A simple txtar parser for Rust

A simple implementation of the go txtar package: a trivial text-based file archive format.

Taken from the original go txtar docs:

The goals for the format are:

• be trivial enough to create and edit by hand.
• be able to store trees of text files describing go command test cases.
• diff nicely in git history and code reviews.

Non-goals include being a completely general archive format, storing binary data, storing file modes, storing special files like symbolic links, and so on.

Txtar format

A txtar archive is zero or more comment lines and then a sequence of file entries. Each file entry begins with a file marker line of the form "-- FILENAME --" and is followed by zero or more file content lines making up the file data. The comment or file content ends at the next file marker line. The file marker line must begin with the three-byte sequence "-- " and end with the three-byte sequence " --", but the enclosed file name can be surrounding by additional white space, all of which is stripped.

If the txtar file is missing a trailing newline on the final line, parsers should consider a final newline to be present anyway.

There are no possible syntax errors in a txtar archive.

Example usage

use simple_txtar::Archive;

let s = r#"All text before the first file entry is considered a comment.

Until we have the first file marker this is still part
of the comment.
-- example.json --
{
  "foo": 1,
  "bar": [ "baz" ]
}
-- example.txt --
Some example text in a separate file from the example json.
"#;

let a = Archive::from(s);

assert_eq!(
    a.comment().lines().next(),
    Some("All text before the first file entry is considered a comment.")
);
assert_eq!(a.comment().lines().last(), Some("of the comment."));

// Files can be accessed using indexing or the `get` method
assert_eq!(Some(&a[0]), a.get("example.json"));

// The Archive itself is also an iterator over the Files it contains
let mut it = a.iter();
assert_eq!(
    it.next().unwrap().name,
    "example.json"
);
assert_eq!(
    it.next().unwrap().content,
    "Some example text in a separate file from the example json.\n"
);