clarify get_or_put status handling

heed/src/database.rs

@@ -2091,18 +2091,23 @@ impl<KC, DC, C> Database<KC, DC, C> {
  let mut data_val = unsafe { crate::into_val(&data_bytes) };
  let flags = (flags | PutFlags::NO_OVERWRITE).bits();
 
- unsafe {
- match ffi::mdb_put(txn.txn.txn, self.dbi, &mut key_val, &mut data_val, flags) {
- lmdb_master_sys::MDB_KEYEXIST => {
- let bytes = crate::from_val(data_val);
- let data = DC::bytes_decode(bytes).map_err(Error::Decoding)?;
- return Ok(Some(data));
- }
- err_code => mdb_result(err_code)?,
+ let result = unsafe {
+ mdb_result(ffi::mdb_put(txn.txn.txn, self.dbi, &mut key_val, &mut data_val, flags))
+ };
+
+ match result {
+ // the value was successfully inserted
+ Ok(()) => Ok(None),
+
+ // the key already exists: the previous value is stored in the data parameter
+ Err(MdbError::KeyExist) => {
+ let bytes = unsafe { crate::from_val(data_val) };
+ let data = DC::bytes_decode(bytes).map_err(Error::Decoding)?;
+ Ok(Some(data))
  }
- }
 
- Ok(None)
+ Err(error) => Err(error.into()),
+ }
  }
 
  /// Attempt to insert a key-value pair in this database, where the value can be directly
@@ -2235,23 +2240,30 @@ impl<KC, DC, C> Database<KC, DC, C> {
  let mut reserved = ffi::reserve_size_val(data_size);
  let flags = (flags | PutFlags::NO_OVERWRITE).bits() | lmdb_master_sys::MDB_RESERVE;
 
- unsafe {
- match ffi::mdb_put(txn.txn.txn, self.dbi, &mut key_val, &mut reserved, flags) {
- lmdb_master_sys::MDB_KEYEXIST => {
- let bytes = crate::from_val(reserved);
- let data = DC::bytes_decode(bytes).map_err(Error::Decoding)?;
- return Ok(Some(data));
+ let result = unsafe {
+ mdb_result(ffi::mdb_put(txn.txn.txn, self.dbi, &mut key_val, &mut reserved, flags))
+ };
+
+ match result {
+ // value was inserted: fill the reserved space
+ Ok(()) => {
+ let mut reserved = unsafe { ReservedSpace::from_val(reserved) };
+ write_func(&mut reserved)?;
+ if reserved.remaining() == 0 {
+ Ok(None)
+ } else {
+ Err(io::Error::from(io::ErrorKind::UnexpectedEof).into())
  }
- err_code => mdb_result(err_code)?,
  }
- }
 
- let mut reserved = unsafe { ReservedSpace::from_val(reserved) };
- write_func(&mut reserved)?;
- if reserved.remaining() == 0 {
- Ok(None)
- } else {
- Err(io::Error::from(io::ErrorKind::UnexpectedEof).into())
+ // the key already exists: the previous value is stored in the data parameter
+ Err(MdbError::KeyExist) => {
+ let bytes = unsafe { crate::from_val(reserved) };
+ let data = DC::bytes_decode(bytes).map_err(Error::Decoding)?;
+ Ok(Some(data))
+ }
+
+ Err(error) => Err(error.into()),
  }
  }
 
@@ -2620,9 +2632,10 @@ pub struct DatabaseStat {
 
 #[cfg(test)]
 mod tests {
- use super::*;
  use heed_types::*;
 
+ use super::*;
+
  #[test]
  fn put_overwrite() -> Result<()> {
  let dir = tempfile::tempdir()?;