How to trim a BytesMut from bytes crate?

Question

Suppose I have a BytesMut, I want to be able to make it trim_bytes.

let some_bytes = BytesMut::from("  hello world  ");
let trim_bytes = some_bytes.some_trim_method();
// trim_bytes = BytesMut::From("hello world");

some_trim_method() is what I've been looking for but there isn't such method in crate.

There is the [`trim_ascii`](https://doc.rust-lang.org/std/primitive.slice.html#method.trim_ascii) method, but it is still unstable and requires nightly. [Here](https://play.rust-lang.org/?version=nightly&mode=debug&edition=2021&gist=243f815139fd6247abfd21d5a0b30150) an exmaple of how to use `trim_ascii`. If you want it to work on stable, I think you'd have to convert `BytesMut` to a `String` first and call [`trim`](https://doc.rust-lang.org/std/string/struct.String.html#method.trim) on it. — Jonas Fassbender, Feb 23 '23 at 16:47
That only works if the bytesmut is correctly encoded such that it is able to parse to String. Also it can be expensive. — realzhujunhao, Feb 24 '23 at 04:12

Chandan · Accepted Answer · 2023-02-24T14:02:11.257

You can also create your own version of trim function for bytes

const TAB: &u8 = &b'\t';
const SPACE: &u8 = &b' ';

fn is_whitespace(c: &u8) -> bool {
    c == TAB || c == SPACE
}

fn is_not_whitespace(c: &u8) -> bool {
    !is_whitespace(c)
}

fn trim_bytes(s: &[u8]) -> &[u8] {
  let l = s.len();
  let (mut i, mut j, mut k) = (0, l - 1, 0);
  loop {
      if (is_not_whitespace(&s[i]) && is_not_whitespace(&s[j])) || i > j || k >= l {
          break;
      }

      if is_whitespace(&s[i]) {
          i += 1;
      }

      if is_whitespace(&s[j]) {
          j -= 1;
      }

      k += 1
  }
  return &s[i..=j];
}

fn main() {
    let result = trim_bytes(&some_bytes);
    println!("{:?}", result);
    assert_eq!(b"hello world", result);
}

or implement trim method on byte type

trait TrimBytes {
    fn trim(&self) -> &Self;
}

impl TrimBytes for [u8] {
    fn trim(&self) -> &[u8] {
        if let Some(first) = self.iter().position(is_not_whitespace) {
            if let Some(last) = self.iter().rposition(is_not_whitespace) {
                &self[first..last + 1]
            } else {
                unreachable!();
            }
        } else {
            &[]
        }
    }
}

fn main() {
    let result = some_bytes.trim();
    println!("{:?}", result);
    assert_eq!(b"hello world", result);
}

How to trim a BytesMut from bytes crate?

1 Answers1