integration: add upstream validator to OCI roundtrip tests

In order to make sure that we don't create invalid OCI images that are
consistently invalid, add additional checks to ensure that both of the
generated OCI images in the round-trip test are valid according to the
upstream validator.

This commit vendors the following packages (deep breath):
* oci/image-tools@7575a09363, which requires
* oci/image-spec@v1.0.0-rc4 [revendor, but is technically an update
  because I couldn't figure out what version was vendored last time]
* oci/runtime-spec@v1.0.0-rc4
* xeipuuv/gojsonschema@6b67b3fab7
* xeipuuv/gojsonreference@e02fc20de9
* xeipuuv/gojsonpointer@e0fe6f6830
* camlistore/go4@7ce08ca145

Signed-off-by: Aleksa Sarai <asarai@suse.de>

vendor/github.com/xeipuuv/gojsonpointer/pointer.go

@@ -0,0 +1,217 @@
+// Copyright 2015 xeipuuv ( https://github.com/xeipuuv )
+//
+// 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.
+
+// author  			xeipuuv
+// author-github 	https://github.com/xeipuuv
+// author-mail		xeipuuv@gmail.com
+//
+// repository-name	gojsonpointer
+// repository-desc	An implementation of JSON Pointer - Go language
+//
+// description		Main and unique file.
+//
+// created      	25-02-2013
+
+package gojsonpointer
+
+import (
+	"errors"
+	"fmt"
+	"reflect"
+	"strconv"
+	"strings"
+)
+
+const (
+	const_empty_pointer     = ``
+	const_pointer_separator = `/`
+
+	const_invalid_start = `JSON pointer must be empty or start with a "` + const_pointer_separator + `"`
+)
+
+type implStruct struct {
+	mode string // "SET" or "GET"
+
+	inDocument interface{}
+
+	setInValue interface{}
+
+	getOutNode interface{}
+	getOutKind reflect.Kind
+	outError   error
+}
+
+func NewJsonPointer(jsonPointerString string) (JsonPointer, error) {
+
+	var p JsonPointer
+	err := p.parse(jsonPointerString)
+	return p, err
+
+}
+
+type JsonPointer struct {
+	referenceTokens []string
+}
+
+// "Constructor", parses the given string JSON pointer
+func (p *JsonPointer) parse(jsonPointerString string) error {
+
+	var err error
+
+	if jsonPointerString != const_empty_pointer {
+		if !strings.HasPrefix(jsonPointerString, const_pointer_separator) {
+			err = errors.New(const_invalid_start)
+		} else {
+			referenceTokens := strings.Split(jsonPointerString, const_pointer_separator)
+			for _, referenceToken := range referenceTokens[1:] {
+				p.referenceTokens = append(p.referenceTokens, referenceToken)
+			}
+		}
+	}
+
+	return err
+}
+
+// Uses the pointer to retrieve a value from a JSON document
+func (p *JsonPointer) Get(document interface{}) (interface{}, reflect.Kind, error) {
+
+	is := &implStruct{mode: "GET", inDocument: document}
+	p.implementation(is)
+	return is.getOutNode, is.getOutKind, is.outError
+
+}
+
+// Uses the pointer to update a value from a JSON document
+func (p *JsonPointer) Set(document interface{}, value interface{}) (interface{}, error) {
+
+	is := &implStruct{mode: "SET", inDocument: document, setInValue: value}
+	p.implementation(is)
+	return document, is.outError
+
+}
+
+// Both Get and Set functions use the same implementation to avoid code duplication
+func (p *JsonPointer) implementation(i *implStruct) {
+
+	kind := reflect.Invalid
+
+	// Full document when empty
+	if len(p.referenceTokens) == 0 {
+		i.getOutNode = i.inDocument
+		i.outError = nil
+		i.getOutKind = kind
+		i.outError = nil
+		return
+	}
+
+	node := i.inDocument
+
+	for ti, token := range p.referenceTokens {
+
+		decodedToken := decodeReferenceToken(token)
+		isLastToken := ti == len(p.referenceTokens)-1
+
+		rValue := reflect.ValueOf(node)
+		kind = rValue.Kind()
+
+		switch kind {
+
+		case reflect.Map:
+			m := node.(map[string]interface{})
+			if _, ok := m[decodedToken]; ok {
+				node = m[decodedToken]
+				if isLastToken && i.mode == "SET" {
+					m[decodedToken] = i.setInValue
+				}
+			} else {
+				i.outError = errors.New(fmt.Sprintf("Object has no key '%s'", token))
+				i.getOutKind = kind
+				i.getOutNode = nil
+				return
+			}
+
+		case reflect.Slice:
+			s := node.([]interface{})
+			tokenIndex, err := strconv.Atoi(token)
+			if err != nil {
+				i.outError = errors.New(fmt.Sprintf("Invalid array index '%s'", token))
+				i.getOutKind = kind
+				i.getOutNode = nil
+				return
+			}
+			sLength := len(s)
+			if tokenIndex < 0 || tokenIndex >= sLength {
+				i.outError = errors.New(fmt.Sprintf("Out of bound array[0,%d] index '%d'", sLength, tokenIndex))
+				i.getOutKind = kind
+				i.getOutNode = nil
+				return
+			}
+
+			node = s[tokenIndex]
+			if isLastToken && i.mode == "SET" {
+				s[tokenIndex] = i.setInValue
+			}
+
+		default:
+			i.outError = errors.New(fmt.Sprintf("Invalid token reference '%s'", token))
+			i.getOutKind = kind
+			i.getOutNode = nil
+			return
+		}
+
+	}
+
+	rValue := reflect.ValueOf(node)
+	kind = rValue.Kind()
+
+	i.getOutNode = node
+	i.getOutKind = kind
+	i.outError = nil
+}
+
+// Pointer to string representation function
+func (p *JsonPointer) String() string {
+
+	if len(p.referenceTokens) == 0 {
+		return const_empty_pointer
+	}
+
+	pointerString := const_pointer_separator + strings.Join(p.referenceTokens, const_pointer_separator)
+
+	return pointerString
+}
+
+// Specific JSON pointer encoding here
+// ~0 => ~
+// ~1 => /
+// ... and vice versa
+
+const (
+	const_encoded_reference_token_0 = `~0`
+	const_encoded_reference_token_1 = `~1`
+	const_decoded_reference_token_0 = `~`
+	const_decoded_reference_token_1 = `/`
+)
+
+func decodeReferenceToken(token string) string {
+	step1 := strings.Replace(token, const_encoded_reference_token_1, const_decoded_reference_token_1, -1)
+	step2 := strings.Replace(step1, const_encoded_reference_token_0, const_decoded_reference_token_0, -1)
+	return step2
+}
+
+func encodeReferenceToken(token string) string {
+	step1 := strings.Replace(token, const_decoded_reference_token_1, const_encoded_reference_token_1, -1)
+	step2 := strings.Replace(step1, const_decoded_reference_token_0, const_encoded_reference_token_0, -1)
+	return step2
+}