feat: add wasm rigging

Signed-off-by: Xe Iaso <me@xeiaso.net>

wasm/anubis/Cargo.toml

@@ -0,0 +1,7 @@
+[package]
+name = "anubis"
+version = "0.1.0"
+edition = "2024"
+
+[dependencies]
+wee_alloc = "0.4"

wasm/anubis/src/lib.rs

@@ -0,0 +1,60 @@
+use std::sync::{LazyLock, Mutex};
+
+extern crate wee_alloc;
+
+#[global_allocator]
+static ALLOC: wee_alloc::WeeAlloc = wee_alloc::WeeAlloc::INIT;
+
+#[cfg(target_arch = "wasm32")]
+mod hostimport {
+    use crate::{DATA_BUFFER, DATA_LENGTH};
+
+    #[link(wasm_import_module = "anubis")]
+    unsafe extern "C" {
+        /// The runtime expects this function to be defined. It is called whenever the Anubis check
+        /// worker processes about 1024 hashes. This can be a no-op if you want.
+        fn anubis_update_nonce(nonce: u32);
+    }
+
+    /// Safe wrapper to `anubis_update_nonce`.
+    pub fn update_nonce(nonce: u32) {
+        unsafe {
+            anubis_update_nonce(nonce);
+        }
+    }
+
+    #[unsafe(no_mangle)]
+    pub extern "C" fn data_ptr() -> *const u8 {
+        let challenge = &DATA_BUFFER;
+        challenge.as_ptr()
+    }
+
+    #[unsafe(no_mangle)]
+    pub extern "C" fn set_data_length(len: u32) {
+        let mut data_length = DATA_LENGTH.lock().unwrap();
+        *data_length = len as usize;
+    }
+}
+
+#[cfg(not(target_arch = "wasm32"))]
+mod hostimport {
+    pub fn update_nonce(_nonce: u32) {
+        // This is intentionally blank
+    }
+}
+
+/// The data buffer is a bit weird in that it doesn't have an explicit length as it can
+/// and will change depending on the challenge input that was sent by the server.
+/// However, it can only fit 4096 bytes of data (one amd64 machine page). This is
+/// slightly overkill for the purposes of an Anubis check, but it's fine to assume
+/// that the browser can afford this much ram usage.
+///
+/// Callers should fetch the base data pointer, write up to 4096 bytes, and then
+/// `set_data_length` the number of bytes they have written
+///
+/// This is also functionally a write-only buffer, so it doesn't really matter that
+/// the length of this buffer isn't exposed.
+pub static DATA_BUFFER: LazyLock<[u8; 4096]> = LazyLock::new(|| [0; 4096]);
+pub static DATA_LENGTH: LazyLock<Mutex<usize>> = LazyLock::new(|| Mutex::new(0));
+
+pub use hostimport::update_nonce;