GET of a 0-byte object must not mmap 1 byte (#9)

* test: GET of a 0-byte object must not ask mmap for 1 byte

Inclusive-end on size=0 is length 1. HEAD already advertises 0.
Darwin mmap fails with EINVAL (500); Linux returns a phantom 0x00.

* fix: empty REST GET is length 0, not mmap(1)

Full GET uses the exclusive window (0, size), matching S3 GetObject
and HEAD Content-Length. size=0 now takes Body::empty() instead of
mmap past EOF.

Author: paulocsanz

crates/server/src/routes/objects.rs

@@ -248,19 +248,19 @@ pub async fn get_object(
     let mut resp_headers = build_object_headers(&info);
 
     let range = parse_range(&headers, info.size)?;
-    let (status, start, end_inclusive) = match range {
-        Some((s, e)) => {
-            resp_headers.insert(
-                header::CONTENT_RANGE,
-                HeaderValue::from_str(&format!("bytes {s}-{e}/{}", info.size))
-                    .map_err(|_| ApiError::Internal(anyhow::anyhow!("content-range encode")))?,
-            );
-            (StatusCode::PARTIAL_CONTENT, s, e)
-        }
-        None => (StatusCode::OK, 0, info.size.saturating_sub(1)),
+    if let Some((s, e)) = range {
+        resp_headers.insert(
+            header::CONTENT_RANGE,
+            HeaderValue::from_str(&format!("bytes {s}-{e}/{}", info.size))
+                .map_err(|_| ApiError::Internal(anyhow::anyhow!("content-range encode")))?,
+        );
+    }
+    let status = if range.is_some() {
+        StatusCode::PARTIAL_CONTENT
+    } else {
+        StatusCode::OK
     };
-
-    let length = end_inclusive.saturating_sub(start).saturating_add(1);
+    let (start, length) = get_window(info.size, range);
     resp_headers.insert(
         header::CONTENT_LENGTH,
         HeaderValue::from_str(&length.to_string())
@@ -718,3 +718,40 @@ fn parse_range(headers: &HeaderMap, size: u64) -> Result<Option<(u64, u64)>, Api
     }
     Ok(Some((start, end)))
 }
+
+/// Byte window for a GET: `(start, length)`.
+///
+/// `range` is the inclusive `(start, end)` from [`parse_range`]. A missing
+/// Range is the exclusive window `(0, size)` — same as S3 `GetObject`.
+/// Inclusive-end (`size.saturating_sub(1) + 1`) turns size=0 into length 1
+/// and mmap's one byte past EOF.
+fn get_window(size: u64, range: Option<(u64, u64)>) -> (u64, u64) {
+    match range {
+        Some((s, e)) => (s, e.saturating_sub(s).saturating_add(1)),
+        None => (0, size),
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::get_window;
+
+    #[test]
+    fn empty_object_full_get_is_zero_bytes() {
+        assert_eq!(
+            get_window(0, None),
+            (0, 0),
+            "GET of a 0-byte object must not ask mmap for 1 byte"
+        );
+    }
+
+    #[test]
+    fn nonempty_full_get_is_the_object_size() {
+        assert_eq!(get_window(10, None), (0, 10));
+    }
+
+    #[test]
+    fn inclusive_range_length() {
+        assert_eq!(get_window(10, Some((2, 5))), (2, 4));
+    }
+}

crates/server/tests/rest/objects.rs

@@ -76,6 +76,65 @@ async fn put_get_head_delete_roundtrip() {
     assert_eq!(res.status(), reqwest::StatusCode::NOT_FOUND);
 }
 
+/// PUT of an empty object is legal. GET without Range must return
+/// Content-Length 0 and an empty body — not mmap 1 byte past EOF
+/// (Darwin 500, Linux a one-byte zero body).
+#[tokio::test]
+async fn empty_object_get_is_zero_bytes() {
+    let bucket = unique_bucket("empty");
+    create_bucket(&bucket, "private").await;
+    let token = bucket_token(&bucket);
+
+    let res = client()
+        .put(url(&format!("/v1/{bucket}/marker")))
+        .bearer_auth(&token)
+        .header("content-type", "application/octet-stream")
+        .body(Vec::<u8>::new())
+        .send()
+        .await
+        .unwrap();
+    assert_eq!(res.status(), reqwest::StatusCode::CREATED);
+    let put_body: serde_json::Value = res.json().await.unwrap();
+    assert_eq!(put_body["size"], 0);
+
+    let res = client()
+        .head(url(&format!("/v1/{bucket}/marker")))
+        .bearer_auth(&token)
+        .send()
+        .await
+        .unwrap();
+    assert_eq!(res.status(), reqwest::StatusCode::OK);
+    assert_eq!(
+        res.headers()
+            .get("content-length")
+            .and_then(|v| v.to_str().ok()),
+        Some("0")
+    );
+
+    let res = client()
+        .get(url(&format!("/v1/{bucket}/marker")))
+        .bearer_auth(&token)
+        .send()
+        .await
+        .unwrap();
+    assert_eq!(
+        res.status(),
+        reqwest::StatusCode::OK,
+        "GET empty must not 500 (mmap past EOF)"
+    );
+    assert_eq!(
+        res.headers()
+            .get("content-length")
+            .and_then(|v| v.to_str().ok()),
+        Some("0")
+    );
+    let bytes = res.bytes().await.unwrap();
+    assert!(
+        bytes.is_empty(),
+        "GET empty must not invent a byte: {bytes:?}"
+    );
+}
+
 #[tokio::test]
 async fn private_object_requires_auth() {
     let bucket = unique_bucket("priv");