Crate fmtbuf

fmtbuf

This library is intended to help write formatted text to fixed buffers.

use fmtbuf::WriteBuf;
use std::fmt::Write;

let mut buf: [u8; 10] = [0; 10];
let mut writer = WriteBuf::new(&mut buf);
if let Err(e) = write!(&mut writer, "🚀🚀🚀") {
    println!("write error: {e:?}");
}
let written_len = match writer.finish_with_or("!", "…") {
    Ok(len) => len, // <- won't be hit since 🚀🚀🚀 is 12 bytes
    Err(len) => {
        println!("writing was truncated");
        len
    }
};
let written = &buf[..written_len];
assert_eq!("🚀…", std::str::from_utf8(written).unwrap());

A few things happened in that example:

1. We stared with a 10 byte buffer
2. Tried to write "🚀🚀🚀" to it, which is encoded as 3 b"\xf0\x9f\x9a\x80"s (12 bytes)
3. This can’t fit into 10 bytes, so only "🚀🚀" is stored and the writer is noted as having truncated writes
4. We finish the buffer with "!" on success or "…" (a.k.a. b"\xe2\x80\xa6") on truncation
5. Since we noted truncation in step #3, we try to write "…", but this can not fit into the buffer either, since 8 ("🚀🚀".len()) + 3 ("…".len()) > 12 (buf.len())
6. Roll the buffer back to the end of the first 🚀, then add …, leaving us with "🚀…"

Structs

WriteBuf

A write buffer pointing to a &mut [u8].

Functions

rfind_utf8_end

Find the end of the last valid UTF-8 code point.