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Raise an error if a Client is created with no servers in config

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This commit is contained in:
Jeremiah Lowin 2025-05-22 11:22:45 -04:00
commit 06b9b98b6c
2 changed files with 17 additions and 1 deletions
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6
src/fastmcp/client/transports.py
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@ -528,8 +528,12 @@ class MCPConfigTransport(ClientTransport):
config = MCPConfig.from_dict(config)
self.config = config
# if there are no servers, raise an error
if len(self.config.mcpServers) == 0:
raise ValueError("No MCP servers defined in the config")
# if there's exactly one server, create a client for that server
if len(self.config.mcpServers) == 1:
elif len(self.config.mcpServers) == 1:
self.transport = list(self.config.mcpServers.values())[0].to_transport()
# otherwise create a composite client

12
tests/client/test_client.py
View file

@ -673,6 +673,18 @@ class TestInferTransport:
assert transport.transport.command == "echo"
assert transport.transport.args == ["hello"]
def test_config_with_no_servers(self):
"""Test that an empty MCPConfig raises a ValueError."""
config = {"mcpServers": {}}
with pytest.raises(ValueError, match="No MCP servers defined in the config"):
infer_transport(config)
def test_mcpconfigtransport_with_no_servers(self):
"""Test that MCPConfigTransport raises a ValueError when initialized with an empty config."""
config = {"mcpServers": {}}
with pytest.raises(ValueError, match="No MCP servers defined in the config"):
MCPConfigTransport(config=config)
def test_infer_composite_client(config):
config = {
"mcpServers": {