1 /*
   2  * Copyright (c) 2015, 2017, 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.incubator.http.internal.hpack;
  26 
  27 import java.nio.ByteBuffer;
  28 import java.util.Arrays;
  29 
  30 final class IntegerWriter {
  31 
  32     private static final int NEW                = 0;
  33     private static final int CONFIGURED         = 1;
  34     private static final int FIRST_BYTE_WRITTEN = 2;
  35     private static final int DONE               = 4;
  36 
  37     private int state = NEW;
  38 
  39     private int payload;
  40     private int N;
  41     private int value;
  42 
  43     //
  44     //      0   1   2   3   4   5   6   7
  45     //    +---+---+---+---+---+---+---+---+
  46     //    |   |   |   |   |   |   |   |   |
  47     //    +---+---+---+-------------------+
  48     //    |<--------->|<----------------->|
  49     //       payload           N=5
  50     //
  51     // payload is the contents of the left-hand side part of the octet;
  52     //         it is truncated to fit into 8-N bits, where 1 <= N <= 8;
  53     //
  54     public IntegerWriter configure(int value, int N, int payload) {
  55         if (state != NEW) {
  56             throw new IllegalStateException("Already configured");
  57         }
  58         if (value < 0) {
  59             throw new IllegalArgumentException("value >= 0: value=" + value);
  60         }
  61         checkPrefix(N);
  62         this.value = value;
  63         this.N = N;
  64         this.payload = payload & 0xFF & (0xFFFFFFFF << N);
  65         state = CONFIGURED;
  66         return this;
  67     }
  68 
  69     public boolean write(ByteBuffer output) {
  70         if (state == NEW) {
  71             throw new IllegalStateException("Configure first");
  72         }
  73         if (state == DONE) {
  74             return true;
  75         }
  76 
  77         if (!output.hasRemaining()) {
  78             return false;
  79         }
  80         if (state == CONFIGURED) {
  81             int max = (2 << (N - 1)) - 1;
  82             if (value < max) {
  83                 output.put((byte) (payload | value));
  84                 state = DONE;
  85                 return true;
  86             }
  87             output.put((byte) (payload | max));
  88             value -= max;
  89             state = FIRST_BYTE_WRITTEN;
  90         }
  91         if (state == FIRST_BYTE_WRITTEN) {
  92             while (value >= 128 && output.hasRemaining()) {
  93                 output.put((byte) (value % 128 + 128));
  94                 value /= 128;
  95             }
  96             if (!output.hasRemaining()) {
  97                 return false;
  98             }
  99             output.put((byte) value);
 100             state = DONE;
 101             return true;
 102         }
 103         throw new InternalError(Arrays.toString(
 104                 new Object[]{state, payload, N, value}));
 105     }
 106 
 107     private static void checkPrefix(int N) {
 108         if (N < 1 || N > 8) {
 109             throw new IllegalArgumentException("1 <= N <= 8: N= " + N);
 110         }
 111     }
 112 
 113     public IntegerWriter reset() {
 114         state = NEW;
 115         return this;
 116     }
 117 }