ioquatix/process-daemon

# Copyright, 2016, by Samuel G. D. Williams. <http://www.codeotaku.com>
# 
# Permission is hereby granted, free of charge, to any person obtaining a copy
# of this software and associated documentation files (the "Software"), to deal
# in the Software without restriction, including without limitation the rights
# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
# copies of the Software, and to permit persons to whom the Software is
# furnished to do so, subject to the following conditions:
# 
# The above copyright notice and this permission notice shall be included in
# all copies or substantial portions of the Software.
# 
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
# THE SOFTWARE.

module Process
    class Daemon
        # Access incoming file descriptors from daemons started by systemd.
        class Listen
            LISTEN_PID = 'LISTEN_PID'
            LISTEN_FDS = 'LISTEN_FDS'
            LISTEN_FDNAMES = 'LISTEN_FDNAMES'
            
            FD_START = 3
            SEPERATOR = ':'
            
            def self.set_close_at_exec(fd)
                fd.fcntl(Fcntl::F_SETFD, Fcntl::FD_CLOEXEC) if defined? Fcntl::F_SETFD
            end
            
            def self.open(fd)
                set_close_at_exec(fd)
                
                return IO.for_fd(fd)
            end
            
            # Returns a Array or Hash of file descriptors. If LISTEN_FDNAMES is set, a Hash is returned which includes key => value pairs for named file descriptors.
            def self.file_descriptors(env = ENV)
                pid, fds, names = env.values_at(LISTEN_PID, LISTEN_FDS, LISTEN_FDNAMES)
                
                # Are the PIDs valid for this process?
                unless pid and Integer(pid) == Process.pid
                    return nil
                end
                
                files = Integer(fds).times.collect do |i|
                    self.open(FD_START + i)
                end
                
                if names
                    names = names.split(SEPARATOR, -1)
                end
                
                self.new(files, names)
            end
            
            def initialize(files, names)
                @files = files
                @names = names
                
                @named = {}
                @unnamed = []
                
                @names.each_with_index do |name, index|
                    if name
                        @named[name] = @files[index]
                    else
                        @unnamed << @files[index]
                    end
                end
            end
            
            attr :files
            attr :names
            
            attr :named
            attr :unnamed
        end
    end
end