api: add mailto parse api (#4829)

close #4620 

This PR introduces a new core API to parse mailto links into a uniform
data format. This could be used to unify the different implementations
on the current platforms.
To complete this PR we have to decide for which APIs we want to expose
this (now) internal API (c, python, json-rpc, etc.), and if we want such
an API at all as it doesn't have a corresponding UI-PR and is not
_really_ needed.

src/tools.rs

@@ -20,6 +20,7 @@ use mailparse::headers::Headers;
 use mailparse::MailHeaderMap;
 use rand::{thread_rng, Rng};
 use tokio::{fs, io};
+use url::Url;
 
 use crate::chat::{add_device_msg, add_device_msg_with_importance};
 use crate::constants::{DC_ELLIPSIS, DC_OUTDATED_WARNING_DAYS};
@@ -481,7 +482,43 @@ pub(crate) fn time() -> i64 {
         .as_secs() as i64
 }
 
-/// Very simple email address wrapper.
+/// Struct containing all mailto information
+#[derive(Debug, Default, Eq, PartialEq)]
+pub struct MailTo {
+    pub to: Vec<EmailAddress>,
+    pub subject: Option<String>,
+    pub body: Option<String>,
+}
+
+/// Parse mailto urls
+pub fn parse_mailto(mailto_url: &str) -> Option<MailTo> {
+    if let Ok(url) = Url::parse(mailto_url) {
+        if url.scheme() == "mailto" {
+            let mut mailto: MailTo = Default::default();
+            // Extract the email address
+            url.path().split(',').for_each(|email| {
+                if let Ok(email) = EmailAddress::new(email) {
+                    mailto.to.push(email);
+                }
+            });
+
+            // Extract query parameters
+            for (key, value) in url.query_pairs() {
+                if key == "subject" {
+                    mailto.subject = Some(value.to_string());
+                } else if key == "body" {
+                    mailto.body = Some(value.to_string());
+                }
+            }
+            Some(mailto)
+        } else {
+            None
+        }
+    } else {
+        None
+    }
+}
+
 ///
 /// Represents an email address, right now just the `name@domain` portion.
 ///
@@ -1283,4 +1320,55 @@ DKIM Results: Passed=true, Works=true, Allow_Keychange=true";
         assert_eq!(remove_subject_prefix("Fwd: Subject"), "Subject");
         assert_eq!(remove_subject_prefix("Fw: Subject"), "Subject");
     }
+
+    #[test]
+    fn test_parse_mailto() {
+        let mailto_url = "mailto:someone@example.com";
+        let reps = parse_mailto(mailto_url);
+        assert_eq!(
+            Some(MailTo {
+                to: vec![EmailAddress {
+                    local: "someone".to_string(),
+                    domain: "example.com".to_string()
+                }],
+                subject: None,
+                body: None
+            }),
+            reps
+        );
+
+        let mailto_url = "mailto:someone@example.com?subject=Hello%20World";
+        let reps = parse_mailto(mailto_url);
+        assert_eq!(
+            Some(MailTo {
+                to: vec![EmailAddress {
+                    local: "someone".to_string(),
+                    domain: "example.com".to_string()
+                }],
+                subject: Some("Hello World".to_string()),
+                body: None
+            }),
+            reps
+        );
+
+        let mailto_url = "mailto:someone@example.com,someoneelse@example.com?subject=Hello%20World&body=This%20is%20a%20test";
+        let reps = parse_mailto(mailto_url);
+        assert_eq!(
+            Some(MailTo {
+                to: vec![
+                    EmailAddress {
+                        local: "someone".to_string(),
+                        domain: "example.com".to_string()
+                    },
+                    EmailAddress {
+                        local: "someoneelse".to_string(),
+                        domain: "example.com".to_string()
+                    }
+                ],
+                subject: Some("Hello World".to_string()),
+                body: Some("This is a test".to_string())
+            }),
+            reps
+        );
+    }
 }