/*

 * Copyright (c) 2002, 2011, Oracle and/or its affiliates. All rights reserved.

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.  Oracle designates this

 * particular file as subject to the "Classpath" exception as provided

 * by Oracle in the LICENSE file that accompanied this code.

 *

 * This code is distributed in the hope that it will be useful, but WITHOUT

 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

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package com.sun.jndi.ldap;

import java.util.Arrays;

import java.util.Hashtable;

import java.util.Random;

import java.util.StringTokenizer;

import java.util.List;

import javax.naming.*;

import javax.naming.directory.*;

import javax.naming.spi.NamingManager;

import javax.naming.ldap.LdapName;

import javax.naming.ldap.Rdn;

/**

 * This class discovers the location of LDAP services by querying DNS.

 * See http://www.ietf.org/internet-drafts/draft-ietf-ldapext-locate-07.txt

 */

class ServiceLocator {

    private static final String SRV_RR = "SRV";

    private static final String[] SRV_RR_ATTR = new String[]{SRV_RR};

    private static final Random random = new Random();

    private ServiceLocator() {

    }

    /**

     * Maps a distinguished name (RFC 2253) to a fully qualified domain name.

     * Processes a sequence of RDNs having a DC attribute.

     * The special RDN "DC=." denotes the root of the domain tree.

     * Multi-valued RDNs, non-DC attributes, binary-valued attributes and the

     * RDN "DC=." all reset the domain name and processing continues.

     *

     * @param dn A string distinguished name (RFC 2253).

     * @return A domain name or null if none can be derived.

     */

    static String mapDnToDomainName(String dn) throws InvalidNameException {

        if (dn == null) {

            return null;

        }

        StringBuilder domain = new StringBuilder();

        LdapName ldapName = new LdapName(dn);

        // process RDNs left-to-right

        //List<Rdn> rdnList = ldapName.getRdns();

        List<Rdn> rdnList = ldapName.getRdns();

        for (int i = rdnList.size() - 1; i >= 0; i--) {

            //Rdn rdn = rdnList.get(i);

            Rdn rdn = rdnList.get(i);

            // single-valued RDN with a DC attribute

            if ((rdn.size() == 1) &&

                ("dc".equalsIgnoreCase(rdn.getType()) )) {

                Object attrval = rdn.getValue();

                if (attrval instanceof String) {

                    if (attrval.equals(".") ||

                        (domain.length() == 1 && domain.charAt(0) == '.')) {

                        domain.setLength(0); // reset (when current or previous

                                             //        RDN value is "DC=.")

                    }

                    if (domain.length() > 0) {

                        domain.append('.');

                    }

                    domain.append(attrval);

                } else {

                    domain.setLength(0); // reset (when binary-valued attribute)

                }

            } else {

                domain.setLength(0); // reset (when multi-valued RDN or non-DC)

            }

        }

        return (domain.length() != 0) ? domain.toString() : null;

    }

    /**

     * Locates the LDAP service for a given domain.

     * Queries DNS for a list of LDAP Service Location Records (SRV) for a

     * given domain name.

     *

     * @param domainName A string domain name.

     * @param environment The possibly null environment of the context.

     * @return An ordered list of hostports for the LDAP service or null if

     *         the service has not been located.

     */

    static String[] getLdapService(String domainName, Hashtable<?,?> environment) {

        if (domainName == null || domainName.length() == 0) {

            return null;

        }

        String dnsUrl = "dns:///_ldap._tcp." + domainName;

        String[] hostports = null;

        try {

            // Create the DNS context using NamingManager rather than using

            // the initial context constructor. This avoids having the initial

            // context constructor call itself (when processing the URL

            // argument in the getAttributes call).

            Context ctx = NamingManager.getURLContext("dns", environment);

            if (!(ctx instanceof DirContext)) {

                return null; // cannot create a DNS context

            }

            Attributes attrs =

                ((DirContext)ctx).getAttributes(dnsUrl, SRV_RR_ATTR);

            Attribute attr;

            if (attrs != null && ((attr = attrs.get(SRV_RR)) != null)) {

                int numValues = attr.size();

                int numRecords = 0;

                SrvRecord[] srvRecords = new SrvRecord[numValues];

                // create the service records

                int i = 0;

                int j = 0;

                while (i < numValues) {

                    try {

                        srvRecords[j] = new SrvRecord((String) attr.get(i));

                        j++;

                    } catch (Exception e) {

                        // ignore bad value

                    }

                    i++;

                }

                numRecords = j;

                // trim

                if (numRecords < numValues) {

                    SrvRecord[] trimmed = new SrvRecord[numRecords];

                    System.arraycopy(srvRecords, 0, trimmed, 0, numRecords);

                    srvRecords = trimmed;

                }

                // Sort the service records in ascending order of their

                // priority value. For records with equal priority, move

                // those with weight 0 to the top of the list.

                if (numRecords > 1) {

                    Arrays.sort(srvRecords);

                }

                // extract the host and port number from each service record

                hostports = extractHostports(srvRecords);

            }

        } catch (NamingException e) {

            // ignore

        }

        return hostports;

    }

    /**

     * Extract hosts and port numbers from a list of SRV records.

     * An array of hostports is returned or null if none were found.

     */

    private static String[] extractHostports(SrvRecord[] srvRecords) {

        String[] hostports = null;

        int head = 0;

        int tail = 0;

        int sublistLength = 0;

        int k = 0;

        for (int i = 0; i < srvRecords.length; i++) {

            if (hostports == null) {

                hostports = new String[srvRecords.length];

            }

            // find the head and tail of the list of records having the same

            // priority value.

            head = i;

            while (i < srvRecords.length - 1 &&

                srvRecords[i].priority == srvRecords[i + 1].priority) {

                i++;

            }

            tail = i;

            // select hostports from the sublist

            sublistLength = (tail - head) + 1;

            for (int j = 0; j < sublistLength; j++) {

                hostports[k++] = selectHostport(srvRecords, head, tail);

            }

        }

        return hostports;

    }

    /*

     * Randomly select a service record in the range [head, tail] and return

     * its hostport value. Follows the algorithm in RFC 2782.

     */

    private static String selectHostport(SrvRecord[] srvRecords, int head,

            int tail) {

        if (head == tail) {

            return srvRecords[head].hostport;

        }

        // compute the running sum for records between head and tail

        int sum = 0;

        for (int i = head; i <= tail; i++) {

            if (srvRecords[i] != null) {

                sum += srvRecords[i].weight;

                srvRecords[i].sum = sum;

            }

        }

        String hostport = null;

        // If all records have zero weight, select first available one;

        // otherwise, randomly select a record according to its weight

        int target = (sum == 0 ? 0 : random.nextInt(sum + 1));

        for (int i = head; i <= tail; i++) {

            if (srvRecords[i] != null && srvRecords[i].sum >= target) {

                hostport = srvRecords[i].hostport;

                srvRecords[i] = null; // make this record unavailable

                break;

            }

        }

        return hostport;

    }

/**

 * This class holds a DNS service (SRV) record.

 * See http://www.ietf.org/rfc/rfc2782.txt

 */

static class SrvRecord implements Comparable<SrvRecord> {

    int priority;

    int weight;

    int sum;

    String hostport;

    /**

     * Creates a service record object from a string record.

     * DNS supplies the string record in the following format:

     * <pre>

     *     <Priority> " " <Weight> " " <Port> " " <Host>

     * </pre>

     */

    SrvRecord(String srvRecord) throws Exception {

        StringTokenizer tokenizer = new StringTokenizer(srvRecord, " ");

        String port;

        if (tokenizer.countTokens() == 4) {

            priority = Integer.parseInt(tokenizer.nextToken());

            weight = Integer.parseInt(tokenizer.nextToken());

            port = tokenizer.nextToken();

            hostport = tokenizer.nextToken() + ":" + port;

        } else {

            throw new IllegalArgumentException();

        }

    }

    /*

     * Sort records in ascending order of priority value. For records with

     * equal priority move those with weight 0 to the top of the list.

     */

    public int compareTo(SrvRecord that) {

        if (priority > that.priority) {

            return 1; // this > that

        } else if (priority < that.priority) {

            return -1; // this < that

        } else if (weight == 0 && that.weight != 0) {

            return -1; // this < that

        } else if (weight != 0 && that.weight == 0) {

            return 1; // this > that

        } else {

            return 0; // this == that

        }

    }

}

}