feat: add skip option

.travis.yml

@@ -18,7 +18,7 @@ matrix:
 
     # Minimum Rust supported channel.
     - os: linux
-      rust: 1.31.0
+      rust: 1.36.0
       env: TARGET=x86_64-unknown-linux-gnu
 
 

Cargo.toml

@@ -13,6 +13,7 @@ edition = "2018"
 [dependencies]
 ansi_term = "0.12"
 atty = "0.2"
+libc = "0.2"
 
 [dependencies.clap]
 version = "2"

README.md

@@ -82,7 +82,7 @@ or Windows Terminal since Windows 10 1903).
 
 ### Via cargo
 
-If you have Rust 1.31 or higher, you can install `hexyl` from source via `cargo`:
+If you have Rust 1.36 or higher, you can install `hexyl` from source via `cargo`:
 ```
 cargo install hexyl
 ```

src/bin/hexyl.rs

@@ -4,13 +4,13 @@ extern crate clap;
 use atty;
 
 use std::fs::File;
-use std::io::{self, prelude::*};
+use std::io::{self, prelude::*, SeekFrom};
 
 use clap::{App, AppSettings, Arg};
 
 use atty::Stream;
 
-use hexyl::{BorderStyle, Printer};
+use hexyl::{BorderStyle, Input, Printer};
 
 fn run() -> Result<(), Box<dyn std::error::Error>> {
     let app = App::new(crate_name!())
@@ -37,6 +37,14 @@ fn run() -> Result<(), Box<dyn std::error::Error>> {
                 .value_name("N")
                 .help("An alias for -n/--length"),
         )
+        .arg(
+            Arg::with_name("skip")
+                .short("s")
+                .long("skip")
+                .takes_value(true)
+                .value_name("N")
+                .help("Skip first N bytes"),
+        )
         .arg(
             Arg::with_name("nosqueezing")
                 .short("v")
@@ -80,17 +88,25 @@ fn run() -> Result<(), Box<dyn std::error::Error>> {
 
     let stdin = io::stdin();
 
-    let mut reader: Box<dyn Read> = match matches.value_of("file") {
-        Some(filename) => Box::new(File::open(filename)?),
-        None => Box::new(stdin.lock()),
+    let mut reader: Input = match matches.value_of("file") {
+        Some(filename) => Input::File(File::open(filename)?),
+        None => Input::Stdin(stdin.lock()),
     };
 
-    let length_arg = matches.value_of("length").or(matches.value_of("bytes"));
+    let skip_arg = matches.value_of("skip").and_then(parse_hex_or_int);
 
-    if let Some(length) = length_arg.and_then(parse_hex_or_int) {
-        reader = Box::new(reader.take(length));
+    if let Some(skip) = skip_arg {
+        reader.seek(SeekFrom::Start(skip))?;
     }
 
+    let length_arg = matches.value_of("length").or(matches.value_of("bytes"));
+
+    let mut reader = if let Some(length) = length_arg.and_then(parse_hex_or_int) {
+        Box::new(reader.take(length))
+    } else {
+        reader.into_inner()
+    };
+
     let show_color = match matches.value_of("color") {
         Some("never") => false,
         Some("auto") => atty::is(Stream::Stdout),
@@ -108,7 +124,7 @@ fn run() -> Result<(), Box<dyn std::error::Error>> {
     let display_offset = matches
         .value_of("display_offset")
         .and_then(parse_hex_or_int)
-        .unwrap_or(0);
+        .unwrap_or(skip_arg.unwrap_or(0));
 
     let stdout = io::stdout();
     let mut stdout_lock = stdout.lock();

src/input.rs

@@ -0,0 +1,48 @@
+use std::fs;
+use std::io::{self, Read, Seek, SeekFrom};
+
+pub enum Input<'a> {
+    File(fs::File),
+    Stdin(io::StdinLock<'a>),
+}
+
+impl<'a> Read for Input<'a> {
+    fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
+        match *self {
+            Input::File(ref mut file) => file.read(buf),
+            Input::Stdin(ref mut stdin) => stdin.read(buf),
+        }
+    }
+}
+
+impl<'a> Seek for Input<'a> {
+    fn seek(&mut self, pos: SeekFrom) -> io::Result<u64> {
+        match *self {
+            Input::File(ref mut file) => {
+                let seek_res = file.seek(pos);
+                if let Err(Some(libc::ESPIPE)) = seek_res.as_ref().map_err(|err| err.raw_os_error())
+                {
+                    return Err(io::Error::new(
+                        io::ErrorKind::Other,
+                        "Using '--seek' is not supported when using a pipe",
+                    )
+                    .into());
+                };
+                seek_res
+            }
+            Input::Stdin(_) => Err(io::Error::new(
+                io::ErrorKind::Other,
+                "Using '--seek' is not supported when reading from STDIN",
+            )),
+        }
+    }
+}
+
+impl<'a> Input<'a> {
+    pub fn into_inner(self) -> Box<dyn Read + 'a> {
+        match self {
+            Input::File(file) => Box::new(file),
+            Input::Stdin(stdin) => Box::new(stdin),
+        }
+    }
+}

src/lib.rs

@@ -1,5 +1,8 @@
+pub(crate) mod input;
 pub mod squeezer;
 
+pub use input::*;
+
 use std::io::{self, Read, Write};
 
 use ansi_term::Color;
@@ -407,7 +410,7 @@ impl<'a, Writer: Write> Printer<'a, Writer> {
     /// is exhausted.
     pub fn print_all<Reader: Read>(
         &mut self,
-        mut reader: Reader
+        mut reader: Reader,
     ) -> Result<(), Box<dyn std::error::Error>> {
         let mut buffer = [0; BUFFER_SIZE];
         'mainloop: loop {