Print console output to stderr instead of stdout

Makes it friendlier with --stdout option
See #20 for discussion

CHANGELOG.md

@@ -1,6 +1,7 @@
 **Version 0.1.2** (unreleased)
  - Fix program version that is displayed when running `oxipng -V`
  - Ensure `--quiet` mode is actually quiet (@SethDusek [#20](https://github.com/shssoichiro/oxipng/pull/20))
+ - Write status/debug information to stderr instead of stdout
  - Use heuristics to determine best combination for `-o1` ([#21](https://github.com/shssoichiro/oxipng/issues/21))
 
 **Version 0.1.1**

src/lib.rs

@@ -7,7 +7,7 @@ extern crate libz_sys;
 
 use std::collections::{HashMap, HashSet};
 use std::fs::{File, copy};
-use std::io::{BufWriter, Write, stdout};
+use std::io::{BufWriter, Write, stderr, stdout};
 use std::path::{Path, PathBuf};
 
 pub mod deflate {
@@ -47,8 +47,8 @@ pub struct Options {
 pub fn optimize(filepath: &Path, opts: &Options) -> Result<(), String> {
     // Decode PNG from file
     if opts.verbosity.is_some() {
-        println!("Processing: {}", filepath.to_str().unwrap())
+        writeln!(&mut stderr(), "Processing: {}", filepath.to_str().unwrap()).ok();
-    };
+    }
     let in_file = Path::new(filepath);
     let mut png = match png::PngData::new(&in_file) {
         Ok(x) => x,
@@ -59,21 +59,33 @@ pub fn optimize(filepath: &Path, opts: &Options) -> Result<(), String> {
     let idat_original_size = png.idat_data.len();
     let file_original_size = filepath.metadata().unwrap().len() as usize;
     if opts.verbosity.is_some() {
-        println!("    {}x{} pixels, PNG format",
+        writeln!(&mut stderr(),
+                 "    {}x{} pixels, PNG format",
                  png.ihdr_data.width,
-                 png.ihdr_data.height);
+                 png.ihdr_data.height)
+            .ok();
         if let Some(palette) = png.palette.clone() {
-            println!("    {} bits/pixel, {} colors in palette",
+            writeln!(&mut stderr(),
+                     "    {} bits/pixel, {} colors in palette",
                      png.ihdr_data.bit_depth,
-                     palette.len() / 3);
+                     palette.len() / 3)
+                .ok();
         } else {
-            println!("    {}x{} bits/pixel, {:?}",
+            writeln!(&mut stderr(),
+                     "    {}x{} bits/pixel, {:?}",
                      png.channels_per_pixel(),
                      png.ihdr_data.bit_depth,
-                     png.ihdr_data.color_type);
+                     png.ihdr_data.color_type)
+                .ok();
         }
-        println!("    IDAT size = {} bytes", idat_original_size);
+        writeln!(&mut stderr(),
-        println!("    File size = {} bytes", file_original_size);
+                 "    IDAT size = {} bytes",
+                 idat_original_size)
+            .ok();
+        writeln!(&mut stderr(),
+                 "    File size = {} bytes",
+                 file_original_size)
+            .ok();
     }
 
     let mut filter = opts.filter.clone();
@@ -149,8 +161,8 @@ pub fn optimize(filepath: &Path, opts: &Options) -> Result<(), String> {
         let combinations = filter.len() * compression.len() * memory.len() * strategies.len();
         let mut results = Vec::with_capacity(combinations);
         if opts.verbosity.is_some() {
-            println!("Trying: {} combinations", combinations)
+            writeln!(&mut stderr(), "Trying: {} combinations", combinations).ok();
-        };
+        }
         crossbeam::scope(|scope| {
             for f in &filter {
                 let filtered = png.filter_image(*f);
@@ -169,12 +181,12 @@ pub fn optimize(filepath: &Path, opts: &Options) -> Result<(), String> {
                                 };
 
                                 if opts.verbosity == Some(1) {
-                                    println!("    zc = {}  zm = {}  zs = {}  f = {}        {} bytes",
+                                    writeln!(&mut stderr(), "    zc = {}  zm = {}  zs = {}  f = {}        {} bytes",
                                              *zc,
                                              *zm,
                                              *zs,
                                              *f,
-                                             new_idat.len());
+                                             new_idat.len()).ok();
                                 }
 
                                 Ok((*f, *zc, *zm, *zs, new_idat.clone()))
@@ -202,13 +214,15 @@ pub fn optimize(filepath: &Path, opts: &Options) -> Result<(), String> {
         if let Some(better) = best {
             png.idat_data = better.4.clone();
             if opts.verbosity.is_some() {
-                println!("Found better combination:");
+                writeln!(&mut stderr(), "Found better combination:").ok();
-                println!("    zc = {}  zm = {}  zs = {}  f = {}        {} bytes",
+                writeln!(&mut stderr(),
+                         "    zc = {}  zm = {}  zs = {}  f = {}        {} bytes",
                          better.1,
                          better.2,
                          better.3,
                          better.0,
-                         png.idat_data.len());
+                         png.idat_data.len())
+                    .ok();
             }
         }
     }
@@ -220,12 +234,12 @@ pub fn optimize(filepath: &Path, opts: &Options) -> Result<(), String> {
 
     let output_data = png.output();
     if file_original_size <= output_data.len() && !opts.force && opts.interlace.is_none() {
-        println!("File already optimized");
+        writeln!(&mut stderr(), "File already optimized").ok();
         return Ok(());
     }
 
     if opts.pretend {
-        println!("Running in pretend mode, no output");
+        writeln!(&mut stderr(), "Running in pretend mode, no output").ok();
     } else {
         if opts.backup {
             match copy(in_file,
@@ -256,38 +270,48 @@ pub fn optimize(filepath: &Path, opts: &Options) -> Result<(), String> {
                 }
             };
             let mut buffer = BufWriter::new(out_file);
-            if opts.verbosity.is_some() {
+            match buffer.write_all(&output_data) {
-                match buffer.write_all(&output_data) {
+                Ok(_) => {
-                    Ok(_) => println!("Output: {}", opts.out_file.display()),
+                    if opts.verbosity.is_some() {
-                    Err(_) => {
+                        writeln!(&mut stderr(), "Output: {}", opts.out_file.display()).ok();
-                        return Err(format!("Unable to write to file {}", opts.out_file.display()))
                     }
                 }
+                Err(_) => {
+                    return Err(format!("Unable to write to file {}", opts.out_file.display()))
+                }
             }
         }
     }
     if opts.verbosity.is_some() {
         if idat_original_size >= png.idat_data.len() {
-            println!("    IDAT size = {} bytes ({} bytes decrease)",
+            writeln!(&mut stderr(),
+                     "    IDAT size = {} bytes ({} bytes decrease)",
                      png.idat_data.len(),
-                     idat_original_size - png.idat_data.len());
+                     idat_original_size - png.idat_data.len())
+                .ok();
         } else {
-            println!("    IDAT size = {} bytes ({} bytes increase)",
+            writeln!(&mut stderr(),
+                     "    IDAT size = {} bytes ({} bytes increase)",
                      png.idat_data.len(),
-                     png.idat_data.len() - idat_original_size);
+                     png.idat_data.len() - idat_original_size)
+                .ok();
         }
         if file_original_size >= output_data.len() {
-            println!("    file size = {} bytes ({} bytes = {:.2}% decrease)",
+            writeln!(&mut stderr(),
+                     "    file size = {} bytes ({} bytes = {:.2}% decrease)",
                      output_data.len(),
                      file_original_size - output_data.len(),
                      (file_original_size - output_data.len()) as f64 / file_original_size as f64 *
-                     100f64);
+                     100f64)
+                .ok();
         } else {
-            println!("    file size = {} bytes ({} bytes = {:.2}% increase)",
+            writeln!(&mut stderr(),
+                     "    file size = {} bytes ({} bytes = {:.2}% increase)",
                      output_data.len(),
                      output_data.len() - file_original_size,
                      (output_data.len() - file_original_size) as f64 / file_original_size as f64 *
-                     100f64);
+                     100f64)
+                .ok();
         }
     }
     Ok(())
@@ -295,13 +319,17 @@ pub fn optimize(filepath: &Path, opts: &Options) -> Result<(), String> {
 
 fn report_reduction(png: &png::PngData) {
     if let Some(palette) = png.palette.clone() {
-        println!("Reducing image to {} bits/pixel, {} colors in palette",
+        writeln!(&mut stderr(),
+                 "Reducing image to {} bits/pixel, {} colors in palette",
                  png.ihdr_data.bit_depth,
-                 palette.len() / 3);
+                 palette.len() / 3)
+            .ok();
     } else {
-        println!("Reducing image to {}x{} bits/pixel, {}",
+        writeln!(&mut stderr(),
+                 "Reducing image to {}x{} bits/pixel, {}",
                  png.channels_per_pixel(),
                  png.ihdr_data.bit_depth,
-                 png.ihdr_data.color_type);
+                 png.ihdr_data.color_type)
+            .ok();
     }
 }

src/main.rs

@@ -5,6 +5,7 @@ extern crate regex;
 use clap::{App, Arg, ArgMatches};
 use regex::Regex;
 use std::collections::HashSet;
+use std::io::{Write, stderr};
 use std::path::PathBuf;
 
 const VERSION_STRING: &'static str = "0.1.1";
@@ -223,7 +224,7 @@ fn main() {
     match parse_opts_into_struct(&matches, &mut opts) {
         Ok(_) => (),
         Err(x) => {
-            println!("{}", x);
+            writeln!(&mut stderr(), "{}", x).ok();
             return ();
         }
     }
@@ -244,7 +245,10 @@ fn handle_optimization(inputs: Vec<PathBuf>, opts: oxipng::Options) {
                 handle_optimization(input.read_dir().unwrap().map(|x| x.unwrap().path()).collect(),
                                     current_opts)
             } else {
-                println!("{} is a directory, skipping", input.display());
+                writeln!(&mut stderr(),
+                         "{} is a directory, skipping",
+                         input.display())
+                    .ok();
             }
             continue;
         }
@@ -255,7 +259,9 @@ fn handle_optimization(inputs: Vec<PathBuf>, opts: oxipng::Options) {
         }
         match oxipng::optimize(&input, &current_opts) {
             Ok(_) => (),
-            Err(x) => println!("{}", x),
+            Err(x) => {
+                writeln!(&mut stderr(), "{}", x).ok();
+            }
         };
     }
 }

tests/filters.rs

@@ -33,7 +33,7 @@ fn get_opts(input: &Path) -> oxipng::Options {
         clobber: true,
         create: true,
         preserve_attrs: false,
-        verbosity: Some(0),
+        verbosity: None,
         filter: filter,
         interlace: None,
         compression: compression,

tests/flags.rs

@@ -33,7 +33,7 @@ fn get_opts(input: &Path) -> oxipng::Options {
         clobber: true,
         create: true,
         preserve_attrs: false,
-        verbosity: Some(0),
+        verbosity: None,
         filter: filter,
         interlace: None,
         compression: compression,
@@ -49,6 +49,61 @@ fn get_opts(input: &Path) -> oxipng::Options {
     }
 }
 
+fn test_it_converts(input: &Path,
+                    output: &Path,
+                    opts: &oxipng::Options,
+                    color_type_in: png::ColorType,
+                    bit_depth_in: png::BitDepth,
+                    color_type_out: png::ColorType,
+                    bit_depth_out: png::BitDepth) {
+    let png = png::PngData::new(input).unwrap();
+
+    assert!(png.ihdr_data.color_type == color_type_in);
+    assert!(png.ihdr_data.bit_depth == bit_depth_in);
+
+    match oxipng::optimize(input, opts) {
+        Ok(_) => (),
+        Err(x) => panic!(x.to_owned()),
+    };
+    assert!(output.exists());
+
+    let png = match png::PngData::new(output) {
+        Ok(x) => x,
+        Err(x) => {
+            remove_file(output).ok();
+            panic!(x.to_owned())
+        }
+    };
+
+    assert!(png.ihdr_data.color_type == color_type_out);
+    assert!(png.ihdr_data.bit_depth == bit_depth_out);
+
+    let old_png = image::open(input).unwrap();
+    let new_png = image::open(output).unwrap();
+
+    // Conversion should be lossless
+    assert!(old_png.pixels().map(|x| x.2.channels().to_owned()).collect::<Vec<Vec<u8>>>() ==
+            new_png.pixels().map(|x| x.2.channels().to_owned()).collect::<Vec<Vec<u8>>>());
+
+    remove_file(output).ok();
+}
+
+#[test]
+fn verbose_mode() {
+    let input = PathBuf::from("tests/files/verbose_mode.png");
+    let mut opts = get_opts(&input);
+    opts.verbosity = Some(1);
+    let output = opts.out_file.clone();
+
+    test_it_converts(&input,
+                     &output,
+                     &opts,
+                     png::ColorType::RGB,
+                     png::BitDepth::Eight,
+                     png::ColorType::RGB,
+                     png::BitDepth::Eight);
+}
+
 #[test]
 fn strip_headers() {
     let input = PathBuf::from("tests/files/strip_headers.png");

tests/reduction.rs

@@ -33,7 +33,7 @@ fn get_opts(input: &Path) -> oxipng::Options {
         clobber: true,
         create: true,
         preserve_attrs: false,
-        verbosity: Some(0),
+        verbosity: None,
         filter: filter,
         interlace: None,
         compression: compression,