From 66bebb36935009ab026fe1c5ec6422a39257fcd6 Mon Sep 17 00:00:00 2001
From: jpk <jpk@goatpr0n.de>
Date: Thu, 15 Dec 2022 11:10:05 +0100
Subject: [PATCH] Support length to read

---
 src/main.rs  |  5 ++++-
 src/tohex.rs | 15 +++++++++++----
 2 files changed, 15 insertions(+), 5 deletions(-)

diff --git a/src/main.rs b/src/main.rs
index c898e9e..7958a99 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -16,6 +16,9 @@ struct Arguments {
     /// Revert a hexdump to binary
     #[arg(short, long)]
     revert: bool,
+    /// Stop after <len> octets
+    #[arg(short, long)]
+    length: Option<usize>,
 
     /// Filename to read, if left out read from stdin
     filename: Option<String>,
@@ -32,7 +35,7 @@ fn main() {
     };
 
     if !args.revert {
-        hexdump(reader);
+        hexdump(reader, args.length.unwrap());
     } else {
         let writer: Box<dyn io::Write> = Box::new(io::stdout());
         bindump(reader, writer);
diff --git a/src/tohex.rs b/src/tohex.rs
index cc3f06f..96cbeb2 100644
--- a/src/tohex.rs
+++ b/src/tohex.rs
@@ -24,22 +24,29 @@ fn dump_to_chr(bytes: &mut [u8]) -> String {
     out_vec.join("")
 }
 
-pub fn hexdump(mut reader: Box<dyn io::Read>) {
+pub fn hexdump(mut reader: Box<dyn io::Read>, length: usize) {
     let mut buf = [0; GLOBAL_BUFFER_LENGTH];
     let mut offset: usize = 0;
+    let mut bytes_left = length;
 
     loop {
         let bytes_read = reader.read(&mut buf);
         match bytes_read {
             Ok(num) => {
-                if num == 0 {
+                let mut to_read = num;
+                if num > bytes_left {
+                    to_read = bytes_left;
+                }
+                bytes_left -= to_read;
+
+                if to_read == 0 {
                     break;
                 } else {
                     println!(
                         "{:08x}: {:40}  {:10}",
                         offset,
-                        dump_to_hex(&mut buf[0..num]),
-                        dump_to_chr(&mut buf[0..num])
+                        dump_to_hex(&mut buf[0..to_read]),
+                        dump_to_chr(&mut buf[0..to_read])
                     );
                     offset += GLOBAL_BUFFER_LENGTH;
                 }