stfu8 0.2.7

Sorta Text Format in UTF-8
Documentation 
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/* Copyright (c) 2018 Garrett Berg, vitiral@gmail.com
 * Original Copyright 2012-2014 The Rust Project Developers
 *
 * Licensed under the Apache License, Version 2.0, <LICENSE-APACHE or
 * http://apache.org/licenses/LICENSE-2.0> or the MIT license <LICENSE-MIT or
 * http://opensource.org/licenses/MIT>, at your option. This file may not be
 * copied, modified, or distributed except according to those terms.
 */
//! This code is practically copy/pasted from the rust std libraries'
//! `run_utf8_validation` function, used by `str::from_utf8`.

use std::str;

use helpers;

/*
Section: UTF-8 validation
*/

/// Pretty much an exact copy of `run_utf8_validation` from the rust stdlib.
pub(crate) fn encode(encoder: &super::Encoder, v: &[u8]) -> String {
    let mut index = 0;
    let len = v.len();
    let mut out = String::with_capacity(len + len / 8);

    while index < len {
        let old_offset = index;

        /// write a single byte that may be ascii.
        /// Escape it correctly no matter what.
        macro_rules! maybe_ascii {
            ($i: expr) => {{
                let b = v[$i];
                match b {
                    helpers::BSLASH => helpers::escape_u8(&mut out, encoder, b),
                    0x20..=0x7e => out.push(b as char), // visible ASCII
                    0x00..=0x1F | 0x7f..=0xFF => helpers::escape_u8(&mut out, encoder, b),
                }
            }};
        }

        /// Escape everything from `old_offset` to current index.
        /// It is invalid STFU-8 (which might be invalid utf8,
        /// or could just be the `\` character...)
        macro_rules! escape_them {
            () => {{
                for i in old_offset..(index + 1) {
                    maybe_ascii!(i);
                }
                index += 1;
                continue;
            }};
        }

        /// write everything from `old_offset` to current-index -- it
        /// is all valid utf8 and stfu8.
        macro_rules! write_them {
            () => {{
                out.push_str(&str::from_utf8(&v[old_offset..(index + 1)]).unwrap());
            }};
        }

        macro_rules! next {
            () => {{
                index += 1;
                if index >= len {
                    index -= 1;
                    escape_them!();
                }
                v[index]
            }};
        }

        let first = v[index];
        if first >= 128 {
            let w = UTF8_CHAR_WIDTH[first as usize];
            // 2-byte encoding is for codepoints  \u{0080} to  \u{07ff}
            //        first  C2 80        last DF BF
            // 3-byte encoding is for codepoints  \u{0800} to  \u{ffff}
            //        first  E0 A0 80     last EF BF BF
            //   excluding surrogates codepoints  \u{d800} to  \u{dfff}
            //               ED A0 80 to       ED BF BF
            // 4-byte encoding is for codepoints \u{1000}0 to \u{10ff}ff
            //        first  F0 90 80 80  last F4 8F BF BF
            //
            // Use the UTF-8 syntax from the RFC
            //
            // https://tools.ietf.org/html/rfc3629
            // UTF8-1      = %x00-7F
            // UTF8-2      = %xC2-DF UTF8-tail
            // UTF8-3      = %xE0 %xA0-BF UTF8-tail / %xE1-EC 2( UTF8-tail ) /
            //               %xED %x80-9F UTF8-tail / %xEE-EF 2( UTF8-tail )
            // UTF8-4      = %xF0 %x90-BF 2( UTF8-tail ) / %xF1-F3 3( UTF8-tail ) /
            //               %xF4 %x80-8F 2( UTF8-tail )
            match w {
                2 => {
                    if next!() & !CONT_MASK != TAG_CONT_U8 {
                        escape_them!(); //orig: err!(Some(1))
                    }
                }
                3 => {
                    match (first, next!()) {
                        (0xE0, 0xA0..=0xBF)
                        | (0xE1..=0xEC, 0x80..=0xBF)
                        | (0xED, 0x80..=0x9F)
                        | (0xEE..=0xEF, 0x80..=0xBF) => {}
                        _ => escape_them!(), // orig: err!(Some(1))
                    }
                    if next!() & !CONT_MASK != TAG_CONT_U8 {
                        escape_them!(); //orig: err!(Some(2))
                    }
                }
                4 => {
                    match (first, next!()) {
                        (0xF0, 0x90..=0xBF) | (0xF1..=0xF3, 0x80..=0xBF) | (0xF4, 0x80..=0x8F) => {}
                        _ => escape_them!(), //orig: err!(Some(1))
                    }
                    if next!() & !CONT_MASK != TAG_CONT_U8 {
                        escape_them!(); //orig: err!(Some(2))
                    }
                    if next!() & !CONT_MASK != TAG_CONT_U8 {
                        escape_them!(); //orig: err!(Some(3))
                    }
                }
                _ => escape_them!(), //orig: err!(Some(1))
            }
            // they were not invalid, so they are valid
            write_them!();
            index += 1;
        } else {
            // Ascii case
            maybe_ascii!(index);
            index += 1;
        }
    }
    out
}

// https://tools.ietf.org/html/rfc3629
static UTF8_CHAR_WIDTH: [u8; 256] = [
    1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, // 0x0F
    1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, // 0x1F
    1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, // 0x2F
    1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, // 0x3F
    1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, // 0x4F
    1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, // 0x5F
    1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, // 0x6F
    1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, // 0x7F
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, // 0x8F
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, // 0x9F
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, // 0xAF
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, // 0xBF
    0, 0, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, // 0xCF
    2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, // 0xDF
    3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, // 0xEF
    4, 4, 4, 4, 4, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, // 0xFF
];

/// Mask of the value bits of a continuation byte.
const CONT_MASK: u8 = 0b0011_1111;
/// Value of the tag bits (tag mask is !`CONT_MASK`) of a continuation byte.
const TAG_CONT_U8: u8 = 0b1000_0000;

#[test]
fn sanity_encode() {
    fn enc(s: &str) -> String {
        let out = encode(&super::Encoder::new(), s.as_bytes());
        // validation, we may use from_utf8_unchecked in the future
        let _ = ::std::str::from_utf8(&out.as_bytes()).unwrap();
        out
    }
    fn assert_enc(s: &str) {
        assert_eq!(enc(s), s);
    }
    assert_enc("foo bar");
    assert_enc("¡ ¢ £ ¤ ¥ ¦ § ¨ © ª « ¬ ­");
    assert_enc(" ʰ ʱ ʲ ʳ ʴ ʵ ʶ ʷ ʸ ʹ ʺ ʻ");
    assert_enc("܀ ܁ ܂ ܃ ܄ ܅ ܆ ܇ ܈ ܉ ܊ ܋ ܌ ܍ ܏");
    assert_enc("Ꭰ Ꭱ Ꭲ Ꭳ Ꭴ Ꭵ Ꭶ Ꭷ Ꭸ Ꭹ");
    assert_enc("ἀ ἁ ἂ ἃ ἄ ἅ ἆ ἇ Ἀ Ἁ");
    assert_enc("                          ​ ‌ ‍ ‎ ‏ ‐ ");
    assert_enc("‑ ‒ – — ― ‖ ‗ ‘ ’ ‚ ‛ “");
    assert_enc("    ⃐ ⃑ ⃒ ⃓ ⃔ ⃕ ⃖ ⃗ ⃘ ⃙ ⃚ ⃛ ⃜ ⃝ ⃞ ⃟ ⃠ ⃡ ⃢ ⃣ ⃤ ⃥ ⃦ ⃧ ⃨ ⃩ ⃪ ");

    // Test that `\` gets escaped
    assert_eq!(
        /**/ enc("¡ ¢ £ ¤ \\¥ ¦ § ¨ © ª « \\¬ ­"),
        /*   */ r"¡ ¢ £ ¤ \\¥ ¦ § ¨ © ª « \\¬ ­"
    );

    // Test that newlines gets escaped
    assert_eq!(
        /**/ enc("Ā ā Ă \nă Ą ą Ć\n ć Ĉ ĉ\n"),
        /*   */ r"Ā ā Ă \nă Ą ą Ć\n ć Ĉ ĉ\n",
    );
}

#[test]
fn sanity_encode_binary() {
    let mut bytes: Vec<u8> = Vec::new();
    bytes.extend_from_slice("¡ ¢ £".as_bytes());
    bytes.extend_from_slice(b"\t\n\r"); // "\x09\x0a\x0d"
    bytes.extend_from_slice(b"\x07\x7f\xFE");
    bytes.extend_from_slice("¤ ¥ ¦".as_bytes());
    assert_eq!(
        encode(&super::Encoder::new(), &bytes),
        r"¡ ¢ £\t\n\r\x07\x7F\xFE¤ ¥ ¦"
    );
}

#[test]
fn sanity_encode_pretty() {
    let expected = "foo\nbar\n";
    let result = encode(&super::Encoder::pretty(), expected.as_bytes());
    assert_eq!(expected, result);
}