Check if a file is of a given type

Question

How can I fix this function? I think that I have to convert the name to String but then I would have to convert it back to str to use ends_with. Should I use another function to do that?

use walkdir::{DirEntry};

fn is_filetype(entry: &DirEntry, _type: &str) -> bool {
    entry.file_name()
        .to_str()
        .to_lowercase()
        .map(|s| s.ends_with(_type))
        .unwrap_or(false)
}

error[E0599]: no method named `to_lowercase` found for enum `Option` in the current scope
  --> src/bin/parse_torrent.rs:45:10
   |
45 |         .to_lowercase()
   |          ^^^^^^^^^^^^ method not found in `Option<&str>`

Answer 1

The easiest way to fix the code provided in the question would probably be to use map_or like @ChayimFriedman suggests in the comments.

fn is_filetype(entry: &DirEntry, _type: &str) -> bool {
    entry
        .file_name()
        .to_str()
        .map_or(false, |s| s.to_lowercase().ends_with(_type))
}

However if we expand this to also look at other approaches there are a few more options. In the past, one approach I used was to use the built in .extension() method.

if path.extension().and_then(OsStr::to_str) == Some("txt") {
    do_the_thing();
}

However, we can probably do better. After a bit of tinkering, here is what I came up with.

pub trait FileExtension {
    fn has_extension<S: AsRef<str>>(&self, extensions: &[S]) -> bool;
}

impl<P: AsRef<Path>> FileExtension for P {
    fn has_extension<S: AsRef<str>>(&self, extensions: &[S]) -> bool {
        if let Some(ref extension) = self.as_ref().extension().and_then(OsStr::to_str) {
            return extensions
                .iter()
                .any(|x| x.as_ref().eq_ignore_ascii_case(extension));
        }

        false
    }
}

This new version gives us a few extra features. We can check for multiple extension types and it gives us more flexibility in what types it uses.

// original
if is_filetype(&dir_entry, "txt") {}

// Alternate
if dir_entry.path().has_extension(&["txt"]) {}

// We can also check for multiple extensions
if dir_entry.path().has_extension(&["png", "jpg", "jpeg", "gif", "bmp"]) {}

That being said, there are some pros/cons:

• Files with extensions like .tar.gz will be read as having an extension of gz.
• Files with names starting with a period will not be misread as extensions (Ex: The folder ~/.ssh is correctly identified as having no extension).
• "magic bytes" at the start of a file are not checked for file types where they are required.