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`](https://learn.microsoft.com/en-us/windows/win32/seccng/processprng)
 /// Apple                  | `CCRandomGenerateBytes`
 /// DragonFly              | [`arc4random_buf`](https://man.dragonflybsd.org/?command=arc4random&section=ANY)
+/// ESP-IDF                | [`esp_fill_random`](https://docs.espressif.com/projects/esp-idf/en/latest/esp32/api-reference/system/random.html#_CPPv415esp_fill_randomPv6size_t)
 /// FreeBSD                | [`arc4random_buf`](https://man.freebsd.org/cgi/man.cgi?query=arc4random&apropos=0&sektion=0&manpath=FreeBSD+15.0-CURRENT&arch=default&format=html)
 /// Fuchsia                | [`cprng_draw`](https://fuchsia.dev/reference/syscalls/cprng_draw)
 /// Haiku                  | `arc4random_buf`

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

@@ -25,6 +25,9 @@ cfg_if::cfg_if! {
     } else if #[cfg(target_os = "emscripten")] {
         mod getentropy;
         pub use getentropy::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;