feat: no_std support

.github/workflows/ci.yml

@@ -67,3 +67,15 @@ jobs:
       - uses: dtolnay/rust-toolchain@stable
       - uses: Swatinem/rust-cache@v2
       - run: cargo test --all --release
+
+  no-std:
+    name: No-std
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: dtolnay/rust-toolchain@stable
+        with:
+          components: clippy
+      - uses: Swatinem/rust-cache@v2
+      - run: cargo check --no-default-features
+      - run: cargo clippy --no-default-features --lib -- -D warnings

Cargo.toml

@@ -12,5 +12,9 @@ keywords = ["ratelimit", "token-bucket", "rate-limiter", "throttle", "concurrenc
 categories = ["concurrency", "algorithms"]
 rust-version = "1.85"
 
+[features]
+default = ["std"]
+std = []
+
 [dependencies]
-thiserror = "2.0"
+thiserror = { version = "2.0", default-features = false }

README.md

@@ -8,8 +8,17 @@ A lock-free token bucket ratelimiter for rate limiting and admission control.
 cargo add ratelimit
 ```
 
+`std` is enabled by default. For `no_std` targets, disable default features:
+
+```toml
+ratelimit = { version = "1", default-features = false }
+```
+
 ## Usage
 
+`Ratelimiter::new`, `Ratelimiter::builder`, and `StdClock` are available with
+the default `std` feature.
+
 ```rust
 use ratelimit::Ratelimiter;
 
@@ -54,6 +63,26 @@ ratelimiter.set_rate(5_000);
 
 A rate of 0 means unlimited -- `try_wait()` will always succeed.
 
+## no_std
+
+Disable default features and provide your own monotonic clock:
+
+```rust
+use core::time::Duration;
+use ratelimit::{Clock, Ratelimiter};
+
+struct FixedClock;
+
+impl Clock for FixedClock {
+    fn elapsed(&self) -> Duration {
+        Duration::from_millis(10)
+    }
+}
+
+let ratelimiter = Ratelimiter::with_clock(1_000, FixedClock);
+assert!(ratelimiter.try_wait().is_ok());
+```
+
 ## Design
 
 This crate implements a lock-free token bucket algorithm. Tokens accumulate