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A Java implementation of the JSON Schema specification
/*
* Copyright (c) 2012, Francis Galiegue
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the Lesser GNU General Public License as
* published by the Free Software Foundation, either version 3 of the
* License, or (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* Lesser GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see
* JSON Pointer is an IETF draft defining a way to address paths within JSON
* documents. Paths apply to containers, ie arrays or nodes. For objects, path
* elements are member names. For arrays, they are indices in the array
* (starting from 0).
*
* The general syntax is {@code #/path/elements/here}. A path element is
* referred to as a "reference token" in the specification.
*
* The difficulty with JSON Pointer is that any JSON String is valid as an
* object member name. These are all valid:
*
*
* - {@code ""} -- the empty string;
* - {@code "/"};
* - {@code "0"};
* - {@code "-1"};
* - {@code "."}, {@code ".."}, {@code "../.."}.
*
*
* The latter example is the reason why a JSON Pointer is always
* absolute.
*
* All instances of this class are thread safe and immutable.
*/
public final class JsonPointer
extends JsonFragment
{
private static final CharMatcher SLASH = CharMatcher.is('/');
private static final CharMatcher ESCAPE_CHAR = CharMatcher.is('~');
private static final BiMap ESCAPE_REPLACEMENT_MAP
= new ImmutableBiMap.Builder()
.put('0', '~')
.put('1', '/')
.build();
private static final CharMatcher ESCAPED = CharMatcher.anyOf("01");
private static final CharMatcher SPECIAL = CharMatcher.anyOf("~/");
/**
* The list of individual elements in the pointer.
*/
private final List elements;
/**
* Constructor
*
* @param input The input string, guaranteed not to be JSON encoded
* @throws JsonSchemaException Illegal JSON Pointer
*/
public JsonPointer(final String input)
throws JsonSchemaException
{
super(input);
final ImmutableList.Builder builder = ImmutableList.builder();
decode(input, builder);
elements = builder.build();
}
private JsonPointer(final String fullPointer, final List elements)
{
super(fullPointer);
this.elements = elements;
}
/**
* Append a path element to this pointer. Returns a new instance.
*
* @param element the element to append
* @return a new instance with the element appended
*/
public JsonPointer append(final String element)
{
final List newElements = new ImmutableList.Builder()
.addAll(elements).add(element).build();
return new JsonPointer(asString + '/' + refTokenEncode(element),
newElements);
}
/**
* Append an array index to this pointer. Returns a new instance.
*
* Note that the index validity is NOT checked for (ie,
* you can append {@code -1} if you want to -- don't do that)
*
* @param index the index to add
* @return a new instance with the index appended
*/
public JsonPointer append(final int index)
{
return append(Integer.toString(index));
}
@Override
public JsonNode resolve(final JsonNode node)
{
JsonNode ret = node;
for (final String pathElement : elements) {
if (!ret.isContainerNode())
return MissingNode.getInstance();
if (ret.isObject())
ret = ret.path(pathElement);
else
try {
ret = ret.path(Integer.parseInt(pathElement));
} catch (NumberFormatException ignored) {
return MissingNode.getInstance();
}
if (ret.isMissingNode())
break;
}
return ret;
}
/**
* Initialize the object
*
* We read the string sequentially, a slash, then a reference token,
* then a slash, etc. Bail out if the string is malformed.
*
* @param input Input string, guaranteed not to be JSON/URI encoded
* @param builder the list builder
* @throws JsonSchemaException the input is not a valid JSON Pointer
*/
private static void decode(final String input,
final ImmutableList.Builder builder)
throws JsonSchemaException
{
String cooked, raw;
String victim = input;
while (!victim.isEmpty()) {
/*
* Skip the /
*/
if (!victim.startsWith("/")) {
final Message.Builder msg
= newMsg("reference token not preceeded by '/'");
throw new JsonSchemaException(msg.build());
}
victim = victim.substring(1);
/*
* Grab the "cooked" reference token
*/
cooked = getNextRefToken(victim);
victim = victim.substring(cooked.length());
/*
* Decode it, push it in the elements list
*/
raw = refTokenDecode(cooked);
builder.add(raw);
}
}
/**
* Grab a (cooked) reference token from an input string
*
* This method is only called from
* {@link #decode(String, ImmutableList.Builder)}, after a delimiter
* ({@code /}) has been swallowed up. The input string is therefore
* guaranteed to start with a reference token, which may be empty.
*
*
* @param input the input string
* @return the cooked reference token
* @throws JsonSchemaException the string is malformed
*/
private static String getNextRefToken(final String input)
throws JsonSchemaException
{
final StringBuilder sb = new StringBuilder();
final char[] array = input.toCharArray();
/*
* If we encounter a /, this is the end of the current token.
*
* If we encounter a ~, ensure that what follows is either 0 or 1.
*
* If we encounter any other character, append it.
*/
boolean inEscape = false;
for (final char c: array) {
if (inEscape) {
if (!ESCAPED.matches(c)) {
final Message.Builder msg = newMsg("bad escape sequence: " +
"'~' not followed by a valid token")
.addInfo("allowed", ESCAPE_REPLACEMENT_MAP.keySet())
.addInfo("found", Character.valueOf(c));
throw new JsonSchemaException(msg.build());
}
sb.append(c);
inEscape = false;
continue;
}
if (SLASH.matches(c))
break;
if (ESCAPE_CHAR.matches(c))
inEscape = true;
sb.append(c);
}
if (inEscape)
throw new JsonSchemaException(newMsg("bad escape sequence: '~' " +
"not followed by any token").build());
return sb.toString();
}
/**
* Turn a cooked reference token into a raw reference token
*
* This means we replace all occurrences of {@code ~0} with {@code ~},
* and all occurrences of {@code ~1} with {@code /}.
*
* It is called from {@link #decode}, in order to push a token into
* {@link #elements}.
*
* @param cooked the cooked token
* @return the raw token
*/
private static String refTokenDecode(final String cooked)
{
final StringBuilder sb = new StringBuilder(cooked.length());
/*
* Replace all occurrences of "~0" with "~", and all occurrences of
* "~1" with "/".
*
* The input is guaranteed to be well formed.
*/
final char[] array = cooked.toCharArray();
boolean inEscape = false;
for (final char c: array) {
if (ESCAPE_CHAR.matches(c)) {
inEscape = true;
continue;
}
if (inEscape) {
sb.append(ESCAPE_REPLACEMENT_MAP.get(c));
inEscape = false;
} else
sb.append(c);
}
return sb.toString();
}
/**
* Make a cooked reference token out of a raw element token
*
* @param raw the raw token
* @return the cooked token
*/
private static String refTokenEncode(final String raw)
{
final StringBuilder sb = new StringBuilder(raw.length());
/*
* Replace all occurrences of "~" with "~0" and all occurrences of "/"
* with "~1".
*/
final char[] array = raw.toCharArray();
for (final char c: array)
if (SPECIAL.matches(c))
sb.append('~').append(ESCAPE_REPLACEMENT_MAP.inverse().get(c));
else
sb.append(c);
return sb.toString();
}
private static Message.Builder newMsg(final String reason)
{
return Domain.REF_RESOLVING.newMessage().setKeyword("$ref")
.setMessage("illegal JSON Pointer").addInfo("reason", reason);
}
}