1 /*

     2  * Copyright (c) 2014, 2016, Oracle and/or its affiliates. All rights reserved.

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

     4  *

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

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

     7  * published by the Free Software Foundation.  Oracle designates this

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

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

    10  *

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

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

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

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

    15  * accompanied this code).

    16  *

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

    18  * 2 along with this work; if not, write to the Free Software Foundation,

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

    20  *

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

    22  * or visit www.oracle.com if you need additional information or have any

    23  * questions.

    24  */

    25 package sun.net.httpclient.hpack;

    26 

    27 import java.nio.ByteBuffer;

    28 import java.util.Arrays;

    29 

    30 import static java.lang.String.format;

    31 

    32 final class IntegerReader {

    33 

    34     private static final int NEW             = 0;

    35     private static final int CONFIGURED      = 1;

    36     private static final int FIRST_BYTE_READ = 2;

    37     private static final int DONE            = 4;

    38 

    39     private int state = NEW;

    40 

    41     private int N;

    42     private int maxValue;

    43     private int value;

    44     private long r;

    45     private long b = 1;

    46 

    47     public IntegerReader configure(int N) {

    48         return configure(N, Integer.MAX_VALUE);

    49     }

    50 

    51     //

    52     // Why is it important to configure 'maxValue' here. After all we can wait

    53     // for the integer to be fully read and then check it. Can't we?

    54     //

    55     // Two reasons.

    56     //

    57     // 1. Value wraps around long won't be unnoticed.

    58     // 2. It can spit out an exception as soon as it becomes clear there's

    59     // an overflow. Therefore, no need to wait for the value to be fully read.

    60     //

    61     public IntegerReader configure(int N, int maxValue) {

    62         if (state != NEW) {

    63             throw new IllegalStateException("Already configured");

    64         }

    65         checkPrefix(N);

    66         if (maxValue < 0) {

    67             throw new IllegalArgumentException(

    68                     "maxValue >= 0: maxValue=" + maxValue);

    69         }

    70         this.maxValue = maxValue;

    71         this.N = N;

    72         state = CONFIGURED;

    73         return this;

    74     }

    75 

    76     public boolean read(ByteBuffer input) {

    77         if (state == NEW) {

    78             throw new IllegalStateException("Configure first");

    79         }

    80         if (state == DONE) {

    81             return true;

    82         }

    83         if (!input.hasRemaining()) {

    84             return false;

    85         }

    86         if (state == CONFIGURED) {

    87             int max = (2 << (N - 1)) - 1;

    88             int n = input.get() & max;

    89             if (n != max) {

    90                 value = n;

    91                 state = DONE;

    92                 return true;

    93             } else {

    94                 r = max;

    95             }

    96             state = FIRST_BYTE_READ;

    97         }

    98         if (state == FIRST_BYTE_READ) {

    99             // variable-length quantity (VLQ)

   100             byte i;

   101             do {

   102                 if (!input.hasRemaining()) {

   103                     return false;

   104                 }

   105                 i = input.get();

   106                 long increment = b * (i & 127);

   107                 if (r + increment > maxValue) {

   108                     throw new IllegalArgumentException(format(

   109                             "Integer overflow: maxValue=%,d, value=%,d",

   110                             maxValue, r + increment));

   111                 }

   112                 r += increment;

   113                 b *= 128;

   114             } while ((128 & i) == 128);

   115 

   116             value = (int) r;

   117             state = DONE;

   118             return true;

   119         }

   120         throw new InternalError(Arrays.toString(

   121                 new Object[]{state, N, maxValue, value, r, b}));

   122     }

   123 

   124     public int get() throws IllegalStateException {

   125         if (state != DONE) {

   126             throw new IllegalStateException("Has not been fully read yet");

   127         }

   128         return value;

   129     }

   130 

   131     private static void checkPrefix(int N) {

   132         if (N < 1 || N > 8) {

   133             throw new IllegalArgumentException("1 <= N <= 8: N= " + N);

   134         }

   135     }

   136 

   137     public IntegerReader reset() {

   138         b = 1;

   139         state = NEW;

   140         return this;

   141     }

   142 }