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index.ts
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index.ts
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import Router from "@koa/router";
import sharp from "sharp";
import crypto from "crypto";
import { stat } from "fs/promises";
import { extname, basename } from "path";
import { Middleware } from "koa";
import { guessResolutions } from "./guessResolutions";
type correctExtension = "jpeg" | "png" | "avif" | "webp";
function isCorrectExtension(type: unknown): type is correctExtension {
const extensions = ["avif", "webp", "jpeg", "png"];
return extensions.includes(type as string);
}
const MONTH = 60 * 60 * 24 * 30;
function encodeFilename({
width,
originalPath,
format,
}: {
width: number;
originalPath: string;
format: string;
}): string {
const filename = basename(originalPath)
.slice(0, -1 * extname(originalPath).length)
.replace(/\./g, "_");
return `${filename}.${width}.${format}`;
}
export default class KoaResponsiveImageRouter extends Router {
router: Router;
hashToResolutions: Record<string, number[]> = {};
hashToLossless: Record<string, boolean> = {};
hashToMetadata: Record<string, Promise<sharp.Metadata> | undefined> = {};
hashToOriginalPath: Record<string, string> = {};
nginxWarningDisplayed = false;
constructor(public static_path: string) {
super();
this.router = new Router();
this.router.get("/:hash/:filename", async (ctx) => {
if (!this.nginxWarningDisplayed && !ctx.headers["x-proxied"]) {
console.log(
"Request for an image probably did not go through a caching proxy, use the following NGINX config to fix that:"
);
console.log(this.makeNginxConfig("/run/nginx-cache", 1024));
this.nginxWarningDisplayed = true;
}
const { hash, filename } = ctx.params;
const resolution = parseInt(filename.split(".")[1]);
const type = extname(filename).split(".").pop();
if (
this.hashToResolutions[hash].find(
(el: number) => el === resolution
) &&
type !== undefined &&
isCorrectExtension(type)
) {
ctx.set("Cache-Control", `public, max-age=${MONTH}, immutable`);
ctx.set("etag", `"${hash}:${filename}"`);
ctx.status = 200; //otherwise the `.fresh` check won't work, see https://koajs.com/
if (ctx.fresh) {
ctx.status = 304;
return;
}
try {
ctx.body = await this.generateImage({
hash,
resolution,
type,
});
ctx.type = `image/${type}`;
} catch (error) {
console.error(error);
ctx.response.status = 404;
}
} else {
ctx.response.status = 404;
}
});
}
async getMetadata(hash: string): Promise<sharp.Metadata> {
if (this.hashToMetadata[hash]) {
return this.hashToMetadata[hash] as Promise<sharp.Metadata>;
} else {
const metadata = sharp(this.hashToOriginalPath[hash]).metadata();
this.hashToMetadata[hash] = metadata;
return metadata;
}
}
private makeImageURL({
hash,
width,
format,
}: {
hash: string;
width: number;
format: string;
}): string {
return `${this.static_path}/${hash}/${encodeFilename({
width,
originalPath: this.hashToOriginalPath[hash],
format,
})}`;
}
makeNginxConfig(cache_path: string, max_size_mb: number): string {
return `http {
proxy_cache_path ${cache_path} keys_zone=cache:10m levels=1:2 inactive=90d max_size=${max_size_mb}m use_temp_path=off;
server {
# ....
location ${this.static_path} {
proxy_cache cache;
proxy_cache_lock on;
proxy_cache_valid 200 90d;
proxy_cache_use_stale updating;
proxy_cache_background_update on;
proxy_set_header X-Proxied true;
proxy_pass http://localhost:8080;
}
}
}`;
}
async image({
resolutions,
sizes_attr,
path,
lossless = false,
lazy = true,
img_style,
}: {
resolutions?: number[];
sizes_attr: string;
path: string;
lossless?: boolean;
lazy?: boolean;
img_style?: string;
}): Promise<string> {
if (!resolutions || !resolutions.length) {
resolutions = guessResolutions(sizes_attr);
}
const hash = await this.getHash(path, resolutions);
this.hashToResolutions[hash] = resolutions;
this.hashToLossless[hash] = lossless;
this.hashToOriginalPath[hash] = path;
const metadata = await this.getMetadata(hash);
resolutions = resolutions.filter(
(width) => width <= (metadata.width || Infinity)
);
const extensions = [
"webp",
"png",
...(lossless ? [] : ["jpg", "avif"]),
];
let html = "<picture>";
for (let j = 0; j < extensions.length; j++) {
html += '\n<source\nsrcset="\n';
for (let i = 0; i < resolutions.length; i++) {
html += `${this.makeImageURL({
hash,
width: resolutions[i],
format: extensions[j],
})} ${resolutions[i]}w`;
if (i !== resolutions.length - 1) {
html += ",";
} else {
html += `\n"`;
}
html += `\n`;
}
html += `src="${this.makeImageURL({
hash,
width: resolutions[Math.round(resolutions.length / 2)],
format: extensions[j],
})}\n`;
html += `sizes="${sizes_attr}"\ntype="image/${extensions[j]}"\n/>\n`;
}
html += `<img ${lazy ? `loading="lazy"` : ""} width="${
metadata.width || 100
}" height="${metadata.height || 100}" ${
img_style ? `style="${img_style}"` : ""
}src="${this.makeImageURL({
hash,
width: resolutions[Math.round(resolutions.length / 2)],
format: "jpeg",
})}" /></picture>`;
return html;
}
getRoutes(): Middleware {
return this.router.routes();
}
private async getHash(original_file_path: string, resolutions: number[]) {
return crypto
.createHash("md5")
.update(
`
${basename(original_file_path)}${(
await stat(original_file_path)
).atime.getTime()}${JSON.stringify(resolutions)}`
)
.digest("hex");
}
private async generateImage({
hash,
resolution,
type,
}: {
hash: string;
resolution: number;
type: correctExtension;
}) {
const lossless = this.hashToLossless[hash];
return await sharp(this.hashToOriginalPath[hash])
.resize(resolution)
.toFormat(type, lossless ? { lossless: true } : {})
.toBuffer();
}
}

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