add progress handler support to sqlite

sqlx-sqlite/src/connection/mod.rs

@@ -1,12 +1,13 @@
 use futures_core::future::BoxFuture;
 use futures_intrusive::sync::MutexGuard;
 use futures_util::future;
-use libsqlite3_sys::sqlite3;
+use libsqlite3_sys::{sqlite3, sqlite3_progress_handler};
 use sqlx_core::common::StatementCache;
 use sqlx_core::error::Error;
 use sqlx_core::transaction::Transaction;
 use std::cmp::Ordering;
 use std::fmt::{self, Debug, Formatter};
+use std::os::raw::{c_int, c_void};
 use std::ptr::NonNull;
 
 use crate::connection::establish::EstablishParams;
@@ -89,6 +90,45 @@ impl SqliteConnection {
 
         Ok(LockedSqliteHandle { guard })
     }
+
+    /// Sets a progress handler that is invoked periodically during long running calls. If the progress callback
+    /// returns `false`, then the operation is interrupted.
+    ///
+    /// `num_ops` is the approximate number of [virtual machine instructions](https://www.sqlite.org/opcode.html)
+    /// that are evaluated between successive invocations of the callback. If `num_ops` is less than one then the
+    /// progress handler is disabled.
+    ///
+    /// Only a single progress handler may be defined at one time per database connection; setting a new progress
+    /// handler cancels the old one.
+    ///
+    /// The progress handler callback must not do anything that will modify the database connection that invoked
+    /// the progress handler. Note that sqlite3_prepare_v2() and sqlite3_step() both modify their database connections
+    /// in this context.
+    pub async fn set_progress_handler<F>(&mut self, num_ops: i32, callback: F)
+    where
+        F: FnMut() -> bool + Send + 'static,
+    {
+        unsafe {
+            let callback = Box::new(callback);
+            if let Ok(mut lock_conn) = self.lock_handle().await {
+                sqlite3_progress_handler(
+                    lock_conn.as_raw_handle().as_mut(),
+                    num_ops,
+                    Some(progress_callback::<F>),
+                    &*callback as *const F as *mut F as *mut _,
+                );
+            }
+        }
+    }
+
+    /// Removes a previously set progress handler on a database connection.
+    pub async fn remove_progress_handler(&mut self) {
+        unsafe {
+            if let Ok(mut lock_conn) = self.lock_handle().await {
+                sqlite3_progress_handler(lock_conn.as_raw_handle().as_mut(), 0, None, 0 as *mut _);
+            }
+        }
+    }
 }
 
 impl Debug for SqliteConnection {
@@ -172,6 +212,21 @@ impl Connection for SqliteConnection {
     }
 }
 
+/// Implements a C binding to a progress callback. The function returns `0` if the
+/// user-provided callback returns `true`, and `1` otherwise to signal an interrupt.
+extern "C" fn progress_callback<F>(callback: *mut c_void) -> c_int
+where
+    F: FnMut() -> bool,
+{
+    unsafe {
+        if (*(callback as *mut F))() {
+            0
+        } else {
+            1
+        }
+    }
+}
+
 impl LockedSqliteHandle<'_> {
     /// Returns the underlying sqlite3* connection handle.
     ///

tests/sqlite/sqlite.rs

@@ -725,3 +725,19 @@ async fn concurrent_read_and_write() {
     read.await;
     write.await;
 }
+
+#[sqlx_macros::test]
+async fn test_query_with_progress_handler() -> anyhow::Result<()> {
+    let mut conn = new::<Sqlite>().await?;
+    conn.set_progress_handler(1, || false).await;
+
+    match sqlx::query("SELECT 'hello' AS title")
+        .fetch_all(&mut conn)
+        .await
+    {
+        Err(sqlx::Error::Database(err)) => assert_eq!(err.message(), String::from("interrupted")),
+        _ => panic!("expected an interrupt"),
+    }
+
+    Ok(())
+}