Created
February 20, 2023 01:56
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| use std::{ | |
| io::{Cursor, Seek, SeekFrom}, | |
| ops::RangeBounds, | |
| }; | |
| /// Tries to get a UTF-8 string from the given buffer at the provided range. | |
| fn str_from_utf8_range(buf: &[u8], range: impl RangeBounds<usize>) -> Option<&str> { | |
| buf.get((range.start_bound().cloned(), range.end_bound().cloned())) | |
| .map(|slice| std::str::from_utf8(slice).expect("valid utf8")) | |
| } | |
| /// Returns the remaining slice as a string slice. Panics if encounters invalid | |
| /// UTF-8 bytes. | |
| fn rem_str<T: AsRef<[u8]>>(cur: &mut Cursor<T>) -> Option<&str> { | |
| str_from_utf8_range(cur.get_ref().as_ref(), (cur.position() as usize)..) | |
| } | |
| /// Gets `n` bytes from the cursor and advances `n`. Panics if the underlying | |
| /// value doesn't have enough capacity for a +n seek. | |
| fn get_str<T: AsRef<[u8]>>(cur: &mut Cursor<T>, n: usize) -> String { | |
| let buf = cur.get_ref().as_ref(); | |
| let hi = cur.position() as usize + n; | |
| assert!(hi <= buf.len()); // high bound must be within buf's bounds | |
| let eaten = str_from_utf8_range(buf, (cur.position() as usize)..hi) | |
| // SAFETY: The assertion above ensures one is always within bounds. | |
| .unwrap() | |
| .to_owned(); | |
| // SAFETY: No I/O is involved. | |
| cur.seek(SeekFrom::Current(n as i64)).unwrap(); | |
| eaten | |
| } | |
| fn main() { | |
| let buf = b"hello world"; | |
| let mut cur = Cursor::new(buf); | |
| println!("remaining is [{:?}]", rem_str(&mut cur)); | |
| println!( | |
| "got [{}], remaining is [{:?}]", | |
| get_str(&mut cur, 5), | |
| rem_str(&mut cur) | |
| ); | |
| println!( | |
| "got [{}], remaining is [{:?}]", | |
| get_str(&mut cur, 1), | |
| rem_str(&mut cur) | |
| ); | |
| println!( | |
| "got [{}], remaining is [{:?}]", | |
| get_str(&mut cur, 5), | |
| rem_str(&mut cur) | |
| ); | |
| println!( | |
| "got [{}], remaining is [{:?}]", | |
| get_str(&mut cur, 0), | |
| rem_str(&mut cur) | |
| ); | |
| // Assuming one never seeks past the end of the buffer, `rem_str` will | |
| // always return `Some("")`. | |
| } |
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