Simplify the decode example's argument parsing

The first argument is now the input jpeg file and the second argument the output png file.
The output file is no longer optional and must not be specified with the --output option.

Author: kaksmet

Cargo.toml

@@ -15,7 +15,6 @@ byteorder = "1.0"
 rayon = { version = "1.0", optional = true }
 
 [dev-dependencies]
-docopt = "0.7"
 png = "0.5"
 walkdir = "1.0"
 

examples/decode.rs

@@ -1,63 +1,44 @@
-extern crate docopt;
 extern crate jpeg_decoder as jpeg;
 extern crate png;
 
-use docopt::Docopt;
 use png::HasParameters;
 use std::env;
 use std::fs::File;
-use std::io::BufReader;
+use std::io::{self, BufReader, Write};
 use std::process;
 
-const USAGE: &'static str = "
-Usage: decode <input> [--output=<file>]
-       decode -h | --help
-
-Options:
-    -h --help                   Show this screen.
-    -o <file>, --output=<file>  Output PNG file.
-";
+fn usage() -> ! {
+    write!(io::stderr(), "usage: decode image.jpg image.png").unwrap();
+    process::exit(1)
+}
 
 fn main() {
-    let args = &Docopt::new(USAGE)
-        .and_then(|d| d.argv(env::args()).parse())
-        .unwrap_or_else(|e| e.exit());
-    let input = args.get_str("<input>");
-    let output = args.get_str("-o");
-    let file = match File::open(input) {
-        Ok(file) => file,
-        Err(error) => {
-            println!("The specified input could not be opened: {}", error);
-            process::exit(1);
-        },
-    };
-    let mut decoder = jpeg::Decoder::new(BufReader::new(file));
-    let mut data = match decoder.decode() {
-        Ok(data) => data,
-        Err(error) => {
-            println!("The image could not be decoded: {}", error);
-            println!("If other software can decode this image successfully then it's likely that this is a bug.");
-            process::exit(1);
-        }
-    };
+    let mut args = env::args().skip(1);
+    let input_path = args.next().unwrap_or_else(|| usage());
+    let output_path = args.next().unwrap_or_else(|| usage());
 
-    if !output.is_empty() {
-        let output_file = File::create(output).unwrap();
-        let info = decoder.info().unwrap();
-        let mut encoder = png::Encoder::new(output_file, info.width as u32, info.height as u32);
-        encoder.set(png::BitDepth::Eight);
+    let input_file = File::open(input_path).expect("The specified input file could not be opened");
+    let mut decoder = jpeg::Decoder::new(BufReader::new(input_file));
+    let mut data = decoder.decode().expect("Decoding failed. If other software can successfully decode the specified JPEG image, then it's likely that there is a bug in jpeg-decoder");
+    let info = decoder.info().unwrap();
 
-        match info.pixel_format {
-            jpeg::PixelFormat::L8     => encoder.set(png::ColorType::Grayscale),
-            jpeg::PixelFormat::RGB24  => encoder.set(png::ColorType::RGB),
-            jpeg::PixelFormat::CMYK32 => {
-                data = cmyk_to_rgb(&mut data);
-                encoder.set(png::ColorType::RGB)
-            },
-        };
+    let output_file = File::create(output_path).unwrap();
+    let mut encoder = png::Encoder::new(output_file, info.width as u32, info.height as u32);
+    encoder.set(png::BitDepth::Eight);
 
-        encoder.write_header().expect("writing png header failed").write_image_data(&data).expect("png encoding failed");
-    }
+    match info.pixel_format {
+        jpeg::PixelFormat::L8     => encoder.set(png::ColorType::Grayscale),
+        jpeg::PixelFormat::RGB24  => encoder.set(png::ColorType::RGB),
+        jpeg::PixelFormat::CMYK32 => {
+            data = cmyk_to_rgb(&mut data);
+            encoder.set(png::ColorType::RGB)
+        },
+    };
+
+    encoder.write_header()
+           .expect("writing png header failed")
+           .write_image_data(&data)
+           .expect("png encoding failed");
 }
 
 fn cmyk_to_rgb(input: &[u8]) -> Vec<u8> {