add system random to stdlib: std/sysrand

lib/std/secrets.nim

@@ -0,0 +1,98 @@
+import os
+
+runnableExamples:
+  doAssert urandom(0).len == 0
+  doAssert urandom(10).len == 10
+  doAssert urandom(20).len == 20
+  doAssert urandom(120).len == 120
+
+
+when defined(posix):
+  import posix
+
+  template processReadBytes(readBytes: int, p: pointer) =
+    if readBytes == 0:
+      break
+    elif readBytes > 0:
+      inc(result, readBytes)
+      cast[ptr pointer](p)[] = cast[pointer](cast[ByteAddress](p) + readBytes)
+    else:
+      if osLastError().int in {EINTR, EAGAIN}:
+        discard
+      else:
+        result = -1
+        break
+
+  proc getDevUrandom(p: pointer, size: int): int =
+    let fd = posix.open("/dev/urandom", O_RDONLY)
+
+    if fd > 0:
+      var stat: Stat
+      if fstat(fd, stat) != -1 and S_ISCHR(stat.st_mode):
+        while result < size:
+          let readBytes = posix.read(fd, p, size - result)
+          processReadBytes(readBytes, p)
+
+      discard posix.close(fd)
+
+when defined(windows):
+  import winlean
+
+  type
+    PVOID = pointer
+    BCRYPT_ALG_HANDLE = PVOID
+    PUCHAR = ptr cuchar
+    NTSTATUS = clong
+
+  const
+    STATUS_SUCCESS = 0x00000000
+    BCRYPT_USE_SYSTEM_PREFERRED_RNG = 0x00000002
+
+  proc bCryptGenRandom(
+    hAlgorithm: BCRYPT_ALG_HANDLE,
+    pbBuffer: PUCHAR,
+    cbBuffer: ULONG,
+    dwFlags: ULONG
+  ): NTSTATUS {.stdcall, importc: "BCryptGenRandom", dynlib: "Bcrypt.dll".}
+
+
+  proc randomBytes(pbBuffer: pointer, cbBuffer: ULONG): int =
+    bCryptGenRandom(nil, cast[PUCHAR](pbBuffer), cbBuffer,
+                            BCRYPT_USE_SYSTEM_PREFERRED_RNG)
+
+  proc urandom*(p: pointer, size: int): int =
+    result = randomBytes(p, ULONG(size))
+
+  proc urandom*(size: int): string =
+    result = newString(size)
+    if urandom(result.cstring, ULONG(size)) != STATUS_SUCCESS:
+      raiseOsError(osLastError())
+
+elif defined(linux):
+  let SYS_getrandom {.importc: "SYS_getrandom", header: "<syscall.h>".}: clong
+
+  proc syscall(n: clong, buf: pointer, bufLen: cint, flags: cuint): int {.importc: "syscall", header: "syscall.h".}
+
+  proc randomBytes(p: pointer, size: int): int =
+    while result < size:
+      let readBytes = syscall(SYS_getrandom, p, cint(size - result), 0)
+      processReadBytes(readBytes, p)
+
+  proc urandom*(p: pointer, size: int): int =
+    result = randomBytes(p, size)
+    if result < 0:
+      result = getDevUrandom(p, size)
+
+  proc urandom*(size: int): string =
+    result = newString(size)
+    if urandom(result.cstring, size) < 0:
+      raiseOsError(osLastError())
+
+else:
+  proc urandom*(p: pointer, size: int): int =
+    result = getDevUrandom(p, size)
+
+  proc urandom*(size: int): string =
+    result = newString(size)
+    if urandom(result.cstring, size) < 0:
+      raiseOsError(osLastError())

tests/stdlib/tsecrets.nim

@@ -0,0 +1,11 @@
+discard """
+  targets: "c cpp"
+"""
+
+import std/secrets
+
+
+doAssert urandom(0).len == 0
+doAssert urandom(10).len == 10
+doAssert urandom(20).len == 20
+doAssert urandom(120).len == 120