Hookup.hs

{-# Language BlockArguments, LambdaCase #-}
{-|
Module      : Hookup
Description : Network connections generalized over TLS and SOCKS
Copyright   : (c) Eric Mertens, 2016
License     : ISC
Maintainer  : emertens@gmail.com

This module provides a uniform interface to network connections
with optional support for TLS and SOCKS.

This library is careful to support both IPv4 and IPv6. It will attempt to
all of the addresses that a domain name resolves to until one the first
successful connection.

Use 'connect' and 'close' to establish and close network connections.

Use 'recv', 'recvLine', and 'send' to receive and transmit data on an
open network connection.

TLS and SOCKS parameters can be provided. When both are provided a connection
will first be established to the SOCKS server and then the TLS connection will
be established through that proxy server. This is most useful when connecting
through a dynamic port forward of an SSH client via the @-D@ flag.

-}
module Hookup
  (
  -- * Connections
  Connection,
  connect,
  connectWithSocket,
  close,
  upgradeTls,

  -- * Reading and writing data
  recv,
  recvLine,
  send,
  putBuf,

  -- * Configuration
  ConnectionParams(..),
  SocksParams(..),
  SocksAuthentication(..),
  TlsParams(..),
  TlsVerify(..),
  PEM.PemPasswordSupply(..),
  defaultTlsParams,

  -- * Errors
  ConnectionFailure(..),
  CommandReply(..)

  -- * SSL Information
  , getClientCertificate
  , getPeerCertificate
  , getPeerCertFingerprintSha1
  , getPeerCertFingerprintSha256
  , getPeerCertFingerprintSha512
  , getPeerPubkeyFingerprintSha1
  , getPeerPubkeyFingerprintSha256
  , getPeerPubkeyFingerprintSha512
  ) where

import           Control.Concurrent
import           Control.Exception
import           Control.Monad (when, unless)
import           System.IO.Error (isDoesNotExistError, ioeGetErrorString)
import           Data.ByteString (ByteString)
import qualified Data.ByteString as B
import qualified Data.ByteString.Char8 as B8
import           Data.Foldable (for_, traverse_)
import           Data.List (intercalate, partition)
import           Data.Maybe (fromMaybe, mapMaybe)
import           Foreign.C.String (withCStringLen)
import           Foreign.Ptr (nullPtr)
import           Network.Socket (AddrInfo, HostName, PortNumber, SockAddr, Socket, Family)
import qualified Network.Socket as Socket
import qualified Network.Socket.ByteString as SocketB
import           OpenSSL.Session (SSL, SSLContext)
import qualified OpenSSL as SSL
import qualified OpenSSL.Session as SSL
import           OpenSSL.X509.SystemStore (contextLoadSystemCerts)
import           OpenSSL.X509 (X509)
import qualified OpenSSL.X509 as X509
import qualified OpenSSL.PEM as PEM
import qualified OpenSSL.EVP.Digest as Digest
import           Data.Attoparsec.ByteString (Parser)
import qualified Data.Attoparsec.ByteString as Parser

import           Hookup.Concurrent (concurrentAttempts)
import           Hookup.OpenSSL
import           Hookup.Socks5

-- | Parameters for 'connect'.
--
-- Common defaults for fields: 'defaultFamily', 'defaultTlsParams'
--
-- When a 'SocksParams' is provided the connection will be established
-- using a SOCKS (version 5) proxy.
--
-- When a 'TlsParams' is provided the connection negotiate TLS at connect
-- time in order to protect the stream.
--
-- The binding hostname can be used to force the connect to use a particular
-- interface or IP protocol version.
data ConnectionParams = ConnectionParams
  { cpHost  :: HostName          -- ^ Destination host
  , cpPort  :: PortNumber        -- ^ Destination TCP port
  , cpSocks :: Maybe SocksParams -- ^ Optional SOCKS parameters
  , cpTls   :: Maybe TlsParams   -- ^ Optional TLS parameters
  , cpBind  :: Maybe HostName    -- ^ Source address to bind
  }
  deriving Show

-- | SOCKS connection parameters
data SocksParams = SocksParams
  { spHost :: HostName   -- ^ SOCKS server host
  , spPort :: PortNumber -- ^ SOCKS server port
  , spAuth :: SocksAuthentication -- ^ SOCKS authentication method
  }
  deriving Show

data SocksAuthentication
  = NoSocksAuthentication -- ^ no credentials
  | UsernamePasswordSocksAuthentication ByteString ByteString -- ^ RFC 1929 username and password
  deriving Show

-- | TLS connection parameters. These parameters are passed to
-- OpenSSL when making a secure connection.
data TlsParams = TlsParams
  { tpClientCertificate  :: Maybe FilePath -- ^ Path to client certificate
  , tpClientPrivateKey   :: Maybe FilePath -- ^ Path to client private key
  , tpClientPrivateKeyPassword :: Maybe ByteString -- ^ Private key decryption password
  , tpServerCertificate  :: Maybe FilePath -- ^ Path to CA certificate bundle
  , tpCipherSuite        :: String -- ^ OpenSSL cipher suite name (e.g. @\"HIGH\"@)
  , tpCipherSuiteTls13   :: Maybe String -- ^ OpenSSL cipher suites for TLS 1.3
  , tpVerify             :: TlsVerify -- ^ Hostname to use when checking certificate validity
  }
  deriving Show

data TlsVerify
  = VerifyDefault -- ^ Use the connection hostname to verify
  | VerifyNone -- ^ No verification
  | VerifyHostname String -- ^ Use the given hostname to verify
  deriving Show

-- | Type for errors that can be thrown by this package.
data ConnectionFailure
  -- | Failure during 'getAddrInfo' resolving remote host
  = HostnameResolutionFailure HostName String
  -- | Failure during 'connect' to remote host
  | ConnectionFailure [ConnectError]
  -- | Failure during 'recvLine'
  | LineTooLong
  -- | Incomplete line during 'recvLine'
  | LineTruncated
  -- | Socks command rejected by server by given reply code
  | SocksError CommandReply
  -- | Socks authentication method was not accepted
  | SocksAuthenticationMethodRejected
  -- | Socks authentication method was not accepted
  | SocksAuthenticationCredentialsRejected
  -- | Username or password were too long
  | SocksBadAuthenticationCredentials
  -- | Socks server sent an invalid message or no message.
  | SocksProtocolError
  -- | Domain name was too long for SOCKS protocol
  | SocksBadDomainName
  deriving Show

-- | 'displayException' implemented for prettier messages
instance Exception ConnectionFailure where
  displayException LineTruncated = "connection closed while reading line"
  displayException LineTooLong   = "line length exceeded maximum"
  displayException (ConnectionFailure xs) =
    "connection attempt failed due to: " ++
      intercalate ", " (map displayException xs)
  displayException (HostnameResolutionFailure h s) =
    "hostname resolution failed (" ++ h ++ "): "  ++ s
  displayException SocksAuthenticationMethodRejected =
    "SOCKS authentication method rejected"
  displayException SocksAuthenticationCredentialsRejected =
    "SOCKS authentication credentials rejected"
  displayException SocksBadAuthenticationCredentials =
    "SOCKS authentication credentials too long"
  displayException SocksProtocolError =
    "SOCKS server protocol error"
  displayException SocksBadDomainName =
    "SOCKS domain name length limit exceeded"
  displayException (SocksError reply) =
    "SOCKS command rejected: " ++
    case reply of
      Succeeded         -> "succeeded"
      GeneralFailure    -> "general SOCKS server failure"
      NotAllowed        -> "connection not allowed by ruleset"
      NetUnreachable    -> "network unreachable"
      HostUnreachable   -> "host unreachable"
      ConnectionRefused -> "connection refused"
      TTLExpired        -> "TTL expired"
      CmdNotSupported   -> "command not supported"
      AddrNotSupported  -> "address type not supported"
      CommandReply n    -> "unknown reply " ++ show n

data ConnectError = ConnectError SockAddr IOError
  deriving Show

instance Exception ConnectError where
  displayException (ConnectError addr e) = show addr ++ ": " ++ displayException e

-- | Default values for TLS that use no client certificates, use
-- system CA root, @\"HIGH\"@ cipher suite, and which validate hostnames.
defaultTlsParams :: TlsParams
defaultTlsParams = TlsParams
  { tpClientCertificate  = Nothing
  , tpClientPrivateKey   = Nothing
  , tpClientPrivateKeyPassword = Nothing
  , tpServerCertificate  = Nothing -- use system provided CAs
  , tpCipherSuite        = "HIGH"
  , tpCipherSuiteTls13   = Nothing
  , tpVerify             = VerifyDefault
  }

------------------------------------------------------------------------
-- Opening sockets
------------------------------------------------------------------------

-- | Open a socket using the given parameters either directly or
-- via a SOCKS server.
openSocket :: ConnectionParams -> IO Socket
openSocket params =
  case cpSocks params of
    Nothing -> openSocket' (cpHost params) (cpPort params) (cpBind params)
    Just sp ->
      bracketOnError
        (openSocket' (spHost sp) (spPort sp) (cpBind params))
        Socket.close
        \sock ->
          sock <$ socksConnect sock (cpHost params) (cpPort params) (spAuth sp)

netParse :: Show a => Socket -> Parser a -> IO a
netParse sock parser =
  do -- receiving 1 byte at a time is not efficient, but these messages
     -- are very short and we don't want to read any more from the socket
     -- than is necessary
     result <- Parser.parseWith
                 (SocketB.recv sock 1)
                 parser
                 B.empty
     case result of
       Parser.Done i x | B.null i -> pure x
       _ -> throwIO SocksProtocolError

socksConnect :: Socket -> HostName -> PortNumber -> SocksAuthentication -> IO ()
socksConnect sock host port auth =
 do case auth of
      NoSocksAuthentication ->
       do SocketB.sendAll sock $
            buildClientHello ClientHello
              { cHelloMethods = [AuthNoAuthenticationRequired] }
          hello <- netParse sock parseServerHello
          unless (sHelloMethod hello == AuthNoAuthenticationRequired)
            (throwIO SocksAuthenticationMethodRejected)

      UsernamePasswordSocksAuthentication u p ->
       do unless (B.length u < 256 && B.length p < 256)
            (throwIO SocksBadAuthenticationCredentials)

          SocketB.sendAll sock $
            buildClientHello ClientHello
              { cHelloMethods = [AuthUsernamePassword] }
          hello <- netParse sock parseServerHello
          unless (sHelloMethod hello == AuthUsernamePassword)
            (throwIO SocksAuthenticationMethodRejected)

          SocketB.sendAll sock $
            buildPlainAuthentication PlainAuthentication
              { plainUsername = u, plainPassword = p }
          status <- netParse sock parsePlainAuthenticationReply
          unless (0 == plainStatus status)
            (throwIO SocksAuthenticationCredentialsRejected)

    let dnBytes = B8.pack host
    unless (B.length dnBytes < 256)
      (throwIO SocksBadDomainName)

    SocketB.sendAll sock $
      buildRequest Request
        { reqCommand  = Connect
        , reqAddress  = Address (DomainName dnBytes) port
        }

    response <- netParse sock parseResponse
    unless (rspReply response == Succeeded )
      (throwIO (SocksError (rspReply response)))

openSocket' ::
  HostName       {- ^ destination      -} ->
  PortNumber     {- ^ destination port -} ->
  Maybe HostName {- ^ source           -} ->
  IO Socket      {- ^ connected socket -}
openSocket' h p mbBind =
  do mbSrc <- traverse (resolve Nothing) mbBind
     dst   <- resolve (Just p) h
     let pairs = interleaveAddressFamilies (matchBindAddrs mbSrc dst)
     when (null pairs)
       (throwIO (HostnameResolutionFailure h "No source/destination address family match"))
     res <- concurrentAttempts connAttemptDelay Socket.close (uncurry connectToAddrInfo <$> pairs)
     case res of
       Left es -> throwIO (ConnectionFailure (mapMaybe fromException es))
       Right s -> pure s

hints :: AddrInfo
hints = Socket.defaultHints
  { Socket.addrSocketType = Socket.Stream
  , Socket.addrFlags      = [Socket.AI_NUMERICSERV]
  }

resolve :: Maybe PortNumber -> HostName -> IO [AddrInfo]
resolve mbPort host =
  do res <- try (Socket.getAddrInfo (Just hints) (Just host) (show<$>mbPort))
     case res of
       Right ais -> pure ais
       Left ioe
         | isDoesNotExistError ioe ->
             throwIO (HostnameResolutionFailure host (ioeGetErrorString ioe))
         | otherwise -> throwIO ioe -- unexpected

-- | When no bind address is specified return the full list of destination
-- addresses with no bind address specified.
--
-- When bind addresses are specified return a subset of the destination list
-- matched up with the first address from the bind list that has the
-- correct address family.
matchBindAddrs :: Maybe [AddrInfo] -> [AddrInfo] -> [(Maybe SockAddr, AddrInfo)]
matchBindAddrs Nothing    dst = [ (Nothing, x) | x <- dst ]
matchBindAddrs (Just src) dst =
  [ (Just (Socket.addrAddress s), d)
  | d <- dst
  , let ss = [s | s <- src, Socket.addrFamily d == Socket.addrFamily s]
  , s <- take 1 ss ]

connAttemptDelay :: Int
connAttemptDelay = 150 * 1000 -- 150ms

-- | Alternate list of addresses between IPv6 and other (IPv4) addresses.
interleaveAddressFamilies :: [(Maybe SockAddr, AddrInfo)] -> [(Maybe SockAddr, AddrInfo)]
interleaveAddressFamilies xs = interleave sixes others
  where
    (sixes, others) = partition is6 xs
    is6 x = Socket.AF_INET6 == Socket.addrFamily (snd x)

    interleave (x:xs) (y:ys) = x : y : interleave xs ys
    interleave []     ys     = ys
    interleave xs     []     = xs

-- | Create a socket and connect to the service identified
-- by the given 'AddrInfo' and return the connected socket.
connectToAddrInfo :: Maybe SockAddr -> AddrInfo -> IO Socket
connectToAddrInfo mbSrc info
  = let addr = Socket.addrAddress info in
    bracketOnError (socket' info) Socket.close \s ->
    do traverse_ (bind' s) mbSrc
       Socket.connect s addr
       pure s
    `catch` (throwIO . ConnectError addr)

-- | A version of 'Socket.bind' that doesn't bother binding on the wildcard
-- address. The effect of binding on a wildcard address in this library
-- is to pick an address family. Because of the matching done earlier this
-- is unnecessary for client connections and causes a local port to be
-- unnecessarily fixed early.
bind' :: Socket -> SockAddr -> IO ()
bind' _ (Socket.SockAddrInet _ 0) = pure ()
bind' _ (Socket.SockAddrInet6 _ _ (0,0,0,0) _) = pure ()
bind' s a = Socket.bind s a

-- | Open a 'Socket' using the parameters from an 'AddrInfo'
socket' :: AddrInfo -> IO Socket
socket' ai =
  Socket.socket
    (Socket.addrFamily     ai)
    (Socket.addrSocketType ai)
    (Socket.addrProtocol   ai)


------------------------------------------------------------------------
-- Generalization of Socket
------------------------------------------------------------------------

data NetworkHandle = SSL (Maybe X509) SSL | Socket Socket

openNetworkHandle ::
  ConnectionParams {- ^ parameters             -} ->
  IO Socket        {- ^ socket creation action -} ->
  IO NetworkHandle {- ^ open network handle    -}
openNetworkHandle params mkSocket =
  case cpTls params of
    Nothing  -> Socket <$> mkSocket
    Just tls ->
        do (clientCert, ssl) <- startTls tls (cpHost params) mkSocket
           pure (SSL clientCert ssl)

closeNetworkHandle :: NetworkHandle -> IO ()
closeNetworkHandle (Socket s) = Socket.close s
closeNetworkHandle (SSL _ s) =
  do SSL.shutdown s SSL.Unidirectional
     traverse_ Socket.close (SSL.sslSocket s)

networkSend :: NetworkHandle -> ByteString -> IO ()
networkSend (Socket s) = SocketB.sendAll s
networkSend (SSL  _ s) = SSL.write       s

networkRecv :: NetworkHandle -> Int -> IO ByteString
networkRecv (Socket s) = SocketB.recv s
networkRecv (SSL  _ s) = SSL.read     s

------------------------------------------------------------------------
-- Sockets with a receive buffer
------------------------------------------------------------------------

-- | A connection to a network service along with its read buffer
-- used for line-oriented protocols. The connection could be a plain
-- network connection, SOCKS connected, or TLS.
data Connection =
  Connection
  {-# UNPACK #-} !(MVar ByteString)
  {-# UNPACK #-} !(MVar NetworkHandle)

-- | Open network connection to TCP service specified by
-- the given parameters.
--
-- The resulting connection MUST be closed with 'close' to avoid leaking
-- resources.
--
-- Throws 'IOError', 'SocksError', 'SSL.ProtocolError', 'ConnectionFailure'
connect ::
  ConnectionParams {- ^ parameters      -} ->
  IO Connection    {- ^ open connection -}
connect params =
 do h <- openNetworkHandle params (openSocket params)
    Connection <$> newMVar B.empty <*> newMVar h

-- | Create a new 'Connection' using an already connected socket.
-- This will attempt to start TLS if configured but will ignore
-- any SOCKS server settings as it is assumed that the socket
-- is already actively connected to the intended service.
--
-- Throws 'SSL.ProtocolError'
connectWithSocket ::
  ConnectionParams {- ^ parameters       -} ->
  Socket           {- ^ connected socket -} ->
  IO Connection    {- ^ open connection  -}
connectWithSocket params sock =
 do h <- openNetworkHandle params (pure sock)
    Connection <$> newMVar B.empty <*> newMVar h

-- | Close network connection.
close ::
  Connection {- ^ open connection -} ->
  IO ()
close (Connection _ m) = withMVar m \h -> closeNetworkHandle h

-- | Receive the next chunk from the stream. This operation will first
-- return the buffer if it contains a non-empty chunk. Otherwise it will
-- request up to the requested number of bytes from the stream.
--
-- Throws: 'IOError', 'SSL.ConnectionAbruptlyTerminated', 'SSL.ProtocolError'
recv ::
  Connection    {- ^ open connection              -} ->
  Int           {- ^ maximum underlying recv size -} ->
  IO ByteString {- ^ next chunk from stream       -}
recv (Connection bufVar hVar) n =
  modifyMVar bufVar \bufChunk ->
  if B.null bufChunk then
   do h <- readMVar hVar
      bs <- networkRecv h n
      pure (B.empty, bs)
  else
      pure (B.empty, bufChunk)

-- | Receive a line from the network connection. Both
-- @"\\r\\n"@ and @"\\n"@ are recognized.
--
-- Returning 'Nothing' means that the peer has closed its half of
-- the connection.
--
-- Unterminated lines will raise a 'LineTruncated' exception. This
-- can happen if the peer transmits some data and closes its end
-- without transmitting a line terminator.
--
-- Throws: 'SSL.ConnectionAbruptlyTerminated', 'SSL.ProtocolError', 'ConnectionFailure', 'IOError'
recvLine ::
  Connection            {- ^ open connection            -} ->
  Int                   {- ^ maximum line length        -} ->
  IO (Maybe ByteString) {- ^ next line or end-of-stream -}
recvLine (Connection bufVar hVar) n =
  modifyMVar bufVar \bs ->
   do h <- readMVar hVar
      go h (B.length bs) bs []
  where
    -- bsn: cached length of concatenation of (bs:bss)
    -- bs : most recent chunk
    -- bss: other chunks ordered from most to least recent
    go h bsn bs bss =
      case B8.elemIndex '\n' bs of
        Just i -> pure (B.tail b, -- tail drops newline
                        Just (cleanEnd (B.concat (reverse (a:bss)))))
          where
            (a,b) = B.splitAt i bs
        Nothing ->
          do when (bsn >= n) (throwIO LineTooLong)
             more <- networkRecv h n
             if B.null more -- connection closed
               then if bsn == 0 then pure (B.empty, Nothing)
                                else throwIO LineTruncated
               else go h (bsn + B.length more) more (bs:bss)

-- | Push a 'ByteString' onto the buffer so that it will be the first
-- bytes to be read on the next receive operation. This could perhaps
-- be useful for putting the unused portion of a 'recv' back into the
-- buffer for future 'recvLine' or 'recv' operations.
putBuf ::
  Connection {- ^ connection         -} ->
  ByteString {- ^ new head of buffer -} ->
  IO ()
putBuf (Connection bufVar _) bs =
  modifyMVar_ bufVar (\old -> pure $! B.append bs old)

-- | Remove the trailing @'\\r'@ if one is found.
cleanEnd :: ByteString -> ByteString
cleanEnd bs
  | B.null bs || B8.last bs /= '\r' = bs
  | otherwise                       = B.init bs

-- | Send bytes on the network connection. This ensures the whole chunk is
-- transmitted, which might take multiple underlying sends.
--
-- Throws: 'IOError', 'SSL.ProtocolError'
send ::
  Connection {- ^ open connection -} ->
  ByteString {- ^ chunk           -} ->
  IO ()
send (Connection _ hVar) bs =
  do h <- readMVar hVar
     networkSend h bs

upgradeTls ::
  TlsParams {- ^ connection params -} ->
  String {- ^ hostname -} ->
  Connection ->
  IO ()
upgradeTls tp hostname (Connection bufVar hVar) =
  modifyMVar_ bufVar \buf ->
  modifyMVar  hVar   \h ->
  case h of
    SSL{} -> pure (h, buf)
    Socket s ->
      do (cert, ssl) <- startTls tp hostname (pure s)
         pure (SSL cert ssl, B.empty)

------------------------------------------------------------------------

-- | Initiate a TLS session on the given socket destined for
-- the given hostname. When successful an active TLS connection
-- is returned with certificate verification successful when
-- requested. This function requires that the TLSParams component
-- of 'ConnectionParams' is set.
startTls ::
  TlsParams {- ^ connection params      -} ->
  String    {- ^ hostname               -} ->
  IO Socket {- ^ socket creation action -} ->
  IO (Maybe X509, SSL) {- ^ (client certificate, connected TLS) -}
startTls tp hostname mkSocket = SSL.withOpenSSL $
 do ctx <- SSL.context

    -- configure context
    SSL.contextSetCiphers          ctx (tpCipherSuite tp)
    traverse_ (contextSetTls13Ciphers ctx) (tpCipherSuiteTls13 tp)
    
    case tpVerify tp of
      VerifyNone -> pure ()
      VerifyDefault ->
       do installVerification ctx hostname
          SSL.contextSetVerificationMode ctx verifyPeer
      VerifyHostname h ->
       do installVerification ctx h
          SSL.contextSetVerificationMode ctx verifyPeer
    
    SSL.contextAddOption           ctx SSL.SSL_OP_ALL
    SSL.contextRemoveOption        ctx SSL.SSL_OP_DONT_INSERT_EMPTY_FRAGMENTS

    -- configure certificates
    setupCaCertificates ctx (tpServerCertificate tp)
    clientCert <- traverse (setupCertificate ctx) (tpClientCertificate tp)

    for_ (tpClientPrivateKey tp) \path ->
      withDefaultPassword ctx (tpClientPrivateKeyPassword tp) $
        SSL.contextSetPrivateKeyFile ctx path

    -- add socket to context
    -- creation of the socket is delayed until this point to avoid
    -- leaking the file descriptor in the cases of exceptions above.
    ssl <- SSL.connection ctx =<< mkSocket

    -- configure hostname used for SNI
    isip <- isIpAddress hostname
    unless isip (SSL.setTlsextHostName ssl hostname)

    SSL.connect ssl

    pure (clientCert, ssl)

isIpAddress :: HostName -> IO Bool
isIpAddress host =
 do res <- try (Socket.getAddrInfo
                  (Just Socket.defaultHints{Socket.addrFlags=[Socket.AI_NUMERICHOST]})
                  (Just host) Nothing)
    case res :: Either IOError [AddrInfo] of
      Right{} -> pure True
      Left {} -> pure False

setupCaCertificates :: SSLContext -> Maybe FilePath -> IO ()
setupCaCertificates ctx mbPath =
  case mbPath of
    Nothing   -> contextLoadSystemCerts ctx
    Just path -> withDefaultPassword ctx Nothing (SSL.contextSetCAFile ctx path)

setupCertificate :: SSLContext -> FilePath -> IO X509
setupCertificate ctx path =
  do x509 <- PEM.readX509 =<< readFile path -- EX
     SSL.contextSetCertificate ctx x509
     pure x509

verifyPeer :: SSL.VerificationMode
verifyPeer = SSL.VerifyPeer
  { SSL.vpFailIfNoPeerCert = True
  , SSL.vpClientOnce       = True
  , SSL.vpCallback         = Nothing
  }

-- | Get peer certificate if one exists.
getPeerCertificate :: Connection -> IO (Maybe X509.X509)
getPeerCertificate (Connection _ hVar) =
  withMVar hVar \case
    Socket{} -> pure Nothing
    SSL _ ssl -> SSL.getPeerCertificate ssl

-- | Get peer certificate if one exists.
getClientCertificate :: Connection -> IO (Maybe X509.X509)
getClientCertificate (Connection _ hVar) =
 do h <- readMVar hVar
    pure case h of
      Socket{} -> Nothing
      SSL c _  -> c

getPeerCertFingerprintSha1 :: Connection -> IO (Maybe ByteString)
getPeerCertFingerprintSha1 = getPeerCertFingerprint "sha1"

getPeerCertFingerprintSha256 :: Connection -> IO (Maybe ByteString)
getPeerCertFingerprintSha256 = getPeerCertFingerprint "sha256"

getPeerCertFingerprintSha512 :: Connection -> IO (Maybe ByteString)
getPeerCertFingerprintSha512 = getPeerCertFingerprint "sha512"

getPeerCertFingerprint :: String -> Connection -> IO (Maybe ByteString)
getPeerCertFingerprint name h =
   do mb <- getPeerCertificate h
      case mb of
        Nothing -> pure Nothing
        Just x509 ->
         do der <- X509.writeDerX509 x509
            mbdigest <- Digest.getDigestByName name
            pure $! case mbdigest of
              Nothing -> Nothing
              Just digest -> Just $! Digest.digestLBS digest der

getPeerPubkeyFingerprintSha1 :: Connection -> IO (Maybe ByteString)
getPeerPubkeyFingerprintSha1 = getPeerPubkeyFingerprint "sha1"

getPeerPubkeyFingerprintSha256 :: Connection -> IO (Maybe ByteString)
getPeerPubkeyFingerprintSha256 = getPeerPubkeyFingerprint "sha256"

getPeerPubkeyFingerprintSha512 :: Connection -> IO (Maybe ByteString)
getPeerPubkeyFingerprintSha512 = getPeerPubkeyFingerprint "sha512"

getPeerPubkeyFingerprint :: String -> Connection -> IO (Maybe ByteString)
getPeerPubkeyFingerprint name h =
 do mb <- getPeerCertificate h
    case mb of
      Nothing -> pure Nothing
      Just x509 ->
       do der <- getPubKeyDer x509
          mbdigest <- Digest.getDigestByName name
          pure $! case mbdigest of
            Nothing -> Nothing
            Just digest -> Just $! Digest.digestBS digest der