Region name validation?

[josb]

Hi,
How would I validate the name of a passed-in region as part of client setup, i.e. before I have a working client (so calling ec2's describe-regions is not possible)?
Thanks,
Jos

[Velfi]

In the Rust SDK, regions are just a special newtype for a Cow<'static, str>. We don't validate them in the client. Instead, we rely on the server to validate them.

You can see a list of valid regions here. You could hardcode that list into your app and check that user input matches one of them.

Alternatively, you could check that user input conforms to the general shape of a Region:

const PREFIX: &[&str] = &[
    "us",
    "af",
    // etc..
];

const MIDDLE: &[&str] = &[
    "east",
    "west",
    // etc...
];

fn validate_region(maybe_region: &str) -> bool {
    let mut parts = maybe_region.split("-");
    let prefix_is_valid = match parts.next().as_ref() {
        Some(prefix) => PREFIX.contains(prefix),
        None => false,
    };
    let middle_is_valid = match parts.next().as_ref() {
        Some(middle) => MIDDLE.contains(middle),
        None => false,
    };
    let number_is_valid = match parts.next().as_ref() {
        // Region numbers currently range from 1 to 3
        Some(number) => number.parse::<u8>().map(|n| n > 0 && n < 4).unwrap_or_default(),
        None => false,
    };
    let only_has_3_parts = parts.next().is_none();
    
    prefix_is_valid && middle_is_valid && number_is_valid && only_has_3_parts
}

fn main() {
    for region in [
        "us-east-1",
        "us-east-1-and-then-some",
        "xx-nowhere-99",
        "definitely not a region",
        "",
    ].into_iter() {
        let valid = if validate_region(region) { "a valid region" } else { "not a valid region" };
        println!("region \"{}\" is {}", region, valid);
    }
}

[Velfi]

I'm going to shop around the idea internally and see how folks feel about it. I'll let you know when I have an update.

[Velfi]

No answer yet, although I found a 3rd-party maintained list in GitHub

[josb]

Thanks for that, @Velfi. However, what I like about your suggested solution is that it doesn't require any external dependencies.

[Velfi]

After speaking with the team, we've decided that this isn't something that we're going to provide in the short term. At this point, your best option, if you want an AWS-owned list that you can access programmatically, is to call this EC2 operation to get a list of Regions and then validate against that:

let shared_config = aws_config::load_from_env().await;
let ec2_client = aws_sdk_ec2::Client::new(&shared_config);
let res = ec2_client.describe_regions()
    .all_regions(true)
    .send()
    .await

let regions: Vec<String> = res.regions.unwrap_or_default()
    .into_iter()
    .flat_map(|region| region.region_name)
    .collect();

// You can then call regions.iter().any(|r| r == "the region you want to validate")

[josb]

Fair enough, @Velfi. Thanks for looking into this!

[github-actions[bot]]

Hello! Reopening this discussion to make it searchable.