annotate third_party/luajit/doc/ext_buffer.html @ 204:e5aed6c36672

[Notes] Added icons and updated styling a bit. Probalby usable now.
author MrJuneJune <me@mrjunejune.com>
date Sun, 15 Feb 2026 11:02:13 -0800
parents 94705b5986b3
children
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1 <!DOCTYPE html>
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2 <html>
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3 <head>
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4 <title>String Buffer Library</title>
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5 <meta charset="utf-8">
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6 <meta name="Copyright" content="Copyright (C) 2005-2023">
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7 <meta name="Language" content="en">
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8 <link rel="stylesheet" type="text/css" href="bluequad.css" media="screen">
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9 <link rel="stylesheet" type="text/css" href="bluequad-print.css" media="print">
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10 <style type="text/css">
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11 .lib {
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12 vertical-align: middle;
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13 margin-left: 5px;
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14 padding: 0 5px;
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15 font-size: 60%;
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16 border-radius: 5px;
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17 background: #c5d5ff;
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18 color: #000;
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19 }
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20 </style>
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21 </head>
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22 <body>
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23 <div id="site">
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24 <a href="https://luajit.org"><span>Lua<span id="logo">JIT</span></span></a>
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25 </div>
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26 <div id="head">
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27 <h1>String Buffer Library</h1>
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28 </div>
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29 <div id="nav">
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30 <ul><li>
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31 <a href="luajit.html">LuaJIT</a>
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32 <ul><li>
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33 <a href="https://luajit.org/download.html">Download <span class="ext">&raquo;</span></a>
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34 </li><li>
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35 <a href="install.html">Installation</a>
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36 </li><li>
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37 <a href="running.html">Running</a>
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38 </li></ul>
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39 </li><li>
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40 <a href="extensions.html">Extensions</a>
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41 <ul><li>
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42 <a href="ext_ffi.html">FFI Library</a>
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43 <ul><li>
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44 <a href="ext_ffi_tutorial.html">FFI Tutorial</a>
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45 </li><li>
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46 <a href="ext_ffi_api.html">ffi.* API</a>
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47 </li><li>
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48 <a href="ext_ffi_semantics.html">FFI Semantics</a>
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49 </li></ul>
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50 </li><li>
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51 <a class="current" href="ext_buffer.html">String Buffers</a>
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52 </li><li>
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53 <a href="ext_jit.html">jit.* Library</a>
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54 </li><li>
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55 <a href="ext_c_api.html">Lua/C API</a>
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56 </li><li>
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57 <a href="ext_profiler.html">Profiler</a>
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58 </li></ul>
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59 </li><li>
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60 <a href="https://luajit.org/status.html">Status <span class="ext">&raquo;</span></a>
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61 </li><li>
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62 <a href="https://luajit.org/faq.html">FAQ <span class="ext">&raquo;</span></a>
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63 </li><li>
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64 <a href="https://luajit.org/list.html">Mailing List <span class="ext">&raquo;</span></a>
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65 </li></ul>
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66 </div>
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67 <div id="main">
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68 <p>
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69 The string buffer library allows <b>high-performance manipulation of
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70 string-like data</b>.
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71 </p>
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72 <p>
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73 Unlike Lua strings, which are constants, string buffers are
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74 <b>mutable</b> sequences of 8-bit (binary-transparent) characters. Data
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75 can be stored, formatted and encoded into a string buffer and later
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76 converted, extracted or decoded.
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77 </p>
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78 <p>
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79 The convenient string buffer API simplifies common string manipulation
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80 tasks, that would otherwise require creating many intermediate strings.
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81 String buffers improve performance by eliminating redundant memory
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82 copies, object creation, string interning and garbage collection
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83 overhead. In conjunction with the FFI library, they allow zero-copy
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84 operations.
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85 </p>
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86 <p>
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87 The string buffer library also includes a high-performance
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88 <a href="serialize">serializer</a> for Lua objects.
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89 </p>
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90
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91 <h2 id="use">Using the String Buffer Library</h2>
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92 <p>
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93 The string buffer library is built into LuaJIT by default, but it's not
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94 loaded by default. Add this to the start of every Lua file that needs
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95 one of its functions:
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96 </p>
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97 <pre class="code">
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98 local buffer = require("string.buffer")
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99 </pre>
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100 <p>
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101 The convention for the syntax shown on this page is that <tt>buffer</tt>
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102 refers to the buffer library and <tt>buf</tt> refers to an individual
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103 buffer object.
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104 </p>
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105 <p>
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106 Please note the difference between a Lua function call, e.g.
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107 <tt>buffer.new()</tt> (with a dot) and a Lua method call, e.g.
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108 <tt>buf:reset()</tt> (with a colon).
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109 </p>
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110
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111 <h3 id="buffer_object">Buffer Objects</h3>
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112 <p>
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113 A buffer object is a garbage-collected Lua object. After creation with
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114 <tt>buffer.new()</tt>, it can (and should) be reused for many operations.
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115 When the last reference to a buffer object is gone, it will eventually
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116 be freed by the garbage collector, along with the allocated buffer
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117 space.
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118 </p>
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119 <p>
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120 Buffers operate like a FIFO (first-in first-out) data structure. Data
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121 can be appended (written) to the end of the buffer and consumed (read)
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122 from the front of the buffer. These operations may be freely mixed.
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123 </p>
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124 <p>
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125 The buffer space that holds the characters is managed automatically
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126 &mdash; it grows as needed and already consumed space is recycled. Use
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127 <tt>buffer.new(size)</tt> and <tt>buf:free()</tt>, if you need more
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128 control.
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129 </p>
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130 <p>
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131 The maximum size of a single buffer is the same as the maximum size of a
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132 Lua string, which is slightly below two gigabytes. For huge data sizes,
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133 neither strings nor buffers are the right data structure &mdash; use the
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134 FFI library to directly map memory or files up to the virtual memory
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135 limit of your OS.
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136 </p>
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137
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138 <h3 id="buffer_overview">Buffer Method Overview</h3>
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139 <ul>
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140 <li>
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141 The <tt>buf:put*()</tt>-like methods append (write) characters to the
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142 end of the buffer.
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143 </li>
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144 <li>
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145 The <tt>buf:get*()</tt>-like methods consume (read) characters from the
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146 front of the buffer.
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147 </li>
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148 <li>
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149 Other methods, like <tt>buf:tostring()</tt> only read the buffer
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150 contents, but don't change the buffer.
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151 </li>
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152 <li>
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153 The <tt>buf:set()</tt> method allows zero-copy consumption of a string
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154 or an FFI cdata object as a buffer.
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155 </li>
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156 <li>
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157 The FFI-specific methods allow zero-copy read/write-style operations or
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158 modifying the buffer contents in-place. Please check the
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159 <a href="#ffi_caveats">FFI caveats</a> below, too.
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160 </li>
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161 <li>
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162 Methods that don't need to return anything specific, return the buffer
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163 object itself as a convenience. This allows method chaining, e.g.:
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164 <tt>buf:reset():encode(obj)</tt> or <tt>buf:skip(len):get()</tt>
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165 </li>
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166 </ul>
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167
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168 <h2 id="create">Buffer Creation and Management</h2>
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169
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170 <h3 id="buffer_new"><tt>local buf = buffer.new([size [,options]])<br>
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171 local buf = buffer.new([options])</tt></h3>
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172 <p>
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173 Creates a new buffer object.
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174 </p>
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175 <p>
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176 The optional <tt>size</tt> argument ensures a minimum initial buffer
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177 size. This is strictly an optimization when the required buffer size is
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178 known beforehand. The buffer space will grow as needed, in any case.
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179 </p>
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180 <p>
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181 The optional table <tt>options</tt> sets various
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182 <a href="#serialize_options">serialization options</a>.
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183 </p>
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184
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185 <h3 id="buffer_reset"><tt>buf = buf:reset()</tt></h3>
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186 <p>
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187 Reset (empty) the buffer. The allocated buffer space is not freed and
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188 may be reused.
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189 </p>
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190
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191 <h3 id="buffer_free"><tt>buf = buf:free()</tt></h3>
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192 <p>
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193 The buffer space of the buffer object is freed. The object itself
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194 remains intact, empty and may be reused.
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195 </p>
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196 <p>
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197 Note: you normally don't need to use this method. The garbage collector
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198 automatically frees the buffer space, when the buffer object is
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199 collected. Use this method, if you need to free the associated memory
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200 immediately.
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201 </p>
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202
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203 <h2 id="write">Buffer Writers</h2>
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204
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205 <h3 id="buffer_put"><tt>buf = buf:put([str|num|obj] [,…])</tt></h3>
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206 <p>
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207 Appends a string <tt>str</tt>, a number <tt>num</tt> or any object
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208 <tt>obj</tt> with a <tt>__tostring</tt> metamethod to the buffer.
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209 Multiple arguments are appended in the given order.
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210 </p>
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211 <p>
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212 Appending a buffer to a buffer is possible and short-circuited
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213 internally. But it still involves a copy. Better combine the buffer
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214 writes to use a single buffer.
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215 </p>
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216
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217 <h3 id="buffer_putf"><tt>buf = buf:putf(format, …)</tt></h3>
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218 <p>
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219 Appends the formatted arguments to the buffer. The <tt>format</tt>
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220 string supports the same options as <tt>string.format()</tt>.
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221 </p>
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222
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223 <h3 id="buffer_putcdata"><tt>buf = buf:putcdata(cdata, len)</tt><span class="lib">FFI</span></h3>
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224 <p>
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225 Appends the given <tt>len</tt> number of bytes from the memory pointed
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226 to by the FFI <tt>cdata</tt> object to the buffer. The object needs to
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227 be convertible to a (constant) pointer.
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228 </p>
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229
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230 <h3 id="buffer_set"><tt>buf = buf:set(str)<br>
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231 buf = buf:set(cdata, len)</tt><span class="lib">FFI</span></h3>
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232 <p>
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233 This method allows zero-copy consumption of a string or an FFI cdata
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234 object as a buffer. It stores a reference to the passed string
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235 <tt>str</tt> or the FFI <tt>cdata</tt> object in the buffer. Any buffer
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236 space originally allocated is freed. This is <i>not</i> an append
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237 operation, unlike the <tt>buf:put*()</tt> methods.
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238 </p>
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239 <p>
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240 After calling this method, the buffer behaves as if
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241 <tt>buf:free():put(str)</tt> or <tt>buf:free():put(cdata,&nbsp;len)</tt>
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242 had been called. However, the data is only referenced and not copied, as
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243 long as the buffer is only consumed.
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244 </p>
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245 <p>
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246 In case the buffer is written to later on, the referenced data is copied
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247 and the object reference is removed (copy-on-write semantics).
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248 </p>
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249 <p>
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250 The stored reference is an anchor for the garbage collector and keeps the
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251 originally passed string or FFI cdata object alive.
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252 </p>
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253
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254 <h3 id="buffer_reserve"><tt>ptr, len = buf:reserve(size)</tt><span class="lib">FFI</span><br>
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255 <tt>buf = buf:commit(used)</tt><span class="lib">FFI</span></h3>
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256 <p>
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257 The <tt>reserve</tt> method reserves at least <tt>size</tt> bytes of
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258 write space in the buffer. It returns an <tt>uint8_t&nbsp;*</tt> FFI
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259 cdata pointer <tt>ptr</tt> that points to this space.
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260 </p>
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261 <p>
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262 The available length in bytes is returned in <tt>len</tt>. This is at
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263 least <tt>size</tt> bytes, but may be more to facilitate efficient
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264 buffer growth. You can either make use of the additional space or ignore
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265 <tt>len</tt> and only use <tt>size</tt> bytes.
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266 </p>
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267 <p>
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268 The <tt>commit</tt> method appends the <tt>used</tt> bytes of the
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269 previously returned write space to the buffer data.
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270 </p>
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271 <p>
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272 This pair of methods allows zero-copy use of C read-style APIs:
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273 </p>
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274 <pre class="code">
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275 local MIN_SIZE = 65536
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276 repeat
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277 local ptr, len = buf:reserve(MIN_SIZE)
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278 local n = C.read(fd, ptr, len)
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279 if n == 0 then break end -- EOF.
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280 if n &lt; 0 then error("read error") end
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281 buf:commit(n)
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282 until false
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283 </pre>
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284 <p>
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285 The reserved write space is <i>not</i> initialized. At least the
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286 <tt>used</tt> bytes <b>must</b> be written to before calling the
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287 <tt>commit</tt> method. There's no need to call the <tt>commit</tt>
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288 method, if nothing is added to the buffer (e.g. on error).
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289 </p>
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290
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291 <h2 id="read">Buffer Readers</h2>
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292
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293 <h3 id="buffer_length"><tt>len = #buf</tt></h3>
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294 <p>
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295 Returns the current length of the buffer data in bytes.
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296 </p>
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297
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298 <h3 id="buffer_concat"><tt>res = str|num|buf .. str|num|buf […]</tt></h3>
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299 <p>
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300 The Lua concatenation operator <tt>..</tt> also accepts buffers, just
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301 like strings or numbers. It always returns a string and not a buffer.
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302 </p>
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303 <p>
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304 Note that although this is supported for convenience, this thwarts one
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305 of the main reasons to use buffers, which is to avoid string
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306 allocations. Rewrite it with <tt>buf:put()</tt> and <tt>buf:get()</tt>.
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307 </p>
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308 <p>
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309 Mixing this with unrelated objects that have a <tt>__concat</tt>
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310 metamethod may not work, since these probably only expect strings.
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311 </p>
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312
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313 <h3 id="buffer_skip"><tt>buf = buf:skip(len)</tt></h3>
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314 <p>
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315 Skips (consumes) <tt>len</tt> bytes from the buffer up to the current
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316 length of the buffer data.
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317 </p>
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318
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319 <h3 id="buffer_get"><tt>str, … = buf:get([len|nil] [,…])</tt></h3>
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320 <p>
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321 Consumes the buffer data and returns one or more strings. If called
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322 without arguments, the whole buffer data is consumed. If called with a
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323 number, up to <tt>len</tt> bytes are consumed. A <tt>nil</tt> argument
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324 consumes the remaining buffer space (this only makes sense as the last
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325 argument). Multiple arguments consume the buffer data in the given
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326 order.
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327 </p>
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328 <p>
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329 Note: a zero length or no remaining buffer data returns an empty string
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330 and not <tt>nil</tt>.
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331 </p>
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332
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333 <h3 id="buffer_tostring"><tt>str = buf:tostring()<br>
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334 str = tostring(buf)</tt></h3>
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335 <p>
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336 Creates a string from the buffer data, but doesn't consume it. The
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337 buffer remains unchanged.
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338 </p>
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339 <p>
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340 Buffer objects also define a <tt>__tostring</tt> metamethod. This means
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341 buffers can be passed to the global <tt>tostring()</tt> function and
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342 many other functions that accept this in place of strings. The important
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343 internal uses in functions like <tt>io.write()</tt> are short-circuited
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344 to avoid the creation of an intermediate string object.
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345 </p>
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346
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347 <h3 id="buffer_ref"><tt>ptr, len = buf:ref()</tt><span class="lib">FFI</span></h3>
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348 <p>
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349 Returns an <tt>uint8_t&nbsp;*</tt> FFI cdata pointer <tt>ptr</tt> that
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350 points to the buffer data. The length of the buffer data in bytes is
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351 returned in <tt>len</tt>.
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352 </p>
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353 <p>
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354 The returned pointer can be directly passed to C functions that expect a
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355 buffer and a length. You can also do bytewise reads
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356 (<tt>local&nbsp;x&nbsp;=&nbsp;ptr[i]</tt>) or writes
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357 (<tt>ptr[i]&nbsp;=&nbsp;0x40</tt>) of the buffer data.
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358 </p>
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359 <p>
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360 In conjunction with the <tt>skip</tt> method, this allows zero-copy use
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361 of C write-style APIs:
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362 </p>
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363 <pre class="code">
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364 repeat
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365 local ptr, len = buf:ref()
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366 if len == 0 then break end
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367 local n = C.write(fd, ptr, len)
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368 if n &lt; 0 then error("write error") end
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369 buf:skip(n)
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370 until n >= len
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371 </pre>
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372 <p>
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373 Unlike Lua strings, buffer data is <i>not</i> implicitly
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374 zero-terminated. It's not safe to pass <tt>ptr</tt> to C functions that
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375 expect zero-terminated strings. If you're not using <tt>len</tt>, then
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376 you're doing something wrong.
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377 </p>
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378
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379 <h2 id="serialize">Serialization of Lua Objects</h2>
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380 <p>
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381 The following functions and methods allow <b>high-speed serialization</b>
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382 (encoding) of a Lua object into a string and decoding it back to a Lua
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383 object. This allows convenient storage and transport of <b>structured
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384 data</b>.
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385 </p>
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386 <p>
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387 The encoded data is in an <a href="#serialize_format">internal binary
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diff changeset
388 format</a>. The data can be stored in files, binary-transparent
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389 databases or transmitted to other LuaJIT instances across threads,
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390 processes or networks.
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diff changeset
391 </p>
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392 <p>
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393 Encoding speed can reach up to 1 Gigabyte/second on a modern desktop- or
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diff changeset
394 server-class system, even when serializing many small objects. Decoding
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395 speed is mostly constrained by object creation cost.
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396 </p>
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397 <p>
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398 The serializer handles most Lua types, common FFI number types and
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399 nested structures. Functions, thread objects, other FFI cdata and full
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400 userdata cannot be serialized (yet).
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401 </p>
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402 <p>
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403 The encoder serializes nested structures as trees. Multiple references
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404 to a single object will be stored separately and create distinct objects
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405 after decoding. Circular references cause an error.
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406 </p>
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407
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408 <h3 id="serialize_methods">Serialization Functions and Methods</h3>
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409
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410 <h3 id="buffer_encode"><tt>str = buffer.encode(obj)<br>
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411 buf = buf:encode(obj)</tt></h3>
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412 <p>
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413 Serializes (encodes) the Lua object <tt>obj</tt>. The stand-alone
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414 function returns a string <tt>str</tt>. The buffer method appends the
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415 encoding to the buffer.
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416 </p>
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417 <p>
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418 <tt>obj</tt> can be any of the supported Lua types &mdash; it doesn't
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419 need to be a Lua table.
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420 </p>
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421 <p>
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422 This function may throw an error when attempting to serialize
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423 unsupported object types, circular references or deeply nested tables.
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424 </p>
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425
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426 <h3 id="buffer_decode"><tt>obj = buffer.decode(str)<br>
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427 obj = buf:decode()</tt></h3>
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428 <p>
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429 The stand-alone function deserializes (decodes) the string
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430 <tt>str</tt>, the buffer method deserializes one object from the
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431 buffer. Both return a Lua object <tt>obj</tt>.
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432 </p>
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433 <p>
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434 The returned object may be any of the supported Lua types &mdash;
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435 even <tt>nil</tt>.
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diff changeset
436 </p>
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437 <p>
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438 This function may throw an error when fed with malformed or incomplete
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439 encoded data. The stand-alone function throws when there's left-over
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440 data after decoding a single top-level object. The buffer method leaves
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441 any left-over data in the buffer.
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442 </p>
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443 <p>
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444 Attempting to deserialize an FFI type will throw an error, if the FFI
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445 library is not built-in or has not been loaded, yet.
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446 </p>
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447
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448 <h3 id="serialize_options">Serialization Options</h3>
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449 <p>
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450 The <tt>options</tt> table passed to <tt>buffer.new()</tt> may contain
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451 the following members (all optional):
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452 </p>
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453 <ul>
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diff changeset
454 <li>
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455 <tt>dict</tt> is a Lua table holding a <b>dictionary of strings</b> that
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456 commonly occur as table keys of objects you are serializing. These keys
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457 are compactly encoded as indexes during serialization. A well-chosen
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diff changeset
458 dictionary saves space and improves serialization performance.
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diff changeset
459 </li>
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diff changeset
460 <li>
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diff changeset
461 <tt>metatable</tt> is a Lua table holding a <b>dictionary of metatables</b>
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diff changeset
462 for the table objects you are serializing.
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diff changeset
463 </li>
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MrJuneJune <me@mrjunejune.com>
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diff changeset
464 </ul>
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diff changeset
465 <p>
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diff changeset
466 <tt>dict</tt> needs to be an array of strings and <tt>metatable</tt> needs
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467 to be an array of tables. Both starting at index 1 and without holes (no
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diff changeset
468 <tt>nil</tt> in between). The tables are anchored in the buffer object and
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469 internally modified into a two-way index (don't do this yourself, just pass
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diff changeset
470 a plain array). The tables must not be modified after they have been passed
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diff changeset
471 to <tt>buffer.new()</tt>.
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diff changeset
472 </p>
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diff changeset
473 <p>
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diff changeset
474 The <tt>dict</tt> and <tt>metatable</tt> tables used by the encoder and
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diff changeset
475 decoder must be the same. Put the most common entries at the front. Extend
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diff changeset
476 at the end to ensure backwards-compatibility &mdash; older encodings can
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diff changeset
477 then still be read. You may also set some indexes to <tt>false</tt> to
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diff changeset
478 explicitly drop backwards-compatibility. Old encodings that use these
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diff changeset
479 indexes will throw an error when decoded.
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diff changeset
480 </p>
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diff changeset
481 <p>
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diff changeset
482 Metatables that are not found in the <tt>metatable</tt> dictionary are
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diff changeset
483 ignored when encoding. Decoding returns a table with a <tt>nil</tt>
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diff changeset
484 metatable.
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diff changeset
485 </p>
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diff changeset
486 <p>
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diff changeset
487 Note: parsing and preparation of the options table is somewhat
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diff changeset
488 expensive. Create a buffer object only once and recycle it for multiple
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diff changeset
489 uses. Avoid mixing encoder and decoder buffers, since the
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diff changeset
490 <tt>buf:set()</tt> method frees the already allocated buffer space:
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diff changeset
491 </p>
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diff changeset
492 <pre class="code">
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493 local options = {
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494 dict = { "commonly", "used", "string", "keys" },
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diff changeset
495 }
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diff changeset
496 local buf_enc = buffer.new(options)
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diff changeset
497 local buf_dec = buffer.new(options)
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diff changeset
498
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diff changeset
499 local function encode(obj)
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diff changeset
500 return buf_enc:reset():encode(obj):get()
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diff changeset
501 end
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diff changeset
502
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parents:
diff changeset
503 local function decode(str)
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diff changeset
504 return buf_dec:set(str):decode()
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505 end
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diff changeset
506 </pre>
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diff changeset
507
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diff changeset
508 <h3 id="serialize_stream">Streaming Serialization</h3>
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diff changeset
509 <p>
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diff changeset
510 In some contexts, it's desirable to do piecewise serialization of large
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diff changeset
511 datasets, also known as <i>streaming</i>.
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diff changeset
512 </p>
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diff changeset
513 <p>
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diff changeset
514 This serialization format can be safely concatenated and supports streaming.
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diff changeset
515 Multiple encodings can simply be appended to a buffer and later decoded
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diff changeset
516 individually:
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diff changeset
517 </p>
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
518 <pre class="code">
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
519 local buf = buffer.new()
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
520 buf:encode(obj1)
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
521 buf:encode(obj2)
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
522 local copy1 = buf:decode()
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
523 local copy2 = buf:decode()
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
524 </pre>
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
525 <p>
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
526 Here's how to iterate over a stream:
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
527 </p>
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
528 <pre class="code">
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
529 while #buf ~= 0 do
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
530 local obj = buf:decode()
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
531 -- Do something with obj.
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
532 end
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
533 </pre>
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
534 <p>
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
535 Since the serialization format doesn't prepend a length to its encoding,
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
536 network applications may need to transmit the length, too.
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
537 </p>
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
538
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
539 <h3 id="serialize_format">Serialization Format Specification</h3>
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
540 <p>
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
541 This serialization format is designed for <b>internal use</b> by LuaJIT
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
542 applications. Serialized data is upwards-compatible and portable across
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
543 all supported LuaJIT platforms.
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
544 </p>
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
545 <p>
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
546 It's an <b>8-bit binary format</b> and not human-readable. It uses e.g.
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
547 embedded zeroes and stores embedded Lua string objects unmodified, which
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
548 are 8-bit-clean, too. Encoded data can be safely concatenated for
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
549 streaming and later decoded one top-level object at a time.
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
550 </p>
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
551 <p>
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
552 The encoding is reasonably compact, but tuned for maximum performance,
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
553 not for minimum space usage. It compresses well with any of the common
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
554 byte-oriented data compression algorithms.
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
555 </p>
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
556 <p>
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
557 Although documented here for reference, this format is explicitly
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
558 <b>not</b> intended to be a 'public standard' for structured data
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
559 interchange across computer languages (like JSON or MessagePack). Please
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
560 do not use it as such.
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
561 </p>
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
562 <p>
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
563 The specification is given below as a context-free grammar with a
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
564 top-level <tt>object</tt> as the starting point. Alternatives are
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
565 separated by the <tt>|</tt> symbol and <tt>*</tt> indicates repeats.
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
566 Grouping is implicit or indicated by <tt>{…}</tt>. Terminals are
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
567 either plain hex numbers, encoded as bytes, or have a <tt>.format</tt>
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
568 suffix.
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
569 </p>
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
570 <pre>
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
571 object → nil | false | true
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
572 | null | lightud32 | lightud64
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
573 | int | num | tab | tab_mt
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
574 | int64 | uint64 | complex
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
575 | string
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
576
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
577 nil → 0x00
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
578 false → 0x01
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
579 true → 0x02
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
580
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
581 null → 0x03 // NULL lightuserdata
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
582 lightud32 → 0x04 data.I // 32 bit lightuserdata
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
583 lightud64 → 0x05 data.L // 64 bit lightuserdata
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
584
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
585 int → 0x06 int.I // int32_t
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
586 num → 0x07 double.L
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
587
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
588 tab → 0x08 // Empty table
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
589 | 0x09 h.U h*{object object} // Key/value hash
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
590 | 0x0a a.U a*object // 0-based array
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
591 | 0x0b a.U a*object h.U h*{object object} // Mixed
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
592 | 0x0c a.U (a-1)*object // 1-based array
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MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
593 | 0x0d a.U (a-1)*object h.U h*{object object} // Mixed
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
594 tab_mt → 0x0e (index-1).U tab // Metatable dict entry
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
595
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
596 int64 → 0x10 int.L // FFI int64_t
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
597 uint64 → 0x11 uint.L // FFI uint64_t
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
598 complex → 0x12 re.L im.L // FFI complex
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
599
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
600 string → (0x20+len).U len*char.B
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
601 | 0x0f (index-1).U // String dict entry
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
602
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
603 .B = 8 bit
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
604 .I = 32 bit little-endian
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
605 .L = 64 bit little-endian
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
606 .U = prefix-encoded 32 bit unsigned number n:
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
607 0x00..0xdf → n.B
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
608 0xe0..0x1fdf → (0xe0|(((n-0xe0)>>8)&0x1f)).B ((n-0xe0)&0xff).B
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
609 0x1fe0.. → 0xff n.I
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
610 </pre>
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
611
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
612 <h2 id="error">Error handling</h2>
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
613 <p>
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
614 Many of the buffer methods can throw an error. Out-of-memory or usage
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
615 errors are best caught with an outer wrapper for larger parts of code.
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
616 There's not much one can do after that, anyway.
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
617 </p>
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
618 <p>
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
619 OTOH, you may want to catch some errors individually. Buffer methods need
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
620 to receive the buffer object as the first argument. The Lua colon-syntax
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
621 <tt>obj:method()</tt> does that implicitly. But to wrap a method with
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
622 <tt>pcall()</tt>, the arguments need to be passed like this:
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
623 </p>
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
624 <pre class="code">
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
625 local ok, err = pcall(buf.encode, buf, obj)
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
626 if not ok then
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
627 -- Handle error in err.
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
628 end
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
629 </pre>
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
630
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
631 <h2 id="ffi_caveats">FFI caveats</h2>
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
632 <p>
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
633 The string buffer library has been designed to work well together with
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
634 the FFI library. But due to the low-level nature of the FFI library,
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
635 some care needs to be taken:
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
636 </p>
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
637 <p>
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
638 First, please remember that FFI pointers are zero-indexed. The space
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
639 returned by <tt>buf:reserve()</tt> and <tt>buf:ref()</tt> starts at the
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
640 returned pointer and ends before <tt>len</tt> bytes after that.
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
641 </p>
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
642 <p>
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
643 I.e. the first valid index is <tt>ptr[0]</tt> and the last valid index
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
644 is <tt>ptr[len-1]</tt>. If the returned length is zero, there's no valid
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
645 index at all. The returned pointer may even be <tt>NULL</tt>.
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
646 </p>
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
MrJuneJune <me@mrjunejune.com>
parents:
diff changeset
647 <p>
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648 The space pointed to by the returned pointer is only valid as long as
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649 the buffer is not modified in any way (neither append, nor consume, nor
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650 reset, etc.). The pointer is also not a GC anchor for the buffer object
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651 itself.
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652 </p>
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653 <p>
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654 Buffer data is only guaranteed to be byte-aligned. Casting the returned
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655 pointer to a data type with higher alignment may cause unaligned
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656 accesses. It depends on the CPU architecture whether this is allowed or
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657 not (it's always OK on x86/x64 and mostly OK on other modern
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658 architectures).
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659 </p>
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660 <p>
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661 FFI pointers or references do not count as GC anchors for an underlying
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662 object. E.g. an <tt>array</tt> allocated with <tt>ffi.new()</tt> is
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663 anchored by <tt>buf:set(array,&nbsp;len)</tt>, but not by
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664 <tt>buf:set(array+offset,&nbsp;len)</tt>. The addition of the offset
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665 creates a new pointer, even when the offset is zero. In this case, you
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666 need to make sure there's still a reference to the original array as
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667 long as its contents are in use by the buffer.
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668 </p>
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669 <p>
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670 Even though each LuaJIT VM instance is single-threaded (but you can
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671 create multiple VMs), FFI data structures can be accessed concurrently.
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672 Be careful when reading/writing FFI cdata from/to buffers to avoid
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673 concurrent accesses or modifications. In particular, the memory
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674 referenced by <tt>buf:set(cdata,&nbsp;len)</tt> must not be modified
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675 while buffer readers are working on it. Shared, but read-only memory
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676 mappings of files are OK, but only if the file does not change.
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677 </p>
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678 <br class="flush">
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679 </div>
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680 <div id="foot">
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681 <hr class="hide">
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682 Copyright &copy; 2005-2023
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683 <span class="noprint">
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684 &middot;
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685 <a href="contact.html">Contact</a>
94705b5986b3 [ThirdParty] Added WRK and luajit for load testing.
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686 </span>
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687 </div>
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688 </body>
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689 </html>