capnproto-rust VS bincode

The only hurdle I have is that while the documentation is extensive it is a little confusing in places and mainly focuses on C++ and the C++ RPC system which is a little different to the Rust code. There are Rust examples in the official repo which I will try and leverage here.

capnproto-rust is the official Rust implementation.

Hi, you seem to know a bit about Sanakirja!

It stores 4kb blobs, right? Does Pijul first parses the data (copying it to other allocations), or uses the data as is? I mean, there are some libraries like cap'n'proto[0] and rkyv[1] that can directly use the file contents as an in-memory data structure, I was wondering if Pijul did anything like that.

I mean, is this btree page [2] stored exactly like this on disk, and does Pijul exploits that to avoid further copying data?

(I guess there's a trouble with compression there: to decompress you really need to write in another buffer)

Also, is the I/O done with something that prevent userspace copies like mmap or io_uring, or does it eventually calls read() to copy the data to its own buffer?

I want to build something like Sanakirja, but with those features, so I'm wondering if there's any overlap.

[0] https://github.com/capnproto/capnproto-rust

[1] https://github.com/rkyv/rkyv

[2] https://docs.rs/sanakirja-core/latest/sanakirja_core/btree/p...

Ermm... actually I meant something like this: playground, but then I realized it's basically (de)serialization, and I just found that we already have a crate for that: bincode.

One, figure out the bincode format (documented here: https://github.com/bincode-org/bincode/blob/trunk/docs/spec.md) and write your own parser. Maybe a one-off that specifically only handles this one data structure would be fairly straightforward.

Step 1: The Deserialize type requests data from the Deserializer with one of the deserialize_type methods. This gives it an opportunity to provide certain metadata about the type: structs provide a list of fields, enums provide a list of variants, tuples provide a length, etc. Some data formats (notably bincode) require this metadata to drive deserializing, as the wire format is not self-describing. Crucially, the Deserialize type also provides a visitor that is capable of receiving the requested data from the Deserializer.

Alternatively, give Bincode a try.

Like separate instructions? I was thinking if a instruction have unknown length I make sure I have some kind of header field that tells the data length of the instruction so receiver knows when next instruction starts. And I was planning on using Bincode with serde to serialize and dezerialize like structs and stuff.

Isn't this essentially bincode?

This is similar in practice to using abi_stable, and end-users will still receive compiled files, but your plugins will be sandboxed and a single build will work on all platforms. The downside is that it's a bit more work because WebAssembly's support for passing complex data types between the host and the WebAssembly code is in the preliminary stages, so you need to do something like using Serde to encode your data into something like Bincode or MessagePack (or JSON and friends) to hand it off between the host and the plugin.

What kind of access do you need to the data ? You should be able to make a safe api to the Vec class by iterating on in in chunks, and using a closure to translate data between u8 and other representations. ( f32, u32 has the fomr_ne_bytes() / to_ne_bytes() methods ) You could make a helper function that takes a format description ( i.e. "fffuucc" , and calculates the size of the chunk, and generates a closure for reading accessing the data, of the layout is completely dynamic. This closure could use an enum to wrap the different primitive types. ) Or if the layouts are known at compile time , you could use procedural macros to generate code for serializaion / deserialization inot the the [u8] , though https://crates.io/crates/bincode may already do that for you )

Apparently there's a lot of discussion going on about that (3 of the 4 open tickets on the bincode implementation are about it), for example this one.