base64/
decode.rs

1use crate::engine::{general_purpose::STANDARD, DecodeEstimate, Engine};
2#[cfg(any(feature = "alloc", test))]
3use alloc::vec::Vec;
4use core::fmt;
5#[cfg(any(feature = "std", test))]
6use std::error;
7
8/// Errors that can occur while decoding.
9#[derive(Clone, Debug, PartialEq, Eq)]
10pub enum DecodeError {
11    /// An invalid byte was found in the input. The offset and offending byte are provided.
12    /// Padding characters (`=`) interspersed in the encoded form will be treated as invalid bytes.
13    InvalidByte(usize, u8),
14    /// The length of the input is invalid.
15    /// A typical cause of this is stray trailing whitespace or other separator bytes.
16    /// In the case where excess trailing bytes have produced an invalid length *and* the last byte
17    /// is also an invalid base64 symbol (as would be the case for whitespace, etc), `InvalidByte`
18    /// will be emitted instead of `InvalidLength` to make the issue easier to debug.
19    InvalidLength,
20    /// The last non-padding input symbol's encoded 6 bits have nonzero bits that will be discarded.
21    /// This is indicative of corrupted or truncated Base64.
22    /// Unlike `InvalidByte`, which reports symbols that aren't in the alphabet, this error is for
23    /// symbols that are in the alphabet but represent nonsensical encodings.
24    InvalidLastSymbol(usize, u8),
25    /// The nature of the padding was not as configured: absent or incorrect when it must be
26    /// canonical, or present when it must be absent, etc.
27    InvalidPadding,
28}
29
30impl fmt::Display for DecodeError {
31    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
32        match *self {
33            Self::InvalidByte(index, byte) => write!(f, "Invalid byte {}, offset {}.", byte, index),
34            Self::InvalidLength => write!(f, "Encoded text cannot have a 6-bit remainder."),
35            Self::InvalidLastSymbol(index, byte) => {
36                write!(f, "Invalid last symbol {}, offset {}.", byte, index)
37            }
38            Self::InvalidPadding => write!(f, "Invalid padding"),
39        }
40    }
41}
42
43#[cfg(any(feature = "std", test))]
44impl error::Error for DecodeError {}
45
46/// Errors that can occur while decoding into a slice.
47#[derive(Clone, Debug, PartialEq, Eq)]
48pub enum DecodeSliceError {
49    /// A [DecodeError] occurred
50    DecodeError(DecodeError),
51    /// The provided slice _may_ be too small.
52    ///
53    /// The check is conservative (assumes the last triplet of output bytes will all be needed).
54    OutputSliceTooSmall,
55}
56
57impl fmt::Display for DecodeSliceError {
58    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
59        match self {
60            Self::DecodeError(e) => write!(f, "DecodeError: {}", e),
61            Self::OutputSliceTooSmall => write!(f, "Output slice too small"),
62        }
63    }
64}
65
66#[cfg(any(feature = "std", test))]
67impl error::Error for DecodeSliceError {
68    fn source(&self) -> Option<&(dyn error::Error + 'static)> {
69        match self {
70            DecodeSliceError::DecodeError(e) => Some(e),
71            DecodeSliceError::OutputSliceTooSmall => None,
72        }
73    }
74}
75
76impl From<DecodeError> for DecodeSliceError {
77    fn from(e: DecodeError) -> Self {
78        DecodeSliceError::DecodeError(e)
79    }
80}
81
82/// Decode base64 using the [`STANDARD` engine](STANDARD).
83///
84/// See [Engine::decode].
85#[deprecated(since = "0.21.0", note = "Use Engine::decode")]
86#[cfg(any(feature = "alloc", test))]
87pub fn decode<T: AsRef<[u8]>>(input: T) -> Result<Vec<u8>, DecodeError> {
88    STANDARD.decode(input)
89}
90
91/// Decode from string reference as octets using the specified [Engine].
92///
93/// See [Engine::decode].
94///Returns a `Result` containing a `Vec<u8>`.
95#[deprecated(since = "0.21.0", note = "Use Engine::decode")]
96#[cfg(any(feature = "alloc", test))]
97pub fn decode_engine<E: Engine, T: AsRef<[u8]>>(
98    input: T,
99    engine: &E,
100) -> Result<Vec<u8>, DecodeError> {
101    engine.decode(input)
102}
103
104/// Decode from string reference as octets.
105///
106/// See [Engine::decode_vec].
107#[cfg(any(feature = "alloc", test))]
108#[deprecated(since = "0.21.0", note = "Use Engine::decode_vec")]
109pub fn decode_engine_vec<E: Engine, T: AsRef<[u8]>>(
110    input: T,
111    buffer: &mut Vec<u8>,
112    engine: &E,
113) -> Result<(), DecodeError> {
114    engine.decode_vec(input, buffer)
115}
116
117/// Decode the input into the provided output slice.
118///
119/// See [Engine::decode_slice].
120#[deprecated(since = "0.21.0", note = "Use Engine::decode_slice")]
121pub fn decode_engine_slice<E: Engine, T: AsRef<[u8]>>(
122    input: T,
123    output: &mut [u8],
124    engine: &E,
125) -> Result<usize, DecodeSliceError> {
126    engine.decode_slice(input, output)
127}
128
129/// Returns a conservative estimate of the decoded size of `encoded_len` base64 symbols (rounded up
130/// to the next group of 3 decoded bytes).
131///
132/// The resulting length will be a safe choice for the size of a decode buffer, but may have up to
133/// 2 trailing bytes that won't end up being needed.
134///
135/// # Examples
136///
137/// ```
138/// use base64::decoded_len_estimate;
139///
140/// assert_eq!(3, decoded_len_estimate(1));
141/// assert_eq!(3, decoded_len_estimate(2));
142/// assert_eq!(3, decoded_len_estimate(3));
143/// assert_eq!(3, decoded_len_estimate(4));
144/// // start of the next quad of encoded symbols
145/// assert_eq!(6, decoded_len_estimate(5));
146/// ```
147pub fn decoded_len_estimate(encoded_len: usize) -> usize {
148    STANDARD
149        .internal_decoded_len_estimate(encoded_len)
150        .decoded_len_estimate()
151}
152
153#[cfg(test)]
154mod tests {
155    use super::*;
156    use crate::{
157        alphabet,
158        engine::{general_purpose, Config, GeneralPurpose},
159        tests::{assert_encode_sanity, random_engine},
160    };
161    use rand::{
162        distributions::{Distribution, Uniform},
163        Rng, SeedableRng,
164    };
165
166    #[test]
167    fn decode_into_nonempty_vec_doesnt_clobber_existing_prefix() {
168        let mut orig_data = Vec::new();
169        let mut encoded_data = String::new();
170        let mut decoded_with_prefix = Vec::new();
171        let mut decoded_without_prefix = Vec::new();
172        let mut prefix = Vec::new();
173
174        let prefix_len_range = Uniform::new(0, 1000);
175        let input_len_range = Uniform::new(0, 1000);
176
177        let mut rng = rand::rngs::SmallRng::from_entropy();
178
179        for _ in 0..10_000 {
180            orig_data.clear();
181            encoded_data.clear();
182            decoded_with_prefix.clear();
183            decoded_without_prefix.clear();
184            prefix.clear();
185
186            let input_len = input_len_range.sample(&mut rng);
187
188            for _ in 0..input_len {
189                orig_data.push(rng.gen());
190            }
191
192            let engine = random_engine(&mut rng);
193            engine.encode_string(&orig_data, &mut encoded_data);
194            assert_encode_sanity(&encoded_data, engine.config().encode_padding(), input_len);
195
196            let prefix_len = prefix_len_range.sample(&mut rng);
197
198            // fill the buf with a prefix
199            for _ in 0..prefix_len {
200                prefix.push(rng.gen());
201            }
202
203            decoded_with_prefix.resize(prefix_len, 0);
204            decoded_with_prefix.copy_from_slice(&prefix);
205
206            // decode into the non-empty buf
207            engine
208                .decode_vec(&encoded_data, &mut decoded_with_prefix)
209                .unwrap();
210            // also decode into the empty buf
211            engine
212                .decode_vec(&encoded_data, &mut decoded_without_prefix)
213                .unwrap();
214
215            assert_eq!(
216                prefix_len + decoded_without_prefix.len(),
217                decoded_with_prefix.len()
218            );
219            assert_eq!(orig_data, decoded_without_prefix);
220
221            // append plain decode onto prefix
222            prefix.append(&mut decoded_without_prefix);
223
224            assert_eq!(prefix, decoded_with_prefix);
225        }
226    }
227
228    #[test]
229    fn decode_slice_doesnt_clobber_existing_prefix_or_suffix() {
230        do_decode_slice_doesnt_clobber_existing_prefix_or_suffix(|e, input, output| {
231            e.decode_slice(input, output).unwrap()
232        })
233    }
234
235    #[test]
236    fn decode_slice_unchecked_doesnt_clobber_existing_prefix_or_suffix() {
237        do_decode_slice_doesnt_clobber_existing_prefix_or_suffix(|e, input, output| {
238            e.decode_slice_unchecked(input, output).unwrap()
239        })
240    }
241
242    #[test]
243    fn decode_engine_estimation_works_for_various_lengths() {
244        let engine = GeneralPurpose::new(&alphabet::STANDARD, general_purpose::NO_PAD);
245        for num_prefix_quads in 0..100 {
246            for suffix in &["AA", "AAA", "AAAA"] {
247                let mut prefix = "AAAA".repeat(num_prefix_quads);
248                prefix.push_str(suffix);
249                // make sure no overflow (and thus a panic) occurs
250                let res = engine.decode(prefix);
251                assert!(res.is_ok());
252            }
253        }
254    }
255
256    #[test]
257    fn decode_slice_output_length_errors() {
258        for num_quads in 1..100 {
259            let input = "AAAA".repeat(num_quads);
260            let mut vec = vec![0; (num_quads - 1) * 3];
261            assert_eq!(
262                DecodeSliceError::OutputSliceTooSmall,
263                STANDARD.decode_slice(&input, &mut vec).unwrap_err()
264            );
265            vec.push(0);
266            assert_eq!(
267                DecodeSliceError::OutputSliceTooSmall,
268                STANDARD.decode_slice(&input, &mut vec).unwrap_err()
269            );
270            vec.push(0);
271            assert_eq!(
272                DecodeSliceError::OutputSliceTooSmall,
273                STANDARD.decode_slice(&input, &mut vec).unwrap_err()
274            );
275            vec.push(0);
276            // now it works
277            assert_eq!(
278                num_quads * 3,
279                STANDARD.decode_slice(&input, &mut vec).unwrap()
280            );
281        }
282    }
283
284    fn do_decode_slice_doesnt_clobber_existing_prefix_or_suffix<
285        F: Fn(&GeneralPurpose, &[u8], &mut [u8]) -> usize,
286    >(
287        call_decode: F,
288    ) {
289        let mut orig_data = Vec::new();
290        let mut encoded_data = String::new();
291        let mut decode_buf = Vec::new();
292        let mut decode_buf_copy: Vec<u8> = Vec::new();
293
294        let input_len_range = Uniform::new(0, 1000);
295
296        let mut rng = rand::rngs::SmallRng::from_entropy();
297
298        for _ in 0..10_000 {
299            orig_data.clear();
300            encoded_data.clear();
301            decode_buf.clear();
302            decode_buf_copy.clear();
303
304            let input_len = input_len_range.sample(&mut rng);
305
306            for _ in 0..input_len {
307                orig_data.push(rng.gen());
308            }
309
310            let engine = random_engine(&mut rng);
311            engine.encode_string(&orig_data, &mut encoded_data);
312            assert_encode_sanity(&encoded_data, engine.config().encode_padding(), input_len);
313
314            // fill the buffer with random garbage, long enough to have some room before and after
315            for _ in 0..5000 {
316                decode_buf.push(rng.gen());
317            }
318
319            // keep a copy for later comparison
320            decode_buf_copy.extend(decode_buf.iter());
321
322            let offset = 1000;
323
324            // decode into the non-empty buf
325            let decode_bytes_written =
326                call_decode(&engine, encoded_data.as_bytes(), &mut decode_buf[offset..]);
327
328            assert_eq!(orig_data.len(), decode_bytes_written);
329            assert_eq!(
330                orig_data,
331                &decode_buf[offset..(offset + decode_bytes_written)]
332            );
333            assert_eq!(&decode_buf_copy[0..offset], &decode_buf[0..offset]);
334            assert_eq!(
335                &decode_buf_copy[offset + decode_bytes_written..],
336                &decode_buf[offset + decode_bytes_written..]
337            );
338        }
339    }
340}
base64/decode.rs

base64/
decode.rs
