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// Copyright 2017 Serde Developers // // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your // option. This file may not be copied, modified, or distributed // except according to those terms. //! # Serde JSON //! //! JSON is a ubiquitous open-standard format that uses human-readable text to //! transmit data objects consisting of key-value pairs. //! //! ```json,ignore //! { //! "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 //! # use serde_json::{Number, Map}; //! # //! # #[allow(dead_code)] //! 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. //! //! ```rust //! extern crate serde_json; //! //! use serde_json::{Value, Error}; //! //! fn untyped_example() -> Result<(), Error> { //! // 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(()) //! } //! # //! # fn main() { //! # untyped_example().unwrap(); //! # } //! ``` //! //! 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.serde.rs/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. //! //! ```rust //! extern crate serde; //! extern crate serde_json; //! //! #[macro_use] //! extern crate serde_derive; //! //! use serde_json::Error; //! //! #[derive(Serialize, Deserialize)] //! struct Person { //! name: String, //! age: u8, //! phones: Vec<String>, //! } //! //! fn typed_example() -> Result<(), Error> { //! // 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(()) //! } //! # //! # fn main() { //! # typed_example().unwrap(); //! # } //! ``` //! //! 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`. //! //! # Constructing JSON values //! //! Serde JSON provides a [`json!` macro][macro] to build `serde_json::Value` //! objects with very natural JSON syntax. In order to use this macro, //! `serde_json` needs to be imported with the `#[macro_use]` attribute. //! //! ```rust //! #[macro_use] //! extern crate serde_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. //! //! ```rust //! # #[macro_use] //! # extern crate serde_json; //! # //! # fn random_phone() -> u16 { 0 } //! # //! # fn main() { //! 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()) //! ] //! }); //! # let _ = john; //! # } //! ``` //! //! This is amazingly convenient but we have the problem we had before with //! `Value` which is that 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. //! //! ```rust //! extern crate serde; //! extern crate serde_json; //! //! #[macro_use] //! extern crate serde_derive; //! //! use serde_json::Error; //! //! #[derive(Serialize, Deserialize)] //! struct Address { //! street: String, //! city: String, //! } //! //! fn print_an_address() -> Result<(), Error> { //! // 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(()) //! } //! # //! # fn main() { //! # print_an_address().unwrap(); //! # } //! ``` //! //! 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)]`. //! //! # No-std support //! //! This crate currently requires the Rust standard library. For JSON support in //! Serde without a standard library, please see the [`serde-json-core`] crate. //! //! [value]: https://docs.serde.rs/serde_json/value/enum.Value.html //! [from_str]: https://docs.serde.rs/serde_json/de/fn.from_str.html //! [from_slice]: https://docs.serde.rs/serde_json/de/fn.from_slice.html //! [from_reader]: https://docs.serde.rs/serde_json/de/fn.from_reader.html //! [to_string]: https://docs.serde.rs/serde_json/ser/fn.to_string.html //! [to_vec]: https://docs.serde.rs/serde_json/ser/fn.to_vec.html //! [to_writer]: https://docs.serde.rs/serde_json/ser/fn.to_writer.html //! [macro]: https://docs.serde.rs/serde_json/macro.json.html //! [`serde-json-core`]: https://japaric.github.io/serde-json-core/serde_json_core/ #![doc(html_root_url = "https://docs.rs/serde_json/1.0.33")] #![cfg_attr(feature = "cargo-clippy", allow(renamed_and_removed_lints))] #![cfg_attr(feature = "cargo-clippy", deny(clippy, clippy_pedantic))] // Ignored clippy lints #![cfg_attr( feature = "cargo-clippy", allow(deprecated_cfg_attr, doc_markdown, needless_pass_by_value,) )] // Ignored clippy_pedantic lints #![cfg_attr(feature = "cargo-clippy", allow( // Deserializer::from_str, into_iter should_implement_trait, // integer and float ser/de requires these sorts of casts cast_possible_truncation, cast_possible_wrap, cast_precision_loss, cast_sign_loss, // string ser/de uses indexing and slicing indexing_slicing, // things are often more readable this way cast_lossless, shadow_reuse, shadow_unrelated, single_match_else, stutter, use_self, // not practical missing_docs_in_private_items, similar_names, // we support older compilers redundant_field_names, ))] #![deny(missing_docs)] #[macro_use] extern crate serde; #[cfg(feature = "preserve_order")] extern crate indexmap; extern crate itoa; extern crate ryu; #[doc(inline)] pub use self::de::{from_reader, from_slice, from_str, Deserializer, StreamDeserializer}; #[doc(inline)] pub use self::error::{Error, Result}; #[doc(inline)] pub use self::ser::{ to_string, to_string_pretty, to_vec, to_vec_pretty, to_writer, to_writer_pretty, Serializer, }; #[doc(inline)] pub use self::value::{from_value, to_value, Map, Number, Value}; // We only use our own error type; no need for From conversions provided by the // standard library's try! macro. This reduces lines of LLVM IR by 4%. macro_rules! try { ($e:expr) => { match $e { ::std::result::Result::Ok(val) => val, ::std::result::Result::Err(err) => return ::std::result::Result::Err(err), } }; } #[macro_use] mod macros; pub mod de; pub mod error; pub mod map; pub mod ser; pub mod value; mod iter; mod number; mod read; #[cfg(feature = "raw_value")] mod raw;