Enum Handler 

#[non_exhaustive]
pub enum Handler {
    AtLeastOnce(AtLeastOnce),
    ExactlyOnce(ExactlyOnce),
}

A handler for acknowledging or rejecting messages.

Example

use google_cloud_pubsub::model::Message;
fn on_message(m: Message, h: Handler) {
  match process(m) {
    Ok(_) => h.ack(),
    Err(e) => {
        println!("failed to process message: {e:?}");
        h.nack();
    }
  }
}

fn process(m: Message) -> anyhow::Result<()> {
  // some business logic here...
}

To acknowledge (ack) a message, you call Handler::ack().

To reject (nack) a message, you call Handler::nack(). The service will redeliver the message.

Exactly-once delivery

If your subscription has exactly-once delivery enabled, you should destructure this enum into its Handler::ExactlyOnce branch.

Only when ExactlyOnce::confirmed_ack() returns Ok can you be certain that the message will not be redelivered.

use google_cloud_pubsub::model::Message;
async fn on_message(m: Message, h: Handler) {
  let Handler::ExactlyOnce(h) = h else {
    panic!("Oops, my subscription does not have exactly-once delivery enabled.")
  };
  match h.confirmed_ack().await {
    Ok(()) => println!("Confirmed ack for message={m:?}. The message will not be redelivered."),
    Err(e) => println!("Failed to confirm ack for message={m:?} with error={e:?}"),
  }
}

Variants (Non-exhaustive)

Non-exhaustive enums could have additional variants added in future. Therefore, when matching against variants of non-exhaustive enums, an extra wildcard arm must be added to account for any future variants.

AtLeastOnce(AtLeastOnce)

ExactlyOnce(ExactlyOnce)

Implementations

impl Handler

pub fn ack(self)

Acknowledge the message associated with this handler.

Example

use google_cloud_pubsub::model::Message;
fn on_message(m: Message, h: Handler) {
  println!("Received message: {m:?}");
  h.ack();
}

Note that the acknowledgement is best effort. The message may still be redelivered to this client, or another client, even if exactly-once delivery is enabled on the subscription.

pub fn nack(self)

Rejects the message associated with this handler.

Example

use google_cloud_pubsub::model::Message;
fn on_message(m: Message, h: Handler) {
  println!("Received message: {m:?}");
  h.nack();
}

The message will be removed from this Subscriber’s lease management. The service will redeliver this message, possibly to another client.

Trait Implementations

impl Debug for Handler

fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), Error>

Formats the value using the given formatter.