version 0.1.7: add comment display utility

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "leangz"
-version = "0.1.6"
+version = "0.1.7"
 edition = "2021"
 default-run = "leangz"
 

src/ltar.rs

@@ -3,9 +3,7 @@ use byteorder::WriteBytesExt;
 use byteorder::LE;
 use memmap2::Mmap;
 use std::fs::File;
-use std::io;
-use std::io::BufRead;
-use std::io::Write;
+use std::io::{self, BufRead, Seek, Write};
 use std::path::{Path, PathBuf};
 
 use crate::lgz;
@@ -155,3 +153,34 @@ pub fn pack(
   }
   Ok(())
 }
+
+pub fn comments<R: BufRead + Seek>(mut tarfile: R) -> Result<Vec<String>, UnpackError> {
+  let mut buf = vec![0; 4];
+  tarfile.read_exact(&mut buf)?;
+  if buf != *b"LTAR" {
+    return Err(UnpackError::BadLtar)
+  }
+  tarfile.read_u64::<LE>()?;
+  let read_cstr = |buf: &mut Vec<_>, tarfile: &mut R| -> Result<bool, UnpackError> {
+    buf.clear();
+    tarfile.read_until(0, buf)?;
+    Ok(buf.pop().is_some())
+  };
+  if !read_cstr(&mut buf, &mut tarfile)? {
+    return Err(UnpackError::BadLtar)
+  }
+  let mut comments = vec![];
+  while read_cstr(&mut buf, &mut tarfile)? {
+    if buf.is_empty() {
+      if !read_cstr(&mut buf, &mut tarfile)? {
+        return Err(UnpackError::BadLtar)
+      }
+      comments.push(std::str::from_utf8(&buf)?.to_string());
+      continue
+    }
+    tarfile.read_u8()?;
+    let len = tarfile.read_u64::<LE>()?;
+    tarfile.seek(io::SeekFrom::Current(len as _))?;
+  }
+  Ok(comments)
+}

src/tar.rs

@@ -10,6 +10,7 @@ use std::sync::atomic::AtomicBool;
 fn main() {
   let help = || panic!("usage: leantar [-v] [-d|-x] [-C BASEDIR] OUT.ltar FILE.trace [FILE ...]");
   let mut do_decompress = false;
+  let mut do_show_comments = false;
   let mut verbose = false;
   let mut force = false;
   let mut from_stdin = false;
@@ -51,11 +52,34 @@ fn main() {
           help();
         }
       }
+      "-k" => {
+        do_show_comments = true;
+        args.next();
+      }
       _ => break,
     }
   }
   let basedir = PathBuf::from(basedir.unwrap_or_else(|| ".".into()));
-  if do_decompress {
+  if do_show_comments {
+    let file = args.next().unwrap_or_else(help);
+    let tarfile = match File::open(&file) {
+      Err(e) if e.kind() == std::io::ErrorKind::NotFound => {
+        eprintln!("{file} not found");
+        std::process::exit(1);
+      }
+      e => BufReader::new(e.unwrap()),
+    };
+    match ltar::comments(tarfile) {
+      Err(e) => {
+        eprintln!("{e}");
+        std::process::exit(1);
+      }
+      Ok(comments) =>
+        for comment in comments {
+          println!("{comment}")
+        },
+    }
+  } else if do_decompress {
     let mut args_vec = vec![];
     for arg in args {
       if arg == "-" {