add str traits for split, between, unquote; consolidate tests

Signed-off-by: Jason Volk <jason@zemos.net>

src/core/utils/string/unquote.rs

@@ -0,0 +1,33 @@
+const QUOTE: char = '"';
+
+/// Slice a string between quotes
+pub trait Unquote<'a> {
+	/// Whether the input is quoted. If this is false the fallible methods of
+	/// this interface will fail.
+	fn is_quoted(&self) -> bool;
+
+	/// Unquotes a string. If the input is not quoted it is simply returned
+	/// as-is. If the input is partially quoted on either end that quote is not
+	/// removed.
+	fn unquote(&self) -> Option<&'a str>;
+
+	/// Unquotes a string. The input must be quoted on each side for Some to be
+	/// returned
+	fn unquote_infallible(&self) -> &'a str;
+}
+
+impl<'a> Unquote<'a> for &'a str {
+	#[inline]
+	fn unquote_infallible(&self) -> &'a str {
+		self.strip_prefix(QUOTE)
+			.unwrap_or(self)
+			.strip_suffix(QUOTE)
+			.unwrap_or(self)
+	}
+
+	#[inline]
+	fn unquote(&self) -> Option<&'a str> { self.strip_prefix(QUOTE).and_then(|s| s.strip_suffix(QUOTE)) }
+
+	#[inline]
+	fn is_quoted(&self) -> bool { self.starts_with(QUOTE) && self.ends_with(QUOTE) }
+}