src/lib.rs

// Copyright 2015 Nicholas Allegra (comex).
// Licensed under the Apache License, Version 2.0 <http://www.apache.org/licenses/LICENSE-2.0> or
// the MIT license <http://opensource.org/licenses/MIT>, at your option. This file may not be
// copied, modified, or distributed except according to those terms.

//! Same idea as (but implementation not directly based on) the Python shlex module.  However, this
//! implementation does not support any of the Python module's customization because it makes
//! parsing slower and is fairly useless.  You only get the default settings of shlex.split, which
//! mimic the POSIX shell:
//! http://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html
//!
//! This implementation also deviates from the Python version in not treating \r specially, which I
//! believe is more compliant.
//!
//! The algorithms in this crate are oblivious to UTF-8 high bytes, so they iterate over the bytes
//! directly as a micro-optimization.

use std::borrow::Cow;

/// An iterator that takes an input string and splits it into the words using the same syntax as
/// the POSIX shell.
pub struct Shlex<'a> {
    in_iter: std::str::Bytes<'a>,
    /// The number of newlines read so far, plus one.
    pub line_no: usize,
    /// An input string is erroneous if it ends while inside a quotation or right after an
    /// unescaped backslash.  Since Iterator does not have a mechanism to return an error, if that
    /// happens, Shlex just throws out the last token, ends the iteration, and sets 'had_error' to
    /// true; best to check it after you're done iterating.
    pub had_error: bool,
}

impl<'a> Shlex<'a> {
    pub fn new(in_str: &'a str) -> Self {
        Shlex {
            in_iter: in_str.bytes(),
            line_no: 1,
            had_error: false,
        }
    }

    fn parse_word(&mut self, mut ch: u8) -> Option<String> {
        let mut result: Vec<u8> = Vec::new();
        loop {
            match ch as char {
                '"' => if let Err(()) = self.parse_double(&mut result) {
                    self.had_error = true;
                    return None;
                },
                '\'' => if let Err(()) = self.parse_single(&mut result) {
                    self.had_error = true;
                    return None;
                },
                '\\' => if let Some(ch2) = self.next_char() {
                    if ch2 != '\n' as u8 { result.push(ch2); }
                } else {
                    self.had_error = true;
                    return None;
                },
                ' ' | '\t' | '\n' => { break; },
                _ => { result.push(ch as u8); },
            }
            if let Some(ch2) = self.next_char() { ch = ch2; } else { break; }
        }
        unsafe { Some(String::from_utf8_unchecked(result)) }
    }

    fn parse_double(&mut self, result: &mut Vec<u8>) -> Result<(), ()> {
        loop {
            if let Some(ch2) = self.next_char() {
                match ch2 as char {
                    '\\' => {
                        if let Some(ch3) = self.next_char() {
                            match ch3 as char {
                                // \$ => $
                                '$' | '`' | '"' | '\\' => { result.push(ch3); },
                                // \<newline> => nothing
                                '\n' => {},
                                // \x => =x
                                _ => { result.push('\\' as u8); result.push(ch3); }
                            }
                        } else {
                            return Err(());
                        }
                    },
                    '"' => { return Ok(()); },
                    _ => { result.push(ch2); },
                }
            } else {
                return Err(());
            }
        }
    }

    fn parse_single(&mut self, result: &mut Vec<u8>) -> Result<(), ()> {
        loop {
            if let Some(ch2) = self.next_char() {
                match ch2 as char {
                    '\\' => {
                        if let Some(ch3) = self.next_char() {
                            match ch3 as char {
                                // for single quotes, only these can be escaped
                                '\'' | '\\' => { result.push(ch3); },
                                _ => { result.push('\\' as u8); result.push(ch3); }
                            }
                        } else {
                            return Err(());
                        }
                    },
                    '\'' => { return Ok(()); },
                    _ => { result.push(ch2); },
                }
            } else {
                return Err(());
            }
        }
    }

    fn next_char(&mut self) -> Option<u8> {
        let res = self.in_iter.next();
        if res == Some('\n' as u8) { self.line_no += 1; }
        res
    }
}

impl<'a> Iterator for Shlex<'a> {
    type Item = String;
    fn next(&mut self) -> Option<String> {
        if let Some(mut ch) = self.next_char() {
            // skip initial whitespace
            loop {
                match ch as char {
                    ' ' | '\t' | '\n' => {},
                    '#' => {
                        while let Some(ch2) = self.next_char() {
                            if ch2 as char == '\n' { break; }
                        }
                    },
                    _ => { break; }
                }
                if let Some(ch2) = self.next_char() { ch = ch2; } else { return None; }
            }
            self.parse_word(ch)
        } else { // no initial character
            None
        }
    }

}

/// Convenience function that consumes the whole string at once.  Returns None if the input was
/// erroneous.
pub fn split(in_str: &str) -> Option<Vec<String>> {
    let mut shl = Shlex::new(in_str);
    let res = shl.by_ref().collect();
    if shl.had_error { None } else { Some(res) }
}

/// Given a single word, return a string suitable to encode it as a shell argument.
pub fn quote(in_str: &str) -> Cow<str> {
    if in_str.len() == 0 {
        "\"\"".into()
    } else if in_str.bytes().any(|c| match c as char {
        '|' | '&' | ';' | '<' | '>' | '(' | ')' | '$' | '`' | '\\' | '"' | '\'' | ' ' | '\t' |
        '\r' | '\n' | '*' | '?' | '[' | '#' | '~' | '=' | '%' => true,
        _ => false
    }) {
        let mut out: Vec<u8> = Vec::new();
        out.push('"' as u8);
        for c in in_str.bytes() {
            match c as char {
                '$' | '`' | '"' | '\\' => out.push('\\' as u8),
                _ => ()
            }
            out.push(c);
        }
        out.push('"' as u8);
        unsafe { String::from_utf8_unchecked(out) }.into()
    } else {
        in_str.into()
    }
}

#[cfg(test)]
static SPLIT_TEST_ITEMS: &'static [(&'static str, Option<&'static [&'static str]>)] = &[
    ("foo$baz", Some(&["foo$baz"])),
    ("foo baz", Some(&["foo", "baz"])),
    ("foo\"bar\"baz", Some(&["foobarbaz"])),
    ("foo \"bar\"baz", Some(&["foo", "barbaz"])),
    ("   foo \nbar", Some(&["foo", "bar"])),
    ("foo\\\nbar", Some(&["foobar"])),
    ("\"foo\\\nbar\"", Some(&["foobar"])),
    ("'baz\\$b'", Some(&["baz\\$b"])),
    ("'baz\\\''", Some(&["baz\'"])),
    ("\\", None),
    ("\"\\", None),
    ("'\\", None),
    ("\"", None),
    ("'", None),
    ("foo #bar\nbaz", Some(&["foo", "baz"])),
    ("foo #bar", Some(&["foo"])),
    ("foo#bar", Some(&["foo#bar"])),
    ("foo\"#bar", None),
];

#[test]
fn test_split() {
    for &(input, output) in SPLIT_TEST_ITEMS {
        assert_eq!(split(input), output.map(|o| o.iter().map(|&x| x.to_owned()).collect()));
    }
}

#[test]
fn test_lineno() {
    let mut sh = Shlex::new("\nfoo\nbar");
    while let Some(word) = sh.next() {
        if word == "bar" {
            assert_eq!(sh.line_no, 3);
        }
    }
}

#[test]
fn test_quote() {
    assert_eq!(quote("foobar"), "foobar");
    assert_eq!(quote("foo bar"), "\"foo bar\"");
    assert_eq!(quote("\""), "\"\\\"\"");
    assert_eq!(quote(""), "\"\"");
}