Warn when enabling socket_telemetry on unsupported platform

[stevenharman]

The structs we depend on for collecting socket telemetry (SOL_TCP and TCP_INFO) don't exist on all platforms. In such cases, these constants won't be defined, and so we should WARN users and not enabled the socket_telemetry option.

NOTE: On macOS, similar structs do exist: Socket::IPPROTO_TCP and Socket::TCP_CONNECTION_INFO, respectively, and we can unpack the binary info thusly:

require 'socket'

sock = TCPSocket.new('example.com', 80)
info = sock.getsockopt(Socket::IPPROTO_TCP, Socket::TCP_CONNECTION_INFO)

# Struct: 2x uint8 (C2), 26x uint32 (L26)
fields = info.unpack("C2L26")

tcp_connection_info = {
  tcpi_state: fields[0],
  tcpi_snd_wscale: fields[1] >> 4,
  tcpi_rcv_wscale: fields[1] & 0x0F,
  tcpi_options: fields[2],
  tcpi_flags: fields[3],
  tcpi_rto: fields[4],
  tcpi_maxseg: fields[5],
  tcpi_snd_ssthresh: fields[6],
  tcpi_snd_cwnd: fields[7],
  tcpi_snd_wnd: fields[8],
  tcpi_rcv_wnd: fields[9],
  tcpi_rttcur: fields[10],
  tcpi_srtt: fields[11],
  tcpi_rttvar: fields[12],
  tcpi_txpackets: fields[13],
  tcpi_rxpackets: fields[14],
  tcpi_txbytes: fields[15],
  tcpi_rxbytes: fields[16],
  tcpi_last_data_recv: fields[17],
  tcpi_last_ack_recv: fields[18],
  tcpi_last_data_sent: fields[19],
  tcpi_last_ack_sent: fields[20],
  tcpi_pmtu: fields[21],
  tcpi_rcv_ssthresh: fields[22],
  tcpi_snd_rexmitpack: fields[23],
  tcpi_rcv_ooopack: fields[24],
  tcpi_snd_zerowin: fields[25],
  # add more fields as needed
}

puts tcp_connection_info

However, macOS doesn't expose the number of unacked connections like various Linux kernels do. There is, as of now, to my knowledge, no way to get this info without using some other OS level tool.

[stevenharman]

This will result in a more useful error message if the line doesn't match.

[stevenharman]

Anyone opposed to this one? It's a nice experience improvement - certainly better than blowing up!

[stevenharman]

@unsign3d Thoughts on getting this one in as well? It's a nice quality of life improvement for folks running on macOS locally, while being fully compatible with how things work now.

[stevenharman]

👋 Hello.

I've rebased this little nice-to-have atop the latest. I'm not sure who to tag as it's unclear who's maintaining this repo (and the published Gem). So I'll try a few of the folks who seem to have been active lately - @unsign3d @stoyanzhekov @jtsaito @amrrbakry

We've been running it in production for over a year now. We are very interested in the future of this plugin and I would be happy to help with maintenance if you need a hand.

Thank you!

[stevenharman]

Oh, and I should note - without this change, it's impossible to successfully run the test suite on macOS. You have to skip the it 'logs socket telemetry' spec from spec/integration/plugin_spec.rb to get a green run of the suite.