about summary refs log tree commit diff
path: root/tvix/nix-compat/src/nixhash/mod.rs
blob: 3b2810b8b0bf521c7b42c31a0e2118c4cbba4b51 (plain) (blame)
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
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
use crate::nixbase32;
use data_encoding::{BASE64, BASE64_NOPAD, HEXLOWER};
use thiserror;

mod algos;
mod with_mode;

pub use algos::HashAlgo;
pub use with_mode::NixHashWithMode;

/// NixHash represents hashes known by Nix.
#[derive(Clone, Debug, Eq, PartialEq)]
pub enum NixHash {
    Md5([u8; 16]),
    Sha1([u8; 20]),
    Sha256([u8; 32]),
    Sha512(Box<[u8; 64]>),
}

/// convenience Result type for all nixhash parsing Results.
pub type Result<V> = std::result::Result<V, Error>;

impl NixHash {
    /// returns the algo as [HashAlgo].
    pub fn algo(&self) -> HashAlgo {
        match self {
            NixHash::Md5(_) => HashAlgo::Md5,
            NixHash::Sha1(_) => HashAlgo::Sha1,
            NixHash::Sha256(_) => HashAlgo::Sha256,
            NixHash::Sha512(_) => HashAlgo::Sha512,
        }
    }

    /// returns the digest as variable-length byte slice.
    pub fn digest_as_bytes(&self) -> &[u8] {
        match self {
            NixHash::Md5(digest) => digest,
            NixHash::Sha1(digest) => digest,
            NixHash::Sha256(digest) => digest,
            NixHash::Sha512(digest) => digest.as_ref(),
        }
    }

    /// Formats a [NixHash] in the Nix default hash format,
    /// which is the algo, followed by a colon, then the lower hex encoded digest.
    pub fn to_nix_hash_string(&self) -> String {
        format!(
            "{}:{}",
            self.algo(),
            HEXLOWER.encode(self.digest_as_bytes())
        )
    }
}

impl TryFrom<(HashAlgo, &[u8])> for NixHash {
    type Error = Error;

    /// Constructs a new [NixHash] by specifying [HashAlgo] and digest.
    /// It can fail if the passed digest length doesn't match what's expected for
    /// the passed algo.
    fn try_from(value: (HashAlgo, &[u8])) -> Result<Self> {
        let (algo, digest) = value;
        from_algo_and_digest(algo, digest)
    }
}

/// Constructs a new [NixHash] by specifying [HashAlgo] and digest.
// It can fail if the passed digest length doesn't match what's expected for
// the passed algo.
pub fn from_algo_and_digest(algo: HashAlgo, digest: &[u8]) -> Result<NixHash> {
    if digest.len() != algo.digest_length() {
        return Err(Error::InvalidEncodedDigestLength(digest.len(), algo));
    }

    Ok(match algo {
        HashAlgo::Md5 => NixHash::Md5(digest.try_into().unwrap()),
        HashAlgo::Sha1 => NixHash::Sha1(digest.try_into().unwrap()),
        HashAlgo::Sha256 => NixHash::Sha256(digest.try_into().unwrap()),
        HashAlgo::Sha512 => NixHash::Sha512(Box::new(digest.try_into().unwrap())),
    })
}

/// Errors related to NixHash construction.
#[derive(Debug, thiserror::Error)]
pub enum Error {
    #[error("invalid hash algo: {0}")]
    InvalidAlgo(String),
    #[error("invalid SRI string: {0}")]
    InvalidSRI(String),
    #[error("invalid encoded digest length '{0}' for algo {1}")]
    InvalidEncodedDigestLength(usize, HashAlgo),
    #[error("invalid base16 encoding: {0}")]
    InvalidBase16Encoding(data_encoding::DecodeError),
    #[error("invalid base32 encoding: {0}")]
    InvalidBase32Encoding(nixbase32::Nixbase32DecodeError),
    #[error("invalid base64 encoding: {0}")]
    InvalidBase64Encoding(data_encoding::DecodeError),
    #[error("conflicting hash algo: {0} (hash_algo) vs {1} (inline)")]
    ConflictingHashAlgos(HashAlgo, HashAlgo),
    #[error("missing inline hash algo, but no externally-specified algo: {0}")]
    MissingInlineHashAlgo(String),
}

/// Nix allows specifying hashes in various encodings, and magically just
/// derives the encoding.
/// This function parses strings to a NixHash.
///
/// Hashes can be:
/// - Nix hash strings
/// - SRI hashes
/// - bare digests
///
/// Encoding for Nix hash strings or bare digests can be:
/// - base16 (lowerhex),
/// - nixbase32,
/// - base64 (StdEncoding)
/// - sri string
///
/// The encoding is derived from the length of the string and the hash type.
/// The hash is communicated out-of-band, but might also be in-band (in the
/// case of a nix hash string or SRI), in which it needs to be consistent with the
/// one communicated out-of-band.
pub fn from_str(s: &str, algo_str: Option<&str>) -> Result<NixHash> {
    // if algo_str is some, parse or bail out
    let algo: Option<HashAlgo> = if let Some(algo_str) = algo_str {
        Some(algo_str.try_into()?)
    } else {
        None
    };

    // Peek at the beginning of the string to detect SRI hashes.
    if s.starts_with("sha1-")
        || s.starts_with("sha256-")
        || s.starts_with("sha512-")
        || s.starts_with("md5-")
    {
        let parsed_nixhash = from_sri_str(s)?;

        // ensure the algo matches with what has been passed externally, if so.
        if let Some(algo) = algo {
            if algo != parsed_nixhash.algo() {
                return Err(Error::ConflictingHashAlgos(algo, parsed_nixhash.algo()));
            }
        }
        return Ok(parsed_nixhash);
    }

    // Peek at the beginning again to see if it's a Nix Hash
    if s.starts_with("sha1:")
        || s.starts_with("sha256:")
        || s.starts_with("sha512:")
        || s.starts_with("md5:")
    {
        let parsed_nixhash = from_nix_str(s)?;
        // ensure the algo matches with what has been passed externally, if so.
        if let Some(algo) = algo {
            if algo != parsed_nixhash.algo() {
                return Err(Error::ConflictingHashAlgos(algo, parsed_nixhash.algo()));
            }
        }
        return Ok(parsed_nixhash);
    }

    // Neither of these, assume a bare digest, so there MUST be an externally-passed algo.
    match algo {
        // Fail if there isn't.
        None => Err(Error::MissingInlineHashAlgo(s.to_string())),
        Some(algo) => decode_digest(s.as_bytes(), algo),
    }
}

/// Parses a Nix hash string ($algo:$digest) to a NixHash.
pub fn from_nix_str(s: &str) -> Result<NixHash> {
    if let Some(rest) = s.strip_prefix("sha1:") {
        decode_digest(rest.as_bytes(), HashAlgo::Sha1)
    } else if let Some(rest) = s.strip_prefix("sha256:") {
        decode_digest(rest.as_bytes(), HashAlgo::Sha256)
    } else if let Some(rest) = s.strip_prefix("sha512:") {
        decode_digest(rest.as_bytes(), HashAlgo::Sha512)
    } else if let Some(rest) = s.strip_prefix("md5:") {
        decode_digest(rest.as_bytes(), HashAlgo::Md5)
    } else {
        Err(Error::InvalidAlgo(s.to_string()))
    }
}

/// Parses a Nix SRI string to a NixHash.
/// Contrary to the SRI spec, Nix doesn't support SRI strings with multiple hashes,
/// only supports sha256 and sha512 from the spec, and supports sha1 and md5
/// additionally.
/// It also accepts SRI strings where the base64 has an with invalid padding.
pub fn from_sri_str(s: &str) -> Result<NixHash> {
    // try to find the first occurence of "-"
    let idx = s.as_bytes().iter().position(|&e| e == b'-');

    if idx.is_none() {
        return Err(Error::InvalidSRI(s.to_string()));
    }

    let idx = idx.unwrap();

    // try to map the part before that `-` to a supported hash algo:
    let algo: HashAlgo = s[..idx].try_into()?;

    // the rest should be the digest (as Nix doesn't support more than one hash in an SRI string).
    let encoded_digest = &s[idx + 1..];

    // decode the digest and algo into a [NixHash]
    match decode_digest(encoded_digest.as_bytes(), algo) {
        // If decoding was successful, pass along
        Ok(nixhash) => Ok(nixhash),
        // For SRI hashes (only), BASE64_NOPAD is also tolerated,
        // so try to parse for this, too.
        // NOTE: As of now, we reject SRI hashes containing additional
        // characters (which upstream Nix seems to simply truncate), as
        // there's no occurence of this is in nixpkgs.
        // It most likely should also be a bug in Nix.
        Err(Error::InvalidEncodedDigestLength(digest_len, hash_algo)) => {
            if encoded_digest.len() == BASE64_NOPAD.encode_len(algo.digest_length()) {
                let digest = BASE64_NOPAD
                    .decode(encoded_digest.as_bytes())
                    .map_err(Error::InvalidBase64Encoding)?;
                Ok(from_algo_and_digest(algo, &digest).unwrap())
            } else {
                Err(Error::InvalidEncodedDigestLength(digest_len, hash_algo))?
            }
        }
        Err(e) => Err(e)?,
    }
}

/// Decode a plain digest depending on the hash algo specified externally.
/// hexlower, nixbase32 and base64 encodings are supported - the encoding is
/// inferred from the input length.
fn decode_digest(s: &[u8], algo: HashAlgo) -> Result<NixHash> {
    // for the chosen hash algo, calculate the expected (decoded) digest length
    // (as bytes)
    let digest = if s.len() == HEXLOWER.encode_len(algo.digest_length()) {
        HEXLOWER
            .decode(s.as_ref())
            .map_err(Error::InvalidBase16Encoding)?
    } else if s.len() == nixbase32::encode_len(algo.digest_length()) {
        nixbase32::decode(s).map_err(Error::InvalidBase32Encoding)?
    } else if s.len() == BASE64.encode_len(algo.digest_length()) {
        BASE64
            .decode(s.as_ref())
            .map_err(Error::InvalidBase64Encoding)?
    } else {
        Err(Error::InvalidEncodedDigestLength(s.len(), algo))?
    };

    Ok(from_algo_and_digest(algo, &digest).unwrap())
}

#[cfg(test)]
mod tests {
    use crate::{
        nixbase32,
        nixhash::{self, HashAlgo, NixHash},
    };
    use data_encoding::{BASE64, BASE64_NOPAD, HEXLOWER};
    use test_case::test_case;
    const DIGEST_SHA1: [u8; 20] = [
        0x60, 0x16, 0x77, 0x79, 0x97, 0xc3, 0x0a, 0xb0, 0x24, 0x13, 0xcf, 0x50, 0x95, 0x62, 0x2c,
        0xd7, 0x92, 0x42, 0x83, 0xac,
    ];

    const DIGEST_SHA256: [u8; 32] = [
        0xa5, 0xce, 0x9c, 0x15, 0x5e, 0xd0, 0x93, 0x97, 0x61, 0x46, 0x46, 0xc9, 0x71, 0x7f, 0xc7,
        0xcd, 0x94, 0xb1, 0x02, 0x3d, 0x7b, 0x76, 0xb6, 0x18, 0xd4, 0x09, 0xe4, 0xfe, 0xfd, 0x6e,
        0x9d, 0x39,
    ];

    const DIGEST_SHA512: [u8; 64] = [
        0xab, 0x40, 0xd0, 0xbe, 0x35, 0x41, 0xf0, 0x77, 0x4b, 0xba, 0x78, 0x15, 0xd1, 0x3d, 0x10,
        0xb0, 0x32, 0x52, 0xe9, 0x6e, 0x95, 0xf7, 0xdb, 0xb4, 0xee, 0x99, 0xa3, 0xb4, 0x31, 0xc2,
        0x16, 0x62, 0xfd, 0x69, 0x71, 0xa0, 0x20, 0x16, 0x0e, 0x39, 0x84, 0x8a, 0xa5, 0xf3, 0x05,
        0xb9, 0xbe, 0x0f, 0x78, 0x72, 0x7b, 0x2b, 0x07, 0x89, 0xe3, 0x9f, 0x12, 0x4d, 0x21, 0xe9,
        0x2b, 0x8f, 0x39, 0xef,
    ];
    const DIGEST_MD5: [u8; 16] = [
        0xc4, 0x87, 0x4a, 0x88, 0x97, 0x44, 0x0b, 0x39, 0x3d, 0x86, 0x2d, 0x8f, 0xd4, 0x59, 0x07,
        0x3f,
    ];

    fn to_base16(digest: &[u8]) -> String {
        HEXLOWER.encode(digest)
    }

    fn to_nixbase32(digest: &[u8]) -> String {
        nixbase32::encode(digest)
    }

    fn to_base64(digest: &[u8]) -> String {
        BASE64.encode(digest)
    }

    fn to_base64_nopad(digest: &[u8]) -> String {
        BASE64_NOPAD.encode(digest)
    }

    // TODO
    fn make_nixhash(algo: &HashAlgo, digest_encoded: String) -> String {
        format!("{}:{}", algo, digest_encoded)
    }
    fn make_sri_string(algo: &HashAlgo, digest_encoded: String) -> String {
        format!("{}-{}", algo, digest_encoded)
    }

    /// Test parsing a hash string in various formats, and also when/how the out-of-band algo is needed.
    #[test_case(&NixHash::Sha1(DIGEST_SHA1); "sha1")]
    #[test_case(&NixHash::Sha256(DIGEST_SHA256); "sha256")]
    #[test_case(&NixHash::Sha512(Box::new(DIGEST_SHA512)); "sha512")]
    #[test_case(&NixHash::Md5(DIGEST_MD5); "md5")]
    fn from_str(expected_hash: &NixHash) {
        let algo = &expected_hash.algo();
        let digest = expected_hash.digest_as_bytes();
        // parse SRI
        {
            // base64 without out-of-band algo
            let s = make_sri_string(algo, to_base64(digest));
            let h = nixhash::from_str(&s, None).expect("must succeed");
            assert_eq!(expected_hash, &h);

            // base64 with out-of-band-algo
            let s = make_sri_string(algo, to_base64(digest));
            let h = nixhash::from_str(&s, Some(&expected_hash.algo().to_string()))
                .expect("must succeed");
            assert_eq!(expected_hash, &h);

            // base64_nopad without out-of-band algo
            let s = make_sri_string(algo, to_base64_nopad(digest));
            let h = nixhash::from_str(&s, None).expect("must succeed");
            assert_eq!(expected_hash, &h);

            // base64_nopad with out-of-band-algo
            let s = make_sri_string(algo, to_base64_nopad(digest));
            let h = nixhash::from_str(&s, Some(&algo.to_string())).expect("must succeed");
            assert_eq!(expected_hash, &h);
        }

        // parse plain base16. should succeed with algo out-of-band, but fail without.
        {
            let s = to_base16(digest);
            nixhash::from_str(&s, None).expect_err("must fail");
            let h = nixhash::from_str(&s, Some(&algo.to_string())).expect("must succeed");
            assert_eq!(expected_hash, &h);
        }

        // parse plain nixbase32. should succeed with algo out-of-band, but fail without.
        {
            let s = to_nixbase32(digest);
            nixhash::from_str(&s, None).expect_err("must fail");
            let h = nixhash::from_str(&s, Some(&algo.to_string())).expect("must succeed");
            assert_eq!(expected_hash, &h);
        }

        // parse plain base64. should succeed with algo out-of-band, but fail without.
        {
            let s = to_base64(digest);
            nixhash::from_str(&s, None).expect_err("must fail");
            let h = nixhash::from_str(&s, Some(&algo.to_string())).expect("must succeed");
            assert_eq!(expected_hash, &h);
        }

        // parse Nix hash strings
        {
            // base16. should succeed with both algo out-of-band and in-band.
            {
                let s = make_nixhash(algo, to_base16(digest));
                assert_eq!(
                    expected_hash,
                    &nixhash::from_str(&s, None).expect("must succeed")
                );
                assert_eq!(
                    expected_hash,
                    &nixhash::from_str(&s, Some(&algo.to_string())).expect("must succeed")
                );
            }
            // nixbase32. should succeed with both algo out-of-band and in-band.
            {
                let s = make_nixhash(algo, to_nixbase32(digest));
                assert_eq!(
                    expected_hash,
                    &nixhash::from_str(&s, None).expect("must succeed")
                );
                assert_eq!(
                    expected_hash,
                    &nixhash::from_str(&s, Some(&algo.to_string())).expect("must succeed")
                );
            }
            // base64. should succeed with both algo out-of-band and in-band.
            {
                let s = make_nixhash(algo, to_base64(digest));
                assert_eq!(
                    expected_hash,
                    &nixhash::from_str(&s, None).expect("must succeed")
                );
                assert_eq!(
                    expected_hash,
                    &nixhash::from_str(&s, Some(&algo.to_string())).expect("must succeed")
                );
            }
        }
    }

    /// Test parsing an SRI hash via the [nixhash::from_sri_str] method.
    #[test]
    fn from_sri_str() {
        let nix_hash = nixhash::from_sri_str("sha256-pc6cFV7Qk5dhRkbJcX/HzZSxAj17drYY1Ank/v1unTk=")
            .expect("must succeed");

        assert_eq!(HashAlgo::Sha256, nix_hash.algo());
        assert_eq!(
            vec![
                0xa5, 0xce, 0x9c, 0x15, 0x5e, 0xd0, 0x93, 0x97, 0x61, 0x46, 0x46, 0xc9, 0x71, 0x7f,
                0xc7, 0xcd, 0x94, 0xb1, 0x02, 0x3d, 0x7b, 0x76, 0xb6, 0x18, 0xd4, 0x09, 0xe4, 0xfe,
                0xfd, 0x6e, 0x9d, 0x39
            ]
            .as_slice(),
            nix_hash.digest_as_bytes()
        )
    }

    /// Ensure we detect truncated base64 digests, where the digest size
    /// doesn't match what's expected from that hash function.
    #[test]
    fn from_sri_str_truncated() {
        nixhash::from_sri_str("sha256-pc6cFV7Qk5dhRkbJcX/HzZSxAj17drYY1Ank")
            .expect_err("must fail");
    }

    /// Ensure we fail on SRI hashes that Nix doesn't support.
    #[test]
    fn from_sri_str_unsupported() {
        nixhash::from_sri_str(
            "sha384-o4UVSl89mIB0sFUK+3jQbG+C9Zc9dRlV/Xd3KAvXEbhqxu0J5OAdg6b6VHKHwQ7U",
        )
        .expect_err("must fail");
    }

    /// Ensure we reject invalid base64 encoding
    #[test]
    fn from_sri_str_invalid_base64() {
        nixhash::from_sri_str("sha256-invalid=base64").expect_err("must fail");
    }

    /// Ensure we reject SRI strings with multiple hashes, as Nix doesn't support that.
    #[test]
    fn from_sri_str_unsupported_multiple() {
        nixhash::from_sri_str("sha256-ngth6szLtC1IJIYyz3lhftzL8SkrJkqPyPve+dGqa1Y= sha512-q0DQvjVB8HdLungV0T0QsDJS6W6V99u07pmjtDHCFmL9aXGgIBYOOYSKpfMFub4PeHJ7KweJ458STSHpK4857w==").expect_err("must fail");
    }

    /// Nix also accepts SRI strings with missing padding, but only in case the
    /// string is expressed as SRI, so it still needs to have a `sha256-` prefix.
    ///
    /// This both seems to work if it is passed with and without specifying the
    /// hash algo out-of-band (hash = "sha256-…" or sha256 = "sha256-…")
    ///
    /// Passing the same broken base64 string, but not as SRI, while passing
    /// the hash algo out-of-band does not work.
    #[test]
    fn sha256_broken_padding() {
        let broken_base64 = "fgIr3TyFGDAXP5+qoAaiMKDg/a1MlT6Fv/S/DaA24S8";
        // if padded with a trailing '='
        let expected_digest = vec![
            0x7e, 0x02, 0x2b, 0xdd, 0x3c, 0x85, 0x18, 0x30, 0x17, 0x3f, 0x9f, 0xaa, 0xa0, 0x06,
            0xa2, 0x30, 0xa0, 0xe0, 0xfd, 0xad, 0x4c, 0x95, 0x3e, 0x85, 0xbf, 0xf4, 0xbf, 0x0d,
            0xa0, 0x36, 0xe1, 0x2f,
        ];

        // passing hash algo out of band should succeed
        let nix_hash = nixhash::from_str(&format!("sha256-{}", &broken_base64), Some("sha256"))
            .expect("must succeed");
        assert_eq!(&expected_digest, &nix_hash.digest_as_bytes());

        // not passing hash algo out of band should succeed
        let nix_hash =
            nixhash::from_str(&format!("sha256-{}", &broken_base64), None).expect("must succeed");
        assert_eq!(&expected_digest, &nix_hash.digest_as_bytes());

        // not passing SRI, but hash algo out of band should fail
        nixhash::from_str(broken_base64, Some("sha256")).expect_err("must fail");
    }
}