关于 rust:Serde 在反序列化嵌套的 JSON 结构时返回 SyntaxError “expected value”

Serde returns a SyntaxError "expected value" when deserializing nested JSON structs

我正在尝试从 Web API(规范)反序列化 Spotify 元数据 JSON。我正在使用 hyper 从服务器中检索 JSON，并使用 serde 将 JSON 转换为我可以在 Rust 中实际使用的东西。从服务器检索 JSON 就好了，但是当我尝试将 JSON 转换为可以使用的对象时，Rust panic并抛出错误：

1	thread '<main>' panicked at 'called 'Result::unwrap()' on an 'Err' value: SyntaxError("expected value", 11, 21)', ../src/libcore/result.rs:746

这一点也没有帮助，因为它根本无法指出哪里出了问题。在搜索网络时，我偶然发现了一个 serde 问题，这让我认为该问题与 JSON 的嵌套结构有关。

谁能看出哪里出了问题？修复错误对我来说是最好的解决方案，但如果另一个板条箱是一个更好的解决方案，我也想听听。我已经尝试过 rustc-serialize，但是那个 crate 无法处理 json 中的"类型"变量。

我使用的代码是：

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#![feature(custom_derive, plugin)]
#![plugin(serde_macros)]
#![feature(custom_attribute)]

extern crate hyper;
extern crate serde;
extern crate serde_json;

use std::io::Read;
use hyper::Client;
use hyper::header::Connection;

#[derive(Serialize, Deserialize)]
struct Track_Full {
album: Album_Simp,
artists: Vec<Artist_Simp>,
available_markets: Vec<String>,
disc_number: u8,
duration_ms: u32,
explicit: bool,
external_ids: External_IDs,
external_urls: External_URLs,
href: String,
id: String,
name: String,
popularity: u8,
preview_url: String,
track_number: u8,
#[serde(rename="type")]
_type: String,
uri: String
}

#[derive(Serialize, Deserialize)]
struct Album_Simp {
album_type: String,
available_markets: Vec<String>,
external_urls: External_URLs,
href: String,
id: String,
images: Vec<Image>,
name: String,
#[serde(rename="type")]
_type: String,
uri: String
}

#[derive(Serialize, Deserialize)]
struct Artist_Simp {
external_urls: External_URLs,
href: String,
id: String,
name: String,
#[serde(rename="type")]
_type: String,
uri: String
}

#[derive(Serialize, Deserialize)]
struct External_IDs {
isrc: String
}

#[derive(Serialize, Deserialize)]
struct External_URLs {
spotify: String
}

#[derive(Serialize, Deserialize)]
struct Image {
height: u8,
url: String,
width: u8
}

fn main() {
// Create a client.
let mut client = Client::new();

// Creating an outgoing request.
let mut res = client.get("https://api.spotify.com/v1/tracks/0eGsygTp906u18L0Oimnem")
// set a header
.header(Connection::close())
// let 'er go!
.send().unwrap();

// Read the Response.
let mut body = String::new();
res.read_to_string(&mut body).unwrap();

println!("{}", body);

let deserialized: Track_Full = serde_json::from_str(&body).unwrap();
}

JSON：

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{
"album" : {
"album_type" :"album",
"available_markets" : ["AD","AR","AT","AU","BE","BG","BO","BR","CH","CL","CO","CR","CY","CZ","DE","DK","DO","EC","EE","ES","FI","FR","GR","GT","HK","HN","HU","IE","IS","IT","LI","LT","LU","LV","MC","MT","MY","NI","NL","NO","NZ","PA","PE","PH","PL","PT","PY","RO","SE","SG","SI","SK","SV","TR","TW","UY" ],
"external_urls" : {
"spotify" :"https://open.spotify.com/album/6TJmQnO44YE5BtTxH8pop1"
},
"href" :"https://api.spotify.com/v1/albums/6TJmQnO44YE5BtTxH8pop1",
"id" :"6TJmQnO44YE5BtTxH8pop1",
"images" : [ {
"height" : 640,
"url" :"https://i.scdn.co/image/8e13218039f81b000553e25522a7f0d7a0600f2e",
"width" : 629
}, {
"height" : 300,
"url" :"https://i.scdn.co/image/8c1e066b5d1045038437d92815d49987f519e44f",
"width" : 295
}, {
"height" : 64,
"url" :"https://i.scdn.co/image/d49268a8fc0768084f4750cf1647709e89a27172",
"width" : 63
} ],
"name" :"Hot Fuss",
"type" :"album",
"uri" :"spotify:album:6TJmQnO44YE5BtTxH8pop1"
},
"artists" : [ {
"external_urls" : {
"spotify" :"https://open.spotify.com/artist/0C0XlULifJtAgn6ZNCW2eu"
},
"href" :"https://api.spotify.com/v1/artists/0C0XlULifJtAgn6ZNCW2eu",
"id" :"0C0XlULifJtAgn6ZNCW2eu",
"name" :"The Killers",
"type" :"artist",
"uri" :"spotify:artist:0C0XlULifJtAgn6ZNCW2eu"
} ],
"available_markets" : ["AD","AR","AT","AU","BE","BG","BO","BR","CH","CL","CO","CR","CY","CZ","DE","DK","DO","EC","EE","ES","FI","FR","GR","GT","HK","HN","HU","IE","IS","IT","LI","LT","LU","LV","MC","MT","MY","NI","NL","NO","NZ","PA","PE","PH","PL","PT","PY","RO","SE","SG","SI","SK","SV","TR","TW","UY" ],
"disc_number" : 1,
"duration_ms" : 222075,
"explicit" : false,
"external_ids" : {
"isrc" :"USIR20400274"
},
"external_urls" : {
"spotify" :"https://open.spotify.com/track/0eGsygTp906u18L0Oimnem"
},
"href" :"https://api.spotify.com/v1/tracks/0eGsygTp906u18L0Oimnem",
"id" :"0eGsygTp906u18L0Oimnem",
"name" :"Mr. Brightside",
"popularity" : 74,
"preview_url" :"https://p.scdn.co/mp3-preview/934da7155ec15deb326635d69d050543ecbee2b4",
"track_number" : 2,
"type" :"track",
"uri" :"spotify:track:0eGsygTp906u18L0Oimnem"
}

您尝试解析一些 JSON，但它失败了。当您在 Result 上调用 unwrap 时，程序会因为这个失败而panic：

1	SyntaxError("expected value", 11, 21)

SyntaxError 的文档说数字是错误的行和列。第 11 行第 21 列是：

1 2	"height" : 640, ^

查看您的结构，您已将高度声明为 u8，一个 8 位无符号数。这具有 0-255 的允许值。 640不适合这个。将值增加到 u32 允许解析 JSON。

此外，Rust 风格是使用 CamelCase 标识符而不是连续大写字母的结构。 External_URLs -> ExternalUrls。编译器实际上会就此发出警告。