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authorDaniel Baumann <daniel.baumann@progress-linux.org>2024-05-04 12:47:55 +0000
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+# Serde JSON &emsp; [![Build Status]][actions] [![Latest Version]][crates.io] [![Rustc Version 1.36+]][rustc]
+
+[Build Status]: https://img.shields.io/github/actions/workflow/status/serde-rs/json/ci.yml?branch=master
+[actions]: https://github.com/serde-rs/json/actions?query=branch%3Amaster
+[Latest Version]: https://img.shields.io/crates/v/serde_json.svg
+[crates.io]: https://crates.io/crates/serde\_json
+[Rustc Version 1.36+]: https://img.shields.io/badge/rustc-1.36+-lightgray.svg
+[rustc]: https://blog.rust-lang.org/2019/07/04/Rust-1.36.0.html
+
+**Serde is a framework for *ser*ializing and *de*serializing Rust data structures efficiently and generically.**
+
+---
+
+```toml
+[dependencies]
+serde_json = "1.0"
+```
+
+You may be looking for:
+
+- [JSON API documentation](https://docs.rs/serde_json)
+- [Serde API documentation](https://docs.rs/serde)
+- [Detailed documentation about Serde](https://serde.rs/)
+- [Setting up `#[derive(Serialize, Deserialize)]`](https://serde.rs/derive.html)
+- [Release notes](https://github.com/serde-rs/json/releases)
+
+JSON is a ubiquitous open-standard format that uses human-readable text to
+transmit data objects consisting of key-value pairs.
+
+```json
+{
+ "name": "John Doe",
+ "age": 43,
+ "address": {
+ "street": "10 Downing Street",
+ "city": "London"
+ },
+ "phones": [
+ "+44 1234567",
+ "+44 2345678"
+ ]
+}
+```
+
+There are three common ways that you might find yourself needing to work with
+JSON data in Rust.
+
+ - **As text data.** 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.
+ - **As an untyped or loosely typed representation.** 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.
+ - **As a strongly typed Rust data structure.** 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.
+
+Serde JSON provides efficient, flexible, safe ways of converting data between
+each of these representations.
+
+## Operating on untyped JSON values
+
+Any valid JSON data can be manipulated in the following recursive enum
+representation. This data structure is [`serde_json::Value`][value].
+
+```rust
+enum Value {
+ Null,
+ Bool(bool),
+ Number(Number),
+ String(String),
+ Array(Vec<Value>),
+ Object(Map<String, Value>),
+}
+```
+
+A string of JSON data can be parsed into a `serde_json::Value` by the
+[`serde_json::from_str`][from_str] function. There is also
+[`from_slice`][from_slice] for parsing from a byte slice &\[u8\] and
+[`from_reader`][from_reader] for parsing from any `io::Read` like a File or a
+TCP stream.
+
+<div align="right">
+<a href="https://play.rust-lang.org/?edition=2018&gist=d69d8e3156d4bb81c4461b60b772ab72" target="_blank">
+<img align="center" width="85" src="https://raw.githubusercontent.com/serde-rs/serde-rs.github.io/master/img/runtab.png">
+</a>
+</div>
+
+```rust
+use serde_json::{Result, Value};
+
+fn untyped_example() -> Result<()> {
+ // Some JSON input data as a &str. Maybe this comes from the user.
+ let data = r#"
+ {
+ "name": "John Doe",
+ "age": 43,
+ "phones": [
+ "+44 1234567",
+ "+44 2345678"
+ ]
+ }"#;
+
+ // Parse the string of data into serde_json::Value.
+ let v: Value = serde_json::from_str(data)?;
+
+ // Access parts of the data by indexing with square brackets.
+ println!("Please call {} at the number {}", v["name"], v["phones"][0]);
+
+ Ok(())
+}
+```
+
+The result of square bracket indexing like `v["name"]` is a borrow of the data
+at that index, so the type is `&Value`. 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 `Value::Null`.
+
+When a `Value` is printed, it is printed as a JSON string. So in the code above,
+the output looks like `Please call "John Doe" at the number "+44 1234567"`. The
+quotation marks appear because `v["name"]` is a `&Value` containing a JSON
+string and its JSON representation is `"John Doe"`. Printing as a plain string
+without quotation marks involves converting from a JSON string to a Rust string
+with [`as_str()`] or avoiding the use of `Value` as described in the following
+section.
+
+[`as_str()`]: https://docs.rs/serde_json/1/serde_json/enum.Value.html#method.as_str
+
+The `Value` 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 `v["name"]` as `v["nmae"]`
+in one of the dozens of places it is used in your code.
+
+## Parsing JSON as strongly typed data structures
+
+Serde provides a powerful way of mapping JSON data into Rust data structures
+largely automatically.
+
+<div align="right">
+<a href="https://play.rust-lang.org/?edition=2018&gist=15cfab66d38ff8a15a9cf1d8d897ac68" target="_blank">
+<img align="center" width="85" src="https://raw.githubusercontent.com/serde-rs/serde-rs.github.io/master/img/runtab.png">
+</a>
+</div>
+
+```rust
+use serde::{Deserialize, Serialize};
+use serde_json::Result;
+
+#[derive(Serialize, Deserialize)]
+struct Person {
+ name: String,
+ age: u8,
+ phones: Vec<String>,
+}
+
+fn typed_example() -> Result<()> {
+ // Some JSON input data as a &str. Maybe this comes from the user.
+ let data = r#"
+ {
+ "name": "John Doe",
+ "age": 43,
+ "phones": [
+ "+44 1234567",
+ "+44 2345678"
+ ]
+ }"#;
+
+ // 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.
+ let p: Person = serde_json::from_str(data)?;
+
+ // Do things just like with any other Rust data structure.
+ println!("Please call {} at the number {}", p.name, p.phones[0]);
+
+ Ok(())
+}
+```
+
+This is the same `serde_json::from_str` function as before, but this time we
+assign the return value to a variable of type `Person` so Serde will
+automatically interpret the input data as a `Person` and produce informative
+error messages if the layout does not conform to what a `Person` is expected to
+look like.
+
+Any type that implements Serde's `Deserialize` trait can be deserialized this
+way. This includes built-in Rust standard library types like `Vec<T>` and
+`HashMap<K, V>`, as well as any structs or enums annotated with
+`#[derive(Deserialize)]`.
+
+Once we have `p` of type `Person`, 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 `serde_json::Value`
+representation. And the Rust compiler can check that when we write
+`p.phones[0]`, then `p.phones` is guaranteed to be a `Vec<String>` so indexing
+into it makes sense and produces a `String`.
+
+The necessary setup for using Serde's derive macros is explained on the *[Using
+derive]* page of the Serde site.
+
+[Using derive]: https://serde.rs/derive.html
+
+## Constructing JSON values
+
+Serde JSON provides a [`json!` macro][macro] to build `serde_json::Value`
+objects with very natural JSON syntax.
+
+<div align="right">
+<a href="https://play.rust-lang.org/?edition=2018&gist=6ccafad431d72b62e77cc34c8e879b24" target="_blank">
+<img align="center" width="85" src="https://raw.githubusercontent.com/serde-rs/serde-rs.github.io/master/img/runtab.png">
+</a>
+</div>
+
+```rust
+use serde_json::json;
+
+fn main() {
+ // The type of `john` is `serde_json::Value`
+ let john = json!({
+ "name": "John Doe",
+ "age": 43,
+ "phones": [
+ "+44 1234567",
+ "+44 2345678"
+ ]
+ });
+
+ println!("first phone number: {}", john["phones"][0]);
+
+ // Convert to a string of JSON and print it out
+ println!("{}", john.to_string());
+}
+```
+
+The `Value::to_string()` function converts a `serde_json::Value` into a `String`
+of JSON text.
+
+One neat thing about the `json!` 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.
+
+<div align="right">
+<a href="https://play.rust-lang.org/?edition=2018&gist=f9101a6e61dfc9e02c6a67f315ed24f2" target="_blank">
+<img align="center" width="85" src="https://raw.githubusercontent.com/serde-rs/serde-rs.github.io/master/img/runtab.png">
+</a>
+</div>
+
+```rust
+let full_name = "John Doe";
+let age_last_year = 42;
+
+// The type of `john` is `serde_json::Value`
+let john = json!({
+ "name": full_name,
+ "age": age_last_year + 1,
+ "phones": [
+ format!("+44 {}", random_phone())
+ ]
+});
+```
+
+This is amazingly convenient, but we have the problem we had before with
+`Value`: 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.
+
+## Creating JSON by serializing data structures
+
+A data structure can be converted to a JSON string by
+[`serde_json::to_string`][to_string]. There is also
+[`serde_json::to_vec`][to_vec] which serializes to a `Vec<u8>` and
+[`serde_json::to_writer`][to_writer] which serializes to any `io::Write`
+such as a File or a TCP stream.
+
+<div align="right">
+<a href="https://play.rust-lang.org/?edition=2018&gist=3472242a08ed2ff88a944f2a2283b0ee" target="_blank">
+<img align="center" width="85" src="https://raw.githubusercontent.com/serde-rs/serde-rs.github.io/master/img/runtab.png">
+</a>
+</div>
+
+```rust
+use serde::{Deserialize, Serialize};
+use serde_json::Result;
+
+#[derive(Serialize, Deserialize)]
+struct Address {
+ street: String,
+ city: String,
+}
+
+fn print_an_address() -> Result<()> {
+ // Some data structure.
+ let address = Address {
+ street: "10 Downing Street".to_owned(),
+ city: "London".to_owned(),
+ };
+
+ // Serialize it to a JSON string.
+ let j = serde_json::to_string(&address)?;
+
+ // Print, write to a file, or send to an HTTP server.
+ println!("{}", j);
+
+ Ok(())
+}
+```
+
+Any type that implements Serde's `Serialize` trait can be serialized this way.
+This includes built-in Rust standard library types like `Vec<T>` and `HashMap<K,
+V>`, as well as any structs or enums annotated with `#[derive(Serialize)]`.
+
+## Performance
+
+It is fast. You should expect in the ballpark of 500 to 1000 megabytes per
+second deserialization and 600 to 900 megabytes per second serialization,
+depending on the characteristics of your data. This is competitive with the
+fastest C and C++ JSON libraries or even 30% faster for many use cases.
+Benchmarks live in the [serde-rs/json-benchmark] repo.
+
+[serde-rs/json-benchmark]: https://github.com/serde-rs/json-benchmark
+
+## Getting help
+
+Serde is one of the most widely used Rust libraries, so any place that
+Rustaceans congregate will be able to help you out. For chat, consider trying
+the [#rust-questions] or [#rust-beginners] channels of the unofficial community
+Discord (invite: <https://discord.gg/rust-lang-community>), the [#rust-usage] or
+[#beginners] channels of the official Rust Project Discord (invite:
+<https://discord.gg/rust-lang>), or the [#general][zulip] stream in Zulip. For
+asynchronous, consider the [\[rust\] tag on StackOverflow][stackoverflow], the
+[/r/rust] subreddit which has a pinned weekly easy questions post, or the Rust
+[Discourse forum][discourse]. It's acceptable to file a support issue in this
+repo, but they tend not to get as many eyes as any of the above and may get
+closed without a response after some time.
+
+[#rust-questions]: https://discord.com/channels/273534239310479360/274215136414400513
+[#rust-beginners]: https://discord.com/channels/273534239310479360/273541522815713281
+[#rust-usage]: https://discord.com/channels/442252698964721669/443150878111694848
+[#beginners]: https://discord.com/channels/442252698964721669/448238009733742612
+[zulip]: https://rust-lang.zulipchat.com/#narrow/stream/122651-general
+[stackoverflow]: https://stackoverflow.com/questions/tagged/rust
+[/r/rust]: https://www.reddit.com/r/rust
+[discourse]: https://users.rust-lang.org
+
+## No-std support
+
+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:
+
+```toml
+[dependencies]
+serde_json = { version = "1.0", default-features = false, features = ["alloc"] }
+```
+
+For JSON support in Serde without a memory allocator, please see the
+[`serde-json-core`] crate.
+
+[`serde-json-core`]: https://github.com/rust-embedded-community/serde-json-core
+
+[value]: https://docs.rs/serde_json/1/serde_json/value/enum.Value.html
+[from_str]: https://docs.rs/serde_json/1/serde_json/de/fn.from_str.html
+[from_slice]: https://docs.rs/serde_json/1/serde_json/de/fn.from_slice.html
+[from_reader]: https://docs.rs/serde_json/1/serde_json/de/fn.from_reader.html
+[to_string]: https://docs.rs/serde_json/1/serde_json/ser/fn.to_string.html
+[to_vec]: https://docs.rs/serde_json/1/serde_json/ser/fn.to_vec.html
+[to_writer]: https://docs.rs/serde_json/1/serde_json/ser/fn.to_writer.html
+[macro]: https://docs.rs/serde_json/1/serde_json/macro.json.html
+
+<br>
+
+#### License
+
+<sup>
+Licensed under either of <a href="LICENSE-APACHE">Apache License, Version
+2.0</a> or <a href="LICENSE-MIT">MIT license</a> at your option.
+</sup>
+
+<br>
+
+<sub>
+Unless you explicitly state otherwise, any contribution intentionally submitted
+for inclusion in this crate by you, as defined in the Apache-2.0 license, shall
+be dual licensed as above, without any additional terms or conditions.
+</sub>