Escape DEL character as \u007f

[sashka]

No description provided.

[dtolnay]

Is there any more context you could provide on this change?

[sashka]

I'm working on a translator for huge machine readable XML to human readable (and editable) JSON and back again. A part of this XML is a hardware keyboard layout, so the user have to be able to see and edit unprintable characters. The most annoying is in my case is the DEL char, which is used pretty broadly.

With this patch I'm trying to fix an extremely specific use case (thousands of cases per file) without breaking anything to the rest of library users.

It'd be great to have a formatter with customizable escape table, but I'm not that good Rust developer so far.

[dtolnay]

You should plug in a formatter that escapes exactly what you want escaped. Something like the following. You can delegate the other Formatter methods to serde_json::ser::PrettyFormatter if you also want indentation.

use serde::Serialize;
use serde_json::json;
use serde_json::ser::CharEscape;
use std::io::{self, Write};

struct EscapedDelFormatter;

impl serde_json::ser::Formatter for EscapedDelFormatter {
    fn write_string_fragment<W>(&mut self, writer: &mut W, fragment: &str) -> io::Result<()>
    where
        W: ?Sized + Write,
    {
        for (i, fragment) in fragment.split('\x7f').enumerate() {
            if i > 0 {
                self.write_char_escape(writer, CharEscape::AsciiControl(0x7f))?;
            }
            writer.write_all(fragment.as_bytes())?;
        }
        Ok(())
    }
}

fn main() {
    let value = json!({ "thing": "as\x7fdf" });
    let mut buf = Vec::new();
    let mut ser = serde_json::Serializer::with_formatter(&mut buf, EscapedDelFormatter);
    value.serialize(&mut ser).unwrap();
    buf.push(b'\n');
    io::stdout().write_all(&buf).unwrap();
}