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    //! Enables base64'd output anywhere you might use a `Display` implementation, like a format string.
    //!
    //! ```
    //! use base64::display::Base64Display;
    //!
    //! let data = vec![0x0, 0x1, 0x2, 0x3];
    //! let wrapper = Base64Display::with_config(&data, base64::STANDARD);
    //!
    //! assert_eq!("base64: AAECAw==", format!("base64: {}", wrapper));
    //! ```

    use super::chunked_encoder::ChunkedEncoder;
    use super::Config;
    use core::fmt::{Display, Formatter};
    use core::{fmt, str};

    /// A convenience wrapper for base64'ing bytes into a format string without heap allocation.
    pub struct Base64Display<'a> {
        bytes: &'a [u8],
        chunked_encoder: ChunkedEncoder,
    }

    impl<'a> Base64Display<'a> {
        /// Create a `Base64Display` with the provided config.
        pub fn with_config(bytes: &[u8], config: Config) -> Base64Display {
            Base64Display {
                bytes,
                chunked_encoder: ChunkedEncoder::new(config),
            }
        }
    }

    impl<'a> Display for Base64Display<'a> {
        fn fmt(&self, formatter: &mut Formatter) -> Result<(), fmt::Error> {
            let mut sink = FormatterSink { f: formatter };
            self.chunked_encoder.encode(self.bytes, &mut sink)
        }
    }

    struct FormatterSink<'a, 'b: 'a> {
        f: &'a mut Formatter<'b>,
    }

    impl<'a, 'b: 'a> super::chunked_encoder::Sink for FormatterSink<'a, 'b> {
        type Error = fmt::Error;

        fn write_encoded_bytes(&mut self, encoded: &[u8]) -> Result<(), Self::Error> {
            // Avoid unsafe. If max performance is needed, write your own display wrapper that uses
            // unsafe here to gain about 10-15%.
            self.f
                .write_str(str::from_utf8(encoded).expect("base64 data was not utf8"))
        }
    }

    #[cfg(test)]
    mod tests {
        use super::super::chunked_encoder::tests::{
            chunked_encode_matches_normal_encode_random, SinkTestHelper,
        };
        use super::super::*;
        use super::*;

        #[test]
        fn basic_display() {
            assert_eq!(
                "~$Zm9vYmFy#*",
                format!("~${}#*", Base64Display::with_config(b"foobar", STANDARD))
            );
            assert_eq!(
                "~$Zm9vYmFyZg==#*",
                format!("~${}#*", Base64Display::with_config(b"foobarf", STANDARD))
            );
        }

        #[test]
        fn display_encode_matches_normal_encode() {
            let helper = DisplaySinkTestHelper;
            chunked_encode_matches_normal_encode_random(&helper);
        }

        struct DisplaySinkTestHelper;

        impl SinkTestHelper for DisplaySinkTestHelper {
            fn encode_to_string(&self, config: Config, bytes: &[u8]) -> String {
                format!("{}", Base64Display::with_config(bytes, config))
            }
        }
    }