Bug fix with verification of magnet url's

When I changed it to just check a str slice against a str, it would never panic since I put in the str wrong, AND I made it so it had t be equal to said str to panic, not the other way around. Yikes.

src/lib.rs

@@ -4,7 +4,6 @@ use regex::Regex;
 extern crate lazy_static;
 
 ///The regexes used to identify specific parts of the magnet
-const MAGNET_URL_RE_STR: &str = r"^(stratum-|)magnet:\?";
 const DISPLAY_NAME_RE_STR: &str = r"dn=([A-Za-z0-9!@#$%^:*<>,?/()_+=.{}\{}\-]*)(&|$|\s)";
 const EXACT_TOPIC_RE_STR: &str = r"xt=urn:(sha1|btih|ed2k|aich|kzhash|md5|tree:tiger):([A-Fa-f0-9]+|[A-Za-z2-7]+)";
 const ADDRESS_TRACKER_RE_STR: &str = r"tr=([A-Za-z0-9!@#$%^:*<>,?/()_+=.{}\{}\-]*)(&|$|\s)";
@@ -135,13 +134,24 @@ pub struct Magnet {
 }
 
 impl Magnet {
+    pub fn gen_magnet_string(&self) -> String {
+        let mut magnet_string =
+        format!("magnet:?xt=urn:{}:{}&dn={}&xl={}&xs={}&kt={}&ws={}&as={}&mt={}", self.hash_type, self.xt, self.dn, self.xl, self.xs, self.kt, self.ws, self.acceptable_source, self.mt);
+
+        for tracker in &self.tr {
+            magnet_string = format!("{}&tr={}", magnet_string, tracker)
+        }
+
+        magnet_string
+
+    }
+
     /**Given a magnet URL, identify the specific parts, and return the Magnet struct. If the program
     can't identify a specific part of the magnet, then it will either give an empty version of what
     its value would normally be (such as an empty string, an empty vector, or in the case of xl, -1)
     */
     pub fn new (magnet_str: &str) -> Magnet {
         lazy_static! {
-            static ref MAGNET_URL_RE: Regex = Regex::new(MAGNET_URL_RE_STR).unwrap();
             static ref DISPLAY_NAME_RE: Regex = Regex::new(DISPLAY_NAME_RE_STR).unwrap();
             static ref EXACT_TOPIC_RE: Regex = Regex::new(EXACT_TOPIC_RE_STR).unwrap();
             static ref EXACT_LENGTH_RE: Regex = Regex::new(EXACT_LENGTH_RE_STR).unwrap();
@@ -154,7 +164,7 @@ impl Magnet {
         }
 
         // Panicking is a temporary fix, in version 2.0.0 it will instead return an Error
-        if MAGNET_URL_RE.is_match(magnet_str) == false {
+        if &magnet_str[0..8] != "magnet:?" {
             panic!("Invalid magnet url")
         }
 
@@ -224,6 +234,8 @@ mod tests {
         assert_eq!(magnet_link.kt, String::new());
         assert_eq!(magnet_link.acceptable_source, String::new());
         assert_eq!(magnet_link.mt, String::new());
+
+        println!("{}", magnet_link.gen_magnet_string());
     }
 
     #[test]