feat: Magnet links with newlines produce a typed error

CHANGELOG.md

@@ -7,6 +7,11 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## UNRELEASED (YYYY-MM-DD)
 
+### Breaking changes
+
+- `MagnetLink` now refuses to parse strings that contain a newline (`\n`), producing
+  a `MagnetLinkError::InvalidURINewLine` error
+
 ## Version 0.3.2 (2025-08-29)
 
 ### Added

src/magnet.rs

@@ -7,6 +7,8 @@ use crate::{InfoHash, InfoHashError, TorrentID};
 pub enum MagnetLinkError {
     /// The URI was not valid according to [`Url::parse`](url::Url::parse).
     InvalidURI { source: url::ParseError },
+    /// The URI contains a newline
+    InvalidURINewLine,
     /// The URI scheme was not `magnet`
     InvalidScheme { scheme: String },
     /// No Bittorrent v1/v2 hash was found in the magnet URI
@@ -29,6 +31,9 @@ impl std::fmt::Display for MagnetLinkError {
             MagnetLinkError::InvalidURI { source } => {
                 write!(f, "Invalid URI: {source}")
             }
+            MagnetLinkError::InvalidURINewLine => {
+                write!(f, "Invalid URI: newlines are not allowed in magnet links")
+            }
             MagnetLinkError::InvalidScheme { scheme } => {
                 write!(f, "Invalid URI scheme: {scheme}")
             }
@@ -87,6 +92,11 @@ impl MagnetLink {
     /// Generates a new MagnetLink from a string. Will fail if the string is not a valid URL, and
     /// in the conditions defined in [`MagnetLink::from_url`](crate::magnet::MagnetLink::from_url).
     pub fn new(s: &str) -> Result<MagnetLink, MagnetLinkError> {
+        // The error returned by Uri::parse when there is a newline is not very obvious, so we
+        // sacrifice performance to save neurons from fellow developers.
+        if s.contains('\n') {
+            return Err(MagnetLinkError::InvalidURINewLine);
+        }
         let u = Url::parse(s)?;
         MagnetLink::from_url(&u)
     }
@@ -329,4 +339,15 @@ mod tests {
             }
         );
     }
+
+    #[test]
+    fn fails_newline_in_magnet() {
+        let mut magnet_url = std::fs::read_to_string("tests/bittorrent-v2-test.magnet").unwrap();
+        magnet_url.push('\n');
+
+        let res = MagnetLink::new(&magnet_url);
+        assert!(res.is_err());
+
+        assert_eq!(res.unwrap_err(), MagnetLinkError::InvalidURINewLine,);
+    }
 }

tests/bittorrent-v1-emma-goldman.magnet

@@ -1 +1 @@
-magnet:?xt=urn:btih:C811B41641A09D192B8ED81B14064FFF55D85CE3&dn=Emma+Goldman+-+Essential+Works+of+Anarchism+%2816+books%29&tr=udp%3A%2F%2Ftracker.coppersurfer.tk%3A6969%2Fannounce&tr=udp%3A%2F%2Ftracker.opentrackr.org%3A1337%2Fannounce&tr=udp%3A%2F%2Fexodus.desync.com%3A6969&tr=udp%3A%2F%2Ftracker.opentrackr.org%3A1337%2Fannounce&tr=http%3A%2F%2Ftracker.openbittorrent.com%3A80%2Fannounce&tr=udp%3A%2F%2Fopentracker.i2p.rocks%3A6969%2Fannounce&tr=udp%3A%2F%2Ftracker.internetwarriors.net%3A1337%2Fannounce&tr=udp%3A%2F%2Ftracker.leechers-paradise.org%3A6969%2Fannounce&tr=udp%3A%2F%2Fcoppersurfer.tk%3A6969%2Fannounce&tr=udp%3A%2F%2Ftracker.zer0day.to%3A1337%2Fannounce
+magnet:?xt=urn:btih:C811B41641A09D192B8ED81B14064FFF55D85CE3&dn=Emma+Goldman+-+Essential+Works+of+Anarchism+%2816+books%29&tr=udp%3A%2F%2Ftracker.coppersurfer.tk%3A6969%2Fannounce&tr=udp%3A%2F%2Ftracker.opentrackr.org%3A1337%2Fannounce&tr=udp%3A%2F%2Fexodus.desync.com%3A6969&tr=udp%3A%2F%2Ftracker.opentrackr.org%3A1337%2Fannounce&tr=http%3A%2F%2Ftracker.openbittorrent.com%3A80%2Fannounce&tr=udp%3A%2F%2Fopentracker.i2p.rocks%3A6969%2Fannounce&tr=udp%3A%2F%2Ftracker.internetwarriors.net%3A1337%2Fannounce&tr=udp%3A%2F%2Ftracker.leechers-paradise.org%3A6969%2Fannounce&tr=udp%3A%2F%2Fcoppersurfer.tk%3A6969%2Fannounce&tr=udp%3A%2F%2Ftracker.zer0day.to%3A1337%2Fannounce

tests/bittorrent-v2-hybrid-test.magnet

@@ -1 +1 @@
-magnet:?xt=urn:btih:631a31dd0a46257d5078c0dee4e66e26f73e42ac&xt=urn:btmh:1220d8dd32ac93357c368556af3ac1d95c9d76bd0dff6fa9833ecdac3d53134efabb&dn=bittorrent-v1-v2-hybrid-test
+magnet:?xt=urn:btih:631a31dd0a46257d5078c0dee4e66e26f73e42ac&xt=urn:btmh:1220d8dd32ac93357c368556af3ac1d95c9d76bd0dff6fa9833ecdac3d53134efabb&dn=bittorrent-v1-v2-hybrid-test

tests/bittorrent-v2-test.magnet

@@ -1 +1 @@
-magnet:?xt=urn:btmh:1220caf1e1c30e81cb361b9ee167c4aa64228a7fa4fa9f6105232b28ad099f3a302e&dn=bittorrent-v2-test
+magnet:?xt=urn:btmh:1220caf1e1c30e81cb361b9ee167c4aa64228a7fa4fa9f6105232b28ad099f3a302e&dn=bittorrent-v2-test