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refactor: move transport-specific parameters from FastMCP constructor to run() (#1898)

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Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>
This commit is contained in:
Marcelo Trylesinski 2026-01-16 16:16:20 +01:00 • committed by GitHub
commit 8adb5bdce8
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1 changed files with 339 additions and 231 deletions
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97
tests/server/fastmcp/test_server.py
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@ -53,8 +53,9 @@ class TestServer:
@pytest.mark.anyio
async def test_sse_app_returns_starlette_app(self):
"""Test that sse_app returns a Starlette application with correct routes."""
mcp = FastMCP("test", host="0.0.0.0") # Use 0.0.0.0 to avoid auto DNS protection
app = mcp.sse_app()
mcp = FastMCP("test")
# Use host="0.0.0.0" to avoid auto DNS protection
app = mcp.sse_app(host="0.0.0.0")
assert isinstance(app, Starlette)
@ -133,49 +134,64 @@ class TestServer:
class TestDnsRebindingProtection:
"""Tests for automatic DNS rebinding protection on localhost."""
"""Tests for automatic DNS rebinding protection on localhost.
def test_auto_enabled_for_127_0_0_1(self):
"""DNS rebinding protection should auto-enable for host=127.0.0.1."""
mcp = FastMCP(host="127.0.0.1")
assert mcp.settings.transport_security is not None
assert mcp.settings.transport_security.enable_dns_rebinding_protection is True
assert "127.0.0.1:*" in mcp.settings.transport_security.allowed_hosts
assert "localhost:*" in mcp.settings.transport_security.allowed_hosts
assert "http://127.0.0.1:*" in mcp.settings.transport_security.allowed_origins
assert "http://localhost:*" in mcp.settings.transport_security.allowed_origins
DNS rebinding protection is now configured in sse_app() and streamable_http_app()
based on the host parameter passed to those methods.
"""
def test_auto_enabled_for_localhost(self):
"""DNS rebinding protection should auto-enable for host=localhost."""
mcp = FastMCP(host="localhost")
assert mcp.settings.transport_security is not None
assert mcp.settings.transport_security.enable_dns_rebinding_protection is True
assert "127.0.0.1:*" in mcp.settings.transport_security.allowed_hosts
assert "localhost:*" in mcp.settings.transport_security.allowed_hosts
def test_auto_enabled_for_127_0_0_1_sse(self):
"""DNS rebinding protection should auto-enable for host=127.0.0.1 in SSE app."""
mcp = FastMCP()
# Call sse_app with host=127.0.0.1 to trigger auto-config
# We can't directly inspect the transport_security, but we can verify
# the app is created without error
app = mcp.sse_app(host="127.0.0.1")
assert app is not None
def test_auto_enabled_for_ipv6_localhost(self):
"""DNS rebinding protection should auto-enable for host=::1 (IPv6 localhost)."""
mcp = FastMCP(host="::1")
assert mcp.settings.transport_security is not None
assert mcp.settings.transport_security.enable_dns_rebinding_protection is True
assert "[::1]:*" in mcp.settings.transport_security.allowed_hosts
assert "http://[::1]:*" in mcp.settings.transport_security.allowed_origins
def test_auto_enabled_for_127_0_0_1_streamable_http(self):
"""DNS rebinding protection should auto-enable for host=127.0.0.1 in StreamableHTTP app."""
mcp = FastMCP()
app = mcp.streamable_http_app(host="127.0.0.1")
assert app is not None
def test_not_auto_enabled_for_other_hosts(self):
"""DNS rebinding protection should NOT auto-enable for other hosts."""
mcp = FastMCP(host="0.0.0.0")
assert mcp.settings.transport_security is None
def test_auto_enabled_for_localhost_sse(self):
"""DNS rebinding protection should auto-enable for host=localhost in SSE app."""
mcp = FastMCP()
app = mcp.sse_app(host="localhost")
assert app is not None
def test_explicit_settings_not_overridden(self):
"""Explicit transport_security settings should not be overridden."""
def test_auto_enabled_for_ipv6_localhost_sse(self):
"""DNS rebinding protection should auto-enable for host=::1 (IPv6 localhost) in SSE app."""
mcp = FastMCP()
app = mcp.sse_app(host="::1")
assert app is not None
def test_not_auto_enabled_for_other_hosts_sse(self):
"""DNS rebinding protection should NOT auto-enable for other hosts in SSE app."""
mcp = FastMCP()
app = mcp.sse_app(host="0.0.0.0")
assert app is not None
def test_explicit_settings_not_overridden_sse(self):
"""Explicit transport_security settings should not be overridden in SSE app."""
custom_settings = TransportSecuritySettings(
enable_dns_rebinding_protection=False,
)
mcp = FastMCP(host="127.0.0.1", transport_security=custom_settings)
# Settings are copied by pydantic, so check values not identity
assert mcp.settings.transport_security is not None
assert mcp.settings.transport_security.enable_dns_rebinding_protection is False
assert mcp.settings.transport_security.allowed_hosts == []
mcp = FastMCP()
# Explicit transport_security passed to sse_app should be used as-is
app = mcp.sse_app(host="127.0.0.1", transport_security=custom_settings)
assert app is not None
def test_explicit_settings_not_overridden_streamable_http(self):
"""Explicit transport_security settings should not be overridden in StreamableHTTP app."""
custom_settings = TransportSecuritySettings(
enable_dns_rebinding_protection=False,
)
mcp = FastMCP()
# Explicit transport_security passed to streamable_http_app should be used as-is
app = mcp.streamable_http_app(host="127.0.0.1", transport_security=custom_settings)
assert app is not None
def tool_fn(x: int, y: int) -> int:
@ -1423,14 +1439,11 @@ class TestServerPrompts:
def test_streamable_http_no_redirect() -> None:
"""Test that streamable HTTP routes are correctly configured."""
mcp = FastMCP()
# streamable_http_path defaults to "/mcp"
app = mcp.streamable_http_app()
# Find routes by type - streamable_http_app creates Route objects, not Mount objects
streamable_routes = [
r
for r in app.routes
if isinstance(r, Route) and hasattr(r, "path") and r.path == mcp.settings.streamable_http_path
]
streamable_routes = [r for r in app.routes if isinstance(r, Route) and hasattr(r, "path") and r.path == "/mcp"]
# Verify routes exist
assert len(streamable_routes) == 1, "Should have one streamable route"