https://ldmsys.net/hangang source code

hangang.js

const http = require('http');
const API_KEY = "[INSERT_API_KEY_HERE]"; // https://data.seoul.go.kr/dataList/OA-15488/S/1/datasetView.do
const url = 'http://openapi.seoul.go.kr:8088/'+API_KEY+'/json/WPOSInformationTime/1/5';

async function getTemp() {
    return new Promise(function(resolve, reject) {
        const req = http.request(url, {
            url: url,
            method: 'GET'
        }, function (res) {
            res.on('data', c => {
                let count = 0, temp = 0.0;
                let data = JSON.parse(c.toString());
                for(let i of data.WPOSInformationTime.row) {
                    parseFloat(i.W_TEMP) && (temp += parseFloat(i.W_TEMP)) && count++;
                }
                resolve(temp/count);
            });
        });

        req.end();
    });
}

(async () => {
    console.log(await getTemp());
})();

const a = http.createServer(async (req, res) => {
    res.writeHead(200, { 'Content-Type': 'application/json', 'Access-Control-Allow-Origin': "*" });
    res.end(JSON.stringify({river: "Han-gang", temp: await getTemp(), source: "Seoul Metropolitan Government"}));
});
a.listen(4264, "0.0.0.0");

Return Only Temperature (Rust)

use std::net::{TcpListener, TcpStream};
use std::io::{Read, Write};
use std::sync::{Arc, Mutex};
use std::time::{SystemTime, Duration};
use reqwest::blocking::Client;
use serde_json::Value;

const API_KEY: &str = "INSERT_YOUR_API_KEY";
const URL: &str = &format!("http://openapi.seoul.go.kr:8088/{}/json/WPOSInformationTime/1/5", API_KEY);

struct Cache {
    last_fetched: SystemTime,
    value: f64,
}

impl Cache {
    fn new() -> Cache {
        Cache {
            last_fetched: SystemTime::now() - Duration::from_secs(301),
            value: 0.0,
        }
    }

    fn should_update(&self) -> bool {
        self.last_fetched.elapsed().unwrap_or(Duration::from_secs(301)) > Duration::from_secs(300)
    }

    fn update_temperature(&mut self) {
        let client = Client::new();
        match client.get(URL).send() {
            Ok(resp) => {
                if resp.status().is_success() {
                    match resp.json::<Value>() {
                        Ok(json) => {
                            let rows = json["WPOSInformationTime"]["row"].as_array();
                            if let Some(rows) = rows {
                                let (sum, count) = rows.iter().fold((0.0, 0), |(acc, cnt), row| {
                                    if let Some(temp_str) = row["W_TEMP"].as_str() {
                                        if let Ok(temp) = temp_str.parse::<f64>() {
                                            (acc + temp, cnt + 1)
                                        } else {
                                            (acc, cnt)
                                        }
                                    } else {
                                        (acc, cnt)
                                    }
                                });
                                if count > 0 {
                                    let avg_temp = sum / count as f64;
                                    self.value = (avg_temp * 1000.0).round() / 1000.0; // Rounded to three decimals
                                } else {
                                    self.value = -1.0;
                                }
                            } else {
                                self.value = -1.0;
                            }
                        },
                        Err(_) => self.value = -1.0,
                    }
                } else {
                    self.value = -1.0;
                }
            },
            Err(_) => self.value = -1.0,
        }
        self.last_fetched = SystemTime::now();
    }
}

fn handle_client(mut stream: TcpStream, cache: Arc<Mutex<Cache>>) {
    let mut cache_guard = cache.lock().unwrap();
    if cache_guard.should_update() {
        cache_guard.update_temperature();
    }

    let response = format!(
        "HTTP/1.1 200 OK\r\nContent-Type: application/json\r\nConnection: close\r\n\r\n{}",
        serde_json::json!({
            "river": "Han-gang",
            "temp": cache_guard.value,
            "source": "Seoul Metropolitan Government"
        }).to_string()
    );

    let _ = stream.write_all(response.as_bytes());
    let _ = stream.flush();
}

fn main() {
    let listener = TcpListener::bind("0.0.0.0:4444").unwrap();
    let cache = Arc::new(Mutex::new(Cache::new()));

    for stream in listener.incoming() {
        if let Ok(stream) = stream {
            let cache_clone = Arc::clone(&cache);
            std::thread::spawn(move || {
                handle_client(stream, cache_clone);
            });
        }
    }
}