fetch: introduce domain type RefPrefix

Better represent the domain by introducing the `RefPrefix` type.
It captures the different `ref-prefix` values that can be used in the
`ls-refs` step of the protocol.

These are turned into their equivalent `ref-prefix` values using
`RefPrefix::into_bstring`.

This better connects the `ProtocolStage::ls_refs` method with the
`ls_refs::run` through the use of the `RefPrefix` type, rather than
any set of `BString` values.

crates/radicle-fetch/src/stage.rs

@@ -89,6 +89,42 @@ pub mod error {
     }
 }
 
+/// A `ref-prefix` used in the `ls-refs` step of the fetch protocol.
+///
+/// Since the Radicle protocol only wants to filter by very specific references,
+/// this type captures the possible reference prefixes.
+#[derive(Clone, Copy, Debug, PartialEq, Eq, PartialOrd, Ord)]
+pub(crate) enum RefPrefix {
+    /// Represents `refs/rad/id`.
+    RadId,
+    /// Represents `"refs/namespaces/<namespace>/refs/rad/id"`.
+    NamespacedRadId { namespace: PublicKey },
+    /// Represents `"refs/namespaces/<namespace>/refs/rad/sigrefs"`.
+    NamespacedRadSigrefs { namespace: PublicKey },
+    /// Represents `"refs/namespaces"`
+    AllNamespaces,
+}
+
+impl RefPrefix {
+    /// Convert the [`RefPrefix`] into its equivalent [`BString`].
+    ///
+    /// See the [`RefPrefix`] variants for their [`BString`] values.
+    pub fn into_bstring(self) -> BString {
+        match self {
+            RefPrefix::RadId => refs::REFS_RAD_ID.as_bstr().into(),
+            RefPrefix::NamespacedRadId { namespace } => {
+                radicle::git::refs::storage::id(&namespace).as_bstr().into()
+            }
+            RefPrefix::NamespacedRadSigrefs { namespace } => {
+                radicle::git::refs::storage::sigrefs(&namespace)
+                    .as_bstr()
+                    .into()
+            }
+            RefPrefix::AllNamespaces => "refs/namespaces".into(),
+        }
+    }
+}
+
 /// A [`ProtocolStage`] describes a single roundtrip with the Radicle
 /// node that is serving the data.
 ///
@@ -107,7 +143,7 @@ pub mod error {
 ///      refdb (in-memory and production).
 pub(crate) trait ProtocolStage {
     /// If and how to perform `ls-refs`.
-    fn ls_refs(&self) -> Option<NonEmpty<BString>>;
+    fn ls_refs(&self) -> Option<NonEmpty<RefPrefix>>;
 
     /// Filter a remote-advertised [`Ref`].
     ///
@@ -163,8 +199,8 @@ pub struct CanonicalId {
 }
 
 impl ProtocolStage for CanonicalId {
-    fn ls_refs(&self) -> Option<NonEmpty<BString>> {
-        Some(NonEmpty::new(refs::REFS_RAD_ID.as_bstr().into()))
+    fn ls_refs(&self) -> Option<NonEmpty<RefPrefix>> {
+        Some(NonEmpty::new(RefPrefix::RadId))
     }
 
     fn ref_filter(&self, r: Ref) -> Option<ReceivedRef> {
@@ -250,17 +286,17 @@ pub struct SpecialRefs {
 }
 
 impl ProtocolStage for SpecialRefs {
-    fn ls_refs(&self) -> Option<NonEmpty<BString>> {
+    fn ls_refs(&self) -> Option<NonEmpty<RefPrefix>> {
         match &self.followed {
-            policy::Allowed::All => Some(NonEmpty::new("refs/namespaces".into())),
+            policy::Allowed::All => Some(NonEmpty::new(RefPrefix::AllNamespaces)),
             policy::Allowed::Followed { remotes } => NonEmpty::collect(
                 remotes
                     .iter()
                     .chain(self.delegates.iter())
                     .flat_map(|remote| {
                         [
-                            BString::from(radicle::git::refs::storage::id(remote).to_string()),
-                            BString::from(radicle::git::refs::storage::sigrefs(remote).to_string()),
+                            RefPrefix::NamespacedRadSigrefs { namespace: *remote },
+                            RefPrefix::NamespacedRadId { namespace: *remote },
                         ]
                     }),
             ),
@@ -331,12 +367,16 @@ pub struct SigrefsAt {
 }
 
 impl ProtocolStage for SigrefsAt {
-    fn ls_refs(&self) -> Option<NonEmpty<BString>> {
+    fn ls_refs(&self) -> Option<NonEmpty<RefPrefix>> {
         // N.b. the `Oid`s are known but the `rad/sigrefs` are still
         // asked for to mark them for updating the fetch state.
-        NonEmpty::collect(self.refs_at.iter().map(|refs_at| {
-            BString::from(radicle::git::refs::storage::sigrefs(&refs_at.remote).to_string())
-        }))
+        NonEmpty::collect(
+            self.refs_at
+                .iter()
+                .map(|refs_at| RefPrefix::NamespacedRadSigrefs {
+                    namespace: refs_at.remote,
+                }),
+        )
     }
 
     // We only asked for `rad/sigrefs` so we should only get
@@ -421,7 +461,7 @@ pub struct DataRefs {
 impl ProtocolStage for DataRefs {
     // We don't need to ask for refs since we have all reference names
     // and `Oid`s in `rad/sigrefs`.
-    fn ls_refs(&self) -> Option<NonEmpty<BString>> {
+    fn ls_refs(&self) -> Option<NonEmpty<RefPrefix>> {
         None
     }
 

crates/radicle-fetch/src/state.rs

@@ -225,7 +225,7 @@ impl FetchState {
         let refs = match step.ls_refs() {
             Some(refs) => handle
                 .transport
-                .ls_refs(refs.into(), handshake)?
+                .ls_refs(refs, handshake)?
                 .into_iter()
                 .filter_map(|r| step.ref_filter(r))
                 .collect::<Vec<_>>(),

crates/radicle-fetch/src/transport.rs

@@ -20,6 +20,7 @@ use thiserror::Error;
 
 use crate::git::packfile::Keepfile;
 use crate::git::repository;
+use crate::stage::RefPrefix;
 
 /// Open a reader and writer stream to pass to the ls-refs and fetch
 /// processes for communicating during their respective protocols.
@@ -104,11 +105,10 @@ where
     /// Perform ls-refs with the server side.
     pub(crate) fn ls_refs(
         &mut self,
-        mut prefixes: Vec<BString>,
+        prefixes: impl IntoIterator<Item = RefPrefix>,
         handshake: &handshake::Outcome,
     ) -> Result<Vec<handshake::Ref>, Error> {
-        prefixes.sort();
-        prefixes.dedup();
+        let prefixes = prefixes.into_iter().collect::<BTreeSet<_>>();
         let (read, write) = self.stream.open();
         Ok(ls_refs::run(
             ls_refs::Config {

crates/radicle-fetch/src/transport/ls_refs.rs

@@ -1,4 +1,5 @@
 use std::borrow::Cow;
+use std::collections::BTreeSet;
 use std::io;
 
 use gix_features::progress::Progress;
@@ -7,6 +8,8 @@ use gix_protocol::ls_refs;
 use gix_protocol::transport::Protocol;
 use gix_transport::bstr::{BString, ByteVec};
 
+use crate::stage::RefPrefix;
+
 use super::{agent_name, Connection};
 
 /// Configuration for running an ls-refs process.
@@ -17,7 +20,7 @@ pub struct Config {
     #[allow(dead_code)]
     pub repo: BString,
     /// Ref prefixes for filtering the output of the ls-refs process.
-    pub prefixes: Vec<BString>,
+    pub prefixes: BTreeSet<RefPrefix>,
 }
 
 /// Run the ls-refs process using the provided `config`.
@@ -51,11 +54,17 @@ where
         )));
     }
 
+    let prefixes = config
+        .prefixes
+        .into_iter()
+        .map(|prefix| prefix.into_bstring())
+        .collect::<BTreeSet<_>>();
+
     let refs = gix_protocol::ls_refs(
         &mut conn,
         capabilities,
         |_caps, args, features| {
-            for prefix in &config.prefixes {
+            for prefix in &prefixes {
                 let mut arg = BString::from("ref-prefix ");
                 arg.push_str(prefix);
                 args.push(arg)
@@ -74,10 +83,7 @@ where
         .into_iter()
         .filter(|r| {
             let (refname, _, _) = r.unpack();
-            config
-                .prefixes
-                .iter()
-                .any(|prefix| refname.starts_with(prefix))
+            prefixes.iter().any(|prefix| refname.starts_with(prefix))
         })
         .collect();