redefined-designs/backend/tests/unit/rembgClient.test.ts

import http from 'http';
import { AddressInfo } from 'net';
import { isRembgConfigured, removeBackground } from '../../src/intake/rembgClient';

/** A real PNG header, so the client's own signature check sees what it expects. */
const PNG = Buffer.from([0x89, 0x50, 0x4e, 0x47, 0x0d, 0x0a, 0x1a, 0x0a, 0, 0, 0, 0]);
const JPEG = Buffer.from([0xff, 0xd8, 0xff, 0xe0, 0, 0, 0, 0, 0, 0, 0, 0]);

interface Capture {
  url: string;
  body: string;
}

/**
 * A stub sidecar on an ephemeral port.
 *
 * Port 0 rather than a fixed number: several ports in the 55000s are
 * Hyper-V-reserved on the development machine and bind with EACCES, and a
 * fixed port would also stop this suite running beside itself.
 *
 * A real HTTP server rather than a mocked `fetch`, because what is being
 * checked is the shape of the request that reaches the wire — above all that
 * `model=u2net` is in it.
 */
async function withStub(
  handler: (req: http.IncomingMessage, res: http.ServerResponse) => void,
  run: (capture: Capture) => Promise<void>
): Promise<void> {
  const capture: Capture = { url: '', body: '' };
  const server = http.createServer((req, res) => {
    capture.url = req.url ?? '';
    const chunks: Buffer[] = [];
    req.on('data', (c: Buffer) => chunks.push(c));
    req.on('end', () => {
      capture.body = Buffer.concat(chunks).toString('latin1');
      handler(req, res);
    });
  });

  await new Promise<void>((resolve) => server.listen(0, '127.0.0.1', resolve));
  const { port } = server.address() as AddressInfo;
  process.env.REMBG_URL = `http://127.0.0.1:${port}`;

  try {
    await run(capture);
  } finally {
    delete process.env.REMBG_URL;
    await new Promise<void>((resolve) => server.close(() => resolve()));
  }
}

function respondWithPng(_req: http.IncomingMessage, res: http.ServerResponse): void {
  res.writeHead(200, { 'Content-Type': 'image/png' });
  res.end(PNG);
}

describe('whether the sidecar is configured', () => {
  it('is false when REMBG_URL is unset', () => {
    delete process.env.REMBG_URL;
    expect(isRembgConfigured()).toBe(false);
  });

  // A variable set to spaces is a configuration mistake, not a value — the
  // same reading envValidation applies everywhere else.
  it('is false when REMBG_URL is blank', () => {
    process.env.REMBG_URL = '   ';
    expect(isRembgConfigured()).toBe(false);
    delete process.env.REMBG_URL;
  });

  it('is true when REMBG_URL is set', () => {
    process.env.REMBG_URL = 'http://rembg-syn:7000';
    expect(isRembgConfigured()).toBe(true);
    delete process.env.REMBG_URL;
  });
});

describe('asking the sidecar to remove a background', () => {
  /**
   * The single most important assertion in this file.
   *
   * The image's default model is `bria-rmbg`, licensed non-commercial, and it
   * is selected by simply not naming a model. Nothing about the returned image
   * would reveal it had been used, so this is the only place it can be caught.
   */
  it('names u2net explicitly, because the default is licensed non-commercial', async () => {
    await withStub(respondWithPng, async (capture) => {
      await removeBackground(JPEG, 'image/jpeg');
      expect(capture.body).toContain('name="model"');
      expect(capture.body).toContain('u2net');
    });
  });

  it('posts the file to /api/remove and returns the PNG it gets back', async () => {
    await withStub(respondWithPng, async (capture) => {
      const out = await removeBackground(JPEG, 'image/jpeg');
      expect(capture.url).toBe('/api/remove');
      expect(capture.body).toContain('name="file"');
      expect(out.subarray(0, 8)).toEqual(PNG.subarray(0, 8));
    });
  });

  it('rejects rather than returning bytes when the sidecar errors', async () => {
    await withStub(
      (_req, res) => {
        res.writeHead(500);
        res.end('boom');
      },
      async () => {
        await expect(removeBackground(JPEG, 'image/jpeg')).rejects.toThrow(/500/);
      }
    );
  });

  // The failure that would otherwise write an HTML error page over a
  // photograph. Checked with the same magic-byte helper the upload path uses,
  // rather than by trusting the Content-Type the sidecar sent.
  it('rejects a response that is not actually a PNG', async () => {
    await withStub(
      (_req, res) => {
        res.writeHead(200, { 'Content-Type': 'image/png' });
        res.end('<html>not an image</html>');
      },
      async () => {
        await expect(removeBackground(JPEG, 'image/jpeg')).rejects.toThrow(/not a PNG/);
      }
    );
  });

  it('rejects when it is not configured at all', async () => {
    delete process.env.REMBG_URL;
    await expect(removeBackground(JPEG, 'image/jpeg')).rejects.toThrow(/REMBG_URL/);
  });
});