fix: pass through a response that is JSON but not an object

CHANGELOG.md

@@ -4,6 +4,15 @@ All notable changes to this project will be documented in this file. The
 format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/).
 
+## [Unreleased]
+
+### Fixed
+
+- `call_runner` no longer raises on a response that is valid JSON but not an
+  object. A top-level array (or scalar) is handed back unparsed in
+  `result.content` with `result.content_type` intact, as an image or ndjson
+  already is, so a runner can pass through an API that answers with one.
+
 ## [1.0.0] - 2026-08-11
 
 The first stable release of the Livepeer Python SDK.

src/livepeer_gateway/live_runner.py

@@ -173,7 +173,8 @@ class LiveRunnerCallResult:
         repr=False,
         compare=False,
     )
-    # Non-JSON responses (an image, say) arrive unparsed in `content`; `data` stays empty.
+    # Responses that are not a JSON object (an image, a JSON array) arrive unparsed
+    # in `content`; `data` stays empty.
     content: bytes | None = field(default=None, repr=False)
     content_type: str = ""
 
@@ -809,8 +810,8 @@ async def call_runner(
     paid via the signer and retried (up to ``max_payment_challenge_retries``), one job,
     one upfront payment. Raises ``LivepeerHTTPError`` on non-402 errors.
 
-    ``application/json`` and ``+json`` types parse into ``result.data``; anything else
-    (an image, ndjson) comes back unparsed in ``result.content`` + ``result.content_type``.
+    A JSON *object* parses into ``result.data``; anything else (an image, ndjson, a
+    top-level JSON array) comes back unparsed in ``result.content`` + ``result.content_type``.
 
     The request asks for no particular format, so the app picks what it returns.
     """
@@ -913,16 +914,21 @@ async def call_runner(
             data: dict[str, Any] = {}
             if is_json:
                 try:
-                    data = json.loads(body)
+                    parsed = json.loads(body)
                 except (UnicodeDecodeError, json.JSONDecodeError) as e:
                     raise LivepeerGatewayError(
                         f"HTTP JSON error: endpoint did not return valid JSON: {e} "
                         f"(url={runner_url}, content_type={content_type})"
                     ) from e
-                if not isinstance(data, dict):
-                    raise LivepeerGatewayError(
-                        f"Live runner call expected JSON object, got {type(data).__name__}"
-                    )
+                # Only an object can carry the protocol fields read below, so
+                # anything else is payload rather than a reply this call speaks:
+                # hand it back unparsed, as ndjson and binary already are. A
+                # runner proxying somebody else's API does not choose its
+                # response shape, and a top-level array is a common one.
+                if isinstance(parsed, dict):
+                    data = parsed
+                else:
+                    is_json = False
             return LiveRunnerCallResult(
                 data,
                 runner_url=runner_url,

tests/test_call_runner_raw.py

@@ -1,9 +1,9 @@
 """Tests for non-JSON (raw byte) responses in call_runner.
 
-Single-document JSON responses (``application/json`` or an RFC 6839 ``+json``
-suffix) keep today's behavior: parsed into ``result.data``, strict about being an
-object. Anything else — binary, or a multi-document format like ndjson — returns
-the body unparsed in ``result.content`` with ``result.content_type`` set.
+A JSON *object* (``application/json`` or an RFC 6839 ``+json`` suffix) parses into
+``result.data``. Anything else — binary, a multi-document format like ndjson, or a
+top-level JSON array — returns the body unparsed in ``result.content`` with
+``result.content_type`` set.
 """
 
 from __future__ import annotations
@@ -154,18 +154,38 @@ async def scenario(base):
     assert all("did not return valid JSON" in str(error) for error in errors)
 
 
-def test_json_array_still_rejected():
+def test_json_array_returns_raw():
+    """A top-level array is data, not a reply this call speaks: hand it back whole."""
+
     async def handler(request):
-        return web.json_response([1, 2, 3])
+        return web.json_response([{"label": "llama", "score": 0.99}])
 
     app = web.Application()
     app.router.add_post("/arr", handler)
 
     async def scenario(base):
         return await call_runner(f"{base}/arr", payload={})
 
-    with pytest.raises(LivepeerGatewayError, match="expected JSON object"):
-        _run(app, scenario)
+    result = _run(app, scenario)
+    assert result.data == {}
+    assert result.content == b'[{"label": "llama", "score": 0.99}]'
+    assert result.content_type == "application/json"  # still says what it is
+    assert result.session_id == ""
+
+
+def test_json_scalar_returns_raw():
+    async def handler(request):
+        return web.json_response("just a string")
+
+    app = web.Application()
+    app.router.add_post("/scalar", handler)
+
+    async def scenario(base):
+        return await call_runner(f"{base}/scalar", payload={})
+
+    result = _run(app, scenario)
+    assert result.data == {}
+    assert result.content == b'"just a string"'
 
 
 def test_http_error_still_raises_with_binary_endpoint():