fix: Harden Content-Length handling for edge cases

- Only set explicit Content-Length when content_range.total > 0, avoiding
  a Content-Length: 0 regression when metadata.size is unknown.
- Use response Content-Length (not metadata.size) in 206 fallback paths
  for GCS and S3 so Content-Length matches the body if Content-Range is
  missing from a 206 response.

Author: lcian

objectstore-server/src/endpoints/objects.rs

@@ -110,10 +110,12 @@ async fn object_get(
     let mut response = (status, metadata_headers, Body::from_stream(stream)).into_response();
     let resp_headers = response.headers_mut();
     resp_headers.insert(http::header::ACCEPT_RANGES, "bytes".parse().unwrap());
-    resp_headers.insert(
-        http::header::CONTENT_LENGTH,
-        content_range.len().to_string().parse().unwrap(),
-    );
+    if content_range.total > 0 {
+        resp_headers.insert(
+            http::header::CONTENT_LENGTH,
+            content_range.len().to_string().parse().unwrap(),
+        );
+    }
     if !content_range.is_full() {
         resp_headers.insert(
             http::header::CONTENT_RANGE,

objectstore-service/src/backend/gcs.rs

@@ -700,7 +700,9 @@ impl Backend for GcsBackend {
                 .get(header::CONTENT_RANGE)
                 .and_then(|v| v.to_str().ok())
                 .and_then(ContentRange::parse)
-                .unwrap_or_else(|| ContentRange::full(metadata.size.unwrap_or(0) as u64))
+                .unwrap_or_else(|| {
+                    ContentRange::full(payload_response.content_length().unwrap_or(0))
+                })
         } else {
             ContentRange::full(metadata.size.unwrap_or(0) as u64)
         };

objectstore-service/src/backend/s3_compatible.rs

@@ -326,7 +326,7 @@ impl<T: TokenProvider> Backend for S3CompatibleBackend<T> {
                 .get(reqwest::header::CONTENT_RANGE)
                 .and_then(|v| v.to_str().ok())
                 .and_then(ContentRange::parse)
-                .unwrap_or_else(|| ContentRange::full(metadata.size.unwrap_or(0) as u64))
+                .unwrap_or_else(|| ContentRange::full(response.content_length().unwrap_or(0)))
         } else {
             ContentRange::full(metadata.size.unwrap_or(0) as u64)
         };