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
use serde::{Deserialize, Deserializer};

/// This helper function enables successful deserialization of versioned structs; new structs may
/// include additional fields if they impl Default and are added to the end of the struct. Right
/// now, this function is targeted at `bincode` deserialization; the error match may need to be
/// updated if another package needs to be used in the future.
pub fn default_on_eof<'de, T, D>(d: D) -> Result<T, D::Error>
where
    D: Deserializer<'de>,
    T: Deserialize<'de> + Default,
{
    let result = T::deserialize(d);
    match result {
        Err(err) if err.to_string() == "io error: unexpected end of file" => Ok(T::default()),
        result => result,
    }
}

#[cfg(test)]
pub mod tests {
    use super::*;
    use bincode::deserialize;
    use serde::Serialize;

    #[test]
    fn test_default_on_eof() {
        #[derive(Serialize, Deserialize, Debug, PartialEq)]
        struct Foo {
            bar: u16,
            #[serde(deserialize_with = "default_on_eof")]
            baz: Option<u16>,
            #[serde(deserialize_with = "default_on_eof")]
            quz: String,
        }

        let data = vec![1, 0];
        assert_eq!(
            Foo {
                bar: 1,
                baz: None,
                quz: "".to_string(),
            },
            deserialize(&data).unwrap()
        );

        let data = vec![1, 0, 0];
        assert_eq!(
            Foo {
                bar: 1,
                baz: None,
                quz: "".to_string(),
            },
            deserialize(&data).unwrap()
        );

        let data = vec![1, 0, 1];
        assert_eq!(
            Foo {
                bar: 1,
                baz: None,
                quz: "".to_string(),
            },
            deserialize(&data).unwrap()
        );

        let data = vec![1, 0, 1, 0];
        assert_eq!(
            Foo {
                bar: 1,
                baz: None,
                quz: "".to_string(),
            },
            deserialize(&data).unwrap()
        );

        let data = vec![1, 0, 1, 0, 0, 1];
        assert_eq!(
            Foo {
                bar: 1,
                baz: Some(0),
                quz: "".to_string(),
            },
            deserialize(&data).unwrap()
        );

        let data = vec![1, 0, 1, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 116];
        assert_eq!(
            Foo {
                bar: 1,
                baz: Some(0),
                quz: "t".to_string(),
            },
            deserialize(&data).unwrap()
        );
    }

    #[test]
    #[should_panic]
    fn test_default_on_eof_additional_untagged_fields() {
        // If later fields are not tagged `deserialize_with = "default_on_eof"`, deserialization
        // will panic on any missing fields/data
        #[derive(Serialize, Deserialize, Debug, PartialEq)]
        struct Foo {
            bar: u16,
            #[serde(deserialize_with = "default_on_eof")]
            baz: Option<u16>,
            quz: String,
        }

        // Fully populated struct will deserialize
        let data = vec![1, 0, 1, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 116];
        assert_eq!(
            Foo {
                bar: 1,
                baz: Some(0),
                quz: "t".to_string(),
            },
            deserialize(&data).unwrap()
        );

        // Will panic because `quz` is missing, even though `baz` is tagged
        let data = vec![1, 0, 1, 0];
        assert_eq!(
            Foo {
                bar: 1,
                baz: None,
                quz: "".to_string(),
            },
            deserialize(&data).unwrap()
        );
    }
}