Pagination support

Some Web API methods defines cursors and pagination, to give you an ability to load a lot of data continually (using batching and continually making many requests).

Examples: conversations.history, conversations.list, users.list, ...

To help with those methods Slack Morphism provides additional a “scroller” implementation, which deal with all scrolling/batching requests for you.

For example for users.list:

use slack_morphism::prelude::*;

use std::time::Duration;

async fn example() -> Result<(), Box<dyn std::error::Error + Send + Sync>> {

    let hyper_connector = SlackClientHyperConnector::new()?;
    let client = SlackClient::new(hyper_connector);
    
    let token_value: SlackApiTokenValue = "xoxb-89.....".into();
    let token: SlackApiToken = SlackApiToken::new(token_value);
    let session = client.open_session(&token);
    
    // Create a first request and specify a batch limit:
    let scroller_req: SlackApiUsersListRequest = SlackApiUsersListRequest::new().with_limit(5);
    
    // Create a scroller from this request
    let scroller = scroller_req.scroller();
    
    // Option 1: Create a Rust Futures Stream from this scroller and use it
    use futures::stream::BoxStream;
    use futures::TryStreamExt;
    
    let mut items_stream = scroller.to_items_stream(&session);
    while let Some(items) = items_stream.try_next().await? {
        println!("users batch: {:#?}", items);
    }
    
    // Option 2: Collect all of the data in a vector (which internally uses the same approach above)
    // Only for Tokio/Hyper for now
    let collected_members: Vec<SlackUser> = scroller
        .collect_items_stream(&session, Duration::from_millis(1000))
        .await?;

    // Option 3: Throttling scrolling with Tokio/Hyper:
    let mut items_throttled_stream =
        scroller.to_items_throttled_stream(&session, Duration::from_millis(500));
    while let Some(items) = items_throttled_stream.try_next().await? {
        println!("res: {:#?}", items);
    }

    Ok(())
}