Fix suffix byte range parsing

app/services/media_server.py

@@ -16,12 +16,17 @@ def build_range_response(file_path: str, range_header: str) -> Response:
     file_size = os.path.getsize(file_path)
     stat = os.stat(file_path)
 
-    # Parse range header: "bytes=start-end"
+    # Parse range header: "bytes=start-end" or suffix-byte-range "bytes=-N"
     range_spec = range_header.replace("bytes=", "").strip()
     parts = range_spec.split("-")
 
-    start = int(parts[0]) if parts[0] else 0
-    end = int(parts[1]) if len(parts) > 1 and parts[1] else file_size - 1
+    if not parts[0] and len(parts) > 1 and parts[1]:
+        suffix_length = int(parts[1])
+        start = max(0, file_size - suffix_length)
+        end = file_size - 1
+    else:
+        start = int(parts[0]) if parts[0] else 0
+        end = int(parts[1]) if len(parts) > 1 and parts[1] else file_size - 1
 
     # Clamp values
     start = max(0, start)

tests/test_media_server.py

@@ -0,0 +1,29 @@
+from pathlib import Path
+
+from app.services.media_server import build_range_response
+
+
+def test_build_range_response_supports_suffix_byte_range(tmp_path: Path):
+    file_path = tmp_path / "sample.bin"
+    content = b"0123456789"
+    file_path.write_bytes(content)
+
+    response = build_range_response(str(file_path), "bytes=-4")
+
+    assert response.status_code == 206
+    assert response.body == b"6789"
+    assert response.headers["content-range"] == "bytes 6-9/10"
+    assert response.headers["content-length"] == "4"
+
+
+def test_build_range_response_keeps_standard_range_behavior(tmp_path: Path):
+    file_path = tmp_path / "sample.bin"
+    content = b"0123456789"
+    file_path.write_bytes(content)
+
+    response = build_range_response(str(file_path), "bytes=2-5")
+
+    assert response.status_code == 206
+    assert response.body == b"2345"
+    assert response.headers["content-range"] == "bytes 2-5/10"
+    assert response.headers["content-length"] == "4"