Add bindings to automatic extension loading API (#1487)

* Add bindings to automatic extension loading API

it doesn't seem possible to directly register an `AutoExtension`.

src/auto_extension.rs

@@ -0,0 +1,57 @@
+//! Automatic axtension loading
+use super::ffi;
+use crate::error::{check, to_sqlite_error};
+use crate::{Connection, Result};
+use std::os::raw::{c_char, c_int};
+
+/// Automatic extension initialization routine
+pub type AutoExtension = fn(Connection) -> Result<()>;
+
+/// Raw automatic extension initialization routine
+pub type RawAutoExtension = unsafe extern "C" fn(
+    db: *mut ffi::sqlite3,
+    pz_err_msg: *mut *mut c_char,
+    _: *const ffi::sqlite3_api_routines,
+) -> c_int;
+
+/// Bridge bewteen `RawAutoExtension` and `AutoExtension`
+///
+/// # Safety
+/// * Opening a database from an auto-extension handler will lead to
+///   an endless recursion of the auto-handler triggering itself
+///   indirectly for each newly-opened database.
+/// * Results are undefined if the given db is closed by an auto-extension.
+/// * The list of auto-extensions should not be manipulated from an auto-extension.
+pub unsafe fn init_auto_extension(
+    db: *mut ffi::sqlite3,
+    pz_err_msg: *mut *mut c_char,
+    ax: AutoExtension,
+) -> c_int {
+    let c = Connection::from_handle(db);
+    match c.and_then(ax) {
+        Err(e) => to_sqlite_error(&e, pz_err_msg),
+        _ => ffi::SQLITE_OK,
+    }
+}
+
+/// Register au auto-extension
+///
+/// # Safety
+/// * Opening a database from an auto-extension handler will lead to
+///   an endless recursion of the auto-handler triggering itself
+///   indirectly for each newly-opened database.
+/// * Results are undefined if the given db is closed by an auto-extension.
+/// * The list of auto-extensions should not be manipulated from an auto-extension.
+pub unsafe fn register_auto_extension(ax: RawAutoExtension) -> Result<()> {
+    check(ffi::sqlite3_auto_extension(Some(ax)))
+}
+
+/// Unregister the initialization routine
+pub fn cancel_auto_extension(ax: RawAutoExtension) -> bool {
+    unsafe { ffi::sqlite3_cancel_auto_extension(Some(ax)) == 1 }
+}
+
+/// Disable all automatic extensions previously registered
+pub fn reset_auto_extension() {
+    unsafe { ffi::sqlite3_reset_auto_extension() }
+}

src/lib.rs

@@ -93,6 +93,8 @@ pub use rusqlite_macros::__bind;
 
 mod error;
 
+#[cfg(not(feature = "loadable_extension"))]
+pub mod auto_extension;
 #[cfg(feature = "backup")]
 #[cfg_attr(docsrs, doc(cfg(feature = "backup")))]
 pub mod backup;