Function rejectLegacyCapabilities

daemon/server/router/container/container_routes.go:835–840

rejectLegacyCapabilities returns an error if the deprecated HostConfig.Capabilities field is present in a request for API version 1.40. The Capabilities field was added in API 1.40 (Docker 19.03) as a way to specify the exact set of kernel capabilities for a container, overriding the CapAdd/CapDrop

(capabilities []string, version string)

// return an explicit error rather than silently ignoring the field when it is
// expected to be supported.
func rejectLegacyCapabilities(capabilities []string, version string) error {
	if len(capabilities) > 0 && versions.Equal(version, "1.40") {
		return errLegacyCapabilities
	}
	return nil
}

// handleMACAddressBC takes care of backward-compatibility for the container-wide MAC address by mutating the
// networkingConfig to set the endpoint-specific MACAddress field introduced in API v1.44. It returns a warning message