Allow reading image from stdin

src/main.rs

@@ -7,13 +7,14 @@ use image::{
 use nix::ioctl_write_ptr;
 use std::{
     fs::File,
+    io::{Cursor, Read, stdin},
     os::fd::AsRawFd,
     path::{Path, PathBuf},
 };
 
 #[derive(Parser)]
 struct Opt {
-    /// Path to the image-blob.
+    /// Path to the image-blob. "-" means stdin.
     pub path: PathBuf,
 
     /// Stamp an image onto the final image. "<x>:<y>:<path>"
@@ -65,9 +66,15 @@ fn to_grayscale(path: &Path, image: DynamicImage) -> GrayAlphaImage {
 }
 
 fn load_wallpaper(path: &Path) -> eyre::Result<GrayAlphaImage> {
-    eprintln!("Opening image at {path:?}");
-
-    let mut image = ImageReader::open(path)?.decode()?;
+    let mut image = if path == Path::new("-") {
+        eprintln!("Reading image from stdin");
+        let mut buf = vec![];
+        stdin().read_to_end(&mut buf)?;
+        ImageReader::new(Cursor::new(buf)).decode()?
+    } else {
+        eprintln!("Opening image at {path:?}");
+        ImageReader::open(path)?.decode()?
+    };
 
     let image_dimensions = (image.width() as usize, image.height() as usize);