Issues with string interpolation

[johnmoxley]

Liquidsoap v2.0.2 via Docker

I have a script where I'm trying to run a simple archiver, which will create files for 30 minute chunks of audio. The intended format of the output file would be DayHHMM (e.g. Mon1300 or Tue0230).

I'm using output.file with the reopen_when option to break up the files into chunks.

Here's a simplified version of my script below:

output_base_path = '/archive/test/'
output_day = { (1w)?"Mon":((2w)?"Tue":((3w)?"Wed":((4w)?"Thu":((5w)?"Fri":((6w)?"Sat":((7w)?"Sun":"Sun")))))) }
output_min = { (00m00s-29m59s)?"00":"30" }

# Having issues here
output_filename = '$(day)%H$(min)__%H%M%S.mp3'

output.file(%mp3,
        output_base_path ^ output_filename % [("day",output_day()),("min",output_min())],
        input,
        reopen_when={0m or 30m})

In the script, I've also prepended __%H%M%S to the filename for testing purposes.

However, when reopen_when executes, it doesn't re-evaluate the output_day and output_min functions, but it will re-evaluate the %H and others.

This results in filenames like:

• Sun2300__230732.mp3 (Script started at 23:07, filename correct)
• Sun2300__233000.mp3 (reopen_when activates, the $(min) part of the string has not been re-evaluated)

Is there a better way to go about this? Thanks for giving this a look, I appreciate any pointers.

[toots]

Thanks for your question. String interpolation is outdated and should be replaced by proper string getters now. I have added a ticket to fully remove it from the code base here: #2221

To answer your question here, the issues comes from the fact that this:

output.file(%mp3,
        output_base_path ^ output_filename % [("day",output_day()),("min",output_min())],
        input,
        reopen_when={0m or 30m})

Means that the line output_base_path ^ output_filename % [("day",output_day()),("min",output_min())] is executed only once, when the script is initially called. It is never executed again and, so, the suffix remains the same.

The solution is to make the whole thing a string getter, i.e. a function of type () -> string. Something like:

output_base_path = "/archive/test/"
day_mappings = [
  (0, "Sun"),
  (1, "Mon"),
  (2, "Tue"),
  (3, "Wed"),
  (4, "Thu"),
  (5, "Fri"),
  (6, "Sat")
]

def output_file() =
  # With 2.1.x: let {hour, min, sec, week_day} = time.local()
  current_time = time.local()
  hour = current_time.hour
  min = current_time.min
  sec = current_time.sec
  week_day = current_time.week_day

  output_min = min < 30 ? "00" : "30"
  output_day = list.assoc(week_day, day_mappings)

  "#{output_base_path}#{output_day}#{hour}#{output_min}_#{hour}#{min}#{sec}.mp3"
end

output.file(%mp3,
        output_file,
        input,
        reopen_when={0m or 30m})

This is based off the ongoing 2.0.3-preview branch, which will come out soon as the next stable release.

[johnmoxley]

Thank you for the detailed reply

[theotherjenkutler]

@toots Is there a version of this that works with 2.0.2? When I use current_time = time.local() it doesn't appear to return a callback. I get an error that current_time has no method for year, month, day, hour, etc.

I should also note that the 2.1.x solution throws a syntax error.

[toots]

Hi! current_time shouldn't be a callback but a record containing all the relevant information. The name of the methods has changed in 2.0.3 to make it more user friend. The doc for the 2.0.2 operator is here: https://www.liquidsoap.info/doc-2.0.2/reference.html#time.local