224 lines
8.5 KiB
Java
224 lines
8.5 KiB
Java
/**
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*
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* Copyright 2003-2005 Jive Software.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package org.jivesoftware.smack.util;
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import java.util.ArrayList;
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import java.util.Collections;
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import java.util.LinkedList;
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import java.util.List;
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import java.util.SortedMap;
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import java.util.TreeMap;
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import java.util.logging.Level;
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import java.util.logging.Logger;
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import org.jivesoftware.smack.util.dns.DNSResolver;
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import org.jivesoftware.smack.util.dns.HostAddress;
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import org.jivesoftware.smack.util.dns.SRVRecord;
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/**
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* Utility class to perform DNS lookups for XMPP services.
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*
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* @author Matt Tucker
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*/
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public class DNSUtil {
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private static final Logger LOGGER = Logger.getLogger(DNSUtil.class.getName());
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private static DNSResolver dnsResolver = null;
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/**
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* Set the DNS resolver that should be used to perform DNS lookups.
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*
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* @param resolver
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*/
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public static void setDNSResolver(DNSResolver resolver) {
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dnsResolver = resolver;
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}
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/**
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* Returns the current DNS resolved used to perform DNS lookups.
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*
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* @return the active DNSResolver
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*/
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public static DNSResolver getDNSResolver() {
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return dnsResolver;
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}
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/**
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* Returns a list of HostAddresses under which the specified XMPP server can be
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* reached at for client-to-server communication. A DNS lookup for a SRV
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* record in the form "_xmpp-client._tcp.example.com" is attempted, according
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* to section 14.4 of RFC 3920. If that lookup fails, a lookup in the older form
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* of "_jabber._tcp.example.com" is attempted since servers that implement an
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* older version of the protocol may be listed using that notation. If that
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* lookup fails as well, it's assumed that the XMPP server lives at the
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* host resolved by a DNS lookup at the specified domain on the default port
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* of 5222.<p>
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*
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* As an example, a lookup for "example.com" may return "im.example.com:5269".
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*
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* @param domain the domain.
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* @return List of HostAddress, which encompasses the hostname and port that the
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* XMPP server can be reached at for the specified domain.
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* @throws Exception
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*/
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public static List<HostAddress> resolveXMPPDomain(final String domain) throws Exception {
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if (dnsResolver == null) {
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List<HostAddress> addresses = new ArrayList<HostAddress>(1);
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addresses.add(new HostAddress(domain, 5222));
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return addresses;
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}
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return resolveDomain(domain, 'c');
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}
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/**
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* Returns a list of HostAddresses under which the specified XMPP server can be
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* reached at for server-to-server communication. A DNS lookup for a SRV
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* record in the form "_xmpp-server._tcp.example.com" is attempted, according
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* to section 14.4 of RFC 3920. If that lookup fails, a lookup in the older form
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* of "_jabber._tcp.example.com" is attempted since servers that implement an
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* older version of the protocol may be listed using that notation. If that
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* lookup fails as well, it's assumed that the XMPP server lives at the
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* host resolved by a DNS lookup at the specified domain on the default port
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* of 5269.<p>
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*
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* As an example, a lookup for "example.com" may return "im.example.com:5269".
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*
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* @param domain the domain.
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* @return List of HostAddress, which encompasses the hostname and port that the
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* XMPP server can be reached at for the specified domain.
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* @throws Exception
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*/
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public static List<HostAddress> resolveXMPPServerDomain(final String domain) throws Exception {
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if (dnsResolver == null) {
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List<HostAddress> addresses = new ArrayList<HostAddress>(1);
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addresses.add(new HostAddress(domain, 5269));
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return addresses;
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}
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return resolveDomain(domain, 's');
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}
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private static List<HostAddress> resolveDomain(String domain, char keyPrefix) throws Exception {
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List<HostAddress> addresses = new ArrayList<HostAddress>();
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// Step one: Do SRV lookups
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String srvDomain;
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if (keyPrefix == 's') {
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srvDomain = "_xmpp-server._tcp." + domain;
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} else if (keyPrefix == 'c') {
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srvDomain = "_xmpp-client._tcp." + domain;
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} else {
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srvDomain = domain;
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}
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List<SRVRecord> srvRecords = dnsResolver.lookupSRVRecords(srvDomain);
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if (LOGGER.isLoggable(Level.FINE)) {
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String logMessage = "Resolved SRV RR for " + srvDomain + ":";
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for (SRVRecord r : srvRecords)
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logMessage += " " + r;
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LOGGER.fine(logMessage);
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}
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List<HostAddress> sortedRecords = sortSRVRecords(srvRecords);
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addresses.addAll(sortedRecords);
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// Step two: Add the hostname to the end of the list
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addresses.add(new HostAddress(domain));
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return addresses;
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}
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/**
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* Sort a given list of SRVRecords as described in RFC 2782
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* Note that we follow the RFC with one exception. In a group of the same priority, only the first entry
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* is calculated by random. The others are ore simply ordered by their priority.
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*
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* @param records
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* @return the list of resolved HostAddresses
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*/
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private static List<HostAddress> sortSRVRecords(List<SRVRecord> records) {
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// RFC 2782, Usage rules: "If there is precisely one SRV RR, and its Target is "."
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// (the root domain), abort."
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if (records.size() == 1 && records.get(0).getFQDN().equals("."))
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return Collections.emptyList();
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// sorting the records improves the performance of the bisection later
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Collections.sort(records);
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// create the priority buckets
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SortedMap<Integer, List<SRVRecord>> buckets = new TreeMap<Integer, List<SRVRecord>>();
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for (SRVRecord r : records) {
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Integer priority = r.getPriority();
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List<SRVRecord> bucket = buckets.get(priority);
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// create the list of SRVRecords if it doesn't exist
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if (bucket == null) {
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bucket = new LinkedList<SRVRecord>();
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buckets.put(priority, bucket);
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}
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bucket.add(r);
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}
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List<HostAddress> res = new ArrayList<HostAddress>(records.size());
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for (Integer priority : buckets.keySet()) {
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List<SRVRecord> bucket = buckets.get(priority);
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int bucketSize;
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while ((bucketSize = bucket.size()) > 0) {
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int[] totals = new int[bucket.size()];
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int running_total = 0;
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int count = 0;
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int zeroWeight = 1;
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for (SRVRecord r : bucket) {
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if (r.getWeight() > 0)
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zeroWeight = 0;
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}
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for (SRVRecord r : bucket) {
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running_total += (r.getWeight() + zeroWeight);
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totals[count] = running_total;
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count++;
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}
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int selectedPos;
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if (running_total == 0) {
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// If running total is 0, then all weights in this priority
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// group are 0. So we simply select one of the weights randomly
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// as the other 'normal' algorithm is unable to handle this case
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selectedPos = (int) (Math.random() * bucketSize);
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} else {
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double rnd = Math.random() * running_total;
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selectedPos = bisect(totals, rnd);
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}
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// add the SRVRecord that was randomly chosen on it's weight
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// to the start of the result list
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SRVRecord chosenSRVRecord = bucket.remove(selectedPos);
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res.add(chosenSRVRecord);
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}
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}
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return res;
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}
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// TODO this is not yet really bisection just a stupid linear search
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private static int bisect(int[] array, double value) {
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int pos = 0;
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for (int element : array) {
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if (value < element)
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break;
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pos++;
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}
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return pos;
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}
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}
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