src/lib.rs


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use std::fs::read;
use std::path::Path;

/// Name of tag file.
pub const CACHEDIR_TAG: &str = "CACHEDIR.TAG";

/// Prefix of contents of tag file.
pub const TAG: &str = "Signature: 8a477f597d28d172789f06886806bc55";

/// Is a given file a cache directory tag?
pub fn is_cachedir_tag(filename: &Path) -> Result<bool, std::io::Error> {
    // Is the filename OK?
    if let Some(basename) = filename.file_name() {
        if basename != CACHEDIR_TAG {
            return Ok(false);
        }
    }

    // Does the file exist? It's OK if it doesn't, but we don't want
    // to try to read it if it doesn't.
    if !filename.exists() {
        return Ok(false);
    }

    // Does the file start with the right prefix?
    let data = read(filename)?;
    if data.len() >= TAG.len() {
        Ok(&data[..TAG.len()] == TAG.as_bytes())
    } else {
        Ok(false)
    }
}