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 * Copyright (c) 2000, 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,
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 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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package com.sun.jndi.dns;


import java.util.ArrayList;
import java.util.Comparator;
import java.util.Enumeration;

import javax.naming.*;


DnsName implements compound names for DNS as specified by RFCs 1034 and 1035, and as updated and clarified by RFCs 1123 and 2181. 
 The labels in a domain name correspond to JNDI atomic names.
Each label must be less than 64 octets in length, and only the
optional root label at the end of the name may be 0 octets long.
The sum of the lengths of all labels in a name, plus the number of
non-root labels plus 1, must be less than 256.  The textual
representation of a domain name consists of the labels, escaped as
needed, dot-separated, and ordered right-to-left.
 A label consists of a sequence of octets, each of which may
have any value from 0 to 255.
 Host names are a subset of domain names.
Their labels contain only ASCII letters, digits, and hyphens, and
none may begin or end with a hyphen.  While names not conforming to
these rules may be valid domain names, they will not be usable by a
number of DNS applications, and should in most cases be avoided.
 DNS does not specify an encoding (such as UTF-8) to use for octets with non-ASCII values. As of this writing there is some work going on in this area, but it is not yet finalized. DnsName currently converts any non-ASCII octets into characters using ISO-LATIN-1 encoding, in effect taking the value of each octet and storing it directly into the low-order byte of a Java character and vice versa.  As a consequence, no
character in a DNS name will ever have a non-zero high-order byte.
When the work on internationalizing domain names has stabilized
(see for example draft-ietf-idn-idna-10.txt), DnsName may be updated to conform to that work. 
 Backslash (\) is used as the escape character in the textual representation of a domain name. The character sequence `\DDD', where DDD is a 3-digit decimal number (with leading zeros if needed), represents the octet whose value is DDD. The character sequence `\C', where C is a character other than '0' through '9', represents the octet whose value is that of C (again using ISO-LATIN-1 encoding); this is particularly useful for escaping '.' or backslash itself. Backslash is otherwise not allowed in a domain name. Note that escape characters are interpreted when a name is parsed. So, for example, the character sequences `S', `\S', and `\083' each represent the same one-octet name. The toString() method does not generally insert escape sequences except where necessary. If, however, the DnsName was constructed using unneeded escapes, those escapes may appear in the toString result. 
 Atomic names passed as parameters to methods of DnsName, and those returned by them, are unescaped. So, for example, (new DnsName()).add("a.b") creates an object representing the one-label domain name a\.b, and calling get(0) on this object returns "a.b". 
 While DNS names are case-preserving, comparisons between them are case-insensitive. When comparing names containing non-ASCII octets, DnsName uses case-insensitive comparison between pairs of ASCII values, and exact binary comparison otherwise. 
 A DnsName instance is not synchronized against concurrent access by multiple threads. 
Author:
Scott Seligman/**
 * {@code DnsName} implements compound names for DNS as specified by
 * RFCs 1034 and 1035, and as updated and clarified by RFCs 1123 and 2181.
 *
 * <p> The labels in a domain name correspond to JNDI atomic names.
 * Each label must be less than 64 octets in length, and only the
 * optional root label at the end of the name may be 0 octets long.
 * The sum of the lengths of all labels in a name, plus the number of
 * non-root labels plus 1, must be less than 256.  The textual
 * representation of a domain name consists of the labels, escaped as
 * needed, dot-separated, and ordered right-to-left.
 *
 * <p> A label consists of a sequence of octets, each of which may
 * have any value from 0 to 255.
 *
 * <p> <em>Host names</em> are a subset of domain names.
 * Their labels contain only ASCII letters, digits, and hyphens, and
 * none may begin or end with a hyphen.  While names not conforming to
 * these rules may be valid domain names, they will not be usable by a
 * number of DNS applications, and should in most cases be avoided.
 *
 * <p> DNS does not specify an encoding (such as UTF-8) to use for
 * octets with non-ASCII values.  As of this writing there is some
 * work going on in this area, but it is not yet finalized.
 * {@code DnsName} currently converts any non-ASCII octets into
 * characters using ISO-LATIN-1 encoding, in effect taking the
 * value of each octet and storing it directly into the low-order byte
 * of a Java character and <i>vice versa</i>.  As a consequence, no
 * character in a DNS name will ever have a non-zero high-order byte.
 * When the work on internationalizing domain names has stabilized
 * (see for example <i>draft-ietf-idn-idna-10.txt</i>), {@code DnsName}
 * may be updated to conform to that work.
 *
 * <p> Backslash ({@code \}) is used as the escape character in the
 * textual representation of a domain name.  The character sequence
 * `{@code \DDD}', where {@code DDD} is a 3-digit decimal number
 * (with leading zeros if needed), represents the octet whose value
 * is {@code DDD}.  The character sequence `{@code \C}', where
 * {@code C} is a character other than {@code '0'} through
 * {@code '9'}, represents the octet whose value is that of
 * {@code C} (again using ISO-LATIN-1 encoding); this is particularly
 * useful for escaping {@code '.'} or backslash itself.  Backslash is
 * otherwise not allowed in a domain name.  Note that escape characters
 * are interpreted when a name is parsed.  So, for example, the character
 * sequences `{@code S}', `{@code \S}', and `{@code \083}' each
 * represent the same one-octet name.  The {@code toString()} method
 * does not generally insert escape sequences except where necessary.
 * If, however, the {@code DnsName} was constructed using unneeded
 * escapes, those escapes may appear in the {@code toString} result.
 *
 * <p> Atomic names passed as parameters to methods of
 * {@code DnsName}, and those returned by them, are unescaped.  So,
 * for example, <code>(new&nbsp;DnsName()).add("a.b")</code> creates an
 * object representing the one-label domain name {@code a\.b}, and
 * calling {@code get(0)} on this object returns {@code "a.b"}.
 *
 * <p> While DNS names are case-preserving, comparisons between them
 * are case-insensitive.  When comparing names containing non-ASCII
 * octets, {@code DnsName} uses case-insensitive comparison
 * between pairs of ASCII values, and exact binary comparison
 * otherwise.

 * <p> A {@code DnsName} instance is not synchronized against
 * concurrent access by multiple threads.
 *
 * @author Scott Seligman
 */


public final class DnsName implements Name {

    // If non-null, the domain name represented by this DnsName.
    private String domain = "";

    // The labels of this domain name, as a list of strings.  Index 0
    // corresponds to the leftmost (least significant) label:  note that
    // this is the reverse of the ordering used by the Name interface.
    private ArrayList<String> labels = new ArrayList<>();

    // The number of octets needed to carry this domain name in a DNS
    // packet.  Equal to the sum of the lengths of each label, plus the
    // number of non-root labels, plus 1.  Must remain less than 256.
    private short octets = 1;


    
Constructs a DnsName representing the empty domain name. /**
     * Constructs a {@code DnsName} representing the empty domain name.
     */
    public DnsName() {
    }

    
Constructs a DnsName representing a given domain name. 
Params:
name –    the domain name to parse
Throws:
InvalidNameException – if name does not conform to DNS syntax./**
     * Constructs a {@code DnsName} representing a given domain name.
     *
     * @param   name    the domain name to parse
     * @throws InvalidNameException if {@code name} does not conform
     *          to DNS syntax.
     */
    public DnsName(String name) throws InvalidNameException {
        parse(name);
    }

    /*
     * Returns a new DnsName with its name components initialized to
     * the components of "n" in the range [beg,end).  Indexing is as
     * for the Name interface, with 0 being the most significant.
     */
    private DnsName(DnsName n, int beg, int end) {
        // Compute indexes into "labels", which has least-significant label
        // at index 0 (opposite to the convention used for "beg" and "end").
        int b = n.size() - end;
        int e = n.size() - beg;
        labels.addAll(n.labels.subList(b, e));

        if (size() == n.size()) {
            domain = n.domain;
            octets = n.octets;
        } else {
            for (String label: labels) {
                if (label.length() > 0) {
                    octets += (short) (label.length() + 1);
                }
            }
        }
    }


    public String toString() {
        if (domain == null) {
            StringBuilder buf = new StringBuilder();
            for (String label: labels) {
                if (buf.length() > 0 || label.length() == 0) {
                    buf.append('.');
                }
                escape(buf, label);
            }
            domain = buf.toString();
        }
        return domain;
    }

    
Does this domain name follow host name syntax?
/**
     * Does this domain name follow <em>host name</em> syntax?
     */
    public boolean isHostName() {
        for (String label: labels) {
            if (!isHostNameLabel(label)) {
                return false;
            }
        }
        return true;
    }

    public short getOctets() {
        return octets;
    }

    public int size() {
        return labels.size();
    }

    public boolean isEmpty() {
        return (size() == 0);
    }

    public int hashCode() {
        int h = 0;
        for (int i = 0; i < size(); i++) {
            h = 31 * h + getKey(i).hashCode();
        }
        return h;
    }

    public boolean equals(Object obj) {
        if (!(obj instanceof Name) || (obj instanceof CompositeName)) {
            return false;
        }
        Name n = (Name) obj;
        return ((size() == n.size()) &&         // shortcut:  do sizes differ?
                (compareTo(obj) == 0));
    }

    public int compareTo(Object obj) {
        Name n = (Name) obj;
        return compareRange(0, size(), n);      // never 0 if sizes differ
    }

    public boolean startsWith(Name n) {
        return ((size() >= n.size()) &&
                (compareRange(0, n.size(), n) == 0));
    }

    public boolean endsWith(Name n) {
        return ((size() >= n.size()) &&
                (compareRange(size() - n.size(), size(), n) == 0));
    }

    public String get(int pos) {
        if (pos < 0 || pos >= size()) {
            throw new ArrayIndexOutOfBoundsException();
        }
        int i = size() - pos - 1;       // index of "pos" component in "labels"
        return labels.get(i);
    }

    public Enumeration<String> getAll() {
        return new Enumeration<String>() {
            int pos = 0;
            public boolean hasMoreElements() {
                return (pos < size());
            }
            public String nextElement() {
                if (pos < size()) {
                    return get(pos++);
                }
                throw new java.util.NoSuchElementException();
            }
        };
    }

    public Name getPrefix(int pos) {
        return new DnsName(this, 0, pos);
    }

    public Name getSuffix(int pos) {
        return new DnsName(this, pos, size());
    }

    public Object clone() {
        return new DnsName(this, 0, size());
    }

    public Object remove(int pos) {
        if (pos < 0 || pos >= size()) {
            throw new ArrayIndexOutOfBoundsException();
        }
        int i = size() - pos - 1;     // index of element to remove in "labels"
        String label = labels.remove(i);
        int len = label.length();
        if (len > 0) {
            octets -= (short) (len + 1);
        }
        domain = null;          // invalidate "domain"
        return label;
    }

    public Name add(String comp) throws InvalidNameException {
        return add(size(), comp);
    }

    public Name add(int pos, String comp) throws InvalidNameException {
        if (pos < 0 || pos > size()) {
            throw new ArrayIndexOutOfBoundsException();
        }
        // Check for empty labels:  may have only one, and only at end.
        int len = comp.length();
        if ((pos > 0 && len == 0) ||
            (pos == 0 && hasRootLabel())) {
                throw new InvalidNameException(
                        "Empty label must be the last label in a domain name");
        }
        // Check total name length.
        if (len > 0) {
            if (octets + len + 1 >= 256) {
                throw new InvalidNameException("Name too long");
            }
            octets += (short) (len + 1);
        }

        int i = size() - pos;   // index for insertion into "labels"
        verifyLabel(comp);
        labels.add(i, comp);

        domain = null;          // invalidate "domain"
        return this;
    }

    public Name addAll(Name suffix) throws InvalidNameException {
        return addAll(size(), suffix);
    }

    public Name addAll(int pos, Name n) throws InvalidNameException {
        if (n instanceof DnsName) {
            // "n" is a DnsName so we can insert it as a whole, rather than
            // verifying and inserting it component-by-component.
            // More code, but less work.
            DnsName dn = (DnsName) n;

            if (dn.isEmpty()) {
                return this;
            }
            // Check for empty labels:  may have only one, and only at end.
            if ((pos > 0 && dn.hasRootLabel()) ||
                (pos == 0 && hasRootLabel())) {
                    throw new InvalidNameException(
                        "Empty label must be the last label in a domain name");
            }

            short newOctets = (short) (octets + dn.octets - 1);
            if (newOctets > 255) {
                throw new InvalidNameException("Name too long");
            }
            octets = newOctets;
            int i = size() - pos;       // index for insertion into "labels"
            labels.addAll(i, dn.labels);

            // Preserve "domain" if we're appending or prepending,
            // otherwise invalidate it.
            if (isEmpty()) {
                domain = dn.domain;
            } else if (domain == null || dn.domain == null) {
                domain = null;
            } else if (pos == 0) {
                domain += (dn.domain.equals(".") ? "" : ".") + dn.domain;
            } else if (pos == size()) {
                domain = dn.domain + (domain.equals(".") ? "" : ".") + domain;
            } else {
                domain = null;
            }

        } else if (n instanceof CompositeName) {
            n = (DnsName) n;            // force ClassCastException

        } else {                // "n" is a compound name, but not a DnsName.
            // Add labels least-significant first:  sometimes more efficient.
            for (int i = n.size() - 1; i >= 0; i--) {
                add(pos, n.get(i));
            }
        }
        return this;
    }


    boolean hasRootLabel() {
        return (!isEmpty() &&
                get(0).equals(""));
    }

    /*
     * Helper method for public comparison methods.  Lexicographically
     * compares components of this name in the range [beg,end) with
     * all components of "n".  Indexing is as for the Name interface,
     * with 0 being the most significant.  Returns negative, zero, or
     * positive as these name components are less than, equal to, or
     * greater than those of "n".
     */
    private int compareRange(int beg, int end, Name n) {
        if (n instanceof CompositeName) {
            n = (DnsName) n;                    // force ClassCastException
        }
        // Loop through labels, starting with most significant.
        int minSize = Math.min(end - beg, n.size());
        for (int i = 0; i < minSize; i++) {
            String label1 = get(i + beg);
            String label2 = n.get(i);

            int j = size() - (i + beg) - 1;     // index of label1 in "labels"
            // assert (label1 == labels.get(j));

            int c = compareLabels(label1, label2);
            if (c != 0) {
                return c;
            }
        }
        return ((end - beg) - n.size());        // longer range wins
    }

    /*
     * Returns a key suitable for hashing the label at index i.
     * Indexing is as for the Name interface, with 0 being the most
     * significant.
     */
    String getKey(int i) {
        return keyForLabel(get(i));
    }


    /*
     * Parses a domain name, setting the values of instance vars accordingly.
     */
    private void parse(String name) throws InvalidNameException {

        StringBuilder label = new StringBuilder();      // label being parsed

        for (int i = 0; i < name.length(); i++) {
            char c = name.charAt(i);

            if (c == '\\') {                    // found an escape sequence
                c = getEscapedOctet(name, i++);
                if (isDigit(name.charAt(i))) {  // sequence is \DDD
                    i += 2;                     // consume remaining digits
                }
                label.append(c);

            } else if (c != '.') {              // an unescaped octet
                label.append(c);

            } else {                            // found '.' separator
                add(0, label.toString());       // check syntax, then add label
                                                //   to end of name
                label.delete(0, i);             // clear buffer for next label
            }
        }

        // If name is neither "." nor "", the octets (zero or more)
        // from the rightmost dot onward are now added as the final
        // label of the name.  Those two are special cases in that for
        // all other domain names, the number of labels is one greater
        // than the number of dot separators.
        if (!name.equals("") && !name.equals(".")) {
            add(0, label.toString());
        }

        domain = name;          // do this last, since add() sets it to null
    }

    /*
     * Returns (as a char) the octet indicated by the escape sequence
     * at a given position within a domain name.
     * @throws InvalidNameException if a valid escape sequence is not found.
     */
    private static char getEscapedOctet(String name, int pos)
                                                throws InvalidNameException {
        try {
            // assert (name.charAt(pos) == '\\');
            char c1 = name.charAt(++pos);
            if (isDigit(c1)) {          // sequence is `\DDD'
                char c2 = name.charAt(++pos);
                char c3 = name.charAt(++pos);
                if (isDigit(c2) && isDigit(c3)) {
                    return (char)
                        ((c1 - '0') * 100 + (c2 - '0') * 10 + (c3 - '0'));
                } else {
                    throw new InvalidNameException(
                            "Invalid escape sequence in " + name);
                }
            } else {                    // sequence is `\C'
                return c1;
            }
        } catch (IndexOutOfBoundsException e) {
            throw new InvalidNameException(
                    "Invalid escape sequence in " + name);
        }
    }

    /*
     * Checks that this label is valid.
     * @throws InvalidNameException if label is not valid.
     */
    private static void verifyLabel(String label) throws InvalidNameException {
        if (label.length() > 63) {
            throw new InvalidNameException(
                    "Label exceeds 63 octets: " + label);
        }
        // Check for two-byte characters.
        for (int i = 0; i < label.length(); i++) {
            char c = label.charAt(i);
            if ((c & 0xFF00) != 0) {
                throw new InvalidNameException(
                        "Label has two-byte char: " + label);
            }
        }
    }

    /*
     * Does this label conform to host name syntax?
     */
    private static boolean isHostNameLabel(String label) {
        for (int i = 0; i < label.length(); i++) {
            char c = label.charAt(i);
            if (!isHostNameChar(c)) {
                return false;
            }
        }
        return !(label.startsWith("-") || label.endsWith("-"));
    }

    private static boolean isHostNameChar(char c) {
        return (c == '-' ||
                c >= 'a' && c <= 'z' ||
                c >= 'A' && c <= 'Z' ||
                c >= '0' && c <= '9');
    }

    private static boolean isDigit(char c) {
        return (c >= '0' && c <= '9');
    }

    /*
     * Append a label to buf, escaping as needed.
     */
    private static void escape(StringBuilder buf, String label) {
        for (int i = 0; i < label.length(); i++) {
            char c = label.charAt(i);
            if (c == '.' || c == '\\') {
                buf.append('\\');
            }
            buf.append(c);
        }
    }

    /*
     * Compares two labels, ignoring case for ASCII values.
     * Returns negative, zero, or positive as the first label
     * is less than, equal to, or greater than the second.
     * See keyForLabel().
     */
    private static int compareLabels(String label1, String label2) {
        int min = Math.min(label1.length(), label2.length());
        for (int i = 0; i < min; i++) {
            char c1 = label1.charAt(i);
            char c2 = label2.charAt(i);
            if (c1 >= 'A' && c1 <= 'Z') {
                c1 += 'a' - 'A';                        // to lower case
            }
            if (c2 >= 'A' && c2 <= 'Z') {
                c2 += 'a' - 'A';                        // to lower case
            }
            if (c1 != c2) {
                return (c1 - c2);
            }
        }
        return (label1.length() - label2.length());     // the longer one wins
    }

    /*
     * Returns a key suitable for hashing a label.  Two labels map to
     * the same key iff they are equal, taking possible case-folding
     * into account.  See compareLabels().
     */
    private static String keyForLabel(String label) {
        StringBuilder sb = new StringBuilder(label.length());
        for (int i = 0; i < label.length(); i++) {
            char c = label.charAt(i);
            if (c >= 'A' && c <= 'Z') {
                c += 'a' - 'A';                         // to lower case
            }
            sb.append(c);
        }
        return sb.toString();
    }


    
Serializes only the domain name string, for compactness and to avoid
any implementation dependency.
@serialData
     The domain name string./**
     * Serializes only the domain name string, for compactness and to avoid
     * any implementation dependency.
     *
     * @serialData      The domain name string.
     */
    private void writeObject(java.io.ObjectOutputStream s)
            throws java.io.IOException {
        s.writeObject(toString());
    }

    private void readObject(java.io.ObjectInputStream s)
            throws java.io.IOException, ClassNotFoundException {
        try {
            parse((String) s.readObject());
        } catch (InvalidNameException e) {
            // shouldn't happen
            throw new java.io.StreamCorruptedException(
                    "Invalid name: " + domain);
        }
    }

    private static final long serialVersionUID = 7040187611324710271L;
}