src/random.cpp

//===----------------------------------------------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//

#include <__config>

#if defined(_LIBCPP_USING_WIN32_RANDOM)
    // Must be defined before including stdlib.h to enable rand_s().
#   define _CRT_RAND_S
#endif // defined(_LIBCPP_USING_WIN32_RANDOM)

#include "limits"
#include "random"
#include "system_error"

#if defined(__sun__)
#   define rename solaris_headers_are_broken
#endif // defined(__sun__)

#include <errno.h>
#include <stdio.h>
#include <stdlib.h>

#if defined(_LIBCPP_USING_GETENTROPY)
#   include <sys/random.h>
#elif defined(_LIBCPP_USING_DEV_RANDOM)
#   include <fcntl.h>
#   include <unistd.h>
#   if __has_include(<sys/ioctl.h>) && __has_include(<linux/random.h>)
#       include <sys/ioctl.h>
#       include <linux/random.h>
#   endif
#elif defined(_LIBCPP_USING_NACL_RANDOM)
#   include <nacl/nacl_random.h>
#elif defined(_LIBCPP_USING_FUCHSIA_CPRNG)
#  include <zircon/syscalls.h>
#endif


_LIBCPP_BEGIN_NAMESPACE_STD

#if defined(_LIBCPP_USING_GETENTROPY)

random_device::random_device(const string& __token)
{
    if (__token != "/dev/urandom")
        __throw_system_error(ENOENT, ("random device not supported " + __token).c_str());
}

random_device::~random_device()
{
}

unsigned
random_device::operator()()
{
    unsigned r;
    size_t n = sizeof(r);
    int err = getentropy(&r, n);
    if (err)
        __throw_system_error(errno, "random_device getentropy failed");
    return r;
}

#elif defined(_LIBCPP_USING_ARC4_RANDOM)

random_device::random_device(const string&)
{
}

random_device::~random_device()
{
}

unsigned
random_device::operator()()
{
    return arc4random();
}

#elif defined(_LIBCPP_USING_DEV_RANDOM)

random_device::random_device(const string& __token)
    : __f_(open(__token.c_str(), O_RDONLY))
{
    if (__f_ < 0)
        __throw_system_error(errno, ("random_device failed to open " + __token).c_str());
}

random_device::~random_device()
{
    close(__f_);
}

unsigned
random_device::operator()()
{
    unsigned r;
    size_t n = sizeof(r);
    char* p = reinterpret_cast<char*>(&r);
    while (n > 0)
    {
        ssize_t s = read(__f_, p, n);
        if (s == 0)
            __throw_system_error(ENODATA, "random_device got EOF");
        if (s == -1)
        {
            if (errno != EINTR)
                __throw_system_error(errno, "random_device got an unexpected error");
            continue;
        }
        n -= static_cast<size_t>(s);
        p += static_cast<size_t>(s);
    }
    return r;
}

#elif defined(_LIBCPP_USING_NACL_RANDOM)

random_device::random_device(const string& __token)
{
    if (__token != "/dev/urandom")
        __throw_system_error(ENOENT, ("random device not supported " + __token).c_str());
    int error = nacl_secure_random_init();
    if (error)
        __throw_system_error(error, ("random device failed to open " + __token).c_str());
}

random_device::~random_device()
{
}

unsigned
random_device::operator()()
{
    unsigned r;
    size_t n = sizeof(r);
    size_t bytes_written;
    int error = nacl_secure_random(&r, n, &bytes_written);
    if (error != 0)
        __throw_system_error(error, "random_device failed getting bytes");
    else if (bytes_written != n)
        __throw_runtime_error("random_device failed to obtain enough bytes");
    return r;
}

#elif defined(_LIBCPP_USING_WIN32_RANDOM)

random_device::random_device(const string& __token)
{
    if (__token != "/dev/urandom")
        __throw_system_error(ENOENT, ("random device not supported " + __token).c_str());
}

random_device::~random_device()
{
}

unsigned
random_device::operator()()
{
    unsigned r;
    errno_t err = rand_s(&r);
    if (err)
        __throw_system_error(err, "random_device rand_s failed.");
    return r;
}

#elif defined(_LIBCPP_USING_FUCHSIA_CPRNG)

random_device::random_device(const string& __token) {
  if (__token != "/dev/urandom")
    __throw_system_error(ENOENT, ("random device not supported " + __token).c_str());
}

random_device::~random_device() {}

unsigned random_device::operator()() {
  // Implicitly link against the vDSO system call ABI without
  // requiring the final link to specify -lzircon explicitly when
  // statically linking libc++.
#  pragma comment(lib, "zircon")

  // The system call cannot fail.  It returns only when the bits are ready.
  unsigned r;
  _zx_cprng_draw(&r, sizeof(r));
  return r;
}

#else
#error "Random device not implemented for this architecture"
#endif

double
random_device::entropy() const noexcept
{
#if defined(_LIBCPP_USING_DEV_RANDOM) && defined(RNDGETENTCNT)
  int ent;
  if (::ioctl(__f_, RNDGETENTCNT, &ent) < 0)
    return 0;

  if (ent < 0)
    return 0;

  if (ent > std::numeric_limits<result_type>::digits)
    return std::numeric_limits<result_type>::digits;

  return ent;
#elif defined(__OpenBSD__) || defined(_LIBCPP_USING_FUCHSIA_CPRNG)
  return std::numeric_limits<result_type>::digits;
#else
  return 0;
#endif
}

_LIBCPP_END_NAMESPACE_STD