Trailing characters in Rust when trying to serialize API response - rust

Question

I'm trying to wrap an API using rust, so long no problems but one endpoint is giving me a big pain in the head.
the endpoint returns a valid JSON as the other endpoints from this API.
The problem is when I try to work with the response I get the following error:
error decoding response body: trailing characters at line 1 column 146
Get function:
pub fn get<T: DeserializeOwned>(&self, endpoint: API, request: Option<String>) -> Result<T> {
let mut url: String = format!("{}{}", self.host, String::from(endpoint));
if let Some(request) = request {
if !request.is_empty() {
url.push_str(format!("?{}", request).as_str());
}
}
let client = &self.inner_client;
let response = client.get(url.as_str()).send()?;
self.handler(response)
}
Handler function:
fn handler<T: DeserializeOwned>(&self, response: Response) -> Result<T> {
match response.status() {
StatusCode::OK => {
let l = response.json::<T>()?;
Ok(l)
},
s => {
bail!(format!("Received response: {:?}", s));
}
}
}
Enpoint funcion:
pub fn get_depth<S>(&self, symbol: S) -> Result<OrderBook>
where
S: Into<String>,
{
let mut parameters: BTreeMap<String, String> = BTreeMap::new();
parameters.insert("symbol".into(), symbol.into());
let request = build_request(parameters);
self.client.get(API::Spot(Spot::Depth), Some(request))
}
Models:
#[derive(Debug, Serialize, Deserialize, Clone)]
#[serde(rename_all = "camelCase")]
pub struct OrderBook {
pub last_update_id: u64,
pub asks: Vec<Asks>,
pub bids: Vec<Bids>,
}
#[derive(PartialEq, Debug, Serialize, Deserialize, Clone)]
pub struct Bids {
#[serde(with = "string_or_float")]
pub price: f64,
#[serde(with = "string_or_float")]
pub qty: f64,
}
#[derive(Debug, Serialize, Deserialize, Clone)]
pub struct Asks {
#[serde(with = "string_or_float")]
pub price: f64,
#[serde(with = "string_or_float")]
pub qty: f64,
}
API response:
{
"lastUpdateId": 1595750078,
"bids": [
[
"0.00001661",
"24250.00000000",
[]
],
[
"0.00001660",
"65159.00000000",
[]
]
],
"asks": [
[
"0.00001662",
"26397.00000000",
[]
],
[
"0.00001663",
"54421.00000000",
[]
]
]
}
I was testing this mocking the API response and removing the empty arrays from asks and bids and it worked flawless. I don't know why the [] is a problem and I can figure out how to solve this problem. So really I will appreciate any help.

Answer 1

Your problem boils down to matching your rust struct with the response structure. I'm using the example with String from your playground link.
Response
{
"lastUpdateId":1595750078,
"bids":[
[
"0.00001661",
"24250.00000000",
[
]
],
[
"0.00001660",
"65159.00000000",
[
]
]
],
"asks":[
[
"0.00001662",
"26397.00000000"
],
[
"0.00001663",
"54421.00000000"
]
]
}
Your Structs
#[derive(Debug, Serialize, Deserialize, Clone)]
#[serde(rename_all = "camelCase")]
pub struct OrderBook {
pub last_update_id: u64,
pub asks: Vec<Asks>,
pub bids: Vec<Bids>,
}
#[derive(Debug, Serialize, Deserialize, Clone)]
pub struct Bids {
pub price: String,
pub qty: String,
}
#[derive(Debug, Serialize, Deserialize, Clone)]
pub struct Asks {
pub price: String,
pub qty: String,
}
Now if you look at the bids json, the empty array is not represented in the Bids structure in your code. Hence calling serde_json::from_str::<OrderBook>(json) fails, as it's encountering a new array where nothing is expected anymore.
Solution
Introduce a new (optional) field in Bids, representing the array. I cannot say which structure this would be, as your example only shows the empty representation. pub x: Vec<()> would also work, though I'm certain the API might sent real data if available.
#[derive(Debug, Serialize, Deserialize, Clone)]
pub struct Bids {
pub price: String,
pub qty: String,
pub something_else: Vec<()>, // or Vec<AnotherStruct>
}