chore: refactor the backend (#17)

Reviewed-on: #17

crates/signed_git/src/cache.rs

@@ -0,0 +1,96 @@
+use std::path::{Path, PathBuf};
+
+use anyhow::{Context, Result};
+use signed_core::{Announcement, RepoAddr};
+
+use crate::remote::{clone_repo, fetch_all};
+
+/// On-disk cache of cloned repositories, keyed by owner pubkey / repo id.
+#[derive(Debug, Clone)]
+pub struct GitCache {
+    root: PathBuf,
+}
+
+impl GitCache {
+    pub fn new(root: PathBuf) -> Self {
+        Self { root }
+    }
+
+    /// The root directory holding the mirror clones.
+    pub fn root(&self) -> &Path {
+        &self.root
+    }
+
+    /// Local path of the clone for a repository.
+    pub fn repo_path(&self, addr: &RepoAddr) -> PathBuf {
+        self.root
+            .join(addr.public_key.to_hex())
+            .join(sanitize_path_component(&addr.identifier))
+    }
+
+    /// Open an existing clone.
+    pub fn open(&self, addr: &RepoAddr) -> Result<Option<gix::Repository>> {
+        let path = self.repo_path(addr);
+        match gix::open(&path) {
+            Ok(repo) => Ok(Some(repo)),
+            Err(gix::open::Error::NotARepository { .. }) => Ok(None),
+            Err(gix::open::Error::Io(e)) if e.kind() == std::io::ErrorKind::NotFound => Ok(None),
+            Err(e) => Err(e.into()),
+        }
+    }
+
+    /// Open the existing clone, fetching it first.
+    pub fn ensure_clone<U: AsRef<str>>(
+        &self,
+        addr: &RepoAddr,
+        clone_urls: &[U],
+    ) -> Result<gix::Repository> {
+        let path = self.repo_path(addr);
+
+        if let Some(repo) = self.open(addr)? {
+            fetch_all(&repo).ok();
+            return Ok(repo);
+        }
+
+        if let Some(parent) = path.parent() {
+            std::fs::create_dir_all(parent)
+                .with_context(|| format!("failed to create {}", parent.display()))?;
+        }
+
+        clone_repo(clone_urls, &path)?;
+        self.open(addr)?
+            .ok_or_else(|| anyhow::anyhow!("clone finished but the repository cannot be opened"))
+    }
+}
+
+/// Map an untrusted repository id or display name to a safe single path component.
+///
+/// Everything outside `[A-Za-z0-9._-]` becomes `_`.
+/// An id that maps to exactly `.` or `..` becomes `_`.
+pub fn sanitize_path_component(id: &str) -> String {
+    let sanitized: String = id
+        .chars()
+        .map(|c| {
+            if c.is_ascii_alphanumeric() || matches!(c, '-' | '_' | '.') {
+                c
+            } else {
+                '_'
+            }
+        })
+        .collect();
+
+    if sanitized == "." || sanitized == ".." {
+        return "_".to_owned();
+    }
+
+    sanitized
+}
+
+/// The refs namespace of a fork's import in the target mirror.
+pub fn fork_namespace(announcement: &Announcement) -> String {
+    format!(
+        "{}/{}",
+        announcement.owner.to_hex(),
+        sanitize_path_component(&announcement.id)
+    )
+}