# encode.rs - source
Source of the Rust file `/home/justine/.cargo/registry/src/github.com-1ecc6299db9ec823/base64-0.13.1/src/encode.rs`.
Keywords: rust, rustlang, rust-lang

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    use crate::{Config, PAD_BYTE};
    #[cfg(any(feature = "alloc", feature = "std", test))]
    use crate::{chunked_encoder, STANDARD};
    #[cfg(any(feature = "alloc", feature = "std", test))]
    use alloc::{string::String, vec};
    use core::convert::TryInto;

    ///Encode arbitrary octets as base64.
    ///Returns a String.
    ///Convenience for `encode_config(input, base64::STANDARD);`.
    ///
    ///# Example
    ///
    ///```rust
    ///extern crate base64;
    ///
    ///fn main() {
    ///    let b64 = base64::encode(b"hello world");
    ///    println!("{}", b64);
    ///}
    ///```
    #[cfg(any(feature = "alloc", feature = "std", test))]
    pub fn encode<T: AsRef<[u8]>>(input: T) -> String {
        encode_config(input, STANDARD)
    }

    ///Encode arbitrary octets as base64.
    ///Returns a String.
    ///
    ///# Example
    ///
    ///```rust
    ///extern crate base64;
    ///
    ///fn main() {
    ///    let b64 = base64::encode_config(b"hello world~", base64::STANDARD);
    ///    println!("{}", b64);
    ///
    ///    let b64_url = base64::encode_config(b"hello internet~", base64::URL_SAFE);
    ///    println!("{}", b64_url);
    ///}
    ///```
    #[cfg(any(feature = "alloc", feature = "std", test))]
    pub fn encode_config<T: AsRef<[u8]>>(input: T, config: Config) -> String {
        let mut buf = match encoded_size(input.as_ref().len(), config) {
            Some(n) => vec![0; n],
            None => panic!("integer overflow when calculating buffer size"),
        };

        encode_with_padding(input.as_ref(), config, buf.len(), &mut buf[..]);

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

    ///Encode arbitrary octets as base64.
    ///Writes into the supplied output buffer, which will grow the buffer if needed.
    ///
    ///# Example
    ///
    ///```rust
    ///extern crate base64;
    ///
    ///fn main() {
    ///    let mut buf = String::new();
    ///    base64::encode_config_buf(b"hello world~", base64::STANDARD, &mut buf);
    ///    println!("{}", buf);
    ///
    ///    buf.clear();
    ///    base64::encode_config_buf(b"hello internet~", base64::URL_SAFE, &mut buf);
    ///    println!("{}", buf);
    ///}
    ///```
    #[cfg(any(feature = "alloc", feature = "std", test))]
    pub fn encode_config_buf<T: AsRef<[u8]>>(input: T, config: Config, buf: &mut String) {
        let input_bytes = input.as_ref();

        {
            let mut sink = chunked_encoder::StringSink::new(buf);
            let encoder = chunked_encoder::ChunkedEncoder::new(config);

            encoder
                .encode(input_bytes, &mut sink)
                .expect("Writing to a String shouldn't fail")
        }
    }

    /// Encode arbitrary octets as base64.
    /// 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).
    ///
    /// # Panics
    ///
    /// If `output` is too small to hold the encoded version of `input`, a panic will result.
    ///
    /// # Example
    ///
    /// ```rust
    /// extern crate base64;
    ///
    /// fn main() {
    ///     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 = base64::encode_config_slice(s,
    ///                             base64::STANDARD, &mut buf);
    ///
    ///     // shorten our vec down to just what was written
    ///     buf.resize(bytes_written, 0);
    ///
    ///     assert_eq!(s, base64::decode(&buf).unwrap().as_slice());
    /// }
    /// ```
    pub fn encode_config_slice<T: AsRef<[u8]>>(input: T, config: Config, output: &mut [u8]) -> usize {
        let input_bytes = input.as_ref();

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

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

        encode_with_padding(&input_bytes, config, encoded_size, &mut b64_output);

        encoded_size
    }

    /// 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.
    fn encode_with_padding(input: &[u8], config: Config, encoded_size: usize, output: &mut [u8]) {
        debug_assert_eq!(encoded_size, output.len());

        let b64_bytes_written = encode_to_slice(input, output, config.char_set.encode_table());

        let padding_bytes = if config.pad {
            add_padding(input.len(), &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!(encoded_size, encoded_bytes);
    }

    #[inline]
    fn read_u64(s: &[u8]) -> u64 {
        u64::from_be_bytes(s[..8].try_into().unwrap())
    }

    /// Encode input bytes to utf8 base64 bytes. Does not pad.
    /// `output` must be long enough to hold the encoded `input` without padding.
    /// Returns the number of bytes written.
    #[inline]
    pub fn encode_to_slice(input: &[u8], output: &mut [u8], encode_table: &[u8; 64]) -> usize {
        let mut input_index: usize = 0;

        const BLOCKS_PER_FAST_LOOP: usize = 4;
        const LOW_SIX_BITS: u64 = 0x3F;

        // we read 8 bytes at a time (u64) but only actually consume 6 of those bytes. Thus, we need
        // 2 trailing bytes to be available to read..
        let last_fast_index = input.len().saturating_sub(BLOCKS_PER_FAST_LOOP * 6 + 2);
        let mut output_index = 0;

        if last_fast_index > 0 {
            while input_index <= last_fast_index {
                // Major performance wins from letting the optimizer do the bounds check once, mostly
                // on the output side
                let input_chunk = &input[input_index..(input_index + (BLOCKS_PER_FAST_LOOP * 6 + 2))];
                let output_chunk = &mut output[output_index..(output_index + BLOCKS_PER_FAST_LOOP * 8)];

                // Hand-unrolling for 32 vs 16 or 8 bytes produces yields performance about equivalent
                // to unsafe pointer code on a Xeon E5-1650v3. 64 byte unrolling was slightly better for
                // large inputs but significantly worse for 50-byte input, unsurprisingly. I suspect
                // that it's a not uncommon use case to encode smallish chunks of data (e.g. a 64-byte
                // SHA-512 digest), so it would be nice if that fit in the unrolled loop at least once.
                // Plus, single-digit percentage performance differences might well be quite different
                // on different hardware.

                let input_u64 = read_u64(&input_chunk[0..]);

                output_chunk[0] = encode_table[((input_u64 >> 58) & LOW_SIX_BITS) as usize];
                output_chunk[1] = encode_table[((input_u64 >> 52) & LOW_SIX_BITS) as usize];
                output_chunk[2] = encode_table[((input_u64 >> 46) & LOW_SIX_BITS) as usize];
                output_chunk[3] = encode_table[((input_u64 >> 40) & LOW_SIX_BITS) as usize];
                output_chunk[4] = encode_table[((input_u64 >> 34) & LOW_SIX_BITS) as usize];
                output_chunk[5] = encode_table[((input_u64 >> 28) & LOW_SIX_BITS) as usize];
                output_chunk[6] = encode_table[((input_u64 >> 22) & LOW_SIX_BITS) as usize];
                output_chunk[7] = encode_table[((input_u64 >> 16) & LOW_SIX_BITS) as usize];

                let input_u64 = read_u64(&input_chunk[6..]);

                output_chunk[8] = encode_table[((input_u64 >> 58) & LOW_SIX_BITS) as usize];
                output_chunk[9] = encode_table[((input_u64 >> 52) & LOW_SIX_BITS) as usize];
                output_chunk[10] = encode_table[((input_u64 >> 46) & LOW_SIX_BITS) as usize];
                output_chunk[11] = encode_table[((input_u64 >> 40) & LOW_SIX_BITS) as usize];
                output_chunk[12] = encode_table[((input_u64 >> 34) & LOW_SIX_BITS) as usize];
                output_chunk[13] = encode_table[((input_u64 >> 28) & LOW_SIX_BITS) as usize];
                output_chunk[14] = encode_table[((input_u64 >> 22) & LOW_SIX_BITS) as usize];
                output_chunk[15] = encode_table[((input_u64 >> 16) & LOW_SIX_BITS) as usize];

                let input_u64 = read_u64(&input_chunk[12..]);

                output_chunk[16] = encode_table[((input_u64 >> 58) & LOW_SIX_BITS) as usize];
                output_chunk[17] = encode_table[((input_u64 >> 52) & LOW_SIX_BITS) as usize];
                output_chunk[18] = encode_table[((input_u64 >> 46) & LOW_SIX_BITS) as usize];
                output_chunk[19] = encode_table[((input_u64 >> 40) & LOW_SIX_BITS) as usize];
                output_chunk[20] = encode_table[((input_u64 >> 34) & LOW_SIX_BITS) as usize];
                output_chunk[21] = encode_table[((input_u64 >> 28) & LOW_SIX_BITS) as usize];
                output_chunk[22] = encode_table[((input_u64 >> 22) & LOW_SIX_BITS) as usize];
                output_chunk[23] = encode_table[((input_u64 >> 16) & LOW_SIX_BITS) as usize];

                let input_u64 = read_u64(&input_chunk[18..]);

                output_chunk[24] = encode_table[((input_u64 >> 58) & LOW_SIX_BITS) as usize];
                output_chunk[25] = encode_table[((input_u64 >> 52) & LOW_SIX_BITS) as usize];
                output_chunk[26] = encode_table[((input_u64 >> 46) & LOW_SIX_BITS) as usize];
                output_chunk[27] = encode_table[((input_u64 >> 40) & LOW_SIX_BITS) as usize];
                output_chunk[28] = encode_table[((input_u64 >> 34) & LOW_SIX_BITS) as usize];
                output_chunk[29] = encode_table[((input_u64 >> 28) & LOW_SIX_BITS) as usize];
                output_chunk[30] = encode_table[((input_u64 >> 22) & LOW_SIX_BITS) as usize];
                output_chunk[31] = encode_table[((input_u64 >> 16) & LOW_SIX_BITS) as usize];

                output_index += BLOCKS_PER_FAST_LOOP * 8;
                input_index += BLOCKS_PER_FAST_LOOP * 6;
            }
        }

        // Encode what's left after the fast loop.

        const LOW_SIX_BITS_U8: u8 = 0x3F;

        let rem = input.len() % 3;
        let start_of_rem = input.len() - rem;

        // start at the first index not handled by fast loop, which may be 0.

        while input_index < start_of_rem {
            let input_chunk = &input[input_index..(input_index + 3)];
            let output_chunk = &mut output[output_index..(output_index + 4)];

            output_chunk[0] = encode_table[(input_chunk[0] >> 2) as usize];
            output_chunk[1] =
                encode_table[((input_chunk[0] << 4 | input_chunk[1] >> 4) & LOW_SIX_BITS_U8) as usize];
            output_chunk[2] =
                encode_table[((input_chunk[1] << 2 | input_chunk[2] >> 6) & LOW_SIX_BITS_U8) as usize];
            output_chunk[3] = encode_table[(input_chunk[2] & LOW_SIX_BITS_U8) as usize];

            input_index += 3;
            output_index += 4;
        }

        if rem == 2 {
            output[output_index] = encode_table[(input[start_of_rem] >> 2) as usize];
            output[output_index + 1] = encode_table[((input[start_of_rem] << 4
                | input[start_of_rem + 1] >> 4)
                & LOW_SIX_BITS_U8) as usize];
            output[output_index + 2] =
                encode_table[((input[start_of_rem + 1] << 2) & LOW_SIX_BITS_U8) as usize];
            output_index += 3;
        } else if rem == 1 {
            output[output_index] = encode_table[(input[start_of_rem] >> 2) as usize];
            output[output_index + 1] =
                encode_table[((input[start_of_rem] << 4) & LOW_SIX_BITS_U8) as usize];
            output_index += 2;
        }

        output_index
    }

    /// calculate the base64 encoded string size, including padding if appropriate
    pub fn encoded_size(bytes_len: usize, config: Config) -> Option<usize> {
        let rem = bytes_len % 3;

        let complete_input_chunks = bytes_len / 3;
        let complete_chunk_output = complete_input_chunks.checked_mul(4);

        if rem > 0 {
            if config.pad {
                complete_chunk_output.and_then(|c| c.checked_add(4))
            } else {
                let encoded_rem = match rem {
                    1 => 2,
                    2 => 3,
                    _ => unreachable!("Impossible remainder"),
                };
                complete_chunk_output.and_then(|c| c.checked_add(encoded_rem))
            }
        } else {
            complete_chunk_output
        }
    }

    /// Write padding characters.
    /// `output` is the slice where padding should be written, of length at least 2.
    ///
    /// Returns the number of padding bytes written.
    pub fn add_padding(input_len: usize, output: &mut [u8]) -> usize {
        let rem = input_len % 3;
        let mut bytes_written = 0;
        for _ in 0..((3 - rem) % 3) {
            output[bytes_written] = PAD_BYTE;
            bytes_written += 1;
        }

        bytes_written
    }

    #[cfg(test)]
    mod tests {
        use super::*;
        use crate::{
            decode::decode_config_buf,
            tests::{assert_encode_sanity, random_config},
            Config, STANDARD, URL_SAFE_NO_PAD,
        };

        use rand::{
            distributions::{Distribution, Uniform},
            FromEntropy, Rng,
        };
        use std;
        use std::str;

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

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

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

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

            assert_encoded_length(54, 72, STANDARD);

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

            assert_encoded_length(58, 80, STANDARD);
        }

        #[test]
        fn encoded_size_correct_no_pad() {
            assert_encoded_length(0, 0, URL_SAFE_NO_PAD);

            assert_encoded_length(1, 2, URL_SAFE_NO_PAD);
            assert_encoded_length(2, 3, URL_SAFE_NO_PAD);
            assert_encoded_length(3, 4, URL_SAFE_NO_PAD);

            assert_encoded_length(4, 6, URL_SAFE_NO_PAD);
            assert_encoded_length(5, 7, URL_SAFE_NO_PAD);
            assert_encoded_length(6, 8, URL_SAFE_NO_PAD);

            assert_encoded_length(7, 10, URL_SAFE_NO_PAD);
            assert_encoded_length(8, 11, URL_SAFE_NO_PAD);
            assert_encoded_length(9, 12, URL_SAFE_NO_PAD);

            assert_encoded_length(54, 72, URL_SAFE_NO_PAD);

            assert_encoded_length(55, 74, URL_SAFE_NO_PAD);
            assert_encoded_length(56, 75, URL_SAFE_NO_PAD);
            assert_encoded_length(57, 76, URL_SAFE_NO_PAD);

            assert_encoded_length(58, 78, URL_SAFE_NO_PAD);
        }

        #[test]
        fn encoded_size_overflow() {
            assert_eq!(None, encoded_size(std::usize::MAX, STANDARD));
        }

        #[test]
        fn encode_config_buf_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 config = random_config(&mut rng);
                encode_config_buf(&orig_data, config, &mut encoded_data_no_prefix);
                encode_config_buf(&orig_data, config, &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, config, input_len);
                assert_encode_sanity(&encoded_data_with_prefix[prefix_len..], config, input_len);

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

                assert_eq!(prefix, encoded_data_with_prefix);

                decode_config_buf(&encoded_data_no_prefix, config, &mut decoded).unwrap();
                assert_eq!(orig_data, decoded);
            }
        }

        #[test]
        fn encode_config_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 config = random_config(&mut rng);

                let encoded_size = encoded_size(input_len, config).unwrap();

                assert_eq!(
                    encoded_size,
                    encode_config_slice(&orig_data, config, &mut encoded_data)
                );

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

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

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

        #[test]
        fn encode_config_slice_fits_into_precisely_sized_slice() {
            let mut orig_data = Vec::new();
            let mut encoded_data = 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();
                decoded.clear();

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

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

                let config = random_config(&mut rng);

                let encoded_size = encoded_size(input_len, config).unwrap();

                encoded_data.resize(encoded_size, 0);

                assert_eq!(
                    encoded_size,
                    encode_config_slice(&orig_data, config, &mut encoded_data)
                );

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

                decode_config_buf(&encoded_data[0..encoded_size], config, &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);

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

                let orig_output_buf = output.to_vec();

                let bytes_written =
                    encode_to_slice(&input, &mut output, config.char_set.encode_table());

                // 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 config = random_config(&mut rng);

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

                let orig_output_buf = output.to_vec();

                encode_with_padding(&input, config, encoded_size, &mut output[0..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 % 3
            for input_len in 0..10 {
                output.clear();

                // fill output with random
                for _ in 0..10 {
                    output.push(rng.gen());
                }

                let orig_output_buf = output.to_vec();

                let bytes_written = add_padding(input_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(input_len: usize, encoded_len: usize, config: Config) {
            assert_eq!(encoded_len, encoded_size(input_len, config).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 = encode_config(&bytes, config);
            assert_encode_sanity(&encoded, config, input_len);

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

        #[test]
        fn encode_imap() {
            assert_eq!(
                encode_config(b"\xFB\xFF", crate::IMAP_MUTF7),
                encode_config(b"\xFB\xFF", crate::STANDARD_NO_PAD).replace("/", ",")
            );
        }
    }