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
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
use crate::ber::*;
use crate::der_constraint_fail_if;
use crate::error::*;
#[cfg(feature = "std")]
use crate::ToDer;
use crate::{BerParser, Class, DerParser, DynTagged, FromBer, FromDer, Length, Tag, ToStatic};
use alloc::borrow::Cow;
use core::convert::TryFrom;
use nom::bytes::streaming::take;

/// BER/DER object header (identifier and length)
#[derive(Clone, Debug)]
pub struct Header<'a> {
    /// Object class: universal, application, context-specific, or private
    pub(crate) class: Class,
    /// Constructed attribute: true if constructed, else false
    pub(crate) constructed: bool,
    /// Tag number
    pub(crate) tag: Tag,
    /// Object length: value if definite, or indefinite
    pub(crate) length: Length,

    /// Optionally, the raw encoding of the tag
    ///
    /// This is useful in some cases, where different representations of the same
    /// BER tags have different meanings (BER only)
    pub(crate) raw_tag: Option<Cow<'a, [u8]>>,
}

impl<'a> Header<'a> {
    /// Build a new BER/DER header from the provided values
    pub const fn new(class: Class, constructed: bool, tag: Tag, length: Length) -> Self {
        Header {
            tag,
            constructed,
            class,
            length,
            raw_tag: None,
        }
    }

    /// Build a new BER/DER header from the provided tag, with default values for other fields
    #[inline]
    pub const fn new_simple(tag: Tag) -> Self {
        let constructed = matches!(tag, Tag::Sequence | Tag::Set);
        Self::new(Class::Universal, constructed, tag, Length::Definite(0))
    }

    /// Set the class of this `Header`
    #[inline]
    pub fn with_class(self, class: Class) -> Self {
        Self { class, ..self }
    }

    /// Set the constructed flags of this `Header`
    #[inline]
    pub fn with_constructed(self, constructed: bool) -> Self {
        Self {
            constructed,
            ..self
        }
    }

    /// Set the tag of this `Header`
    #[inline]
    pub fn with_tag(self, tag: Tag) -> Self {
        Self { tag, ..self }
    }

    /// Set the length of this `Header`
    #[inline]
    pub fn with_length(self, length: Length) -> Self {
        Self { length, ..self }
    }

    /// Update header to add reference to raw tag
    #[inline]
    pub fn with_raw_tag(self, raw_tag: Option<Cow<'a, [u8]>>) -> Self {
        Header { raw_tag, ..self }
    }

    /// Return the class of this header.
    #[inline]
    pub const fn class(&self) -> Class {
        self.class
    }

    /// Return true if this header has the 'constructed' flag.
    #[inline]
    pub const fn constructed(&self) -> bool {
        self.constructed
    }

    /// Return the tag of this header.
    #[inline]
    pub const fn tag(&self) -> Tag {
        self.tag
    }

    /// Return the length of this header.
    #[inline]
    pub const fn length(&self) -> Length {
        self.length
    }

    /// Return the raw tag encoding, if it was stored in this object
    #[inline]
    pub fn raw_tag(&self) -> Option<&[u8]> {
        self.raw_tag.as_ref().map(|cow| cow.as_ref())
    }

    /// Test if object is primitive
    #[inline]
    pub const fn is_primitive(&self) -> bool {
        !self.constructed
    }

    /// Test if object is constructed
    #[inline]
    pub const fn is_constructed(&self) -> bool {
        self.constructed
    }

    /// Return error if class is not the expected class
    #[inline]
    pub const fn assert_class(&self, class: Class) -> Result<()> {
        self.class.assert_eq(class)
    }

    /// Return error if tag is not the expected tag
    #[inline]
    pub const fn assert_tag(&self, tag: Tag) -> Result<()> {
        self.tag.assert_eq(tag)
    }

    /// Return error if object is not primitive
    #[inline]
    pub const fn assert_primitive(&self) -> Result<()> {
        if self.is_primitive() {
            Ok(())
        } else {
            Err(Error::ConstructUnexpected)
        }
    }

    /// Return error if object is primitive
    #[inline]
    pub const fn assert_constructed(&self) -> Result<()> {
        if !self.is_primitive() {
            Ok(())
        } else {
            Err(Error::ConstructExpected)
        }
    }

    /// Test if object class is Universal
    #[inline]
    pub const fn is_universal(&self) -> bool {
        self.class as u8 == Class::Universal as u8
    }
    /// Test if object class is Application
    #[inline]
    pub const fn is_application(&self) -> bool {
        self.class as u8 == Class::Application as u8
    }
    /// Test if object class is Context-specific
    #[inline]
    pub const fn is_contextspecific(&self) -> bool {
        self.class as u8 == Class::ContextSpecific as u8
    }
    /// Test if object class is Private
    #[inline]
    pub const fn is_private(&self) -> bool {
        self.class as u8 == Class::Private as u8
    }

    /// Return error if object length is definite
    #[inline]
    pub const fn assert_definite(&self) -> Result<()> {
        if self.length.is_definite() {
            Ok(())
        } else {
            Err(Error::DerConstraintFailed(DerConstraint::IndefiniteLength))
        }
    }

    /// Get the content following a BER header
    #[inline]
    pub fn parse_ber_content<'i>(&'_ self, i: &'i [u8]) -> ParseResult<'i, &'i [u8]> {
        // defaults to maximum depth 8
        // depth is used only if BER, and length is indefinite
        BerParser::get_object_content(i, self, 8)
    }

    /// Get the content following a DER header
    #[inline]
    pub fn parse_der_content<'i>(&'_ self, i: &'i [u8]) -> ParseResult<'i, &'i [u8]> {
        self.assert_definite()?;
        DerParser::get_object_content(i, self, 8)
    }
}

impl From<Tag> for Header<'_> {
    #[inline]
    fn from(tag: Tag) -> Self {
        let constructed = matches!(tag, Tag::Sequence | Tag::Set);
        Self::new(Class::Universal, constructed, tag, Length::Definite(0))
    }
}

impl<'a> ToStatic for Header<'a> {
    type Owned = Header<'static>;

    fn to_static(&self) -> Self::Owned {
        let raw_tag: Option<Cow<'static, [u8]>> =
            self.raw_tag.as_ref().map(|b| Cow::Owned(b.to_vec()));
        Header {
            tag: self.tag,
            constructed: self.constructed,
            class: self.class,
            length: self.length,
            raw_tag,
        }
    }
}

impl<'a> FromBer<'a> for Header<'a> {
    fn from_ber(bytes: &'a [u8]) -> ParseResult<Self> {
        let (i1, el) = parse_identifier(bytes)?;
        let class = match Class::try_from(el.0) {
            Ok(c) => c,
            Err(_) => unreachable!(), // Cannot fail, we have read exactly 2 bits
        };
        let (i2, len) = parse_ber_length_byte(i1)?;
        let (i3, len) = match (len.0, len.1) {
            (0, l1) => {
                // Short form: MSB is 0, the rest encodes the length (which can be 0) (8.1.3.4)
                (i2, Length::Definite(usize::from(l1)))
            }
            (_, 0) => {
                // Indefinite form: MSB is 1, the rest is 0 (8.1.3.6)
                // If encoding is primitive, definite form shall be used (8.1.3.2)
                if el.1 == 0 {
                    return Err(nom::Err::Error(Error::ConstructExpected));
                }
                (i2, Length::Indefinite)
            }
            (_, l1) => {
                // if len is 0xff -> error (8.1.3.5)
                if l1 == 0b0111_1111 {
                    return Err(nom::Err::Error(Error::InvalidLength));
                }
                let (i3, llen) = take(l1)(i2)?;
                match bytes_to_u64(llen) {
                    Ok(l) => {
                        let l =
                            usize::try_from(l).or(Err(nom::Err::Error(Error::InvalidLength)))?;
                        (i3, Length::Definite(l))
                    }
                    Err(_) => {
                        return Err(nom::Err::Error(Error::InvalidLength));
                    }
                }
            }
        };
        let constructed = el.1 != 0;
        let hdr = Header::new(class, constructed, Tag(el.2), len).with_raw_tag(Some(el.3.into()));
        Ok((i3, hdr))
    }
}

impl<'a> FromDer<'a> for Header<'a> {
    fn from_der(bytes: &'a [u8]) -> ParseResult<Self> {
        let (i1, el) = parse_identifier(bytes)?;
        let class = match Class::try_from(el.0) {
            Ok(c) => c,
            Err(_) => unreachable!(), // Cannot fail, we have read exactly 2 bits
        };
        let (i2, len) = parse_ber_length_byte(i1)?;
        let (i3, len) = match (len.0, len.1) {
            (0, l1) => {
                // Short form: MSB is 0, the rest encodes the length (which can be 0) (8.1.3.4)
                (i2, Length::Definite(usize::from(l1)))
            }
            (_, 0) => {
                // Indefinite form is not allowed in DER (10.1)
                return Err(nom::Err::Error(Error::DerConstraintFailed(
                    DerConstraint::IndefiniteLength,
                )));
            }
            (_, l1) => {
                // if len is 0xff -> error (8.1.3.5)
                if l1 == 0b0111_1111 {
                    return Err(nom::Err::Error(Error::InvalidLength));
                }
                // DER(9.1) if len is 0 (indefinite form), obj must be constructed
                der_constraint_fail_if!(
                    &i[1..],
                    len.1 == 0 && el.1 != 1,
                    DerConstraint::NotConstructed
                );
                let (i3, llen) = take(l1)(i2)?;
                match bytes_to_u64(llen) {
                    Ok(l) => {
                        // DER: should have been encoded in short form (< 127)
                        // XXX der_constraint_fail_if!(i, l < 127);
                        let l =
                            usize::try_from(l).or(Err(nom::Err::Error(Error::InvalidLength)))?;
                        (i3, Length::Definite(l))
                    }
                    Err(_) => {
                        return Err(nom::Err::Error(Error::InvalidLength));
                    }
                }
            }
        };
        let constructed = el.1 != 0;
        let hdr = Header::new(class, constructed, Tag(el.2), len).with_raw_tag(Some(el.3.into()));
        Ok((i3, hdr))
    }
}

impl DynTagged for (Class, bool, Tag) {
    fn tag(&self) -> Tag {
        self.2
    }
}

#[cfg(feature = "std")]
impl ToDer for (Class, bool, Tag) {
    fn to_der_len(&self) -> Result<usize> {
        let (_, _, tag) = self;
        match tag.0 {
            0..=30 => Ok(1),
            t => {
                let mut sz = 1;
                let mut val = t;
                loop {
                    if val <= 127 {
                        return Ok(sz + 1);
                    } else {
                        val >>= 7;
                        sz += 1;
                    }
                }
            }
        }
    }

    fn write_der_header(&self, writer: &mut dyn std::io::Write) -> SerializeResult<usize> {
        let (class, constructed, tag) = self;
        let b0 = (*class as u8) << 6;
        let b0 = b0 | if *constructed { 0b10_0000 } else { 0 };
        if tag.0 > 30 {
            let mut val = tag.0;

            const BUF_SZ: usize = 8;
            let mut buffer = [0u8; BUF_SZ];
            let mut current_index = BUF_SZ - 1;

            // first byte: class+constructed+0x1f
            let b0 = b0 | 0b1_1111;
            let mut sz = writer.write(&[b0])?;

            // now write bytes from right (last) to left

            // last encoded byte
            buffer[current_index] = (val & 0x7f) as u8;
            val >>= 7;

            while val > 0 {
                current_index -= 1;
                if current_index == 0 {
                    return Err(SerializeError::InvalidLength);
                }
                buffer[current_index] = (val & 0x7f) as u8 | 0x80;
                val >>= 7;
            }

            sz += writer.write(&buffer[current_index..])?;
            Ok(sz)
        } else {
            let b0 = b0 | (tag.0 as u8);
            let sz = writer.write(&[b0])?;
            Ok(sz)
        }
    }

    fn write_der_content(&self, _writer: &mut dyn std::io::Write) -> SerializeResult<usize> {
        Ok(0)
    }
}

impl DynTagged for Header<'_> {
    fn tag(&self) -> Tag {
        self.tag
    }
}

#[cfg(feature = "std")]
impl ToDer for Header<'_> {
    fn to_der_len(&self) -> Result<usize> {
        let tag_len = (self.class, self.constructed, self.tag).to_der_len()?;
        let len_len = self.length.to_der_len()?;
        Ok(tag_len + len_len)
    }

    fn write_der_header(&self, writer: &mut dyn std::io::Write) -> SerializeResult<usize> {
        let sz = (self.class, self.constructed, self.tag).write_der_header(writer)?;
        let sz = sz + self.length.write_der_header(writer)?;
        Ok(sz)
    }

    fn write_der_content(&self, _writer: &mut dyn std::io::Write) -> SerializeResult<usize> {
        Ok(0)
    }

    fn write_der_raw(&self, writer: &mut dyn std::io::Write) -> SerializeResult<usize> {
        // use raw_tag if present
        let sz = match &self.raw_tag {
            Some(t) => writer.write(t)?,
            None => (self.class, self.constructed, self.tag).write_der_header(writer)?,
        };
        let sz = sz + self.length.write_der_header(writer)?;
        Ok(sz)
    }
}

/// Compare two BER headers. `len` fields are compared only if both objects have it set (same for `raw_tag`)
impl<'a> PartialEq<Header<'a>> for Header<'a> {
    fn eq(&self, other: &Header) -> bool {
        self.class == other.class
            && self.tag == other.tag
            && self.constructed == other.constructed
            && {
                if self.length.is_null() && other.length.is_null() {
                    self.length == other.length
                } else {
                    true
                }
            }
            && {
                // it tag is present for both, compare it
                if self.raw_tag.as_ref().xor(other.raw_tag.as_ref()).is_none() {
                    self.raw_tag == other.raw_tag
                } else {
                    true
                }
            }
    }
}

impl Eq for Header<'_> {}

#[cfg(test)]
mod tests {
    use crate::*;
    use hex_literal::hex;

    /// Generic tests on methods, and coverage tests
    #[test]
    fn methods_header() {
        // Getters
        let input = &hex! {"02 01 00"};
        let (rem, header) = Header::from_ber(input).expect("parsing header failed");
        assert_eq!(header.class(), Class::Universal);
        assert_eq!(header.tag(), Tag::Integer);
        assert!(header.assert_primitive().is_ok());
        assert!(header.assert_constructed().is_err());
        assert!(header.is_universal());
        assert!(!header.is_application());
        assert!(!header.is_private());
        assert_eq!(rem, &input[2..]);

        // test PartialEq
        let hdr2 = Header::new_simple(Tag::Integer);
        assert_eq!(header, hdr2);

        // builder methods
        let hdr3 = hdr2
            .with_class(Class::ContextSpecific)
            .with_constructed(true)
            .with_length(Length::Definite(1));
        assert!(hdr3.constructed());
        assert!(hdr3.is_constructed());
        assert!(hdr3.assert_constructed().is_ok());
        assert!(hdr3.is_contextspecific());
        let xx = hdr3.to_der_vec().expect("serialize failed");
        assert_eq!(&xx, &[0xa2, 0x01]);

        // indefinite length
        let hdr4 = hdr3.with_length(Length::Indefinite);
        assert!(hdr4.assert_definite().is_err());
        let xx = hdr4.to_der_vec().expect("serialize failed");
        assert_eq!(&xx, &[0xa2, 0x80]);

        // parse_*_content
        let hdr = Header::new_simple(Tag(2)).with_length(Length::Definite(1));
        let (_, r) = hdr.parse_ber_content(&input[2..]).unwrap();
        assert_eq!(r, &input[2..]);
        let (_, r) = hdr.parse_der_content(&input[2..]).unwrap();
        assert_eq!(r, &input[2..]);
    }
}