Initial API setup

Right now we are just listing files in a given subdirectory with not
authentication.

src/files.rs

@@ -0,0 +1,33 @@
+use std::ffi::OsStr;
+use std::fs::read_dir;
+use std::io;
+use std::path::{Path, PathBuf};
+
+pub fn list_files(dir: PathBuf) -> io::Result<Vec<PathBuf>> {
+    let files = read_dir(dir)?
+        .map(|res| res.unwrap())
+        .filter(|entry| is_image_or_video(&entry.path()) || entry.file_type().unwrap().is_dir())
+        .map(|entry| entry.path())
+        .map(|path: PathBuf| {
+            let relative = path.strip_prefix(std::env::current_dir().unwrap()).unwrap();
+            relative.to_path_buf()
+        })
+        .collect::<Vec<PathBuf>>();
+
+    Ok(files)
+}
+
+fn is_image_or_video(path: &Path) -> bool {
+    let extension = &path
+        .extension()
+        .unwrap_or_else(|| OsStr::new(""))
+        .to_str()
+        .unwrap_or_else(|| "")
+        .to_lowercase();
+
+    return extension == &"png"
+        || extension == &"jpg"
+        || extension == &"jpeg"
+        || extension == &"rs"
+        || extension == &"mp4";
+}