Function record 

pub fn record(
    bytes: &[u8],
    from: usize,
    dialect: Dialect,
    eof: bool,
    out: &mut Vec<String>,
) -> Result<Option<usize>>

Reads the record starting at from into out, and answers where the next one starts.

None means the buffer does not hold a whole record: either it ran out mid line and more bytes may follow, or a quoted field was left open. With eof set there are no more bytes, so a last line with no newline on the end is a record like any other and only an open quote is short.

Errors

When a quoted field has something other than a delimiter or a line ending after its closing quote, which is a file that is not the file it claims to be and reading past it would invent data.