Fix HTTP transport timeout defaulting to 5 seconds

[jlowin]

Forward-port of #2848 for FastMCP 3.x.

When StreamableHttpTransport was updated to use the new streamable_http_client API, the code path for creating an httpx client when no factory is provided used httpx.AsyncClient() directly. Without an explicit timeout, httpx defaults to 5 seconds for all operations.

This caused tools taking longer than 5 seconds to fail with a 409 Conflict error as the client's SSE stream would timeout and trigger reconnection logic that conflicts with the existing GET stream.

The fix uses create_mcp_http_client() from the MCP SDK which sets appropriate defaults (30s connect, 5min read timeout) and enables follow_redirects.

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Prevent test timeout from 6s tool duration

This test exercises a 6‑second tool call, but the repo’s pytest configuration sets a default timeout of 5 seconds (pyproject.toml → timeout = 5), so the test will time out under the normal test run even when the fix works. That makes CI fail for the new test in any environment where pytest-timeout is enabled (as it is here). Consider adding @pytest.mark.timeout(10) or shortening the duration so the test completes within the global timeout.

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📥 Commits

Reviewing files that changed from the base of the PR and between 4f671d9 and 9b33a05.

⛔ Files ignored due to path filters (2)

• loq.toml is excluded by none and included by none
• tests/integration_tests/test_timeout_fix.py is excluded by none and included by none

📒 Files selected for processing (1)

• src/fastmcp/client/transports.py

Walkthrough

This pull request refactors timeout handling in the StreamableHttpTransport.connect_session method. It introduces explicit timeout variable management derived from read_timeout_seconds and updates the HTTP client construction logic. When an httpx_client_factory is provided, the timeout is now passed along with headers, auth, and follow_redirects parameters. When no factory is provided, the code now uses create_mcp_http_client from the MCP utilities instead of direct httpx client configuration. The change maintains backward compatibility while centralizing timeout encapsulation as httpx.Timeout objects.

Possibly related PRs

• Adopt streamable_http_client API from MCP SDK #2620: Modifies HTTP client construction and timeout handling in StreamableHttpTransport within the same transports file.

🚥 Pre-merge checks | ✅ 1 | ❌ 2

❌ Failed checks (2 warnings)

Check name	Status	Explanation	Resolution
Description check	⚠️ Warning	The description provides clear context about the issue and fix, but is missing the required contributors checklist with issue reference, testing confirmation, and self-review confirmation.	Add the contributors checklist items including the issue number reference (#2848 forward-port context), test confirmation, and review readiness markers.
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (1 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately describes the main change: fixing HTTP transport timeout defaults from 5 seconds to appropriate values.

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Actionable comments posted: 1

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Reviewing files that changed from the base of the PR and between 18c71f9 and 4f671d9.

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• tests/integration_tests/test_timeout_fix.py is excluded by none and included by none

📒 Files selected for processing (1)

• src/fastmcp/client/transports.py

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src/**/*.py

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• src/fastmcp/client/transports.py

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🔇 Additional comments (2)

src/fastmcp/client/transports.py (2)

256-262: LGTM - timeout handling is straightforward.

The conversion from timedelta to httpx.Timeout is correct. Note that httpx.Timeout(seconds) sets all timeout types (connect, read, write, pool) to the same value, which is a reasonable default when users specify a single timeout duration.

---

28-28: Verify stability and support status of private module import.

The import from mcp.shared._httpx_utils uses a private-designated module (underscore prefix), but web search indicates both McpHttpClientFactory and create_mcp_http_client are documented in the MCP SDK source and referenced in official docs. However, confirm whether this is an officially supported public API or internal implementation detail, and whether version pinning or an alternative approach is recommended.