oro_pretty_json/
lib.rs

1//! Utility for pretty printing JSON while preserving the order of keys and
2//! the original indentation and line endings from a JSON source.
3
4use serde_json::{Error, Value};
5
6#[derive(Debug, PartialEq, Eq)]
7pub struct Formatted {
8    pub value: Value,
9    pub character: char,
10    pub count: usize,
11    pub line_end: String,
12    pub trailing_line_end: bool,
13}
14
15pub fn from_str(json: impl AsRef<str>) -> Result<Formatted, Error> {
16    let json = json.as_ref();
17    let value = serde_json::from_str(json)?;
18    let (character, count) = detect_indentation(json).unwrap_or((' ', 2));
19    let (line_end, trailing_line_end) = detect_line_end(json).unwrap_or(("\n".into(), false));
20    Ok(Formatted {
21        value,
22        character,
23        count,
24        line_end,
25        trailing_line_end,
26    })
27}
28
29pub fn to_string_pretty(formatted: &Formatted) -> Result<String, Error> {
30    let json = serde_json::to_string_pretty(&formatted.value)?;
31    let mut ret = String::new();
32    let mut past_first_line = false;
33    for line in json.lines() {
34        if past_first_line {
35            ret.push_str(&formatted.line_end);
36        } else {
37            past_first_line = true;
38        }
39        let indent_chars = line.find(|c: char| !is_json_whitespace(c)).unwrap_or(0);
40        ret.push_str(
41            &formatted
42                .character
43                .to_string()
44                .repeat(formatted.count * (indent_chars / 2)),
45        );
46        ret.push_str(&line[indent_chars..]);
47    }
48    if formatted.trailing_line_end {
49        ret.push_str(&formatted.line_end);
50    }
51    Ok(ret)
52}
53
54fn detect_indentation(json: &str) -> Option<(char, usize)> {
55    let mut lines = json.lines();
56    lines.next()?;
57    let second_line = lines.next()?;
58    let mut indent = 0;
59    let mut character = None;
60    let mut last_whitespace_char = None;
61    for c in second_line.chars() {
62        if is_json_whitespace(c) {
63            indent += 1;
64            last_whitespace_char = Some(c);
65        } else {
66            character = last_whitespace_char;
67            break;
68        }
69    }
70    character.map(|c| (c, indent))
71}
72
73fn detect_line_end(json: &str) -> Option<(String, bool)> {
74    json.find(['\r', '\n'])
75        .map(|idx| {
76            let c = json
77                .get(idx..idx + 1)
78                .expect("we already know there's a char there");
79            if c == "\r" && json.get(idx..idx + 2) == Some("\r\n") {
80                return "\r\n".into();
81            }
82            c.into()
83        })
84        .map(|end| (end, matches!(json.chars().last(), Some('\n' | '\r'))))
85}
86
87fn is_json_whitespace(c: char) -> bool {
88    matches!(c, ' ' | '\t' | '\r' | '\n')
89}
90
91#[cfg(test)]
92mod tests {
93    use super::Formatted;
94
95    #[test]
96    fn basic() -> Result<(), serde_json::Error> {
97        let json = "{\n      \"a\": 1,\n      \"b\": 2\n}";
98        let ind = super::from_str(json)?;
99
100        assert_eq!(
101            ind,
102            Formatted {
103                value: serde_json::json!({
104                    "a": 1,
105                    "b": 2
106                }),
107                character: ' ',
108                count: 6,
109                line_end: "\n".into(),
110                trailing_line_end: false,
111            }
112        );
113
114        assert_eq!(super::to_string_pretty(&ind)?, json);
115
116        let json = "{\r\n\t\"a\": 1,\r\n\t\"b\": 2\r\n}\r\n";
117        let ind = super::from_str(json)?;
118
119        assert_eq!(
120            ind,
121            Formatted {
122                value: serde_json::json!({
123                    "a": 1,
124                    "b": 2
125                }),
126                character: '\t',
127                count: 1,
128                line_end: "\r\n".into(),
129                trailing_line_end: true,
130            }
131        );
132
133        Ok(())
134    }
135}
oro_pretty_json/lib.rs

oro_pretty_json/
lib.rs
