botnet VS Cap'n Proto

I was/am working on a project (https://github.com/JMS55/botnet), where users upload scripts compiled to WASM to control entities on a game server, so that they can write custom behavior.

Never heard of extism before, but second using WASM for plugins/scripting/extensions. I'm using it for botnet(1). Each player uploads a WASM program to control their bots. Both the server and the bot SDK are written in Rust, and can share some code.

4. Speed

I'm hoping to write my thesis for my master's degree on this topic this year. I'm also in the process of writing a game like screeps, where users provide a WASM script to control units for an RTS-style game (without combat though) https://github.com/JMS55/botnet.

It's amazing how simple it is to constrain memory usage, runtime duration, and secure exported functions to a WASM VM. Performance is also great - currently about ~6 microseconds per tick per unit, up to ~200 microseconds when doing expensive pathfinding. All that, while letting you program your units in Rust - the same language as the server is written in, while being able to share code with the server, and not having to use something more script-y like lua.

The boilerplate sucks, but it works well when you don't need a ton of different functions. I use wasm as a scripting language for running isolated untrusted scripts in a game I'm developing, and it works really well https://github.com/JMS55/botnet.

I'm working on a Screeps-like game using WebAssembly. You compile a script to WebAssembly, and for each robot you control on the server, it runs the script in an isolated environment to choose an action for that robot. The goal is to write a program to coordinate your robots to gather resources and expand your control of the server.

Here's an example bot script: https://github.com/JMS55/botnet/blob/master/example_bot/src/...

The basic infrastructure of the project is more or less in place, besides a visual replay viewer which I'm working on right now. What's needed is a bunch of work in designing game mechanics and APIs. I don't actually have any plans beyond bots running around and harvesting randomly generated resources at the moment. Feel free to open a discussion on the github page if you're interested in Rust, WebAssembly, and video games.

https://github.com/JMS55/botnet

Yeah I pretty much only use my own alternate container implementations (from KJ[0]), which avoid these footguns, but the result is everyone complains our project is written in Kenton-Language rather than C++ and there's no Stack Overflow for it and we can't hire engineers who know how to write it... oops.

[0] https://github.com/capnproto/capnproto/blob/v2/kjdoc/tour.md

- may massively reduce the latency involved.

Those sharing Cap'n Proto-encoded data may have particular interest. Cap'n Proto (https://capnproto.org) is fantastic at its core task - in-place serialization with zero-copy - and we wanted to make the IPC (inter-process communication) involving capnp-serialized messages be zero-copy, end-to-end.

That said, we paid equal attention to other varieties of payload; it's not limited to capnp-encoded messages. For example there is painless (<-- I hope!) zero-copy transmission of arbitrary combinations of STL-compliant native C++ data structures.

To help determine whether Flow-IPC is relevant to you we wrote an intro blog post. It works through an example, summarizes the available features, and has some performance results. https://www.linode.com/blog/open-source/flow-ipc-introductio...

Of course there's nothing wrong with going straight to the GitHub link and getting into the README and docs.

Currently Flow-IPC is for Linux. (macOS/ARM64 and Windows support could follow soon, depending on demand/contributions.)

FWIW, my C++ toolkit library, KJ, does the same thing.[0]

But presumably you could still write a condition predicate which looks at things which aren't actually part of the mutex-wrapped structure? Or does is the Rust type system able to enforce that the callback can only consider the mutex-wrapped value and values that are constant over the lifetime of the wait? (You need the latter e.g. if you are waiting for the mutex-wrapped value to compare equal to some local variable...)

[0] https://github.com/capnproto/capnproto/blob/e6ad6f919aeb381b...

The second one is to encode data in such a way that you can read it and operate on it directly from the buffer. You write data in a layout that is the same, or easily transformed as types in memory. To do that you usually need to encode with a known schema, only Sized types to efficiently compute fields locations as offsets in the buffer, and you usually represent pointers as offset into the encode. You can look at capnproto protocol for instance https://capnproto.org/

Worked well for Cap'n Proto (the cerealization protocol)! https://capnproto.org/

With all due respect, you read completely wrong.

* The very first use case for which Cap'n Proto was designed was to be the protocol that Sandstorm.io used to talk between sandbox and supervisor -- an explicitly adversarial security scenario.

* The documentation explicitly calls out how implementations should manage resource exhaustion problems like deep recursion depth (stack overflow risk).

* The implementation has been fuzz-tested multiple ways, including as part of Google's oss-fuzz.

* When there are security bugs, I issue advisories like this:

https://github.com/capnproto/capnproto/tree/v2/security-advi...

* The primary aim of the entire project is to be a Capability-Based Security RPC protocol.

I like how they use capability-based security [0] and use Cap'n Proto protocol. This is another technology that is slow to get broad adoption, but has many things going for when compared to e.g. Protocol Buffers (Cap'n Proto is created by the primary author of Protobuf v2, Kenton Varda).

[0] https://sandstorm.io/how-it-works#capabilities

[1] https://capnproto.org

Related but not Rust-specific: FlatBuffers, Cap'n Proto.