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

//! Base64 encoding support.
use cvt_n;
use error::ErrorStack;
use ffi;
use libc::c_int;

/// Encodes a slice of bytes to a base64 string.
///
/// This corresponds to [`EVP_EncodeBlock`].
///
/// # Panics
///
/// Panics if the input length or computed output length overflow a signed C integer.
///
/// [`EVP_EncodeBlock`]: https://www.openssl.org/docs/man1.1.1/man3/EVP_DecodeBlock.html
pub fn encode_block(src: &[u8]) -> String {
    assert!(src.len() <= c_int::max_value() as usize);
    let src_len = src.len() as c_int;

    let len = encoded_len(src_len).unwrap();
    let mut out = Vec::with_capacity(len as usize);

    // SAFETY: `encoded_len` ensures space for 4 output characters
    // for every 3 input bytes including padding and nul terminator.
    // `EVP_EncodeBlock` will write only single byte ASCII characters.
    // `EVP_EncodeBlock` will only write to not read from `out`.
    unsafe {
        let out_len = ffi::EVP_EncodeBlock(out.as_mut_ptr(), src.as_ptr(), src_len);
        out.set_len(out_len as usize);
        String::from_utf8_unchecked(out)
    }
}

/// Decodes a base64-encoded string to bytes.
///
/// This corresponds to [`EVP_DecodeBlock`].
///
/// # Panics
///
/// Panics if the input length or computed output length overflow a signed C integer.
///
/// [`EVP_DecodeBlock`]: https://www.openssl.org/docs/man1.1.1/man3/EVP_DecodeBlock.html
pub fn decode_block(src: &str) -> Result<Vec<u8>, ErrorStack> {
    let src = src.trim();

    assert!(src.len() <= c_int::max_value() as usize);
    let src_len = src.len() as c_int;

    let len = decoded_len(src_len).unwrap();
    let mut out = Vec::with_capacity(len as usize);

    // SAFETY: `decoded_len` ensures space for 3 output bytes
    // for every 4 input characters including padding.
    // `EVP_DecodeBlock` can write fewer bytes after stripping
    // leading and trailing whitespace, but never more.
    // `EVP_DecodeBlock` will only write to not read from `out`.
    unsafe {
        let out_len = cvt_n(ffi::EVP_DecodeBlock(
            out.as_mut_ptr(),
            src.as_ptr(),
            src_len,
        ))?;
        out.set_len(out_len as usize);
    }

    if src.ends_with('=') {
        out.pop();
        if src.ends_with("==") {
            out.pop();
        }
    }

    Ok(out)
}

fn encoded_len(src_len: c_int) -> Option<c_int> {
    let mut len = (src_len / 3).checked_mul(4)?;

    if src_len % 3 != 0 {
        len = len.checked_add(4)?;
    }

    len = len.checked_add(1)?;

    Some(len)
}

fn decoded_len(src_len: c_int) -> Option<c_int> {
    let mut len = (src_len / 4).checked_mul(3)?;

    if src_len % 4 != 0 {
        len = len.checked_add(3)?;
    }

    Some(len)
}

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

    #[test]
    fn test_encode_block() {
        assert_eq!("".to_string(), encode_block(b""));
        assert_eq!("Zg==".to_string(), encode_block(b"f"));
        assert_eq!("Zm8=".to_string(), encode_block(b"fo"));
        assert_eq!("Zm9v".to_string(), encode_block(b"foo"));
        assert_eq!("Zm9vYg==".to_string(), encode_block(b"foob"));
        assert_eq!("Zm9vYmE=".to_string(), encode_block(b"fooba"));
        assert_eq!("Zm9vYmFy".to_string(), encode_block(b"foobar"));
    }

    #[test]
    fn test_decode_block() {
        assert_eq!(b"".to_vec(), decode_block("").unwrap());
        assert_eq!(b"f".to_vec(), decode_block("Zg==").unwrap());
        assert_eq!(b"fo".to_vec(), decode_block("Zm8=").unwrap());
        assert_eq!(b"foo".to_vec(), decode_block("Zm9v").unwrap());
        assert_eq!(b"foob".to_vec(), decode_block("Zm9vYg==").unwrap());
        assert_eq!(b"fooba".to_vec(), decode_block("Zm9vYmE=").unwrap());
        assert_eq!(b"foobar".to_vec(), decode_block("Zm9vYmFy").unwrap());
    }

    #[test]
    fn test_strip_whitespace() {
        assert_eq!(b"foobar".to_vec(), decode_block(" Zm9vYmFy\n").unwrap());
        assert_eq!(b"foob".to_vec(), decode_block(" Zm9vYg==\n").unwrap());
    }
}