std: implement DefaultRandomSource on ESP-IDF

Author: joboet

library/std/src/random.rs

@@ -25,6 +25,7 @@ use crate::sys::random as sys;
 /// Windows                | [`ProcessPrng`]
 /// macOS and other UNIXes | [`getentropy`]
 /// other Apple platforms  | `CCRandomGenerateBytes`
+/// ESP-IDF                | [`esp_fill_random`]
 /// Fuchsia                | [`cprng_draw`]
 /// Hermit                 | `read_entropy`
 /// Horizon                | `getrandom` shim
@@ -45,6 +46,7 @@ use crate::sys::random as sys;
 /// [`/dev/urandom`]: https://www.man7.org/linux/man-pages/man4/random.4.html
 /// [`ProcessPrng`]: https://learn.microsoft.com/en-us/windows/win32/seccng/processprng
 /// [`getentropy`]: https://pubs.opengroup.org/onlinepubs/9799919799/functions/getentropy.html
+/// [`esp_fill_random`]: https://docs.espressif.com/projects/esp-idf/en/latest/esp32/api-reference/system/random.html#_CPPv415esp_fill_randomPv6size_t
 /// [`cprng_draw`]: https://fuchsia.dev/reference/syscalls/cprng_draw
 /// [`kern.arandom`]: https://man.netbsd.org/rnd.4
 /// [`rdrand`]: https://en.wikipedia.org/wiki/RDRAND

library/std/src/sys/random/espidf.rs

@@ -0,0 +1,9 @@
+use crate::ffi::c_void;
+
+extern "C" {
+    fn esp_fill_random(buf: *mut c_void, len: usize);
+}
+
+pub fn fill_bytes(bytes: &mut [u8], _best_effort: bool) {
+    unsafe { esp_fill_random(bytes.as_mut_ptr().cast(), bytes.len()) }
+}

library/std/src/sys/random/mod.rs

@@ -24,6 +24,9 @@ cfg_if::cfg_if! {
     } else if #[cfg(all(target_vendor = "apple", not(target_os = "macos")))] {
         mod apple;
         pub use apple::fill_bytes;
+    } else if #[cfg(target_os = "espidf")] {
+        mod espidf;
+        pub use espidf::fill_bytes;
     } else if #[cfg(target_os = "fuchsia")] {
         mod fuchsia;
         pub use fuchsia::fill_bytes;