updated headers to prevent 302 error

downloader.mjs

@@ -0,0 +1,114 @@
+import fs from 'fs';
+import client from 'https';
+import zlib from 'zlib';
+
+function getTimeString(count) {
+    let date = new Date(Date.now() - count * 60000 * 5);
+    return (
+        date.getFullYear().toString()
+        + (date.getMonth() + 1).toString().padStart(2, "0")
+        + date.getDate().toString().padStart(2, "0")
+        + date.getHours().toString().padStart(2, "0")
+        + (date.getMinutes() - date.getMinutes() % 5).toString().padStart(2, "0")
+    );
+}
+
+function downloadImage(time_string, filepath) {
+    return new Promise((resolve, reject) => {
+        let options = {
+            hostname: 'www.nea.gov.sg',
+            port: 443,
+            path: `/docs/default-source/rain-area/dpsri_70km_${time_string}0000dBR.dpsri.png`,
+            headers: {
+                "Host":"www.nea.gov.sg",
+                "User-Agent": "Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:129.0) Gecko/20100101 Firefox/129.0",
+                "Accept": "image/avif,image/webp,image/png,image/svg+xml,image/*;q=0.8,*/*;q=0.5",
+                "Accept-Language": "en-US,en;q=0.5",
+                "Accept-Encoding": "gzip, deflate, br, zstd",
+                "DNT": "1",
+                "Connection": "keep-alive",
+                "Sec-Fetch-Dest": "image",
+                "Sec-Fetch-Mode": "no-cors",
+                "Sec-Fetch-Site": "same-origin",
+                "Priority": "u=5, i",
+                "Pragma": "no-cache",
+                "Cache-Control": "no-cache",
+                "TE": "trailers",
+            }
+        }
+        client.get(options, (res) => {
+            console.log(`Downloading ${time_string}`);
+            if (res.statusCode >= 200 && res.statusCode < 400 && res.headers['content-type'] === 'image/png') {
+                let stream = fs.createWriteStream(filepath);
+                if (res.headers['content-encoding'] === 'gzip') {
+                    res.pipe(zlib.createGunzip()).pipe(stream)
+                        .on('error', reject)
+                        .once('close', () => resolve(filepath));
+                }
+                else {
+                    res.pipe(stream)
+                        .on('error', reject)
+                        .once('close', () => resolve(filepath));
+                }
+            } else {
+                // Consume response data to free up memory
+                console.log(`Failed to download /docs/default-source/rain-area/dpsri_70km_${time_string}0000dBR.dpsri.png with status code ${res.statusCode}`);
+                res.resume();
+                reject(new Error(res.statusCode));
+            }
+        });
+    });
+}
+
+export async function initImages(count) {
+    let files = fs.readdirSync('images/');
+    for (let i = count; i >= 0; i--) {
+        let time_string = getTimeString(i);
+        let filename = `images/${time_string}.png`;
+        if (files.includes(`${time_string}.png`)) {
+            continue;
+        }
+        try {
+            await downloadImage(time_string, filename)
+        } catch (error) {
+            //Response 302, we've reached the latest available image
+            if (error.message === '302') {
+                console.log('Could not download image after ' + time_string);
+                return;
+            }
+        }
+    }
+}
+
+export async function updateImages(count) {
+    let time_strings = [];
+    for (let i = count; i >= 0; i--) {
+        time_strings.push(getTimeString(i));
+    }
+    let files = fs.readdirSync('images/');
+    let image_count = files.length;
+
+    let updated = false;
+
+    //Try to download new images
+    for (let time_string of time_strings) {
+        if (!files.includes(`${time_string}.png`)) {
+            try {
+                await downloadImage(time_string, `images/${time_string}.png`);
+                updated = true;
+                image_count++;
+            } catch (error) {
+                console.log("No more images available");
+                break;
+            }
+        }
+    }
+
+    //Remove old files
+    for (let file of files.sort().slice(0, image_count - count)) {
+        console.log(`Deleting ${file}`);
+        fs.unlinkSync(`images/${file}`);
+    }
+
+    return updated;
+}