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<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/features/binary_formats/ubjson/" rel="canonical"><link href=../messagepack/ rel=prev><link href=../../binary_values/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>UBJSON - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new URL("../../..",location),__md_hash=e=>[...e].reduce(((e,_)=>(e<<5)-e+_.charCodeAt(0)),0),__md_get=(e,_=localStorage,t=__md_scope)=>JSON.parse(_.getItem(t.pathname+"."+e)),__md_set=(e,_,t=localStorage,a=__md_scope)=>{try{t.setItem(a.pathname+"."+e,JSON.stringify(_))}catch(e){}}</script></head> <body dir=ltr data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo> <input class=md-toggle data-md-toggle=drawer type=checkbox id=__drawer autocomplete=off> <input class=md-toggle data-md-toggle=search type=checkbox id=__search autocomplete=off> <label class=md-overlay for=__drawer></label> <div data-md-component=skip> <a href=#ubjson class=md-skip> Skip to content </a> </div> <div data-md-component=announce> </div> <header class=md-header data-md-component=header> <nav class="md-header__inner md-grid" aria-label=Header> <a href=../../.. title="JSON for Modern C++" class="md-header__button md-logo" aria-label="JSON for Modern C++" data-md-component=logo> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> UBJSON </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to dark mode" type=radio name=__palette 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23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 1.5-5-5v-.79l-.27-.27A6.52 6.52 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5 14 14 12 14 9.5 12 5 9.5 5"/></svg> </laLine truncated
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<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/features/binary_formats/ubjson/" rel="canonical"><link href=../messagepack/ rel=prev><link href=../../binary_values/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>UBJSON - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new URL("../../..",location),__md_hash=e=>[...e].reduce(((e,_)=>(e<<5)-e+_.charCodeAt(0)),0),__md_get=(e,_=localStorage,t=__md_scope)=>JSON.parse(_.getItem(t.pathname+"."+e)),__md_set=(e,_,t=localStorage,a=__md_scope)=>{try{t.setItem(a.pathname+"."+e,JSON.stringify(_))}catch(e){}}</script></head> <body dir=ltr data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo> <input class=md-toggle data-md-toggle=drawer type=checkbox id=__drawer autocomplete=off> <input class=md-toggle data-md-toggle=search type=checkbox id=__search autocomplete=off> <label class=md-overlay for=__drawer></label> <div data-md-component=skip> <a href=#ubjson class=md-skip> Skip to content </a> </div> <div data-md-component=announce> </div> <header class=md-header data-md-component=header> <nav class="md-header__inner md-grid" aria-label=Header> <a href=../../.. title="JSON for Modern C++" class="md-header__button md-logo" aria-label="JSON for Modern C++" data-md-component=logo> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> UBJSON </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to dark mode" type=radio name=__palette id=__palette_0> <label class="md-header__button md-icon" title="Switch to dark mode" for=__palette_1 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a4 4 0 0 0-4 4 4 4 0 0 0 4 4 4 4 0 0 0 4-4 4 4 0 0 0-4-4m0 10a6 6 0 0 1-6-6 6 6 0 0 1 6-6 6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> <input class=md-option data-md-color-media="(prefers-color-scheme: dark)" data-md-color-scheme=slate data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to light mode" type=radio name=__palette id=__palette_1> <label class="md-header__button md-icon" title="Switch to light mode" for=__palette_0 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 18c-.89 0-1.74-.2-2.5-.55C11.56 16.5 13 14.42 13 12s-1.44-4.5-3.5-5.45C10.26 6.2 11.11 6 12 6a6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 1.5-5-5v-.79l-.27-.27A6.52 6.52 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5 14 14 12 14 9.5 12 5 9.5 5"/></svg> </laLine truncated
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<span class=w> </span><span class=nt>"id"</span><span class=p>:</span><span class=w> </span><span class=mi>300</span><span class=p>,</span>
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<span class=w> </span><span class=nt>"name"</span><span class=p>:</span><span class=w> </span><span class=s2>"json"</span><span class=p>,</span>
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<span class=w> </span><span class=nt>"pi"</span><span class=p>:</span><span class=w> </span><span class=mf>3.14</span><span class=p>,</span>
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<span class=w> </span><span class=nt>"tags"</span><span class=p>:</span><span class=w> </span><span class=p>[</span>
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<span class=w> </span><span class=s2>"a"</span><span class=p>,</span>
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<span class=w> </span><span class=s2>"b"</span>
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<span class=w> </span><span class=p>]</span>
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<span class=p>}</span>
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</code></pre></div> <p><code>to_ubjson</code> encodes it to 51 bytes (shown in hexadecimal; the encoding contains no whitespace). The colors mark the role of each byte: <span class="bl bl-t">type/marker</span> <span class="bl bl-l">length/count/size</span> <span class="bl bl-d">data</span>.</p> <div class=byte-layout markdown=0><table> <thead><tr><th>JSON</th><th>Bytes</th><th>Meaning</th></tr></thead><tbody> <tr><td><code>{</code></td><td><span class="bl bl-t">7B</span></td><td>object start (<code>{</code>)</td></tr> <tr><td><code>"id": 300,</code></td><td><span class="bl bl-l">69 02</span> <span class="bl bl-d">69 64</span> <span class="bl bl-t">49</span> <span class="bl bl-d">01 2C</span></td><td>key: length 2 as int8 (<code>i</code>), then UTF-8 bytes; value: int16 (<code>I</code>), big-endian</td></tr> <tr><td><code>"name": "json",</code></td><td><span class="bl bl-l">69 04</span> <span class="bl bl-d">6E 61 6D 65</span> <span class="bl bl-t">53</span> <span class="bl bl-l">69 04</span> <span class="bl bl-d">6A 73 6F 6E</span></td><td>key: length 4; value: string (<code>S</code>), length 4 as int8, UTF-8 bytes</td></tr> <tr><td><code>"pi": 3.14,</code></td><td><span class="bl bl-l">69 02</span> <span class="bl bl-d">70 69</span> <span class="bl bl-t">44</span> <span class="bl bl-d">40 09 1E B8 51 EB 85 1F</span></td><td>key: length 2; value: float64 (<code>D</code>), big-endian</td></tr> <tr><td><code>"tags": [</code></td><td><span class="bl bl-l">69 04</span> <span class="bl bl-d">74 61 67 73</span> <span class="bl bl-t">5B</span></td><td>key: length 4; value: array start (<code>[</code>)</td></tr> <tr><td><code>"a",</code></td><td><span class="bl bl-t">53</span> <span class="bl bl-l">69 01</span> <span class="bl bl-d">61</span></td><td>string, length 1</td></tr> <tr><td><code>"b"</code></td><td><span class="bl bl-t">53</span> <span class="bl bl-l">69 01</span> <span class="bl bl-d">62</span></td><td>string, length 1</td></tr> <tr><td><code>]</code></td><td><span class="bl bl-t">5D</span></td><td>array end (<code>]</code>)</td></tr> <tr><td><code>}</code></td><td><span class="bl bl-t">7D</span></td><td>object end (<code>}</code>)</td></tr> </tbody></table></div> <h2 id=serialization>Serialization<a class=headerlink href=#serialization title="Permanent link">¶</a></h2> <p>The library uses the following mapping from <abbr title="JavaScript Object Notation">JSON</abbr> values types to <abbr title="Universal Binary JSON">UBJSON</abbr> types according to the <abbr title="Universal Binary JSON">UBJSON</abbr> specification:</p> <table> <thead> <tr> <th><abbr title="JavaScript Object Notation">JSON</abbr> value type</th> <th>value/range</th> <th><abbr title="Universal Binary JSON">UBJSON</abbr> type</th> <th>marker</th> </tr> </thead> <tbody> <tr> <td>null</td> <td><code>null</code></td> <td>null</td> <td><code>Z</code></td> </tr> <tr> <td>boolean</td> <td><code>true</code></td> <td>true</td> <td><code>T</code></td> </tr> <tr> <td>boolean</td> <td><code>false</code></td> <td>false</td> <td><code>F</code></td> </tr> <tr> <td>number_integer</td> <td>-9223372036854775808..-2147483649</td> <td>int64</td> <td><code>L</code></td> </tr> <tr> <td>number_integer</td> <td>-2147483648..-32769</td> <td>int32</td> <td><code>l</code></td> </tr> <tr> <td>number_integer</td> <td>-32768..-129</td> <td>int16</td> <td><code>I</code></td> </tr> <tr> <td>number_integer</td> <td>-128..127</td> <td>int8</td> <td><code>i</code></td> </tr> <tr> <td>number_integer</td> <td>128..255</td> <td>uint8</td> <td><code>U</code></td> </tr> <tr> <td>number_integer</td> <td>256..32767</td> <td>int16</td> <td><code>I</code></td> </tr> <tr> <td>number_integer</td> <td>32768..2147483647</td> <td>int32</td> <td><code>l</code></td> </tr> <tr> <td>number_integer</td> <td>2147483648..9223372036854775807</td> <td>int64</td> <td><code>L</code></td> </tr> <tr> <td>number_unsigned</td> <td>0..127</td> <td>int8</td> <td><code>i</code></td> </tr> <tr> <td>number_unsigned</td> <td>128..255</td> <td>uint8</td> <td><code>U</code></td> </tr> <tr> <td>number_unsigned</td> <td>256..32767</td> <td>int16</td> <td><code>I</code></td> </tr> <tr> <td>number_unsigned</td> <td>32768..2147483647</td> <td>int32</td> <td><code>l</code></td> </tr> <tr> <td>number_unsigned</td> <td>2147483648..9223372036854775807</td> <td>int64</td> <td><code>L</code></td> </tr> <tr> <td>number_unsigned</td> <td>9223372036854775808..18446744073709551615</td> <td>high-precision</td> <td><code>H</code></td> </tr> <tr> <td>number_float</td> <td><em>any value</em></td> <td>float64 (float32 if <code>number_float_t</code> is <code>float</code>)</td> <td><code>D</code> (<code>d</code>)</td> </tr> <tr> <td>string</td> <td><em>with shortest length indicator</em></td> <td>string</td> <td><code>S</code></td> </tr> <tr> <td>array</td> <td><em>see notes on optimized format</em></td> <td>array</td> <td><code>[</code></td> </tr> <trLine truncated
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||||
<span class=cp>#include</span><span class=w> </span><span class=cpf><iomanip></span>
|
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<span class=cp>#include</span><span class=w> </span><span class=cpf><nlohmann/json.hpp></span>
|
||||
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<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
|
||||
<span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
|
||||
<span class=k>using</span><span class=w> </span><span class=k>namespace</span><span class=w> </span><span class=nn>nlohmann</span><span class=o>::</span><span class=nn>literals</span><span class=p>;</span>
|
||||
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||||
<span class=c1>// function to print UBJSON's diagnostic format</span>
|
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@@ -10,11 +19,11 @@
|
||||
<span class=p>{</span>
|
||||
<span class=w> </span><span class=k>if</span><span class=w> </span><span class=p>(</span><span class=mi>32</span><span class=w> </span><span class=o><</span><span class=w> </span><span class=kt>byte</span><span class=w> </span><span class=k>and</span><span class=w> </span><span class=kt>byte</span><span class=w> </span><span class=o><</span><span class=w> </span><span class=mi>128</span><span class=p>)</span>
|
||||
<span class=w> </span><span class=p>{</span>
|
||||
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o><<</span><span class=w> </span><span class=p>(</span><span class=kt>char</span><span class=p>)</span><span class=kt>byte</span><span class=p>;</span>
|
||||
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o><<</span><span class=w> </span><span class=k>static_cast</span><span class=o><</span><span class=kt>char</span><span class=o>></span><span class=p>(</span><span class=kt>byte</span><span class=p>);</span>
|
||||
<span class=w> </span><span class=p>}</span>
|
||||
<span class=w> </span><span class=k>else</span>
|
||||
<span class=w> </span><span class=p>{</span>
|
||||
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o><<</span><span class=w> </span><span class=p>(</span><span class=kt>int</span><span class=p>)</span><span class=kt>byte</span><span class=p>;</span>
|
||||
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o><<</span><span class=w> </span><span class=k>static_cast</span><span class=o><</span><span class=kt>int</span><span class=o>></span><span class=p>(</span><span class=kt>byte</span><span class=p>);</span>
|
||||
<span class=w> </span><span class=p>}</span>
|
||||
<span class=p>}</span>
|
||||
|
||||
@@ -31,7 +40,7 @@
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||||
<span class=w> </span><span class=p>{</span>
|
||||
<span class=w> </span><span class=n>print_byte</span><span class=p>(</span><span class=kt>byte</span><span class=p>);</span>
|
||||
<span class=w> </span><span class=p>}</span>
|
||||
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o><<</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>endl</span><span class=p>;</span>
|
||||
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o><<</span><span class=w> </span><span class=sc>'\n'</span><span class=p>;</span>
|
||||
|
||||
<span class=w> </span><span class=c1>// create an array of numbers</span>
|
||||
<span class=w> </span><span class=n>json</span><span class=w> </span><span class=n>array</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=p>{</span><span class=mi>1</span><span class=p>,</span><span class=w> </span><span class=mi>2</span><span class=p>,</span><span class=w> </span><span class=mi>3</span><span class=p>,</span><span class=w> </span><span class=mi>4</span><span class=p>,</span><span class=w> </span><span class=mi>5</span><span class=p>,</span><span class=w> </span><span class=mi>6</span><span class=p>,</span><span class=w> </span><span class=mi>7</span><span class=p>,</span><span class=w> </span><span class=mi>8</span><span class=p>};</span>
|
||||
@@ -48,38 +57,29 @@
|
||||
<span class=w> </span><span class=p>{</span>
|
||||
<span class=w> </span><span class=n>print_byte</span><span class=p>(</span><span class=kt>byte</span><span class=p>);</span>
|
||||
<span class=w> </span><span class=p>}</span>
|
||||
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o><<</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>endl</span><span class=p>;</span>
|
||||
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o><<</span><span class=w> </span><span class=sc>'\n'</span><span class=p>;</span>
|
||||
|
||||
<span class=w> </span><span class=k>for</span><span class=w> </span><span class=p>(</span><span class=k>auto</span><span class=o>&</span><span class=w> </span><span class=kt>byte</span><span class=w> </span><span class=o>:</span><span class=w> </span><span class=n>v_array_size</span><span class=p>)</span>
|
||||
<span class=w> </span><span class=p>{</span>
|
||||
<span class=w> </span><span class=n>print_byte</span><span class=p>(</span><span class=kt>byte</span><span class=p>);</span>
|
||||
<span class=w> </span><span class=p>}</span>
|
||||
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o><<</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>endl</span><span class=p>;</span>
|
||||
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o><<</span><span class=w> </span><span class=sc>'\n'</span><span class=p>;</span>
|
||||
|
||||
<span class=w> </span><span class=k>for</span><span class=w> </span><span class=p>(</span><span class=k>auto</span><span class=o>&</span><span class=w> </span><span class=kt>byte</span><span class=w> </span><span class=o>:</span><span class=w> </span><span class=n>v_array_size_and_type</span><span class=p>)</span>
|
||||
<span class=w> </span><span class=p>{</span>
|
||||
<span class=w> </span><span class=n>print_byte</span><span class=p>(</span><span class=kt>byte</span><span class=p>);</span>
|
||||
<span class=w> </span><span class=p>}</span>
|
||||
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o><<</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>endl</span><span class=p>;</span>
|
||||
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o><<</span><span class=w> </span><span class=sc>'\n'</span><span class=p>;</span>
|
||||
<span class=p>}</span>
|
||||
</code></pre></div> <p>Output:</p> <div class=highlight><pre><span></span><code><span class=p>{</span><span class=n>i7compactTi6schemaF</span><span class=p>}</span>
|
||||
<span class=p>[</span><span class=n>i1i2i3i4i5i6i7i8</span><span class=p>]</span>
|
||||
<span class=p>[</span><span class=err>#</span><span class=n>i8i1i2i3i4i5i6i7i8</span>
|
||||
<span class=p>[</span><span class=n>$i</span><span class=err>#</span><span class=n>i812345678</span>
|
||||
</code></pre></div> </details> <h3 id=byte-layout>Byte layout<a class=headerlink href=#byte-layout title="Permanent link">¶</a></h3> <p>Consider the following <abbr title="JavaScript Object Notation">JSON</abbr> value (shown formatted for readability):</p> <div class=highlight><pre><span></span><code><span class=p>{</span>
|
||||
<span class=w> </span><span class=nt>"id"</span><span class=p>:</span><span class=w> </span><span class=mi>300</span><span class=p>,</span>
|
||||
<span class=w> </span><span class=nt>"name"</span><span class=p>:</span><span class=w> </span><span class=s2>"json"</span><span class=p>,</span>
|
||||
<span class=w> </span><span class=nt>"pi"</span><span class=p>:</span><span class=w> </span><span class=mf>3.14</span><span class=p>,</span>
|
||||
<span class=w> </span><span class=nt>"tags"</span><span class=p>:</span><span class=w> </span><span class=p>[</span>
|
||||
<span class=w> </span><span class=s2>"a"</span><span class=p>,</span>
|
||||
<span class=w> </span><span class=s2>"b"</span>
|
||||
<span class=w> </span><span class=p>]</span>
|
||||
<span class=p>}</span>
|
||||
</code></pre></div> <p><code>to_ubjson</code> encodes it to 51 bytes (shown in hexadecimal; the encoding contains no whitespace). The colors mark the role of each byte: <span class="bl bl-t">type/marker</span> <span class="bl bl-l">length/count/size</span> <span class="bl bl-d">data</span>.</p> <div class=byte-layout markdown=0><table> <thead><tr><th>JSON</th><th>Bytes</th><th>Meaning</th></tr></thead><tbody> <tr><td><code>{</code></td><td><span class="bl bl-t">7B</span></td><td>object start (<code>{</code>)</td></tr> <tr><td><code>"id": 300,</code></td><td><span class="bl bl-l">69 02</span> <span class="bl bl-d">69 64</span> <span class="bl bl-t">49</span> <span class="bl bl-d">01 2C</span></td><td>key: length 2 as int8 (<code>i</code>), then UTF-8 bytes; value: int16 (<code>I</code>), big-endian</td></tr> <tr><td><code>"name": "json",</code></td><td><span class="bl bl-l">69 04</span> <span class="bl bl-d">6E 61 6D 65</span> <span class="bl bl-t">53</span> <span class="bl bl-l">69 04</span> <span class="bl bl-d">6A 73 6F 6E</span></td><td>key: length 4; value: string (<code>S</code>), length 4 as int8, UTF-8 bytes</td></tr> <tr><td><code>"pi": 3.14,</code></td><td><span class="bl bl-l">69 02</span> <span class="bl bl-d">70 69</span> <span class="bl bl-t">44</span> <span class="bl bl-d">40 09 1E B8 51 EB 85 1F</span></td><td>key: length 2; value: float64 (<code>D</code>), big-endian</td></tr> <tr><td><code>"tags": [</code></td><td><span class="bl bl-l">69 04</span> <span class="bl bl-d">74 61 67 73</span> <span class="bl bl-t">5B</span></td><td>key: length 4; value: array start (<code>[</code>)</td></tr> <tr><td><code>"a",</code></td><td><span class="bl bl-t">53</span> <span class="bl bl-l">69 01</span> <span class="bl bl-d">61</span></td><td>string, length 1</td></tr> <tr><td><code>"b"</code></td><td><span class="bl bl-t">53</span> <span class="bl bl-l">69 01</span> <span class="bl bl-d">62</span></td><td>string, length 1</td></tr> <tr><td><code>]</code></td><td><span class="bl bl-t">5D</span></td><td>array end (<code>]</code>)</td></tr> <tr><td><code>}</code></td><td><span class="bl bl-t">7D</span></td><td>object end (<code>}</code>)</td></tr> </tbody></table></div> <h2 id=deserialization>Deserialization<a class=headerlink href=#deserialization title="Permanent link">¶</a></h2> <p>The library maps <abbr title="Universal Binary JSON">UBJSON</abbr> types to <abbr title="JavaScript Object Notation">JSON</abbr> value types as follows:</p> <table> <thead> <tr> <th><abbr title="Universal Binary JSON">UBJSON</abbr> type</th> <th><abbr title="JavaScript Object Notation">JSON</abbr> value type</th> <th>marker</th> </tr> </thead> <tbody> <tr> <td>no-op</td> <td><em>no value, next value is read</em></td> <td><code>N</code></td> </tr> <tr> <td>null</td> <td><code>null</code></td> <td><code>Z</code></td> </tr> <tr> <td>false</td> <td><code>false</code></td> <td><code>F</code></td> </tr> <tr> <td>true</td> <td><code>true</code></td> <td><code>T</code></td> </tr> <tr> <td>float32</td> <td>number_float</td> <td><code>d</code></td> </tr> <tr> <td>float64</td> <td>number_float</td> <td><code>D</code></td> </tr> <tr> <td>uint8</td> <td>number_unsigned</td> <td><code>U</code></td> </tr> <tr> <td>int8</td> <td>number_integer</td> <td><code>i</code></td> </tr> <tr> <td>int16</td> <td>number_integer</td> <td><code>I</code></td> </tr> <tr> <td>int32</td> <td>number_integer</td> <td><code>l</code></td> </tr> <tr> <td>int64</td> <td>number_integer</td> <td><code>L</code></td> </tr> <tr> <td>string</td> <td>string</td> <td><code>S</code></td> </tr> <tr> <td>char</td> <td>string</td> <td><code>C</code></td> </tr> <tr> <td>array</td> <td>array (optimized values are supported)</td> <td><code>[</code></td> </tr> <tr> <td>object</td> <td>object (optimized values are supported)</td> <td><code>{</code></td> </tr> </tbody> </table> <div class="admonition success"> <p class=admonition-title>Complete mapping</p> <p>The mapping is <strong>complete</strong> in the sense that any <abbr title="Universal Binary JSON">UBJSON</abbr> value can be converted to a <abbr title="JavaScript Object Notation">JSON</abbr> value.</p> </div> <div class="admonition warning"> <p class=admonition-title>Ill-formed <abbr title="Unicode Transformation Format">UTF</abbr>-8 in string values and object keys</p> <p><abbr title="Universal Binary JSON">UBJSON</abbr>'s required string encoding is <abbr title="Unicode Transformation Format">UTF</abbr>-8, but checking it on read is opt-in: with the <a href=../../../api/basic_json/from_ubjson/ ><code>error_handler</code></a> parameter left at <code>keep</code> (the default), <code>from_ubjson()</code> accepts a string value or object key whose bytes are not valid <abbr title="Unicode Transformation Format">UTF</abbr>-8 and hands them back unchanged. Passing <code>error_handler_t::strict</code> makes <code>from_ubjson()</code> check and throw <a href=.Line truncated
|
||||
</code></pre></div> </details> <h2 id=deserialization>Deserialization<a class=headerlink href=#deserialization title="Permanent link">¶</a></h2> <p>The library maps <abbr title="Universal Binary JSON">UBJSON</abbr> types to <abbr title="JavaScript Object Notation">JSON</abbr> value types as follows:</p> <table> <thead> <tr> <th><abbr title="Universal Binary JSON">UBJSON</abbr> type</th> <th><abbr title="JavaScript Object Notation">JSON</abbr> value type</th> <th>marker</th> </tr> </thead> <tbody> <tr> <td>no-op</td> <td><em>no value, next value is read</em></td> <td><code>N</code></td> </tr> <tr> <td>null</td> <td><code>null</code></td> <td><code>Z</code></td> </tr> <tr> <td>false</td> <td><code>false</code></td> <td><code>F</code></td> </tr> <tr> <td>true</td> <td><code>true</code></td> <td><code>T</code></td> </tr> <tr> <td>float32</td> <td>number_float</td> <td><code>d</code></td> </tr> <tr> <td>float64</td> <td>number_float</td> <td><code>D</code></td> </tr> <tr> <td>uint8</td> <td>number_unsigned</td> <td><code>U</code></td> </tr> <tr> <td>int8</td> <td>number_integer</td> <td><code>i</code></td> </tr> <tr> <td>int16</td> <td>number_integer</td> <td><code>I</code></td> </tr> <tr> <td>int32</td> <td>number_integer</td> <td><code>l</code></td> </tr> <tr> <td>int64</td> <td>number_integer</td> <td><code>L</code></td> </tr> <tr> <td>string</td> <td>string</td> <td><code>S</code></td> </tr> <tr> <td>char</td> <td>string</td> <td><code>C</code></td> </tr> <tr> <td>high-precision</td> <td>number_unsigned, number_integer, or number_float</td> <td><code>H</code></td> </tr> <tr> <td>array</td> <td>array (optimized values are supported)</td> <td><code>[</code></td> </tr> <tr> <td>object</td> <td>object (optimized values are supported)</td> <td><code>{</code></td> </tr> </tbody> </table> <div class="admonition info"> <p class=admonition-title>High-precision numbers</p> <p>The payload of <code>H</code> is a length-prefixed string that is parsed as a <abbr title="JavaScript Object Notation">JSON</abbr> number (surrounding whitespace is ignored). Integer text in the range of <code>number_unsigned_t</code> (non-negative) or <code>number_integer_t</code> (negative) is stored as such; any other valid number text (larger or smaller integers, fractions, and exponents such as <code>1e2</code>) is stored as <code>number_float</code>, so precision may be lost. Text that is not a valid <abbr title="JavaScript Object Notation">JSON</abbr> number raises <a href=../../../home/exceptions/#jsonexceptionparse_error115><code>parse_error.115</code></a>, a number outside the range of <code>number_float_t</code> (<code>1e999</code>) raises <a href=../../../home/exceptions/#jsonexceptionout_of_range406><code>out_of_range.406</code></a>.</p> </div> <div class="admonition success"> <p class=admonition-title>Complete mapping</p> <p>Every well-formed <abbr title="Universal Binary JSON">UBJSON</abbr> value can be converted to a <abbr title="JavaScript Object Notation">JSON</abbr> value, with these exceptions: a high-precision number outside the range of <code>number_float_t</code> (<a href=../../../home/exceptions/#jsonexceptionout_of_range406><code>out_of_range.406</code></a>), an optimized array of <code>Z</code>, <code>T</code>, or <code>F</code> with more than 1,048,576 elements, and a count that exceeds the capacity of the container (<a href=../../../home/exceptions/#jsonexceptionout_of_range408><code>out_of_range.408</code></a>). High-precision numbers that do not fit an integer type are stored as floating-point numbers and may lose precision. Ill-formed input is rejected with a parse error.</p> </div> <div class="admonition info"> <p class=admonition-title>Duplicate object keys</p> <p>If an object contains the same key more than once, the last value is kept (the <abbr title="Universal Binary JSON">UBJSON</abbr> specification does not address duplicate keys).</p> </div> <div class="admonition info"> <p class=admonition-title>Type marker of optimized containers</p> <p>The type marker after <code>$</code> must be one of <code>Z</code>, <code>N</code>, <code>T</code>, <code>F</code>, <code>i</code>, <code>U</code>, <code>I</code>, <code>l</code>, <code>L</code>, <code>d</code>, <code>D</code>, <code>H</code>, <code>C</code>, <code>S</code>, <code>[</code>, or <code>{</code>. It is checked even if the count is 0; any other marker raises <a href=../../../home/exceptions/#jsonexceptionparse_error112><code>parse_error.112</code></a>. A counted object typed <code>N</code> (<code>{$N#i1 ...</code>) is not supported.</p> </div> <div class="admonition warning"> <p class=admonition-title>Ill-formed <abbr title="Unicode Transformation Format">UTF</abbr>-8 in string values and object keys</p> <p><abbr title="Universal Binary JSON">UBJSON</abbr>'s required string encoding is <abbr title="Unicode Transformation Format">UTF</abbr>-8, but checking it on read is opt-in: with the <a href=../../../api/basic_json/from_ubjson/ ><code>error_handler</codLine truncated
|
||||
<span class=cp>#include</span><span class=w> </span><span class=cpf><iomanip></span>
|
||||
<span class=cp>#include</span><span class=w> </span><span class=cpf><nlohmann/json.hpp></span>
|
||||
|
||||
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
|
||||
<span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
|
||||
|
||||
<span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span>
|
||||
<span class=p>{</span>
|
||||
@@ -93,10 +93,10 @@
|
||||
<span class=w> </span><span class=n>json</span><span class=w> </span><span class=n>j</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>json</span><span class=o>::</span><span class=n>from_ubjson</span><span class=p>(</span><span class=n>v</span><span class=p>);</span>
|
||||
|
||||
<span class=w> </span><span class=c1>// print the deserialized JSON value</span>
|
||||
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o><<</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>setw</span><span class=p>(</span><span class=mi>2</span><span class=p>)</span><span class=w> </span><span class=o><<</span><span class=w> </span><span class=n>j</span><span class=w> </span><span class=o><<</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>endl</span><span class=p>;</span>
|
||||
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o><<</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>setw</span><span class=p>(</span><span class=mi>2</span><span class=p>)</span><span class=w> </span><span class=o><<</span><span class=w> </span><span class=n>j</span><span class=w> </span><span class=o><<</span><span class=w> </span><span class=sc>'\n'</span><span class=p>;</span>
|
||||
<span class=p>}</span>
|
||||
</code></pre></div> <p>Output:</p> <div class=highlight><pre><span></span><code><span class=p>{</span>
|
||||
<span class=w> </span><span class=nt>"compact"</span><span class=p>:</span><span class=w> </span><span class=kc>true</span><span class=p>,</span>
|
||||
<span class=w> </span><span class=nt>"schema"</span><span class=p>:</span><span class=w> </span><span class=mi>0</span>
|
||||
<span class=p>}</span>
|
||||
</code></pre></div> </details> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="October 24, 2026 15:57:44 UTC">October 24, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright © 2013-2026 Niels Lohmann </div> </div> <div class=md-social> <a href="https://github.com/nlohmann" target="_blank" rel="noopener" title="github.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 512 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - 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|
||||
</code></pre></div> </details> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="October 26, 2026 17:25:45 UTC">October 26, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright © 2013-2026 Niels Lohmann </div> </div> <div class=md-social> <a href="https://github.com/nlohmann" target="_blank" rel="noopener" title="github.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 512 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - 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|
||||
@@ -4,154 +4,11 @@ Universal Binary JSON (UBJSON) is a binary form directly imitating JSON, but req
|
||||
|
||||
References
|
||||
|
||||
- [UBJSON Website](http://ubjson.org)
|
||||
- [UBJSON Website](https://ubjson.org)
|
||||
|
||||
## Serialization
|
||||
## Byte layout
|
||||
|
||||
The library uses the following mapping from JSON values types to UBJSON types according to the UBJSON specification:
|
||||
|
||||
| JSON value type | value/range | UBJSON type | marker |
|
||||
| --------------- | ----------------------------------------- | -------------- | ------ |
|
||||
| null | `null` | null | `Z` |
|
||||
| boolean | `true` | true | `T` |
|
||||
| boolean | `false` | false | `F` |
|
||||
| number_integer | -9223372036854775808..-2147483649 | int64 | `L` |
|
||||
| number_integer | -2147483648..-32769 | int32 | `l` |
|
||||
| number_integer | -32768..-129 | int16 | `I` |
|
||||
| number_integer | -128..127 | int8 | `i` |
|
||||
| number_integer | 128..255 | uint8 | `U` |
|
||||
| number_integer | 256..32767 | int16 | `I` |
|
||||
| number_integer | 32768..2147483647 | int32 | `l` |
|
||||
| number_integer | 2147483648..9223372036854775807 | int64 | `L` |
|
||||
| number_unsigned | 0..127 | int8 | `i` |
|
||||
| number_unsigned | 128..255 | uint8 | `U` |
|
||||
| number_unsigned | 256..32767 | int16 | `I` |
|
||||
| number_unsigned | 32768..2147483647 | int32 | `l` |
|
||||
| number_unsigned | 2147483648..9223372036854775807 | int64 | `L` |
|
||||
| number_unsigned | 9223372036854775808..18446744073709551615 | high-precision | `H` |
|
||||
| number_float | *any value* | float64 | `D` |
|
||||
| string | *with shortest length indicator* | string | `S` |
|
||||
| array | *see notes on optimized format* | array | `[` |
|
||||
| object | *see notes on optimized format* | map | `{` |
|
||||
|
||||
Complete mapping
|
||||
|
||||
The mapping is **complete** in the sense that any JSON value type can be converted to a UBJSON value.
|
||||
|
||||
Any UBJSON output created by `to_ubjson` can be successfully parsed by `from_ubjson`.
|
||||
|
||||
Size constraints
|
||||
|
||||
The following values can **not** be converted to a UBJSON value:
|
||||
|
||||
- strings with more than 9223372036854775807 bytes (theoretical)
|
||||
|
||||
UTF-8 validation of string values and object keys
|
||||
|
||||
UBJSON's required string encoding is UTF-8. By default (the [`error_handler`](https://json.nlohmann.me/api/basic_json/to_ubjson/index.md) parameter left at `keep`), `to_ubjson()` writes the bytes of string values and object keys unchanged, even if they are not valid UTF-8. With `error_handler_t::strict`, it throws [`type_error.316`](https://json.nlohmann.me/home/exceptions/#jsonexceptiontype_error316) for ill-formed UTF-8 instead; `replace`/`ignore` sanitize the string. [`JSON_STRICT_BINARY_UTF8`](https://json.nlohmann.me/api/macros/json_strict_binary_utf8/index.md) makes `strict` the default.
|
||||
|
||||
Unused UBJSON markers
|
||||
|
||||
The following markers are not used in the conversion:
|
||||
|
||||
- `Z`: no-op values are not created.
|
||||
- `C`: single-byte strings are serialized with `S` markers.
|
||||
|
||||
NaN/infinity handling
|
||||
|
||||
If NaN or Infinity are stored inside a JSON number, they are serialized properly. This behavior differs from the [`dump()`](https://json.nlohmann.me/api/basic_json/dump/index.md) function which serializes NaN or Infinity to `null`.
|
||||
|
||||
Optimized formats
|
||||
|
||||
The optimized formats for containers are supported: Parameter `use_size` adds size information to the beginning of a container and removes the closing marker. Parameter `use_type` further checks whether all elements of a container have the same type and adds the type marker to the beginning of the container. The `use_type` parameter must only be used together with `use_size = true`.
|
||||
|
||||
Note that `use_size = true` alone may result in larger representations - the benefit of this parameter is that the receiving side is immediately informed on the number of elements of the container.
|
||||
|
||||
An array whose type marker is `Z` (null), `T` (true) or `F` (false) stores no payload at all, because the marker already is the value. Its declared count is therefore the only thing that decides how much memory the receiving side allocates, and a handful of bytes can describe billions of elements. `from_ubjson` rejects such an array with [`out_of_range.408`](https://json.nlohmann.me/home/exceptions/#jsonexceptionout_of_range408) when the count exceeds 1,048,576 (`1 << 20`), and `to_ubjson` writes longer arrays of these types without the annotation, so any value it produces can be read back.
|
||||
|
||||
Binary values
|
||||
|
||||
If the JSON data contains the binary type, the value stored is a list of integers, as suggested by the UBJSON documentation. In particular, this means that serialization and the deserialization of a JSON containing binary values into UBJSON and back will result in a different JSON object.
|
||||
|
||||
Example: serialize JSON values to UBJSON, with and without size/type optimization
|
||||
|
||||
```
|
||||
#include <iostream>
|
||||
#include <iomanip>
|
||||
#include <nlohmann/json.hpp>
|
||||
|
||||
using json = nlohmann::json;
|
||||
using namespace nlohmann::literals;
|
||||
|
||||
// function to print UBJSON's diagnostic format
|
||||
void print_byte(uint8_t byte)
|
||||
{
|
||||
if (32 < byte and byte < 128)
|
||||
{
|
||||
std::cout << (char)byte;
|
||||
}
|
||||
else
|
||||
{
|
||||
std::cout << (int)byte;
|
||||
}
|
||||
}
|
||||
|
||||
int main()
|
||||
{
|
||||
// create a JSON value
|
||||
json j = R"({"compact": true, "schema": false})"_json;
|
||||
|
||||
// serialize it to UBJSON
|
||||
std::vector<std::uint8_t> v = json::to_ubjson(j);
|
||||
|
||||
// print the vector content
|
||||
for (auto& byte : v)
|
||||
{
|
||||
print_byte(byte);
|
||||
}
|
||||
std::cout << std::endl;
|
||||
|
||||
// create an array of numbers
|
||||
json array = {1, 2, 3, 4, 5, 6, 7, 8};
|
||||
|
||||
// serialize it to UBJSON using default representation
|
||||
std::vector<std::uint8_t> v_array = json::to_ubjson(array);
|
||||
// serialize it to UBJSON using size optimization
|
||||
std::vector<std::uint8_t> v_array_size = json::to_ubjson(array, true);
|
||||
// serialize it to UBJSON using type optimization
|
||||
std::vector<std::uint8_t> v_array_size_and_type = json::to_ubjson(array, true, true);
|
||||
|
||||
// print the vector contents
|
||||
for (auto& byte : v_array)
|
||||
{
|
||||
print_byte(byte);
|
||||
}
|
||||
std::cout << std::endl;
|
||||
|
||||
for (auto& byte : v_array_size)
|
||||
{
|
||||
print_byte(byte);
|
||||
}
|
||||
std::cout << std::endl;
|
||||
|
||||
for (auto& byte : v_array_size_and_type)
|
||||
{
|
||||
print_byte(byte);
|
||||
}
|
||||
std::cout << std::endl;
|
||||
}
|
||||
```
|
||||
|
||||
Output:
|
||||
|
||||
```
|
||||
{i7compactTi6schemaF}
|
||||
[i1i2i3i4i5i6i7i8]
|
||||
[#i8i1i2i3i4i5i6i7i8
|
||||
[$i#i812345678
|
||||
```
|
||||
|
||||
### Byte layout
|
||||
UBJSON is built from just a one-byte, human-readable ASCII *type marker* (for example, `i` for int8, `S` for string, `[` for array) followed by the payload of that type. Strings and the like are prefixed with their length, which is itself a UBJSON integer value including its marker. Numbers are stored in big-endian byte order. Containers can be written in two ways: as an *unoptimized* container that is opened with `[` or `{` and closed with `]` or `}`, or as an *optimized* container that declares a count (`#`) after the opening marker, optionally preceded by an element type (`$`); an element type is only allowed together with a count. An optimized container saves the closing marker and, with a type, the per-element markers.
|
||||
|
||||
Consider the following JSON value (shown formatted for readability):
|
||||
|
||||
@@ -181,31 +38,191 @@ Consider the following JSON value (shown formatted for readability):
|
||||
| `]` | 5D | array end (`]`) |
|
||||
| `}` | 7D | object end (`}`) |
|
||||
|
||||
## Serialization
|
||||
|
||||
The library uses the following mapping from JSON values types to UBJSON types according to the UBJSON specification:
|
||||
|
||||
| JSON value type | value/range | UBJSON type | marker |
|
||||
| --------------- | ----------------------------------------- | ------------------------------------------------ | --------- |
|
||||
| null | `null` | null | `Z` |
|
||||
| boolean | `true` | true | `T` |
|
||||
| boolean | `false` | false | `F` |
|
||||
| number_integer | -9223372036854775808..-2147483649 | int64 | `L` |
|
||||
| number_integer | -2147483648..-32769 | int32 | `l` |
|
||||
| number_integer | -32768..-129 | int16 | `I` |
|
||||
| number_integer | -128..127 | int8 | `i` |
|
||||
| number_integer | 128..255 | uint8 | `U` |
|
||||
| number_integer | 256..32767 | int16 | `I` |
|
||||
| number_integer | 32768..2147483647 | int32 | `l` |
|
||||
| number_integer | 2147483648..9223372036854775807 | int64 | `L` |
|
||||
| number_unsigned | 0..127 | int8 | `i` |
|
||||
| number_unsigned | 128..255 | uint8 | `U` |
|
||||
| number_unsigned | 256..32767 | int16 | `I` |
|
||||
| number_unsigned | 32768..2147483647 | int32 | `l` |
|
||||
| number_unsigned | 2147483648..9223372036854775807 | int64 | `L` |
|
||||
| number_unsigned | 9223372036854775808..18446744073709551615 | high-precision | `H` |
|
||||
| number_float | *any value* | float64 (float32 if `number_float_t` is `float`) | `D` (`d`) |
|
||||
| string | *with shortest length indicator* | string | `S` |
|
||||
| array | *see notes on optimized format* | array | `[` |
|
||||
| object | *see notes on optimized format* | object | `{` |
|
||||
|
||||
Complete mapping
|
||||
|
||||
The mapping is **complete** in the sense that any JSON value type can be converted to a UBJSON value.
|
||||
|
||||
Any UBJSON output created by `to_ubjson` can be successfully parsed by `from_ubjson`.
|
||||
|
||||
Size constraints
|
||||
|
||||
The following values can **not** be converted to a UBJSON value:
|
||||
|
||||
- strings with more than 9223372036854775807 bytes (theoretical)
|
||||
|
||||
UTF-8 validation of string values and object keys
|
||||
|
||||
UBJSON's required string encoding is UTF-8. By default (the [`error_handler`](https://json.nlohmann.me/api/basic_json/to_ubjson/index.md) parameter left at `keep`), `to_ubjson()` writes the bytes of string values and object keys unchanged, even if they are not valid UTF-8. With `error_handler_t::strict`, it throws [`type_error.316`](https://json.nlohmann.me/home/exceptions/#jsonexceptiontype_error316) for ill-formed UTF-8 instead; `replace`/`ignore` sanitize the string. [`JSON_STRICT_BINARY_UTF8`](https://json.nlohmann.me/api/macros/json_strict_binary_utf8/index.md) makes `strict` the default.
|
||||
|
||||
Unused UBJSON markers
|
||||
|
||||
The following markers are not used in the conversion:
|
||||
|
||||
- `N`: no-op values are never written (they are skipped when reading).
|
||||
- `C`: single-byte strings are serialized with `S` markers.
|
||||
|
||||
NaN/infinity handling
|
||||
|
||||
NaN and infinity are written as IEEE 754 float64 values (`D`) and read back unchanged. This differs from [`dump()`](https://json.nlohmann.me/api/basic_json/dump/index.md), which serializes them to `null`, and from the UBJSON specification, which encodes infinity as `null` (it does not mention NaN); other UBJSON readers may therefore not accept these values.
|
||||
|
||||
Optimized formats
|
||||
|
||||
The optimized formats for containers are supported: Parameter `use_size` adds size information to the beginning of a container and removes the closing marker. Parameter `use_type` further checks whether all elements of a container have the same type and adds the type marker to the beginning of the container. The `use_type` parameter must only be used together with `use_size = true`: combining `use_type` with `use_size = false` throws [`other_error.502`](https://json.nlohmann.me/home/exceptions/#jsonexceptionother_error502) if the value contains a non-empty array, object, or binary value.
|
||||
|
||||
Two elements have the same type if they are written with the same type marker. For example, `[1, 2]` is written with the type `i`, but `[1, 200]` (`i`, `U`), `[true, false]` (`T`, `F`), and `[1, 2.5]` (`i`, `D`) are not; an empty container is never given a `$` annotation of its own (an array of empty arrays is still typed `[`).
|
||||
|
||||
Note that `use_size = true` alone may result in larger representations - the benefit of this parameter is that the receiving side is immediately informed on the number of elements of the container.
|
||||
|
||||
An array whose type marker is `Z` (null), `T` (true) or `F` (false) stores no payload at all, because the marker already is the value. Its declared count is therefore the only thing that decides how much memory the receiving side allocates, and a handful of bytes can describe billions of elements. `from_ubjson` rejects such an array with [`out_of_range.408`](https://json.nlohmann.me/home/exceptions/#jsonexceptionout_of_range408) when the count exceeds 1,048,576 (`1 << 20`), and `to_ubjson` writes longer arrays of these types in the counted but untyped form: the `$` type marker is dropped, the `#` count is kept, and every element is written with its own marker (`[#l 1048577 Z Z ...`), so any value it produces can be read back. Objects and untyped counted arrays are not subject to this limit.
|
||||
|
||||
Binary values
|
||||
|
||||
If the JSON data contains the binary type, the value stored is a list of integers, as suggested by the UBJSON documentation. In particular, this means that serialization and the deserialization of a JSON containing binary values into UBJSON and back will result in a different JSON object.
|
||||
|
||||
Example: serialize JSON values to UBJSON, with and without size/type optimization
|
||||
|
||||
```
|
||||
#include <iostream>
|
||||
#include <iomanip>
|
||||
#include <nlohmann/json.hpp>
|
||||
|
||||
using nlohmann::json;
|
||||
using namespace nlohmann::literals;
|
||||
|
||||
// function to print UBJSON's diagnostic format
|
||||
void print_byte(uint8_t byte)
|
||||
{
|
||||
if (32 < byte and byte < 128)
|
||||
{
|
||||
std::cout << static_cast<char>(byte);
|
||||
}
|
||||
else
|
||||
{
|
||||
std::cout << static_cast<int>(byte);
|
||||
}
|
||||
}
|
||||
|
||||
int main()
|
||||
{
|
||||
// create a JSON value
|
||||
json j = R"({"compact": true, "schema": false})"_json;
|
||||
|
||||
// serialize it to UBJSON
|
||||
std::vector<std::uint8_t> v = json::to_ubjson(j);
|
||||
|
||||
// print the vector content
|
||||
for (auto& byte : v)
|
||||
{
|
||||
print_byte(byte);
|
||||
}
|
||||
std::cout << '\n';
|
||||
|
||||
// create an array of numbers
|
||||
json array = {1, 2, 3, 4, 5, 6, 7, 8};
|
||||
|
||||
// serialize it to UBJSON using default representation
|
||||
std::vector<std::uint8_t> v_array = json::to_ubjson(array);
|
||||
// serialize it to UBJSON using size optimization
|
||||
std::vector<std::uint8_t> v_array_size = json::to_ubjson(array, true);
|
||||
// serialize it to UBJSON using type optimization
|
||||
std::vector<std::uint8_t> v_array_size_and_type = json::to_ubjson(array, true, true);
|
||||
|
||||
// print the vector contents
|
||||
for (auto& byte : v_array)
|
||||
{
|
||||
print_byte(byte);
|
||||
}
|
||||
std::cout << '\n';
|
||||
|
||||
for (auto& byte : v_array_size)
|
||||
{
|
||||
print_byte(byte);
|
||||
}
|
||||
std::cout << '\n';
|
||||
|
||||
for (auto& byte : v_array_size_and_type)
|
||||
{
|
||||
print_byte(byte);
|
||||
}
|
||||
std::cout << '\n';
|
||||
}
|
||||
```
|
||||
|
||||
Output:
|
||||
|
||||
```
|
||||
{i7compactTi6schemaF}
|
||||
[i1i2i3i4i5i6i7i8]
|
||||
[#i8i1i2i3i4i5i6i7i8
|
||||
[$i#i812345678
|
||||
```
|
||||
|
||||
## Deserialization
|
||||
|
||||
The library maps UBJSON types to JSON value types as follows:
|
||||
|
||||
| UBJSON type | JSON value type | marker |
|
||||
| ----------- | --------------------------------------- | ------ |
|
||||
| no-op | *no value, next value is read* | `N` |
|
||||
| null | `null` | `Z` |
|
||||
| false | `false` | `F` |
|
||||
| true | `true` | `T` |
|
||||
| float32 | number_float | `d` |
|
||||
| float64 | number_float | `D` |
|
||||
| uint8 | number_unsigned | `U` |
|
||||
| int8 | number_integer | `i` |
|
||||
| int16 | number_integer | `I` |
|
||||
| int32 | number_integer | `l` |
|
||||
| int64 | number_integer | `L` |
|
||||
| string | string | `S` |
|
||||
| char | string | `C` |
|
||||
| array | array (optimized values are supported) | `[` |
|
||||
| object | object (optimized values are supported) | `{` |
|
||||
| UBJSON type | JSON value type | marker |
|
||||
| -------------- | ------------------------------------------------ | ------ |
|
||||
| no-op | *no value, next value is read* | `N` |
|
||||
| null | `null` | `Z` |
|
||||
| false | `false` | `F` |
|
||||
| true | `true` | `T` |
|
||||
| float32 | number_float | `d` |
|
||||
| float64 | number_float | `D` |
|
||||
| uint8 | number_unsigned | `U` |
|
||||
| int8 | number_integer | `i` |
|
||||
| int16 | number_integer | `I` |
|
||||
| int32 | number_integer | `l` |
|
||||
| int64 | number_integer | `L` |
|
||||
| string | string | `S` |
|
||||
| char | string | `C` |
|
||||
| high-precision | number_unsigned, number_integer, or number_float | `H` |
|
||||
| array | array (optimized values are supported) | `[` |
|
||||
| object | object (optimized values are supported) | `{` |
|
||||
|
||||
High-precision numbers
|
||||
|
||||
The payload of `H` is a length-prefixed string that is parsed as a JSON number (surrounding whitespace is ignored). Integer text in the range of `number_unsigned_t` (non-negative) or `number_integer_t` (negative) is stored as such; any other valid number text (larger or smaller integers, fractions, and exponents such as `1e2`) is stored as `number_float`, so precision may be lost. Text that is not a valid JSON number raises [`parse_error.115`](https://json.nlohmann.me/home/exceptions/#jsonexceptionparse_error115), a number outside the range of `number_float_t` (`1e999`) raises [`out_of_range.406`](https://json.nlohmann.me/home/exceptions/#jsonexceptionout_of_range406).
|
||||
|
||||
Complete mapping
|
||||
|
||||
The mapping is **complete** in the sense that any UBJSON value can be converted to a JSON value.
|
||||
Every well-formed UBJSON value can be converted to a JSON value, with these exceptions: a high-precision number outside the range of `number_float_t` ([`out_of_range.406`](https://json.nlohmann.me/home/exceptions/#jsonexceptionout_of_range406)), an optimized array of `Z`, `T`, or `F` with more than 1,048,576 elements, and a count that exceeds the capacity of the container ([`out_of_range.408`](https://json.nlohmann.me/home/exceptions/#jsonexceptionout_of_range408)). High-precision numbers that do not fit an integer type are stored as floating-point numbers and may lose precision. Ill-formed input is rejected with a parse error.
|
||||
|
||||
Duplicate object keys
|
||||
|
||||
If an object contains the same key more than once, the last value is kept (the UBJSON specification does not address duplicate keys).
|
||||
|
||||
Type marker of optimized containers
|
||||
|
||||
The type marker after `$` must be one of `Z`, `N`, `T`, `F`, `i`, `U`, `I`, `l`, `L`, `d`, `D`, `H`, `C`, `S`, `[`, or `{`. It is checked even if the count is 0; any other marker raises [`parse_error.112`](https://json.nlohmann.me/home/exceptions/#jsonexceptionparse_error112). A counted object typed `N` (`{$N#i1 ...`) is not supported.
|
||||
|
||||
Ill-formed UTF-8 in string values and object keys
|
||||
|
||||
@@ -218,7 +235,7 @@ Example: deserialize a JSON value from UBJSON
|
||||
#include <iomanip>
|
||||
#include <nlohmann/json.hpp>
|
||||
|
||||
using json = nlohmann::json;
|
||||
using nlohmann::json;
|
||||
|
||||
int main()
|
||||
{
|
||||
@@ -232,7 +249,7 @@ int main()
|
||||
json j = json::from_ubjson(v);
|
||||
|
||||
// print the deserialized JSON value
|
||||
std::cout << std::setw(2) << j << std::endl;
|
||||
std::cout << std::setw(2) << j << '\n';
|
||||
}
|
||||
```
|
||||
|
||||
|
||||
Reference in new issue
Block a user