#[repr(C)]
pub struct RawValue { /* private fields */ }
Expand description

Reference to a range of bytes encompassing a single valid JSON value in the input data.

A RawValue can be used to defer parsing parts of a payload until later, or to avoid parsing it at all in the case that part of the payload just needs to be transferred verbatim into a different output object.

When serializing, a value of this type will retain its original formatting and will not be minified or pretty-printed.

Note

RawValue is only available if serde_json is built with the "raw_value" feature.

[dependencies]
serde_json = { version = "1.0", features = ["raw_value"] }

Example

use serde::{Deserialize, Serialize};
use serde_json::{Result, value::RawValue};

#[derive(Deserialize)]
struct Input<'a> {
    code: u32,
    #[serde(borrow)]
    payload: &'a RawValue,
}

#[derive(Serialize)]
struct Output<'a> {
    info: (u32, &'a RawValue),
}

// Efficiently rearrange JSON input containing separate "code" and "payload"
// keys into a single "info" key holding an array of code and payload.
//
// This could be done equivalently using serde_json::Value as the type for
// payload, but &RawValue will perform better because it does not require
// memory allocation. The correct range of bytes is borrowed from the input
// data and pasted verbatim into the output.
fn rearrange(input: &str) -> Result<String> {
    let input: Input = serde_json::from_str(input)?;

    let output = Output {
        info: (input.code, input.payload),
    };

    serde_json::to_string(&output)
}

fn main() -> Result<()> {
    let out = rearrange(r#" {"code": 200, "payload": {}} "#)?;

    assert_eq!(out, r#"{"info":[200,{}]}"#);

    Ok(())
}

Ownership

The typical usage of RawValue will be in the borrowed form:

#[derive(Deserialize)]
struct SomeStruct<'a> {
    #[serde(borrow)]
    raw_value: &'a RawValue,
}

The borrowed form is suitable when deserializing through serde_json::from_str and serde_json::from_slice which support borrowing from the input data without memory allocation.

When deserializing through serde_json::from_reader you will need to use the boxed form of RawValue instead. This is almost as efficient but involves buffering the raw value from the I/O stream into memory.

#[derive(Deserialize)]
struct SomeStruct {
    raw_value: Box<RawValue>,
}

Implementations

Convert an owned String of JSON data to an owned RawValue.

This function is equivalent to serde_json::from_str::<Box<RawValue>> except that we avoid an allocation and memcpy if both of the following are true:

  • the input has no leading or trailing whitespace, and
  • the input has capacity equal to its length.

Access the JSON text underlying a raw value.

Example
use serde::Deserialize;
use serde_json::{Result, value::RawValue};

#[derive(Deserialize)]
struct Response<'a> {
    code: u32,
    #[serde(borrow)]
    payload: &'a RawValue,
}

fn process(input: &str) -> Result<()> {
    let response: Response = serde_json::from_str(input)?;

    let payload = response.payload.get();
    if payload.starts_with('{') {
        // handle a payload which is a JSON map
    } else {
        // handle any other type
    }

    Ok(())
}

fn main() -> Result<()> {
    process(r#" {"code": 200, "payload": {}} "#)?;
    Ok(())
}

Trait Implementations

Formats the value using the given formatter. Read more

Deserialize this value from the given Serde deserializer. Read more

Formats the value using the given formatter. Read more

Serialize this value into the given Serde serializer. Read more

The resulting type after obtaining ownership.

Creates owned data from borrowed data, usually by cloning. Read more

🔬 This is a nightly-only experimental API. (toowned_clone_into)

Uses borrowed data to replace owned data, usually by cloning. Read more

Auto Trait Implementations

Blanket Implementations

Gets the TypeId of self. Read more

Immutably borrows from an owned value. Read more

Mutably borrows from an owned value. Read more

Converts the given value to a String. Read more