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<?php
namespace MediaWiki\Rest;
use MediaWiki\Rest\HeaderParser\HttpDate;
use MediaWiki\Rest\HeaderParser\IfNoneMatch;
use RuntimeException;
use Wikimedia\Timestamp\ConvertibleTimestamp;
class ConditionalHeaderUtil {
/** @var bool */
private $varnishETagHack = true;
/** @var callback|string|null */
private $eTag;
/** @var callback|string|int|null */
private $lastModified;
/** @var callback|bool */
private $hasRepresentation;
private IfNoneMatch $eTagParser;
private ?array $eTagParts = null;
public function __construct() {
$this->eTagParser = new IfNoneMatch;
}
/**
* Initialize the object with information about the requested resource.
*
* @param callable|string|null $eTag The entity-tag (including quotes), or null if
* it is unknown. Can also be provided as a callback for later evaluation.
* @param callable|string|int|null $lastModified The Last-Modified date in a format
* accepted by ConvertibleTimestamp, or null if it is unknown.
* Can also be provided as a callback for later evaluation.
* @param callable|bool|null $hasRepresentation Whether the server can serve a
* representation of the target resource. This should be true if the
* resource exists, and false if it does not exist. It is used for
* wildcard validators -- the intended use case is to abort a PUT if the
* resource does (or does not) exist. If null is passed, we assume that
* the resource exists if an ETag or last-modified data was specified for it.
* Can also be provided as a callback for later evaluation.
*/
public function setValidators(
$eTag,
$lastModified,
$hasRepresentation = null
) {
$this->eTag = $eTag;
$this->lastModified = $lastModified;
$this->hasRepresentation = $hasRepresentation;
}
/**
* If the Varnish ETag hack is disabled by calling this method,
* strong ETag comparison will follow RFC 7232, rejecting all weak
* ETags for If-Match comparison.
*
* @param bool $hack
*/
public function setVarnishETagHack( $hack ) {
$this->varnishETagHack = $hack;
}
private function getETag(): ?string {
if ( is_callable( $this->eTag ) ) {
// resolve callback
$this->eTag = ( $this->eTag )();
}
return $this->eTag;
}
private function getETagParts(): ?array {
if ( $this->eTagParts !== null ) {
return $this->eTagParts;
}
$eTag = $this->getETag();
if ( $eTag === null ) {
return null;
}
$this->eTagParts = $this->eTagParser->parseETag( $eTag );
if ( !$this->eTagParts ) {
throw new RuntimeException( 'Invalid ETag returned by handler: `' .
$this->eTagParser->getLastError() . '`' );
}
return $this->eTagParts;
}
private function getLastModified(): ?int {
if ( is_callable( $this->lastModified ) ) {
// resolve callback
$this->lastModified = ( $this->lastModified )();
}
if ( is_string( $this->lastModified ) ) {
// normalize to int
$this->lastModified = (int)ConvertibleTimestamp::convert(
TS_UNIX,
$this->lastModified
);
}
// should be int or null now.
return $this->lastModified;
}
private function hasRepresentation(): bool {
if ( is_callable( $this->hasRepresentation ) ) {
// resolve callback
$this->hasRepresentation = ( $this->hasRepresentation )();
}
if ( $this->hasRepresentation === null ) {
// apply fallback
$this->hasRepresentation = $this->getETag() !== null
|| $this->getLastModified() !== null;
}
return $this->hasRepresentation;
}
/**
* Check conditional request headers in the order required by RFC 7232 section 6.
*
* @param RequestInterface $request
* @return int|null The status code to immediately return, or null to
* continue processing the request.
*/
public function checkPreconditions( RequestInterface $request ) {
$getOrHead = in_array( $request->getMethod(), [ 'GET', 'HEAD' ] );
if ( $request->hasHeader( 'If-Match' ) ) {
$im = $request->getHeader( 'If-Match' );
$match = false;
foreach ( $this->eTagParser->parseHeaderList( $im ) as $tag ) {
if ( ( $tag['whole'] === '*' && $this->hasRepresentation() ) ||
$this->strongCompare( $this->getETagParts(), $tag )
) {
$match = true;
break;
}
}
if ( !$match ) {
return 412;
}
} elseif ( $request->hasHeader( 'If-Unmodified-Since' ) ) {
$requestDate = HttpDate::parse( $request->getHeader( 'If-Unmodified-Since' )[0] );
$lastModified = $this->getLastModified();
if ( $requestDate !== null
&& ( $lastModified === null || $lastModified > $requestDate )
) {
return 412;
}
}
if ( $request->hasHeader( 'If-None-Match' ) ) {
$inm = $request->getHeader( 'If-None-Match' );
foreach ( $this->eTagParser->parseHeaderList( $inm ) as $tag ) {
if ( ( $tag['whole'] === '*' && $this->hasRepresentation() ) ||
$this->weakCompare( $this->getETagParts(), $tag )
) {
return $getOrHead ? 304 : 412;
}
}
} elseif ( $getOrHead && $request->hasHeader( 'If-Modified-Since' ) ) {
$requestDate = HttpDate::parse( $request->getHeader( 'If-Modified-Since' )[0] );
$lastModified = $this->getLastModified();
if ( $requestDate !== null && $lastModified !== null
&& $lastModified <= $requestDate
) {
return 304;
}
}
// RFC 7232 states that If-Range should be evaluated here. However, the
// purpose of If-Range is to cause the Range request header to be
// conditionally ignored, not to immediately send a response, so it
// doesn't fit here. RFC 7232 only requires that If-Range be checked
// after the other conditional header fields, a requirement that is
// satisfied if it is processed in Handler::execute().
return null;
}
/**
* Set Last-Modified and ETag headers in the response according to the cached
* values set by setValidators(), which are also used for precondition checks.
*
* If the headers are already present in the response, the existing headers
* take precedence.
*/
public function applyResponseHeaders( ResponseInterface $response ) {
if ( $response->getStatusCode() >= 400
|| $response->getStatusCode() === 301
|| $response->getStatusCode() === 307
) {
// Don't add Last-Modified and ETag for errors, including 412.
// Note that 304 responses are required to have these headers set.
// See IETF RFC 7232 section 4.
return;
}
$lastModified = $this->getLastModified();
if ( $lastModified !== null && !$response->hasHeader( 'Last-Modified' ) ) {
$response->setHeader( 'Last-Modified', HttpDate::format( $lastModified ) );
}
$eTag = $this->getETag();
if ( $eTag !== null && !$response->hasHeader( 'ETag' ) ) {
$response->setHeader( 'ETag', $eTag );
}
}
/**
* The weak comparison function, per RFC 7232, section 2.3.2.
*
* @param array|null $resourceETag ETag generated by the handler, parsed tag info array
* @param array|null $headerETag ETag supplied by the client, parsed tag info array
* @return bool
*/
private function weakCompare( $resourceETag, $headerETag ) {
if ( $resourceETag === null || $headerETag === null ) {
return false;
}
return $resourceETag['contents'] === $headerETag['contents'];
}
/**
* The strong comparison function
*
* A strong ETag returned by the server may have been "weakened" by Varnish when applying
* compression. So optionally ignore the weakness of the header.
* {@link https://varnish-cache.org/docs/6.0/users-guide/compression.html}.
* @see T238849 and T310710
*
* @param array|null $resourceETag ETag generated by the handler, parsed tag info array
* @param array|null $headerETag ETag supplied by the client, parsed tag info array
*
* @return bool
*/
private function strongCompare( $resourceETag, $headerETag ) {
if ( $resourceETag === null || $headerETag === null ) {
return false;
}
return !$resourceETag['weak']
&& ( $this->varnishETagHack || !$headerETag['weak'] )
&& $resourceETag['contents'] === $headerETag['contents'];
}
}