Basically, for when Regex is overkill and you just want to extract substrings between deterministic start and end patterns. This Rust function will find every occurrence of a matching start/end pattern and return the contents in between.

extract.rs

pub fn extract(input: &str, pattern_start: &str, pattern_end: &str) -> Vec<String> {
    let mut matches = Vec::new();
    let mut position = 0;

    while let Some(match_index) = input[position..].find(pattern_start) {
        let start_index = position + match_index;
        position = start_index + pattern_start.len();

        if let Some(match_index) = input[position..].find(pattern_end) {
            let end_index = position + match_index;
            matches.push(input[position..end_index].to_string());
            position = end_index + pattern_end.len();
        } else {
            break;
        }
    }

    matches
}

when_regex_is_overkill.rs

fn main() {
    let some_html = dont_ask_where_it_came_from();
    let links = extract(some_html, "<a href=\"", "\"");
  
    for link in links {
        println!("You've now got links from HTML! {}", link);
    }
}