# -*- encoding: binary -*-
# Copyright (C) 2013-2016 all contributors <yahns-public@yhbt.net>
# License: GPL-3.0+ (https://www.gnu.org/licenses/gpl-3.0.txt)
# frozen_string_literal: true
require 'socket'
require 'rack/request'
require 'timeout'

require_relative 'proxy_http_response'
require_relative 'req_res'

class Yahns::ProxyPass # :nodoc:
  attr_reader :proxy_buffering, :response_headers

  def initialize(dest, opts = {})
    case dest
    when %r{\Aunix:([^:]+)(?::(/.*))?\z}
      path = $2
      @sockaddr = Socket.sockaddr_un($1)
    when %r{\Ahttp://([^/]+)(/.*)?\z}
      path = $2
      host, port = $1.split(':')
      @sockaddr = Socket.sockaddr_in(port || 80, host)
    else
      raise ArgumentError, "destination must be an HTTP URL or unix: path"
    end
    @response_headers = opts[:response_headers] || {}
    @proxy_buffering = opts[:proxy_buffering]
    @proxy_buffering = true if @proxy_buffering.nil? # allow false

    # It's wrong to send the backend Server tag through.  Let users say
    # { "Server => "yahns" } if they want to advertise for us, but don't
    # advertise by default (for security)
    @response_headers['Server'] ||= :ignore
    init_path_vars(path)
  end

  def init_path_vars(path)
    path ||= '$fullpath'
    # methods from Rack::Request we want:
    allow = %w(fullpath host_with_port host port url path)
    want = path.scan(/\$(\w+)/).flatten! || []
    diff = want - allow
    diff.empty? or
             raise ArgumentError, "vars not allowed: #{diff.uniq.join(' ')}"

    # kill leading slash just in case...
    @path = path.gsub(%r{\A/(\$(?:fullpath|path))}, '\1')
  end

  def call(env)
    # 3-way handshake for TCP backends while we generate the request header
    rr = Yahns::ReqRes.start(@sockaddr)
    c = env['rack.hijack'].call

    req = Rack::Request.new(env)
    req = @path.gsub(/\$(\w+)/) { req.__send__($1) }

    # start the connection asynchronously and early so TCP can do a
    case ver = env['HTTP_VERSION']
    when 'HTTP/1.1' # leave alone, response may be chunked
    else # no chunking for HTTP/1.0 and HTTP/0.9
      ver = 'HTTP/1.0'.freeze
    end

    addr = env['REMOTE_ADDR']
    xff = env['HTTP_X_FORWARDED_FOR']
    xff = xff =~ /\S/ ? "#{xff}, #{addr}" : addr
    req = "#{env['REQUEST_METHOD']} #{req} #{ver}\r\n" \
          "X-Forwarded-Proto: #{env['rack.url_scheme']}\r\n" \
          "X-Forwarded-For: #{xff}\r\n".dup

    # pass most HTTP_* headers through as-is
    chunked = false
    env.each do |key, val|
      %r{\AHTTP_(\w+)\z} =~ key or next
      key = $1
      # trailers are folded into the header, so do not send the Trailer:
      # header in the request
      next if /\A(?:VERSION|CONNECTION|KEEP_ALIVE|X_FORWARDED_FOR|TRAILER)/ =~
         key
      'TRANSFER_ENCODING'.freeze == key && val =~ /\bchunked\b/i and
        chunked = true
      key.tr!('_'.freeze, '-'.freeze)
      req << "#{key}: #{val}\r\n"
    end

    # special cases which Rack does not prefix:
    ctype = env["CONTENT_TYPE"] and req << "Content-Type: #{ctype}\r\n"
    clen = env["CONTENT_LENGTH"] and req << "Content-Length: #{clen}\r\n"
    input = chunked || (clen && clen.to_i > 0) ? env['rack.input'] : nil

    # finally, prepare to emit the headers
    rr.req_start(c, req << "\r\n".freeze, input, chunked, self)

    # this probably breaks fewer middlewares than returning whatever else...
    [ 500, [], [] ]
  rescue => e
    Yahns::Log.exception(env['rack.logger'], 'proxy_pass', e)
    [ 502, { 'Content-Length' => '0', 'Content-Type' => 'text/plain' }, [] ]
  end
end