Prevent archive overwrite races

1 files changed, 10 insertions, 2 deletions

diff --git a/src/archive.rs b/src/archive.rs
index ad424c4..c0a2195 100644
--- a/src/archive.rs
+++ b/src/archive.rs
@@ -27,6 +27,9 @@ impl NativeTarWriter {
 
         let output = output.as_ref();
         reject_output_inside_rootfs(rootfs, output)?;
+        if output.exists() {
+            bail!("archive output already exists; refusing to overwrite it: {}", output.display());
+        }
         let temporary = temporary_output_path(output)?;
         let result = (|| {
             let file = OpenOptions::new()
@@ -39,13 +42,18 @@ impl NativeTarWriter {
             archive
                 .finish()
                 .with_context(|| format!("finish archive {}", temporary.display()))?;
-            fs::rename(&temporary, output).with_context(|| {
+            // `rename` replaces an existing destination on Unix. Publishing via
+            // a hard link instead gives this same-directory temporary file an
+            // atomic no-replace final name.
+            fs::hard_link(&temporary, output).with_context(|| {
                 format!(
                     "publish completed archive {} as {}",
                     temporary.display(),
                     output.display()
                 )
-            })
+            })?;
+            fs::remove_file(&temporary)
+                .with_context(|| format!("remove temporary archive {}", temporary.display()))
         })();
         if result.is_err() {
             let _ = fs::remove_file(&temporary);