open-consul/lib/map_walker.go

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package lib
import (
"fmt"
"reflect"
"github.com/mitchellh/copystructure"
"github.com/mitchellh/mapstructure"
"github.com/mitchellh/reflectwalk"
)
// MapWalk will traverse through the supplied input which should be a
// map[string]interface{} (or something compatible that we can coerce
// to a map[string]interface{}) and from it create a new map[string]interface{}
// with all internal values coerced to JSON compatible types. i.e. a []uint8
// can be converted (in most cases) to a string so it will not be base64 encoded
// when output in JSON
func MapWalk(input interface{}) (map[string]interface{}, error) {
mapCopyRaw, err := copystructure.Copy(input)
if err != nil {
return nil, err
}
mapCopy, ok := mapCopyRaw.(map[string]interface{})
if !ok {
return nil, fmt.Errorf("internal error: input to MapWalk is not a map[string]interface{}")
}
if err := reflectwalk.Walk(mapCopy, &mapWalker{}); err != nil {
return nil, err
}
return mapCopy, nil
}
var typMapIfaceIface = reflect.TypeOf(map[interface{}]interface{}{})
var typByteSlice = reflect.TypeOf([]byte{})
// mapWalker implements interfaces for the reflectwalk package
// (github.com/mitchellh/reflectwalk) that can be used to automatically
// make a JSON compatible map safe for JSON usage. This is currently
// targeted at the map[string]interface{}
//
// Most of the implementation here is just keeping track of where we are
// in the reflectwalk process, so that we can replace values. The key logic
// is in Slice() and SliceElem().
//
// In particular we're looking to replace two cases the msgpack codec causes:
//
// 1.) String values get turned into byte slices. JSON will base64-encode
// this and we don't want that, so we convert them back to strings.
//
// 2.) Nested maps turn into map[interface{}]interface{}. JSON cannot
// encode this, so we need to turn it back into map[string]interface{}.
//
type mapWalker struct {
lastValue reflect.Value // lastValue of map, required for replacement
loc, lastLoc reflectwalk.Location // locations
cs []reflect.Value // container stack
csKey []reflect.Value // container keys (maps) stack
csData interface{} // current container data
sliceIndex []int // slice index stack (one for each slice in cs)
}
func (w *mapWalker) Enter(loc reflectwalk.Location) error {
w.lastLoc = w.loc
w.loc = loc
return nil
}
func (w *mapWalker) Exit(loc reflectwalk.Location) error {
w.loc = reflectwalk.None
w.lastLoc = reflectwalk.None
switch loc {
case reflectwalk.Map:
w.cs = w.cs[:len(w.cs)-1]
case reflectwalk.MapValue:
w.csKey = w.csKey[:len(w.csKey)-1]
case reflectwalk.Slice:
// Split any values that need to be split
w.cs = w.cs[:len(w.cs)-1]
case reflectwalk.SliceElem:
w.csKey = w.csKey[:len(w.csKey)-1]
w.sliceIndex = w.sliceIndex[:len(w.sliceIndex)-1]
}
return nil
}
func (w *mapWalker) Map(m reflect.Value) error {
w.cs = append(w.cs, m)
return nil
}
func (w *mapWalker) MapElem(m, k, v reflect.Value) error {
w.csData = k
w.csKey = append(w.csKey, k)
w.lastValue = v
// We're looking specifically for map[interface{}]interface{}, but the
// values in a map could be wrapped up in interface{} so we need to unwrap
// that first. Therefore, we do three checks: 1.) is it valid? so we
// don't panic, 2.) is it an interface{}? so we can unwrap it and 3.)
// after unwrapping the interface do we have the map we expect?
if !v.IsValid() {
return nil
}
if v.Kind() != reflect.Interface {
return nil
}
if inner := v.Elem(); inner.Type() == typMapIfaceIface {
// map[interface{}]interface{}, attempt to weakly decode into string keys
var target map[string]interface{}
if err := mapstructure.WeakDecode(v.Interface(), &target); err != nil {
return err
}
m.SetMapIndex(k, reflect.ValueOf(target))
}
return nil
}
func (w *mapWalker) Slice(v reflect.Value) error {
// If we find a []byte slice, it is an HCL-string converted to []byte.
// Convert it back to a Go string and replace the value so that JSON
// doesn't base64-encode it.
if v.Type() == typByteSlice {
resultVal := reflect.ValueOf(string(v.Interface().([]byte)))
switch w.lastLoc {
case reflectwalk.MapKey:
m := w.cs[len(w.cs)-1]
// Delete the old value
var zero reflect.Value
m.SetMapIndex(w.csData.(reflect.Value), zero)
// Set the new key with the existing value
m.SetMapIndex(resultVal, w.lastValue)
// Set the key to be the new key
w.csData = resultVal
case reflectwalk.MapValue:
// If we're in a map, then the only way to set a map value is
// to set it directly.
m := w.cs[len(w.cs)-1]
mk := w.csData.(reflect.Value)
m.SetMapIndex(mk, resultVal)
case reflectwalk.Slice:
s := w.cs[len(w.cs)-1]
s.Index(w.sliceIndex[len(w.sliceIndex)-1]).Set(resultVal)
default:
return fmt.Errorf("cannot convert []byte")
}
}
w.cs = append(w.cs, v)
return nil
}
func (w *mapWalker) SliceElem(i int, elem reflect.Value) error {
w.csKey = append(w.csKey, reflect.ValueOf(i))
w.sliceIndex = append(w.sliceIndex, i)
// We're looking specifically for map[interface{}]interface{}, but the
// values in a slice are wrapped up in interface{} so we need to unwrap
// that first. Therefore, we do three checks: 1.) is it valid? so we
// don't panic, 2.) is it an interface{}? so we can unwrap it and 3.)
// after unwrapping the interface do we have the map we expect?
if !elem.IsValid() {
return nil
}
if elem.Kind() != reflect.Interface {
return nil
}
if inner := elem.Elem(); inner.Type() == typMapIfaceIface {
// map[interface{}]interface{}, attempt to weakly decode into string keys
var target map[string]interface{}
if err := mapstructure.WeakDecode(inner.Interface(), &target); err != nil {
return err
}
elem.Set(reflect.ValueOf(target))
} else if inner := elem.Elem(); inner.Type() == typByteSlice {
elem.Set(reflect.ValueOf(string(inner.Interface().([]byte))))
}
return nil
}