bearssl: use rand helpers (#113)

websock/utils.nim

@@ -7,35 +7,25 @@
 ## This file may not be copied, modified, or distributed except according to
 ## those terms.
 
-import bearssl
-export bearssl
+import bearssl/[hash, rand]
+export rand
 
-## Random helpers: similar as in stdlib, but with BrHmacDrbgContext rng
+## Random helpers: similar as in stdlib, but with HmacDrbgContext rng
 const randMax = 18_446_744_073_709_551_615'u64
 
 type
-  Rng* = ref BrHmacDrbgContext
+  Rng* = ref HmacDrbgContext
 
 proc newRng*(): Rng =
   # You should only create one instance of the RNG per application / library
   # Ref is used so that it can be shared between components
-  # TODO consider moving to bearssl
-  var seeder = brPrngSeederSystem(nil)
-  if seeder == nil:
-    return nil
-
-  var rng = Rng()
-  brHmacDrbgInit(addr rng[], addr sha256Vtable, nil, 0)
-  if seeder(addr rng.vtable) == 0:
-    return nil
-
-  rng
+  HmacDrbgContext.new()
 
 proc rand*(rng: Rng, max: Natural): int =
   if max == 0: return 0
   var x: uint64
   while true:
-    brHmacDrbgGenerate(addr rng[], addr x, csize_t(sizeof(x)))
+    let x = rng[].generate(uint64)
     if x < randMax - (randMax mod (uint64(max) + 1'u64)): # against modulo bias
       return int(x mod (uint64(max) + 1'u64))