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

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

src/core/utils/string/between.rs

@@ -0,0 +1,26 @@
+type Delim<'a> = (&'a str, &'a str);
+
+/// Slice a string between a pair of delimeters.
+pub trait Between<'a> {
+	/// Extract a string between the delimeters. If the delimeters were not
+	/// found None is returned, otherwise the first extraction is returned.
+	fn between(&self, delim: Delim<'_>) -> Option<&'a str>;
+
+	/// Extract a string between the delimeters. If the delimeters were not
+	/// found the original string is returned; take note of this behavior,
+	/// if an empty slice is desired for this case use the fallible version and
+	/// unwrap to EMPTY.
+	fn between_infallible(&self, delim: Delim<'_>) -> &'a str;
+}
+
+impl<'a> Between<'a> for &'a str {
+	#[inline]
+	fn between_infallible(&self, delim: Delim<'_>) -> &'a str { self.between(delim).unwrap_or(self) }
+
+	#[inline]
+	fn between(&self, delim: Delim<'_>) -> Option<&'a str> {
+		self.split_once(delim.0)
+			.and_then(|(_, b)| b.rsplit_once(delim.1))
+			.map(|(a, _)| a)
+	}
+}