fix: pass max_line_length to readline() to prevent LineTooLong on large SSE lines with MTLS.#2437
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…ge SSE lines with MTLS. When using AsyncAuthorizedSession (Vertex AI + ADC), the google-auth library creates its own internal aiohttp.ClientSession with the default read_bufsize=2**16. This gives the underlying StreamReader a _high_water of 131072 bytes, which is the effective limit for readline(). Streaming responses from thinking models can include large thoughtSignature fields, or generated images, that push a single SSE data: line beyond 131072 bytes, causing aiohttp to raise LineTooLong. The fix passes max_line_length=READ_BUFFER_SIZE (4MB) explicitly to every readline() call in _aiter_response_stream(), overriding the limit regardless of which code path created the underlying session. This covers both the direct AiohttpClientSession path (API key auth) and the AsyncAuthorizedSession path (Vertex AI + ADC). Test: added test_aiohttp_large_sse_line_with_thought_signature which uses a mock that enforces the real aiohttp LineTooLong limit, and streams a 150KB SSE line that would previously fail. Manually verified, this test fails before the change. PiperOrigin-RevId: 916020090
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fix: pass max_line_length to readline() to prevent LineTooLong on large SSE lines with MTLS.
When using AsyncAuthorizedSession (Vertex AI + ADC), the google-auth library
creates its own internal aiohttp.ClientSession with the default
read_bufsize=2**16. This gives the underlying StreamReader a _high_water of
131072 bytes, which is the effective limit for readline().
Streaming responses from thinking models can include large thoughtSignature
fields, or generated images, that push a single SSE data: line beyond 131072 bytes, causing aiohttp to raise LineTooLong.
The fix passes max_line_length=READ_BUFFER_SIZE (4MB) explicitly to every
readline() call in _aiter_response_stream(), overriding the limit regardless
of which code path created the underlying session. This covers both the direct
AiohttpClientSession path (API key auth) and the AsyncAuthorizedSession path
(Vertex AI + ADC).
Test: added test_aiohttp_large_sse_line_with_thought_signature which uses a
mock that enforces the real aiohttp LineTooLong limit, and streams a 150KB SSE
line that would previously fail. Manually verified, this test fails before the change.