Argument order resulting in: "invalid digit found in string"

[bernardoamc]

First thank you for structopt, it's such a great piece of software. :)

I'm not sure if what I've encountered is a bug or expected behaviour, but I would love to hear if there are alternatives where I can accept a single value regardless of order for my argument. This situation can be best explained with the following examples:

Problematic input order

$ cargo run -- -b 1 --p 80 127.0.0.1
error: Invalid value for '--ports <ports>...': invalid digit found in string

Working alternatives

$ cargo run -- -b 1 -p 80, 127.0.0.1
// OR
$ cargo run --  -p 80 -b 1 127.0.0.1

I'm not sure if I have the wrong mental model and it's expected that this wouldn't work with FromStr.

Minimum setup in order to replicate:

pub struct Opts {
    #[structopt(use_delimiter = true)]
    pub addresses: Vec<String>,

    #[structopt(short, long, use_delimiter = true)]
    pub ports: Option<Vec<u16>>,

    #[structopt(short, long, default_value = "4500")]
    pub batch_size: u16,
}

[CreepySkeleton]

Nit: I think you're confusing --p with -p in the first example.

Anyway, the problem here is that clap first parses the args according to the spec, and only then tries to validate them. You're expecting that -p 80 127.0.0.1 is parsed as <option> <value> <FromStr failed, stop here>, but it's parsed as <option> <value1> <value2, validation will fail>. Basically, there's no way to say "this option takes multiple values, but only as long as the validator passes". See clap-rs/clap#2122

We can't do anything about it in structopt. As a workaround, I suggest you to redesign your CLI:

• Make -p take only one value, but allow it to occur more than once:

  #[structopt(short, long, use_delimiter = true, number_of_values = 1)]
  pub ports: Vec<u16>,

  cargo run -- -b 1 -p 80 -p 22 127.0.0.1
  

• Make address an option instead of positional argument.

[bernardoamc]

I see, thank you for the insight @CreepySkeleton! Thinking in retrospect it makes a lot of sense.

Multiple -p are not an option due to the sheer amount of ports, but making address an option might be possible. Worst case scenario I might take the custom parser route and do the validation myself for this argument. Thank you so much for the help!