task 4

internal/pipeline/build.go

@@ -378,16 +378,8 @@ func planOrBuildHAKs(p *project.Project, progress ProgressFunc, writeArchives bo
 			if err := os.MkdirAll(filepath.Dir(hakPath), 0o755); err != nil {
 				return BuildResult{}, fmt.Errorf("create hak archive dir: %w", err)
 			}
-			hakOutput, err := os.Create(hakPath)
-			if err != nil {
-				return BuildResult{}, fmt.Errorf("create hak archive: %w", err)
-			}
-			if err := erf.Write(hakOutput, erf.New("HAK ", resourceSlice(chunk.Assets))); err != nil {
-				hakOutput.Close()
-				return BuildResult{}, fmt.Errorf("write hak archive: %w", err)
-			}
-			if err := hakOutput.Close(); err != nil {
-				return BuildResult{}, fmt.Errorf("close hak archive: %w", err)
+			if err := writeHAKArchive(hakPath, resourceSlice(chunk.Assets)); err != nil {
+				return BuildResult{}, err
 			}
 		}
 
@@ -488,23 +480,36 @@ func buildDirectHAKs(p *project.Project, progress ProgressFunc, writeArchives bo
 	return result, nil
 }
 
-// writeHAKArchive writes a HAK archive, removing any partial output if the ERF
-// writer or a streamed source SHA verification fails, so a corrupt input never
-// leaves a completed .hak behind.
+// writeHAKArchive publishes a completed HAK atomically, so a failed write never
+// leaves a partial archive at the final path.
 func writeHAKArchive(hakPath string, resources []erf.Resource) error {
-	output, err := os.Create(hakPath)
+	tmpPath := hakPath + ".tmp"
+	if err := os.Remove(tmpPath); err != nil && !errors.Is(err, os.ErrNotExist) {
+		return fmt.Errorf("remove stale temporary hak %s: %w", tmpPath, err)
+	}
+
+	output, err := os.OpenFile(tmpPath, os.O_CREATE|os.O_EXCL|os.O_WRONLY, 0o644)
 	if err != nil {
-		return fmt.Errorf("create hak archive: %w", err)
+		return fmt.Errorf("create temporary hak archive %s: %w", tmpPath, err)
 	}
 	if err := erf.Write(output, erf.New("HAK ", resources)); err != nil {
 		output.Close()
-		os.Remove(hakPath)
+		os.Remove(tmpPath)
 		return fmt.Errorf("write hak archive: %w", err)
 	}
+	if err := output.Sync(); err != nil {
+		output.Close()
+		os.Remove(tmpPath)
+		return fmt.Errorf("sync hak archive: %w", err)
+	}
 	if err := output.Close(); err != nil {
-		os.Remove(hakPath)
+		os.Remove(tmpPath)
 		return fmt.Errorf("close hak archive: %w", err)
 	}
+	if err := os.Rename(tmpPath, hakPath); err != nil {
+		os.Remove(tmpPath)
+		return fmt.Errorf("publish hak archive %s: %w", hakPath, err)
+	}
 	return nil
 }