How to make serde deserialize BigInt as u64? - rust

Question

I'm using toml and num-bigint with the serde feature to deserialize the following data:
[[trades]]
action = "Buy"
date_time = 2019-04-15T15:36:00+01:00
fee = [1, [44000000]]
id = "#1"
price = [-1, [20154500000]]
quantity = [1, [200000000]]
But I'm getting this error:
Error: Error { inner: ErrorInner { kind: Custom, line: Some(7), col: 14, at: Some(156), message: "invalid value: integer `20154500000`, expected u32", key: ["trades", "price"] } }
Of course, if I make the price value smaller than u32::MAX, the program compiles fine. But I want to use this high value, because I'm scaling numbers by 1e8 to avoid dealing with floating-point arithmetic.
Is it possible to make serde deserialize BigInts to u64 instead?
use num_bigint::BigInt;
use serde_derive::Deserialize;
use toml::from_str;
use toml::value::Datetime;
#[derive(Debug, Deserialize)]
pub struct Trade {
pub action: String,
pub date_time: Datetime,
pub fee: BigInt,
pub id: Option<String>,
pub price: BigInt,
pub quantity: BigInt,
}
#[derive(Debug, Deserialize)]
pub struct TradeTable {
pub trades: Vec<Trade>,
}
fn main() {
let trades_string: String = String::from("[[trades]]\naction = \"Buy\"\ndate_time = 2019-04-15T15:36:00+01:00\nexchange = \"Degiro\"\nfee = [1, [44000000]]\nid = \"#1\"\nprice = [-1, [20154500000]]\nquantity = [1, [200000000]]");
let trade_table: TradeTable = from_str(&trades_string).unwrap();
let trades: Vec<Trade> = trade_table.trades;
}
Also, here's a link to a Rust Playground. Note that you will need to copy the code to your local machine, because you need the serde feature from num-bigint:
Cargo.toml
[dependencies.num-bigint]
version = "0.2.6"
features = ["serde"]

Answer 1

How did you create this file -- did you make it by serializing a BigInt, or did you write it by hand?
I wrote the data by hand.
Your data is invalid, the following work:
use num_bigint::BigInt;
use std::str::FromStr;
#[derive(Debug, serde::Serialize, serde::Deserialize, PartialEq)]
pub struct Trade {
pub price: BigInt,
}
fn main() {
let price = BigInt::from_str("-201545000000000").unwrap();
let trade = Trade { price };
let j = serde_json::to_string(&trade).unwrap();
println!("{}", j);
let a: Trade = serde_json::from_str(&j).unwrap();
assert_eq!(trade, a);
let j = toml::to_string(&trade).unwrap();
println!("{}", j);
let b: Trade = toml::from_str(&j).unwrap();
assert_eq!(trade, b);
}
You are not supposed to create it by hand.