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Implement JSON-LD context URL resolution.

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This commit is contained in:
Dave Longley 2012-05-07 17:12:10 -04:00
parent 52fa975894
commit 4c847440c7
1 changed files with 238 additions and 143 deletions
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241
jsonld.php
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@ -45,7 +45,7 @@
* [strict] use strict mode (default: true).
* [optimize] true to optimize the compaction (default: false).
* [graph] true to always output a top-level graph (default: false).
* [resolver(url, callback(err, jsonCtx))] the URL resolver to use.
* [resolver(url)] the URL resolver to use.
*
* @return mixed the compacted JSON-LD output.
*/
@ -60,7 +60,7 @@ function jsonld_compact($input, $ctx, $options=array()) {
* @param mixed $input the JSON-LD object to expand.
* @param assoc[$options] the options to use:
* [base] the base IRI to use.
* [resolver(url, callback(err, jsonCtx))] the URL resolver to use.
* [resolver(url)] the URL resolver to use.
*
* @return array the expanded JSON-LD output.
*/
@ -80,7 +80,7 @@ function jsonld_expand($input, $options=array()) {
* [explicit] default @explicit flag (default: false).
* [omitDefault] default @omitDefault flag (default: false).
* [optimize] optimize when compacting (default: false).
* [resolver(url, callback(err, jsonCtx))] the URL resolver to use.
* [resolver(url)] the URL resolver to use.
*
* @return stdClass the framed JSON-LD output.
*/
@ -97,7 +97,7 @@ function jsonld_frame($input, $frame, $options=array()) {
* [base] the base IRI to use.
* [format] the format if output is a string:
* 'application/nquads' for N-Quads (default).
* [resolver(url, callback(err, jsonCtx))] the URL resolver to use.
* [resolver(url)] the URL resolver to use.
*
* @return array the normalized output.
*/
@ -132,7 +132,7 @@ function jsonld_from_rdf($input, $options=array()) {
* [base] the base IRI to use.
* [format] the format to use to output a string:
* 'application/nquads' for N-Quads (default).
* [resolver(url, callback(err, jsonCtx))] the URL resolver to use.
* [resolver(url)] the URL resolver to use.
*
* @return array all RDF statements in the JSON-LD object.
*/
@ -141,6 +141,47 @@ function jsonld_to_rdf($input, $options=array()) {
return $p->toRDF($input, $options);
}
/** The default JSON-LD URL resolver. */
$jsonld_default_url_resolver = null;
/**
* Sets the default JSON-LD URL resolver.
*
* @param callable resolver(url) the URL resolver to use.
*/
function jsonld_set_url_resolver($resolver) {
global $jsonld_default_url_resolver;
$jsonld_default_url_resolver = $resolver;
}
/**
* Retrieves JSON-LD at the given URL.
*
* @param string $url the URL to to resolve.
*
* @return the JSON-LD.
*/
function jsonld_resolve_url($url) {
global $jsonld_default_url_resolver;
if($jsonld_default_url_resolver !== null) {
return call_user_func($jsonld_default_url_resolver, $url);
}
// default JSON-LD GET implementation
$opts = array('http' =>
array(
'method' => "GET",
'header' =>
"Accept: application/ld+json\r\n" .
"User-Agent: PaySwarm PHP Client/1.0\r\n"));
$stream = stream_context_create($opts);
$result = @file_get_contents($url, false, $stream);
if($result === false) {
throw new Exception("Could not GET url: '$url'");
}
return $result;
}
/**
* A JSON-LD processor.
*/
@ -156,6 +197,9 @@ class JsonLdProcessor {
const RDF_NIL = 'http://www.w3.org/1999/02/22-rdf-syntax-ns#nil';
const RDF_TYPE = 'http://www.w3.org/1999/02/22-rdf-syntax-ns#type';
/** Restraints */
const MAX_CONTEXT_URLS = 10;
/**
* Constructs a JSON-LD processor.
*/
@ -183,7 +227,6 @@ class JsonLdProcessor {
isset($options['optimize']) or $options['optimize'] = false;
isset($options['graph']) or $options['graph'] = false;
isset($options['activeCtx']) or $options['activeCtx'] = false;
// FIXME: implement jsonld_resolve_url
isset($options['resolver']) or $options['resolver'] = 'jsonld_resolve_url';
// expand input
@ -283,19 +326,25 @@ class JsonLdProcessor {
* @param mixed $input the JSON-LD object to expand.
* @param assoc $options the options to use:
* [base] the base IRI to use.
* [resolver(url, callback(err, jsonCtx))] the URL resolver to use.
* [resolver(url)] the URL resolver to use.
*
* @return array the expanded JSON-LD output.
*/
public function expand($input, $options) {
// set default options
isset($options['base']) or $options['base'] = '';
// FIXME: implement jsonld_resolve_url
isset($options['resolver']) or $options['resolver'] = 'jsonld_resolve_url';
// resolve all @context URLs in the input
$input = self::copy($input);
$this->_resolveUrls($input, $options['resolver']);
try {
$this->_resolveContextUrls($input, new stdClass(), $options['resolver']);
}
catch(Exception $e) {
throw new JsonLdException(
'Could not perform JSON-LD expansion.',
'jsonld.ExpandError', null, $e);
}
// do expansion
$ctx = $this->_getInitialContext();
@ -321,7 +370,7 @@ class JsonLdProcessor {
* [explicit] default @explicit flag (default: false).
* [omitDefault] default @omitDefault flag (default: false).
* [optimize] optimize when compacting (default: false).
* [resolver(url, callback(err, jsonCtx))] the URL resolver to use.
* [resolver(url)] the URL resolver to use.
*
* @return stdClass the framed JSON-LD output.
*/
@ -332,7 +381,6 @@ class JsonLdProcessor {
isset($options['explicit']) or $options['explicit'] = false;
isset($options['omitDefault']) or $options['omitDefault'] = false;
isset($options['optimize']) or $options['optimize'] = false;
// FIXME: implement jsonld_resolve_url
isset($options['resolver']) or $options['resolver'] = 'jsonld_resolve_url';
// preserve frame context
@ -343,20 +391,20 @@ class JsonLdProcessor {
// expand input
$_input = $this->expand($input, $options);
}
catch(JsonLdException $e) {
catch(Exception $e) {
throw new JsonLdException(
'Could not expand input before framing.',
'jsonld.FrameError', $e);
'jsonld.FrameError', null, $e);
}
try {
// expand frame
$_frame = $this->expand($frame, $options);
}
catch(JsonLdException $e) {
catch(Exception $e) {
throw new JsonLdException(
'Could not expand frame before framing.',
'jsonld.FrameError', $e);
'jsonld.FrameError', null, $e);
}
// do framing
@ -368,10 +416,10 @@ class JsonLdProcessor {
$options['activeCtx'] = true;
$result = $this->compact($framed, $ctx, $options);
}
catch(JsonLdException $e) {
catch(Exception $e) {
throw new JsonLdException(
'Could not compact framed output.',
'jsonld.FrameError', $e);
'jsonld.FrameError', null, $e);
}
$compacted = $result['compacted'];
@ -390,24 +438,23 @@ class JsonLdProcessor {
* @param mixed $input the JSON-LD object to normalize.
* @param assoc $options the options to use:
* [base] the base IRI to use.
* [resolver(url, callback(err, jsonCtx))] the URL resolver to use.
* [resolver(url)] the URL resolver to use.
*
* @return array the JSON-LD normalized output.
*/
public function normalize($input, $options) {
// set default options
isset($options['base']) or $options['base'] = '';
// FIXME: implement jsonld_resolve_url
isset($options['resolver']) or $options['resolver'] = 'jsonld_resolve_url';
try {
// expand input then do normalization
$expanded = $this->expand($input, $options);
}
catch(JsonLdException $e) {
catch(Exception $e) {
throw new JsonLdException(
'Could not expand input before normalization.',
'jsonld.NormalizeError', $e);
'jsonld.NormalizeError', null, $e);
}
// do normalization
@ -456,14 +503,13 @@ class JsonLdProcessor {
* [base] the base IRI to use.
* [format] the format to use to output a string:
* 'application/nquads' for N-Quads (default).
* [resolver(url, callback(err, jsonCtx))] the URL resolver to use.
* [resolver(url)] the URL resolver to use.
*
* @return array all RDF statements in the JSON-LD object.
*/
public function toRDF($input, $options) {
// set default options
isset($options['base']) or $options['base'] = '';
// FIXME: implement jsonld_resolve_url
isset($options['resolver']) or $options['resolver'] = 'jsonld_resolve_url';
try {
@ -510,7 +556,7 @@ class JsonLdProcessor {
* @param stdClass $active_ctx the current active context.
* @param mixed $local_ctx the local context to process.
* @param assoc $options the options to use:
* [resolver(url, callback(err, jsonCtx))] the URL resolver to use.
* [resolver(url)] the URL resolver to use.
*
* @return stdClass the new active context.
*/
@ -522,15 +568,21 @@ class JsonLdProcessor {
// set default options
isset($options['base']) or $options['base'] = '';
// FIXME: implement jsonld_resolve_url
isset($options['resolver']) or $options['resolver'] = 'jsonld_resolve_url';
// resolve URLs in local_ctx
$local_ctx = self::copy($local_ctx);
if(is_object($local_ctx) && !property_exists($local_ctx, '@context')) {
$local_ctx = (object)array('@context' => $local_ctx);
$ctx = self::copy($local_ctx);
if(is_object($ctx) && !property_exists($ctx, '@context')) {
$ctx = (object)array('@context' => $ctx);
}
try {
$this->_resolveContextUrls($ctx, new stdClass(), $options['resolver']);
}
catch(Exception $e) {
throw new JsonLdException(
'Could not process JSON-LD context.',
'jsonld.ContextError', null, $e);
}
$ctx = $this->_resolveUrls($local_ctx, $options['resolver']);
// process context
return $this->_processContext($active_ctx, $ctx, $options);
@ -3085,75 +3137,115 @@ class JsonLdProcessor {
}
/**
* Resolves external @context URLs using the given URL resolver. Each instance
* of @context in the input that refers to a URL will be replaced with the
* JSON @context found at that URL.
* Finds all @context URLs in the given JSON-LD input.
*
* @param mixed $input the JSON-LD object with possible contexts.
* @param callable $resolver(url, callback(err, jsonCtx)) the URL resolver.
*
* @return mixed the result.
* @param mixed $input the JSON-LD input.
* @param stdClass $urls a map of URLs (url => false/@contexts).
* @param bool $replace true to replace the URLs in the given input with
* the @contexts from the urls map, false not to.
*/
protected function _resolveUrls($input, $resolver) {
// keeps track of resolved URLs (prevents duplicate work)
$urls = new stdClass();
// finds URLs in @context properties and replaces them with their
// resolved @contexts if replace is true
$findUrls = function($input, $replace) use (&$findUrls, $urls) {
protected function _findContextUrls($input, $urls, $replace) {
$count = count((array)$urls);
if(is_array($input)) {
$output = array();
foreach($input as $v) {
$output[] = $findUrls($v, $replace);
foreach($input as $e) {
$this->_findContextUrls($e, $urls, $replace);
}
return $output;
}
else if(is_object($input)) {
foreach($input as $k => $v) {
foreach($input as $k => &$v) {
if($k !== '@context') {
$input->{$k} = $findUrls($v, $replace);
$this->_findContextUrls($v, $urls, $replace);
continue;
}
// array @context
if(is_array($v)) {
foreach($v as $i => $url) {
if(is_string($url)) {
// replace w/resolved @context if requested
$length = count($v);
for($i = 0; $i < $length; ++$i) {
if(is_string($v[$i])) {
$url = $v[$i];
// replace w/@context if requested
if($replace) {
$v[$i] = $urls->{$url};
$ctx = $urls->{$url};
if(is_array($ctx)) {
// add flattened context
array_splice($v, $i, 1, $ctx);
$i += count($ctx);
$length += count($ctx);
}
// unresolved @context found
else {
$v[$i] = $ctx;
}
}
// @context URL found
else if(!property_exists($urls, $url)) {
$urls->{$url} = new stdClass();
$urls->{$url} = false;
}
}
}
}
// string @context
else if(is_string($v)) {
// replace w/resolved @context if requested
// replace w/@context if requested
if($replace) {
$input->{$key} = $urls->{$v};
$input->{$k} = $urls->{$v};
}
// unresolved @context found
// @context URL found
else if(!property_exists($urls, $v)) {
$urls->{$v} = new stdClass();
$urls->{$v} = false;
}
}
}
}
}
return $input;
};
$input = $findUrls($input, false);
// resolve all URLs
foreach($urls as $url => $v) {
/**
* Resolves external @context URLs using the given URL resolver. Each
* instance of @context in the input that refers to a URL will be replaced
* with the JSON @context found at that URL.
*
* @param mixed $input the JSON-LD input with possible contexts.
* @param stdClass $cycles an object for tracking context cycles.
* @param callable $resolver(url) the URL resolver.
*
* @return mixed the result.
*/
protected function _resolveContextUrls(&$input, $cycles, $resolver) {
if(count((array)$cycles) > self::MAX_CONTEXT_URLS) {
throw new JsonLdException(
'Maximum number of @context URLs exceeded.',
'jsonld.ContextUrlError', array('max' => self::MAX_CONTEXT_URLS));
}
// for tracking the URLs to resolve
$urls = new stdClass();
// find all URLs in the given input
$this->_findContextUrls($input, $urls, false);
// queue all unresolved URLs
$queue = array();
foreach($urls as $url => $ctx) {
if($ctx === false) {
// validate URL
if(filter_var($url, FILTER_VALIDATE_URL) === false) {
throw new JsonLdException(
'Malformed URL.', 'jsonld.InvalidUrl', array('url' => $url));
}
$queue[] = $url;
}
}
// resolve URLs in queue
foreach($queue as $url) {
// check for context URL cycle
if(property_exists($cycles, $url)) {
throw new JsonLdException(
'Cyclical @context URLs detected.',
'jsonld.ContextUrlError', array('url' => $url));
}
$_cycles = self::copy($cycles);
$_cycles->{$url} = true;
// resolve URL
$ctx = $resolver($url);
@ -3195,15 +3287,18 @@ class JsonLdProcessor {
'jsonld.InvalidUrl', array('url' => $url));
}
// FIXME: needs to recurse to resolve URLs in the result, and
// detect cycles, and limit recursion
if(property_exists($ctx, '@context')) {
$urls->{$url} = $ctx->{'@context'};
}
// use empty context if no @context key is present
if(!property_exists($ctx, '@context')) {
$ctx = (object)array('@context' => new stdClass());
}
// do url replacement
return $findUrls($input, true);
// recurse
$this->_resolveContextUrls($ctx, $_cycles, $resolver);
$urls->{$url} = $ctx->{'@context'};
}
// replace all URLS in the input
$this->_findContextUrls($input, $urls, true);
}
/**
@ -3634,10 +3729,10 @@ class JsonLdException extends Exception {
public function __toString() {
$rval = __CLASS__ . ": [{$this->type}]: {$this->message}\n";
if($this->details) {
$rval .= 'details: ' . print_r($this->details, true) . "\n";
$rval .= 'Details: ' . print_r($this->details, true) . "\n";
}
if($this->cause) {
$rval .= 'cause: ' . $this->cause;
$rval .= 'Cause: ' . $this->cause;
}
$rval .= $this->getTraceAsString() . "\n";
return $rval;