID: The project ID (e.g. "my-project") or the project number
// (e.g. "987654321") can be provided.
// - ZONE: The Google Cloud zone (e.g. "us-central1-a") of the corresponding
// topic.
// - SUBSCRIPTION_ID: The ID of the subscription (e.g. "my-subscription"). See
// https://cloud.google.com/pubsub/docs/admin#resource_names for information
// about valid subscription IDs.
Name
string
// The path of the topic that this subscription is attached to, in the format:
// "projects/PROJECT_ID/locations/ZONE/topics/TOPIC_ID". This cannot be
// changed after creation.
Topic
string
// Whether a message should be delivered to subscribers immediately after it
// has been published or after it has been successfully written to storage.
DeliveryRequirement
DeliveryRequirement
}
SubscriptionConfig describes the properties of a Pub/Sub Lite subscription, which is attached to a Pub/Sub Lite topic. See https://cloud.google.com/pubsub/lite/docs/subscriptions for more information about how subscriptions are configured.
SubscriptionConfigToUpdate
type
SubscriptionConfigToUpdate
struct
{
// The full path of the subscription to update, in the format:
// "projects/PROJECT_ID/locations/ZONE/subscriptions/SUBSCRIPTION_ID".
// Required.
Name
string
// If non-zero, updates the message delivery requirement.
DeliveryRequirement
DeliveryRequirement
}
SubscriptionConfigToUpdate specifies the properties to update for a subscription.
SubscriptionIterator
type
SubscriptionIterator
struct
{
// contains filtered or unexported fields
}
SubscriptionIterator is an iterator that returns a list of subscription configs.
func (*SubscriptionIterator) Next
func
(
s
*
SubscriptionIterator
)
Next
()
(
*
SubscriptionConfig
,
error
)
Next returns the next subscription config. The second return value will be iterator.Done if there are no more subscription configs.
SubscriptionPathIterator
type
SubscriptionPathIterator
struct
{
// contains filtered or unexported fields
}
SubscriptionPathIterator is an iterator that returns a list of subscription paths.
func (*SubscriptionPathIterator) Next
func
(
sp
*
SubscriptionPathIterator
)
Next
()
(
string
,
error
)
Next returns the next subscription path, which has format: "projects/PROJECT_ID/locations/ZONE/subscriptions/SUBSCRIPTION_ID". The second return value will be iterator.Done if there are no more subscription paths.
TopicConfig
type
TopicConfig
struct
{
// The full path of the topic, in the format:
// "projects/PROJECT_ID/locations/ZONE/topics/TOPIC_ID".
//
// - PROJECT_ID: The project ID (e.g. "my-project") or the project number
// (e.g. "987654321") can be provided.
// - ZONE: The Google Cloud zone (e.g. "us-central1-a") where the topic is
// located. See https://cloud.google.com/pubsub/lite/docs/locations for the
// list of zones where Pub/Sub Lite is available.
// - TOPIC_ID: The ID of the topic (e.g. "my-topic"). See
// https://cloud.google.com/pubsub/docs/admin#resource_names for information
// about valid topic IDs.
Name
string
// The number of partitions in the topic. Must be at least 1. Can be increased
// after creation, but not decreased.
PartitionCount
int
// Publish throughput capacity per partition in MiB/s.
// Must be >= 4 and <= 16.="" publishcapacitymibpersec=""> int
// Subscribe throughput capacity per partition in MiB/s.
// Must be >= 4 and <= 32.="" subscribecapacitymibpersec=""> int
// The provisioned storage, in bytes, per partition. If the number of bytes
// stored in any of the topic's partitions grows beyond this value, older
// messages will be dropped to make room for newer ones, regardless of the
// value of `RetentionDuration`. Must be >= 30 GiB.
PerPartitionBytes
int64
// How long a published message is retained. If set to `InfiniteRetention`,
// messages will be retained as long as the bytes retained for each partition
// is below `PerPartitionBytes`. Otherwise, must be > 0.
RetentionDuration
time
.
Duration
}
TopicConfig describes the properties of a Pub/Sub Lite topic. See https://cloud.google.com/pubsub/lite/docs/topics for more information about how topics are configured.
TopicConfigToUpdate
type
TopicConfigToUpdate
struct
{
// The full path of the topic to update, in the format:
// "projects/PROJECT_ID/locations/ZONE/topics/TOPIC_ID". Required.
Name
string
// If non-zero, will update the number of partitions in the topic.
// Set value must be >= 1. The number of partitions can only be increased, not
// decreased.
PartitionCount
int
// If non-zero, will update the publish throughput capacity per partition.
// Set value must be >= 4 and <= 16.="" publishcapacitymibpersec=""> int
// If non-zero, will update the subscribe throughput capacity per partition.
// Set value must be >= 4 and <= 32.="" subscribecapacitymibpersec=""> int
// If non-zero, will update the provisioned storage per partition.
// Set value must be >= 30 GiB.
PerPartitionBytes
int64
// If specified, will update how long a published message is retained. To
// clear a retention duration (i.e. retain messages as long as there is
// available storage), set this to `InfiniteRetention`.
RetentionDuration
optional
.
Duration
}
TopicConfigToUpdate specifies the properties to update for a topic.
TopicIterator
type
TopicIterator
struct
{
// contains filtered or unexported fields
}
TopicIterator is an iterator that returns a list of topic configs.
func (*TopicIterator) Next
func
(
t
*
TopicIterator
)
Next
()
(
*
TopicConfig
,
error
)
Next returns the next topic config. The second return value will be iterator.Done if there are no more topic configs.
