I previously wrote about my plan to rewrite ReductStore in Rust. I am happy to announce that the migration is now complete. It was a very interesting experience, and I would like to share it here.
I wrote ReductStore in C++20, utilizing coroutines and ranges.
For the HTTP frontend, I used uWebSockets as an HTTP server and its event loop for coroutines.
The storage engine was implemented from scratch.
I used Protobuf as a JSON and binary serializer in both the HTTP frontend and the storage engine. Many of the structures were shared between the two.
I managed dependencies with Conan and used CMake as a build system.
Codebase about 20k lines with unit tests.
I have been developing in C++ and Python for about five years. Mostly, I write services for data acquisition, processing, and storage. I like OOP, design patterns, and my C++ smells Java. However, I avoid using exceptions and follow the RAII approach.
In Rust, I have only written the “Hello, World” example.
I work on the project in my spare time 10-20 hours a week.
Initially, I planned to use the cxx.rs library and rewrite the project in small steps by wrapping Rust code and integrating it into C++.
[SPOILER] I wasn’t able to handle this…
ReductStore has its own simple logger and uses environment variables for configuration. The code was trivial and it was good to start with Rust.
Here, I learned the basics of Rust memory management, borrowing, and references. All these concepts I already knew from C++, so it was easy to understand. However, rustc did not want to compile my code in the beginning.
The biggest problem was that cxx.rs throws an exception when a Rust function returns an Err. It did
not work for me because I did not use exceptions and my C++ functions returned a structure with a result or an error. I
had to write additional wrappers to work around it. This was a very buggy layer and a source of frustration for me.
ReductStore offers token authentication and an API for token management. I implemented it in C++ using OOP patterns such as Repository and Strategy. This was a great opportunity for me to learn Rust’s traits and dynamic polymorphism.
During the process, I also discovered prost. In comparison with the C++ implementation and especially the Python
implementation by Google, prost is amazing. However, it seems like magic to me, mostly because I don’t understand how
it works in detail.
Although I was able to integrate the new authentication module in C++, the cost was too high. As a result, I decided to move forward with the next steps without C++ integration.
The storage engine was designed to store records in pre-allocated blocks and provide parallel read/write streaming to the same block. The engine can also be configured to remove old blocks to keep a bucket quota. Thus, it should keep track of all readers and writers and remove a block only when it is no longer in use.
Next, it was time to learn about Rust’s smart pointers. My background in C++ helped me a lot here. However, I was a bit
surprised that I had to use nested pointers for mutable access (*Rc<RefCell
Although the storage engine was the biggest part of the project, it didn’t take too long to rewrite because it only uses a file system and Protobuf. Thus, I didn’t have to learn many new things.
Well… here, I broke my neck. The C++ implementation of the HTTP layer was asynchronous, so I wanted the same in Rust. I first tried to use hyper, but unfortunately, I couldn’t make it work with JSON and streaming bodies in the same service. I realized that I had to learn a lot about hyper, which doesn’t have rich documentation, before starting to use it.
Then I tried axum and it worked. The framework is really awesome, and I felt as if I was using Python Flask or Fast API.
However, I later discovered that my *Rc
That was the easiest part. I like using C++, but I hate its build systems. Therefore, I felt a bit sorry when I deleted the last CMakeLists.txt.
Now, ReductStore is written in Rust and developed as a Rust project. I’m planning to write a client SDK and rewritte Reduct CLI in Rust. I also would like to provide the storage engine separated from the HTTP backend as a feature, so that you can use it in you Rust applications if you need keep a history of data.
The project is open source ad contributions are welcome.
If you’re a C++ developer you shouldn’t have any problems to learn Rust. However, if you decided to rewrite you C++ codebase, it isn’t so easy. Cxx.rs library is useful, but the glue code is ugly and buggy. For me it would make sense to rewrite my code in one step
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