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
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
/// DNS name validation according to RFC1035, but with underscores allowed.
use std::error::Error as StdError;
use std::fmt;

/// A type which encapsulates an owned string that is a syntactically valid DNS name.
#[derive(Clone, Eq, Hash, PartialEq, Debug)]
pub struct DnsName(String);

impl<'a> DnsName {
    /// Produce a borrowed `DnsNameRef` from this owned `DnsName`.
    pub fn borrow(&'a self) -> DnsNameRef<'a> {
        DnsNameRef(self.as_ref())
    }

    /// Validate the given bytes are a DNS name if they are viewed as ASCII.
    pub fn try_from_ascii(bytes: &[u8]) -> Result<Self, InvalidDnsNameError> {
        // nb. a sequence of bytes that is accepted by `validate()` is both
        // valid UTF-8, and valid ASCII.
        String::from_utf8(bytes.to_vec())
            .map_err(|_| InvalidDnsNameError)
            .and_then(Self::try_from)
    }
}

impl TryFrom<String> for DnsName {
    type Error = InvalidDnsNameError;

    fn try_from(value: String) -> Result<Self, Self::Error> {
        validate(value.as_bytes())?;
        Ok(Self(value))
    }
}

impl AsRef<str> for DnsName {
    fn as_ref(&self) -> &str {
        AsRef::<str>::as_ref(&self.0)
    }
}

/// A type which encapsulates a borrowed string that is a syntactically valid DNS name.
#[derive(Eq, Hash, PartialEq, Debug)]
pub struct DnsNameRef<'a>(&'a str);

impl<'a> DnsNameRef<'a> {
    /// Copy this object to produce an owned `DnsName`.
    pub fn to_owned(&'a self) -> DnsName {
        DnsName(self.0.to_string())
    }

    /// Copy this object to produce an owned `DnsName`, smashing the case to lowercase
    /// in one operation.
    pub fn to_lowercase_owned(&'a self) -> DnsName {
        DnsName(self.0.to_lowercase())
    }
}

impl<'a> TryFrom<&'a str> for DnsNameRef<'a> {
    type Error = InvalidDnsNameError;

    fn try_from(value: &'a str) -> Result<Self, Self::Error> {
        validate(value.as_bytes())?;
        Ok(DnsNameRef(value))
    }
}

impl<'a> AsRef<str> for DnsNameRef<'a> {
    fn as_ref(&self) -> &str {
        self.0
    }
}

/// The provided input could not be parsed because
/// it is not a syntactically-valid DNS Name.
#[derive(Debug)]
pub struct InvalidDnsNameError;

impl fmt::Display for InvalidDnsNameError {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        f.write_str("invalid dns name")
    }
}

impl StdError for InvalidDnsNameError {}

fn validate(input: &[u8]) -> Result<(), InvalidDnsNameError> {
    use State::*;
    let mut state = Start;

    /// "Labels must be 63 characters or less."
    const MAX_LABEL_LENGTH: usize = 63;

    /// https://devblogs.microsoft.com/oldnewthing/20120412-00/?p=7873
    const MAX_NAME_LENGTH: usize = 253;

    if input.len() > MAX_NAME_LENGTH {
        return Err(InvalidDnsNameError);
    }

    for ch in input {
        state = match (state, ch) {
            (Start | Next | NextAfterNumericOnly | Hyphen { .. }, b'.') => {
                return Err(InvalidDnsNameError)
            }
            (Subsequent { .. }, b'.') => Next,
            (NumericOnly { .. }, b'.') => NextAfterNumericOnly,
            (Subsequent { len } | NumericOnly { len } | Hyphen { len }, _)
                if len >= MAX_LABEL_LENGTH =>
            {
                return Err(InvalidDnsNameError)
            }
            (Start | Next | NextAfterNumericOnly, b'0'..=b'9') => NumericOnly { len: 1 },
            (NumericOnly { len }, b'0'..=b'9') => NumericOnly { len: len + 1 },
            (Start | Next | NextAfterNumericOnly, b'a'..=b'z' | b'A'..=b'Z' | b'_') => {
                Subsequent { len: 1 }
            }
            (Subsequent { len } | NumericOnly { len } | Hyphen { len }, b'-') => {
                Hyphen { len: len + 1 }
            }
            (
                Subsequent { len } | NumericOnly { len } | Hyphen { len },
                b'a'..=b'z' | b'A'..=b'Z' | b'_' | b'0'..=b'9',
            ) => Subsequent { len: len + 1 },
            _ => return Err(InvalidDnsNameError),
        };
    }

    if matches!(
        state,
        Start | Hyphen { .. } | NumericOnly { .. } | NextAfterNumericOnly
    ) {
        return Err(InvalidDnsNameError);
    }

    Ok(())
}

enum State {
    Start,
    Next,
    NumericOnly { len: usize },
    NextAfterNumericOnly,
    Subsequent { len: usize },
    Hyphen { len: usize },
}

#[cfg(test)]
mod test {
    static TESTS: &[(&str, bool)] = &[
        ("", false),
        ("localhost", true),
        ("LOCALHOST", true),
        (".localhost", false),
        ("..localhost", false),
        ("1.2.3.4", false),
        ("127.0.0.1", false),
        ("absolute.", true),
        ("absolute..", false),
        ("multiple.labels.absolute.", true),
        ("foo.bar.com", true),
        ("infix-hyphen-allowed.com", true),
        ("-prefixhypheninvalid.com", false),
        ("suffixhypheninvalid--", false),
        ("suffixhypheninvalid-.com", false),
        ("foo.lastlabelendswithhyphen-", false),
        ("infix_underscore_allowed.com", true),
        ("_prefixunderscorevalid.com", true),
        ("labelendswithnumber1.bar.com", true),
        ("xn--bcher-kva.example", true),
        (
            "sixtythreesixtythreesixtythreesixtythreesixtythreesixtythreesix.com",
            true,
        ),
        (
            "sixtyfoursixtyfoursixtyfoursixtyfoursixtyfoursixtyfoursixtyfours.com",
            false,
        ),
        (
            "012345678901234567890123456789012345678901234567890123456789012.com",
            true,
        ),
        (
            "0123456789012345678901234567890123456789012345678901234567890123.com",
            false,
        ),
        (
            "01234567890123456789012345678901234567890123456789012345678901-.com",
            false,
        ),
        (
            "012345678901234567890123456789012345678901234567890123456789012-.com",
            false,
        ),
        ("numeric-only-final-label.1", false),
        ("numeric-only-final-label.absolute.1.", false),
        ("1starts-with-number.com", true),
        ("1Starts-with-number.com", true),
        ("1.2.3.4.com", true),
        ("123.numeric-only-first-label", true),
        ("a123b.com", true),
        ("numeric-only-middle-label.4.com", true),
        ("1000-sans.badssl.com", true),
        ("twohundredandfiftythreecharacters.twohundredandfiftythreecharacters.twohundredandfiftythreecharacters.twohundredandfiftythreecharacters.twohundredandfiftythreecharacters.twohundredandfiftythreecharacters.twohundredandfiftythreecharacters.twohundredandfi", true),
        ("twohundredandfiftyfourcharacters.twohundredandfiftyfourcharacters.twohundredandfiftyfourcharacters.twohundredandfiftyfourcharacters.twohundredandfiftyfourcharacters.twohundredandfiftyfourcharacters.twohundredandfiftyfourcharacters.twohundredandfiftyfourc", false),
    ];

    #[test]
    fn test_validation() {
        for (input, expected) in TESTS {
            println!("test: {:?} expected valid? {:?}", input, expected);
            let name_ref = super::DnsNameRef::try_from(*input);
            assert_eq!(*expected, name_ref.is_ok());
            let name = super::DnsName::try_from(input.to_string());
            assert_eq!(*expected, name.is_ok());
        }
    }

    #[test]
    fn error_is_debug() {
        assert_eq!(
            format!("{:?}", super::InvalidDnsNameError),
            "InvalidDnsNameError"
        );
    }

    #[test]
    fn error_is_display() {
        assert_eq!(
            format!("{}", super::InvalidDnsNameError),
            "invalid dns name"
        );
    }

    #[test]
    fn dns_name_is_debug() {
        let example = super::DnsName::try_from("example.com".to_string()).unwrap();
        assert_eq!(format!("{:?}", example), "DnsName(\"example.com\")");
    }

    #[test]
    fn dns_name_traits() {
        let example = super::DnsName::try_from("example.com".to_string()).unwrap();
        assert_eq!(example, example); // PartialEq

        use std::collections::HashSet;
        let mut h = HashSet::<super::DnsName>::new();
        h.insert(example);
    }

    #[test]
    fn try_from_ascii_rejects_bad_utf8() {
        assert_eq!(
            format!("{:?}", super::DnsName::try_from_ascii(b"\x80")),
            "Err(InvalidDnsNameError)"
        );
    }

    #[test]
    fn dns_name_ref_is_debug() {
        let example = super::DnsNameRef::try_from("example.com").unwrap();
        assert_eq!(format!("{:?}", example), "DnsNameRef(\"example.com\")");
    }

    #[test]
    fn dns_name_ref_traits() {
        let example = super::DnsNameRef::try_from("example.com").unwrap();
        assert_eq!(example, example); // PartialEq

        use std::collections::HashSet;
        let mut h = HashSet::<super::DnsNameRef>::new();
        h.insert(example);
    }
}