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features/binary_formats/bon8.md
+4 -1
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@@ -204,7 +204,10 @@ of the message are reported as [parse_error.110](../../home/exceptions.md#jsonex
arrays and objects with up to four elements that are terminated by 0xFE, unsorted object keys, or a 0xFF after a
string that would also end without it, are accepted. A second 0xFF is not a terminator but an empty string.
Strings must be valid UTF-8, and a string at the very end of a message must be terminated by 0xFF.
Strings must be valid UTF-8, and a string at the very end of a message must be terminated by 0xFF. This also
holds when `strict` is false and more data follows the value: the byte that would end the string belongs to the
next value, and reading it would remove it from the input, so the missing 0xFF is reported as
[parse_error.110](../../home/exceptions.md#jsonexceptionparse_error110).
Duplicate object keys are accepted; the last value wins (`ordered_json` keeps the position of the first occurrence).
The specification does not say how to treat them; the HikoGUI reference decoder keeps the first value.
features/binary_formats/bon8/index.html
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@@ -30,7 +30,7 @@
<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>0x89</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>0xf9</span><span class=w> </span><span class=mh>0x66</span><span class=w> </span><span class=mh>0x6f</span><span class=w> </span><span class=mh>0x72</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>0x74</span><span class=w> </span><span class=mh>0xff</span><span class=w> </span><span class=mh>0x42</span><span class=w> </span><span class=mh>0x4f</span><span class=w> </span><span class=mh>0x4e</span><span class=w> </span><span class=mh>0x38</span><span class=w> </span><span class=mh>0xff</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>0x90</span><span class=w> </span>
</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 Object Notation 8">BON8</abbr> types to <abbr title="JavaScript Object Notation">JSON</abbr> value types as follows:</p> <table> <thead> <tr> <th><abbr title="Binary Object Notation 8">BON8</abbr> type</th> <th><abbr title="JavaScript Object Notation">JSON</abbr> value type</th> <th>first byte</th> </tr> </thead> <tbody> <tr> <td><abbr title="Unicode Transformation Format">UTF</abbr>-8 string</td> <td>string</td> <td>0x00..0x7F</td> </tr> <tr> <td>array with count</td> <td>array</td> <td>0x80..0x84</td> </tr> <tr> <td>array (terminated by 0xFE)</td> <td>array</td> <td>0x85</td> </tr> <tr> <td>object with count</td> <td>object</td> <td>0x86..0x8A</td> </tr> <tr> <td>object (terminated by 0xFE)</td> <td>object</td> <td>0x8B</td> </tr> <tr> <td>int32</td> <td>number_unsigned or number_integer</td> <td>0x8C</td> </tr> <tr> <td>int64</td> <td>number_unsigned or number_integer</td> <td>0x8D</td> </tr> <tr> <td>binary32</td> <td>number_float</td> <td>0x8E</td> </tr> <tr> <td>binary64</td> <td>number_float</td> <td>0x8F</td> </tr> <tr> <td>1-byte positive integer</td> <td>number_unsigned</td> <td>0x90..0xB7</td> </tr> <tr> <td>1-byte negative integer</td> <td>number_integer</td> <td>0xB8..0xC1</td> </tr> <tr> <td><abbr title="Unicode Transformation Format">UTF</abbr>-8 string</td> <td>string</td> <td>0xC2..0xF4, followed by 0x80..0xBF</td> </tr> <tr> <td>2- to 4-byte positive integer</td> <td>number_unsigned</td> <td>0xC2..0xF7, followed by 0x00..0x7F</td> </tr> <tr> <td>2- to 4-byte negative integer</td> <td>number_integer</td> <td>0xC2..0xF7, followed by 0xC0..0xFF</td> </tr> <tr> <td>false</td> <td><code>false</code></td> <td>0xF8</td> </tr> <tr> <td>true</td> <td><code>true</code></td> <td>0xF9</td> </tr> <tr> <td>null</td> <td><code>null</code></td> <td>0xFA</td> </tr> <tr> <td>-1.0</td> <td>number_float</td> <td>0xFB</td> </tr> <tr> <td>0.0</td> <td>number_float</td> <td>0xFC</td> </tr> <tr> <td>1.0</td> <td>number_float</td> <td>0xFD</td> </tr> <tr> <td>empty string</td> <td>string</td> <td>0xFF</td> </tr> </tbody> </table> <p>Non-negative integers are read as number_unsigned, negative integers as number_integer.</p> <p>A byte 0xF5..0xF7 followed by 0x80..0xBF is neither a string nor an integer and is rejected with <a href=../../../home/exceptions/#jsonexceptionparse_error112>parse_error.112</a> (invalid <abbr title="Unicode Transformation Format">UTF</abbr>-8 byte). The same error is reported for any other invalid byte (such as a stray 0xFE), for ill-formed <abbr title="Unicode Transformation Format">UTF</abbr>-8, and for an object key that is not a string. Input that ends prematurely, trailing data after the value, and a missing final 0xFF after a string at the end of the message are reported as <a href=../../../home/exceptions/#jsonexceptionparse_error110>parse_error.110</a>.</p> <div class="admonition info"> <p class=admonition-title>Non-canonical input</p> <p>Values that do not use the canonical representation, such as integers with a longer encoding than necessary, arrays and objects with up to four elements that are terminated by 0xFE, unsorted object keys, or a 0xFF after a string that would also end without it, are accepted. A second 0xFF is not a terminator but an empty string.</p> <p>Strings must be valid <abbr title="Unicode Transformation Format">UTF</abbr>-8, and a string at the very end of a message must be terminated by 0xFF.</p> <p>Duplicate object keys are accepted; the last value wins (<code>ordered_json</code> keeps the position of the first occurrence). The specification does not say how to treat them; the HikoGUI reference decoder keeps the first value.</p> </div> <div class="admonition info"> <p class=admonition-title>Round trips</p> <p>Any <abbr title="Binary Object Notation 8">BON8</abbr> output created by <code>to_bon8</code> can be successfully parsed by <code>from_bon8</code>.</p> </div> <details class=example> <summary>Example: deserialize a <abbr title="JavaScript Object Notation">JSON</abbr> value from <abbr title="Binary Object Notation 8">BON8</abbr></summary> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
</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 Object Notation 8">BON8</abbr> types to <abbr title="JavaScript Object Notation">JSON</abbr> value types as follows:</p> <table> <thead> <tr> <th><abbr title="Binary Object Notation 8">BON8</abbr> type</th> <th><abbr title="JavaScript Object Notation">JSON</abbr> value type</th> <th>first byte</th> </tr> </thead> <tbody> <tr> <td><abbr title="Unicode Transformation Format">UTF</abbr>-8 string</td> <td>string</td> <td>0x00..0x7F</td> </tr> <tr> <td>array with count</td> <td>array</td> <td>0x80..0x84</td> </tr> <tr> <td>array (terminated by 0xFE)</td> <td>array</td> <td>0x85</td> </tr> <tr> <td>object with count</td> <td>object</td> <td>0x86..0x8A</td> </tr> <tr> <td>object (terminated by 0xFE)</td> <td>object</td> <td>0x8B</td> </tr> <tr> <td>int32</td> <td>number_unsigned or number_integer</td> <td>0x8C</td> </tr> <tr> <td>int64</td> <td>number_unsigned or number_integer</td> <td>0x8D</td> </tr> <tr> <td>binary32</td> <td>number_float</td> <td>0x8E</td> </tr> <tr> <td>binary64</td> <td>number_float</td> <td>0x8F</td> </tr> <tr> <td>1-byte positive integer</td> <td>number_unsigned</td> <td>0x90..0xB7</td> </tr> <tr> <td>1-byte negative integer</td> <td>number_integer</td> <td>0xB8..0xC1</td> </tr> <tr> <td><abbr title="Unicode Transformation Format">UTF</abbr>-8 string</td> <td>string</td> <td>0xC2..0xF4, followed by 0x80..0xBF</td> </tr> <tr> <td>2- to 4-byte positive integer</td> <td>number_unsigned</td> <td>0xC2..0xF7, followed by 0x00..0x7F</td> </tr> <tr> <td>2- to 4-byte negative integer</td> <td>number_integer</td> <td>0xC2..0xF7, followed by 0xC0..0xFF</td> </tr> <tr> <td>false</td> <td><code>false</code></td> <td>0xF8</td> </tr> <tr> <td>true</td> <td><code>true</code></td> <td>0xF9</td> </tr> <tr> <td>null</td> <td><code>null</code></td> <td>0xFA</td> </tr> <tr> <td>-1.0</td> <td>number_float</td> <td>0xFB</td> </tr> <tr> <td>0.0</td> <td>number_float</td> <td>0xFC</td> </tr> <tr> <td>1.0</td> <td>number_float</td> <td>0xFD</td> </tr> <tr> <td>empty string</td> <td>string</td> <td>0xFF</td> </tr> </tbody> </table> <p>Non-negative integers are read as number_unsigned, negative integers as number_integer.</p> <p>A byte 0xF5..0xF7 followed by 0x80..0xBF is neither a string nor an integer and is rejected with <a href=../../../home/exceptions/#jsonexceptionparse_error112>parse_error.112</a> (invalid <abbr title="Unicode Transformation Format">UTF</abbr>-8 byte). The same error is reported for any other invalid byte (such as a stray 0xFE), for ill-formed <abbr title="Unicode Transformation Format">UTF</abbr>-8, and for an object key that is not a string. Input that ends prematurely, trailing data after the value, and a missing final 0xFF after a string at the end of the message are reported as <a href=../../../home/exceptions/#jsonexceptionparse_error110>parse_error.110</a>.</p> <div class="admonition info"> <p class=admonition-title>Non-canonical input</p> <p>Values that do not use the canonical representation, such as integers with a longer encoding than necessary, arrays and objects with up to four elements that are terminated by 0xFE, unsorted object keys, or a 0xFF after a string that would also end without it, are accepted. A second 0xFF is not a terminator but an empty string.</p> <p>Strings must be valid <abbr title="Unicode Transformation Format">UTF</abbr>-8, and a string at the very end of a message must be terminated by 0xFF. This also holds when <code>strict</code> is false and more data follows the value: the byte that would end the string belongs to the next value, and reading it would remove it from the input, so the missing 0xFF is reported as <a href=../../../home/exceptions/#jsonexceptionparse_error110>parse_error.110</a>.</p> <p>Duplicate object keys are accepted; the last value wins (<code>ordered_json</code> keeps the position of the first occurrence). The specification does not say how to treat them; the HikoGUI reference decoder keeps the first value.</p> </div> <div class="admonition info"> <p class=admonition-title>Round trips</p> <p>Any <abbr title="Binary Object Notation 8">BON8</abbr> output created by <code>to_bon8</code> can be successfully parsed by <code>from_bon8</code>.</p> </div> <details class=example> <summary>Example: deserialize a <abbr title="JavaScript Object Notation">JSON</abbr> value from <abbr title="Binary Object Notation 8">BON8</abbr></summary> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
<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>
@@ -56,4 +56,4 @@
<span class=w> </span><span class=nt>"format"</span><span class=p>:</span><span class=w> </span><span class=s2>"BON8"</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> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li><a href=../ >Binary formats</a> - overview and comparison of the supported binary formats</li> <li><a href=../../binary_values/ >Binary values</a> - how binary values and subtypes map to <abbr title="Binary Object Notation 8">BON8</abbr></li> <li><a href=../../../api/basic_json/to_bon8/ ><code>to_bon8</code></a> - serialize a <abbr title="JavaScript Object Notation">JSON</abbr> value to <abbr title="Binary Object Notation 8">BON8</abbr></li> <li><a href=../../../api/basic_json/from_bon8/ ><code>from_bon8</code></a> - parse a <abbr title="JavaScript Object Notation">JSON</abbr> value from <abbr title="Binary Object Notation 8">BON8</abbr></li> <li><a href=../../../api/macros/json_strict_binary_utf8/ ><code>JSON_STRICT_BINARY_UTF8</code></a> - reject ill-formed <abbr title="Unicode Transformation Format">UTF</abbr>-8 in strings</li> <li><a href=../../parsing/sax_interface/ ><abbr title="Simple API for XML">SAX</abbr> interface</a> - decode binary formats without building a value</li> </ul> <!-- 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 27, 2026 06:41:42 UTC">October 27, 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> <nav class="md-footer__inner md-grid" aria-label=Footer> <a href=../bjdata/ class="md-footer__link md-footer__link--prev" aria-label="Previous: BJData"> <div class="md-footer__button md-icon"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M20 11v2H8l5.5 5.5-1.42 1.42L4.16 12l7.92-7.92L13.5 5.5 8 11z"/></svg> </div> <div class=md-footer__title> <span class=md-footer__direction> Previous </span> <div class=md-ellipsis> BJData </div> </div> </a> <a href=../bson/ class="md-footer__link md-footer__link--next" aria-label="Next: BSON"> <div class=md-footer__title> <span class=md-footer__direction> Next </span> <div class=md-ellipsis> BSON </div> </div> <div class="md-footer__button md-icon"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M4 11v2h12l-5.5 5.5 1.42 1.42L19.84 12l-7.92-7.92L10.5 5.5 16 11z"/></svg> </div> </a> </nav> <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> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li><a href=../ >Binary formats</a> - overview and comparison of the supported binary formats</li> <li><a href=../../binary_values/ >Binary values</a> - how binary values and subtypes map to <abbr title="Binary Object Notation 8">BON8</abbr></li> <li><a href=../../../api/basic_json/to_bon8/ ><code>to_bon8</code></a> - serialize a <abbr title="JavaScript Object Notation">JSON</abbr> value to <abbr title="Binary Object Notation 8">BON8</abbr></li> <li><a href=../../../api/basic_json/from_bon8/ ><code>from_bon8</code></a> - parse a <abbr title="JavaScript Object Notation">JSON</abbr> value from <abbr title="Binary Object Notation 8">BON8</abbr></li> <li><a href=../../../api/macros/json_strict_binary_utf8/ ><code>JSON_STRICT_BINARY_UTF8</code></a> - reject ill-formed <abbr title="Unicode Transformation Format">UTF</abbr>-8 in strings</li> <li><a href=../../parsing/sax_interface/ ><abbr title="Simple API for XML">SAX</abbr> interface</a> - decode binary formats without building a value</li> </ul> <!-- 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="November 13, 2026 16:54:30 UTC">November 13, 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> <nav class="md-footer__inner md-grid" aria-label=Footer> <a href=../bjdata/ class="md-footer__link md-footer__link--prev" aria-label="Previous: BJData"> <div class="md-footer__button md-icon"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M20 11v2H8l5.5 5.5-1.42 1.42L4.16 12l7.92-7.92L13.5 5.5 8 11z"/></svg> </div> <div class=md-footer__title> <span class=md-footer__direction> Previous </span> <div class=md-ellipsis> BJData </div> </div> </a> <a href=../bson/ class="md-footer__link md-footer__link--next" aria-label="Next: BSON"> <div class=md-footer__title> <span class=md-footer__direction> Next </span> <div class=md-ellipsis> BSON </div> </div> <div class="md-footer__button md-icon"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M4 11v2h12l-5.5 5.5 1.42 1.42L19.84 12l-7.92-7.92L10.5 5.5 16 11z"/></svg> </div> </a> </nav> <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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features/binary_formats/bon8/index.md
+1 -1
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@@ -179,7 +179,7 @@ Non-canonical input
Values that do not use the canonical representation, such as integers with a longer encoding than necessary, arrays and objects with up to four elements that are terminated by 0xFE, unsorted object keys, or a 0xFF after a string that would also end without it, are accepted. A second 0xFF is not a terminator but an empty string.
Strings must be valid UTF-8, and a string at the very end of a message must be terminated by 0xFF.
Strings must be valid UTF-8, and a string at the very end of a message must be terminated by 0xFF. This also holds when `strict` is false and more data follows the value: the byte that would end the string belongs to the next value, and reading it would remove it from the input, so the missing 0xFF is reported as [parse_error.110](https://json.nlohmann.me/home/exceptions/#jsonexceptionparse_error110).
Duplicate object keys are accepted; the last value wins (`ordered_json` keeps the position of the first occurrence). The specification does not say how to treat them; the HikoGUI reference decoder keeps the first value.
features/parsing/untrusted_input.md
+36 -6
View File
@@ -64,13 +64,13 @@ stack for the nesting.)
The call stack still needs room for the levels that are recursed into, and the default limit assumes a stack of ordinary
size. The stack that an operation needs is roughly proportional to the limit; with the default of 128 levels, the most
demanding operation (`dump` in an unoptimized build) needed up to 288 KiB, and an optimized build needed 48 KiB or less,
in measurements on macOS with arm64. The most demanding operation needed this much stack at the limits `0`, `32`,
`128`, and `254`:
demanding operations (copying a value and converting it to another `basic_json` type, in an unoptimized build) needed
up to 224 KiB, and an optimized build needed 48 KiB or less, in measurements on macOS with arm64. The most demanding
operation needed this much stack at the limits `0`, `32`, `128`, and `254`:
| Stack needed, in KiB | limit 0 | limit 32 | limit 128 (default) | limit 254 |
|---|---:|---:|---:|---:|
| unoptimized build (`-O0`) | 16 or less | 80 | 288 | 576 |
| unoptimized build (`-O0`) | 16 or less | 64 | 224 | 448 |
| optimized build (`-O2`) | 16 or less | 16 or less | 48 | 112 |
A thread with a smaller stack (a task of a real-time operating system, a fiber, or a thread of the musl C library, whose
@@ -81,6 +81,20 @@ result. See the [documentation of the macro](../../api/macros/json_recursion_dep
the speed, and the rules for choosing a value. Destroying a value (its destructor) recurses over the same number of
levels and then continues without the call stack, and needs 32 KiB or less at every limit.
!!! warning "Indented output and flattened keys grow with the depth"
Some results are larger than the value by a factor of its nesting depth.
[`dump`](../../api/basic_json/dump.md) with an `indent` of `n` (and likewise `operator<<` with `std::setw(n)` and
[`basic_json_view::dump`](../../api/basic_json_view/dump.md)) writes up to `n` characters per nesting level in
front of every line, and [`flatten`](../../api/basic_json/flatten.md) repeats the path of every value in its key.
For the 80,001-byte array `[1,[1,...[1,1]...]]` with 20,000 levels, `dump(1)` returns 600 MB, `dump(4)` 2.4 GB,
and the keys of `flatten()` hold 400 MB. A compact `dump()` without indentation stays the size of the value. If you
pretty-print, log, or flatten untrusted input, limit its nesting depth while parsing, for example with a
[parser callback](parser_callbacks.md#recipe-max-nesting-depth-via-a-callback): with a limit of `d`, every line has
at most `n * d` indentation characters, and every flattened key has at most `d` reference tokens.
[`JSON_RECURSION_DEPTH_LIMIT`](../../api/macros/json_recursion_depth_limit.md) does not help here: it changes only
how much of the call stack a walk uses, never its result, and it does not limit the depth that `parse()` accepts.
## Input size
The library does not limit the overall size of a JSON text; a value nested or wide enough will use memory
@@ -140,6 +154,20 @@ values for a repeated key ends up in the parsed object. If your application must
silently resolving them one way or another, see the
[parser callback recipe for rejecting duplicate keys](parser_callbacks.md#recipe-rejecting-duplicate-object-keys).
## Objects with many keys in `ordered_json`
[`ordered_json`](../../api/ordered_json.md) keeps the members of an object in a vector in insertion order
([`ordered_map`](../../api/ordered_map.md)) and finds a key by searching all members. Parsing JSON text into an
`ordered_json` avoids that search for objects with many keys and takes linear time. The binary readers
([`from_cbor`](../../api/basic_json/from_cbor.md), [`from_msgpack`](../../api/basic_json/from_msgpack.md),
[`from_ubjson`](../../api/basic_json/from_ubjson.md), [`from_bjdata`](../../api/basic_json/from_bjdata.md),
[`from_bson`](../../api/basic_json/from_bson.md), and [`from_bon8`](../../api/basic_json/from_bon8.md)) do not yet:
reading an object of `n` keys into an `ordered_json` costs time proportional to `n²`. A flat object of 40,000 keys
(about 300 KB of CBOR) takes about 1.3 s, against a few milliseconds as JSON text or into a `json`
([#6104](https://github.com/nlohmann/json/issues/6104)). `json` is not affected. If you read untrusted binary input
into `ordered_json`, bound the input size more tightly, read it into a `json`, or reject objects with many keys in a
[SAX handler](sax_interface.md).
## Numbers
A number whose value cannot be represented — for instance `1E1000`, which overflows `double` — is rejected while
@@ -171,9 +199,11 @@ indices (or the pointer as a whole) before using them, or use [`at`](../../api/b
- Wrap parsing in a `#!cpp try`/`#!cpp catch` block, or use `allow_exceptions=false`/`accept()` if your environment
cannot use exceptions; never let `JSON_NOEXCEPTION`'s `abort()` be the first time you think about error handling.
- If the input's nesting depth matters to you, enforce your own limit with a
[parser callback](parser_callbacks.md#recipe-max-nesting-depth-via-a-callback) or a
- If the input's nesting depth matters to you (for example because you pretty-print, log, or flatten it), enforce your
own limit with a [parser callback](parser_callbacks.md#recipe-max-nesting-depth-via-a-callback) or a
[SAX handler](sax_interface.md); the library bounds the call stack but not memory use.
- If you read untrusted binary input into `ordered_json`, mind that objects with many keys are
[slow to read](#objects-with-many-keys-in-ordered_json).
- Bound the size of the input itself before parsing, independent of the library's own bounded allocations for binary
format lengths.
- Decide up front how you want a string with invalid UTF-8 — from any source, not only parsing — to be serialized
features/parsing/untrusted_input/index.html
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features/parsing/untrusted_input/index.md
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@@ -24,15 +24,19 @@ Neither the parser nor the binary readers impose a limit on how deep the input m
Once a value has been parsed, operations that walk it recursively — serializing it with [`dump`](https://json.nlohmann.me/api/basic_json/dump/index.md), hashing it, copying it, comparing two values with `==`, `<`, or (in C++20) `<=>`, merging with [`update`](https://json.nlohmann.me/api/basic_json/update/index.md), applying a [`merge_patch`](https://json.nlohmann.me/api/basic_json/merge_patch/index.md), creating a patch with [`diff`](https://json.nlohmann.me/api/basic_json/diff/index.md) or [`merge_diff`](https://json.nlohmann.me/api/basic_json/merge_diff/index.md), converting it to another `basic_json` type, destroying it, and the binary writers (`to_cbor`, `to_msgpack`, ...) — descend at most [`JSON_RECURSION_DEPTH_LIMIT`](https://json.nlohmann.me/api/macros/json_recursion_depth_limit/index.md) levels on the call stack, 128 by default, and continue below that with an explicit stack on the heap. So the call stack does not grow with the nesting depth of the value, however deeply it is nested. ([`flatten`](https://json.nlohmann.me/api/basic_json/flatten/index.md), [`unflatten`](https://json.nlohmann.me/api/basic_json/unflatten/index.md), and [`to_bson`](https://json.nlohmann.me/api/basic_json/to_bson/index.md) never use the call stack for the nesting.)
The call stack still needs room for the levels that are recursed into, and the default limit assumes a stack of ordinary size. The stack that an operation needs is roughly proportional to the limit; with the default of 128 levels, the most demanding operation (`dump` in an unoptimized build) needed up to 288 KiB, and an optimized build needed 48 KiB or less, in measurements on macOS with arm64. The most demanding operation needed this much stack at the limits `0`, `32`, `128`, and `254`:
The call stack still needs room for the levels that are recursed into, and the default limit assumes a stack of ordinary size. The stack that an operation needs is roughly proportional to the limit; with the default of 128 levels, the most demanding operations (copying a value and converting it to another `basic_json` type, in an unoptimized build) needed up to 224 KiB, and an optimized build needed 48 KiB or less, in measurements on macOS with arm64. The most demanding operation needed this much stack at the limits `0`, `32`, `128`, and `254`:
| Stack needed, in KiB | limit 0 | limit 32 | limit 128 (default) | limit 254 |
| ------------------------- | ---------- | ---------- | ------------------- | --------- |
| unoptimized build (`-O0`) | 16 or less | 80 | 288 | 576 |
| unoptimized build (`-O0`) | 16 or less | 64 | 224 | 448 |
| optimized build (`-O2`) | 16 or less | 16 or less | 48 | 112 |
A thread with a smaller stack (a task of a real-time operating system, a fiber, or a thread of the musl C library, whose default stack is 128 KiB) can still overflow its stack on deeply nested input, which is why the limit can be lowered: define `JSON_RECURSION_DEPTH_LIMIT` to a smaller value, down to `0`, before including the library. Such a limit changes only the stack that is needed and the speed (values nested more deeply than the limit are walked more slowly), never a result. See the [documentation of the macro](https://json.nlohmann.me/api/macros/json_recursion_depth_limit/index.md) for the complete tables, the speed, and the rules for choosing a value. Destroying a value (its destructor) recurses over the same number of levels and then continues without the call stack, and needs 32 KiB or less at every limit.
Indented output and flattened keys grow with the depth
Some results are larger than the value by a factor of its nesting depth. [`dump`](https://json.nlohmann.me/api/basic_json/dump/index.md) with an `indent` of `n` (and likewise `operator<<` with `std::setw(n)` and [`basic_json_view::dump`](https://json.nlohmann.me/api/basic_json_view/dump/index.md)) writes up to `n` characters per nesting level in front of every line, and [`flatten`](https://json.nlohmann.me/api/basic_json/flatten/index.md) repeats the path of every value in its key. For the 80,001-byte array `[1,[1,...[1,1]...]]` with 20,000 levels, `dump(1)` returns 600 MB, `dump(4)` 2.4 GB, and the keys of `flatten()` hold 400 MB. A compact `dump()` without indentation stays the size of the value. If you pretty-print, log, or flatten untrusted input, limit its nesting depth while parsing, for example with a [parser callback](https://json.nlohmann.me/features/parsing/parser_callbacks/#recipe-max-nesting-depth-via-a-callback): with a limit of `d`, every line has at most `n * d` indentation characters, and every flattened key has at most `d` reference tokens. [`JSON_RECURSION_DEPTH_LIMIT`](https://json.nlohmann.me/api/macros/json_recursion_depth_limit/index.md) does not help here: it changes only how much of the call stack a walk uses, never its result, and it does not limit the depth that `parse()` accepts.
## Input size
The library does not limit the overall size of a JSON text; a value nested or wide enough will use memory proportional to the input. If you parse untrusted input of unbounded size, check the size of the file or stream yourself before — or while — handing it to `parse()`.
@@ -60,6 +64,10 @@ Parsing is not the only place invalid UTF-8 matters: a string that reached a `js
The JSON specification leaves the handling of repeated keys in an object up to the implementation, and this library does too: as described in [`object_t`](https://json.nlohmann.me/api/basic_json/object_t/#behavior), it is unspecified which of the values for a repeated key ends up in the parsed object. If your application must reject duplicate keys instead of silently resolving them one way or another, see the [parser callback recipe for rejecting duplicate keys](https://json.nlohmann.me/features/parsing/parser_callbacks/#recipe-rejecting-duplicate-object-keys).
## Objects with many keys in `ordered_json`
[`ordered_json`](https://json.nlohmann.me/api/ordered_json/index.md) keeps the members of an object in a vector in insertion order ([`ordered_map`](https://json.nlohmann.me/api/ordered_map/index.md)) and finds a key by searching all members. Parsing JSON text into an `ordered_json` avoids that search for objects with many keys and takes linear time. The binary readers ([`from_cbor`](https://json.nlohmann.me/api/basic_json/from_cbor/index.md), [`from_msgpack`](https://json.nlohmann.me/api/basic_json/from_msgpack/index.md), [`from_ubjson`](https://json.nlohmann.me/api/basic_json/from_ubjson/index.md), [`from_bjdata`](https://json.nlohmann.me/api/basic_json/from_bjdata/index.md), [`from_bson`](https://json.nlohmann.me/api/basic_json/from_bson/index.md), and [`from_bon8`](https://json.nlohmann.me/api/basic_json/from_bon8/index.md)) do not yet: reading an object of `n` keys into an `ordered_json` costs time proportional to `n²`. A flat object of 40,000 keys (about 300 KB of CBOR) takes about 1.3 s, against a few milliseconds as JSON text or into a `json` ([#6104](https://github.com/nlohmann/json/issues/6104)). `json` is not affected. If you read untrusted binary input into `ordered_json`, bound the input size more tightly, read it into a `json`, or reject objects with many keys in a [SAX handler](https://json.nlohmann.me/features/parsing/sax_interface/index.md).
## Numbers
A number whose value cannot be represented — for instance `1E1000`, which overflows `double` — is rejected while parsing as [`out_of_range.406`](https://json.nlohmann.me/home/exceptions/#jsonexceptionout_of_range406) rather than silently becoming infinity. An integer that is syntactically valid but does not fit the 64-bit integer types is not rejected; it is instead stored as a `double`, which may lose precision for very large values. See [number limits](https://json.nlohmann.me/features/types/number_handling/#number-limits) for the exact ranges and an example.
@@ -75,7 +83,8 @@ A [JSON Pointer](https://json.nlohmann.me/features/json_pointer/index.md) can co
## Checklist
- Wrap parsing in a `try`/`catch` block, or use `allow_exceptions=false`/`accept()` if your environment cannot use exceptions; never let `JSON_NOEXCEPTION`'s `abort()` be the first time you think about error handling.
- If the input's nesting depth matters to you, enforce your own limit with a [parser callback](https://json.nlohmann.me/features/parsing/parser_callbacks/#recipe-max-nesting-depth-via-a-callback) or a [SAX handler](https://json.nlohmann.me/features/parsing/sax_interface/index.md); the library bounds the call stack but not memory use.
- If the input's nesting depth matters to you (for example because you pretty-print, log, or flatten it), enforce your own limit with a [parser callback](https://json.nlohmann.me/features/parsing/parser_callbacks/#recipe-max-nesting-depth-via-a-callback) or a [SAX handler](https://json.nlohmann.me/features/parsing/sax_interface/index.md); the library bounds the call stack but not memory use.
- If you read untrusted binary input into `ordered_json`, mind that objects with many keys are [slow to read](#objects-with-many-keys-in-ordered_json).
- Bound the size of the input itself before parsing, independent of the library's own bounded allocations for binary format lengths.
- Decide up front how you want a string with invalid UTF-8 — from any source, not only parsing — to be serialized (`strict`, `replace`, or `ignore`), rather than discovering it from an uncaught `type_error.316`.
- For untrusted input in a binary format, pass `error_handler_t::strict` to the `from_*` function if the strings must be valid UTF-8; by default they are not checked (BON8 always checks).