SQLite

The sqlite feature serves the lease and advisory lock forms in the service's process: one writer at a time, times as text, and no server to run in tests.

SQLite locks the whole database for a writer, so no claim can hold rows for a handler. Its dialect implements no row lock form, and a subscription to a table without locked_until or advisory_lock does not compile. A lease claim is one UPDATE .. RETURNING that leases its rows, and one writer at a time keeps two claims apart. The rows of one lease claim come in no particular order. A subscription mounted with workers(n) claims a row for every worker in that one statement. A writer that finds the write lock taken waits in SQLite's busy handler, which sleeps a millisecond or more instead of queueing it. So a transactional subscription whose handlers write runs one worker in the advisory lock form, where its deliveries' transactions would mostly wait for each other (Workers). A claim of the service's own opens its transaction with BEGIN IMMEDIATE and comes with a Fetch of its own.

The advisory lock form keeps its keys in the process, beside the pool. One process therefore serves a database file: two processes on one file may deliver a row twice. A table in that form needs no time column, so it needs neither chrono nor time. A transaction the crate opens takes the mode the table declares: deferred, immediate or exclusive.

SQLite keeps times as text and compares them as text. chrono times sort exactly. time values sort right only across seconds, so with them a lease may end up to a second late, and a delayed retry may come back up to a second early or late (QueueTime). The AsyncAPI document describes the server by its protocol alone, with no host.

An in-memory database named in a shared-cache URL, sqlite:file:<name>?mode=memory&cache=shared, serves every connection that names it and lives while one of them is open. A test runs the service on one with no server.

Example

Thumbnails in the advisory lock form: two workers each hold a row's key in the process while their handler runs.

Macros
Manual

examples/sqlx_databases_sqlite.rs
use ruststream_sqlx::prelude::*;
use sqlx::Connection;
use sqlx::sqlite::SqlitePoolOptions;

/// One row of `thumbnail_jobs`, held by the lock on its key while a handler runs.
#[derive(Inbox, sqlx::FromRow)]
#[inbox(table = "thumbnail_jobs", advisory_lock = "thumbnails-{id}")]
struct MakeThumbnail {
    #[field(id, generated)]
    id: i64,
    #[field(attempt, generated)]
    attempt: i16,
    #[field(payload)]
    payload: Vec<u8>,
}

// The keys live in this process: one process serves the database file.
#[subscriber(InboxQueue::<MakeThumbnail>::new("thumbnails"))]
async fn thumbnail(image: &Image) -> HandlerOutcome {
    tracing::info!(path = %image.path, "making a thumbnail");
    HandlerOutcome::ack()
}

/// The service on the database `url` names.
fn service(url: &str) -> RustStream {
    let schema_url = url.to_owned();
    // Nothing connects here: the broker builds its pool when the service starts.
    let broker = SqlxBroker::from_url(url, SqlitePoolOptions::new());
    RustStream::new(AppInfo::new("thumbnails", "0.1.0"))
        // The table, created before the subscription checks it.
        .on_startup(async move |()| {
            let mut conn = SqliteConnection::connect(&schema_url).await?;
            sqlx::raw_sql(SCHEMA).execute(&mut conn).await?;
            conn.close().await
        })
        .with_broker(broker.route::<MakeThumbnail>("thumbnails"), |b| {
            b.include(thumbnail.workers(nonzero!(2)));
        })
}

#[ruststream::app]
fn app() -> impl App {
    service("sqlite:thumbnails.db?mode=rwc")
}

examples/manual/sqlx_databases_sqlite.rs
use ruststream_sqlx::prelude::*;
use sqlx::Connection;
use sqlx::sqlite::SqlitePoolOptions;

/// One row of `thumbnail_jobs`, held by the lock on its key while a handler runs.
#[derive(sqlx::FromRow)]
struct MakeThumbnail {
    id: i64,
    attempt: i16,
    payload: Vec<u8>,
}

impl InboxTable for MakeThumbnail {
    type Id = i64;
    type Table = InboxSpec<(Advisory, Attempt, Payload)>;
    const TABLE: Self::Table = InboxSpec::new("thumbnail_jobs", Column::new("id").generated())
        .advisory(&[KeyPart::Literal("thumbnails-"), KeyPart::Column("id")])
        .attempt(Column::new("attempt").generated())
        .payload(Column::new("payload"));

    fn id(&self) -> &i64 {
        &self.id
    }
}

impl AttemptRow for MakeThumbnail {
    type Attempt = i16;

    fn attempt(&self) -> &i16 {
        &self.attempt
    }
}

impl PayloadRow for MakeThumbnail {
    type Column = Vec<u8>;

    fn payload(&self) -> &[u8] {
        &self.payload
    }
}

struct Thumbnail;

impl Handle<Image> for Thumbnail {
    fn handle(
        &self,
        image: &Image,
        _outs: &(),
        _ctx: &mut Context<'_>,
    ) -> impl Future<Output = Result<(), HandlerOutcome>> {
        tracing::info!(path = %image.path, "making a thumbnail");
        ready(Ok(()))
    }
}

/// The service on the database `url` names.
fn service(url: &str) -> RustStream {
    let schema_url = url.to_owned();
    // Nothing connects here: the broker builds its pool when the service starts.
    let broker = SqlxBroker::from_url(url, SqlitePoolOptions::new());
    RustStream::new(AppInfo::new("thumbnails", "0.1.0"))
        // The table, created before the subscription checks it.
        .on_startup(async move |()| {
            let mut conn = SqliteConnection::connect(&schema_url).await?;
            sqlx::raw_sql(SCHEMA).execute(&mut conn).await?;
            conn.close().await
        })
        .with_broker(broker.route::<MakeThumbnail>("thumbnails"), |b| {
            // The keys live in this process: one process serves the database file.
            let thumbnail = subscriber("thumbnails", Thumbnail)
                .map_source(|_| InboxQueue::<MakeThumbnail>::new("thumbnails"));
            b.include(thumbnail.workers(nonzero!(2)).build());
        })
}

#[ruststream::app]
fn app() -> impl App {
    service("sqlite:thumbnails.db?mode=rwc")
}

Example​

Example