Handle multiline YAML commands with backslashes

Author: msabramo

src/mcp/client/config/mcp_servers_config.py

@@ -29,8 +29,16 @@ class StdioServerConfig(MCPServerConfig):
     env: dict[str, str] | None = None
 
     def _parse_command(self) -> list[str]:
-        """Parse the command string into parts, handling quotes properly."""
-        return shlex.split(self.command)
+        """Parse the command string into parts, handling quotes properly.
+
+        Strips unnecessary whitespace and newlines to handle YAML multi-line strings.
+        Treats backslashes followed by newlines as line continuations.
+        """
+        # Handle backslash line continuations by removing them and the following newline
+        cleaned_command = self.command.replace("\\\n", " ")
+        # Then normalize all whitespace (including remaining newlines) to single spaces
+        cleaned_command = " ".join(cleaned_command.split())
+        return shlex.split(cleaned_command)
 
     @property
     def effective_command(self) -> str:

tests/client/config/mcp.yaml

@@ -8,6 +8,12 @@ mcpServers:
   filesystem:
     command: npx -y @modelcontextprotocol/server-filesystem /Users/username/Desktop /path/to/other/allowed/dir
 
+  filesystem_multi_line:
+    command: >
+      npx -y @modelcontextprotocol/server-filesystem \
+        /Users/username/Desktop \
+        /path/to/other/allowed/dir
+
   # Stdio server with full command string
   # The library will automatically parse this.
   # The effective_command will be "python" and effective_args will be ["-m", "my_server"]

tests/client/config/test_yaml_functionality.py

@@ -98,12 +98,11 @@ def test_npx_filesystem_server(mcp_yaml_config_file: Path):
     assert filesystem_server.args is None  # No explicit args
     assert filesystem_server.env is None  # No environment variables
 
-    # Test the effective command parsing
+    # Test the effective command and args parsing
     assert filesystem_server.effective_command == "npx"
-    expected_args = [
+    assert filesystem_server.effective_args == [
         "-y", 
         "@modelcontextprotocol/server-filesystem", 
         "/Users/username/Desktop", 
         "/path/to/other/allowed/dir"
     ]
-    assert filesystem_server.effective_args == expected_args