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Use ptr::write/ptr::read to initialize and destroy file handle #77

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Merged
carlsverre merged 2 commits into from
Mar 1, 2026
Merged

Use ptr::write/ptr::read to initialize and destroy file handle #77

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dd922a6
Use `ptr::write`/`ptr::read` to initialize and destroy file handle
bkoropoff Feb 24, 2026
92beaea
added safety comments, made x_close more safe
carlsverre Mar 1, 2026
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70 changes: 49 additions & 21 deletions src/vfs.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -7,7 +7,7 @@ use alloc::boxed::Box;
use alloc::ffi::CString;
use alloc::format;
use alloc::string::String;
use core::mem::{self, ManuallyDrop, MaybeUninit, size_of};
use core::mem::{ManuallyDrop, size_of};
use core::slice;
use core::{
ffi::{CStr, c_char, c_int, c_void},
Expand Down Expand Up @@ -45,7 +45,7 @@ pub type VfsResult<T> = Result<T, SqliteErr>;
struct FileWrapper<Handle> {
file: ffi::sqlite3_file,
vfs: *mut ffi::sqlite3_vfs,
handle: MaybeUninit<Handle>,
handle: Handle,
}

struct AppData<Vfs> {
Expand Down Expand Up @@ -371,7 +371,6 @@ unsafe extern "C" fn x_open<T: Vfs>(
let vfs = unwrap_vfs!(p_vfs, T)?;
let handle = vfs.open(name.as_ref().map(|s| s.as_ref()), opts)?;

let out_file = unwrap_file!(p_file, T)?;
let appdata = unwrap_appdata!(p_vfs, T)?;

if let Some(p_out_flags) = unsafe { p_out_flags.as_mut() } {
Expand All @@ -385,9 +384,19 @@ unsafe extern "C" fn x_open<T: Vfs>(
*p_out_flags = out_flags;
}

out_file.file.pMethods = &appdata.io_methods;
out_file.vfs = p_vfs;
out_file.handle.write(handle);
let out_file = p_file.cast::<FileWrapper<T::Handle>>();
// Safety: SQLite owns the heap allocation backing p_file (it handles malloc/free).
// We use ptr::write to initialize that allocation directly.
unsafe {
core::ptr::write(
out_file,
FileWrapper {
file: ffi::sqlite3_file { pMethods: &appdata.io_methods },
vfs: p_vfs,
handle,
},
);
}

Ok(vars::SQLITE_OK)
})
Expand Down Expand Up @@ -447,10 +456,23 @@ unsafe extern "C" fn x_full_pathname<T: Vfs>(

unsafe extern "C" fn x_close<T: Vfs>(p_file: *mut ffi::sqlite3_file) -> c_int {
fallible(|| {
let file = unwrap_file!(p_file, T)?;
let vfs = unwrap_vfs!(file.vfs, T)?;
let handle = mem::replace(&mut file.handle, MaybeUninit::uninit());
let handle = unsafe { handle.assume_init() };
// Safety: SQLite owns the heap allocation backing p_file (it handles
// malloc/free). We use ptr::read to copy our Handle out of that
// allocation so it can be passed to vfs.close() and properly dropped.
// SQLite will not call any other file methods after x_close without
// first calling x_open to reinitialize the handle.
let (vfs, handle) = unsafe {
// verify p_file is not null and get a mutable reference
let p_file_ref = p_file.as_mut().ok_or(vars::SQLITE_INTERNAL)?;
// set pMethods to null, signaling to SQLite that the file is closed
p_file_ref.pMethods = core::ptr::null();

// extract a copy of the FileWrapper
let file = core::ptr::read(p_file.cast::<FileWrapper<T::Handle>>());
(file.vfs, file.handle)
};

let vfs = unwrap_vfs!(vfs, T)?;
vfs.close(handle)?;
Ok(vars::SQLITE_OK)
})
Expand All @@ -468,7 +490,7 @@ unsafe extern "C" fn x_read<T: Vfs>(
let buf_len: usize = i_amt.try_into().map_err(|_| vars::SQLITE_IOERR_READ)?;
let offset: usize = i_ofst.try_into().map_err(|_| vars::SQLITE_IOERR_READ)?;
let buf = unsafe { slice::from_raw_parts_mut(buf.cast::<u8>(), buf_len) };
vfs.read(unsafe { file.handle.assume_init_mut() }, offset, buf)?;
vfs.read(&mut file.handle, offset, buf)?;
Ok(vars::SQLITE_OK)
})
}
Expand All @@ -485,7 +507,7 @@ unsafe extern "C" fn x_write<T: Vfs>(
let buf_len: usize = i_amt.try_into().map_err(|_| vars::SQLITE_IOERR_WRITE)?;
let offset: usize = i_ofst.try_into().map_err(|_| vars::SQLITE_IOERR_WRITE)?;
let buf = unsafe { slice::from_raw_parts(buf.cast::<u8>(), buf_len) };
let n = vfs.write(unsafe { file.handle.assume_init_mut() }, offset, buf)?;
let n = vfs.write(&mut file.handle, offset, buf)?;
if n != buf_len {
return Err(vars::SQLITE_IOERR_WRITE);
}
Expand All @@ -501,7 +523,7 @@ unsafe extern "C" fn x_truncate<T: Vfs>(
let file = unwrap_file!(p_file, T)?;
let vfs = unwrap_vfs!(file.vfs, T)?;
let size: usize = size.try_into().map_err(|_| vars::SQLITE_IOERR_TRUNCATE)?;
vfs.truncate(unsafe { file.handle.assume_init_mut() }, size)?;
vfs.truncate(&mut file.handle, size)?;
Ok(vars::SQLITE_OK)
})
}
Expand All @@ -510,7 +532,7 @@ unsafe extern "C" fn x_sync<T: Vfs>(p_file: *mut ffi::sqlite3_file, _flags: c_in
fallible(|| {
let file = unwrap_file!(p_file, T)?;
let vfs = unwrap_vfs!(file.vfs, T)?;
vfs.sync(unsafe { file.handle.assume_init_mut() })?;
vfs.sync(&mut file.handle)?;
Ok(vars::SQLITE_OK)
})
}
Expand All @@ -522,7 +544,7 @@ unsafe extern "C" fn x_file_size<T: Vfs>(
fallible(|| {
let file = unwrap_file!(p_file, T)?;
let vfs = unwrap_vfs!(file.vfs, T)?;
let size = vfs.file_size(unsafe { file.handle.assume_init_mut() })?;
let size = vfs.file_size(&mut file.handle)?;
let p_size = unsafe { p_size.as_mut() }.ok_or(vars::SQLITE_INTERNAL)?;
*p_size = size.try_into().map_err(|_| vars::SQLITE_IOERR_FSTAT)?;
Ok(vars::SQLITE_OK)
Expand All @@ -534,7 +556,7 @@ unsafe extern "C" fn x_lock<T: Vfs>(p_file: *mut ffi::sqlite3_file, raw_lock: c_
let level: LockLevel = raw_lock.into();
let file = unwrap_file!(p_file, T)?;
let vfs = unwrap_vfs!(file.vfs, T)?;
vfs.lock(unsafe { file.handle.assume_init_mut() }, level)?;
vfs.lock(&mut file.handle, level)?;
Ok(vars::SQLITE_OK)
})
}
Expand All @@ -544,7 +566,7 @@ unsafe extern "C" fn x_unlock<T: Vfs>(p_file: *mut ffi::sqlite3_file, raw_lock:
let level: LockLevel = raw_lock.into();
let file = unwrap_file!(p_file, T)?;
let vfs = unwrap_vfs!(file.vfs, T)?;
vfs.unlock(unsafe { file.handle.assume_init_mut() }, level)?;
vfs.unlock(&mut file.handle, level)?;
Ok(vars::SQLITE_OK)
})
}
Expand All @@ -557,7 +579,7 @@ unsafe extern "C" fn x_check_reserved_lock<T: Vfs>(
let file = unwrap_file!(p_file, T)?;
let vfs = unwrap_vfs!(file.vfs, T)?;
unsafe {
*p_out = vfs.check_reserved_lock(file.handle.assume_init_mut())? as c_int;
*p_out = vfs.check_reserved_lock(&mut file.handle)? as c_int;
}
Ok(vars::SQLITE_OK)
})
Expand Down Expand Up @@ -598,7 +620,7 @@ unsafe extern "C" fn x_file_control<T: Vfs>(
};
let pragma = Pragma { name: &name, arg: arg.as_deref() };

let (result, msg) = match vfs.pragma(unsafe { file.handle.assume_init_mut() }, pragma) {
let (result, msg) = match vfs.pragma(&mut file.handle, pragma) {
Ok(msg) => (Ok(vars::SQLITE_OK), msg),
Err(PragmaErr::NotFound) => (Err(vars::SQLITE_NOTFOUND), None),
Err(PragmaErr::Fail(err, msg)) => (Err(err), msg),
Expand All @@ -623,15 +645,15 @@ unsafe extern "C" fn x_sector_size<T: Vfs>(p_file: *mut ffi::sqlite3_file) -> c_
fallible(|| {
let file = unwrap_file!(p_file, T)?;
let vfs = unwrap_vfs!(file.vfs, T)?;
vfs.sector_size(unsafe { file.handle.assume_init_mut() })
vfs.sector_size(&mut file.handle)
})
}

unsafe extern "C" fn x_device_characteristics<T: Vfs>(p_file: *mut ffi::sqlite3_file) -> c_int {
fallible(|| {
let file = unwrap_file!(p_file, T)?;
let vfs = unwrap_vfs!(file.vfs, T)?;
vfs.device_characteristics(unsafe { file.handle.assume_init_mut() })
vfs.device_characteristics(&mut file.handle)
})
}

Expand Down Expand Up @@ -818,13 +840,19 @@ mod tests {
let n = blob.write(b"hello")?;
assert_eq!(n, 5);

blob.close()?;

// query the table for the blob and print it
let mut stmt = conn.prepare("select data from b")?;
let mut rows = stmt.query([])?;
while let Some(row) = rows.next()? {
let data: Vec<u8> = row.get(0)?;
assert_eq!(&data[0..5], b"hello");
}
drop(rows);
drop(stmt);

conn.close().expect("failed to close connection");

Ok(())
}
Expand Down