1 /*

     2  * Copyright (c) 2014, 2018, 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 jdk.internal.net.http.hpack;

    26 

    27 import java.io.IOException;

    28 import java.nio.ByteBuffer;

    29 import java.util.Arrays;

    30 

    31 import static java.lang.String.format;

    32 

    33 final class IntegerReader {

    34 

    35     private static final int NEW             = 0;

    36     private static final int CONFIGURED      = 1;

    37     private static final int FIRST_BYTE_READ = 2;

    38     private static final int DONE            = 4;

    39 

    40     private int state = NEW;

    41 

    42     private int N;

    43     private int maxValue;

    44     private int value;

    45     private long r;

    46     private long b = 1;

    47 

    48     public IntegerReader configure(int N) {

    49         return configure(N, Integer.MAX_VALUE);

    50     }

    51 

    52     //

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

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

    55     //

    56     // Two reasons.

    57     //

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

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

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

    61     //

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

    63         if (state != NEW) {

    64             throw new IllegalStateException("Already configured");

    65         }

    66         checkPrefix(N);

    67         if (maxValue < 0) {

    68             throw new IllegalArgumentException(

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

    70         }

    71         this.maxValue = maxValue;

    72         this.N = N;

    73         state = CONFIGURED;

    74         return this;

    75     }

    76 

    77     public boolean read(ByteBuffer input) throws IOException {

    78         if (state == NEW) {

    79             throw new IllegalStateException("Configure first");

    80         }

    81         if (state == DONE) {

    82             return true;

    83         }

    84         if (!input.hasRemaining()) {

    85             return false;

    86         }

    87         if (state == CONFIGURED) {

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

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

    90             if (n != max) {

    91                 value = n;

    92                 state = DONE;

    93                 return true;

    94             } else {

    95                 r = max;

    96             }

    97             state = FIRST_BYTE_READ;

    98         }

    99         if (state == FIRST_BYTE_READ) {

   100             // variable-length quantity (VLQ)

   101             byte i;

   102             do {

   103                 if (!input.hasRemaining()) {

   104                     return false;

   105                 }

   106                 i = input.get();

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

   108                 if (r + increment > maxValue) {

   109                     throw new IOException(format(

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

   111                             maxValue, r + increment));

   112                 }

   113                 r += increment;

   114                 b *= 128;

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

   116 

   117             value = (int) r;

   118             state = DONE;

   119             return true;

   120         }

   121         throw new InternalError(Arrays.toString(

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

   123     }

   124 

   125     public int get() throws IllegalStateException {

   126         if (state != DONE) {

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

   128         }

   129         return value;

   130     }

   131 

   132     private static void checkPrefix(int N) {

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

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

   135         }

   136     }

   137 

   138     public IntegerReader reset() {

   139         b = 1;

   140         state = NEW;

   141         return this;

   142     }

   143 }