230 lines
22 KiB
HTML
230 lines
22 KiB
HTML
<!DOCTYPE html><html lang="en"><head><meta charset="utf-8"><meta name="viewport" content="width=device-width, initial-scale=1.0"><meta name="generator" content="rustdoc"><meta name="description" content="Serde JSON"><title>serde_json - Rust</title><script>if(window.location.protocol!=="file:")document.head.insertAdjacentHTML("beforeend","SourceSerif4-Regular-6b053e98.ttf.woff2,FiraSans-Italic-81dc35de.woff2,FiraSans-Regular-0fe48ade.woff2,FiraSans-MediumItalic-ccf7e434.woff2,FiraSans-Medium-e1aa3f0a.woff2,SourceCodePro-Regular-8badfe75.ttf.woff2,SourceCodePro-Semibold-aa29a496.ttf.woff2".split(",").map(f=>`<link rel="preload" as="font" type="font/woff2"href="../static.files/${f}">`).join(""))</script><link rel="stylesheet" href="../static.files/normalize-9960930a.css"><link rel="stylesheet" href="../static.files/rustdoc-ca0dd0c4.css"><meta name="rustdoc-vars" data-root-path="../" data-static-root-path="../static.files/" data-current-crate="serde_json" data-themes="" data-resource-suffix="" data-rustdoc-version="1.93.1 (01f6ddf75 2026-02-11) (Arch Linux rust 1:1.93.1-1)" data-channel="1.93.1" data-search-js="search-9e2438ea.js" data-stringdex-js="stringdex-a3946164.js" data-settings-js="settings-c38705f0.js" ><script src="../static.files/storage-e2aeef58.js"></script><script defer src="../crates.js"></script><script defer src="../static.files/main-a410ff4d.js"></script><noscript><link rel="stylesheet" href="../static.files/noscript-263c88ec.css"></noscript><link rel="alternate icon" type="image/png" href="../static.files/favicon-32x32-eab170b8.png"><link rel="icon" type="image/svg+xml" href="../static.files/favicon-044be391.svg"></head><body class="rustdoc mod crate"><!--[if lte IE 11]><div class="warning">This old browser is unsupported and will most likely display funky things.</div><![endif]--><rustdoc-topbar><h2><a href="#">Crate serde_json</a></h2></rustdoc-topbar><nav class="sidebar"><div class="sidebar-crate"><h2><a href="../serde_json/index.html">serde_<wbr>json</a><span class="version">1.0.149</span></h2></div><div class="sidebar-elems"><ul class="block"><li><a id="all-types" href="all.html">All Items</a></li></ul><section id="rustdoc-toc"><h3><a href="#">Sections</a></h3><ul class="block top-toc"><li><a href="#serde-json" title="Serde JSON">Serde JSON</a></li><li><a href="#operating-on-untyped-json-values" title="Operating on untyped JSON values">Operating on untyped JSON values</a></li><li><a href="#parsing-json-as-strongly-typed-data-structures" title="Parsing JSON as strongly typed data structures">Parsing JSON as strongly typed data structures</a></li><li><a href="#constructing-json-values" title="Constructing JSON values">Constructing JSON values</a></li><li><a href="#creating-json-by-serializing-data-structures" title="Creating JSON by serializing data structures">Creating JSON by serializing data structures</a></li><li><a href="#no-std-support" title="No-std support">No-std support</a></li></ul><h3><a href="#modules">Crate Items</a></h3><ul class="block"><li><a href="#modules" title="Modules">Modules</a></li><li><a href="#macros" title="Macros">Macros</a></li><li><a href="#structs" title="Structs">Structs</a></li><li><a href="#enums" title="Enums">Enums</a></li><li><a href="#functions" title="Functions">Functions</a></li><li><a href="#types" title="Type Aliases">Type Aliases</a></li></ul></section><div id="rustdoc-modnav"></div></div></nav><div class="sidebar-resizer" title="Drag to resize sidebar"></div><main><div class="width-limiter"><section id="main-content" class="content"><div class="main-heading"><h1>Crate <span>serde_<wbr>json</span> <button id="copy-path" title="Copy item path to clipboard">Copy item path</button></h1><rustdoc-toolbar></rustdoc-toolbar><span class="sub-heading"><a class="src" href="../src/serde_json/lib.rs.html#1-441">Source</a> </span></div><details class="toggle top-doc" open><summary class="hideme"><span>Expand description</span></summary><div class="docblock"><h2 id="serde-json"><a class="doc-anchor" href="#serde-json">§</a>Serde JSON</h2>
|
||
<p>JSON is a ubiquitous open-standard format that uses human-readable text to
|
||
transmit data objects consisting of key-value pairs.</p>
|
||
<div class="example-wrap"><pre class="language-json"><code>{
|
||
"name": "John Doe",
|
||
"age": 43,
|
||
"address": {
|
||
"street": "10 Downing Street",
|
||
"city": "London"
|
||
},
|
||
"phones": [
|
||
"+44 1234567",
|
||
"+44 2345678"
|
||
]
|
||
}</code></pre></div>
|
||
<p>There are three common ways that you might find yourself needing to work
|
||
with JSON data in Rust.</p>
|
||
<ul>
|
||
<li><strong>As text data.</strong> An unprocessed string of JSON data that you receive on
|
||
an HTTP endpoint, read from a file, or prepare to send to a remote
|
||
server.</li>
|
||
<li><strong>As an untyped or loosely typed representation.</strong> Maybe you want to
|
||
check that some JSON data is valid before passing it on, but without
|
||
knowing the structure of what it contains. Or you want to do very basic
|
||
manipulations like insert a key in a particular spot.</li>
|
||
<li><strong>As a strongly typed Rust data structure.</strong> When you expect all or most
|
||
of your data to conform to a particular structure and want to get real
|
||
work done without JSON’s loosey-goosey nature tripping you up.</li>
|
||
</ul>
|
||
<p>Serde JSON provides efficient, flexible, safe ways of converting data
|
||
between each of these representations.</p>
|
||
<h2 id="operating-on-untyped-json-values"><a class="doc-anchor" href="#operating-on-untyped-json-values">§</a>Operating on untyped JSON values</h2>
|
||
<p>Any valid JSON data can be manipulated in the following recursive enum
|
||
representation. This data structure is <a href="enum.Value.html" title="enum serde_json::Value"><code>serde_json::Value</code></a>.</p>
|
||
|
||
<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">enum </span>Value {
|
||
Null,
|
||
Bool(bool),
|
||
Number(Number),
|
||
String(String),
|
||
Array(Vec<Value>),
|
||
Object(Map<String, Value>),
|
||
}</code></pre></div>
|
||
<p>A string of JSON data can be parsed into a <code>serde_json::Value</code> by the
|
||
<a href="fn.from_str.html" title="fn serde_json::from_str"><code>serde_json::from_str</code></a> function. There is also <a href="fn.from_slice.html" title="fn serde_json::from_slice"><code>from_slice</code></a>
|
||
for parsing from a byte slice <code>&[u8]</code> and <a href="fn.from_reader.html" title="fn serde_json::from_reader"><code>from_reader</code></a> for parsing from
|
||
any <code>io::Read</code> like a File or a TCP stream.</p>
|
||
|
||
<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use </span>serde_json::{<span class="prelude-ty">Result</span>, Value};
|
||
|
||
<span class="kw">fn </span>untyped_example() -> <span class="prelude-ty">Result</span><()> {
|
||
<span class="comment">// Some JSON input data as a &str. Maybe this comes from the user.
|
||
</span><span class="kw">let </span>data = <span class="string">r#"
|
||
{
|
||
"name": "John Doe",
|
||
"age": 43,
|
||
"phones": [
|
||
"+44 1234567",
|
||
"+44 2345678"
|
||
]
|
||
}"#</span>;
|
||
|
||
<span class="comment">// Parse the string of data into serde_json::Value.
|
||
</span><span class="kw">let </span>v: Value = serde_json::from_str(data)<span class="question-mark">?</span>;
|
||
|
||
<span class="comment">// Access parts of the data by indexing with square brackets.
|
||
</span><span class="macro">println!</span>(<span class="string">"Please call {} at the number {}"</span>, v[<span class="string">"name"</span>], v[<span class="string">"phones"</span>][<span class="number">0</span>]);
|
||
|
||
<span class="prelude-val">Ok</span>(())
|
||
}</code></pre></div>
|
||
<p>The result of square bracket indexing like <code>v["name"]</code> is a borrow of the
|
||
data at that index, so the type is <code>&Value</code>. A JSON map can be indexed with
|
||
string keys, while a JSON array can be indexed with integer keys. If the
|
||
type of the data is not right for the type with which it is being indexed,
|
||
or if a map does not contain the key being indexed, or if the index into a
|
||
vector is out of bounds, the returned element is <code>Value::Null</code>.</p>
|
||
<p>When a <code>Value</code> is printed, it is printed as a JSON string. So in the code
|
||
above, the output looks like <code>Please call "John Doe" at the number "+44 1234567"</code>. The quotation marks appear because <code>v["name"]</code> is a <code>&Value</code>
|
||
containing a JSON string and its JSON representation is <code>"John Doe"</code>.
|
||
Printing as a plain string without quotation marks involves converting from
|
||
a JSON string to a Rust string with <a href="enum.Value.html#method.as_str" title="method serde_json::Value::as_str"><code>as_str()</code></a> or avoiding the use of
|
||
<code>Value</code> as described in the following section.</p>
|
||
<p>The <code>Value</code> representation is sufficient for very basic tasks but can be
|
||
tedious to work with for anything more significant. Error handling is
|
||
verbose to implement correctly, for example imagine trying to detect the
|
||
presence of unrecognized fields in the input data. The compiler is powerless
|
||
to help you when you make a mistake, for example imagine typoing <code>v["name"]</code>
|
||
as <code>v["nmae"]</code> in one of the dozens of places it is used in your code.</p>
|
||
<h2 id="parsing-json-as-strongly-typed-data-structures"><a class="doc-anchor" href="#parsing-json-as-strongly-typed-data-structures">§</a>Parsing JSON as strongly typed data structures</h2>
|
||
<p>Serde provides a powerful way of mapping JSON data into Rust data structures
|
||
largely automatically.</p>
|
||
|
||
<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use </span>serde::{Deserialize, Serialize};
|
||
<span class="kw">use </span>serde_json::Result;
|
||
|
||
<span class="attr">#[derive(Serialize, Deserialize)]
|
||
</span><span class="kw">struct </span>Person {
|
||
name: String,
|
||
age: u8,
|
||
phones: Vec<String>,
|
||
}
|
||
|
||
<span class="kw">fn </span>typed_example() -> <span class="prelude-ty">Result</span><()> {
|
||
<span class="comment">// Some JSON input data as a &str. Maybe this comes from the user.
|
||
</span><span class="kw">let </span>data = <span class="string">r#"
|
||
{
|
||
"name": "John Doe",
|
||
"age": 43,
|
||
"phones": [
|
||
"+44 1234567",
|
||
"+44 2345678"
|
||
]
|
||
}"#</span>;
|
||
|
||
<span class="comment">// Parse the string of data into a Person object. This is exactly the
|
||
// same function as the one that produced serde_json::Value above, but
|
||
// now we are asking it for a Person as output.
|
||
</span><span class="kw">let </span>p: Person = serde_json::from_str(data)<span class="question-mark">?</span>;
|
||
|
||
<span class="comment">// Do things just like with any other Rust data structure.
|
||
</span><span class="macro">println!</span>(<span class="string">"Please call {} at the number {}"</span>, p.name, p.phones[<span class="number">0</span>]);
|
||
|
||
<span class="prelude-val">Ok</span>(())
|
||
}</code></pre></div>
|
||
<p>This is the same <code>serde_json::from_str</code> function as before, but this time we
|
||
assign the return value to a variable of type <code>Person</code> so Serde will
|
||
automatically interpret the input data as a <code>Person</code> and produce informative
|
||
error messages if the layout does not conform to what a <code>Person</code> is expected
|
||
to look like.</p>
|
||
<p>Any type that implements Serde’s <code>Deserialize</code> trait can be deserialized
|
||
this way. This includes built-in Rust standard library types like <code>Vec<T></code>
|
||
and <code>HashMap<K, V></code>, as well as any structs or enums annotated with
|
||
<code>#[derive(Deserialize)]</code>.</p>
|
||
<p>Once we have <code>p</code> of type <code>Person</code>, our IDE and the Rust compiler can help us
|
||
use it correctly like they do for any other Rust code. The IDE can
|
||
autocomplete field names to prevent typos, which was impossible in the
|
||
<code>serde_json::Value</code> representation. And the Rust compiler can check that
|
||
when we write <code>p.phones[0]</code>, then <code>p.phones</code> is guaranteed to be a
|
||
<code>Vec<String></code> so indexing into it makes sense and produces a <code>String</code>.</p>
|
||
<h2 id="constructing-json-values"><a class="doc-anchor" href="#constructing-json-values">§</a>Constructing JSON values</h2>
|
||
<p>Serde JSON provides a <a href="macro.json.html" title="macro serde_json::json"><code>json!</code> macro</a> to build <code>serde_json::Value</code>
|
||
objects with very natural JSON syntax.</p>
|
||
|
||
<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use </span>serde_json::json;
|
||
|
||
<span class="kw">fn </span>main() {
|
||
<span class="comment">// The type of `john` is `serde_json::Value`
|
||
</span><span class="kw">let </span>john = <span class="macro">json!</span>({
|
||
<span class="string">"name"</span>: <span class="string">"John Doe"</span>,
|
||
<span class="string">"age"</span>: <span class="number">43</span>,
|
||
<span class="string">"phones"</span>: [
|
||
<span class="string">"+44 1234567"</span>,
|
||
<span class="string">"+44 2345678"
|
||
</span>]
|
||
});
|
||
|
||
<span class="macro">println!</span>(<span class="string">"first phone number: {}"</span>, john[<span class="string">"phones"</span>][<span class="number">0</span>]);
|
||
|
||
<span class="comment">// Convert to a string of JSON and print it out
|
||
</span><span class="macro">println!</span>(<span class="string">"{}"</span>, john.to_string());
|
||
}</code></pre></div>
|
||
<p>The <code>Value::to_string()</code> function converts a <code>serde_json::Value</code> into a
|
||
<code>String</code> of JSON text.</p>
|
||
<p>One neat thing about the <code>json!</code> macro is that variables and expressions can
|
||
be interpolated directly into the JSON value as you are building it. Serde
|
||
will check at compile time that the value you are interpolating is able to
|
||
be represented as JSON.</p>
|
||
|
||
<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">let </span>full_name = <span class="string">"John Doe"</span>;
|
||
<span class="kw">let </span>age_last_year = <span class="number">42</span>;
|
||
|
||
<span class="comment">// The type of `john` is `serde_json::Value`
|
||
</span><span class="kw">let </span>john = <span class="macro">json!</span>({
|
||
<span class="string">"name"</span>: full_name,
|
||
<span class="string">"age"</span>: age_last_year + <span class="number">1</span>,
|
||
<span class="string">"phones"</span>: [
|
||
<span class="macro">format!</span>(<span class="string">"+44 {}"</span>, random_phone())
|
||
]
|
||
});</code></pre></div>
|
||
<p>This is amazingly convenient, but we have the problem we had before with
|
||
<code>Value</code>: the IDE and Rust compiler cannot help us if we get it wrong. Serde
|
||
JSON provides a better way of serializing strongly-typed data structures
|
||
into JSON text.</p>
|
||
<h2 id="creating-json-by-serializing-data-structures"><a class="doc-anchor" href="#creating-json-by-serializing-data-structures">§</a>Creating JSON by serializing data structures</h2>
|
||
<p>A data structure can be converted to a JSON string by
|
||
<a href="fn.to_string.html" title="fn serde_json::to_string"><code>serde_json::to_string</code></a>. There is also
|
||
<a href="fn.to_vec.html" title="fn serde_json::to_vec"><code>serde_json::to_vec</code></a> which serializes to a <code>Vec<u8></code> and
|
||
<a href="fn.to_writer.html" title="fn serde_json::to_writer"><code>serde_json::to_writer</code></a> which serializes to any <code>io::Write</code>
|
||
such as a File or a TCP stream.</p>
|
||
|
||
<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use </span>serde::{Deserialize, Serialize};
|
||
<span class="kw">use </span>serde_json::Result;
|
||
|
||
<span class="attr">#[derive(Serialize, Deserialize)]
|
||
</span><span class="kw">struct </span>Address {
|
||
street: String,
|
||
city: String,
|
||
}
|
||
|
||
<span class="kw">fn </span>print_an_address() -> <span class="prelude-ty">Result</span><()> {
|
||
<span class="comment">// Some data structure.
|
||
</span><span class="kw">let </span>address = Address {
|
||
street: <span class="string">"10 Downing Street"</span>.to_owned(),
|
||
city: <span class="string">"London"</span>.to_owned(),
|
||
};
|
||
|
||
<span class="comment">// Serialize it to a JSON string.
|
||
</span><span class="kw">let </span>j = serde_json::to_string(<span class="kw-2">&</span>address)<span class="question-mark">?</span>;
|
||
|
||
<span class="comment">// Print, write to a file, or send to an HTTP server.
|
||
</span><span class="macro">println!</span>(<span class="string">"{}"</span>, j);
|
||
|
||
<span class="prelude-val">Ok</span>(())
|
||
}</code></pre></div>
|
||
<p>Any type that implements Serde’s <code>Serialize</code> trait can be serialized this
|
||
way. This includes built-in Rust standard library types like <code>Vec<T></code> and
|
||
<code>HashMap<K, V></code>, as well as any structs or enums annotated with
|
||
<code>#[derive(Serialize)]</code>.</p>
|
||
<h2 id="no-std-support"><a class="doc-anchor" href="#no-std-support">§</a>No-std support</h2>
|
||
<p>As long as there is a memory allocator, it is possible to use serde_json
|
||
without the rest of the Rust standard library. Disable the default “std”
|
||
feature and enable the “alloc” feature:</p>
|
||
<div class="example-wrap"><pre class="language-toml"><code>[dependencies]
|
||
serde_json = { version = "1.0", default-features = false, features = ["alloc"] }</code></pre></div>
|
||
<p>For JSON support in Serde without a memory allocator, please see the
|
||
<a href="https://github.com/rust-embedded-community/serde-json-core"><code>serde-json-core</code></a> crate.</p>
|
||
</div></details><h2 id="modules" class="section-header">Modules<a href="#modules" class="anchor">§</a></h2><dl class="item-table"><dt><a class="mod" href="de/index.html" title="mod serde_json::de">de</a></dt><dd>Deserialize JSON data to a Rust data structure.</dd><dt><a class="mod" href="error/index.html" title="mod serde_json::error">error</a></dt><dd>When serializing or deserializing JSON goes wrong.</dd><dt><a class="mod" href="map/index.html" title="mod serde_json::map">map</a></dt><dd>A map of String to serde_json::Value.</dd><dt><a class="mod" href="ser/index.html" title="mod serde_json::ser">ser</a></dt><dd>Serialize a Rust data structure into JSON data.</dd><dt><a class="mod" href="value/index.html" title="mod serde_json::value">value</a></dt><dd>The Value enum, a loosely typed way of representing any valid JSON value.</dd></dl><h2 id="macros" class="section-header">Macros<a href="#macros" class="anchor">§</a></h2><dl class="item-table"><dt><a class="macro" href="macro.json.html" title="macro serde_json::json">json</a></dt><dd>Construct a <code>serde_json::Value</code> from a JSON literal.</dd></dl><h2 id="structs" class="section-header">Structs<a href="#structs" class="anchor">§</a></h2><dl class="item-table"><dt><a class="struct" href="struct.Deserializer.html" title="struct serde_json::Deserializer">Deserializer</a></dt><dd>A structure that deserializes JSON into Rust values.</dd><dt><a class="struct" href="struct.Error.html" title="struct serde_json::Error">Error</a></dt><dd>This type represents all possible errors that can occur when serializing or
|
||
deserializing JSON data.</dd><dt><a class="struct" href="struct.Map.html" title="struct serde_json::Map">Map</a></dt><dd>Represents a JSON key/value type.</dd><dt><a class="struct" href="struct.Number.html" title="struct serde_json::Number">Number</a></dt><dd>Represents a JSON number, whether integer or floating point.</dd><dt><a class="struct" href="struct.Serializer.html" title="struct serde_json::Serializer">Serializer</a></dt><dd>A structure for serializing Rust values into JSON.</dd><dt><a class="struct" href="struct.StreamDeserializer.html" title="struct serde_json::StreamDeserializer">Stream<wbr>Deserializer</a></dt><dd>Iterator that deserializes a stream into multiple JSON values.</dd></dl><h2 id="enums" class="section-header">Enums<a href="#enums" class="anchor">§</a></h2><dl class="item-table"><dt><a class="enum" href="enum.Value.html" title="enum serde_json::Value">Value</a></dt><dd>Represents any valid JSON value.</dd></dl><h2 id="functions" class="section-header">Functions<a href="#functions" class="anchor">§</a></h2><dl class="item-table"><dt><a class="fn" href="fn.from_reader.html" title="fn serde_json::from_reader">from_<wbr>reader</a></dt><dd>Deserialize an instance of type <code>T</code> from an I/O stream of JSON.</dd><dt><a class="fn" href="fn.from_slice.html" title="fn serde_json::from_slice">from_<wbr>slice</a></dt><dd>Deserialize an instance of type <code>T</code> from bytes of JSON text.</dd><dt><a class="fn" href="fn.from_str.html" title="fn serde_json::from_str">from_<wbr>str</a></dt><dd>Deserialize an instance of type <code>T</code> from a string of JSON text.</dd><dt><a class="fn" href="fn.from_value.html" title="fn serde_json::from_value">from_<wbr>value</a></dt><dd>Interpret a <code>serde_json::Value</code> as an instance of type <code>T</code>.</dd><dt><a class="fn" href="fn.to_string.html" title="fn serde_json::to_string">to_<wbr>string</a></dt><dd>Serialize the given data structure as a String of JSON.</dd><dt><a class="fn" href="fn.to_string_pretty.html" title="fn serde_json::to_string_pretty">to_<wbr>string_<wbr>pretty</a></dt><dd>Serialize the given data structure as a pretty-printed String of JSON.</dd><dt><a class="fn" href="fn.to_value.html" title="fn serde_json::to_value">to_<wbr>value</a></dt><dd>Convert a <code>T</code> into <code>serde_json::Value</code> which is an enum that can represent
|
||
any valid JSON data.</dd><dt><a class="fn" href="fn.to_vec.html" title="fn serde_json::to_vec">to_vec</a></dt><dd>Serialize the given data structure as a JSON byte vector.</dd><dt><a class="fn" href="fn.to_vec_pretty.html" title="fn serde_json::to_vec_pretty">to_<wbr>vec_<wbr>pretty</a></dt><dd>Serialize the given data structure as a pretty-printed JSON byte vector.</dd><dt><a class="fn" href="fn.to_writer.html" title="fn serde_json::to_writer">to_<wbr>writer</a></dt><dd>Serialize the given data structure as JSON into the I/O stream.</dd><dt><a class="fn" href="fn.to_writer_pretty.html" title="fn serde_json::to_writer_pretty">to_<wbr>writer_<wbr>pretty</a></dt><dd>Serialize the given data structure as pretty-printed JSON into the I/O
|
||
stream.</dd></dl><h2 id="types" class="section-header">Type Aliases<a href="#types" class="anchor">§</a></h2><dl class="item-table"><dt><a class="type" href="type.Result.html" title="type serde_json::Result">Result</a></dt><dd>Alias for a <code>Result</code> with the error type <code>serde_json::Error</code>.</dd></dl></section></div></main></body></html> |