cloudinit/config/validate/node.go

/*
   Copyright 2014 CoreOS, Inc.

   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 validate

import (
	"fmt"
	"reflect"
	"regexp"
)

var (
	yamlKey  = regexp.MustCompile(`^ *-? ?(?P<key>.*?):`)
	yamlElem = regexp.MustCompile(`^ *-`)
)

type node struct {
	name     string
	line     int
	children []node
	field    reflect.StructField
	reflect.Value
}

// Child attempts to find the child with the given name in the node's list of
// children. If no such child is found, an invalid node is returned.
func (n node) Child(name string) node {
	for _, c := range n.children {
		if c.name == name {
			return c
		}
	}
	return node{}
}

// HumanType returns the human-consumable string representation of the type of
// the node.
func (n node) HumanType() string {
	switch k := n.Kind(); k {
	case reflect.Slice:
		c := n.Type().Elem()
		return "[]" + node{Value: reflect.New(c).Elem()}.HumanType()
	default:
		return k.String()
	}
}

// NewNode returns the node representation of the given value. The context
// will be used in an attempt to determine line numbers for the given value.
func NewNode(value interface{}, context context) node {
	var n node
	toNode(value, context, &n)
	return n
}

// toNode converts the given value into a node and then recursively processes
// each of the nodes components (e.g. fields, array elements, keys).
func toNode(v interface{}, c context, n *node) {
	vv := reflect.ValueOf(v)
	if !vv.IsValid() {
		return
	}

	n.Value = vv
	switch vv.Kind() {
	case reflect.Struct:
		// Walk over each field in the structure, skipping unexported fields,
		// and create a node for it.
		for i := 0; i < vv.Type().NumField(); i++ {
			ft := vv.Type().Field(i)
			k := ft.Tag.Get("yaml")
			if k == "-" || k == "" {
				continue
			}

			cn := node{name: k, field: ft}
			c, ok := findKey(cn.name, c)
			if ok {
				cn.line = c.lineNumber
			}
			toNode(vv.Field(i).Interface(), c, &cn)
			n.children = append(n.children, cn)
		}
	case reflect.Map:
		// Walk over each key in the map and create a node for it.
		v := v.(map[interface{}]interface{})
		for k, cv := range v {
			cn := node{name: fmt.Sprintf("%s", k)}
			c, ok := findKey(cn.name, c)
			if ok {
				cn.line = c.lineNumber
			}
			toNode(cv, c, &cn)
			n.children = append(n.children, cn)
		}
	case reflect.Slice:
		// Walk over each element in the slice and create a node for it.
		// While iterating over the slice, preserve the context after it
		// is modified. This allows the line numbers to reflect the current
		// element instead of the first.
		for i := 0; i < vv.Len(); i++ {
			cn := node{
				name:  fmt.Sprintf("%s[%d]", n.name, i),
				field: n.field,
			}
			var ok bool
			c, ok = findElem(c)
			if ok {
				cn.line = c.lineNumber
			}
			toNode(vv.Index(i).Interface(), c, &cn)
			n.children = append(n.children, cn)
			c.Increment()
		}
	case reflect.String, reflect.Int, reflect.Bool:
	default:
		panic(fmt.Sprintf("toNode(): unhandled kind %s", vv.Kind()))
	}
}

// findKey attempts to find the requested key within the provided context.
// A modified copy of the context is returned with every line up to the key
// incremented past. A boolean, true if the key was found, is also returned.
func findKey(key string, context context) (context, bool) {
	return find(yamlKey, key, context)
}

// findElem attempts to find an array element within the provided context.
// A modified copy of the context is returned with every line up to the array
// element incremented past. A boolean, true if the key was found, is also
// returned.
func findElem(context context) (context, bool) {
	return find(yamlElem, "", context)
}

func find(exp *regexp.Regexp, key string, context context) (context, bool) {
	for len(context.currentLine) > 0 || len(context.remainingLines) > 0 {
		matches := exp.FindStringSubmatch(context.currentLine)
		if len(matches) > 0 && (key == "" || matches[1] == key) {
			return context, true
		}

		context.Increment()
	}
	return context, false
}