hexyl: add display offset option

src/bin/hexyl.rs

@@ -69,6 +69,14 @@ fn run() -> Result<(), Box<dyn std::error::Error>> {
                 .possible_values(&["unicode", "ascii", "none"])
                 .default_value("unicode")
                 .help("Whether to draw a border with unicode or ASCII characters, or none at all"),
+        )
+        .arg(
+            Arg::with_name("display_offset")
+                .short("o")
+                .long("display-offset")
+                .takes_value(true)
+                .value_name("OFFSET")
+                .help("Add OFFSET to the displayed file position."),
         );
 
     let matches = app.get_matches_safe()?;
@@ -82,13 +90,7 @@ fn run() -> Result<(), Box<dyn std::error::Error>> {
 
     let length_arg = matches.value_of("length").or(matches.value_of("bytes"));
 
-    if let Some(length) = length_arg.and_then(|n| {
-        if n.starts_with("0x") {
-            u64::from_str_radix(n.trim_start_matches("0x"), 16).ok()
-        } else {
-            n.parse::<u64>().ok()
-        }
-    }) {
+    if let Some(length) = length_arg.and_then(parse_hex_or_int) {
         reader = Box::new(reader.take(length));
     }
 
@@ -106,6 +108,11 @@ fn run() -> Result<(), Box<dyn std::error::Error>> {
 
     let squeeze = !matches.is_present("nosqueezing");
 
+    let display_offset = matches
+        .value_of("display_offset")
+        .and_then(parse_hex_or_int)
+        .unwrap_or(0);
+
     // Set up Ctrl-C handler
     let cancelled = Arc::new(AtomicBool::new(false));
     let c = cancelled.clone();
@@ -119,6 +126,7 @@ fn run() -> Result<(), Box<dyn std::error::Error>> {
     let mut stdout_lock = stdout.lock();
 
     let mut printer = Printer::new(&mut stdout_lock, show_color, border_style, squeeze);
+    printer.display_offset(display_offset as usize);
     printer.print_all(&mut reader, Some(cancelled))?;
 
     Ok(())
@@ -148,3 +156,11 @@ fn main() {
         std::process::exit(1);
     }
 }
+
+fn parse_hex_or_int(n: &str) -> Option<u64> {
+    if n.starts_with("0x") {
+        u64::from_str_radix(n.trim_start_matches("0x"), 16).ok()
+    } else {
+        n.parse::<u64>().ok()
+    }
+}

src/lib.rs

@@ -155,6 +155,7 @@ pub struct Printer<'a, Writer: Write> {
     byte_hex_table: Vec<String>,
     byte_char_table: Vec<String>,
     squeezer: Squeezer,
+    display_offset: usize,
 }
 
 impl<'a, Writer: Write> Printer<'a, Writer> {
@@ -193,9 +194,15 @@ impl<'a, Writer: Write> Printer<'a, Writer> {
                 })
                 .collect(),
             squeezer: Squeezer::new(use_squeeze),
+            display_offset: 0,
         }
     }
 
+    pub fn display_offset(&mut self, display_offset: usize) -> &mut Self {
+        self.display_offset = display_offset;
+        self
+    }
+
     pub fn header(&mut self) {
         if let Some(border_elements) = self.border_style.header_elems() {
             let h = border_elements.horizontal_line;
@@ -241,7 +248,7 @@ impl<'a, Writer: Write> Printer<'a, Writer> {
         }
 
         let style = COLOR_OFFSET.normal();
-        let byte_index = format!("{:08x}", self.idx - 1);
+        let byte_index = format!("{:08x}", (self.idx - 1) + self.display_offset);
         let formatted_string = if self.show_color {
             format!("{}", style.paint(byte_index))
         } else {
@@ -456,19 +463,45 @@ mod tests {
     #[test]
     fn empty_file_passes() {
         let input = io::empty();
-        let expected_string = "┌────────┬─────────────────────────┬─────────────────────────┬────────┬────────┐
+        let expected_string =
+            "┌────────┬─────────────────────────┬─────────────────────────┬────────┬────────┐
 └────────┴─────────────────────────┴─────────────────────────┴────────┴────────┘
-".to_owned();
+"
+            .to_owned();
         assert_print_all_output(input, expected_string);
     }
 
     #[test]
     fn short_input_passes() {
         let input = io::Cursor::new(b"spam");
-        let expected_string = "┌────────┬─────────────────────────┬─────────────────────────┬────────┬────────┐
+        let expected_string =
+            "┌────────┬─────────────────────────┬─────────────────────────┬────────┬────────┐
 │00000000│ 73 70 61 6d             ┊                         │spam    ┊        │
 └────────┴─────────────────────────┴─────────────────────────┴────────┴────────┘
-".to_owned();
+"
+            .to_owned();
         assert_print_all_output(input, expected_string);
     }
+
+    #[test]
+    fn display_offset() {
+        let input = io::Cursor::new(b"spamspamspamspamspam");
+        let expected_string =
+            "┌────────┬─────────────────────────┬─────────────────────────┬────────┬────────┐
+│deadbeef│ 73 70 61 6d 73 70 61 6d ┊ 73 70 61 6d 73 70 61 6d │spamspam┊spamspam│
+│deadbeff│ 73 70 61 6d             ┊                         │spam    ┊        │
+└────────┴─────────────────────────┴─────────────────────────┴────────┴────────┘
+"
+            .to_owned();
+
+        let mut output = vec![];
+        let mut printer: Printer<Vec<u8>> =
+            Printer::new(&mut output, false, BorderStyle::Unicode, true);
+        printer.display_offset(0xdeadbeef);
+
+        printer.print_all(input, None).unwrap();
+
+        let actual_string: &str = str::from_utf8(&output).unwrap();
+        assert_eq!(actual_string, expected_string)
+    }
 }