Cannot use Path option to load a file from Google Cloud Storage

[Red Daly]

Sorry for the quick bug report. Essentially the issue is that Picocli options of type Path do not seem to work with https://github.com/googleapis/java-storage-nio.

@CommandLine.Option(
        names = ["--csv"],
        required = true,
        description = [
            "Path to a CSV to parse.",
        ],
    )
    private lateinit var csv: Path

/// ...

csv.readText() // fails

Path.of(URI.create("gs://blah/blah.csv")).readText() // works

[Remko Popma]

Thank you for raising this @reddaly!

I am not sure I understand the issue from the information exception you provided.

Can you provide a failing test, or otherwise more details on how to reproduce the issue?
(What input was provided, what exactly happens when you say "doesn't work"? NullPointerException? Or IOException? Something else?)

[Red Daly]

I'll try to get a failing test and more details at some point. For now I'm working around the issue with

class FooCommand { 

@CommandLine.Option(
        names = ["--csv"],
        required = true,
        description = [
            "Path to a CSV to parse.",
        ],
        converter = [PathFlagConverter::class],
    )
    private lateinit var csv: Path

}

/**
 * A PicoCLI converter for parsing a [Path]. Unlike the default parser for the [Path] type, this
 * converter will parse "gs://"-style URLs as [Path] objects using
 * https://github.com/googleapis/java-storage-nio. This is a workaround for
 * https://github.com/remkop/picocli/issues/2269.
 */
class PathFlagConverter : CommandLine.ITypeConverter<Path> {
    override fun convert(value: String): Path =
        if (value.startsWith("gs://")) {
            CloudStorageUri(value).path
        } else {
            Path.of(value)
        }
}

Where CloudStorageUri(value).path is essentially equivalent to Path.of(URI.create(value))

[Remko Popma]

Having a custom converter sounds like a perfect solution actually! 👍

[Red Daly]

It certainly works. It is easy to forget, though. The issue is that it's surprising that a custom converter is needed. Elsewhere Path can be used with these types of URLs without special handling.

[Remko Popma]

If the Path.of(URI.create(String)) invocation works with “normal” local files then perhaps I should change the default type converter for Path to use that invocation.

[Remko Popma]

@reddaly
It looks like it is not feasible to make the Path.of(URI.create(String)) invocation the default for picocli's built-in Path type converter.
For Windows local file paths, a common path like "C:\\Users\\remko\\hello.txt" cannot be used to construct a URI. Attempting to construct a URI with that path results in a java.nio.file.FileSystemNotFoundException: Provider "C" not installed error.

Therefore, the current Path type converter used by picocli (which returns the result of Paths.get(String) to create a Path object, is correct.

Applications that need to construct a URI may be better off declaring the option as an URI instead of as a Path.
For example:

@Command
class MyCommand : Runnable {
    @Option(names = ["--csv"], required = true, description = [ "Path to a CSV to parse." ])
    private lateinit var csv: URI

    override fun run() {
        Path path = Paths.get(csv);
        // do something with the path...
    }
}

However, the above will fail for user input like --csv C:\\something, which may not be desirable.

If you need something that handles both local filesystem locations (like C:\something) as well as URI-based paths like "gs://something", then you will need to do what you did: have a custom Path type converter, or declare the option as a String, and put the logic for converting the user input to a Path object in the business logic.

I like your current solution.