radicle-surf: Repository.blob_at() to retrieve a blob using its oid.

Signed-off-by: Han Xu <keepsimple@gmail.com>

radicle-surf/src/repo.rs

@@ -48,6 +48,7 @@ use crate::{
 
 /// Enumeration of errors that can occur in repo operations.
 pub mod error {
+    use crate::Oid;
     use std::path::PathBuf;
     use thiserror::Error;
 
@@ -56,6 +57,8 @@ pub mod error {
     pub enum Repo {
         #[error("path not found for: {0}")]
         PathNotFound(PathBuf),
+        #[error("blob not found for: {0}")]
+        BlobNotFound(Oid),
     }
 }
 
@@ -301,6 +304,20 @@ impl Repository {
         Ok(Blob::<BlobRef<'a>>::new(file.id(), git2_blob, last_commit))
     }
 
+    /// Retrieves the blob with `oid` in `commit`.
+    pub fn blob_at<'a, C: ToCommit>(
+        &'a self,
+        commit: C,
+        oid: Oid,
+    ) -> Result<Blob<BlobRef<'a>>, Error> {
+        let commit = commit
+            .to_commit(self)
+            .map_err(|e| Error::ToCommit(e.into()))?;
+        let git2_blob = self.find_blob(oid)?;
+        let last_commit = self.find_commit_of_blob(oid, &commit)?;
+        Ok(Blob::<BlobRef<'a>>::new(oid, git2_blob, last_commit))
+    }
+
     /// Returns the last commit, if exists, for a `path` in the history of
     /// `rev`.
     pub fn last_commit<P, C>(&self, path: &P, rev: C) -> Result<Option<Commit>, Error>
@@ -524,6 +541,53 @@ impl Repository {
         Ok(diff)
     }
 
+    /// Returns true if the diff between `from` and `to` creates `oid`.
+    fn diff_commits_has_oid(
+        &self,
+        from: Option<&git2::Commit>,
+        to: &git2::Commit,
+        oid: &git2::Oid,
+    ) -> Result<bool, Error> {
+        let diff = self.diff_commits(None, from, to)?;
+        for delta in diff.deltas() {
+            if &delta.new_file().id() == oid {
+                return Ok(true);
+            }
+        }
+        Ok(false)
+    }
+
+    /// Returns whether `oid` was created in `commit` or not.
+    fn is_oid_in_commit(&self, oid: Oid, commit: &git2::Commit) -> Result<bool, Error> {
+        if commit.parent_count() == 0 {
+            return self.diff_commits_has_oid(None, commit, oid.as_ref());
+        }
+
+        for p in commit.parents() {
+            if self.diff_commits_has_oid(Some(&p), commit, oid.as_ref())? {
+                return Ok(true);
+            }
+        }
+
+        Ok(false)
+    }
+
+    /// Returns the commit that created the blob with `oid`.
+    ///
+    /// It is assumed that `oid` exists in `head`.
+    fn find_commit_of_blob(&self, oid: Oid, head: &Commit) -> Result<Commit, Error> {
+        let mut revwalk = self.revwalk()?;
+        revwalk.push(head.id.into())?;
+        for commit_id in revwalk {
+            let commit_id = commit_id?;
+            let git2_commit = self.inner.find_commit(commit_id)?;
+            if self.is_oid_in_commit(oid, &git2_commit)? {
+                return Ok(Commit::try_from(git2_commit)?);
+            }
+        }
+        Err(Error::Repo(error::Repo::BlobNotFound(oid)))
+    }
+
     /// Returns a full reference name with namespace(s) included.
     pub(crate) fn namespaced_refname<'a>(
         &'a self,

radicle-surf/t/src/source.rs

@@ -1,7 +1,7 @@
 use std::path::PathBuf;
 
 use radicle_git_ext::ref_format::refname;
-use radicle_surf::{Branch, Glob, Repository};
+use radicle_surf::{Branch, Glob, Oid, Repository};
 use serde_json::json;
 
 const GIT_PLATINUM: &str = "../data/git-platinum";
@@ -175,6 +175,32 @@ fn repo_blob() {
     assert_eq!(json_ref, json_owned);
 }
 
+#[test]
+fn repo_blob_at() {
+    let repo = Repository::open(GIT_PLATINUM).unwrap();
+    let oid = Oid::try_from("b84992d24be67536837f5ab45a943f1b3f501878").unwrap();
+
+    // Retrieve the blob using its oid.
+    let blob = repo
+        .blob_at("27acd68c7504755aa11023300890bb85bbd69d45", oid)
+        .unwrap();
+
+    // Verify the blob oid.
+    let blob_oid = blob.object_id();
+    assert_eq!(blob_oid, oid);
+
+    // Verify the commit that created the blob.
+    let blob_commit = blob.commit();
+    assert_eq!(
+        blob_commit.id.to_string(),
+        "e24124b7538658220b5aaf3b6ef53758f0a106dc"
+    );
+
+    // Verify the blob content ("memory.rs").
+    assert!(!blob.is_binary());
+    assert_eq!(blob.size(), 6253);
+}
+
 #[test]
 fn tree_ordering() {
     let repo = Repository::open(GIT_PLATINUM).unwrap();