Allow to set daemon and server configurations in a file.

Read configuration after flags making this the priority:

1- Apply configuration from file.
2- Apply configuration from flags.

Reload configuration when a signal is received, USR2 in Linux:

- Reload router if the debug configuration changes.
- Reload daemon labels.
- Reload cluster discovery.

Signed-off-by: David Calavera <david.calavera@gmail.com>

opts/opts.go

@@ -100,6 +100,35 @@ func (opts *ListOpts) Len() int {
 	return len((*opts.values))
 }
 
+// NamedOption is an interface that list and map options
+// with names implement.
+type NamedOption interface {
+	Name() string
+}
+
+// NamedListOpts is a ListOpts with a configuration name.
+// This struct is useful to keep reference to the assigned
+// field name in the internal configuration struct.
+type NamedListOpts struct {
+	name string
+	ListOpts
+}
+
+var _ NamedOption = &NamedListOpts{}
+
+// NewNamedListOptsRef creates a reference to a new NamedListOpts struct.
+func NewNamedListOptsRef(name string, values *[]string, validator ValidatorFctType) *NamedListOpts {
+	return &NamedListOpts{
+		name:     name,
+		ListOpts: *NewListOptsRef(values, validator),
+	}
+}
+
+// Name returns the name of the NamedListOpts in the configuration.
+func (o *NamedListOpts) Name() string {
+	return o.name
+}
+
 //MapOpts holds a map of values and a validation function.
 type MapOpts struct {
 	values    map[string]string
@@ -145,6 +174,29 @@ func NewMapOpts(values map[string]string, validator ValidatorFctType) *MapOpts {
 	}
 }
 
+// NamedMapOpts is a MapOpts struct with a configuration name.
+// This struct is useful to keep reference to the assigned
+// field name in the internal configuration struct.
+type NamedMapOpts struct {
+	name string
+	MapOpts
+}
+
+var _ NamedOption = &NamedMapOpts{}
+
+// NewNamedMapOpts creates a reference to a new NamedMapOpts struct.
+func NewNamedMapOpts(name string, values map[string]string, validator ValidatorFctType) *NamedMapOpts {
+	return &NamedMapOpts{
+		name:    name,
+		MapOpts: *NewMapOpts(values, validator),
+	}
+}
+
+// Name returns the name of the NamedMapOpts in the configuration.
+func (o *NamedMapOpts) Name() string {
+	return o.name
+}
+
 // ValidatorFctType defines a validator function that returns a validated string and/or an error.
 type ValidatorFctType func(val string) (string, error)
 

opts/opts_test.go

@@ -198,3 +198,35 @@ func logOptsValidator(val string) (string, error) {
 	}
 	return "", fmt.Errorf("invalid key %s", vals[0])
 }
+
+func TestNamedListOpts(t *testing.T) {
+	var v []string
+	o := NewNamedListOptsRef("foo-name", &v, nil)
+
+	o.Set("foo")
+	if o.String() != "[foo]" {
+		t.Errorf("%s != [foo]", o.String())
+	}
+	if o.Name() != "foo-name" {
+		t.Errorf("%s != foo-name", o.Name())
+	}
+	if len(v) != 1 {
+		t.Errorf("expected foo to be in the values, got %v", v)
+	}
+}
+
+func TestNamedMapOpts(t *testing.T) {
+	tmpMap := make(map[string]string)
+	o := NewNamedMapOpts("max-name", tmpMap, nil)
+
+	o.Set("max-size=1")
+	if o.String() != "map[max-size:1]" {
+		t.Errorf("%s != [map[max-size:1]", o.String())
+	}
+	if o.Name() != "max-name" {
+		t.Errorf("%s != max-name", o.Name())
+	}
+	if _, exist := tmpMap["max-size"]; !exist {
+		t.Errorf("expected map-size to be in the values, got %v", tmpMap)
+	}
+}