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
//! Provides the [Engine] abstraction and out of the box implementations.
#[cfg(any(feature = "alloc", feature = "std", test))]
use crate::chunked_encoder;
use crate::{
    encode::{encode_with_padding, EncodeSliceError},
    encoded_len, DecodeError, DecodeSliceError,
};
#[cfg(any(feature = "alloc", feature = "std", test))]
use alloc::vec::Vec;

#[cfg(any(feature = "alloc", feature = "std", test))]
use alloc::{string::String, vec};

pub mod general_purpose;

#[cfg(test)]
mod naive;

#[cfg(test)]
mod tests;

pub use general_purpose::{GeneralPurpose, GeneralPurposeConfig};

/// An `Engine` provides low-level encoding and decoding operations that all other higher-level parts of the API use. Users of the library will generally not need to implement this.
///
/// Different implementations offer different characteristics. The library currently ships with
/// [GeneralPurpose] that offers good speed and works on any CPU, with more choices
/// coming later, like a constant-time one when side channel resistance is called for, and vendor-specific vectorized ones for more speed.
///
/// See [general_purpose::STANDARD_NO_PAD] if you just want standard base64. Otherwise, when possible, it's
/// recommended to store the engine in a `const` so that references to it won't pose any lifetime
/// issues, and to avoid repeating the cost of engine setup.
///
/// Since almost nobody will need to implement `Engine`, docs for internal methods are hidden.
// When adding an implementation of Engine, include them in the engine test suite:
// - add an implementation of [engine::tests::EngineWrapper]
// - add the implementation to the `all_engines` macro
// All tests run on all engines listed in the macro.
pub trait Engine: Send + Sync {
    /// The config type used by this engine
    type Config: Config;
    /// The decode estimate used by this engine
    type DecodeEstimate: DecodeEstimate;

    /// This is not meant to be called directly; it is only for `Engine` implementors.
    /// See the other `encode*` functions on this trait.
    ///
    /// Encode the `input` bytes into the `output` buffer based on the mapping in `encode_table`.
    ///
    /// `output` will be long enough to hold the encoded data.
    ///
    /// Returns the number of bytes written.
    ///
    /// No padding should be written; that is handled separately.
    ///
    /// Must not write any bytes into the output slice other than the encoded data.
    #[doc(hidden)]
    fn internal_encode(&self, input: &[u8], output: &mut [u8]) -> usize;

    /// This is not meant to be called directly; it is only for `Engine` implementors.
    ///
    /// As an optimization to prevent the decoded length from being calculated twice, it is
    /// sometimes helpful to have a conservative estimate of the decoded size before doing the
    /// decoding, so this calculation is done separately and passed to [Engine::decode()] as needed.
    ///
    /// # Panics
    ///
    /// Panics if decoded length estimation overflows.
    #[doc(hidden)]
    fn internal_decoded_len_estimate(&self, input_len: usize) -> Self::DecodeEstimate;

    /// This is not meant to be called directly; it is only for `Engine` implementors.
    /// See the other `decode*` functions on this trait.
    ///
    /// Decode `input` base64 bytes into the `output` buffer.
    ///
    /// `decode_estimate` is the result of [Engine::internal_decoded_len_estimate()], which is passed in to avoid
    /// calculating it again (expensive on short inputs).`
    ///
    /// Returns the number of bytes written to `output`.
    ///
    /// Each complete 4-byte chunk of encoded data decodes to 3 bytes of decoded data, but this
    /// function must also handle the final possibly partial chunk.
    /// If the input length is not a multiple of 4, or uses padding bytes to reach a multiple of 4,
    /// the trailing 2 or 3 bytes must decode to 1 or 2 bytes, respectively, as per the
    /// [RFC](https://tools.ietf.org/html/rfc4648#section-3.5).
    ///
    /// Decoding must not write any bytes into the output slice other than the decoded data.
    ///
    /// Non-canonical trailing bits in the final tokens or non-canonical padding must be reported as
    /// errors unless the engine is configured otherwise.
    ///
    /// # Panics
    ///
    /// Panics if `output` is too small.
    #[doc(hidden)]
    fn internal_decode(
        &self,
        input: &[u8],
        output: &mut [u8],
        decode_estimate: Self::DecodeEstimate,
    ) -> Result<usize, DecodeError>;

    /// Returns the config for this engine.
    fn config(&self) -> &Self::Config;

    /// Encode arbitrary octets as base64 using the provided `Engine`.
    /// Returns a `String`.
    ///
    /// # Example
    ///
    /// ```rust
    /// use base64::{Engine as _, engine::{self, general_purpose}, alphabet};
    ///
    /// let b64 = general_purpose::STANDARD.encode(b"hello world~");
    /// println!("{}", b64);
    ///
    /// const CUSTOM_ENGINE: engine::GeneralPurpose =
    ///     engine::GeneralPurpose::new(&alphabet::URL_SAFE, general_purpose::NO_PAD);
    ///
    /// let b64_url = CUSTOM_ENGINE.encode(b"hello internet~");
    #[cfg(any(feature = "alloc", feature = "std", test))]
    fn encode<T: AsRef<[u8]>>(&self, input: T) -> String {
        let encoded_size = encoded_len(input.as_ref().len(), self.config().encode_padding())
            .expect("integer overflow when calculating buffer size");
        let mut buf = vec![0; encoded_size];

        encode_with_padding(input.as_ref(), &mut buf[..], self, encoded_size);

        String::from_utf8(buf).expect("Invalid UTF8")
    }

    /// Encode arbitrary octets as base64 into a supplied `String`.
    /// Writes into the supplied `String`, which may allocate if its internal buffer isn't big enough.
    ///
    /// # Example
    ///
    /// ```rust
    /// use base64::{Engine as _, engine::{self, general_purpose}, alphabet};
    /// const CUSTOM_ENGINE: engine::GeneralPurpose =
    ///     engine::GeneralPurpose::new(&alphabet::URL_SAFE, general_purpose::NO_PAD);
    ///
    /// fn main() {
    ///     let mut buf = String::new();
    ///     general_purpose::STANDARD.encode_string(b"hello world~", &mut buf);
    ///     println!("{}", buf);
    ///
    ///     buf.clear();
    ///     CUSTOM_ENGINE.encode_string(b"hello internet~", &mut buf);
    ///     println!("{}", buf);
    /// }
    /// ```
    #[cfg(any(feature = "alloc", feature = "std", test))]
    fn encode_string<T: AsRef<[u8]>>(&self, input: T, output_buf: &mut String) {
        let input_bytes = input.as_ref();

        {
            let mut sink = chunked_encoder::StringSink::new(output_buf);

            chunked_encoder::ChunkedEncoder::new(self)
                .encode(input_bytes, &mut sink)
                .expect("Writing to a String shouldn't fail");
        }
    }

    /// Encode arbitrary octets as base64 into a supplied slice.
    /// Writes into the supplied output buffer.
    ///
    /// This is useful if you wish to avoid allocation entirely (e.g. encoding into a stack-resident
    /// or statically-allocated buffer).
    ///
    /// # Example
    ///
    /// ```rust
    /// use base64::{Engine as _, engine::general_purpose};
    /// let s = b"hello internet!";
    /// let mut buf = Vec::new();
    /// // make sure we'll have a slice big enough for base64 + padding
    /// buf.resize(s.len() * 4 / 3 + 4, 0);
    ///
    /// let bytes_written = general_purpose::STANDARD.encode_slice(s, &mut buf).unwrap();
    ///
    /// // shorten our vec down to just what was written
    /// buf.truncate(bytes_written);
    ///
    /// assert_eq!(s, general_purpose::STANDARD.decode(&buf).unwrap().as_slice());
    /// ```
    fn encode_slice<T: AsRef<[u8]>>(
        &self,
        input: T,
        output_buf: &mut [u8],
    ) -> Result<usize, EncodeSliceError> {
        let input_bytes = input.as_ref();

        let encoded_size = encoded_len(input_bytes.len(), self.config().encode_padding())
            .expect("usize overflow when calculating buffer size");

        if output_buf.len() < encoded_size {
            return Err(EncodeSliceError::OutputSliceTooSmall);
        }

        let b64_output = &mut output_buf[0..encoded_size];

        encode_with_padding(input_bytes, b64_output, self, encoded_size);

        Ok(encoded_size)
    }

    /// Decode from string reference as octets using the specified [Engine].
    /// Returns a `Result` containing a `Vec<u8>`.
    ///
    /// # Example
    ///
    /// ```rust
    /// use base64::{Engine as _, alphabet, engine::{self, general_purpose}};
    ///
    /// let bytes = general_purpose::STANDARD
    ///     .decode("aGVsbG8gd29ybGR+Cg==").unwrap();
    /// println!("{:?}", bytes);
    ///
    /// // custom engine setup
    /// let bytes_url = engine::GeneralPurpose::new(
    ///              &alphabet::URL_SAFE,
    ///              general_purpose::NO_PAD)
    ///     .decode("aGVsbG8gaW50ZXJuZXR-Cg").unwrap();
    /// println!("{:?}", bytes_url);
    /// ```
    ///
    /// # Panics
    ///
    /// Panics if decoded length estimation overflows.
    /// This would happen for sizes within a few bytes of the maximum value of `usize`.
    #[cfg(any(feature = "alloc", feature = "std", test))]
    fn decode<T: AsRef<[u8]>>(&self, input: T) -> Result<Vec<u8>, DecodeError> {
        let input_bytes = input.as_ref();

        let estimate = self.internal_decoded_len_estimate(input_bytes.len());
        let mut buffer = vec![0; estimate.decoded_len_estimate()];

        let bytes_written = self.internal_decode(input_bytes, &mut buffer, estimate)?;
        buffer.truncate(bytes_written);

        Ok(buffer)
    }

    /// Decode from string reference as octets.
    /// Writes into the supplied `Vec`, which may allocate if its internal buffer isn't big enough.
    /// Returns a `Result` containing an empty tuple, aka `()`.
    ///
    /// # Example
    ///
    /// ```rust
    /// use base64::{Engine as _, alphabet, engine::{self, general_purpose}};
    /// const CUSTOM_ENGINE: engine::GeneralPurpose =
    ///     engine::GeneralPurpose::new(&alphabet::URL_SAFE, general_purpose::PAD);
    ///
    /// fn main() {
    ///     use base64::Engine;
    ///     let mut buffer = Vec::<u8>::new();
    ///     // with the default engine
    ///     general_purpose::STANDARD
    ///         .decode_vec("aGVsbG8gd29ybGR+Cg==", &mut buffer,).unwrap();
    ///     println!("{:?}", buffer);
    ///
    ///     buffer.clear();
    ///
    ///     // with a custom engine
    ///     CUSTOM_ENGINE.decode_vec(
    ///         "aGVsbG8gaW50ZXJuZXR-Cg==",
    ///         &mut buffer,
    ///     ).unwrap();
    ///     println!("{:?}", buffer);
    /// }
    /// ```
    ///
    /// # Panics
    ///
    /// Panics if decoded length estimation overflows.
    /// This would happen for sizes within a few bytes of the maximum value of `usize`.
    #[cfg(any(feature = "alloc", feature = "std", test))]
    fn decode_vec<T: AsRef<[u8]>>(
        &self,
        input: T,
        buffer: &mut Vec<u8>,
    ) -> Result<(), DecodeError> {
        let input_bytes = input.as_ref();

        let starting_output_len = buffer.len();

        let estimate = self.internal_decoded_len_estimate(input_bytes.len());
        let total_len_estimate = estimate
            .decoded_len_estimate()
            .checked_add(starting_output_len)
            .expect("Overflow when calculating output buffer length");
        buffer.resize(total_len_estimate, 0);

        let buffer_slice = &mut buffer.as_mut_slice()[starting_output_len..];
        let bytes_written = self.internal_decode(input_bytes, buffer_slice, estimate)?;

        buffer.truncate(starting_output_len + bytes_written);

        Ok(())
    }

    /// Decode the input into the provided output slice.
    ///
    /// Returns an error if `output` is smaller than the estimated decoded length.
    ///
    /// This will not write any bytes past exactly what is decoded (no stray garbage bytes at the end).
    ///
    /// See [crate::decoded_len_estimate] for calculating buffer sizes.
    ///
    /// See [Engine::decode_slice_unchecked] for a version that panics instead of returning an error
    /// if the output buffer is too small.
    ///
    /// # Panics
    ///
    /// Panics if decoded length estimation overflows.
    /// This would happen for sizes within a few bytes of the maximum value of `usize`.
    fn decode_slice<T: AsRef<[u8]>>(
        &self,
        input: T,
        output: &mut [u8],
    ) -> Result<usize, DecodeSliceError> {
        let input_bytes = input.as_ref();

        let estimate = self.internal_decoded_len_estimate(input_bytes.len());
        if output.len() < estimate.decoded_len_estimate() {
            return Err(DecodeSliceError::OutputSliceTooSmall);
        }

        self.internal_decode(input_bytes, output, estimate)
            .map_err(|e| e.into())
    }

    /// Decode the input into the provided output slice.
    ///
    /// This will not write any bytes past exactly what is decoded (no stray garbage bytes at the end).
    ///
    /// See [crate::decoded_len_estimate] for calculating buffer sizes.
    ///
    /// See [Engine::decode_slice] for a version that returns an error instead of panicking if the output
    /// buffer is too small.
    ///
    /// # Panics
    ///
    /// Panics if decoded length estimation overflows.
    /// This would happen for sizes within a few bytes of the maximum value of `usize`.
    ///
    /// Panics if the provided output buffer is too small for the decoded data.
    fn decode_slice_unchecked<T: AsRef<[u8]>>(
        &self,
        input: T,
        output: &mut [u8],
    ) -> Result<usize, DecodeError> {
        let input_bytes = input.as_ref();

        self.internal_decode(
            input_bytes,
            output,
            self.internal_decoded_len_estimate(input_bytes.len()),
        )
    }
}

/// The minimal level of configuration that engines must support.
pub trait Config {
    /// Returns `true` if padding should be added after the encoded output.
    ///
    /// Padding is added outside the engine's encode() since the engine may be used
    /// to encode only a chunk of the overall output, so it can't always know when
    /// the output is "done" and would therefore need padding (if configured).
    // It could be provided as a separate parameter when encoding, but that feels like
    // leaking an implementation detail to the user, and it's hopefully more convenient
    // to have to only pass one thing (the engine) to any part of the API.
    fn encode_padding(&self) -> bool;
}

/// The decode estimate used by an engine implementation. Users do not need to interact with this;
/// it is only for engine implementors.
///
/// Implementors may store relevant data here when constructing this to avoid having to calculate
/// them again during actual decoding.
pub trait DecodeEstimate {
    /// Returns a conservative (err on the side of too big) estimate of the decoded length to use
    /// for pre-allocating buffers, etc.
    ///
    /// The estimate must be no larger than the next largest complete triple of decoded bytes.
    /// That is, the final quad of tokens to decode may be assumed to be complete with no padding.
    ///
    /// # Panics
    ///
    /// Panics if decoded length estimation overflows.
    /// This would happen for sizes within a few bytes of the maximum value of `usize`.
    fn decoded_len_estimate(&self) -> usize;
}

/// Controls how pad bytes are handled when decoding.
///
/// Each [Engine] must support at least the behavior indicated by
/// [DecodePaddingMode::RequireCanonical], and may support other modes.
#[derive(Clone, Copy, Debug, PartialEq, Eq)]
pub enum DecodePaddingMode {
    /// Canonical padding is allowed, but any fewer padding bytes than that is also allowed.
    Indifferent,
    /// Padding must be canonical (0, 1, or 2 `=` as needed to produce a 4 byte suffix).
    RequireCanonical,
    /// Padding must be absent -- for when you want predictable padding, without any wasted bytes.
    RequireNone,
}