    {-# LINE 1 "src/Hookup/OpenSSL.hsc" #-}
    {-# Language CApiFFI #-}
    {-|
    Module      : Hookup.OpenSSL
    Description : Hack into the internals of OpenSSL to add missing functionality
    Copyright   : (c) Eric Mertens, 2016
    License     : ISC
    Maintainer  : emertens@gmail.com
    -}

    {-# LINE 17 "src/Hookup/OpenSSL.hsc" #-}

    module Hookup.OpenSSL (installVerification, getPubKeyDer) where

    import           Control.Monad (unless)
    import           Foreign.C (CString(..), CSize(..), CUInt(..), CInt(..), withCStringLen)
    import           Foreign.Ptr (Ptr, castPtr, nullPtr)
    import           Foreign.Marshal (with)
    import           OpenSSL.Session (SSLContext, SSLContext_, withContext)
    import           OpenSSL.X509 (withX509Ptr, X509, X509_)
    import           Data.ByteString (ByteString)
    import qualified Data.ByteString.Internal as B

    ------------------------------------------------------------------------
    -- Bindings to hostname verification interface
    ------------------------------------------------------------------------

    data X509_VERIFY_PARAM_
    data {-# CTYPE "openssl/ssl.h" "X509_PUBKEY" #-} X509_PUBKEY_
    data {-# CTYPE "openssl/ssl.h" "X509" #-} X509__

    -- X509_VERIFY_PARAM *SSL_CTX_get0_param(SSL_CTX *ctx);
    foreign import ccall unsafe "SSL_CTX_get0_param"
      sslGet0Param ::
        Ptr SSLContext_ {- ^ ctx -} ->
        IO (Ptr X509_VERIFY_PARAM_)

    -- void X509_VERIFY_PARAM_set_hostflags(X509_VERIFY_PARAM *param, unsigned int flags);
    foreign import ccall unsafe "X509_VERIFY_PARAM_set_hostflags"
      x509VerifyParamSetHostflags ::
        Ptr X509_VERIFY_PARAM_ {- ^ param -} ->
        CUInt                  {- ^ flags -} ->
        IO ()

    -- int X509_VERIFY_PARAM_set1_host(X509_VERIFY_PARAM *param, const char *name, size_t namelen);
    foreign import ccall unsafe "X509_VERIFY_PARAM_set1_host"
      x509VerifyParamSet1Host ::
        Ptr X509_VERIFY_PARAM_ {- ^ param                -} ->
        CString                {- ^ name                 -} ->
        CSize                  {- ^ namelen              -} ->
        IO CInt                {- ^ 1 success, 0 failure -}

    -- X509_PUBKEY *X509_get_X509_PUBKEY(X509 *x);
    foreign import capi unsafe "openssl/x509.h X509_get_X509_PUBKEY"
      x509getX509Pubkey ::
        Ptr X509__ -> IO (Ptr X509_PUBKEY_)

    -- int i2d_X509_PUBKEY(X509_PUBKEY *p, unsigned char **ppout);
    foreign import ccall unsafe "i2d_X509_PUBKEY"
      i2dX509Pubkey ::
        Ptr X509_PUBKEY_ ->
        Ptr CString ->
        IO CInt

    getPubKeyDer :: X509 -> IO ByteString
    getPubKeyDer x509 =
      withX509Ptr x509 $ \x509ptr ->
      do pubkey <- x509getX509Pubkey (castPtr x509ptr)
         len    <- fromIntegral <$> i2dX509Pubkey pubkey nullPtr
         B.create len $ \bsPtr ->
            with (castPtr bsPtr) $ \ptrPtr ->
               () <$ i2dX509Pubkey pubkey ptrPtr

    -- | Add hostname checking to the certificate verification step.
    -- Partial wildcards matching is disabled.
    installVerification :: SSLContext -> String {- ^ hostname -} -> IO ()
    installVerification ctx host =
      withContext ctx     $ \ctxPtr ->
      withCStringLen host $ \(ptr,len) ->
        do param <- sslGet0Param ctxPtr
           x509VerifyParamSetHostflags param
             (4)
    {-# LINE 89 "src/Hookup/OpenSSL.hsc" #-}
           success <- x509VerifyParamSet1Host param ptr (fromIntegral len)
           unless (success == 1) (fail "Unable to set verification host")