Add verify_is_remote_object

src/protocol/verification.rs

@@ -1,6 +1,7 @@
 //! Verify that received data is valid
 
-use crate::error::Error;
+use crate::{config::Data, error::Error, fetch::object_id::ObjectId, traits::Object};
+use serde::Deserialize;
 use url::Url;
 
 /// Check that both urls have the same domain. If not, return UrlVerificationError.
@@ -36,3 +37,32 @@ pub fn verify_urls_match(a: &Url, b: &Url) -> Result<(), Error> {
     }
     Ok(())
 }
+
+/// Check that the given ID doesn't match the local domain.
+///
+/// It is important to verify this to avoid local objects from being overwritten. In general
+/// locally created objects should be considered authorative, while incoming federated data
+/// is untrusted. Lack of such a check could allow an attacker to rewrite local posts. It could
+/// also result in an `object.local` field being overwritten with `false` for local objects, resulting in invalid data.
+///
+/// ```
+/// # use url::Url;
+/// # use activitypub_federation::protocol::verification::verify_is_remote_object;
+/// let a = Url::parse("https://example.com/u/name")?;
+/// assert!(verify_is_remote_object(&a, &b).is_ok());
+/// # Ok::<(), url::ParseError>(())
+/// ```
+pub fn verify_is_remote_object<Kind, R: Clone>(
+    id: &ObjectId<Kind>,
+    data: &Data<<Kind as Object>::DataType>,
+) -> Result<(), Error>
+where
+    Kind: Object<DataType = R> + Send + 'static,
+    for<'de2> <Kind as Object>::Kind: Deserialize<'de2>,
+{
+    if id.is_local(data) {
+        Err(Error::UrlVerificationError("Object is not remote"))
+    } else {
+        Ok(())
+    }
+}