Don't fall over on unknown schemes e.g. mailto:

quickpeep_raker/src/raking/references.rs

@@ -6,6 +6,10 @@ use quickpeep_utils::dates::date_to_quickpeep_days;
 use reqwest::Url;
 use std::collections::BTreeSet;
 
+/// Supported schemes.
+/// References in all other schemes will be ignored.
+pub const SUPPORTED_SCHEMES: [&'static str; 2] = ["http", "https"];
+
 pub fn find_references(
     doc: &Vec<DenseTree>,
     feeds: &Vec<Url>,
@@ -41,11 +45,18 @@ pub fn find_references(
                 } => {
                     if !nofollow {
                         if let Ok(full_url) = page_url.join(&href) {
+                            if SUPPORTED_SCHEMES.contains(&full_url.scheme()) {
                                 refs.insert(RakedReference {
                                     target: clean_url(&full_url).to_string(),
                                     kind: ReferenceKind::Link,
                                     last_mod: None,
                                 });
+                            } else {
+                                debug!(
+                                    "ignoring reference {:?}: not a supported scheme",
+                                    full_url.as_str()
+                                )
+                            }
                         } else {
                             debug!("Can't join {:?} + {:?} to get full URL", page_url, href);
                         }