Introduce a FieldPath type for validation

pkg/util/validation/fieldpath.go

@@ -0,0 +1,91 @@
+/*
+Copyright 2015 The Kubernetes Authors All rights reserved.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package validation
+
+import (
+	"bytes"
+	"fmt"
+	"strconv"
+)
+
+// FieldPath represents the path from some root to a particular field.
+type FieldPath struct {
+	name   string     // the name of this field or "" if this is an index
+	index  string     // if name == "", this is a subscript (index or map key) of the previous element
+	parent *FieldPath // nil if this is the root element
+}
+
+// NewFieldPath creates a root FieldPath object.
+func NewFieldPath(name string, moreNames ...string) *FieldPath {
+	r := &FieldPath{name: name, parent: nil}
+	for _, anotherName := range moreNames {
+		r = &FieldPath{name: anotherName, parent: r}
+	}
+	return r
+}
+
+// Root returns the root element of this FieldPath.
+func (fp *FieldPath) Root() *FieldPath {
+	for ; fp.parent != nil; fp = fp.parent {
+		// Do nothing.
+	}
+	return fp
+}
+
+// Child creates a new FieldPath that is a child of the method receiver.
+func (fp *FieldPath) Child(name string, moreNames ...string) *FieldPath {
+	r := NewFieldPath(name, moreNames...)
+	r.Root().parent = fp
+	return r
+}
+
+// Index indicates that the previous FieldPath is to be subscripted by an int.
+// This sets the same underlying value as Key.
+func (fp *FieldPath) Index(index int) *FieldPath {
+	return &FieldPath{index: strconv.Itoa(index), parent: fp}
+}
+
+// Key indicates that the previous FieldPath is to be subscripted by a string.
+// This sets the same underlying value as Index.
+func (fp *FieldPath) Key(key string) *FieldPath {
+	return &FieldPath{index: key, parent: fp}
+}
+
+// String produces a string representation of the FieldPath.
+func (fp *FieldPath) String() string {
+	// make a slice to iterate
+	elems := []*FieldPath{}
+	for p := fp; p != nil; p = p.parent {
+		elems = append(elems, p)
+	}
+
+	// iterate, but it has to be backwards
+	buf := bytes.NewBuffer(nil)
+	for i := range elems {
+		p := elems[len(elems)-1-i]
+		if p.parent != nil && len(p.name) > 0 {
+			// This is either the root or it is a subscript.
+			buf.WriteString(".")
+		}
+		if len(p.name) > 0 {
+			buf.WriteString(p.name)
+		} else {
+			fmt.Fprintf(buf, "[%s]", p.index)
+		}
+	}
+	return buf.String()
+}