1 files changed, 78 insertions, 0 deletions
diff --git a/document_tree/src/url.rs b/document_tree/src/url.rs
new file mode 100644
index 0000000..31a0536
--- /dev/null
+++ b/document_tree/src/url.rs
@@ -0,0 +1,78 @@
+use std::fmt;
+use std::str::FromStr;
+
+use url::{self,ParseError};
+use serde_derive::Serialize;
+
+
+fn starts_with_scheme(input: &str) -> bool {
+	let scheme = input.split(':').next().unwrap();
+	if scheme == input || scheme.is_empty() {
+		return false;
+	}
+	let mut chars = input.chars();
+	// First character.
+	if !chars.next().unwrap().is_ascii_alphabetic() {
+		return false;
+	}
+	for ch in chars {
+		if !ch.is_ascii_alphanumeric() && ch != '+' && ch != '-' && ch != '.' {
+			return false;
+		}
+	}
+	true
+}
+
+/// The string representation of a URL, either absolute or relative, that has
+/// been verified as a valid URL on construction.
+#[derive(Debug,PartialEq,Serialize,Clone)]
+#[serde(transparent)]
+pub struct Url(String);
+
+impl Url {
+	pub fn parse_absolute(input: &str) -> Result<Self, ParseError> {
+		Ok(url::Url::parse(input)?.into())
+	}
+	pub fn parse_relative(input: &str) -> Result<Self, ParseError> {
+		// We're assuming that any scheme through which RsT documents are being
+		// accessed is a hierarchical scheme, and so we can parse relative to a
+		// random hierarchical URL.
+		if input.starts_with('/') || !starts_with_scheme(input) {
+			// Continue only if the parse succeeded, disregarding its result.
+			let random_base_url = url::Url::parse("https://a/b").unwrap();
+			url::Url::options()
+				.base_url(Some(&random_base_url))
+				.parse(input)?;
+			Ok(Url(input.into()))
+		} else {
+			// If this is a URL at all, it's an absolute one.
+			// There's no appropriate variant of url::ParseError really.
+			Err(ParseError::SetHostOnCannotBeABaseUrl)
+		}
+	}
+	pub fn as_str(&self) -> &str {
+		self.0.as_str()
+	}
+}
+
+impl From<url::Url> for Url {
+	fn from(url: url::Url) -> Self {
+		Url(url.into_string())
+	}
+}
+
+
+impl fmt::Display for Url {
+	fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+		write!(f, "{}", self.as_str())
+	}
+}
+
+
+impl FromStr for Url {
+	type Err = ParseError;
+	fn from_str(input: &str) -> Result<Self, Self::Err> {
+		Url::parse_absolute(input)
+			.or_else(|_| Url::parse_relative(input))
+	}
+}