Struct Deserializer

pub struct Deserializer<R> { /* private fields */ }

A structure that deserializes JSON into Rust values.

Implementations

impl<'de, R> Deserializer<R>

where R: Read<'de>,

pub fn new(read: R) -> Self

Create a JSON deserializer from one of the possible serde_json input sources.

Typically it is more convenient to use one of these methods instead:

• Deserializer::from_str
• Deserializer::from_slice
• Deserializer::from_reader

impl<R> Deserializer<IoRead<R>>

where R: Read,

pub fn from_reader(reader: R) -> Self

Creates a JSON deserializer from an io::Read.

Reader-based deserializers do not support deserializing borrowed types like &str, since the std::io::Read trait has no non-copying methods – everything it does involves copying bytes out of the data source.

impl<'a> Deserializer<SliceRead<'a>>

pub fn from_slice(bytes: &'a [u8]) -> Self

Creates a JSON deserializer from a &[u8].

impl<'a> Deserializer<StrRead<'a>>

pub fn from_str(s: &'a str) -> Self

Creates a JSON deserializer from a &str.

impl<'de, R: Read<'de>> Deserializer<R>

pub fn end(&mut self) -> Result<()>

The Deserializer::end method should be called after a value has been fully deserialized. This allows the Deserializer to validate that the input stream is at the end or that it only has trailing whitespace.

pub fn into_iter<T>(self) -> StreamDeserializer<'de, R, T>

where T: Deserialize<'de>,

Turn a JSON deserializer into an iterator over values of type T.

pub fn disable_recursion_limit(&mut self)

Parse arbitrarily deep JSON structures without any consideration for overflowing the stack.

You will want to provide some other way to protect against stack overflows, such as by wrapping your Deserializer in the dynamically growing stack adapter provided by the serde_stacker crate. Additionally you will need to be careful around other recursive operations on the parsed result which may overflow the stack after deserialization has completed, including, but not limited to, Display and Debug and Drop impls.

This method is only available if serde_json is built with the "unbounded_depth" feature.

Examples

use serde::Deserialize;
use serde_json::Value;

fn main() {
    let mut json = String::new();
    for _ in 0..10000 {
        json = format!("[{}]", json);
    }

    let mut deserializer = serde_json::Deserializer::from_str(&json);
    deserializer.disable_recursion_limit();
    let deserializer = serde_stacker::Deserializer::new(&mut deserializer);
    let value = Value::deserialize(deserializer).unwrap();

    carefully_drop_nested_arrays(value);
}

fn carefully_drop_nested_arrays(value: Value) {
    let mut stack = vec![value];
    while let Some(value) = stack.pop() {
        if let Value::Array(array) = value {
            stack.extend(array);
        }
    }
}

Trait Implementations

impl<'de, 'a, R: Read<'de>> Deserializer<'de> for &'a mut Deserializer<R>

fn deserialize_bytes<V>(self, visitor: V) -> Result<V::Value>

where V: Visitor<'de>,

Parses a JSON string as bytes. Note that this function does not check whether the bytes represent a valid UTF-8 string.

The relevant part of the JSON specification is Section 8.2 of RFC 7159:

When all the strings represented in a JSON text are composed entirely of Unicode characters (however escaped), then that JSON text is interoperable in the sense that all software implementations that parse it will agree on the contents of names and of string values in objects and arrays.

However, the ABNF in this specification allows member names and string values to contain bit sequences that cannot encode Unicode characters; for example, “\uDEAD” (a single unpaired UTF-16 surrogate). Instances of this have been observed, for example, when a library truncates a UTF-16 string without checking whether the truncation split a surrogate pair. The behavior of software that receives JSON texts containing such values is unpredictable; for example, implementations might return different values for the length of a string value or even suffer fatal runtime exceptions.

The behavior of serde_json is specified to fail on non-UTF-8 strings when deserializing into Rust UTF-8 string types such as String, and succeed with the bytes representing the WTF-8 encoding of code points when deserializing using this method.

Escape sequences are processed as usual, and for \uXXXX escapes it is still checked if the hex number represents a valid Unicode code point.

Examples

You can use this to parse JSON strings containing invalid UTF-8 bytes, or unpaired surrogates.

use serde_bytes::ByteBuf;

fn look_at_bytes() -> Result<(), serde_json::Error> {
    let json_data = b"\"some bytes: \xe5\x00\xe5\"";
    let bytes: ByteBuf = serde_json::from_slice(json_data)?;

    assert_eq!(b'\xe5', bytes[12]);
    assert_eq!(b'\0', bytes[13]);
    assert_eq!(b'\xe5', bytes[14]);

    Ok(())
}

Backslash escape sequences like \n are still interpreted and required to be valid. \u escape sequences are required to represent a valid Unicode code point or lone surrogate.

use serde_bytes::ByteBuf;

fn look_at_bytes() -> Result<(), serde_json::Error> {
    let json_data = b"\"lone surrogate: \\uD801\"";
    let bytes: ByteBuf = serde_json::from_slice(json_data)?;
    let expected = b"lone surrogate: \xED\xA0\x81";
    assert_eq!(expected, bytes.as_slice());
    Ok(())
}

fn deserialize_option<V>(self, visitor: V) -> Result<V::Value>

where V: Visitor<'de>,

Parses a null as a None, and any other values as a Some(...).

fn deserialize_newtype_struct<V>( self, name: &str, visitor: V, ) -> Result<V::Value>

where V: Visitor<'de>,

Parses a newtype struct as the underlying value.

fn deserialize_enum<V>( self, _name: &str, _variants: &'static [&'static str], visitor: V, ) -> Result<V::Value>

where V: Visitor<'de>,

Parses an enum as an object like {"$KEY":$VALUE}, where $VALUE is either a straight value, a [..], or a {..}.

type Error = Error

The error type that can be returned if some error occurs during deserialization.

fn deserialize_any<V>(self, visitor: V) -> Result<V::Value>

where V: Visitor<'de>,

Require the Deserializer to figure out how to drive the visitor based on what data type is in the input.

fn deserialize_bool<V>(self, visitor: V) -> Result<V::Value>

where V: Visitor<'de>,

Hint that the Deserialize type is expecting a bool value.

fn deserialize_i8<V>(self, visitor: V) -> Result<V::Value>

where V: Visitor<'de>,

Hint that the Deserialize type is expecting an i8 value.

fn deserialize_i16<V>(self, visitor: V) -> Result<V::Value>

where V: Visitor<'de>,

Hint that the Deserialize type is expecting an i16 value.

fn deserialize_i32<V>(self, visitor: V) -> Result<V::Value>

where V: Visitor<'de>,

Hint that the Deserialize type is expecting an i32 value.

fn deserialize_i64<V>(self, visitor: V) -> Result<V::Value>

where V: Visitor<'de>,

Hint that the Deserialize type is expecting an i64 value.

fn deserialize_u8<V>(self, visitor: V) -> Result<V::Value>

where V: Visitor<'de>,

Hint that the Deserialize type is expecting a u8 value.

fn deserialize_u16<V>(self, visitor: V) -> Result<V::Value>

where V: Visitor<'de>,

Hint that the Deserialize type is expecting a u16 value.

fn deserialize_u32<V>(self, visitor: V) -> Result<V::Value>

where V: Visitor<'de>,

Hint that the Deserialize type is expecting a u32 value.

fn deserialize_u64<V>(self, visitor: V) -> Result<V::Value>

where V: Visitor<'de>,

Hint that the Deserialize type is expecting a u64 value.

fn deserialize_f32<V>(self, visitor: V) -> Result<V::Value>

where V: Visitor<'de>,

Hint that the Deserialize type is expecting a f32 value.

fn deserialize_f64<V>(self, visitor: V) -> Result<V::Value>

where V: Visitor<'de>,

Hint that the Deserialize type is expecting a f64 value.

fn deserialize_i128<V>(self, visitor: V) -> Result<V::Value>

where V: Visitor<'de>,

Hint that the Deserialize type is expecting an i128 value.

fn deserialize_u128<V>(self, visitor: V) -> Result<V::Value>

where V: Visitor<'de>,

Hint that the Deserialize type is expecting an u128 value.

fn deserialize_char<V>(self, visitor: V) -> Result<V::Value>

where V: Visitor<'de>,

Hint that the Deserialize type is expecting a char value.

fn deserialize_str<V>(self, visitor: V) -> Result<V::Value>

where V: Visitor<'de>,

Hint that the Deserialize type is expecting a string value and does not benefit from taking ownership of buffered data owned by the Deserializer.

fn deserialize_string<V>(self, visitor: V) -> Result<V::Value>

where V: Visitor<'de>,

Hint that the Deserialize type is expecting a string value and would benefit from taking ownership of buffered data owned by the Deserializer.

fn deserialize_byte_buf<V>(self, visitor: V) -> Result<V::Value>

where V: Visitor<'de>,

Hint that the Deserialize type is expecting a byte array and would benefit from taking ownership of buffered data owned by the Deserializer.

fn deserialize_unit<V>(self, visitor: V) -> Result<V::Value>

where V: Visitor<'de>,

Hint that the Deserialize type is expecting a unit value.

fn deserialize_unit_struct<V>( self, _name: &'static str, visitor: V, ) -> Result<V::Value>

where V: Visitor<'de>,

Hint that the Deserialize type is expecting a unit struct with a particular name.

fn deserialize_seq<V>(self, visitor: V) -> Result<V::Value>

where V: Visitor<'de>,

Hint that the Deserialize type is expecting a sequence of values.

fn deserialize_tuple<V>(self, _len: usize, visitor: V) -> Result<V::Value>

where V: Visitor<'de>,

Hint that the Deserialize type is expecting a sequence of values and knows how many values there are without looking at the serialized data.

fn deserialize_tuple_struct<V>( self, _name: &'static str, _len: usize, visitor: V, ) -> Result<V::Value>

where V: Visitor<'de>,

Hint that the Deserialize type is expecting a tuple struct with a particular name and number of fields.

fn deserialize_map<V>(self, visitor: V) -> Result<V::Value>

where V: Visitor<'de>,

Hint that the Deserialize type is expecting a map of key-value pairs.

fn deserialize_struct<V>( self, _name: &'static str, _fields: &'static [&'static str], visitor: V, ) -> Result<V::Value>

where V: Visitor<'de>,

Hint that the Deserialize type is expecting a struct with a particular name and fields.

fn deserialize_identifier<V>(self, visitor: V) -> Result<V::Value>

where V: Visitor<'de>,

Hint that the Deserialize type is expecting the name of a struct field or the discriminant of an enum variant.

fn deserialize_ignored_any<V>(self, visitor: V) -> Result<V::Value>

where V: Visitor<'de>,

Hint that the Deserialize type needs to deserialize a value whose type doesn’t matter because it is ignored.

fn is_human_readable(&self) -> bool

Determine whether Deserialize implementations should expect to deserialize their human-readable form.