k_pg_proxy

#!/usr/bin/env ruby

require "base64"
require "digest"
require "json"
require "openssl"
require "securerandom"
require "socket"

PROXY_PORT = 10_000
THREADS = 10
CONTEXT = ARGV.first || `kubectl config current-context`.strip

def parse_startup_message(client_socket)
  length = client_socket.read(4).unpack("L>").first - 4
  version = client_socket.read(4).unpack("L>").first

  if version == 80877103
    puts "Handling SSLRequest"
    client_socket.write("N") # we're not accepting SSL

    length = client_socket.read(4).unpack("L>").first
    _version = client_socket.read(4).unpack("L>").first
  end

  puts "Handling StartupMessage"
  # "user\x00username\x00database\x00dbname\x00\x00" -> { "user" => "username", "database" => "dbname", ... }
  client_socket.read(length - 8).split("\x00").each_slice(2).to_a.to_h
end

def send_startup_message(pg_socket, user:, database:)
  puts "Sending StartupMessage to #{database}"

  message = [0, 196608]
  message_size = 4 + 4
  pack_string = "L>L>"
  ["user", user, "database", database].each do |param|
    message << param
    message_size += param.size + 1
    pack_string << "Z*"
  end
  message << 0
  message_size += 1
  pack_string << "C"
  message[0] = message_size
  startup_message = message.pack(pack_string)

  pg_socket.write(startup_message)
end

def handle_authentication(pg_socket, password:)
  puts "Handling AuthenticationSASL"

  char_tag = pg_socket.read(1)

  if char_tag == "E"
    length = pg_socket.read(4).unpack1("L>") - 4
    payload = pg_socket.read(length)
    puts "Postgres Error:"
    puts payload.split("\x00")
    return
  end

  raise "expected authentication response but got #{char_tag}" unless char_tag == "R"

  length = pg_socket.read(4).unpack1("L>") - 4
  type = pg_socket.read(4).unpack1("L>")
  payload = pg_socket.read(length - 4)

  scram_sha_256 = "SCRAM-SHA-256"
  unless type == 10 && payload.include?(scram_sha_256)
    raise "don't know how to handle authentication request type #{type} with payload #{payload}"
  end

  puts "Sending SASLInitialResponse"

  nonce = SecureRandom.urlsafe_base64(18)
  first_message = "n,,n=,r=#{nonce}"

  length = 4 + scram_sha_256.bytesize + 1 + 4 + first_message.bytesize

  sasl_initial_response = ["p", length, scram_sha_256, first_message.bytesize, first_message]
  message = sasl_initial_response.pack("ZL>Z*L>a*")
  pg_socket.write(message)

  puts "Handling AuthenticationSASLContinue"

  char_tag = pg_socket.read(1)

  if char_tag == "E"
    length = pg_socket.read(4).unpack1("L>") - 4
    payload = pg_socket.read(length)
    puts "Postgres Error:"
    puts payload.split("\x00")
    raise
  end

  raise "expected authentication response but got #{char_tag}" unless char_tag == "R"

  length = pg_socket.read(4).unpack1("L>") - 4
  type = pg_socket.read(4).unpack1("L>")

  raise "expected authentication response but got #{type}" unless type == 11

  payload = pg_socket.read(length - 4)

  puts "Sending SASLResponse"

  # "r=foo,s=bar==,i=4096" -> { "r" => "foo", "s" => "bar==", "i" => "4096" }
  params = payload.split(",").map { |pair| pair.split("=", 2) }.to_h
  r = params.fetch("r")
  s = params.fetch("s")
  i = params.fetch("i").to_i

  raise "expected authentication response to start with #{nonce} but it was #{r}" unless r.start_with?(nonce)

  # biws == base64 of "n,,"
  final_msg_without_proof = "c=biws,r=#{r}"

  digest = OpenSSL::Digest.new("SHA256")

  salted_pass = OpenSSL::PKCS5.pbkdf2_hmac(password, Base64.strict_decode64(s), i, digest.digest_length, digest)
  client_key = OpenSSL::HMAC.digest("sha256", salted_pass, "Client Key")
  auth_msg = "n=,r=#{nonce},#{payload},#{final_msg_without_proof}"
  client_sig = OpenSSL::HMAC.digest("sha256", OpenSSL::Digest.new("SHA256").update(client_key).digest, auth_msg)

  # These could be used for verifying the final server message but YAGNI
  # server_key = OpenSSL::HMAC.digest("sha256", salted_pass, "Server Key")
  # server_sig = OpenSSL::HMAC.digest("sha256", server_key, auth_msg)

  client_key_ints = client_key.unpack("C*")
  client_sig_ints = client_sig.unpack("C*")
  whatever = client_key_ints.map.with_index { |client_key_int, index| client_key_int ^ client_sig_ints[index] }
  proof = Base64.strict_encode64(whatever.pack("C*"))
  sasl_response_string = "#{final_msg_without_proof},p=#{proof}"

  sasl_response = ["p", sasl_response_string.bytesize + 4, sasl_response_string]
  message = sasl_response.pack("ZL>a*")

  pg_socket.write(message)

  puts "Handling AuthenticationSASLFinal"

  char_tag = pg_socket.read(1)

  if char_tag == "E"
    length = pg_socket.read(4).unpack1("L>") - 4
    payload = pg_socket.read(length)
    puts "Postgres Error!"
    puts payload.split("\x00")
    raise
  end

  length = pg_socket.read(4).unpack1("L>") - 4
  type = pg_socket.read(4).unpack1("L>")

  raise "expected AuthenticationSASLFinal response but got #{char_tag} / #{type}" unless type == 12

  pg_socket.read(length - 4) # we could verify the final response but YAGNI

  puts "Handling AuthenticationOk"

  char_tag = pg_socket.read(1)
  length = pg_socket.read(4).unpack1("L>") - 4
  type = pg_socket.read(length).unpack1("L>")

  raise "expected AuthenticationOk response but got #{char_tag} / #{type}" unless type == 0

  true
end

def forward(from_socket, to_socket)
  loop do
    data = from_socket.recv(1024)
    return if data.nil?
    return if data == "X\x00\x00\x00\x04" # Terminate message

    to_socket.send(data, 0)
  rescue Errno::ECONNRESET, IOError => e
    # `recv': stream closed in another thread (IOError)
    # `recv': closed stream (IOError)
    puts e.message unless e.message[/closed in another thread/]
    return
  end
end

def handle_connection(client_socket, connection_number)
  params = parse_startup_message(client_socket)
  database = params.fetch("database")

  # Start port forward and connect to Kubernetes Postgres
  primary_pod = `kubectl --context #{CONTEXT} get pod -o name -l postgres-operator.crunchydata.com/cluster=#{database},postgres-operator.crunchydata.com/role=master`.chomp # rubocop:disable Layout/LineLength
  port_forward_port = PROXY_PORT + connection_number
  port_forward_pid = spawn(
    "kubectl --context #{CONTEXT} port-forward #{primary_pod} #{port_forward_port}:5432",
    err: File::NULL,
  )
  Process.detach(port_forward_pid)
  sleep 1 # TODO: proper test to see if kubectl port-forward is ready
  pg_socket = TCPSocket.new("localhost", port_forward_port)

  # Pretend AuthenticationOk to avoid client giving up prematurely
  authentication_ok = ["R", 8, 0].pack("aL>L>")
  client_socket.write(authentication_ok)

  cluster = `kubectl --context #{CONTEXT} get postgrescluster #{database} -o json`
  abort "Error: postgrescluster '#{database}' not found" if cluster.empty?

  cluster = JSON.parse(cluster)
  user ||= cluster.dig("spec", "users", 0, "name")
  unless user
    puts "No users found in PostgresCluster spec, using default user '#{database}'"
    user = database
  end

  secret = JSON.parse(`kubectl --context #{CONTEXT} get secret #{database}-pguser-#{user} -o json`).fetch("data")

  send_startup_message(
    pg_socket,
    user: Base64.strict_decode64(secret.fetch("user")),
    database: Base64.strict_decode64(secret.fetch("dbname")),
  )
  success = handle_authentication(pg_socket, password: Base64.strict_decode64(secret.fetch("password")))

  unless success
    client_socket.close
    pg_socket.close
    Process.kill("QUIT", port_forward_pid)
    puts "Error: Failed to connect to #{database}"
    return
  end

  client_forward = Thread.new { forward(client_socket, pg_socket) }
  pg_forward = Thread.new { forward(pg_socket, client_socket) }

  loop do
    if client_forward.alive? && pg_forward.alive?
      sleep 1
    else
      puts "Disconnecting from #{database}"
      return
    end
  end
rescue Errno::ECONNRESET
  puts "handle_connection: Errno::ECONNRESET handling database #{database}"
ensure
  Process.kill("QUIT", port_forward_pid) rescue nil # rubocop:disable Style/RescueModifier
  client_socket&.close
  pg_socket&.close
end

puts "Listening for Postgres connections on localhost:#{PROXY_PORT}"
puts "Just pass the name of the kubernetes database and leave the rest to me!"
puts ""
puts "EXAMPLE:"
puts "psql -h localhost -p #{PROXY_PORT} -d mynewsdesk-staging"
server = TCPServer.new(PROXY_PORT)
connection_number = 0

loop do
  puts ""
  client_socket = server.accept
  connection_number += 1

  Thread.new { handle_connection(client_socket, connection_number) }
rescue Interrupt
  puts ""
  puts "CTRL+C received, exiting..."
  exit
end