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

use std::str;

/// Implements types and methods for content verification
use sha2::{self, Digest};

/// DigestAlgorithm declares the supported algorithms
#[derive(strum::Display, Clone, Debug)]
pub enum DigestAlgorithm {
  Sha256(sha2::Sha256),
}

impl std::str::FromStr for DigestAlgorithm {
  type Err = ContentDigestError;

  fn from_str(name: &str) -> Result<Self, Self::Err> {
    match name {
      "sha256" => Ok(DigestAlgorithm::Sha256(sha2::Sha256::new())),
      _ => Err(ContentDigestError::AlgorithmUnknown(name.to_string())),
    }
  }
}

#[derive(Debug, thiserror::Error)]
pub enum ContentDigestError {
  #[error("digest {0} does not have algorithm prefix")]
  BadDigest(String),
  #[error("unknown algorithm: {0}")]
  AlgorithmUnknown(String),
  #[error("verification failed: expected '{expected}', got '{got}'")]
  Verify { expected: String, got: String },
}

/// ContentDigest stores a digest and its DigestAlgorithm
#[derive(Clone, Debug)]
pub struct ContentDigest {
  digest: String,
  algorithm: DigestAlgorithm,
}

impl ContentDigest {
  /// try_new attempts to parse the digest string and create a ContentDigest instance from it
  ///
  /// Success depends on
  /// - the string having an "algorithm:" prefix
  /// - the algorithm being supported by DigestAlgorithm
  pub fn try_new(digest: &str) -> std::result::Result<Self, ContentDigestError> {
    let digest_split = digest.split(':').collect::<Vec<&str>>();

    if digest_split.len() != 2 {
      return Err(ContentDigestError::BadDigest(digest.to_string()));
    }

    let algorithm = std::str::FromStr::from_str(digest_split[0])?;
    Ok(ContentDigest {
      digest: digest.to_string(),
      algorithm,
    })
  }

  pub fn update(&mut self, input: &[u8]) {
    self.algorithm.update(input)
  }

  pub fn verify(self) -> std::result::Result<(), ContentDigestError> {
    let digest = self.algorithm.digest();
    if digest != self.digest {
      return Err(ContentDigestError::Verify {
        expected: self.digest,
        got: digest,
      });
    }
    Ok(())
  }
}

impl std::fmt::Display for ContentDigest {
  fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
    write!(f, "{}:{}", self.algorithm, self.digest)
  }
}

impl DigestAlgorithm {
  fn update(&mut self, input: &[u8]) {
    match self {
      DigestAlgorithm::Sha256(hash) => {
        hash.update(input);
      }
    }
  }

  fn digest(self) -> String {
    let (algo, digest) = match self {
      DigestAlgorithm::Sha256(hash) => ("sha256", hash.finalize()),
    };
    format!("{}:{:x}", algo, &digest)
  }
}

#[cfg(test)]
mod tests {
  use sha2;

  use super::*;

  type Fallible<T> = Result<T, crate::Error>;

  #[test]
  fn try_new_succeeds_with_correct_digest() -> Fallible<()> {
    let correct_digest = "sha256:0000000000000000000000000000000000000000000000000000000000000000";
    ContentDigest::try_new(correct_digest)?;

    Ok(())
  }

  #[test]
  fn try_new_fails_with_incorrect_digest() {
    for incorrect_digest in &[
      "invalid",
      "invalid:",
      "invalid:0000000000000000000000000000000000000000000000000000000000000000",
    ] {
      if ContentDigest::try_new(incorrect_digest).is_ok() {
        panic!("expected try_new to fail for incorrect digest {}", incorrect_digest);
      }
    }
  }

  #[test]
  fn verify_succeeds_with_same_content() -> Fallible<()> {
    let blob: &[u8] = b"somecontent";
    let mut content_digest =
      ContentDigest::try_new("sha256:d5a3477d91583e65a7aba6f6db7a53e2de739bc7bf8f4a08f0df0457b637f1fb")?;
    content_digest.update(blob);
    content_digest.verify().map_err(Into::into)
  }

  #[test]
  fn verify_chunked_succeeds_with_same_content() -> Fallible<()> {
    let mut content_digest =
      ContentDigest::try_new("sha256:d5a3477d91583e65a7aba6f6db7a53e2de739bc7bf8f4a08f0df0457b637f1fb")?;
    content_digest.update(b"some");
    content_digest.update(b"content");
    content_digest.verify().map_err(Into::into)
  }

  #[test]
  fn verify_fails_with_different_content() -> Fallible<()> {
    let blob: &[u8] = b"somecontent";
    let different_blob: &[u8] = b"someothercontent";

    let mut expected_digest = DigestAlgorithm::Sha256(sha2::Sha256::new());
    expected_digest.update(different_blob);
    let expected_digest = expected_digest.digest();

    let mut content_digest = ContentDigest::try_new(&expected_digest)?;
    content_digest.update(blob);
    if content_digest.verify().is_ok() {
      panic!("expected try_verify to fail for a different blob");
    }
    Ok(())
  }
}