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
#[cfg(any(feature = "alloc", test))]
use alloc::string::String;
use core::fmt;
#[cfg(any(feature = "std", test))]
use std::error;

#[cfg(any(feature = "alloc", test))]
use crate::engine::general_purpose::STANDARD;
use crate::engine::{Config, Engine};
use crate::PAD_BYTE;

/// Encode arbitrary octets as base64 using the [`STANDARD` engine](STANDARD).
///
/// See [Engine::encode].
#[allow(unused)]
#[deprecated(since = "0.21.0", note = "Use Engine::encode")]
#[cfg(any(feature = "alloc", test))]
pub fn encode<T: AsRef<[u8]>>(input: T) -> String {
    STANDARD.encode(input)
}

///Encode arbitrary octets as base64 using the provided `Engine` into a new `String`.
///
/// See [Engine::encode].
#[allow(unused)]
#[deprecated(since = "0.21.0", note = "Use Engine::encode")]
#[cfg(any(feature = "alloc", test))]
pub fn encode_engine<E: Engine, T: AsRef<[u8]>>(input: T, engine: &E) -> String {
    engine.encode(input)
}

///Encode arbitrary octets as base64 into a supplied `String`.
///
/// See [Engine::encode_string].
#[allow(unused)]
#[deprecated(since = "0.21.0", note = "Use Engine::encode_string")]
#[cfg(any(feature = "alloc", test))]
pub fn encode_engine_string<E: Engine, T: AsRef<[u8]>>(
    input: T,
    output_buf: &mut String,
    engine: &E,
) {
    engine.encode_string(input, output_buf)
}

/// Encode arbitrary octets as base64 into a supplied slice.
///
/// See [Engine::encode_slice].
#[allow(unused)]
#[deprecated(since = "0.21.0", note = "Use Engine::encode_slice")]
pub fn encode_engine_slice<E: Engine, T: AsRef<[u8]>>(
    input: T,
    output_buf: &mut [u8],
    engine: &E,
) -> Result<usize, EncodeSliceError> {
    engine.encode_slice(input, output_buf)
}

/// B64-encode and pad (if configured).
///
/// This helper exists to avoid recalculating encoded_size, which is relatively expensive on short
/// inputs.
///
/// `encoded_size` is the encoded size calculated for `input`.
///
/// `output` must be of size `encoded_size`.
///
/// All bytes in `output` will be written to since it is exactly the size of the output.
pub(crate) fn encode_with_padding<E: Engine + ?Sized>(
    input: &[u8],
    output: &mut [u8],
    engine: &E,
    expected_encoded_size: usize,
) {
    debug_assert_eq!(expected_encoded_size, output.len());

    let b64_bytes_written = engine.internal_encode(input, output);

    let padding_bytes = if engine.config().encode_padding() {
        add_padding(b64_bytes_written, &mut output[b64_bytes_written..])
    } else {
        0
    };

    let encoded_bytes = b64_bytes_written
        .checked_add(padding_bytes)
        .expect("usize overflow when calculating b64 length");

    debug_assert_eq!(expected_encoded_size, encoded_bytes);
}

/// Calculate the base64 encoded length for a given input length, optionally including any
/// appropriate padding bytes.
///
/// Returns `None` if the encoded length can't be represented in `usize`. This will happen for
/// input lengths in approximately the top quarter of the range of `usize`.
pub const fn encoded_len(bytes_len: usize, padding: bool) -> Option<usize> {
    let rem = bytes_len % 3;

    let complete_input_chunks = bytes_len / 3;
    // `?` is disallowed in const, and `let Some(_) = _ else` requires 1.65.0, whereas this
    // messier syntax works on 1.48
    let complete_chunk_output =
        if let Some(complete_chunk_output) = complete_input_chunks.checked_mul(4) {
            complete_chunk_output
        } else {
            return None;
        };

    if rem > 0 {
        if padding {
            complete_chunk_output.checked_add(4)
        } else {
            let encoded_rem = match rem {
                1 => 2,
                // only other possible remainder is 2
                // can't use a separate _ => unreachable!() in const fns in ancient rust versions
                _ => 3,
            };
            complete_chunk_output.checked_add(encoded_rem)
        }
    } else {
        Some(complete_chunk_output)
    }
}

/// Write padding characters.
/// `unpadded_output_len` is the size of the unpadded but base64 encoded data.
/// `output` is the slice where padding should be written, of length at least 2.
///
/// Returns the number of padding bytes written.
pub(crate) fn add_padding(unpadded_output_len: usize, output: &mut [u8]) -> usize {
    let pad_bytes = (4 - (unpadded_output_len % 4)) % 4;
    // for just a couple bytes, this has better performance than using
    // .fill(), or iterating over mutable refs, which call memset()
    #[allow(clippy::needless_range_loop)]
    for i in 0..pad_bytes {
        output[i] = PAD_BYTE;
    }

    pad_bytes
}

/// Errors that can occur while encoding into a slice.
#[derive(Clone, Debug, PartialEq, Eq)]
pub enum EncodeSliceError {
    /// The provided slice is too small.
    OutputSliceTooSmall,
}

impl fmt::Display for EncodeSliceError {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        match self {
            Self::OutputSliceTooSmall => write!(f, "Output slice too small"),
        }
    }
}

#[cfg(any(feature = "std", test))]
impl error::Error for EncodeSliceError {}

#[cfg(test)]
mod tests {
    use super::*;

    use crate::{
        alphabet,
        engine::general_purpose::{GeneralPurpose, NO_PAD, STANDARD},
        tests::{assert_encode_sanity, random_config, random_engine},
    };
    use rand::{
        distributions::{Distribution, Uniform},
        Rng, SeedableRng,
    };
    use std::str;

    const URL_SAFE_NO_PAD_ENGINE: GeneralPurpose = GeneralPurpose::new(&alphabet::URL_SAFE, NO_PAD);

    #[test]
    fn encoded_size_correct_standard() {
        assert_encoded_length(0, 0, &STANDARD, true);

        assert_encoded_length(1, 4, &STANDARD, true);
        assert_encoded_length(2, 4, &STANDARD, true);
        assert_encoded_length(3, 4, &STANDARD, true);

        assert_encoded_length(4, 8, &STANDARD, true);
        assert_encoded_length(5, 8, &STANDARD, true);
        assert_encoded_length(6, 8, &STANDARD, true);

        assert_encoded_length(7, 12, &STANDARD, true);
        assert_encoded_length(8, 12, &STANDARD, true);
        assert_encoded_length(9, 12, &STANDARD, true);

        assert_encoded_length(54, 72, &STANDARD, true);

        assert_encoded_length(55, 76, &STANDARD, true);
        assert_encoded_length(56, 76, &STANDARD, true);
        assert_encoded_length(57, 76, &STANDARD, true);

        assert_encoded_length(58, 80, &STANDARD, true);
    }

    #[test]
    fn encoded_size_correct_no_pad() {
        assert_encoded_length(0, 0, &URL_SAFE_NO_PAD_ENGINE, false);

        assert_encoded_length(1, 2, &URL_SAFE_NO_PAD_ENGINE, false);
        assert_encoded_length(2, 3, &URL_SAFE_NO_PAD_ENGINE, false);
        assert_encoded_length(3, 4, &URL_SAFE_NO_PAD_ENGINE, false);

        assert_encoded_length(4, 6, &URL_SAFE_NO_PAD_ENGINE, false);
        assert_encoded_length(5, 7, &URL_SAFE_NO_PAD_ENGINE, false);
        assert_encoded_length(6, 8, &URL_SAFE_NO_PAD_ENGINE, false);

        assert_encoded_length(7, 10, &URL_SAFE_NO_PAD_ENGINE, false);
        assert_encoded_length(8, 11, &URL_SAFE_NO_PAD_ENGINE, false);
        assert_encoded_length(9, 12, &URL_SAFE_NO_PAD_ENGINE, false);

        assert_encoded_length(54, 72, &URL_SAFE_NO_PAD_ENGINE, false);

        assert_encoded_length(55, 74, &URL_SAFE_NO_PAD_ENGINE, false);
        assert_encoded_length(56, 75, &URL_SAFE_NO_PAD_ENGINE, false);
        assert_encoded_length(57, 76, &URL_SAFE_NO_PAD_ENGINE, false);

        assert_encoded_length(58, 78, &URL_SAFE_NO_PAD_ENGINE, false);
    }

    #[test]
    fn encoded_size_overflow() {
        assert_eq!(None, encoded_len(usize::MAX, true));
    }

    #[test]
    fn encode_engine_string_into_nonempty_buffer_doesnt_clobber_prefix() {
        let mut orig_data = Vec::new();
        let mut prefix = String::new();
        let mut encoded_data_no_prefix = String::new();
        let mut encoded_data_with_prefix = String::new();
        let mut decoded = Vec::new();

        let prefix_len_range = Uniform::new(0, 1000);
        let input_len_range = Uniform::new(0, 1000);

        let mut rng = rand::rngs::SmallRng::from_entropy();

        for _ in 0..10_000 {
            orig_data.clear();
            prefix.clear();
            encoded_data_no_prefix.clear();
            encoded_data_with_prefix.clear();
            decoded.clear();

            let input_len = input_len_range.sample(&mut rng);

            for _ in 0..input_len {
                orig_data.push(rng.gen());
            }

            let prefix_len = prefix_len_range.sample(&mut rng);
            for _ in 0..prefix_len {
                // getting convenient random single-byte printable chars that aren't base64 is
                // annoying
                prefix.push('#');
            }
            encoded_data_with_prefix.push_str(&prefix);

            let engine = random_engine(&mut rng);
            engine.encode_string(&orig_data, &mut encoded_data_no_prefix);
            engine.encode_string(&orig_data, &mut encoded_data_with_prefix);

            assert_eq!(
                encoded_data_no_prefix.len() + prefix_len,
                encoded_data_with_prefix.len()
            );
            assert_encode_sanity(
                &encoded_data_no_prefix,
                engine.config().encode_padding(),
                input_len,
            );
            assert_encode_sanity(
                &encoded_data_with_prefix[prefix_len..],
                engine.config().encode_padding(),
                input_len,
            );

            // append plain encode onto prefix
            prefix.push_str(&encoded_data_no_prefix);

            assert_eq!(prefix, encoded_data_with_prefix);

            engine
                .decode_vec(&encoded_data_no_prefix, &mut decoded)
                .unwrap();
            assert_eq!(orig_data, decoded);
        }
    }

    #[test]
    fn encode_engine_slice_into_nonempty_buffer_doesnt_clobber_suffix() {
        let mut orig_data = Vec::new();
        let mut encoded_data = Vec::new();
        let mut encoded_data_original_state = Vec::new();
        let mut decoded = Vec::new();

        let input_len_range = Uniform::new(0, 1000);

        let mut rng = rand::rngs::SmallRng::from_entropy();

        for _ in 0..10_000 {
            orig_data.clear();
            encoded_data.clear();
            encoded_data_original_state.clear();
            decoded.clear();

            let input_len = input_len_range.sample(&mut rng);

            for _ in 0..input_len {
                orig_data.push(rng.gen());
            }

            // plenty of existing garbage in the encoded buffer
            for _ in 0..10 * input_len {
                encoded_data.push(rng.gen());
            }

            encoded_data_original_state.extend_from_slice(&encoded_data);

            let engine = random_engine(&mut rng);

            let encoded_size = encoded_len(input_len, engine.config().encode_padding()).unwrap();

            assert_eq!(
                encoded_size,
                engine.encode_slice(&orig_data, &mut encoded_data).unwrap()
            );

            assert_encode_sanity(
                str::from_utf8(&encoded_data[0..encoded_size]).unwrap(),
                engine.config().encode_padding(),
                input_len,
            );

            assert_eq!(
                &encoded_data[encoded_size..],
                &encoded_data_original_state[encoded_size..]
            );

            engine
                .decode_vec(&encoded_data[0..encoded_size], &mut decoded)
                .unwrap();
            assert_eq!(orig_data, decoded);
        }
    }

    #[test]
    fn encode_to_slice_random_valid_utf8() {
        let mut input = Vec::new();
        let mut output = Vec::new();

        let input_len_range = Uniform::new(0, 1000);

        let mut rng = rand::rngs::SmallRng::from_entropy();

        for _ in 0..10_000 {
            input.clear();
            output.clear();

            let input_len = input_len_range.sample(&mut rng);

            for _ in 0..input_len {
                input.push(rng.gen());
            }

            let config = random_config(&mut rng);
            let engine = random_engine(&mut rng);

            // fill up the output buffer with garbage
            let encoded_size = encoded_len(input_len, config.encode_padding()).unwrap();
            for _ in 0..encoded_size {
                output.push(rng.gen());
            }

            let orig_output_buf = output.clone();

            let bytes_written = engine.internal_encode(&input, &mut output);

            // make sure the part beyond bytes_written is the same garbage it was before
            assert_eq!(orig_output_buf[bytes_written..], output[bytes_written..]);

            // make sure the encoded bytes are UTF-8
            let _ = str::from_utf8(&output[0..bytes_written]).unwrap();
        }
    }

    #[test]
    fn encode_with_padding_random_valid_utf8() {
        let mut input = Vec::new();
        let mut output = Vec::new();

        let input_len_range = Uniform::new(0, 1000);

        let mut rng = rand::rngs::SmallRng::from_entropy();

        for _ in 0..10_000 {
            input.clear();
            output.clear();

            let input_len = input_len_range.sample(&mut rng);

            for _ in 0..input_len {
                input.push(rng.gen());
            }

            let engine = random_engine(&mut rng);

            // fill up the output buffer with garbage
            let encoded_size = encoded_len(input_len, engine.config().encode_padding()).unwrap();
            for _ in 0..encoded_size + 1000 {
                output.push(rng.gen());
            }

            let orig_output_buf = output.clone();

            encode_with_padding(&input, &mut output[0..encoded_size], &engine, encoded_size);

            // make sure the part beyond b64 is the same garbage it was before
            assert_eq!(orig_output_buf[encoded_size..], output[encoded_size..]);

            // make sure the encoded bytes are UTF-8
            let _ = str::from_utf8(&output[0..encoded_size]).unwrap();
        }
    }

    #[test]
    fn add_padding_random_valid_utf8() {
        let mut output = Vec::new();

        let mut rng = rand::rngs::SmallRng::from_entropy();

        // cover our bases for length % 4
        for unpadded_output_len in 0..20 {
            output.clear();

            // fill output with random
            for _ in 0..100 {
                output.push(rng.gen());
            }

            let orig_output_buf = output.clone();

            let bytes_written = add_padding(unpadded_output_len, &mut output);

            // make sure the part beyond bytes_written is the same garbage it was before
            assert_eq!(orig_output_buf[bytes_written..], output[bytes_written..]);

            // make sure the encoded bytes are UTF-8
            let _ = str::from_utf8(&output[0..bytes_written]).unwrap();
        }
    }

    fn assert_encoded_length<E: Engine>(
        input_len: usize,
        enc_len: usize,
        engine: &E,
        padded: bool,
    ) {
        assert_eq!(enc_len, encoded_len(input_len, padded).unwrap());

        let mut bytes: Vec<u8> = Vec::new();
        let mut rng = rand::rngs::SmallRng::from_entropy();

        for _ in 0..input_len {
            bytes.push(rng.gen());
        }

        let encoded = engine.encode(&bytes);
        assert_encode_sanity(&encoded, padded, input_len);

        assert_eq!(enc_len, encoded.len());
    }

    #[test]
    fn encode_imap() {
        assert_eq!(
            &GeneralPurpose::new(&alphabet::IMAP_MUTF7, NO_PAD).encode(b"\xFB\xFF"),
            &GeneralPurpose::new(&alphabet::STANDARD, NO_PAD)
                .encode(b"\xFB\xFF")
                .replace('/', ",")
        );
    }
}