Convert results to return a PngError

Closes #44

.travis.yml

@@ -11,7 +11,7 @@ matrix:
       env: TARGET=x86_64-apple-darwin
       cache: cargo
     - os: linux
-      rust: 1.8.0
+      rust: 1.9.0
       env: TARGET=x86_64-unknown-linux-gnu
       cache: cargo
     - os: linux

CHANGELOG.md

@@ -1,6 +1,7 @@
 **Version 0.11.0 (unreleased)**
- - [SEMVER_MAJOR] Bump minimum rustc version to 1.8.0, required by dependencies
+ - [SEMVER_MAJOR] Bump minimum rustc version to 1.9.0, required by dependencies
  - [SEMVER_MINOR] Allow calling optimization presets via crate using `Options::from_preset`
+ - [SEMVER_MAJOR] Return proper `PngError` type which implements `std::error::Error` from `Result`s
 
 **Version 0.10.0**
  - [SEMVER_MINOR] Make clap and regex dependencies optional

Cargo.lock

@@ -7,9 +7,9 @@ dependencies = [
  "clap 2.10.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "clippy 0.0.81 (registry+https://github.com/rust-lang/crates.io-index)",
  "crc 1.3.0 (registry+https://github.com/rust-lang/crates.io-index)",
- "image 0.10.1 (registry+https://github.com/rust-lang/crates.io-index)",
+ "image 0.10.3 (registry+https://github.com/rust-lang/crates.io-index)",
- "itertools 0.4.17 (registry+https://github.com/rust-lang/crates.io-index)",
+ "itertools 0.4.18 (registry+https://github.com/rust-lang/crates.io-index)",
- "libc 0.2.14 (registry+https://github.com/rust-lang/crates.io-index)",
+ "libc 0.2.15 (registry+https://github.com/rust-lang/crates.io-index)",
  "libz-sys 1.0.5 (registry+https://github.com/rust-lang/crates.io-index)",
  "miniz-sys 0.1.7 (registry+https://github.com/rust-lang/crates.io-index)",
  "num_cpus 1.0.0 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -52,7 +52,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
  "ansi_term 0.8.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "bitflags 0.7.0 (registry+https://github.com/rust-lang/crates.io-index)",
- "libc 0.2.14 (registry+https://github.com/rust-lang/crates.io-index)",
+ "libc 0.2.15 (registry+https://github.com/rust-lang/crates.io-index)",
  "strsim 0.4.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "term_size 0.1.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "unicode-width 0.1.3 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -73,7 +73,7 @@ version = "0.0.81"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
  "matches 0.1.2 (registry+https://github.com/rust-lang/crates.io-index)",
- "quine-mc_cluskey 0.2.3 (registry+https://github.com/rust-lang/crates.io-index)",
+ "quine-mc_cluskey 0.2.4 (registry+https://github.com/rust-lang/crates.io-index)",
  "regex-syntax 0.3.4 (registry+https://github.com/rust-lang/crates.io-index)",
  "rustc-serialize 0.3.19 (registry+https://github.com/rust-lang/crates.io-index)",
  "semver 0.2.3 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -91,7 +91,7 @@ dependencies = [
 
 [[package]]
 name = "crossbeam"
-version = "0.2.9"
+version = "0.2.10"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 
 [[package]]
@@ -107,7 +107,7 @@ name = "flate2"
 version = "0.2.14"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
- "libc 0.2.14 (registry+https://github.com/rust-lang/crates.io-index)",
+ "libc 0.2.15 (registry+https://github.com/rust-lang/crates.io-index)",
  "miniz-sys 0.1.7 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
@@ -123,7 +123,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 
 [[package]]
 name = "image"
-version = "0.10.1"
+version = "0.10.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
  "byteorder 0.5.3 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -142,7 +142,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 
 [[package]]
 name = "itertools"
-version = "0.4.17"
+version = "0.4.18"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 
 [[package]]
@@ -161,7 +161,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 
 [[package]]
 name = "libc"
-version = "0.2.14"
+version = "0.2.15"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 
 [[package]]
@@ -170,7 +170,7 @@ version = "1.0.5"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
  "gcc 0.3.32 (registry+https://github.com/rust-lang/crates.io-index)",
- "libc 0.2.14 (registry+https://github.com/rust-lang/crates.io-index)",
+ "libc 0.2.15 (registry+https://github.com/rust-lang/crates.io-index)",
  "pkg-config 0.3.8 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
@@ -184,7 +184,7 @@ name = "memchr"
 version = "0.1.11"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
- "libc 0.2.14 (registry+https://github.com/rust-lang/crates.io-index)",
+ "libc 0.2.15 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
 [[package]]
@@ -193,7 +193,7 @@ version = "0.1.7"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
  "gcc 0.3.32 (registry+https://github.com/rust-lang/crates.io-index)",
- "libc 0.2.14 (registry+https://github.com/rust-lang/crates.io-index)",
+ "libc 0.2.15 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
 [[package]]
@@ -260,7 +260,7 @@ name = "num_cpus"
 version = "1.0.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
- "libc 0.2.14 (registry+https://github.com/rust-lang/crates.io-index)",
+ "libc 0.2.15 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
 [[package]]
@@ -281,7 +281,7 @@ dependencies = [
 
 [[package]]
 name = "quine-mc_cluskey"
-version = "0.2.3"
+version = "0.2.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 
 [[package]]
@@ -289,7 +289,7 @@ name = "rand"
 version = "0.3.14"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
- "libc 0.2.14 (registry+https://github.com/rust-lang/crates.io-index)",
+ "libc 0.2.15 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
 [[package]]
@@ -320,7 +320,7 @@ name = "scoped-pool"
 version = "1.0.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
- "crossbeam 0.2.9 (registry+https://github.com/rust-lang/crates.io-index)",
+ "crossbeam 0.2.10 (registry+https://github.com/rust-lang/crates.io-index)",
  "scopeguard 0.1.2 (registry+https://github.com/rust-lang/crates.io-index)",
  "variance 0.1.3 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
@@ -353,7 +353,7 @@ name = "term_size"
 version = "0.1.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
- "libc 0.2.14 (registry+https://github.com/rust-lang/crates.io-index)",
+ "libc 0.2.15 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
 [[package]]
@@ -362,7 +362,7 @@ version = "2.0.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
  "kernel32-sys 0.2.2 (registry+https://github.com/rust-lang/crates.io-index)",
- "libc 0.2.14 (registry+https://github.com/rust-lang/crates.io-index)",
+ "libc 0.2.15 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
 [[package]]
@@ -426,17 +426,17 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 "checksum clippy 0.0.81 (registry+https://github.com/rust-lang/crates.io-index)" = "4eb4e734b771514b74b44e0d04e176e572d6e0637e32fe112331a0063a22ef39"
 "checksum clippy_lints 0.0.81 (registry+https://github.com/rust-lang/crates.io-index)" = "cd863204278a2011c4bf82417e7e8b869afd949410ce8d0dab14da2c79b96af9"
 "checksum crc 1.3.0 (registry+https://github.com/rust-lang/crates.io-index)" = "2a3f9159e74024e2cdb6f574e9117cdc2e91523a890930a022823d17abedc90a"
-"checksum crossbeam 0.2.9 (registry+https://github.com/rust-lang/crates.io-index)" = "fb974f835e90390c5f9dfac00f05b06dc117299f5ea4e85fbc7bb443af4911cc"
+"checksum crossbeam 0.2.10 (registry+https://github.com/rust-lang/crates.io-index)" = "0c5ea215664ca264da8a9d9c3be80d2eaf30923c259d03e870388eb927508f97"
 "checksum enum_primitive 0.1.0 (registry+https://github.com/rust-lang/crates.io-index)" = "f79eff5be92a4d7d5bddf7daa7d650717ea71628634efe6ca7bcda85b2183c23"
 "checksum flate2 0.2.14 (registry+https://github.com/rust-lang/crates.io-index)" = "3eeb481e957304178d2e782f2da1257f1434dfecbae883bafb61ada2a9fea3bb"
 "checksum gcc 0.3.32 (registry+https://github.com/rust-lang/crates.io-index)" = "dcb000abd6df9df4c637f75190297ebe56c1d7e66b56bbf3b4aa7aece15f61a2"
 "checksum glob 0.2.11 (registry+https://github.com/rust-lang/crates.io-index)" = "8be18de09a56b60ed0edf84bc9df007e30040691af7acd1c41874faac5895bfb"
-"checksum image 0.10.1 (registry+https://github.com/rust-lang/crates.io-index)" = "b7cd7efa3558b1acd537f2a6f9bcf15c4ae4842da38d2e2ea7c9ad023f36239b"
+"checksum image 0.10.3 (registry+https://github.com/rust-lang/crates.io-index)" = "559d5ebbe9ec73111799e49c07717944b244f8accf5de33a8a8128bc3ecd2e00"
 "checksum inflate 0.1.1 (registry+https://github.com/rust-lang/crates.io-index)" = "e7e0062d2dc2f17d2f13750d95316ae8a2ff909af0fda957084f5defd87c43bb"
-"checksum itertools 0.4.17 (registry+https://github.com/rust-lang/crates.io-index)" = "7ddb83e0e9730d830afba4e6839077948b4efa22075f7cd80a3867ec286c610f"
+"checksum itertools 0.4.18 (registry+https://github.com/rust-lang/crates.io-index)" = "6f15d694e7f7d46ef7a6951db981b33f132472f91d11b5a0f44d3980b87ccbc3"
 "checksum kernel32-sys 0.2.2 (registry+https://github.com/rust-lang/crates.io-index)" = "7507624b29483431c0ba2d82aece8ca6cdba9382bff4ddd0f7490560c056098d"
 "checksum lazy_static 0.2.1 (registry+https://github.com/rust-lang/crates.io-index)" = "49247ec2a285bb3dcb23cbd9c35193c025e7251bfce77c1d5da97e6362dffe7f"
-"checksum libc 0.2.14 (registry+https://github.com/rust-lang/crates.io-index)" = "39dfaaa0f4da0f1a06876c5d94329d739ad0150868069cc235f1ddf80a0480e7"
+"checksum libc 0.2.15 (registry+https://github.com/rust-lang/crates.io-index)" = "23e3757828fa702a20072c37ff47938e9dd331b92fac6e223d26d4b7a55f7ee2"
 "checksum libz-sys 1.0.5 (registry+https://github.com/rust-lang/crates.io-index)" = "ab80d82d16acfbf5c0e731297db302378896c0cffbc428dddc61d995a82e15cf"
 "checksum matches 0.1.2 (registry+https://github.com/rust-lang/crates.io-index)" = "15305656809ce5a4805b1ff2946892810992197ce1270ff79baded852187942e"
 "checksum memchr 0.1.11 (registry+https://github.com/rust-lang/crates.io-index)" = "d8b629fb514376c675b98c1421e80b151d3817ac42d7c667717d282761418d20"
@@ -451,7 +451,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 "checksum num_cpus 1.0.0 (registry+https://github.com/rust-lang/crates.io-index)" = "a859041cbf7a70ea1ece4b87d1a2c6ef364dcb68749c88db1f97304b9ec09d5f"
 "checksum pkg-config 0.3.8 (registry+https://github.com/rust-lang/crates.io-index)" = "8cee804ecc7eaf201a4a207241472cc870e825206f6c031e3ee2a72fa425f2fa"
 "checksum png 0.5.2 (registry+https://github.com/rust-lang/crates.io-index)" = "06208e2ee243e3118a55dda9318f821f206d8563fb8d4df258767f8e62bb0997"
-"checksum quine-mc_cluskey 0.2.3 (registry+https://github.com/rust-lang/crates.io-index)" = "e8f9a75e9319beed349f32bb252bcd7cafe4cce6c57a9ddcc9a8ffd3c49c3659"
+"checksum quine-mc_cluskey 0.2.4 (registry+https://github.com/rust-lang/crates.io-index)" = "07589615d719a60c8dd8a4622e7946465dfef20d1a428f969e3443e7386d5f45"
 "checksum rand 0.3.14 (registry+https://github.com/rust-lang/crates.io-index)" = "2791d88c6defac799c3f20d74f094ca33b9332612d9aef9078519c82e4fe04a5"
 "checksum regex 0.1.73 (registry+https://github.com/rust-lang/crates.io-index)" = "56b7ee9f764ecf412c6e2fff779bca4b22980517ae335a21aeaf4e32625a5df2"
 "checksum regex-syntax 0.3.4 (registry+https://github.com/rust-lang/crates.io-index)" = "31040aad7470ad9d8c46302dcffba337bb4289ca5da2e3cd6e37b64109a85199"

README.md

@@ -27,7 +27,7 @@ cp target/release/oxipng /usr/local/bin
 Please note that zlib is a required build dependency. Oxipng should work with any 1.x version of zlib,
 but you are advised to use the latest version (currently 1.2.8) for security and bug fixes.
 
-The current minimum supported Rust version is **1.8.0**. Oxipng may compile on earlier versions of Rust,
+The current minimum supported Rust version is **1.9.0**. Oxipng may compile on earlier versions of Rust,
 but there is no guarantee.
 
 Oxipng follows Semantic Versioning.

src/deflate/deflate.rs

@@ -1,10 +1,11 @@
+use error::PngError;
 use libz_sys;
 use miniz_sys;
 use libc::c_int;
 use std::cmp::max;
 
 /// Decompress a data stream using the DEFLATE algorithm
-pub fn inflate(data: &[u8]) -> Result<Vec<u8>, String> {
+pub fn inflate(data: &[u8]) -> Result<Vec<u8>, PngError> {
     let mut input = data.to_owned();
     let mut stream = super::libz_stream::Stream::new_decompress();
     let mut output = Vec::with_capacity(data.len());
@@ -12,7 +13,7 @@ pub fn inflate(data: &[u8]) -> Result<Vec<u8>, String> {
         match stream.decompress_vec(input.as_mut(), output.as_mut()) {
             libz_sys::Z_OK => output.reserve(data.len()),
             libz_sys::Z_STREAM_END => break,
-            c => return Err(format!("Error code on decompress: {}", c)),
+            c => return Err(PngError::new(&format!("Error code on decompress: {}", c))),
         }
     }
     output.shrink_to_fit();
@@ -21,7 +22,7 @@ pub fn inflate(data: &[u8]) -> Result<Vec<u8>, String> {
 }
 
 /// Compress a data stream using the zlib implementation of the DEFLATE algorithm
-pub fn deflate(data: &[u8], zc: u8, zm: u8, zs: u8, zw: u8) -> Result<Vec<u8>, String> {
+pub fn deflate(data: &[u8], zc: u8, zm: u8, zs: u8, zw: u8) -> Result<Vec<u8>, PngError> {
     let mut input = data.to_owned();
     // Compressed input should be smaller than decompressed, so allocate less than data.len()
     // However, it needs a minimum capacity in order to handle very small images
@@ -36,7 +37,7 @@ pub fn deflate(data: &[u8], zc: u8, zm: u8, zs: u8, zw: u8) -> Result<Vec<u8>, S
             match stream.compress_vec(input.as_mut(), output.as_mut()) {
                 miniz_sys::MZ_OK => output.reserve(max(1024, data.len() / 20)),
                 miniz_sys::MZ_STREAM_END => break,
-                c => return Err(format!("Error code on compress: {}", c)),
+                c => return Err(PngError::new(&format!("Error code on compress: {}", c))),
             }
         }
     } else {
@@ -49,7 +50,7 @@ pub fn deflate(data: &[u8], zc: u8, zm: u8, zs: u8, zw: u8) -> Result<Vec<u8>, S
             match stream.compress_vec(input.as_mut(), output.as_mut()) {
                 libz_sys::Z_OK => output.reserve(max(1024, data.len() / 20)),
                 libz_sys::Z_STREAM_END => break,
-                c => return Err(format!("Error code on compress: {}", c)),
+                c => return Err(PngError::new(&format!("Error code on compress: {}", c))),
             }
         }
     }

src/error.rs

@@ -0,0 +1,25 @@
+use std::error::Error;
+use std::fmt;
+
+#[derive(Debug)]
+pub struct PngError {
+    description: String,
+}
+
+impl Error for PngError {
+    fn description(&self) -> &str {
+        &self.description
+    }
+}
+
+impl fmt::Display for PngError {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f, "{}", self.description)
+    }
+}
+
+impl PngError {
+    pub fn new(description: &str) -> PngError {
+        PngError { description: description.to_owned() }
+    }
+}

src/headers.rs

@@ -1,6 +1,7 @@
 use byteorder::{BigEndian, ReadBytesExt};
 use colors::{BitDepth, ColorType};
 use crc::crc32;
+use error::PngError;
 use std::io::Cursor;
 
 #[derive(Debug, Clone, Copy)]
@@ -45,7 +46,7 @@ pub fn file_header_is_valid(bytes: &[u8]) -> bool {
 pub fn parse_next_header(byte_data: &[u8],
                          byte_offset: &mut usize,
                          fix_errors: bool)
-                         -> Result<Option<(String, Vec<u8>)>, String> {
+                         -> Result<Option<(String, Vec<u8>)>, PngError> {
     let mut rdr = Cursor::new(byte_data.iter()
         .skip(*byte_offset)
         .take(4)
@@ -53,14 +54,14 @@ pub fn parse_next_header(byte_data: &[u8],
         .collect::<Vec<u8>>());
     let length: u32 = match rdr.read_u32::<BigEndian>() {
         Ok(x) => x,
-        Err(_) => return Err("Invalid data found--unable to read PNG file".to_owned()),
+        Err(_) => return Err(PngError::new("Invalid data found; unable to read PNG file")),
     };
     *byte_offset += 4;
 
     let mut header_bytes: Vec<u8> = byte_data.iter().skip(*byte_offset).take(4).cloned().collect();
     let header = match String::from_utf8(header_bytes.clone()) {
         Ok(x) => x,
-        Err(_) => return Err("Invalid data found--unable to read PNG file".to_owned()),
+        Err(_) => return Err(PngError::new("Invalid data found; unable to read PNG file")),
     };
     if header == "IEND" {
         // End of data
@@ -81,19 +82,19 @@ pub fn parse_next_header(byte_data: &[u8],
         .collect::<Vec<u8>>());
     let crc: u32 = match rdr.read_u32::<BigEndian>() {
         Ok(x) => x,
-        Err(_) => return Err("Invalid data found--unable to read PNG file".to_owned()),
+        Err(_) => return Err(PngError::new("Invalid data found; unable to read PNG file")),
     };
     *byte_offset += 4;
     header_bytes.extend(data.clone());
     if !fix_errors && crc32::checksum_ieee(header_bytes.as_ref()) != crc {
-        return Err(format!("Corrupt data chunk found--CRC Mismatch in {}\nThis may be recoverable by using --fix",
+        return Err(PngError::new(&format!("CRC Mismatch in {} header; May be recoverable by using --fix",
-                           header));
+                                          header)));
     }
 
     Ok(Some((header, data)))
 }
 
-pub fn parse_ihdr_header(byte_data: &[u8]) -> Result<IhdrData, String> {
+pub fn parse_ihdr_header(byte_data: &[u8]) -> Result<IhdrData, PngError> {
     let mut rdr = Cursor::new(&byte_data[0..8]);
     Ok(IhdrData {
         color_type: match byte_data[9] {
@@ -102,7 +103,7 @@ pub fn parse_ihdr_header(byte_data: &[u8]) -> Result<IhdrData, String> {
             3 => ColorType::Indexed,
             4 => ColorType::GrayscaleAlpha,
             6 => ColorType::RGBA,
-            _ => return Err("Unexpected color type in header".to_owned()),
+            _ => return Err(PngError::new("Unexpected color type in header")),
         },
         bit_depth: match byte_data[8] {
             1 => BitDepth::One,
@@ -110,7 +111,7 @@ pub fn parse_ihdr_header(byte_data: &[u8]) -> Result<IhdrData, String> {
             4 => BitDepth::Four,
             8 => BitDepth::Eight,
             16 => BitDepth::Sixteen,
-            _ => return Err("Unexpected bit depth in header".to_owned()),
+            _ => return Err(PngError::new("Unexpected bit depth in header")),
         },
         width: rdr.read_u32::<BigEndian>().unwrap(),
         height: rdr.read_u32::<BigEndian>().unwrap(),

src/lib.rs

@@ -8,6 +8,7 @@ extern crate miniz_sys;
 extern crate num_cpus;
 extern crate scoped_pool;
 
+use error::PngError;
 use headers::Headers;
 use scoped_pool::Pool;
 use std::collections::{HashMap, HashSet};
@@ -22,6 +23,7 @@ pub mod deflate {
     pub mod libz_stream;
     pub mod miniz_stream;
 }
+mod error;
 mod filters;
 pub mod headers;
 mod interlace;
@@ -270,7 +272,7 @@ impl Default for Options {
 }
 
 /// Perform optimization on the input file using the options provided
-pub fn optimize(filepath: &Path, opts: &Options) -> Result<(), String> {
+pub fn optimize(filepath: &Path, opts: &Options) -> Result<(), PngError> {
     // Read in the file and try to decode as PNG.
     if opts.verbosity.is_some() {
         writeln!(&mut stderr(), "Processing: {}", filepath.to_str().unwrap()).ok();
@@ -305,8 +307,8 @@ pub fn optimize(filepath: &Path, opts: &Options) -> Result<(), String> {
                                                           .unwrap()))) {
                 Ok(x) => x,
                 Err(_) => {
-                    return Err(format!("Unable to write to backup file at {}",
+                    return Err(PngError::new(&format!("Unable to write to backup file at {}",
-                                       opts.out_file.display()))
+                                                      opts.out_file.display())))
                 }
             };
         }
@@ -315,13 +317,14 @@ pub fn optimize(filepath: &Path, opts: &Options) -> Result<(), String> {
             let mut buffer = BufWriter::new(stdout());
             match buffer.write_all(&optimized_output) {
                 Ok(_) => (),
-                Err(_) => return Err("Unable to write to stdout".to_owned()),
+                Err(_) => return Err(PngError::new("Unable to write to stdout")),
             }
         } else {
             let out_file = match File::create(&opts.out_file) {
                 Ok(x) => x,
                 Err(_) => {
-                    return Err(format!("Unable to write to file {}", opts.out_file.display()))
+                    return Err(PngError::new(&format!("Unable to write to file {}",
+                                                      opts.out_file.display())))
                 }
             };
 
@@ -377,7 +380,8 @@ pub fn optimize(filepath: &Path, opts: &Options) -> Result<(), String> {
                     }
                 }
                 Err(_) => {
-                    return Err(format!("Unable to write to file {}", opts.out_file.display()))
+                    return Err(PngError::new(&format!("Unable to write to file {}",
+                                                      opts.out_file.display())))
                 }
             }
         }
@@ -387,7 +391,7 @@ pub fn optimize(filepath: &Path, opts: &Options) -> Result<(), String> {
 
 /// Perform optimization on the input file using the options provided, where the file is already
 /// loaded in-memory
-pub fn optimize_from_memory(data: &[u8], opts: &Options) -> Result<Vec<u8>, String> {
+pub fn optimize_from_memory(data: &[u8], opts: &Options) -> Result<Vec<u8>, PngError> {
     // Read in the file and try to decode as PNG.
     if opts.verbosity.is_some() {
         writeln!(&mut stderr(), "Processing from memory").ok();

src/png.rs

@@ -2,6 +2,7 @@ use bit_vec::BitVec;
 use byteorder::{BigEndian, WriteBytesExt};
 use colors::{BitDepth, ColorType};
 use crc::crc32;
+use error::PngError;
 use filters::*;
 use headers::*;
 use interlace::{interlace_image, deinterlace_image};
@@ -181,28 +182,28 @@ pub struct PngData {
 
 impl PngData {
     /// Create a new `PngData` struct by opening a file
-    pub fn new(filepath: &Path, fix_errors: bool) -> Result<PngData, String> {
+    pub fn new(filepath: &Path, fix_errors: bool) -> Result<PngData, PngError> {
         let mut file = match File::open(filepath) {
             Ok(f) => f,
-            Err(_) => return Err("Failed to open file for reading".to_owned()),
+            Err(_) => return Err(PngError::new("Failed to open file for reading")),
         };
         let mut byte_data: Vec<u8> = Vec::new();
         // Read raw png data into memory
         match file.read_to_end(&mut byte_data) {
             Ok(_) => (),
-            Err(_) => return Err("Failed to read from file".to_owned()),
+            Err(_) => return Err(PngError::new("Failed to read from file")),
         }
 
         PngData::from_slice(&byte_data, fix_errors)
     }
 
     /// Create a new `PngData` struct by reading a slice
-    pub fn from_slice(byte_data: &[u8], fix_errors: bool) -> Result<PngData, String> {
+    pub fn from_slice(byte_data: &[u8], fix_errors: bool) -> Result<PngData, PngError> {
         let mut byte_offset: usize = 0;
         // Test that png header is valid
         let header: Vec<u8> = byte_data.iter().take(8).cloned().collect();
         if !file_header_is_valid(header.as_ref()) {
-            return Err("Invalid PNG header detected".to_owned());
+            return Err(PngError::new("Invalid PNG header detected"));
         }
         byte_offset += 8;
         // Read the data headers
@@ -226,10 +227,10 @@ impl PngData {
         }
         // Parse the headers into our PngData
         if idat_headers.is_empty() {
-            return Err("Image data was empty, skipping".to_owned());
+            return Err(PngError::new("Image data was empty, skipping"));
         }
         if aux_headers.get("IHDR").is_none() {
-            return Err("Image header data was missing, skipping".to_owned());
+            return Err(PngError::new("Image header data was missing, skipping"));
         }
         let ihdr_header = match parse_ihdr_header(aux_headers.remove("IHDR").unwrap().as_ref()) {
             Ok(x) => x,
@@ -388,11 +389,7 @@ impl PngData {
                     // http://www.libpng.org/pub/png/book/chapter09.html
                     let mut trials: HashMap<u8, Vec<u8>> = HashMap::with_capacity(5);
                     // Avoid vertical filtering on first line of each interlacing pass
-                    for filter in if last_pass == line.pass {
+                    for filter in if last_pass == line.pass { 0..5 } else { 0..2 } {
-                        0..5
-                    } else {
-                        0..2
-                    } {
                         trials.insert(filter, filter_line(filter, bpp, &line.data, &last_line));
                     }
                     let (best_filter, best_line) = trials.iter()

tests/filters.rs

@@ -6,6 +6,7 @@ use image::Pixel;
 use oxipng::colors::{BitDepth, ColorType};
 use oxipng::png;
 use std::collections::HashSet;
+use std::error::Error;
 use std::fs::remove_file;
 use std::path::Path;
 use std::path::PathBuf;
@@ -36,7 +37,7 @@ fn test_it_converts(input: &Path,
 
     match oxipng::optimize(input, opts) {
         Ok(_) => (),
-        Err(x) => panic!(x.to_owned()),
+        Err(x) => panic!(x.description().to_owned()),
     };
     assert!(output.exists());
 
@@ -44,7 +45,7 @@ fn test_it_converts(input: &Path,
         Ok(x) => x,
         Err(x) => {
             remove_file(output).ok();
-            panic!(x.to_owned())
+            panic!(x.description().to_owned())
         }
     };
 

tests/flags.rs

@@ -7,6 +7,7 @@ use oxipng::colors::{BitDepth, ColorType};
 use oxipng::headers::Headers;
 use oxipng::png;
 use std::collections::HashSet;
+use std::error::Error;
 use std::fs::remove_file;
 use std::path::Path;
 use std::path::PathBuf;
@@ -37,7 +38,7 @@ fn test_it_converts(input: &Path,
 
     match oxipng::optimize(input, opts) {
         Ok(_) => (),
-        Err(x) => panic!(x.to_owned()),
+        Err(x) => panic!(x.description().to_owned()),
     };
     assert!(output.exists());
 
@@ -45,7 +46,7 @@ fn test_it_converts(input: &Path,
         Ok(x) => x,
         Err(x) => {
             remove_file(output).ok();
-            panic!(x.to_owned())
+            panic!(x.description().to_owned())
         }
     };
 
@@ -93,7 +94,7 @@ fn strip_headers_list() {
 
     match oxipng::optimize(&input, &opts) {
         Ok(_) => (),
-        Err(x) => panic!(x.to_owned()),
+        Err(x) => panic!(x.description().to_owned()),
     };
     assert!(output.exists());
 
@@ -101,7 +102,7 @@ fn strip_headers_list() {
         Ok(x) => x,
         Err(x) => {
             remove_file(output).ok();
-            panic!(x.to_owned())
+            panic!(x.description().to_owned())
         }
     };
 
@@ -134,7 +135,7 @@ fn strip_headers_safe() {
 
     match oxipng::optimize(&input, &opts) {
         Ok(_) => (),
-        Err(x) => panic!(x.to_owned()),
+        Err(x) => panic!(x.description().to_owned()),
     };
     assert!(output.exists());
 
@@ -142,7 +143,7 @@ fn strip_headers_safe() {
         Ok(x) => x,
         Err(x) => {
             remove_file(output).ok();
-            panic!(x.to_owned())
+            panic!(x.description().to_owned())
         }
     };
 
@@ -175,7 +176,7 @@ fn strip_headers_all() {
 
     match oxipng::optimize(&input, &opts) {
         Ok(_) => (),
-        Err(x) => panic!(x.to_owned()),
+        Err(x) => panic!(x.description().to_owned()),
     };
     assert!(output.exists());
 
@@ -183,7 +184,7 @@ fn strip_headers_all() {
         Ok(x) => x,
         Err(x) => {
             remove_file(output).ok();
-            panic!(x.to_owned())
+            panic!(x.description().to_owned())
         }
     };
 
@@ -216,7 +217,7 @@ fn strip_headers_none() {
 
     match oxipng::optimize(&input, &opts) {
         Ok(_) => (),
-        Err(x) => panic!(x.to_owned()),
+        Err(x) => panic!(x.description().to_owned()),
     };
     assert!(output.exists());
 
@@ -224,7 +225,7 @@ fn strip_headers_none() {
         Ok(x) => x,
         Err(x) => {
             remove_file(output).ok();
-            panic!(x.to_owned())
+            panic!(x.description().to_owned())
         }
     };
 
@@ -255,7 +256,7 @@ fn interlacing_0_to_1() {
 
     match oxipng::optimize(&input, &opts) {
         Ok(_) => (),
-        Err(x) => panic!(x.to_owned()),
+        Err(x) => panic!(x.description().to_owned()),
     };
     assert!(output.exists());
 
@@ -263,7 +264,7 @@ fn interlacing_0_to_1() {
         Ok(x) => x,
         Err(x) => {
             remove_file(output).ok();
-            panic!(x.to_owned())
+            panic!(x.description().to_owned())
         }
     };
 
@@ -292,7 +293,7 @@ fn interlacing_1_to_0() {
 
     match oxipng::optimize(&input, &opts) {
         Ok(_) => (),
-        Err(x) => panic!(x.to_owned()),
+        Err(x) => panic!(x.description().to_owned()),
     };
     assert!(output.exists());
 
@@ -300,7 +301,7 @@ fn interlacing_1_to_0() {
         Ok(x) => x,
         Err(x) => {
             remove_file(output).ok();
-            panic!(x.to_owned())
+            panic!(x.description().to_owned())
         }
     };
 
@@ -331,7 +332,7 @@ fn interlacing_0_to_1_small_files() {
 
     match oxipng::optimize(&input, &opts) {
         Ok(_) => (),
-        Err(x) => panic!(x.to_owned()),
+        Err(x) => panic!(x.description().to_owned()),
     };
     assert!(output.exists());
 
@@ -339,7 +340,7 @@ fn interlacing_0_to_1_small_files() {
         Ok(x) => x,
         Err(x) => {
             remove_file(output).ok();
-            panic!(x.to_owned())
+            panic!(x.description().to_owned())
         }
     };
 
@@ -372,7 +373,7 @@ fn interlacing_1_to_0_small_files() {
 
     match oxipng::optimize(&input, &opts) {
         Ok(_) => (),
-        Err(x) => panic!(x.to_owned()),
+        Err(x) => panic!(x.description().to_owned()),
     };
     assert!(output.exists());
 
@@ -380,7 +381,7 @@ fn interlacing_1_to_0_small_files() {
         Ok(x) => x,
         Err(x) => {
             remove_file(output).ok();
-            panic!(x.to_owned())
+            panic!(x.description().to_owned())
         }
     };
 
@@ -414,7 +415,7 @@ fn interlaced_0_to_1_other_filter_mode() {
 
     match oxipng::optimize(&input, &opts) {
         Ok(_) => (),
-        Err(x) => panic!(x.to_owned()),
+        Err(x) => panic!(x.description().to_owned()),
     };
     assert!(output.exists());
 
@@ -422,7 +423,7 @@ fn interlaced_0_to_1_other_filter_mode() {
         Ok(x) => x,
         Err(x) => {
             remove_file(output).ok();
-            panic!(x.to_owned())
+            panic!(x.description().to_owned())
         }
     };
 
@@ -470,7 +471,7 @@ fn fix_errors() {
 
     match oxipng::optimize(&input, &opts) {
         Ok(_) => (),
-        Err(x) => panic!(x.to_owned()),
+        Err(x) => panic!(x.description().to_owned()),
     };
     assert!(output.exists());
 
@@ -478,7 +479,7 @@ fn fix_errors() {
         Ok(x) => x,
         Err(x) => {
             remove_file(output).ok();
-            panic!(x.to_owned())
+            panic!(x.description().to_owned())
         }
     };
 
@@ -504,7 +505,7 @@ fn issue_42() {
 
     match oxipng::optimize(&input, &opts) {
         Ok(_) => (),
-        Err(x) => panic!(x.to_owned()),
+        Err(x) => panic!(x.description().to_owned()),
     };
     assert!(output.exists());
 
@@ -512,7 +513,7 @@ fn issue_42() {
         Ok(x) => x,
         Err(x) => {
             remove_file(output).ok();
-            panic!(x.to_owned())
+            panic!(x.description().to_owned())
         }
     };
 

tests/interlaced.rs

@@ -6,6 +6,7 @@ use image::Pixel;
 use oxipng::colors::{BitDepth, ColorType};
 use oxipng::png;
 use std::collections::HashSet;
+use std::error::Error;
 use std::fs::remove_file;
 use std::path::Path;
 use std::path::PathBuf;
@@ -37,7 +38,7 @@ fn test_it_converts(input: &Path,
 
     match oxipng::optimize(input, opts) {
         Ok(_) => (),
-        Err(x) => panic!(x.to_owned()),
+        Err(x) => panic!(x.description().to_owned()),
     };
     assert!(output.exists());
 
@@ -45,7 +46,7 @@ fn test_it_converts(input: &Path,
         Ok(x) => x,
         Err(x) => {
             remove_file(output).ok();
-            panic!(x.to_owned())
+            panic!(x.description().to_owned())
         }
     };
 

tests/reduction.rs

@@ -6,6 +6,7 @@ use image::Pixel;
 use oxipng::colors::{BitDepth, ColorType};
 use oxipng::png;
 use std::collections::HashSet;
+use std::error::Error;
 use std::fs::remove_file;
 use std::path::Path;
 use std::path::PathBuf;
@@ -37,7 +38,7 @@ fn test_it_converts(input: &Path,
 
     match oxipng::optimize(input, opts) {
         Ok(_) => (),
-        Err(x) => panic!(x.to_owned()),
+        Err(x) => panic!(x.description().to_owned()),
     };
     assert!(output.exists());
 
@@ -45,7 +46,7 @@ fn test_it_converts(input: &Path,
         Ok(x) => x,
         Err(x) => {
             remove_file(output).ok();
-            panic!(x.to_owned())
+            panic!(x.description().to_owned())
         }
     };
 
@@ -1247,7 +1248,7 @@ fn palette_should_be_reduced_with_dupes() {
 
     match oxipng::optimize(&input, &opts) {
         Ok(_) => (),
-        Err(x) => panic!(x.to_owned()),
+        Err(x) => panic!(x.description().to_owned()),
     };
     assert!(output.exists());
 
@@ -1255,7 +1256,7 @@ fn palette_should_be_reduced_with_dupes() {
         Ok(x) => x,
         Err(x) => {
             remove_file(&output).ok();
-            panic!(x.to_owned())
+            panic!(x.description().to_owned())
         }
     };
 
@@ -1287,7 +1288,7 @@ fn palette_should_be_reduced_with_unused() {
 
     match oxipng::optimize(&input, &opts) {
         Ok(_) => (),
-        Err(x) => panic!(x.to_owned()),
+        Err(x) => panic!(x.description().to_owned()),
     };
     assert!(output.exists());
 
@@ -1295,7 +1296,7 @@ fn palette_should_be_reduced_with_unused() {
         Ok(x) => x,
         Err(x) => {
             remove_file(&output).ok();
-            panic!(x.to_owned())
+            panic!(x.description().to_owned())
         }
     };
 
@@ -1327,7 +1328,7 @@ fn palette_should_be_reduced_with_both() {
 
     match oxipng::optimize(&input, &opts) {
         Ok(_) => (),
-        Err(x) => panic!(x.to_owned()),
+        Err(x) => panic!(x.description().to_owned()),
     };
     assert!(output.exists());
 
@@ -1335,7 +1336,7 @@ fn palette_should_be_reduced_with_both() {
         Ok(x) => x,
         Err(x) => {
             remove_file(&output).ok();
-            panic!(x.to_owned())
+            panic!(x.description().to_owned())
         }
     };