gistfile1.txt

extern crate serde; // 1.0.85
extern crate serde_json; // 1.0.37

use serde::{Deserialize, Serialize};

//use serde_json::{Map, Value};
//type Capabilities = Map<String, Value>;

trait DriverCapabilities {
    fn browser_name() -> String;
}

struct FirefoxCapabilities;

impl DriverCapabilities for FirefoxCapabilities {
    fn browser_name() -> String {
        "firefox".to_string()
    }
}

#[derive(Debug, Serialize, Deserialize)]
#[serde(rename_all = "camelCase")]
struct NewSessionParameters {
    always_match: Option<Capabilities<DriverCapabilities>>,
    first_match: Option<Vec<Capabilities<DriverCapabilities>>>,
}

#[derive(Debug, Serialize, Deserialize)]
struct Capabilities<DriverCapabilities> {
    #[serde(rename = "browserName", default = "DriverCapabilities::browser_name")]
    browser_name: String,
}

fn main() -> Result<(), std::io::Error> {
    let body = r#"
        {
            "alwaysMatch": {"foo": "bar"},
            "firstMatch": [
                {},
                {}
            ]
        }
    "#;
    let params: NewSessionParameters<FirefoxCapabilities> = serde_json::from_str(body)?;
    dbg!(params);
    
    Ok(())
}