在 Rust 中使用 Serde 反序列化递归 XML

Question

我正在尝试使用 Rust 中的 Serde 和 Quick-XML 反序列化 MathML。由于 MathML 的递归性质，我在尝试编写结构时遇到了麻烦。这是一个最小的、可重现的示例：

use quick_xml;
use serde::Deserialize;

#[derive(Debug, Deserialize)]
#[serde(rename = "math", rename_all = "camelCase")]
pub enum MathNode {
    Apply(Vec<MathNode>),
    Ci(Vec<MathNode>),
    Text(String),
    #[serde(rename = "math")]
    Root(Vec<MathNode>),
}

pub fn parse(doc: &str) -> Result<MathNode, quick_xml::DeError> {
    let raw_model = quick_xml::de::from_str(doc);
    raw_model
}

pub fn main() {
    let test = "<math>
                    <apply>
                        <ci type=\"integer\">5</ci>
                    </apply>
                </math>";
    let parsed = parse(test);
    println!("{:?}", parsed);
}

存在堆栈溢出，可能是由于此处和此处建议的无限循环所致。我尝试实施他们的建议，但没有成功。

Answer 1

以下是如何使用 serde 解析嵌套 XML 结构的示例。此代码基于此答案。示例 XML 具有名为measuredValue 的节点，该节点被放置到Vec<structs::Data>.

货物.toml：

[dependencies]
serde_derive = "1.0"
serde = "1.0"
serde-xml-rs = "0.4"
serde_json = "1.0.64"

结构.rs：

// XML-root
#[derive(Deserialize, Debug)]
pub(crate) struct D2LogicalModel {
    pub(crate) payloadPublication: PayloadPublication,
}

// payloadPublication
#[derive(Deserialize, Debug)]
pub(crate) struct PayloadPublication {
    lang: String,
    pub(crate) publicationTime: PublicationTime,
    pub(crate) siteMeasurements: Vec<SiteMeasurements>,
}

#[derive(Deserialize, Debug)]
pub(crate) struct PublicationTime {
    #[serde(rename = "$value")]
    pub(crate) publicationTime: String,
}

// // siteMeasurements, the various weather measurements are below (sub-root).
#[derive(Deserialize, Debug)]
pub(crate) struct SiteMeasurements {
    pub(crate) measurementSiteReference: MeasurementSiteReference,
    pub(crate) measurementTimeDefault: MeasurementTimeDefault,
    #[serde(default)]
    pub(crate) measuredValue: Vec<MeasuredValue_>,
}

#[derive(Deserialize, Debug)]
pub(crate) struct MeasurementSiteReference {
    pub(crate) id: u16,
    targetClass: String,
    version: u16,
}

#[derive(Deserialize, Debug)]
pub(crate) struct MeasurementTimeDefault {
    #[serde(rename = "$value")]
    pub(crate) measurementTimeDefault: String,
}

// Common for all measurements.
#[derive(Deserialize, Debug)]
pub(crate) struct MeasuredValue_ {
    pub(crate) index: u16,
    pub(crate) measuredValue: MeasuredValue,
}

#[derive(Deserialize, Debug)]
pub(crate) struct MeasuredValue {
    pub(crate) basicData: BasicData,
}

// Split based on type of measurement. Below this point the tree is different.
#[derive(Deserialize, Debug, Default)]
pub(crate) struct BasicData {
    #[serde(default)]
    pub(crate) precipitationDetail: PrecipitationDetail,
    #[serde(default)]
    pub(crate) wind: Wind,
    #[serde(default)]
    pub(crate) temperature: Temperature_, // Add underscore since this collides with another struct
}

// precipitationIntensity
#[derive(Deserialize, Debug, Default)]
pub(crate) struct PrecipitationDetail {
    #[serde(default)]
    pub(crate) precipitationIntensity: PrecipitationIntensity,
}

#[derive(Deserialize, Debug, Default)]
pub(crate) struct PrecipitationIntensity {
    #[serde(default = "precipitation_intensity")]
    pub(crate) field_description: String,
    #[serde(default)]
    pub(crate) millimetresPerHourIntensity: MillimetresPerHourIntensity,
}

#[derive(Deserialize, Debug, Default)]
pub(crate) struct MillimetresPerHourIntensity {
    #[serde(rename = "$value")]
    pub(crate) millimetresPerHourIntensity: f32,
}

#[derive(Deserialize, Debug, Default)]
pub(crate) struct Temperature {
    #[serde(rename = "$value")]
    pub(crate) temperature: f32,
}

// windSpeed
#[derive(Deserialize, Debug, Default)]
pub(crate) struct Wind {
    #[serde(default)]
    pub(crate) windSpeed: WindSpeed,
}

#[derive(Deserialize, Debug, Default)]
pub(crate) struct WindSpeed {
    #[serde(default = "wind_speed")]
    pub(crate) field_description: String,
    #[serde(default)]
    pub(crate) speed: Speed,
}

#[derive(Deserialize, Debug, Default)]
pub(crate) struct Speed {
    #[serde(rename = "$value")]
    pub(crate) speed: f32,
}

// airTemperature
#[derive(Deserialize, Debug, Default)]
pub(crate) struct Temperature_ {
    #[serde(default)]
    pub(crate) airTemperature: AirTemperature,
}

#[derive(Deserialize, Debug, Default)]
pub(crate) struct AirTemperature {
    #[serde(default = "air_temperature")]
    pub(crate) field_description: String,
    #[serde(default)]
    pub(crate) temperature: Temperature,
}

// Add default values in serde.
fn precipitation_intensity() -> String {
    "precipitation_intensity".to_string()
}

fn wind_speed() -> String {
    "wind_speed".to_string()
}

fn air_temperature() -> String {
    "air_temperature".to_string()
}

#[derive(Serialize)]
pub(crate) struct WeatherMeasurement {
    pub(crate) measurement_time_default: String,
    pub(crate) id: u16,
    pub(crate) data: Vec<Data>,
}

#[derive(Serialize)]
pub(crate) struct Data {
    pub(crate) index: u16,
    pub(crate) field_description: String,
    pub(crate) measurement: f32,
}

主要.rs：

#![allow(non_snake_case)]

mod structs;

use std::fs;

#[macro_use]
extern crate serde_derive;
extern crate serde;
extern crate serde_xml_rs;

fn main() -> Result<(), Box<dyn std::error::Error>> {
    println!("Goodbye XML!");

    let filename = "./sample.xml";
    let content= fs::read_to_string(filename).expect("Unable to read file");

    let d2LogicalModel: structs::D2LogicalModel =  serde_xml_rs::from_str(&*content).unwrap();

    let mut measurements: Vec<structs::WeatherMeasurement> = Vec::new();

    for site in &d2LogicalModel.payloadPublication.siteMeasurements {
        // The actual weather data
        let mut readings: Vec<structs::Data> = Vec::new();

        let measurement_time_default = &site.measurementTimeDefault.measurementTimeDefault;
        let id = &site.measurementSiteReference.id;

        for measured_value in &site.measuredValue {
            let index = &measured_value.index;
            let weather_node = &measured_value.measuredValue.basicData;

            // precipitationIntensity
            let field_description = &weather_node
                .precipitationDetail
                .precipitationIntensity
                .field_description;
            if !field_description.is_empty() {
                let measurement = &weather_node
                    .precipitationDetail
                    .precipitationIntensity
                    .millimetresPerHourIntensity
                    .millimetresPerHourIntensity;
                let r = structs::Data {
                    index: *index,
                    field_description: field_description.clone(),
                    measurement: *measurement,
                };
                readings.push(r);
                /*println!("measurement time-default: {}, id: {}, index: {}, field description: {}, measurement: {}",
                measurement_time_default, id, index, field_description, measurement);*/
            };

            // windSpeed
            let field_description = &weather_node.wind.windSpeed.field_description;
            if !field_description.is_empty() {
                let measurement = &weather_node.wind.windSpeed.speed.speed;
                let r = structs::Data {
                    index: *index,
                    field_description: field_description.clone(),
                    measurement: *measurement,
                };
                readings.push(r);
                /*println!("measurement time-default: {}, id: {}, index: {}, field description: {}, measurement: {}",
                measurement_time_default, id, index, field_description, measurement);*/
            };

            // airTemperature
            let field_description = &weather_node.temperature.airTemperature.field_description;
            if !field_description.is_empty() {
                let measurement = &weather_node
                    .temperature
                    .airTemperature
                    .temperature
                    .temperature;
                let r = structs::Data {
                    index: *index,
                    field_description: field_description.clone(),
                    measurement: *measurement,
                };
                readings.push(r);
                /*println!("measurement time-default: {}, id: {}, index: {}, field description: {}, measurement: {}",
                measurement_time_default, id, index, field_description, measurement);*/
            };

        }

        let wm = structs::WeatherMeasurement {
            measurement_time_default: measurement_time_default.clone(),
            id: *id,
            data: readings,
        };
        measurements.push(wm);
        // Add final struct here
    }

    let jm = serde_json::to_string(&measurements)?;
    println!("{:?}", &jm);

    Ok(())
}

样本.xml：

<d2LogicalModel modelBaseVersion="2" xmlns="http://datex2.eu/schema/2/2_0">
    <payloadPublication lang="nob" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:type="MeasuredDataPublication">
        <publicationTime>2021-03-24T21:02:28.762+01:00</publicationTime>
        <siteMeasurements>
            <measurementSiteReference id="228" targetClass="MeasurementSiteRecord" version="3576"/>
            <measurementTimeDefault>2021-03-24T20:50:00+01:00</measurementTimeDefault>
            <measuredValue index="2501">
                <measuredValue>
                    <basicData xsi:type="PrecipitationInformation">
                        <precipitationDetail>
                            <precipitationIntensity>
                                <millimetresPerHourIntensity>0.0</millimetresPerHourIntensity>
                            </precipitationIntensity>
                        </precipitationDetail>
                    </basicData>
                </measuredValue>
            </measuredValue>
            <measuredValue index="901">
                <measuredValue>
                    <basicData xsi:type="WindInformation">
                        <wind>
                            <windSpeed>
                                <speed>21.24</speed>
                            </windSpeed>
                        </wind>
                    </basicData>
                </measuredValue>
            </measuredValue>
            <measuredValue index="101">
                <measuredValue>
                    <basicData xsi:type="TemperatureInformation">
                        <temperature>
                            <airTemperature>
                                <temperature>0.2</temperature>
                            </airTemperature>
                        </temperature>
                    </basicData>
                </measuredValue>
            </measuredValue>
        </siteMeasurements>
    </payloadPublication>
</d2LogicalModel>