open-consul/agent/config/merge.go

66 lines
1.6 KiB
Go

package config
import (
"fmt"
"reflect"
)
// Merge recursively combines a set of config file structures into a single structure
// according to the following rules:
//
// * only values of type struct, slice, map and pointer to simple types are allowed. Other types panic.
// * when merging two structs the result is the recursive merge of all fields according to the rules below
// * when merging two slices the result is the second slice appended to the first
// * when merging two maps the result is the second map overlaid on the first
// * when merging two pointer values the result is the second value if it is not nil, otherwise the first
func Merge(files ...Config) Config {
var a Config
for _, b := range files {
a = merge(a, b).(Config)
}
return a
}
func merge(a, b interface{}) interface{} {
return mergeValue(reflect.ValueOf(a), reflect.ValueOf(b)).Interface()
}
func mergeValue(a, b reflect.Value) reflect.Value {
switch a.Kind() {
case reflect.Map:
r := reflect.MakeMap(a.Type())
for _, k := range a.MapKeys() {
v := a.MapIndex(k)
r.SetMapIndex(k, v)
}
for _, k := range b.MapKeys() {
v := b.MapIndex(k)
r.SetMapIndex(k, v)
}
return r
case reflect.Ptr:
if !b.IsNil() {
return b
}
return a
case reflect.Slice:
if !a.IsValid() {
a = reflect.Zero(a.Type())
}
return reflect.AppendSlice(a, b)
case reflect.Struct:
r := reflect.New(a.Type()) // &struct{}
for i := 0; i < a.NumField(); i++ {
v := mergeValue(a.Field(i), b.Field(i))
r.Elem().Field(i).Set(v)
}
return r.Elem() // *struct
default:
panic(fmt.Sprintf("unsupported element type: %v", a.Type()))
}
}