SRT improvements

[toots]

This PR improves the SRT operators:

• Create ground set socket type
• Add methods on sockets to:
  • Get some relevant options
  • Get stats
  • Close socket
• Get rid of stats duppy task and inputs/outputs operator stats() method
• Export sockets() method in inputs/outputs operators to have direct, per-socket access to stats.
• Add support for the following options in inputs/outputs
  • pbkeylen and passphrase to enable support for encrypted content
  • streamid and listen_callback to enable support for authentication and more.
• Fix output in listener mode to:
  • Prevent listening socket from restarting when listening client disconnect
  • Allow more than one listener connected to the output.

Breaking changes

• The stats method on srt inputs and outputs is gone, replaced by sockets():

# o = output.srt(mode="listener", max_clients=2, %mp3, fallible=true, s);;
# o.socket();;
[("127.0.0.1", <srt_socket>.{bistats = <fun>, bstats = <fun>, close = <fun>, status = <fun>, connection_timeout = <fun>, read_timeout = <fun>, write_timeout = <fun>, enforced_encryption = <fun>, streamid = <fun>, passphrase = <fun>, pbkeylen = <fun>})]

Sockets are indexed by the caller's ip. You can for instance close it:

# let [(_, s)] = o.sockets()
# s.close()

Or gather stats:

# s.bstats();;
{pktRcvFilterLoss = 0, pktRcvFilterSupply = 0, pktRcvFilterExtra = 0, pktSndFilterExtra = 0, pktRcvFilterLossTotal = 0, pktRcvFilterSupplyTotal = 0, pktRcvFilterExtraTotal = 0, pktSndFilterExtraTotal = 0, msRcvTsbPdDelay = 120, msRcvBuf = 0, byteRcvBuf = 0, pktRcvBuf = 0, msSndTsbPdDelay = 120, msSndBuf = 1, byteSndBuf = 1360, pktSndBuf = 1, byteMSS = 1500, mbpsMaxBW = 1000., byteAvailRcvBuf = 12286500, byteAvailSndBuf = 12286500, mbpsBandwidth = 0.144, msRTT = 0.146, pktFlightSize = 0, pktCongestionWindow = 8192, pktFlowWindow = 8090, usPktSndPeriod = 10., byteRcvUndecrypt = 0, byteRcvDrop = 0, byteSndDrop = 0, byteRetrans = 0, byteRecv = 0, byteSent = 1218560, pktRcvUndecrypt = 0, pktRcvDrop = 0, pktSndDrop = 0, pktRcvBelated = 0, pktRcvAvgBelatedTime = -2.18902815023e-230, pktReorderDistance = 0, usSndDuration = 10038345, mbpsRecvRate = 0., mbpsSendRate = 0.132294856276, pktRecvNAK = 0, pktSentNAK = 0, pktRecvACK = 896, pktSentACK = 0, pktRcvRetrans = 0, pktRetrans = 0, pktRcvLoss = 0, pktSndLoss = 0, pktRecv = 0, pktSent = 896, byteRcvUndecryptTotal = 0, byteRcvDropTotal = 0, byteSndDropTotal = 0, byteRetransTotal = 0, byteRecvTotal = 0, byteSentTotal = 1218560, pktRcvUndecryptTotal = 0, pktRcvDropTotal = 0, pktSndDropTotal = 0, usSndDurationTotal = 10038345, pktRecvNAKTotal = 0, pktSentNAKTotal = 0, pktRecvACKTotal = 896, pktSentACKTotal = 0, pktRetransTotal = 0, pktRcvLossTotal = 0, pktSndLossTotal = 0, pktRecvTotal = 0, pktSentTotal = 896, msTimeStamp = 73687}

(that's a lot!)

This should allow to re-implement the old stats behavior using a recurrent task while also allowing more operations.

Full type for a srt socket:

- : srt_socket
    .{
      bistats : (?clear : bool?, ?instantaneous : bool?) ->
                {
                  byteAvailRcvBuf : int,
                  byteAvailSndBuf : int,
                  byteMSS : int,
                  byteRcvBuf : int,
                  byteRcvDrop : int,
                  byteRcvDropTotal : int,
                  byteRcvUndecrypt : int,
                  byteRcvUndecryptTotal : int,
                  byteRecv : int,
                  byteRecvTotal : int,
                  byteRetrans : int,
                  byteRetransTotal : int,
                  byteSent : int,
                  byteSentTotal : int,
                  byteSndBuf : int,
                  byteSndDrop : int,
                  byteSndDropTotal : int,
                  mbpsBandwidth : float,
                  mbpsMaxBW : float,
                  mbpsRecvRate : float,
                  mbpsSendRate : float,
                  msRTT : float,
                  msRcvBuf : int,
                  msRcvTsbPdDelay : int,
                  msSndBuf : int,
                  msSndTsbPdDelay : int,
                  msTimeStamp : int,
                  pktCongestionWindow : int,
                  pktFlightSize : int,
                  pktFlowWindow : int,
                  pktRcvAvgBelatedTime : float,
                  pktRcvBelated : int,
                  pktRcvBuf : int,
                  pktRcvDrop : int,
                  pktRcvDropTotal : int,
                  pktRcvFilterExtra : int,
                  pktRcvFilterExtraTotal : int,
                  pktRcvFilterLoss : int,
                  pktRcvFilterLossTotal : int,
                  pktRcvFilterSupply : int,
                  pktRcvFilterSupplyTotal : int,
                  pktRcvLoss : int,
                  pktRcvLossTotal : int,
                  pktRcvRetrans : int,
                  pktRcvUndecrypt : int,
                  pktRcvUndecryptTotal : int,
                  pktRecv : int,
                  pktRecvACK : int,
                  pktRecvACKTotal : int,
                  pktRecvNAK : int,
                  pktRecvNAKTotal : int,
                  pktRecvTotal : int,
                  pktReorderDistance : int,
                  pktRetrans : int,
                  pktRetransTotal : int,
                  pktSent : int,
                  pktSentACK : int,
                  pktSentACKTotal : int,
                  pktSentNAK : int,
                  pktSentNAKTotal : int,
                  pktSentTotal : int,
                  pktSndBuf : int,
                  pktSndDrop : int,
                  pktSndDropTotal : int,
                  pktSndFilterExtra : int,
                  pktSndFilterExtraTotal : int,
                  pktSndLoss : int,
                  pktSndLossTotal : int,
                  usPktSndPeriod : float,
                  usSndDuration : int,
                  usSndDurationTotal : int},
      bstats : (?clear : bool?) ->
               {
                 byteAvailRcvBuf : int,
                 byteAvailSndBuf : int,
                 byteMSS : int,
                 byteRcvBuf : int,
                 byteRcvDrop : int,
                 byteRcvDropTotal : int,
                 byteRcvUndecrypt : int,
                 byteRcvUndecryptTotal : int,
                 byteRecv : int,
                 byteRecvTotal : int,
                 byteRetrans : int,
                 byteRetransTotal : int,
                 byteSent : int,
                 byteSentTotal : int,
                 byteSndBuf : int,
                 byteSndDrop : int,
                 byteSndDropTotal : int,
                 mbpsBandwidth : float,
                 mbpsMaxBW : float,
                 mbpsRecvRate : float,
                 mbpsSendRate : float,
                 msRTT : float,
                 msRcvBuf : int,
                 msRcvTsbPdDelay : int,
                 msSndBuf : int,
                 msSndTsbPdDelay : int,
                 msTimeStamp : int,
                 pktCongestionWindow : int,
                 pktFlightSize : int,
                 pktFlowWindow : int,
                 pktRcvAvgBelatedTime : float,
                 pktRcvBelated : int,
                 pktRcvBuf : int,
                 pktRcvDrop : int,
                 pktRcvDropTotal : int,
                 pktRcvFilterExtra : int,
                 pktRcvFilterExtraTotal : int,
                 pktRcvFilterLoss : int,
                 pktRcvFilterLossTotal : int,
                 pktRcvFilterSupply : int,
                 pktRcvFilterSupplyTotal : int,
                 pktRcvLoss : int,
                 pktRcvLossTotal : int,
                 pktRcvRetrans : int,
                 pktRcvUndecrypt : int,
                 pktRcvUndecryptTotal : int,
                 pktRecv : int,
                 pktRecvACK : int,
                 pktRecvACKTotal : int,
                 pktRecvNAK : int,
                 pktRecvNAKTotal : int,
                 pktRecvTotal : int,
                 pktReorderDistance : int,
                 pktRetrans : int,
                 pktRetransTotal : int,
                 pktSent : int,
                 pktSentACK : int,
                 pktSentACKTotal : int,
                 pktSentNAK : int,
                 pktSentNAKTotal : int,
                 pktSentTotal : int,
                 pktSndBuf : int,
                 pktSndDrop : int,
                 pktSndDropTotal : int,
                 pktSndFilterExtra : int,
                 pktSndFilterExtraTotal : int,
                 pktSndLoss : int,
                 pktSndLossTotal : int,
                 usPktSndPeriod : float,
                 usSndDuration : int,
                 usSndDurationTotal : int},
      close : () -> unit,
      connection_timeout : () -> int,
      enforced_encryption : () -> bool,
      passphrase : () -> string,
      pbkeylen : () -> int,
      read_timeout : () -> int,
      status : () -> string,
      streamid : () -> string,
      write_timeout : () -> int

Fixes: #2556