Method decoded_len

base64ct/src/decoder.rs:435–502

Get the total length of the data decoded from this line reader.

(&self)

    /// Get the total length of the data decoded from this line reader.
    fn decoded_len<E: Encoding>(&self) -> Result<usize, Error> {
        let mut buffer = [0u8; 4];
        let mut lines = self.clone();
        let mut line = match lines.next().transpose()? {
            Some(l) => l,
            None => return Ok(0),
        };
        let mut base64_len = 0usize;

        loop {
            base64_len = base64_len.checked_add(line.len()).ok_or(InvalidLength)?;

            match lines.next().transpose()? {
                Some(l) => {
                    // Store the end of the line in the buffer so we can
                    // reassemble the last block to determine the real length
                    buffer.copy_from_slice(line.slice_tail(4)?);

                    line = l
                }

                // To compute an exact decoded length we need to decode the
                // last Base64 block and get the decoded length.
                //
                // This is what the somewhat complex code below is doing.
                None => {
                    // Compute number of bytes in the last block (may be unpadded)
                    let base64_last_block_len = match base64_len % 4 {
                        0 => 4,
                        n => n,
                    };

                    // Compute decoded length without the last block
                    let decoded_len = encoding::decoded_len(
                        base64_len
                            .checked_sub(base64_last_block_len)
                            .ok_or(InvalidLength)?,
                    );

                    // Compute the decoded length of the last block
                    let mut out = [0u8; 3];
                    let last_block_len = if line.len() < base64_last_block_len {
                        let buffered_part_len = base64_last_block_len
                            .checked_sub(line.len())
                            .ok_or(InvalidLength)?;

                        let offset = 4usize.checked_sub(buffered_part_len).ok_or(InvalidLength)?;

                        for i in 0..buffered_part_len {
                            buffer[i] = buffer[offset.checked_add(i).ok_or(InvalidLength)?];
                        }

                        buffer[buffered_part_len..][..line.len()].copy_from_slice(line.remaining);
                        let buffer_len = buffered_part_len
                            .checked_add(line.len())
                            .ok_or(InvalidLength)?;

                        E::decode(&buffer[..buffer_len], &mut out)?.len()