rc: add GetStructMissingOK

fs/rc/params.go

@@ -202,3 +202,13 @@ func (p Params) GetStruct(key string, out interface{}) error {
 	}
 	return nil
 }
+
+// GetStructMissingOK works like GetStruct but doesn't return an error
+// if the key is missing
+func (p Params) GetStructMissingOK(key string, out interface{}) error {
+	_, ok := p[key]
+	if !ok {
+		return nil
+	}
+	return p.GetStruct(key, out)
+}

fs/rc/params_test.go

@@ -249,3 +249,32 @@ func TestParamsGetStruct(t *testing.T) {
 	assert.Equal(t, 4.2, out.Float)
 	assert.Equal(t, true, IsErrParamInvalid(e3), e3.Error())
 }
+
+func TestParamsGetStructMissingOK(t *testing.T) {
+	in := Params{
+		"struct": Params{
+			"String": "one",
+			"Float":  4.2,
+		},
+	}
+	var out struct {
+		String string
+		Float  float64
+	}
+	e1 := in.GetStructMissingOK("struct", &out)
+	assert.NoError(t, e1)
+	assert.Equal(t, "one", out.String)
+	assert.Equal(t, 4.2, out.Float)
+
+	e2 := in.GetStructMissingOK("notOK", &out)
+	assert.NoError(t, e2)
+	assert.Equal(t, "one", out.String)
+	assert.Equal(t, 4.2, out.Float)
+
+	in["struct"] = "string"
+	e3 := in.GetStructMissingOK("struct", &out)
+	assert.Error(t, e3)
+	assert.Equal(t, "one", out.String)
+	assert.Equal(t, 4.2, out.Float)
+	assert.Equal(t, true, IsErrParamInvalid(e3), e3.Error())
+}