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83 lines
3.3 KiB
Java
83 lines
3.3 KiB
Java
// URLLicense.java
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// (C) 2007 by Michael Peter Christen; mc@yacy.net, Frankfurt a. M., Germany
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// first published 03.07.2007 on http://yacy.net
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//
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// This is a part of YaCy, a peer-to-peer based web search engine
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//
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// $LastChangedDate$
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// $LastChangedRevision$
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// $LastChangedBy$
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//
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// LICENSE
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//
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// This program is free software; you can redistribute it and/or modify
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// it under the terms of the GNU General Public License as published by
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// the Free Software Foundation; either version 2 of the License, or
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// (at your option) any later version.
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//
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// This program is distributed in the hope that it will be useful,
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// but WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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// GNU General Public License for more details.
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//
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// You should have received a copy of the GNU General Public License
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// along with this program; if not, write to the Free Software
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// Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
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package net.yacy.data;
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import java.util.Collections;
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import java.util.Map;
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import java.util.UUID;
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import net.yacy.cora.document.id.DigestURL;
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import net.yacy.cora.storage.SizeLimitedMap;
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/**
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* This class defines a license-generation for URLs.
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* It is used in case of preview-Image-fetching to grant also non-authorized users the usage of a image-fetcher servlet,
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* but to prevent them to use this servlet as a proxy.
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*/
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public class URLLicense {
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private static final int maxQueue = 10000;
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/** Map URLs by licence keys */
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private static final Map<String, String> permissions = Collections.synchronizedMap(new SizeLimitedMap<String, String>(maxQueue));
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/**
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* Generates and stores a unique licence key for delayed url data fetching.
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* @param url URL for whose data should be fectched later
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* @return licence key generated or null when url is null
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*/
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public static String aquireLicense(final DigestURL url) {
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if (url == null) return null;
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/* Generate license key : it must absolutely be a unique key, not related to url parameter (thus url.hash can not be used).
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* If the same key is generated for each call of this method with the same url parameter,
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* problem may occur concurrent non authorized users try to fetch same url content.
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* Example scenario (emulated in URLLicenseConcurrentTest) :
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* 1 - userA aquireLicence for url
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* 2 - userB aquireLicence for same url as A
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* 3 - userA releaseLicense : he can now fetch url content
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* 4 - userB releaseLicense : if the same license was generated, it has been already released and url content can not be fetched! */
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String license = UUID.randomUUID().toString();
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permissions.put(license, url.toNormalform(true));
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// return the license key
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return license;
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}
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/**
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* Use it to retrieve source url and to ensures YaCy url containing this licence code can not be reused by non-authorized users.
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* @param license unique code associated to source url
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* @return source url or null licence is no more valid
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* @throws NullPointerException when license is null
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*/
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public static String releaseLicense(final String license) {
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return permissions.remove(license);
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}
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}
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