Add utility for working with file names, port JSON model to use it

src/snapshot_middleware/util.rs

@@ -0,0 +1,20 @@
+use std::path::Path;
+
+/// If the given string ends up with the given suffix, returns the portion of
+/// the string before the suffix.
+pub fn match_trailing<'a>(input: &'a str, suffix: &str) -> Option<&'a str> {
+    if input.ends_with(suffix) {
+        let end = input.len().saturating_sub(suffix.len());
+        Some(&input[..end])
+    } else {
+        None
+    }
+}
+
+/// If the given path has a file name, and that file name ends with the given
+/// suffix, returns the portion of the file name before the given suffix.
+pub fn match_file_name<'a>(path: &'a Path, suffix: &str) -> Option<&'a str> {
+    let file_name = path.file_name()?.to_str()?;
+
+    match_trailing(&file_name, suffix)
+}