From 98dd0cf23355a1f87af14c10098b9545605ac556 Mon Sep 17 00:00:00 2001
From: amesgen <amesgen@amesgen.de>
Date: Tue, 23 Jul 2024 22:13:45 +0200
Subject: [PATCH 1/2] `build-type: Simple`

for cross compilation (eg to WASM)
---
 entropy.cabal | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/entropy.cabal b/entropy.cabal
index 45720f0..feb61a9 100644
--- a/entropy.cabal
+++ b/entropy.cabal
@@ -17,7 +17,7 @@ homepage:       https://github.com/TomMD/entropy
 bug-reports:    https://github.com/TomMD/entropy/issues
 stability:      stable
 
-build-type:     Custom
+build-type:     Simple
 
 tested-with:
   GHC == 9.10.1

From f771c8010f001b87c5ccf9b61703b6912f7062d5 Mon Sep 17 00:00:00 2001
From: amesgen <amesgen@amesgen.de>
Date: Tue, 13 Aug 2024 21:32:13 +0200
Subject: [PATCH 2/2] WASI: implement in terms of `getentropy`

This isn't really WASI-specific; it should work for any platform that has
`getentropy`.
---
 System/Entropy.hs     |  2 ++
 System/EntropyWasi.hs | 39 +++++++++++++++++++++++++++++++++++++++
 entropy.cabal         |  7 +++++--
 3 files changed, 46 insertions(+), 2 deletions(-)
 create mode 100644 System/EntropyWasi.hs

diff --git a/System/Entropy.hs b/System/Entropy.hs
index 9868fe5..50eb301 100644
--- a/System/Entropy.hs
+++ b/System/Entropy.hs
@@ -27,6 +27,8 @@ module System.Entropy
 import System.EntropyGhcjs
 #elif defined(isWindows)
 import System.EntropyWindows
+#elif wasi_HOST_OS
+import System.EntropyWasi
 #else
 import System.EntropyNix
 #endif
diff --git a/System/EntropyWasi.hs b/System/EntropyWasi.hs
new file mode 100644
index 0000000..667b516
--- /dev/null
+++ b/System/EntropyWasi.hs
@@ -0,0 +1,39 @@
+{-# LANGUAGE CApiFFI #-}
+
+module System.EntropyWasi where
+
+import Control.Monad (when)
+import Data.ByteString (ByteString)
+import Data.ByteString.Internal as B
+import Data.Word (Word8)
+import Foreign.C.Types
+import Foreign.Ptr
+
+data CryptHandle = BogusCryptHandle
+
+openHandle :: IO CryptHandle
+openHandle = pure BogusCryptHandle
+
+hGetEntropy :: CryptHandle -> Int -> IO ByteString
+hGetEntropy BogusCryptHandle = \n -> B.create n $ go (fromIntegral n)
+  where
+    go :: CSize -> Ptr Word8 -> IO ()
+    go n ptr
+      | n <= 256 = getentropy' ptr n
+      | otherwise = do
+          getentropy' ptr 256
+          go (n - 256) (ptr `plusPtr` 256)
+
+    getentropy' ptr n = do
+      res <- getentropy ptr n
+      when (res /= 0) $
+        fail "getentropy failed"
+
+foreign import capi safe "unistd.h getentropy"
+  getentropy :: Ptr Word8 -> CSize -> IO CInt
+
+closeHandle :: CryptHandle -> IO ()
+closeHandle BogusCryptHandle = pure ()
+
+hardwareRandom :: Int -> IO (Maybe ByteString)
+hardwareRandom _ = pure Nothing
diff --git a/entropy.cabal b/entropy.cabal
index feb61a9..f2adf0a 100644
--- a/entropy.cabal
+++ b/entropy.cabal
@@ -1,4 +1,4 @@
-cabal-version:  >=1.10
+cabal-version:  3.8
 name:           entropy
 version:        0.4.1.10
 x-revision:     2
@@ -7,7 +7,7 @@ description:    A mostly platform independent method to obtain cryptographically
                 Users looking for cryptographically strong (number-theoretically
                 sound) PRNGs should see the 'DRBG' package too.
 synopsis:       A platform independent entropy source
-license:        BSD3
+license:        BSD-3-Clause
 license-file:   LICENSE
 copyright:      Thomas DuBuisson <thomas.dubuisson@gmail.com>
 author:         Thomas DuBuisson <thomas.dubuisson@gmail.com>
@@ -61,6 +61,8 @@ library
   else {
     if os(windows)
       other-modules: System.EntropyWindows
+    elif os(wasi)
+      other-modules: System.EntropyWasi
     else {
       other-modules: System.EntropyNix
     }
@@ -90,6 +92,7 @@ library
       cpp-options: -DisWindows
       cc-options:  -DisWindows
       extra-libraries: advapi32
+    elif os(wasi)
     else
       Build-Depends: unix
       c-sources: cbits/getrandom.c cbits/random_initialized.c