Add support for using rand for rng

.github/workflows/ci.yml

@@ -100,6 +100,9 @@ jobs:
 
       - name: Version features
         run: wasm-pack test --node -- --features "js v1 v3 v4 v5"
+
+      - name: Fast rng
+        run: wasm-pack test --node -- --features "js v4 fast-rng"
 
   embedded:
     name: Build / Embedded

Cargo.toml

@@ -53,15 +53,21 @@ repository = "uuid-rs/uuid"
 
 [features]
 default = ["std"]
-guid = ["winapi"]
 std = []
 macros = ["uuid-macros"]
+
 v1 = ["atomic"]
 v3 = ["md-5"]
-v4 = ["getrandom"]
+v4 = ["rng"]
 v5 = ["sha-1"]
+
+guid = ["winapi"]
+
 js = ["getrandom", "getrandom/js"]
 
+rng = ["getrandom"]
+fast-rng = ["rng", "rand"]
+
 # Unstable features (these also need RUSTFLAGS="--cfg uuid_unstable" to work)
 zerocopy-unstable = ["zerocopy"]
 
@@ -70,6 +76,11 @@ zerocopy-unstable = ["zerocopy"]
 optional = true
 version = "0.2"
 
+# Private
+[dependencies.rand]
+optional = true
+version = "0.8"
+
 # Private
 [dependencies.atomic]
 default-features = false

README.md

@@ -45,6 +45,9 @@ various pieces of functionality:
   UUID based on the SHA1 hash of some data.
 * `serde` - adds the ability to serialize and deserialize a `Uuid` using the
   `serde` crate.
+* `fast-rng` - when combined with `v4` uses a faster algorithm for generating
+  random UUIDs. This feature requires more dependencies to compile, but is just
+  as suitable for UUIDs as the default algorithm.
 
 You need to enable one of the following Cargo features together with the
 `v4` feature if you're targeting `wasm32-unknown-unknown` target:

benches/v4.rs

@@ -0,0 +1,12 @@
+#![cfg(feature = "v4")]
+
+#![feature(test)]
+extern crate test;
+
+use test::Bencher;
+use uuid::Uuid;
+
+#[bench]
+fn new_v4(b: &mut Bencher) {
+    b.iter(|| Uuid::new_v4());
+}

src/lib.rs

@@ -42,6 +42,9 @@
 //!   UUID based on the SHA1 hash of some data.
 //! * `serde` - adds the ability to serialize and deserialize a UUID using the
 //!   `serde` crate.
+//! * `fast-rng` - when combined with `v4` uses a faster algorithm for generating
+//!   random UUIDs. This feature requires more dependencies to compile, but is just
+//!   as suitable for UUIDs as the default algorithm.
 //!
 //! By default, `uuid` can be depended on with:
 //!
@@ -54,7 +57,7 @@
 //!
 //! ```toml
 //! [dependencies]
-//! uuid = { version = "0.8", features = ["serde", "v4"] }
+//! uuid = { version = "0.8", features = ["serde", "v4", "fast-rng"] }
 //! ```
 //!
 //! You can disable default features with:
@@ -190,19 +193,22 @@ mod error;
 mod parser;
 
 pub mod fmt;
+
 #[cfg(feature = "v1")]
 pub mod v1;
-
-#[cfg(feature = "serde")]
-mod serde_support;
-#[cfg(feature = "slog")]
-mod slog_support;
 #[cfg(feature = "v3")]
 mod v3;
 #[cfg(feature = "v4")]
 mod v4;
 #[cfg(feature = "v5")]
 mod v5;
+
+#[cfg(feature = "rng")]
+mod rng;
+#[cfg(feature = "serde")]
+mod serde_support;
+#[cfg(feature = "slog")]
+mod slog_support;
 #[cfg(all(windows, feature = "winapi"))]
 mod winapi_support;
 

src/rng.rs

@@ -0,0 +1,25 @@
+#[cfg(feature = "v4")]
+pub(crate) fn bytes() -> [u8; 16] {
+    #[cfg(not(feature = "fast-rng"))]
+    {
+        let mut bytes = [0u8; 16];
+
+        getrandom::getrandom(&mut bytes).unwrap_or_else(|err| {
+            // NB: getrandom::Error has no source; this is adequate display
+            panic!("could not retrieve random bytes for uuid: {}", err)
+        });
+
+        bytes
+    }
+
+    #[cfg(feature = "fast-rng")]
+    {
+        use rand::RngCore;
+        let mut rng = rand::thread_rng();
+
+        let mut bytes = [0u8; 16];
+        rng.fill_bytes(&mut bytes);
+
+        bytes
+    }
+}

src/v4.rs

@@ -27,13 +27,7 @@ impl Uuid {
     /// [`getrandom`]: https://crates.io/crates/getrandom
     /// [from_random_bytes]: struct.Builder.html#method.from_random_bytes
     pub fn new_v4() -> Uuid {
-        let mut bytes = [0u8; 16];
-        getrandom::getrandom(&mut bytes).unwrap_or_else(|err| {
-            // NB: getrandom::Error has no source; this is adequate display
-            panic!("could not retrieve random bytes for uuid: {}", err)
-        });
-
-        crate::Builder::from_bytes(bytes)
+        crate::Builder::from_bytes(crate::rng::bytes())
             .set_variant(Variant::RFC4122)
             .set_version(Version::Random)
             .build()