A Rust port of BuntDB

I did search for crates implementing BTree but found only one crate maintained: https://github.com/nimrodshn/btree

However it's disk-backed and has completely different API than: https://github.com/tidwall/btree

I tried going with BTreeSet and implementing wrapper structs like: OrdByKeyItem and OrdByExpItem but I'm not sure this is a viable path.

Currently Tx::commit() has a very naive implementation of writing to disk:

https://github.com/bartlomieju/rusty_buntdb/blob/29ef544b91d08ca36d0313893c7cf7f807e91cf2/src/lib.rs#L1344-L1352

It should be updated to handle partial writes like Go version does:

https://github.com/tidwall/buntdb/blob/89544ad8fc446ae7c798e487951dc06739092b6b/buntdb.go#L1188-L1211

Currently all of the code is in src/lib.rs. I did that in an effort to port the Go version as closely as possible. Given that Rust code is a bit more verbose in some situations the file is already at over 2,5k lines.

I believe in the long run it will be beneficial to split the library into multiple modules, it should help spot "non-rusty" code that could be made better after initial port.

Proposed modules:

• src/db.rs - Db struct
• src/tx.rs - Tx struct
• src/index.rs - Index struct
• src/error.rs - DbError struct
• src/tree_utils.rs - helper functions for traversing BTreeC

Currently Tx::lock and Tx::unlock are stubbed out:

https://github.com/bartlomieju/rusty_buntdb/blob/29ef544b91d08ca36d0313893c7cf7f807e91cf2/src/lib.rs#L1246-L1264

This is fine for now as DB runs on single thread but needs to be fixed prior to making DB multithreaded (#7). Since Rust RwLock return a "guards" that unlock when they are dropped, those guards need to be stored on the Tx struct.

Currently Db is not thread-safe, but we need to make it so to enable background sync (Db::background_manager is currently stubbed out).

Need to be especially careful when interacting with BTreeC which is using C-based data structure.

CI will verify that the crate builds, is formatted and clippy doesn't complain. However tests are currently disabled because there's only a single one and it panics.

Closes #4

I copy-pasted most of the docs from the Go implementation. These docstrings need to be reviewed and fixed to properly reference methods/structs in Rust implementation (including proper linking in docs.rs).

Currently most of the methods use String type. This is needlessly expensive and causes a lot of clones or .to_string() calls throughout the codebase.

Most of the occurences should be changed to &str or something along the lines impl String.

I will look into this once most of the tests are passing.

• [x] index_int
• [x] index_string
• [x] index_binary index_string_case_sensitive
• [x] index_float
• [ ] index_json
• [ ] index_json_case_sensitive

Reference: https://github.com/tidwall/buntdb/blob/89544ad8fc446ae7c798e487951dc06739092b6b/buntdb.go#L2197-L2245

Special care needs to be taken when considering JSON methods; I believe https://crates.io/crates/gjson doesn't have case-insensitive comparison as of now.

match is used when matching indexes and should be ported as a utility module matcher.rs (match is a keyword in Rust so it would require prefixing each occurrence with r#).