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| 1 | <?php |
| 2 | |
| 3 | namespace Wikimedia\Purtle; |
| 4 | |
| 5 | use LogicException; |
| 6 | |
| 7 | /** |
| 8 | * RdfWriter implementation for generating JSON-LD output. |
| 9 | * |
| 10 | * @license GPL-2.0-or-later |
| 11 | * @author C. Scott Ananian |
| 12 | */ |
| 13 | class JsonLdRdfWriter extends RdfWriterBase { |
| 14 | |
| 15 | /** |
| 16 | * The JSON-LD "@context", which maps terms to IRIs. This is shared with all sub-writers, and a |
| 17 | * single context is emitted when the writer is finalized. |
| 18 | * |
| 19 | * @see https://www.w3.org/TR/json-ld/#the-context |
| 20 | * |
| 21 | * @var array[] |
| 22 | */ |
| 23 | protected $context = []; |
| 24 | |
| 25 | /** |
| 26 | * A set of predicates which rely on the default typing rules for |
| 27 | * JSON-LD; that is, values for the predicate have been emitted which |
| 28 | * would be broken if an explicit "@type" was added to the context |
| 29 | * for the predicate. |
| 30 | * |
| 31 | * @var bool[] |
| 32 | */ |
| 33 | protected $defaulted = []; |
| 34 | |
| 35 | /** |
| 36 | * The JSON-LD "@graph", which lists all the nodes described by this JSON-LD object. |
| 37 | * We apply an optimization eliminating the "@graph" entry if it consists |
| 38 | * of a single node; in that case we will set $this->graph to null in |
| 39 | * #finishJson() to ensure that the deferred callback in #finishDocument() |
| 40 | * doesn't later emit "@graph". |
| 41 | * |
| 42 | * @see https://www.w3.org/TR/json-ld/#named-graphs |
| 43 | * |
| 44 | * @var array|null |
| 45 | */ |
| 46 | private $graph = []; |
| 47 | |
| 48 | /** |
| 49 | * A collection of predicates about a specific subject. The |
| 50 | * subject is identified by the "@id" key in this array; the other |
| 51 | * keys identify JSON-LD properties. |
| 52 | * |
| 53 | * @see https://www.w3.org/TR/json-ld/#dfn-edge |
| 54 | * |
| 55 | * @var array |
| 56 | */ |
| 57 | private $predicates = []; |
| 58 | |
| 59 | /** |
| 60 | * A sequence of zero or more IRIs, nodes, or values, which are the |
| 61 | * destination targets of the current predicates. |
| 62 | * |
| 63 | * @see https://www.w3.org/TR/json-ld/#dfn-list |
| 64 | * |
| 65 | * @var array |
| 66 | */ |
| 67 | private $values = []; |
| 68 | |
| 69 | /** |
| 70 | * True iff we have written the opening of the "@graph" field. |
| 71 | * |
| 72 | * @var bool |
| 73 | */ |
| 74 | private $wroteGraph = false; |
| 75 | |
| 76 | /** |
| 77 | * JSON-LD objects describing a single node can omit the "@graph" field; |
| 78 | * this variable remains false only so long as we can guarantee that |
| 79 | * only a single node has been described. |
| 80 | * |
| 81 | * @var bool |
| 82 | */ |
| 83 | private $disableGraphOpt = false; |
| 84 | |
| 85 | /** |
| 86 | * The IRI for the RDF `type` property. |
| 87 | */ |
| 88 | private const RDF_TYPE_IRI = 'http://www.w3.org/1999/02/22-rdf-syntax-ns#type'; |
| 89 | |
| 90 | /** |
| 91 | * The type internally used for "default type", which is a string or |
| 92 | * otherwise default-coerced type. |
| 93 | */ |
| 94 | private const DEFAULT_TYPE = '@purtle@default@'; |
| 95 | |
| 96 | /** |
| 97 | * @param string $role |
| 98 | * @param BNodeLabeler|null $labeler |
| 99 | */ |
| 100 | public function __construct( $role = parent::DOCUMENT_ROLE, BNodeLabeler $labeler = null ) { |
| 101 | parent::__construct( $role, $labeler ); |
| 102 | |
| 103 | // The following named methods are protected, not private, so we |
| 104 | // can invoke them directly w/o function wrappers. |
| 105 | $this->transitionTable[self::STATE_START][self::STATE_DOCUMENT] = |
| 106 | [ $this, 'beginJson' ]; |
| 107 | $this->transitionTable[self::STATE_DOCUMENT][self::STATE_FINISH] = |
| 108 | [ $this, 'finishJson' ]; |
| 109 | $this->transitionTable[self::STATE_OBJECT][self::STATE_PREDICATE] = |
| 110 | [ $this, 'finishPredicate' ]; |
| 111 | $this->transitionTable[self::STATE_OBJECT][self::STATE_SUBJECT] = |
| 112 | [ $this, 'finishSubject' ]; |
| 113 | $this->transitionTable[self::STATE_OBJECT][self::STATE_DOCUMENT] = |
| 114 | [ $this, 'finishDocument' ]; |
| 115 | } |
| 116 | |
| 117 | /** |
| 118 | * Emit $val as JSON, with $indent extra indentations on each line. |
| 119 | * @param array $val |
| 120 | * @param int $indent |
| 121 | * @return string the JSON string for $val |
| 122 | */ |
| 123 | public function encode( $val, $indent ) { |
| 124 | $str = json_encode( $val, JSON_PRETTY_PRINT | JSON_UNESCAPED_SLASHES ); |
| 125 | // Strip outermost open/close braces/brackets |
| 126 | $str = preg_replace( '/^[[{]\n?|\n?[}\]]$/', '', $str ); |
| 127 | |
| 128 | if ( $indent > 0 ) { |
| 129 | // add extra indentation |
| 130 | $str = preg_replace( '/^/m', str_repeat( ' ', $indent ), $str ); |
| 131 | } |
| 132 | |
| 133 | return $str; |
| 134 | } |
| 135 | |
| 136 | /** |
| 137 | * Return a "compact IRI" corresponding to the given base/local pair. |
| 138 | * This adds entries to the "@context" key when needed to allow use |
| 139 | * of a given prefix. |
| 140 | * @see https://www.w3.org/TR/json-ld/#dfn-compact-iri |
| 141 | * |
| 142 | * @param string $base A QName prefix if $local is given, or an IRI if $local is null. |
| 143 | * @param string|null $local A QName suffix, or null if $base is an IRI. |
| 144 | * |
| 145 | * @return string A compact IRI. |
| 146 | */ |
| 147 | private function compactify( $base, $local = null ) { |
| 148 | $this->expandShorthand( $base, $local ); |
| 149 | |
| 150 | if ( $local === null ) { |
| 151 | return $base; |
| 152 | } else { |
| 153 | if ( $base !== '_' && isset( $this->prefixes[ $base ] ) ) { |
| 154 | if ( $base === '' ) { |
| 155 | // Empty prefix not supported; use full IRI |
| 156 | return $this->prefixes[ $base ] . $local; |
| 157 | } |
| 158 | if ( !isset( $this->context[ $base ] ) ) { |
| 159 | $this->context[ $base ] = $this->prefixes[ $base ]; |
| 160 | } |
| 161 | if ( $this->context[ $base ] !== $this->prefixes[ $base ] ) { |
| 162 | // Context name conflict; use full IRI |
| 163 | return $this->prefixes[ $base ] . $local; |
| 164 | } |
| 165 | } |
| 166 | return $base . ':' . $local; |
| 167 | } |
| 168 | } |
| 169 | |
| 170 | /** |
| 171 | * Return an absolute IRI from the given base/local pair. |
| 172 | * @see https://www.w3.org/TR/json-ld/#dfn-absolute-iri |
| 173 | * |
| 174 | * @param string $base A QName prefix if $local is given, or an IRI if $local is null. |
| 175 | * @param string|null $local A QName suffix, or null if $base is an IRI. |
| 176 | * |
| 177 | * @return string|null An absolute IRI, or null if it cannot be constructed. |
| 178 | */ |
| 179 | private function toIRI( $base, $local ) { |
| 180 | $this->expandShorthand( $base, $local ); |
| 181 | $this->expandQName( $base, $local ); |
| 182 | if ( $local !== null ) { |
| 183 | throw new LogicException( 'Unknown prefix: ' . $base ); |
| 184 | } |
| 185 | return $base; |
| 186 | } |
| 187 | |
| 188 | /** |
| 189 | * Return a appropriate term for the current predicate value. |
| 190 | * |
| 191 | * @return string |
| 192 | */ |
| 193 | private function getCurrentTerm() { |
| 194 | [ $base, $local ] = $this->currentPredicate; |
| 195 | $predIRI = $this->toIRI( $base, $local ); |
| 196 | if ( $predIRI === self::RDF_TYPE_IRI ) { |
| 197 | return $predIRI; |
| 198 | } |
| 199 | $this->expandShorthand( $base, $local ); |
| 200 | if ( $local === null ) { |
| 201 | return $base; |
| 202 | } elseif ( $base !== '_' && !isset( $this->prefixes[ $local ] ) ) { |
| 203 | // Prefixes get priority over field names in @context |
| 204 | $pred = $this->compactify( $base, $local ); |
| 205 | if ( !isset( $this->context[ $local ] ) ) { |
| 206 | $this->context[ $local ] = [ '@id' => $pred ]; |
| 207 | } |
| 208 | if ( $this->context[ $local ][ '@id' ] === $pred ) { |
| 209 | return $local; |
| 210 | } |
| 211 | return $pred; |
| 212 | } |
| 213 | return $this->compactify( $base, $local ); |
| 214 | } |
| 215 | |
| 216 | /** |
| 217 | * Write document header. |
| 218 | */ |
| 219 | protected function beginJson() { |
| 220 | if ( $this->role === self::DOCUMENT_ROLE ) { |
| 221 | $this->write( "{\n" ); |
| 222 | $this->write( function () { |
| 223 | // If this buffer is drained early, disable @graph optimization |
| 224 | $this->disableGraphOpt = true; |
| 225 | return ''; |
| 226 | } ); |
| 227 | } |
| 228 | } |
| 229 | |
| 230 | /** |
| 231 | * Write document footer. |
| 232 | */ |
| 233 | protected function finishJson() { |
| 234 | // If we haven't drained yet, and @graph has only 1 element, then we |
| 235 | // can optimize our output and hoist the single node to top level. |
| 236 | if ( $this->role === self::DOCUMENT_ROLE ) { |
| 237 | if ( ( !$this->disableGraphOpt ) && count( $this->graph ) === 1 ) { |
| 238 | $this->write( $this->encode( $this->graph[0], 0 ) ); |
| 239 | $this->graph = null; // We're done with @graph. |
| 240 | } else { |
| 241 | $this->disableGraphOpt = true; |
| 242 | $this->write( "\n ]" ); |
| 243 | } |
| 244 | } |
| 245 | |
| 246 | if ( count( $this->context ) ) { |
| 247 | // Write @context field. |
| 248 | $this->write( ",\n" ); |
| 249 | $this->write( $this->encode( [ |
| 250 | '@context' => $this->context |
| 251 | ], 0 ) ); |
| 252 | } |
| 253 | |
| 254 | $this->write( "\n}" ); |
| 255 | } |
| 256 | |
| 257 | protected function finishDocument() { |
| 258 | $this->finishSubject(); |
| 259 | $this->write( function () { |
| 260 | // if this is drained before finishJson(), then disable |
| 261 | // the graph optimization and dump what we've got so far. |
| 262 | $str = ''; |
| 263 | if ( $this->graph !== null && count( $this->graph ) > 0 ) { |
| 264 | $this->disableGraphOpt = true; |
| 265 | if ( $this->role === self::DOCUMENT_ROLE && !$this->wroteGraph ) { |
| 266 | $str .= " \"@graph\": [\n"; |
| 267 | $this->wroteGraph = true; |
| 268 | } else { |
| 269 | $str .= ",\n"; |
| 270 | } |
| 271 | $str .= $this->encode( $this->graph, 1 ); |
| 272 | $this->graph = []; |
| 273 | return $str; |
| 274 | } |
| 275 | // Delay; maybe we'll be able to optimize this later. |
| 276 | return $str; |
| 277 | } ); |
| 278 | } |
| 279 | |
| 280 | /** |
| 281 | * @param string $base |
| 282 | * @param string|null $local |
| 283 | */ |
| 284 | protected function writeSubject( $base, $local = null ) { |
| 285 | $this->predicates = [ |
| 286 | '@id' => $this->compactify( $base, $local ) |
| 287 | ]; |
| 288 | } |
| 289 | |
| 290 | protected function finishSubject() { |
| 291 | $this->finishPredicate(); |
| 292 | $this->graph[] = $this->predicates; |
| 293 | } |
| 294 | |
| 295 | /** |
| 296 | * @param string $base |
| 297 | * @param string|null $local |
| 298 | */ |
| 299 | protected function writePredicate( $base, $local = null ) { |
| 300 | // no op |
| 301 | } |
| 302 | |
| 303 | /** |
| 304 | * @param string $base |
| 305 | * @param string|null $local |
| 306 | */ |
| 307 | protected function writeResource( $base, $local = null ) { |
| 308 | $pred = $this->getCurrentTerm(); |
| 309 | $value = $this->compactify( $base, $local ); |
| 310 | $this->addTypedValue( '@id', $value, [ |
| 311 | '@id' => $value |
| 312 | ], ( $pred === self::RDF_TYPE_IRI ) ); |
| 313 | } |
| 314 | |
| 315 | /** |
| 316 | * @param string $text |
| 317 | * @param string|null $language |
| 318 | */ |
| 319 | protected function writeText( $text, $language = null ) { |
| 320 | if ( !$this->isValidLanguageCode( $language ) ) { |
| 321 | $this->addTypedValue( self::DEFAULT_TYPE, $text ); |
| 322 | } else { |
| 323 | $expanded = [ |
| 324 | '@language' => $language, |
| 325 | '@value' => $text |
| 326 | ]; |
| 327 | $this->addTypedValue( self::DEFAULT_TYPE, $expanded, $expanded ); |
| 328 | } |
| 329 | } |
| 330 | |
| 331 | /** |
| 332 | * @param string $literal |
| 333 | * @param string|null $typeBase |
| 334 | * @param string|null $typeLocal |
| 335 | */ |
| 336 | public function writeValue( $literal, $typeBase, $typeLocal = null ) { |
| 337 | if ( $typeBase === null && $typeLocal === null ) { |
| 338 | $this->addTypedValue( self::DEFAULT_TYPE, $literal ); |
| 339 | return; |
| 340 | } |
| 341 | |
| 342 | switch ( $this->toIRI( $typeBase, $typeLocal ) ) { |
| 343 | case 'http://www.w3.org/2001/XMLSchema#string': |
| 344 | $this->addTypedValue( self::DEFAULT_TYPE, strval( $literal ) ); |
| 345 | return; |
| 346 | case 'http://www.w3.org/2001/XMLSchema#integer': |
| 347 | $this->addTypedValue( self::DEFAULT_TYPE, intval( $literal ) ); |
| 348 | return; |
| 349 | case 'http://www.w3.org/2001/XMLSchema#boolean': |
| 350 | $this->addTypedValue( self::DEFAULT_TYPE, ( $literal === 'true' ) ); |
| 351 | return; |
| 352 | case 'http://www.w3.org/2001/XMLSchema#double': |
| 353 | $v = floatval( $literal ); |
| 354 | // Only "numbers with fractions" are xsd:double. We need |
| 355 | // to verify that the JSON string will contain a decimal |
| 356 | // point, otherwise the value would be interpreted as an |
| 357 | // xsd:integer. |
| 358 | // TODO: consider instead using JSON_PRESERVE_ZERO_FRACTION |
| 359 | // in $this->encode() once our required PHP >= 5.6.6. |
| 360 | // OTOH, the spec language is ambiguous about whether "5." |
| 361 | // would be considered an integer or a double. |
| 362 | if ( strpos( json_encode( $v ), '.' ) !== false ) { |
| 363 | $this->addTypedValue( self::DEFAULT_TYPE, $v ); |
| 364 | return; |
| 365 | } |
| 366 | } |
| 367 | |
| 368 | $type = $this->compactify( $typeBase, $typeLocal ); |
| 369 | $literal = strval( $literal ); |
| 370 | $this->addTypedValue( $type, $literal, [ |
| 371 | '@type' => $type, |
| 372 | '@value' => $literal |
| 373 | ] ); |
| 374 | } |
| 375 | |
| 376 | /** |
| 377 | * Add a typed value for the given predicate. If possible, adds a |
| 378 | * default type to the context to avoid having to repeat type information |
| 379 | * in each value for this predicate. If there is already a default |
| 380 | * type which conflicts with this one, or if $forceExpand is true, |
| 381 | * then use the "expanded" value which will explicitly override any |
| 382 | * default type. |
| 383 | * |
| 384 | * @param string $type The compactified JSON-LD @type for this value, or |
| 385 | * self::DEFAULT_TYPE to indicate the default JSON-LD type coercion rules |
| 386 | * should be used. |
| 387 | * @param string|int|float|bool $simpleVal The "simple" representation |
| 388 | * for this value, used if the type can be hoisted into the context. |
| 389 | * @param array|null $expandedVal The "expanded" representation for this |
| 390 | * value, used if the context @type conflicts with this value; or null |
| 391 | * to use "@value" for the expanded representation. |
| 392 | * @param bool $forceExpand If true, don't try to add this type to the |
| 393 | * context. Defaults to false. |
| 394 | */ |
| 395 | protected function addTypedValue( $type, $simpleVal, $expandedVal = null, $forceExpand = false ) { |
| 396 | if ( !$forceExpand ) { |
| 397 | $pred = $this->getCurrentTerm(); |
| 398 | if ( $type === self::DEFAULT_TYPE ) { |
| 399 | if ( !isset( $this->context[ $pred ][ '@type' ] ) ) { |
| 400 | $this->defaulted[ $pred ] = true; |
| 401 | } |
| 402 | if ( isset( $this->defaulted[ $pred ] ) ) { |
| 403 | $this->values[] = $simpleVal; |
| 404 | return; |
| 405 | } |
| 406 | } elseif ( !isset( $this->defaulted[ $pred ] ) ) { |
| 407 | if ( !isset( $this->context[ $pred ] ) ) { |
| 408 | $this->context[ $pred ] = []; |
| 409 | } |
| 410 | if ( !isset( $this->context[ $pred ][ '@type' ] ) ) { |
| 411 | $this->context[ $pred ][ '@type' ] = $type; |
| 412 | } |
| 413 | if ( $this->context[ $pred ][ '@type' ] === $type ) { |
| 414 | $this->values[] = $simpleVal; |
| 415 | return; |
| 416 | } |
| 417 | } |
| 418 | } |
| 419 | if ( $expandedVal === null ) { |
| 420 | $this->values[] = [ '@value' => $simpleVal ]; |
| 421 | } else { |
| 422 | $this->values[] = $expandedVal; |
| 423 | } |
| 424 | } |
| 425 | |
| 426 | protected function finishPredicate() { |
| 427 | $name = $this->getCurrentTerm(); |
| 428 | |
| 429 | if ( $name === self::RDF_TYPE_IRI ) { |
| 430 | $name = '@type'; |
| 431 | $this->values = array_map( static function ( array $val ) { |
| 432 | return $val[ '@id' ]; |
| 433 | }, $this->values ); |
| 434 | } |
| 435 | if ( isset( $this->predicates[$name] ) ) { |
| 436 | $was = $this->predicates[$name]; |
| 437 | // Wrap $was into a numeric indexed array if it isn't already. |
| 438 | // Note that $was could have non-numeric indices, eg |
| 439 | // [ "@id" => "foo" ], in which was it still needs to be wrapped. |
| 440 | if ( !( is_array( $was ) && isset( $was[0] ) ) ) { |
| 441 | $was = [ $was ]; |
| 442 | } |
| 443 | $this->values = array_merge( $was, $this->values ); |
| 444 | } |
| 445 | |
| 446 | $cnt = count( $this->values ); |
| 447 | if ( $cnt === 0 ) { |
| 448 | throw new LogicException( 'finishPredicate can\'t be called without at least one value' ); |
| 449 | } elseif ( $cnt === 1 ) { |
| 450 | $this->predicates[$name] = $this->values[0]; |
| 451 | } else { |
| 452 | $this->predicates[$name] = $this->values; |
| 453 | } |
| 454 | |
| 455 | $this->values = []; |
| 456 | } |
| 457 | |
| 458 | /** |
| 459 | * @param string $role |
| 460 | * @param BNodeLabeler $labeler |
| 461 | * |
| 462 | * @return RdfWriterBase |
| 463 | */ |
| 464 | protected function newSubWriter( $role, BNodeLabeler $labeler ) { |
| 465 | $writer = new self( $role, $labeler ); |
| 466 | |
| 467 | // Have subwriter share context with this parent. |
| 468 | $writer->context = &$this->context; |
| 469 | $writer->defaulted = &$this->defaulted; |
| 470 | |
| 471 | // We can't use the @graph optimization. |
| 472 | $this->disableGraphOpt = true; |
| 473 | |
| 474 | return $writer; |
| 475 | } |
| 476 | |
| 477 | /** |
| 478 | * @return string a MIME type |
| 479 | */ |
| 480 | public function getMimeType() { |
| 481 | return 'application/ld+json; charset=UTF-8'; |
| 482 | } |
| 483 | |
| 484 | } |