rust 42 lines · 9 steps

Parsing INI files in Rust

A streaming parser that reads an INI file line by line into a nested map of sections and key-value pairs.

Explained by highlit

Intermediate parsing file-io hashmap error-handling iterators

1use std::collections::HashMap;
2use std::fs::File;
3use std::io::{self, BufRead, BufReader};
4use std::path::Path;
5 
6type Ini = HashMap<String, HashMap<String, String>>;
7 
8pub fn parse_ini<P: AsRef<Path>>(path: P) -> io::Result<Ini> {
9    let reader = BufReader::new(File::open(path)?);
10    let mut sections: Ini = HashMap::new();
11    let mut current = String::new();
12    sections.entry(current.clone()).or_default();
13 
14    for line in reader.lines() {
15        let line = line?;
16        let trimmed = line.trim();
17 
18        if trimmed.is_empty() || trimmed.starts_with('#') || trimmed.starts_with(';') {
19            continue;
20        }
21 
22        if let Some(name) = trimmed.strip_prefix('[').and_then(|s| s.strip_suffix(']')) {
23            current = name.trim().to_string();
24            sections.entry(current.clone()).or_default();
25            continue;
26        }
27 
28        if let Some((key, value)) = trimmed.split_once('=') {
29            let value = value.trim();
30            let value = value
31                .strip_prefix('"')
32                .and_then(|v| v.strip_suffix('"'))
33                .unwrap_or(value);
34            sections
35                .get_mut(&current)
36                .unwrap()
37                .insert(key.trim().to_string(), value.to_string());
38        }
39    }
40 
41    Ok(sections)
42}

01 / 01

STEP 01

Walkthrough

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Three takeaways

1Tracking a mutable current-section string lets a flat line loop build a nested structure.
2The ? operator threads I/O failures out cleanly so the parser body stays focused on parsing.
3or_default and get_mut give ergonomic insert-or-fetch access to nested HashMaps without manual existence checks.

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