🍱 Add Deno serve QR server example (#19)

Author: AnandChowdhary

README.md

@@ -16,7 +16,7 @@ This is a port of [zenozeng/node-yaqrcode](https://github.com/zenozeng/node-yaqr
 
 ```ts
 import { qrcode } from "https://deno.land/x/qrcode/mod.ts";
-const base64Image = qrcode("bitcoin:ADDRESS?amount=0.5&label=ORDER"); // data:image/gif;base64,...
+const base64Image = await qrcode("bitcoin:ADDRESS?amount=0.5&label=ORDER"); // data:image/gif;base64,...
 ```
 
 ![QR code](https://upload.wikimedia.org/wikipedia/commons/thumb/d/d0/QR_code_for_mobile_English_Wikipedia.svg/240px-QR_code_for_mobile_English_Wikipedia.svg.png)
@@ -26,6 +26,23 @@ You can also add a custom size by specifying `size` in the second parameter:
 ```ts
 const fixedSizeImage = await qrcode("bitcoin:ADDRESS?amount=0.5&label=ORDER", { size: 500 });
 ```
+
+### Deno.serve example
+
+The `examples/server.ts` file exposes QR codes over HTTP using `Deno.serve`:
+
+```bash
+deno run --allow-net examples/server.ts
+```
+
+Then open a URL like this to receive a GIF response:
+
+```text
+http://localhost:4000/?data=Hello%20World!&size=250&typeNumber=5&errorCorrection=L
+```
+
+Short query parameters are also supported for compact URLs: `d`, `s`, `v`, and `e`.
+
 ### CLI with [DPX](https://github.com/denorg/dpx)
 
 After [installing DPX](https://github.com/denorg/dpx), you can directly use the CLI using the `dpx` command:

examples/server.ts

@@ -0,0 +1,150 @@
+import { qrcode } from "../mod.ts";
+
+const GIF_DATA_URL_PREFIX = "data:image/gif;base64,";
+const TYPE_NUMBERS = [
+  0,
+  1,
+  2,
+  3,
+  4,
+  5,
+  6,
+  7,
+  8,
+  9,
+  10,
+  11,
+  12,
+  13,
+  14,
+  15,
+  16,
+  17,
+  18,
+  19,
+  20,
+  21,
+  22,
+  23,
+  24,
+  25,
+  26,
+  27,
+  28,
+  29,
+  30,
+  31,
+  32,
+  33,
+  34,
+  35,
+  36,
+  37,
+  38,
+  39,
+  40,
+] as const;
+const ERROR_CORRECTION_LEVELS = ["L", "M", "Q", "H"] as const;
+
+type TypeNumberOption = (typeof TYPE_NUMBERS)[number];
+type ErrorCorrectionLevelOption = (typeof ERROR_CORRECTION_LEVELS)[number];
+
+function parseIntegerParam(
+  value: string | null,
+  fallback: number,
+  min: number,
+  max: number,
+): number {
+  if (value === null || value.trim() === "") return fallback;
+
+  const parsed = Number(value);
+
+  if (!Number.isInteger(parsed)) return fallback;
+
+  return Math.min(max, Math.max(min, parsed));
+}
+
+function parseTypeNumber(value: string | null): TypeNumberOption {
+  return TYPE_NUMBERS[parseIntegerParam(value, 4, 0, 40)] ?? 4;
+}
+
+function parseErrorCorrectionLevel(
+  value: string | null,
+): ErrorCorrectionLevelOption {
+  return ERROR_CORRECTION_LEVELS.includes(value as ErrorCorrectionLevelOption)
+    ? value as ErrorCorrectionLevelOption
+    : "M";
+}
+
+function dataUrlToBytes(dataUrl: string): Uint8Array {
+  if (!dataUrl.startsWith(GIF_DATA_URL_PREFIX)) {
+    throw new Error("Expected qrcode() to return a GIF data URL");
+  }
+
+  return Uint8Array.from(
+    atob(dataUrl.slice(GIF_DATA_URL_PREFIX.length)),
+    (character) => character.charCodeAt(0),
+  );
+}
+
+const commonHeaders = {
+  "access-control-allow-origin": "*",
+  "access-control-allow-methods": "GET, HEAD, OPTIONS",
+  "cache-control": "no-store",
+};
+
+export async function handleRequest(request: Request): Promise<Response> {
+  if (request.method === "OPTIONS") {
+    return new Response(null, {
+      status: 204,
+      headers: commonHeaders,
+    });
+  }
+
+  if (request.method !== "GET" && request.method !== "HEAD") {
+    return new Response("Method not allowed", {
+      status: 405,
+      headers: {
+        ...commonHeaders,
+        allow: "GET, HEAD, OPTIONS",
+        "content-type": "text/plain; charset=utf-8",
+      },
+    });
+  }
+
+  const url = new URL(request.url);
+  const data = url.searchParams.get("data") ?? url.searchParams.get("d") ??
+    "Hello World!";
+  const size = parseIntegerParam(
+    url.searchParams.get("size") ?? url.searchParams.get("s"),
+    250,
+    100,
+    1000,
+  );
+  const typeNumber = parseTypeNumber(
+    url.searchParams.get("typeNumber") ?? url.searchParams.get("v"),
+  );
+  const errorCorrectLevel = parseErrorCorrectionLevel(
+    url.searchParams.get("errorCorrection") ?? url.searchParams.get("e"),
+  );
+
+  const dataUrl = await qrcode(data, {
+    errorCorrectLevel,
+    size,
+    typeNumber,
+  });
+  const gif = dataUrlToBytes(dataUrl);
+
+  return new Response(request.method === "HEAD" ? null : gif, {
+    status: 200,
+    headers: {
+      ...commonHeaders,
+      "content-length": String(gif.byteLength),
+      "content-type": "image/gif",
+    },
+  });
+}
+
+if (import.meta.main) {
+  Deno.serve({ port: 4000 }, handleRequest);
+}

examples/server_test.ts

@@ -0,0 +1,53 @@
+import {
+  assert,
+  assertEquals,
+} from "https://deno.land/std@0.224.0/testing/asserts.ts";
+import { handleRequest } from "./server.ts";
+
+Deno.test("server example returns a GIF response", async (): Promise<void> => {
+  const response = await handleRequest(
+    new Request("http://localhost/?d=Hello%20World%21&v=5&e=L&s=250"),
+  );
+  const bytes = new Uint8Array(await response.arrayBuffer());
+
+  assertEquals(response.status, 200);
+  assertEquals(response.headers.get("content-type"), "image/gif");
+  assertEquals(new TextDecoder().decode(bytes.slice(0, 6)), "GIF87a");
+  assert(bytes.byteLength > 0);
+});
+
+Deno.test("server example handles HEAD without a body", async (): Promise<void> => {
+  const response = await handleRequest(
+    new Request("http://localhost/?data=Hello", { method: "HEAD" }),
+  );
+
+  assertEquals(response.status, 200);
+  assertEquals(response.headers.get("content-type"), "image/gif");
+  assertEquals((await response.arrayBuffer()).byteLength, 0);
+});
+
+Deno.test("server example falls back when optional query params are missing or blank", async (): Promise<void> => {
+  const [defaults, explicitFallbacks] = await Promise.all([
+    handleRequest(new Request("http://localhost/?data=Hello&s=&v=&e=bad")),
+    handleRequest(
+      new Request(
+        "http://localhost/?data=Hello&size=250&typeNumber=4&errorCorrection=M",
+      ),
+    ),
+  ]);
+
+  assertEquals(defaults.status, 200);
+  assertEquals(
+    new Uint8Array(await defaults.arrayBuffer()),
+    new Uint8Array(await explicitFallbacks.arrayBuffer()),
+  );
+});
+
+Deno.test("server example rejects unsupported methods", async (): Promise<void> => {
+  const response = await handleRequest(
+    new Request("http://localhost/", { method: "POST" }),
+  );
+
+  assertEquals(response.status, 405);
+  assertEquals(response.headers.get("allow"), "GET, HEAD, OPTIONS");
+});