A Write implementation that base64-encodes data using the provided config and accumulates the resulting base64 utf8 &str in a StrConsumer implementation (typically String), which is then exposed via into_inner().

Examples

Buffer base64 in a new String:

use std::io::Write;
use base64::engine::general_purpose;

let mut enc = base64::write::EncoderStringWriter::new(&general_purpose::STANDARD);

enc.write_all(b"asdf").unwrap();

// get the resulting String
let b64_string = enc.into_inner();

assert_eq!("YXNkZg==", &b64_string);

Or, append to an existing String, which implements StrConsumer:

use std::io::Write;
use base64::engine::general_purpose;

let mut buf = String::from("base64: ");

let mut enc = base64::write::EncoderStringWriter::from_consumer(
    &mut buf,
    &general_purpose::STANDARD);

enc.write_all(b"asdf").unwrap();

// release the &mut reference on buf
let _ = enc.into_inner();

assert_eq!("base64: YXNkZg==", &buf);

Performance

Because it has to validate that the base64 is UTF-8, it is about 80% as fast as writing plain bytes to a io::Write.