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

 *

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 * 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.

 *

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package jdk.dns.client.internal;

import jdk.dns.client.ex.DnsInvalidNameException;

import java.util.ArrayList;

/**

 * {@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

 */

// Stripped copy with removed serialization code and jndi.Name interface

public final class DnsName {

    // 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 {@code DnsName} representing the empty domain name.

     */

    public DnsName() {

    }

    /**

     * Constructs a {@code DnsName} representing a given domain name.

     *

     * @param name the domain name to parse

     * @throws DnsInvalidNameException if {@code name} does not conform

     *                                 to DNS syntax.

     */

    public DnsName(String name) throws DnsInvalidNameException {

        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 <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 DnsName)) {

            return false;

        }

        DnsName n = (DnsName) obj;

        return ((size() == n.size()) &&         // shortcut:  do sizes differ?

                (compareTo(obj) == 0));

    }

    public int compareTo(Object obj) {

        DnsName n = (DnsName) obj;

        return compareRange(0, size(), n);      // never 0 if sizes differ

    }

    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 DnsName getPrefix(int pos) {

        return new DnsName(this, 0, pos);

    }

    public DnsName getSuffix(int pos) {

        return new DnsName(this, pos, size());

    }

    public Object clone() {

        return new DnsName(this, 0, size());

    }

    public DnsName add(int pos, String comp) throws DnsInvalidNameException {

        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 DnsInvalidNameException(

                    "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 DnsInvalidNameException("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 DnsName addAll(int pos, DnsName n) throws DnsInvalidNameException {

        // "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.

        if (n.isEmpty()) {

            return this;

        }

        // Check for empty labels:  may have only one, and only at end.

        if ((pos > 0 && n.hasRootLabel()) ||

                (pos == 0 && hasRootLabel())) {

            throw new DnsInvalidNameException(

                    "Empty label must be the last label in a domain name");

        }

        short newOctets = (short) (octets + n.octets - 1);

        if (newOctets > 255) {

            throw new DnsInvalidNameException("Name too long");

        }

        octets = newOctets;

        int i = size() - pos;       // index for insertion into "labels"

        labels.addAll(i, n.labels);

        // Preserve "domain" if we're appending or prepending,

        // otherwise invalidate it.

        if (isEmpty()) {

            domain = n.domain;

        } else if (domain == null || n.domain == null) {

            domain = null;

        } else if (pos == 0) {

            domain += (n.domain.equals(".") ? "" : ".") + n.domain;

        } else if (pos == size()) {

            domain = n.domain + (domain.equals(".") ? "" : ".") + domain;

        } else {

            domain = null;

        }

        return this;

    }

    boolean hasRootLabel() {

        return (!isEmpty() &&

                get(0).isEmpty());

    }

    /*

     * 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, DnsName n) {

        // aee: Removed CompositeName ClassCastException generation here

        // 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 DnsInvalidNameException {

        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.isEmpty() && !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 DnsInvalidNameException {

        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 DnsInvalidNameException(

                            "Invalid escape sequence in " + name);

                }

            } else {                    // sequence is `\C'

                return c1;

            }

        } catch (IndexOutOfBoundsException e) {

            throw new DnsInvalidNameException(

                    "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 DnsInvalidNameException {

        if (label.length() > 63) {

            throw new DnsInvalidNameException(

                    "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 DnsInvalidNameException(

                        "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();

    }

}