Interaction with a running process - keyboard-events

Question

Let's have a simple example:
Process.run("ping", {"google.com"}) do |proc|
proc.output.each_line { |line| puts line }
end
which runs a process, constantly reading its output and printing the output to stdout. Currently, when I press a key, it just appears along with the output of the running process, but I'd like to have some kind of key processing, so I would be able to manage the running process from the keyboard: stop it, or restart it with modified arguments. How to do that?
Or, to narrow the question down, how to make this output-input pair to be non-blocking for each other? Currently it takes one step and then waits for its counterpart to happen.
Process.run("ping", {"google.com"}) do |proc|
until proc.output.closed?
puts proc.output.gets
puts "Got key: #{STDIN.raw &.read_char}"
end
end

Answer 1

Using a terminal for interactive input is not as simple as it might seem. You can try with STDIN.raw &.read_char. But this is limited and likely won't get you very far.
A tool which is usually used for this is readline. There are Crystal bindings in the stdlib (see Readline). They're currently undocumented, but should work. You could also try https://github.com/Papierkorb/fancyline which is a pure Crystal implementation of readline.

Answer 2

This examples shows how to handle STDIN and a single TCP session. This works by spawning the handlers to fibers. With some lines more you can share a bash or REPL session with multiple clients.
example 1: long running process
#Long running Process, here an interactive shell for example
spawn do
begin
cmd = "bash -i"
Process.run(cmd, shell: true) do | p |
pp p
my.bashpid = p.pid
my.bashinputfd = p.input.dup #get copy of current fd
p.input.puts("exec 2>&1") #stderr > stdout
p.input.puts("echo connected to bash") #send to STDIN of bash
while line = p.output.read_line
puts line #send to STDOUT
#send output of shell process to all online clients
Mc.get_clients.each do |all|
all.puts (line) #send to Client
end
end
end
rescue exception
puts "Error: #{exception.message}"
puts "Shell process has ended, program exits"
exit
end
end
example 2:
require "socket"
#public vars
channel = Channel(String).new
csocket = Socket.tcp(Socket::Family::INET)
socket_conn=false
puts "Welcome:"
spawn do
server = TCPServer.new("0.0.0.0", 9090)
loop do #handle tcp client reconnects - do forever
socket = server.accept
csocket = socket.dup
socket_conn=true
p! socket_conn
print "\r"
while line = socket.gets
channel.send(line)
end
socket_conn=false
p! socket_conn
print "\r"
end
end
spawn do #handle stdin input char by char - do until ctrl-c pressed
while (char = STDIN.raw &.read_char) != '\u{3}' #ctrl-c
channel.send(char.to_s)
end
channel.send('\u{3}'.to_s)
end
loop do #do until cttrl-c
r = channel.receive
if r == "\u0003" #handle ctrl-c from channel
break
end
p! socket_conn
print "\r"
p! r
print "\r"
if socket_conn
csocket.puts "got: #{r}"
end
puts "got: #{r}"
print "\r"
end