1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165

#![cfg_attr(docsrs, feature(doc_cfg))]

#[cfg_attr(docsrs, doc(cfg(feature = "const-format")))]
#[cfg(feature = "const-format")]
pub use fhtml_macros::formatcp;
pub use fhtml_macros::write;

#[doc(hidden)]
pub mod _internal {
    #[cfg(feature = "const-format")]
    pub use ::const_format::*;
}

/// Writes formatted HTML to a `String`.
///
/// Similar to [`std::format!`], this macro returns an owned `String` with the
/// formatted content.
///
/// The syntax and overall behaviour is identical to [`fhtml::write!`], where
/// more detailed documentation can be found.
///
/// [`std::format!`]: std::format
/// [`fhtml::write!`]: crate::write
///
/// # Examples
///
/// ## Simple usage
///
/// ```rust
/// fhtml::format!(<div>"Hello, World!"</div>); // "<div>Hello, World!</div>"
/// ```
#[macro_export]
macro_rules! format {
    ($($t:tt)*) => {{
        use ::std::fmt::Write;

        let mut output = String::new();
        let _ = $crate::write!(output, $($t)*);
        output
    }};
}

/// Escapes special HTML characters in a string.
///
/// This function takes an input string and replaces certain characters with
/// their corresponding HTML escape sequences. The following characters are
/// escaped:
///
/// - `&` becomes `&amp;`
/// - `<` becomes `&lt;`
/// - `>` becomes `&gt;`
/// - `"` becomes `&quot;`
/// - `'` becomes `&#39;`
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// let raw = "Hello, <world> & 'friends'";
/// let escaped = fhtml::escape(raw);
/// assert_eq!(escaped, "Hello, &lt;world&gt; &amp; &#39;friends&#39;");
/// ```
///
/// This is useful for preventing HTML injection attacks when displaying
/// untrusted input in a web page.
///
/// # Parameters
///
/// - `input`: A value that can be converted to a string slice (`&str`). This
///   includes `String` and `&str`.
///
/// # Returns
///
/// A `String` with the special HTML characters replaced by their escape
/// sequences.
///
/// # Performance
///
/// The function preallocates a `String` with the same length as the input,
/// which could save some reallocation costs if the input contains few
/// characters that need to be escaped.
#[inline]
pub fn escape<T: AsRef<str>>(input: T) -> String {
    let input = input.as_ref();
    let mut escaped = String::with_capacity(input.len());
    for c in input.chars() {
        match c {
            '&' => escaped.push_str("&amp;"),
            '<' => escaped.push_str("&lt;"),
            '>' => escaped.push_str("&gt;"),
            '"' => escaped.push_str("&quot;"),
            '\'' => escaped.push_str("&#39;"),
            _ => escaped.push(c),
        }
    }
    escaped
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn escape_ampersand() {
        assert_eq!(escape("&"), "&amp;");
        assert_eq!(escape("This & that"), "This &amp; that");
    }

    #[test]
    fn escape_less_than() {
        assert_eq!(escape("<"), "&lt;");
        assert_eq!(escape("a < b"), "a &lt; b");
    }

    #[test]
    fn escape_greater_than() {
        assert_eq!(escape(">"), "&gt;");
        assert_eq!(escape("a > b"), "a &gt; b");
    }

    #[test]
    fn escape_double_quote() {
        assert_eq!(escape("\""), "&quot;");
        assert_eq!(escape("She said \"hello\""), "She said &quot;hello&quot;");
    }

    #[test]
    fn escape_single_quote() {
        assert_eq!(escape("'"), "&#39;");
        assert_eq!(escape("It's a test"), "It&#39;s a test");
    }

    #[test]
    fn escape_multiple_special_chars() {
        assert_eq!(
            escape("<div> & \"text\""),
            "&lt;div&gt; &amp; &quot;text&quot;"
        );
        assert_eq!(escape("5 > 3 & 2 < 4"), "5 &gt; 3 &amp; 2 &lt; 4");
    }

    #[test]
    fn escape_no_special_chars() {
        assert_eq!(escape("Hello, world!"), "Hello, world!");
        assert_eq!(escape("Rust programming"), "Rust programming");
    }

    #[test]
    fn escape_empty_string() {
        assert_eq!(escape(""), "");
    }

    #[test]
    fn escape_mixed_input() {
        assert_eq!(
            escape("The price is 5 > 4 & 3 < 6"),
            "The price is 5 &gt; 4 &amp; 3 &lt; 6"
        );
        assert_eq!(
            escape("Use 'single' and \"double\" quotes"),
            "Use &#39;single&#39; and &quot;double&quot; quotes"
        );
    }
}