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// hexrev.rs
use std::fs::{self, File};
use std::io::{self, BufReader, BufWriter, Read, Write};
use std::path::Path;
/// Reversible hex <-> bytes helper.
/// - `hex_to_bin` ignores non-hex (whitespace/newlines/etc.) like `xxd -r -p`.
/// - `hex_to_bin_strict` errors on ANY non-hex character.
/// - `bin_to_hex` emits lowercase by default; can uppercase and wrap lines.
pub struct HexRev;
impl HexRev {
#[inline]
fn hex_val(b: u8) -> Option<u8> {
match b {
b'0'..=b'9' => Some(b - b'0'),
b'a'..=b'f' => Some(b - b'a' + 10),
b'A'..=b'F' => Some(b - b'A' + 10),
_ => None,
}
}
/// Streaming plain-hex -> bytes, *ignoring* non-hex (matches `xxd -r -p` feel).
/// Errors on odd number of hex digits.
pub fn hex_to_bin<R: Read, W: Write>(mut r: R, mut w: W) -> io::Result<()> {
let mut buf = [0u8; 8192];
let mut have_high = false;
let mut high = 0u8;
loop {
let n = r.read(&mut buf)?;
if n == 0 {
break;
}
for &b in &buf[..n] {
if let Some(v) = Self::hex_val(b) {
if !have_high {
high = v << 4;
have_high = true;
} else {
w.write_all(&[high | v])?;
have_high = false;
}
} // else: ignore
}
}
if have_high {
return Err(io::Error::new(
io::ErrorKind::InvalidData,
"odd number of hex digits in input",
));
}
Ok(())
}
/// Streaming plain-hex -> bytes in **strict** mode:
/// - Only [0-9a-fA-F] are allowed; ANY other byte (including whitespace) is an error.
/// - Errors on odd number of hex digits.
pub fn hex_to_bin_strict<R: Read, W: Write>(mut r: R, mut w: W) -> io::Result<()> {
let mut buf = [0u8; 8192];
let mut have_high = false;
let mut high = 0u8;
loop {
let n = r.read(&mut buf)?;
if n == 0 {
break;
}
for &b in &buf[..n] {
let v = match Self::hex_val(b) {
Some(v) => v,
None => {
return Err(io::Error::new(
io::ErrorKind::InvalidData,
format!("non-hex character: 0x{b:02X}"),
))
}
};
if !have_high {
high = v << 4;
have_high = true;
} else {
w.write_all(&[high | v])?;
have_high = false;
}
}
}
if have_high {
return Err(io::Error::new(
io::ErrorKind::InvalidData,
"odd number of hex digits in input",
));
}
Ok(())
}
/// Convenience: hex text file -> binary file (permissive).
pub fn hex_to_bin_paths(input: &Path, output: &Path) -> io::Result<()> {
let rdr = BufReader::new(File::open(input)?);
if let Some(parent) = output.parent() {
if !parent.as_os_str().is_empty() {
fs::create_dir_all(parent)?;
}
}
let wtr = BufWriter::new(File::create(output)?);
Self::hex_to_bin(rdr, wtr)
}
/// Convenience: hex text file -> binary file (strict).
pub fn hex_to_bin_paths_strict(input: &Path, output: &Path) -> io::Result<()> {
let rdr = BufReader::new(File::open(input)?);
if let Some(parent) = output.parent() {
if !parent.as_os_str().is_empty() {
fs::create_dir_all(parent)?;
}
}
let wtr = BufWriter::new(File::create(output)?);
Self::hex_to_bin_strict(rdr, wtr)
}
/// Streaming bytes -> plain hex.
///
/// - `uppercase`: A–F if true, a–f if false.
/// - `line_width_bytes`: if `Some(n)`, insert '\n' after every `n` bytes (like `xxd -p`, which
/// uses 60 by default). If `None`, writes one long line with no trailing newline.
pub fn bin_to_hex<R: Read, W: Write>(
mut r: R,
mut w: W,
uppercase: bool,
line_width_bytes: Option<usize>,
) -> io::Result<()> {
let mut buf = [0u8; 8192];
let mut line_count = 0usize;
let lut_lower = *b"0123456789abcdef";
let lut_upper = *b"0123456789ABCDEF";
let lut = if uppercase { lut_upper } else { lut_lower };
loop {
let n = r.read(&mut buf)?;
if n == 0 {
break;
}
for &byte in &buf[..n] {
let hi = (byte >> 4) as usize;
let lo = (byte & 0x0F) as usize;
w.write_all(&[lut[hi], lut[lo]])?;
line_count += 1;
if let Some(wrap) = line_width_bytes {
if wrap > 0 && line_count == wrap {
w.write_all(b"\n")?;
line_count = 0;
}
}
}
}
Ok(())
}
/// Convenience: binary file -> hex text file.
pub fn bin_to_hex_paths(
input: &Path,
output: &Path,
uppercase: bool,
line_width_bytes: Option<usize>,
) -> io::Result<()> {
let rdr = BufReader::new(File::open(input)?);
if let Some(parent) = output.parent() {
if !parent.as_os_str().is_empty() {
fs::create_dir_all(parent)?;
}
}
let mut wtr = BufWriter::new(File::create(output)?);
Self::bin_to_hex(rdr, &mut wtr, uppercase, line_width_bytes)?;
// If line wrapping was used and the last line wasn't empty, add final newline to match common tools.
if line_width_bytes.is_some() {
wtr.write_all(b"\n")?;
}
Ok(())
}
}
//
// -------- Optional CLI entrypoint (same file) --------
// Enable by compiling with the feature flag `bin`:
//
// rustc --cfg feature="bin" hexrev.rs -O -o hexrev
// or inside Cargo: cargo run --features bin -- <subcommand> ...
//
// #[cfg(feature = "bin")]
#[cfg_attr(not(test), allow(dead_code))]
pub fn main() -> io::Result<()> {
use std::env;
fn usage() -> ! {
eprintln!("Usage:");
eprintln!(" hexrev to-bin [--strict] <input_hex.txt|- > <output_bin|- >");
eprintln!(" hexrev to-hex [--upper] [--width BYTES] <input_bin|- > <output_hex|- >");
eprintln!();
eprintln!("Defaults:");
eprintln!(" to-hex width: 60 bytes per line (like `xxd -p`).");
std::process::exit(2);
}
let mut args = env::args().skip(1);
let Some(cmd) = args.next() else { usage() };
match cmd.as_str() {
"to-bin" => {
let mut strict = false;
// Parse flags (only --strict)
let mut next = args.next();
while let Some(a) = next.clone() {
if a == "--strict" {
strict = true;
next = args.next();
} else {
break;
}
}
let input = next.unwrap_or_else(|| usage());
let output = args.next().unwrap_or_else(|| usage());
if args.next().is_some() {
usage()
}
// stdin/stdout support
let reader: Box<dyn Read> = if input == "-" {
Box::new(io::stdin())
} else {
Box::new(BufReader::new(File::open(&input)?))
};
let writer: Box<dyn Write> = if output == "-" {
Box::new(io::stdout())
} else {
let p = Path::new(&output);
if let Some(parent) = p.parent() {
if !parent.as_os_str().is_empty() {
fs::create_dir_all(parent)?;
}
}
Box::new(BufWriter::new(File::create(p)?))
};
if strict {
HexRev::hex_to_bin_strict(reader, writer)
} else {
HexRev::hex_to_bin(reader, writer)
}
}
"to-hex" => {
let mut uppercase = false;
let mut width: Option<usize> = Some(60); // match xxd -p default-ish
// Parse flags: --upper, --width N
while let Some(a) = args.next() {
if a == "--upper" {
uppercase = true;
} else if a == "--width" {
let n = args.next().unwrap_or_else(|| {
eprintln!("--width requires a number");
std::process::exit(2);
});
let parsed = n.parse::<usize>().unwrap_or_else(|_| {
eprintln!("invalid width: {n}");
std::process::exit(2);
});
width = Some(parsed);
} else {
// We've reached positional args
let input = a;
let output = args.next().unwrap_or_else(|| usage());
if args.next().is_some() {
usage()
}
let reader: Box<dyn Read> = if input == "-" {
Box::new(io::stdin())
} else {
Box::new(BufReader::new(File::open(&input)?))
};
let writer: Box<dyn Write> = if output == "-" {
Box::new(io::stdout())
} else {
let p = Path::new(&output);
if let Some(parent) = p.parent() {
if !parent.as_os_str().is_empty() {
fs::create_dir_all(parent)?;
}
}
Box::new(BufWriter::new(File::create(p)?))
};
return HexRev::bin_to_hex(reader, writer, uppercase, width);
}
}
usage()
}
_ => usage(),
}
}