feat: add skip option

resolves #16 and #87

src/bin/hexyl.rs

@@ -3,14 +3,15 @@ extern crate clap;
 
 use atty;
 
+use std::cell::RefCell;
 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 +38,14 @@ 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")
@@ -80,16 +89,24 @@ 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(RefCell::new(stdin.lock())),
     };
 
+    let skip_arg = matches.value_of("skip");
+
+    if let Some(length) = skip_arg.and_then(parse_hex_or_int) {
+        reader.seek(SeekFrom::Start(length))?;
+    }
+
     let length_arg = matches.value_of("length").or(matches.value_of("bytes"));
 
-    if let Some(length) = length_arg.and_then(parse_hex_or_int) {
-        reader = Box::new(reader.take(length));
-    }
+    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,

src/input.rs

@@ -0,0 +1,38 @@
+use std::cell::RefCell;
+use std::fs;
+use std::io::{self, Read, Seek, SeekFrom};
+
+pub enum Input<'a> {
+    File(fs::File),
+    Stdin(RefCell<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.borrow_mut().read(buf),
+        }
+    }
+}
+
+impl<'a> Seek for Input<'a> {
+    fn seek(&mut self, pos: SeekFrom) -> io::Result<u64> {
+        match *self {
+            Input::File(ref mut file) => file.seek(pos),
+            Input::Stdin(_) => Err(io::Error::new(
+                io::ErrorKind::Other,
+                "not supported by stdin-input",
+            )),
+        }
+    }
+}
+
+impl<'a> Input<'a> {
+    pub fn into_inner(self) -> Box<dyn Read + 'a> {
+        match self {
+            Self::File(file) => Box::new(file),
+            Self::Stdin(stdin) => Box::new(stdin.into_inner()),
+        }
+    }
+}

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 {