Interface to the random number generator of the operating system.
Getrandom doesn't have a blanket implementation for all Unix-like operating
systems that reads from
/dev/urandom. This ensures all supported operating
systems are using the recommended interface and respect maximum buffer
The three Emscripten targets
Emscripten's emulation of
/dev/random on web browsers and Node.js.
The bare WASM target
methods directly, using either
wasm-bindgen depending on what
features are activated for this crate. Note that if both features are
wasm-bindgen will be used. If neither feature is enabled,
getrandom will always fail.
The WASI target
wasm32-wasi uses the
__wasi_random_get function defined
by the WASI standard.
It is possible that early in the boot process the OS hasn't had enough time yet to collect entropy to securely seed its RNG, especially on virtual machines.
Some operating systems always block the thread until the RNG is securely seeded. This can take anywhere from a few seconds to more than a minute. Others make a best effort to use a seed from before the shutdown and don't document much.
A few, Linux, NetBSD and Solaris, offer a choice between blocking and getting an error; in these cases we always choose to block.
On Linux (when the
genrandom system call is not available) and on NetBSD
/dev/urandom never blocks, even when the OS hasn't collected
enough entropy yet. To avoid returning low-entropy bytes, we first read from
/dev/random and only switch to
/dev/urandom once this has succeeded.
We always choose failure over returning insecure "random" bytes. In general,
on supported platforms, failure is highly unlikely, though not impossible.
If an error does occur, then it is likely that it will occur on every call to
getrandom, hence after the first successful call one can be reasonably
confident that no errors will occur.
On unsupported platforms,
getrandom always fails with
The crate uses the following custom error codes:
0x57f4c500(dec: 1475659008) - an unknown error. Constant:
0x57f4c501(dec: 1475659009) - no generator is available. Constant:
0x57f4c580(dec: 1475659136) -
0x57f4c581(dec: 1475659137) -
These codes are provided for reference only and should not be matched upon
(but you can match on
Error constants). The codes may change in future and
such change will not be considered a breaking one.
Other error codes will originate from an underlying system. In case if such error is encountered, please consult with your system documentation.
The error type.