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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/bson/" rel="canonical"><link href=../bon8/ rel=prev><link href=../cbor/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>BSON - 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=#bson 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> BSON </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> </label> <div class=md-search dLine truncated
<!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/bson/" rel="canonical"><link href=../bon8/ rel=prev><link href=../cbor/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>BSON - 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=#bson 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> BSON </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> </label> <div class=md-search dLine truncated
<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_bson</code> encodes it to 69 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-l">45 00 00 00</span></td><td>document size: 69 bytes (int32, little-endian)</td></tr> <tr><td><code>&quot;id&quot;: 300,</code></td><td><span class="bl bl-t">10</span> <span class="bl bl-d">69 64 00</span> <span class="bl bl-d">2C 01 00 00</span></td><td>int32 element; key as NUL-terminated string; value (little-endian)</td></tr> <tr><td><code>&quot;name&quot;: &quot;json&quot;,</code></td><td><span class="bl bl-t">02</span> <span class="bl bl-d">6E 61 6D 65 00</span> <span class="bl bl-l">05 00 00 00</span> <span class="bl bl-d">6A 73 6F 6E 00</span></td><td>string element; key; length incl. NUL (int32); NUL-terminated UTF-8 bytes</td></tr> <tr><td><code>&quot;pi&quot;: 3.14,</code></td><td><span class="bl bl-t">01</span> <span class="bl bl-d">70 69 00</span> <span class="bl bl-d">1F 85 EB 51 B8 1E 09 40</span></td><td>double element; key; value (little-endian)</td></tr> <tr><td><code>&quot;tags&quot;: [</code></td><td><span class="bl bl-t">04</span> <span class="bl bl-d">74 61 67 73 00</span> <span class="bl bl-l">17 00 00 00</span></td><td>array element; key; embedded document of 23 bytes (keys are the indices)</td></tr> <tr><td><code>&quot;a&quot;,</code></td><td><span class="bl bl-t">02</span> <span class="bl bl-d">30 00</span> <span class="bl bl-l">02 00 00 00</span> <span class="bl bl-d">61 00</span></td><td>string element; key <code>&quot;0&quot;</code>; length 2; <code>a</code> + NUL</td></tr> <tr><td><code>&quot;b&quot;</code></td><td><span class="bl bl-t">02</span> <span class="bl bl-d">31 00</span> <span class="bl bl-l">02 00 00 00</span> <span class="bl bl-d">62 00</span></td><td>string element; key <code>&quot;1&quot;</code>; length 2; <code>b</code> + NUL</td></tr> <tr><td><code>]</code></td><td><span class="bl bl-t">00</span></td><td>end of the array document</td></tr> <tr><td><code>}</code></td><td><span class="bl bl-t">00</span></td><td>end of the document</td></tr> </tbody></table></div> <h2 id=serialization>Serialization<a class=headerlink href=#serialization title="Permanent link">&para;</a></h2> <p>The library uses the following mapping from <abbr title="JavaScript Object Notation">JSON</abbr> values types to <abbr title="Binary JSON">BSON</abbr> types:</p> <table> <thead> <tr> <th><abbr title="JavaScript Object Notation">JSON</abbr> value type</th> <th>value/range</th> <th><abbr title="Binary JSON">BSON</abbr> type</th> <th>marker</th> </tr> </thead> <tbody> <tr> <td>null</td> <td><code>null</code></td> <td>null</td> <td>0x0A</td> </tr> <tr> <td>boolean</td> <td><code>true</code>, <code>false</code></td> <td>boolean</td> <td>0x08</td> </tr> <tr> <td>number_integer</td> <td>-9223372036854775808..-2147483649</td> <td>int64</td> <td>0x12</td> </tr> <tr> <td>number_integer</td> <td>-2147483648..2147483647</td> <td>int32</td> <td>0x10</td> </tr> <tr> <td>number_integer</td> <td>2147483648..9223372036854775807</td> <td>int64</td> <td>0x12</td> </tr> <tr> <td>number_unsigned</td> <td>0..2147483647</td> <td>int32</td> <td>0x10</td> </tr> <tr> <td>number_unsigned</td> <td>2147483648..9223372036854775807</td> <td>int64</td> <td>0x12</td> </tr> <tr> <td>number_unsigned</td> <td>9223372036854775808..18446744073709551615</td> <td>uint64</td> <td>0x11</td> </tr> <tr> <td>number_float</td> <td><em>any value</em></td> <td>double</td> <td>0x01</td> </tr> <tr> <td>string</td> <td><em>any value</em></td> <td>string</td> <td>0x02</td> </tr> <tr> <td>array</td> <td><em>any value</em></td> <td>document</td> <td>0x04</td> </tr> <tr> <td>object</td> <td><em>any value</em></td> <td>document</td> <td>0x03</td> </tr> <tr> <td>binary</td> <td><em>any value</em></td> <td>binary</td> <td>0x05</td> </tr> </tbody> </table> <div class="admonition warning"> <p class=admonition-title>Incomplete mapping</p> <p>The mapping is <strong>incomplete</strong>, since only <abbr title="JavaScript Object Notation">JSON</abbr>-objects (and things contained therein) can be serialized to <abbr title="Binary JSON">BSON</abbr>. Also, keys may not contain U+0000, since they are serialized as zero-terminated C strings.</p> </div> <div class="admonition info"> <p class=admonition-title>Order of object members</p> <p>The members of an object are written in the order in which iteration visits them: sorted by key for <a href=../../../api/json/ ><code>json</code></a>, in insertion order for <a href=../../../api/ordered_json/ ><code>ordered_json</code></a>.</p> </div> <div class="admonition warning"> <p class=admonition-title><abbr title="Binary JSON">BSON</abbr> type 0x11 interoperabilitLine truncated
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iomanip&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</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=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>
<span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span>
@@ -16,25 +25,16 @@
<span class=w> </span><span class=c1>// print the vector content</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>&amp;</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</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>&lt;&lt;</span><span class=w> </span><span class=s>"0x"</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>hex</span><span class=w> </span><span class=o>&lt;&lt;</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>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>setfill</span><span class=p>(</span><span class=sc>'0'</span><span class=p>)</span><span class=w> </span><span class=o>&lt;&lt;</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=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>" "</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>&lt;&lt;</span><span class=w> </span><span class=s>"0x"</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>hex</span><span class=w> </span><span class=o>&lt;&lt;</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>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>setfill</span><span class=p>(</span><span class=sc>'0'</span><span class=p>)</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=k>static_cast</span><span class=o>&lt;</span><span class=kt>int</span><span class=o>&gt;</span><span class=p>(</span><span class=kt>byte</span><span class=p>)</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>" "</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>&lt;&lt;</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>&lt;&lt;</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=mh>0x1b</span><span class=w> </span><span class=mh>0x00</span><span class=w> </span><span class=mh>0x00</span><span class=w> </span><span class=mh>0x00</span><span class=w> </span><span class=mh>0x08</span><span class=w> </span><span class=mh>0x63</span><span class=w> </span><span class=mh>0x6f</span><span class=w> </span><span class=mh>0x6d</span><span class=w> </span><span class=mh>0x70</span><span class=w> </span><span class=mh>0x61</span><span class=w> </span><span class=mh>0x63</span><span class=w> </span><span class=mh>0x74</span><span class=w> </span><span class=mh>0x00</span><span class=w> </span><span class=mh>0x01</span><span class=w> </span><span class=mh>0x10</span><span class=w> </span><span class=mh>0x73</span><span class=w> </span><span class=mh>0x63</span><span class=w> </span><span class=mh>0x68</span><span class=w> </span><span class=mh>0x65</span><span class=w> </span><span class=mh>0x6d</span><span class=w> </span><span class=mh>0x61</span><span class=w> </span><span class=mh>0x00</span><span class=w> </span><span class=mh>0x00</span><span class=w> </span><span class=mh>0x00</span><span class=w> </span><span class=mh>0x00</span><span class=w> </span><span class=mh>0x00</span><span class=w> </span><span class=mh>0x00</span><span class=w> </span>
</code></pre></div> </details> <h3 id=byte-layout>Byte layout<a class=headerlink href=#byte-layout title="Permanent link">&para;</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_bson</code> encodes it to 69 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-l">45 00 00 00</span></td><td>document size: 69 bytes (int32, little-endian)</td></tr> <tr><td><code>&quot;id&quot;: 300,</code></td><td><span class="bl bl-t">10</span> <span class="bl bl-d">69 64 00</span> <span class="bl bl-d">2C 01 00 00</span></td><td>int32 element; key as NUL-terminated string; value (little-endian)</td></tr> <tr><td><code>&quot;name&quot;: &quot;json&quot;,</code></td><td><span class="bl bl-t">02</span> <span class="bl bl-d">6E 61 6D 65 00</span> <span class="bl bl-l">05 00 00 00</span> <span class="bl bl-d">6A 73 6F 6E 00</span></td><td>string element; key; length incl. NUL (int32); NUL-terminated UTF-8 bytes</td></tr> <tr><td><code>&quot;pi&quot;: 3.14,</code></td><td><span class="bl bl-t">01</span> <span class="bl bl-d">70 69 00</span> <span class="bl bl-d">1F 85 EB 51 B8 1E 09 40</span></td><td>double element; key; value (little-endian)</td></tr> <tr><td><code>&quot;tags&quot;: [</code></td><td><span class="bl bl-t">04</span> <span class="bl bl-d">74 61 67 73 00</span> <span class="bl bl-l">17 00 00 00</span></td><td>array element; key; embedded document of 23 bytes (keys are the indices)</td></tr> <tr><td><code>&quot;a&quot;,</code></td><td><span class="bl bl-t">02</span> <span class="bl bl-d">30 00</span> <span class="bl bl-l">02 00 00 00</span> <span class="bl bl-d">61 00</span></td><td>string element; key <code>&quot;0&quot;</code>; length 2; <code>a</code> + NUL</td></tr> <tr><td><code>&quot;b&quot;</code></td><td><span class="bl bl-t">02</span> <span class="bl bl-d">31 00</span> <span class="bl bl-l">02 00 00 00</span> <span class="bl bl-d">62 00</span></td><td>string element; key <code>&quot;1&quot;</code>; length 2; <code>b</code> + NUL</td></tr> <tr><td><code>]</code></td><td><span class="bl bl-t">00</span></td><td>end of the array document</td></tr> <tr><td><code>}</code></td><td><span class="bl bl-t">00</span></td><td>end of the document</td></tr> </tbody></table></div> <h2 id=deserialization>Deserialization<a class=headerlink href=#deserialization title="Permanent link">&para;</a></h2> <p>The library maps <abbr title="Binary JSON">BSON</abbr> record types to <abbr title="JavaScript Object Notation">JSON</abbr> value types as follows:</p> <table> <thead> <tr> <th><abbr title="Binary JSON">BSON</abbr> type</th> <th><abbr title="Binary JSON">BSON</abbr> marker byte</th> <th><abbr title="JavaScript Object Notation">JSON</abbr> value type</th> </tr> </thead> <tbody> <tr> <td>double</td> <td>0x01</td> <td>number_float</td> </tr> <tr> <td>string</td> <td>0x02</td> <td>string</td> </tr> <tr> <td>document</td> <td>0x03</td> <td>object</td> </tr> <tr> <td>array</td> <td>0x04</td> <td>array</td> </tr> <tr> <td>binary</td> <td>0x05</td> <td>binary</td> </tr> <tr> <td>undefined</td> <td>0x06</td> <td><em>unsupported</em></td> </tr> <tr> <td>ObjectId</td> <td>0x07</td> <td><em>unsupported</em></td> </tr> <tr> <td>boolean</td> <td>0x08</td> <td>boolean</td> </tr> <tr> <td>UTC Date-Time</td> <td>0x09</td> <td><em>unsupported</em></td> </tr> <tr> <td>null</td> <td>0x0A</td> <td>null</td> </tr> <tr> <td>Regular Expr.</td> <td>0x0B</td> <td><em>unsupported</em></td> </tr> <tr> <td>DB Pointer</td> <td>0x0C</td> <td><em>unsupported</em></td> </tr> <tr> <td>JavaScript Code</td> <td>0x0D</td> <td><em>unsupported</em></td> </tr> <tr> <td>Symbol</td> <td>0x0E</td> <td><em>unsupported</em></td> </tr> <tr> <td>JavaScript Code w/ scope</td> <td>0x0F</td> <td><em>unsupported</em></td> </tr> <tr> <td>int32</td> <td>0x10</td> <td>number_integer</td> </tr> <tr> <td>uint64(Timestamp)</td> <td>0x11</td> <td>number_unsigned</td> </tr> <tr> <td>int64</td> <td>0x12</td> <td>number_integer</td> </tr> <tr> <td>128-bit decimal float</td> <td>0x13</td> <td><em>unsupported</em></td> </tr> <tr> <td>Max Key</td> <td>0x7F</td> <td><em>unsupported</em></td> </tr> <tr> <td>Min Key</td> <td>0xFF</td> <td><em>unsupported</em></td> </tr> </tbody> </table> <div class="admonition warning"> <p class=admonition-title>Incomplete mapping</p> <p>The mapping is <strong>incomplete</strong>. The unsupported mappings are indicated in the table above.</p> </div> <div class="admonition note"> <p class=admonition-title>Handling of <abbr title="Binary JSON">BSON</abbr> type 0x11</p> <p>This library deserializes <abbr title="Binary JSON">BSON</abbr> type <code>0x11</code> (Timestamp) as a <code>number_unsigned</code> value. The 64-bit value is preserved, but the Timestamp type information is not.</p> </div> <div class="admonition warning"> <p class=admonition-title>Lenient <abbr tLine truncated
</code></pre></div> </details> <h2 id=deserialization>Deserialization<a class=headerlink href=#deserialization title="Permanent link">&para;</a></h2> <p>The library maps <abbr title="Binary JSON">BSON</abbr> record types to <abbr title="JavaScript Object Notation">JSON</abbr> value types as follows:</p> <table> <thead> <tr> <th><abbr title="Binary JSON">BSON</abbr> type</th> <th><abbr title="Binary JSON">BSON</abbr> marker byte</th> <th><abbr title="JavaScript Object Notation">JSON</abbr> value type</th> </tr> </thead> <tbody> <tr> <td>double</td> <td>0x01</td> <td>number_float</td> </tr> <tr> <td>string</td> <td>0x02</td> <td>string</td> </tr> <tr> <td>document</td> <td>0x03</td> <td>object</td> </tr> <tr> <td>array</td> <td>0x04</td> <td>array</td> </tr> <tr> <td>binary</td> <td>0x05</td> <td>binary</td> </tr> <tr> <td>undefined</td> <td>0x06</td> <td><em>unsupported</em></td> </tr> <tr> <td>ObjectId</td> <td>0x07</td> <td><em>unsupported</em></td> </tr> <tr> <td>boolean</td> <td>0x08</td> <td>boolean</td> </tr> <tr> <td>UTC Date-Time</td> <td>0x09</td> <td><em>unsupported</em></td> </tr> <tr> <td>null</td> <td>0x0A</td> <td>null</td> </tr> <tr> <td>Regular Expr.</td> <td>0x0B</td> <td><em>unsupported</em></td> </tr> <tr> <td>DB Pointer</td> <td>0x0C</td> <td><em>unsupported</em></td> </tr> <tr> <td>JavaScript Code</td> <td>0x0D</td> <td><em>unsupported</em></td> </tr> <tr> <td>Symbol</td> <td>0x0E</td> <td><em>unsupported</em></td> </tr> <tr> <td>JavaScript Code w/ scope</td> <td>0x0F</td> <td><em>unsupported</em></td> </tr> <tr> <td>int32</td> <td>0x10</td> <td>number_integer</td> </tr> <tr> <td>uint64(Timestamp)</td> <td>0x11</td> <td>number_unsigned</td> </tr> <tr> <td>int64</td> <td>0x12</td> <td>number_integer</td> </tr> <tr> <td>128-bit decimal float</td> <td>0x13</td> <td><em>unsupported</em></td> </tr> <tr> <td>Max Key</td> <td>0x7F</td> <td><em>unsupported</em></td> </tr> <tr> <td>Min Key</td> <td>0xFF</td> <td><em>unsupported</em></td> </tr> </tbody> </table> <div class="admonition warning"> <p class=admonition-title>Incomplete mapping</p> <p>The mapping is <strong>incomplete</strong>. The unsupported mappings are indicated in the table above.</p> </div> <div class="admonition note"> <p class=admonition-title>Handling of <abbr title="Binary JSON">BSON</abbr> type 0x11</p> <p>This library deserializes <abbr title="Binary JSON">BSON</abbr> type <code>0x11</code> (Timestamp) as a <code>number_unsigned</code> value. The 64-bit value is preserved, but the Timestamp type information is not.</p> </div> <div class="admonition warning"> <p class=admonition-title>Lenient <abbr title="Binary JSON">BSON</abbr> input handling</p> <p>The <abbr title="Binary JSON">BSON</abbr> reader is lenient in a few areas where the <abbr title="Binary JSON">BSON</abbr> specification is more restrictive:</p> <ul> <li>array element keys are not checked against the required decimal sequence (<code>0</code>, <code>1</code>, <code>2</code>, ...),</li> <li>any non-zero byte is accepted as <code>true</code> for the boolean type,</li> <li>the payloads of the binary subtypes <code>0x03</code> (UUID, old), <code>0x04</code> (UUID), and <code>0x05</code> (MD5) are not checked to have 16 bytes,</li> <li>duplicate keys within a document are accepted; the last value wins (<code>{"a": 1, "a": 2}</code> is read as <code>{"a": 2}</code>), while a <abbr title="Simple API for XML">SAX</abbr> handler receives every occurrence,</li> <li>a <code>string</code> value may contain embedded <code>0x00</code> bytes, and</li> <li>with <code>strict</code> set to <code>false</code>, bytes after the end of the document are ignored.</li> </ul> <p>If <abbr title="Binary JSON">BSON</abbr> input must be validated for strict specification compliance, validate it separately before passing it to <code>from_bson()</code>.</p> </div> <div class="admonition note"> <p class=admonition-title>Document size</p> <p>Every document starts with its size. <code>from_bson()</code> rejects a document with <a href=../../../home/exceptions/#jsonexceptionparse_error112><code>parse_error.112</code></a> if the size is less than 5 (the size prefix and the terminator), if an embedded document does not end before the end of the document that contains it, if the elements do not fit into the declared size, or if the size does not match the number of bytes read when the terminating <code>0x00</code> byte is reached. A size that is too small is detected before an element is read whose type byte and name no longer fit; an element that starts inside the declared size but extends past it is read, and reported to a <abbr title="Simple API for XML">SAX</abbr> handler, before the mismatch is found at the terminator. A size that is too large is likewise found only at the terminator. Passing <code>strict</code> as <code>false</code> skips only the check for bytes after the end of the document (<a href=../../../home/exceptions/#jsonexceptionparse_error110><code>parse_error.110</code></a>), not Line truncated
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iomanip&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</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>
@@ -49,10 +49,10 @@
<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_bson</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>&lt;&lt;</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>&lt;&lt;</span><span class=w> </span><span class=n>j</span><span class=w> </span><span class=o>&lt;&lt;</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>&lt;&lt;</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>&lt;&lt;</span><span class=w> </span><span class=n>j</span><span class=w> </span><span class=o>&lt;&lt;</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 &copy; 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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 17:25:46 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 &copy; 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+87 -70
View File
@@ -7,72 +7,9 @@ References
- [BSON Website](http://bsonspec.org) - the main source on BSON
- [BSON Specification](http://bsonspec.org/spec.html) - the specification
## Serialization
## Byte layout
The library uses the following mapping from JSON values types to BSON types:
| JSON value type | value/range | BSON type | marker |
| --------------- | ----------------------------------------- | --------- | ------ |
| null | `null` | null | 0x0A |
| boolean | `true`, `false` | boolean | 0x08 |
| number_integer | -9223372036854775808..-2147483649 | int64 | 0x12 |
| number_integer | -2147483648..2147483647 | int32 | 0x10 |
| number_integer | 2147483648..9223372036854775807 | int64 | 0x12 |
| number_unsigned | 0..2147483647 | int32 | 0x10 |
| number_unsigned | 2147483648..9223372036854775807 | int64 | 0x12 |
| number_unsigned | 9223372036854775808..18446744073709551615 | uint64 | 0x11 |
| number_float | *any value* | double | 0x01 |
| string | *any value* | string | 0x02 |
| array | *any value* | document | 0x04 |
| object | *any value* | document | 0x03 |
| binary | *any value* | binary | 0x05 |
Incomplete mapping
The mapping is **incomplete**, since only JSON-objects (and things contained therein) can be serialized to BSON. Also, keys may not contain U+0000, since they are serialized a zero-terminated c-strings.
BSON type 0x11 interoperability
The BSON specification defines type `0x11` as a Timestamp. This library uses marker `0x11` when serializing `number_unsigned` values in the range `9223372036854775808..18446744073709551615`. Other BSON implementations may therefore interpret these values as Timestamps instead of unsigned integers.
Binary values without a subtype
BSON requires every binary value to have a subtype. If a binary value has no subtype, this library serializes it with the generic subtype `0x00`. After deserialization, `has_subtype()` returns `true` and `subtype()` returns `0`. As a result, serializing and deserializing a JSON object containing such a value produces a different JSON object, even though the binary data is unchanged.
Example: serialize a JSON value to BSON
```
#include <iostream>
#include <iomanip>
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using namespace nlohmann::literals;
int main()
{
// create a JSON value
json j = R"({"compact": true, "schema": 0})"_json;
// serialize it to BSON
std::vector<std::uint8_t> v = json::to_bson(j);
// print the vector content
for (auto& byte : v)
{
std::cout << "0x" << std::hex << std::setw(2) << std::setfill('0') << (int)byte << " ";
}
std::cout << std::endl;
}
```
Output:
```
0x1b 0x00 0x00 0x00 0x08 0x63 0x6f 0x6d 0x70 0x61 0x63 0x74 0x00 0x01 0x10 0x73 0x63 0x68 0x65 0x6d 0x61 0x00 0x00 0x00 0x00 0x00 0x00
```
### Byte layout
A BSON document is a length-prefixed sequence of *elements*. The first four bytes hold the total size of the document (little-endian int32), followed by the elements, and a final `0x00` byte ends the document. Each element starts with a one-byte type, followed by its key as a NUL-terminated string and the value, whose encoding depends on the type. Arrays are documents whose keys are the decimal indices `"0"`, `"1"`, ...; nesting is expressed by embedding documents. Because every document announces its size, a reader can skip over it without parsing its content. The top level of a BSON value is always a document, which is why only JSON objects can be serialized.
Consider the following JSON value (shown formatted for readability):
@@ -102,6 +39,79 @@ Consider the following JSON value (shown formatted for readability):
| `]` | 00 | end of the array document |
| `}` | 00 | end of the document |
## Serialization
The library uses the following mapping from JSON values types to BSON types:
| JSON value type | value/range | BSON type | marker |
| --------------- | ----------------------------------------- | --------- | ------ |
| null | `null` | null | 0x0A |
| boolean | `true`, `false` | boolean | 0x08 |
| number_integer | -9223372036854775808..-2147483649 | int64 | 0x12 |
| number_integer | -2147483648..2147483647 | int32 | 0x10 |
| number_integer | 2147483648..9223372036854775807 | int64 | 0x12 |
| number_unsigned | 0..2147483647 | int32 | 0x10 |
| number_unsigned | 2147483648..9223372036854775807 | int64 | 0x12 |
| number_unsigned | 9223372036854775808..18446744073709551615 | uint64 | 0x11 |
| number_float | *any value* | double | 0x01 |
| string | *any value* | string | 0x02 |
| array | *any value* | document | 0x04 |
| object | *any value* | document | 0x03 |
| binary | *any value* | binary | 0x05 |
Incomplete mapping
The mapping is **incomplete**, since only JSON-objects (and things contained therein) can be serialized to BSON. Also, keys may not contain U+0000, since they are serialized as zero-terminated C strings.
Order of object members
The members of an object are written in the order in which iteration visits them: sorted by key for [`json`](https://json.nlohmann.me/api/json/index.md), in insertion order for [`ordered_json`](https://json.nlohmann.me/api/ordered_json/index.md).
BSON type 0x11 interoperability
The BSON specification defines type `0x11` as a Timestamp. This library uses marker `0x11` when serializing `number_unsigned` values in the range `9223372036854775808..18446744073709551615`. Other BSON implementations may therefore interpret these values as Timestamps instead of unsigned integers.
Binary values without a subtype
BSON requires every binary value to have a subtype. If a binary value has no subtype, this library serializes it with the generic subtype `0x00`. After deserialization, `has_subtype()` returns `true` and `subtype()` returns `0`. As a result, serializing and deserializing a JSON object containing such a value produces a different JSON object, even though the binary data is unchanged.
Binary subtype 0x02 (old binary)
The BSON specification defines the payload of the "binary (old)" subtype `0x02` as an int32 followed by that many bytes, so the value is preceded by two lengths: the length of the binary element and, as the first four bytes of the payload, the number of bytes that follow. A binary value with subtype `2` is therefore written with the outer length 4 bytes larger than its size and the size as inner length: `binary({1, 2, 3}, 2)` becomes `07 00 00 00 02 03 00 00 00 01 02 03`. When reading, the inner length is checked and removed, so the value contains only the bytes that follow it. `from_bson()` throws [`parse_error.112`](https://json.nlohmann.me/home/exceptions/#jsonexceptionparse_error112) if the outer length is less than 4 or the inner length is not the outer length minus 4. Versions before 3.13.0 did not write the inner length and returned it as part of the payload; BSON data written by those versions with subtype 2 is not readable any more and must be written again.
Example: serialize a JSON value to BSON
```
#include <iostream>
#include <iomanip>
#include <nlohmann/json.hpp>
using nlohmann::json;
using namespace nlohmann::literals;
int main()
{
// create a JSON value
json j = R"({"compact": true, "schema": 0})"_json;
// serialize it to BSON
std::vector<std::uint8_t> v = json::to_bson(j);
// print the vector content
for (auto& byte : v)
{
std::cout << "0x" << std::hex << std::setw(2) << std::setfill('0') << static_cast<int>(byte) << " ";
}
std::cout << '\n';
}
```
Output:
```
0x1b 0x00 0x00 0x00 0x08 0x63 0x6f 0x6d 0x70 0x61 0x63 0x74 0x00 0x01 0x10 0x73 0x63 0x68 0x65 0x6d 0x61 0x00 0x00 0x00 0x00 0x00 0x00
```
## Deserialization
The library maps BSON record types to JSON value types as follows:
@@ -143,14 +153,21 @@ Lenient BSON input handling
The BSON reader is lenient in a few areas where the BSON specification is more restrictive:
- array element keys are not checked against the required decimal sequence (`0`, `1`, `2`, ...),
- any non-zero byte is accepted as `true` for the boolean type, and
- the payload for binary subtype `0x02` is returned as-is, including its inner length prefix.
- any non-zero byte is accepted as `true` for the boolean type,
- the payloads of the binary subtypes `0x03` (UUID, old), `0x04` (UUID), and `0x05` (MD5) are not checked to have 16 bytes,
- duplicate keys within a document are accepted; the last value wins (`{"a": 1, "a": 2}` is read as `{"a": 2}`), while a SAX handler receives every occurrence,
- a `string` value may contain embedded `0x00` bytes, and
- with `strict` set to `false`, bytes after the end of the document are ignored.
If BSON input must be validated for strict specification compliance, validate it separately before passing it to `from_bson()`.
Document size
Every document starts with its size. `from_bson()` rejects a document with [`parse_error.112`](https://json.nlohmann.me/home/exceptions/#jsonexceptionparse_error112) if the size is less than 5 (the size prefix and the terminator), if an embedded document does not end before the end of the document that contains it, if the elements do not fit into the declared size, or if the size does not match the number of bytes read when the terminating `0x00` byte is reached. A size that is too small is detected before an element is read whose type byte and name no longer fit; an element that starts inside the declared size but extends past it is read, and reported to a SAX handler, before the mismatch is found at the terminator. A size that is too large is likewise found only at the terminator. Passing `strict` as `false` skips only the check for bytes after the end of the document ([`parse_error.110`](https://json.nlohmann.me/home/exceptions/#jsonexceptionparse_error110)), not the document size checks.
Ill-formed UTF-8 in string values
The BSON specification requires `string` values (type `0x02`) to be valid UTF-8, but this is not required of a decoder, so checking is opt-in: with the [`error_handler`](https://json.nlohmann.me/api/basic_json/from_bson/index.md) parameter left at `keep` (the default), `from_bson()` accepts a `string` value whose bytes are not valid UTF-8 and hands them back unchanged. Passing `error_handler_t::strict` makes `from_bson()` check and throw [`parse_error.113`](https://json.nlohmann.me/home/exceptions/#jsonexceptionparse_error113) for ill-formed UTF-8, and `replace`/`ignore` sanitize the string instead of keeping it. However, [`dump()`](https://json.nlohmann.me/api/basic_json/dump/index.md) still requires valid UTF-8 and throws [`type_error.316`](https://json.nlohmann.me/home/exceptions/#jsonexceptiontype_error316) for a value read with the default `keep` handler, unless an error handler is passed that replaces or ignores the ill-formed bytes. `to_bson()`'s own `error_handler` parameter defaults to `keep`, so such a string value or element (key) name is written unchanged; with `strict` (the default if [`JSON_STRICT_BINARY_UTF8`](https://json.nlohmann.me/api/macros/json_strict_binary_utf8/index.md) is enabled), it throws the same exception instead. Element (key) names are never validated on read, since they are read byte-by-byte as a C string. `binary` values (type `0x05`) are unaffected, since they are not required to hold text.
The BSON specification requires `string` values (type `0x02`) to be valid UTF-8, but this is not required of a decoder, so checking is opt-in: with the [`error_handler`](https://json.nlohmann.me/api/basic_json/from_bson/index.md) parameter left at `keep` (the default), `from_bson()` accepts a `string` value whose bytes are not valid UTF-8 and hands them back unchanged. Passing `error_handler_t::strict` makes `from_bson()` check and throw [`parse_error.113`](https://json.nlohmann.me/home/exceptions/#jsonexceptionparse_error113) for ill-formed UTF-8, and `replace`/`ignore` sanitize the string instead of keeping it. However, [`dump()`](https://json.nlohmann.me/api/basic_json/dump/index.md) still requires valid UTF-8 and throws [`type_error.316`](https://json.nlohmann.me/home/exceptions/#jsonexceptiontype_error316) for a value read with the default `keep` handler, unless an error handler is passed that replaces or ignores the ill-formed bytes. `to_bson()`'s own `error_handler` parameter defaults to `keep`, so such a string value or element (key) name is written unchanged; with `strict` (the default if [`JSON_STRICT_BINARY_UTF8`](https://json.nlohmann.me/api/macros/json_strict_binary_utf8/index.md) is enabled), it throws the same exception instead. Element (key) names are treated like string values: with `keep` they are read unchanged, with `strict`, `replace`, or `ignore` they are checked and handled in the same way. `binary` values (type `0x05`) are unaffected, since they are not required to hold text.
Example: deserialize a JSON value from BSON
@@ -159,7 +176,7 @@ Example: deserialize a JSON value from BSON
#include <iomanip>
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using nlohmann::json;
int main()
{
@@ -174,7 +191,7 @@ int main()
json j = json::from_bson(v);
// print the deserialized JSON value
std::cout << std::setw(2) << j << std::endl;
std::cout << std::setw(2) << j << '\n';
}
```