Make wifi collector fail gracefully if metrics not available

vendor/github.com/mdlayher/wifi/client.go

@@ -1,5 +1,15 @@
 package wifi
 
+import (
+	"errors"
+)
+
+var (
+	// errNotStation is returned when attempting to query station info for
+	// an interface which is not a station.
+	errNotStation = errors.New("interface is not a station")
+)
+
 // A Client is a type which can access WiFi device actions and statistics
 // using operating system-specific operations.
 type Client struct {
@@ -18,6 +28,11 @@ func New() (*Client, error) {
 	}, nil
 }
 
+// Close releases resources used by a Client.
+func (c *Client) Close() error {
+	return c.c.Close()
+}
+
 // Interfaces returns a list of the system's WiFi network interfaces.
 func (c *Client) Interfaces() ([]*Interface, error) {
 	return c.c.Interfaces()
@@ -26,11 +41,16 @@ func (c *Client) Interfaces() ([]*Interface, error) {
 // StationInfo retrieves statistics about a WiFi interface operating in
 // station mode.
 func (c *Client) StationInfo(ifi *Interface) (*StationInfo, error) {
+	if ifi.Type != InterfaceTypeStation {
+		return nil, errNotStation
+	}
+
 	return c.c.StationInfo(ifi)
 }
 
 // An osClient is the operating system-specific implementation of Client.
 type osClient interface {
+	Close() error
 	Interfaces() ([]*Interface, error)
 	StationInfo(ifi *Interface) (*StationInfo, error)
 }

vendor/github.com/mdlayher/wifi/client_linux.go

@@ -36,6 +36,7 @@ type client struct {
 // genl is an interface over generic netlink, so netlink interactions can
 // be stubbed in tests.
 type genl interface {
+	Close() error
 	GetFamily(name string) (genetlink.Family, error)
 	Execute(m genetlink.Message, family uint16, flags netlink.HeaderFlags) ([]genetlink.Message, error)
 }
@@ -66,6 +67,11 @@ func initClient(c genl) (*client, error) {
 	}, nil
 }
 
+// Close closes the client's generic netlink connection.
+func (c *client) Close() error {
+	return c.c.Close()
+}
+
 // Interfaces requests that nl80211 return a list of all WiFi interfaces present
 // on this system.
 func (c *client) Interfaces() ([]*Interface, error) {
@@ -117,7 +123,12 @@ func (c *client) StationInfo(ifi *Interface) (*StationInfo, error) {
 		return nil, err
 	}
 
-	if len(msgs) > 1 {
+	switch len(msgs) {
+	case 0:
+		return nil, os.ErrNotExist
+	case 1:
+		break
+	default:
 		return nil, errMultipleMessages
 	}
 

vendor/github.com/mdlayher/wifi/client_others.go

@@ -24,6 +24,11 @@ func newClient() (*client, error) {
 	return nil, errUnimplemented
 }
 
+// Close always returns an error.
+func (c *client) Close() error {
+	return errUnimplemented
+}
+
 // Interfaces always returns an error.
 func (c *client) Interfaces() ([]*Interface, error) {
 	return nil, errUnimplemented