| <!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"><meta name="keywords" content="rust, rustlang, rust-lang, serde_json"><title>serde_json - Rust</title><link rel="preload" as="font" type="font/woff2" crossorigin href="../SourceSerif4-Regular.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../FiraSans-Regular.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../FiraSans-Medium.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../SourceCodePro-Regular.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../SourceSerif4-Bold.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../SourceCodePro-Semibold.ttf.woff2"><link rel="stylesheet" href="../normalize.css"><link rel="stylesheet" href="../rustdoc.css" id="mainThemeStyle"><link rel="stylesheet" href="../ayu.css" disabled><link rel="stylesheet" href="../dark.css" disabled><link rel="stylesheet" href="../light.css" id="themeStyle"><script id="default-settings" ></script><script src="../storage.js"></script><script defer src="../crates.js"></script><script defer src="../main.js"></script><noscript><link rel="stylesheet" href="../noscript.css"></noscript><link rel="alternate icon" type="image/png" href="../favicon-16x16.png"><link rel="alternate icon" type="image/png" href="../favicon-32x32.png"><link rel="icon" type="image/svg+xml" href="../favicon.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]--><nav class="mobile-topbar"><button class="sidebar-menu-toggle">☰</button><a class="sidebar-logo" href="../serde_json/index.html"><div class="logo-container"><img class="rust-logo" src="../rust-logo.svg" alt="logo"></div></a><h2></h2></nav><nav class="sidebar"><a class="sidebar-logo" href="../serde_json/index.html"><div class="logo-container"><img class="rust-logo" src="../rust-logo.svg" alt="logo"></div></a><h2 class="location"><a href="#">Crate serde_json</a></h2><div class="sidebar-elems"><ul class="block"><li class="version">Version 1.0.96</li><li><a id="all-types" href="all.html">All Items</a></li></ul><section><ul class="block"><li><a href="#modules">Modules</a></li><li><a href="#macros">Macros</a></li><li><a href="#structs">Structs</a></li><li><a href="#enums">Enums</a></li><li><a href="#functions">Functions</a></li><li><a href="#types">Type Definitions</a></li></ul></section></div></nav><main><div class="width-limiter"><nav class="sub"><form class="search-form"><div class="search-container"><span></span><input class="search-input" name="search" autocomplete="off" spellcheck="false" placeholder="Click or press ‘S’ to search, ‘?’ for more options…" type="search"><div id="help-button" title="help" tabindex="-1"><a href="../help.html">?</a></div><div id="settings-menu" tabindex="-1"><a href="../settings.html" title="settings"><img width="22" height="22" alt="Change settings" src="../wheel.svg"></a></div></div></form></nav><section id="main-content" class="content"><div class="main-heading"><h1 class="fqn">Crate <a class="mod" href="#">serde_json</a><button id="copy-path" onclick="copy_path(this)" title="Copy item path to clipboard"><img src="../clipboard.svg" width="19" height="18" alt="Copy item path"></button></h1><span class="out-of-band"><a class="srclink" href="../src/serde_json/lib.rs.html#1-422">source</a> · <a id="toggle-all-docs" href="javascript:void(0)" title="collapse all docs">[<span class="inner">−</span>]</a></span></div><details class="rustdoc-toggle top-doc" open><summary class="hideme"><span>Expand description</span></summary><div class="docblock"><h2 id="serde-json"><a href="#serde-json">Serde JSON</a></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 href="#operating-on-untyped-json-values">Operating on untyped JSON values</a></h2> |
| <p>Any valid JSON data can be manipulated in the following recursive enum |
| representation. This data structure is <a href="enum.Value.html"><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"><code>serde_json::from_str</code></a> function. There is also |
| <a href="fn.from_slice.html"><code>from_slice</code></a> for parsing from a byte slice &[u8] and |
| <a href="fn.from_reader.html"><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"><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 href="#parsing-json-as-strongly-typed-data-structures">Parsing JSON as strongly typed data structures</a></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="attribute">#[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 href="#constructing-json-values">Constructing JSON values</a></h2> |
| <p>Serde JSON provides a <a href="macro.json.html"><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 href="#creating-json-by-serializing-data-structures">Creating JSON by serializing data structures</a></h2> |
| <p>A data structure can be converted to a JSON string by |
| <a href="fn.to_string.html"><code>serde_json::to_string</code></a>. There is also |
| <a href="fn.to_vec.html"><code>serde_json::to_vec</code></a> which serializes to a <code>Vec<u8></code> and |
| <a href="fn.to_writer.html"><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="attribute">#[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 href="#no-std-support">No-std support</a></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="small-section-header"><a href="#modules">Modules</a></h2><div class="item-table"><div class="item-row"><div class="item-left module-item"><a class="mod" href="de/index.html" title="serde_json::de mod">de</a></div><div class="item-right docblock-short">Deserialize JSON data to a Rust data structure.</div></div><div class="item-row"><div class="item-left module-item"><a class="mod" href="error/index.html" title="serde_json::error mod">error</a></div><div class="item-right docblock-short">When serializing or deserializing JSON goes wrong.</div></div><div class="item-row"><div class="item-left module-item"><a class="mod" href="map/index.html" title="serde_json::map mod">map</a></div><div class="item-right docblock-short">A map of String to serde_json::Value.</div></div><div class="item-row"><div class="item-left module-item"><a class="mod" href="ser/index.html" title="serde_json::ser mod">ser</a></div><div class="item-right docblock-short">Serialize a Rust data structure into JSON data.</div></div><div class="item-row"><div class="item-left module-item"><a class="mod" href="value/index.html" title="serde_json::value mod">value</a></div><div class="item-right docblock-short">The Value enum, a loosely typed way of representing any valid JSON value.</div></div></div><h2 id="macros" class="small-section-header"><a href="#macros">Macros</a></h2><div class="item-table"><div class="item-row"><div class="item-left module-item"><a class="macro" href="macro.json.html" title="serde_json::json macro">json</a></div><div class="item-right docblock-short">Construct a <code>serde_json::Value</code> from a JSON literal.</div></div></div><h2 id="structs" class="small-section-header"><a href="#structs">Structs</a></h2><div class="item-table"><div class="item-row"><div class="item-left module-item"><a class="struct" href="struct.Deserializer.html" title="serde_json::Deserializer struct">Deserializer</a></div><div class="item-right docblock-short">A structure that deserializes JSON into Rust values.</div></div><div class="item-row"><div class="item-left module-item"><a class="struct" href="struct.Error.html" title="serde_json::Error struct">Error</a></div><div class="item-right docblock-short">This type represents all possible errors that can occur when serializing or |
| deserializing JSON data.</div></div><div class="item-row"><div class="item-left module-item"><a class="struct" href="struct.Map.html" title="serde_json::Map struct">Map</a></div><div class="item-right docblock-short">Represents a JSON key/value type.</div></div><div class="item-row"><div class="item-left module-item"><a class="struct" href="struct.Number.html" title="serde_json::Number struct">Number</a></div><div class="item-right docblock-short">Represents a JSON number, whether integer or floating point.</div></div><div class="item-row"><div class="item-left module-item"><a class="struct" href="struct.Serializer.html" title="serde_json::Serializer struct">Serializer</a></div><div class="item-right docblock-short">A structure for serializing Rust values into JSON.</div></div><div class="item-row"><div class="item-left module-item"><a class="struct" href="struct.StreamDeserializer.html" title="serde_json::StreamDeserializer struct">StreamDeserializer</a></div><div class="item-right docblock-short">Iterator that deserializes a stream into multiple JSON values.</div></div></div><h2 id="enums" class="small-section-header"><a href="#enums">Enums</a></h2><div class="item-table"><div class="item-row"><div class="item-left module-item"><a class="enum" href="enum.Value.html" title="serde_json::Value enum">Value</a></div><div class="item-right docblock-short">Represents any valid JSON value.</div></div></div><h2 id="functions" class="small-section-header"><a href="#functions">Functions</a></h2><div class="item-table"><div class="item-row"><div class="item-left module-item"><a class="fn" href="fn.from_reader.html" title="serde_json::from_reader fn">from_reader</a></div><div class="item-right docblock-short">Deserialize an instance of type <code>T</code> from an IO stream of JSON.</div></div><div class="item-row"><div class="item-left module-item"><a class="fn" href="fn.from_slice.html" title="serde_json::from_slice fn">from_slice</a></div><div class="item-right docblock-short">Deserialize an instance of type <code>T</code> from bytes of JSON text.</div></div><div class="item-row"><div class="item-left module-item"><a class="fn" href="fn.from_str.html" title="serde_json::from_str fn">from_str</a></div><div class="item-right docblock-short">Deserialize an instance of type <code>T</code> from a string of JSON text.</div></div><div class="item-row"><div class="item-left module-item"><a class="fn" href="fn.from_value.html" title="serde_json::from_value fn">from_value</a></div><div class="item-right docblock-short">Interpret a <code>serde_json::Value</code> as an instance of type <code>T</code>.</div></div><div class="item-row"><div class="item-left module-item"><a class="fn" href="fn.to_string.html" title="serde_json::to_string fn">to_string</a></div><div class="item-right docblock-short">Serialize the given data structure as a String of JSON.</div></div><div class="item-row"><div class="item-left module-item"><a class="fn" href="fn.to_string_pretty.html" title="serde_json::to_string_pretty fn">to_string_pretty</a></div><div class="item-right docblock-short">Serialize the given data structure as a pretty-printed String of JSON.</div></div><div class="item-row"><div class="item-left module-item"><a class="fn" href="fn.to_value.html" title="serde_json::to_value fn">to_value</a></div><div class="item-right docblock-short">Convert a <code>T</code> into <code>serde_json::Value</code> which is an enum that can represent |
| any valid JSON data.</div></div><div class="item-row"><div class="item-left module-item"><a class="fn" href="fn.to_vec.html" title="serde_json::to_vec fn">to_vec</a></div><div class="item-right docblock-short">Serialize the given data structure as a JSON byte vector.</div></div><div class="item-row"><div class="item-left module-item"><a class="fn" href="fn.to_vec_pretty.html" title="serde_json::to_vec_pretty fn">to_vec_pretty</a></div><div class="item-right docblock-short">Serialize the given data structure as a pretty-printed JSON byte vector.</div></div><div class="item-row"><div class="item-left module-item"><a class="fn" href="fn.to_writer.html" title="serde_json::to_writer fn">to_writer</a></div><div class="item-right docblock-short">Serialize the given data structure as JSON into the IO stream.</div></div><div class="item-row"><div class="item-left module-item"><a class="fn" href="fn.to_writer_pretty.html" title="serde_json::to_writer_pretty fn">to_writer_pretty</a></div><div class="item-right docblock-short">Serialize the given data structure as pretty-printed JSON into the IO |
| stream.</div></div></div><h2 id="types" class="small-section-header"><a href="#types">Type Definitions</a></h2><div class="item-table"><div class="item-row"><div class="item-left module-item"><a class="type" href="type.Result.html" title="serde_json::Result type">Result</a></div><div class="item-right docblock-short">Alias for a <code>Result</code> with the error type <code>serde_json::Error</code>.</div></div></div></section></div></main><div id="rustdoc-vars" data-root-path="../" data-current-crate="serde_json" data-themes="ayu,dark,light" data-resource-suffix="" data-rustdoc-version="1.66.0-nightly (5c8bff74b 2022-10-21)" ></div></body></html> |
