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

/// An error that occurs when parsing a human readable size description.
///
/// This error provides an end user friendly message describing why the
/// description couldn't be parsed and what the expected format is.
#[derive(Clone, Debug, Eq, PartialEq)]
pub struct ParseSizeError {
    original: String,
    kind: ParseSizeErrorKind,
}

#[derive(Clone, Debug, Eq, PartialEq)]
enum ParseSizeErrorKind {
    InvalidFormat,
    InvalidInt(std::num::ParseIntError),
    Overflow,
}

impl ParseSizeError {
    fn format(original: &str) -> ParseSizeError {
        ParseSizeError {
            original: original.to_string(),
            kind: ParseSizeErrorKind::InvalidFormat,
        }
    }

    fn int(original: &str, err: std::num::ParseIntError) -> ParseSizeError {
        ParseSizeError {
            original: original.to_string(),
            kind: ParseSizeErrorKind::InvalidInt(err),
        }
    }

    fn overflow(original: &str) -> ParseSizeError {
        ParseSizeError {
            original: original.to_string(),
            kind: ParseSizeErrorKind::Overflow,
        }
    }
}

impl std::error::Error for ParseSizeError {}

impl std::fmt::Display for ParseSizeError {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        use self::ParseSizeErrorKind::*;

        match self.kind {
            InvalidFormat => write!(
                f,
                "invalid format for size '{}', which should be a non-empty \
                 sequence of digits followed by an optional 'K', 'M' or 'G' \
                 suffix",
                self.original
            ),
            InvalidInt(ref err) => write!(
                f,
                "invalid integer found in size '{}': {}",
                self.original, err
            ),
            Overflow => write!(f, "size too big in '{}'", self.original),
        }
    }
}

impl From<ParseSizeError> for std::io::Error {
    fn from(size_err: ParseSizeError) -> std::io::Error {
        std::io::Error::new(std::io::ErrorKind::Other, size_err)
    }
}

/// Parse a human readable size like `2M` into a corresponding number of bytes.
///
/// Supported size suffixes are `K` (for kilobyte), `M` (for megabyte) and `G`
/// (for gigabyte). If a size suffix is missing, then the size is interpreted
/// as bytes. If the size is too big to fit into a `u64`, then this returns an
/// error.
///
/// Additional suffixes may be added over time.
pub fn parse_human_readable_size(size: &str) -> Result<u64, ParseSizeError> {
    let digits_end =
        size.as_bytes().iter().take_while(|&b| b.is_ascii_digit()).count();
    let digits = &size[..digits_end];
    if digits.is_empty() {
        return Err(ParseSizeError::format(size));
    }
    let value =
        digits.parse::<u64>().map_err(|e| ParseSizeError::int(size, e))?;

    let suffix = &size[digits_end..];
    if suffix.is_empty() {
        return Ok(value);
    }
    let bytes = match suffix {
        "K" => value.checked_mul(1 << 10),
        "M" => value.checked_mul(1 << 20),
        "G" => value.checked_mul(1 << 30),
        _ => return Err(ParseSizeError::format(size)),
    };
    bytes.ok_or_else(|| ParseSizeError::overflow(size))
}

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

    #[test]
    fn suffix_none() {
        let x = parse_human_readable_size("123").unwrap();
        assert_eq!(123, x);
    }

    #[test]
    fn suffix_k() {
        let x = parse_human_readable_size("123K").unwrap();
        assert_eq!(123 * (1 << 10), x);
    }

    #[test]
    fn suffix_m() {
        let x = parse_human_readable_size("123M").unwrap();
        assert_eq!(123 * (1 << 20), x);
    }

    #[test]
    fn suffix_g() {
        let x = parse_human_readable_size("123G").unwrap();
        assert_eq!(123 * (1 << 30), x);
    }

    #[test]
    fn invalid_empty() {
        assert!(parse_human_readable_size("").is_err());
    }

    #[test]
    fn invalid_non_digit() {
        assert!(parse_human_readable_size("a").is_err());
    }

    #[test]
    fn invalid_overflow() {
        assert!(parse_human_readable_size("9999999999999999G").is_err());
    }

    #[test]
    fn invalid_suffix() {
        assert!(parse_human_readable_size("123T").is_err());
    }
}