prometheus/service/uploads.js

/**
 * POST /api/upload — accept a file, scan it, hand back a signed scan report.
 *
 * This endpoint is the floor of the submit path. It does not publish anything
 * on chain, it does not collect payment, it does not need the publisher's
 * identity. All it does is:
 *
 *   1. Receive the file bytes (multipart/form-data, `file` field).
 *   2. Spool to a temp file while hashing to SHA-256.
 *   3. Hand the file to clamd (or MOCK_SCAN) for a verdict.
 *   4. Keep the file if clean, discard it otherwise.
 *   5. Sign the verdict with the service key and return it.
 *
 * A clean upload leaves `uploads/<sha256>.bin` on disk plus a
 * `uploads/<sha256>.json` sidecar with the metadata. The signed report in
 * the response is the artifact the manifest-signing step will attach to the
 * APS1 record later.
 *
 * The file-size cap is deliberately generous — apps can be big — but every
 * byte over the cap is dropped and the upload rejected: letting one request
 * fill the disk is worse than making a publisher try again.
 */

import { createHash } from 'node:crypto';
import { createReadStream, createWriteStream } from 'node:fs';
import { mkdir, rename, unlink, writeFile } from 'node:fs/promises';
import { randomUUID } from 'node:crypto';
import { resolve, dirname } from 'node:path';
import { fileURLToPath } from 'node:url';
import { pipeline } from 'node:stream/promises';
import { PassThrough } from 'node:stream';
import Busboy from 'busboy';
import { scanStream } from './clamd.js';
import { signReport } from './signing.js';

const UPLOAD_DIR = process.env.PROMETHEUS_UPLOAD_DIR
  || resolve(dirname(fileURLToPath(import.meta.url)), '..', 'uploads');

// 200 MiB — fits every Android APK and most desktop installers; publishers
// of larger binaries self-host and submit a manifest with the external URL +
// SHA. The service's cap and Caddy's `request_body { max_size 200MB }` on
// the prometheus.x vhost must stay in sync — if Caddy rejects first, the
// browser gets an HTML 413 page that the JSON parser cannot read.
// Change via env rather than code so an operator can tighten per-instance.
const MAX_FILE_BYTES = Number(process.env.PROMETHEUS_MAX_UPLOAD_BYTES)
  || 200 * 1024 * 1024;

/**
 * Express-style handler attached to `/api/upload`.
 */
export async function handleUpload(req, res) {
  if (req.method !== 'POST') {
    return respond(res, 405, { ok: false, error: 'method not allowed' });
  }

  const contentType = String(req.headers['content-type'] || '');
  if (!contentType.startsWith('multipart/form-data')) {
    return respond(res, 415, {
      ok: false,
      error: 'content-type must be multipart/form-data with a `file` field',
    });
  }

  await mkdir(UPLOAD_DIR, { recursive: true });

  const tempId = randomUUID();
  const tempPath = resolve(UPLOAD_DIR, `.tmp-${tempId}`);

  let gotFile = false;
  let truncated = false;
  let originalName = '';
  let mimeType = 'application/octet-stream';

  // We let busboy drive. The one 'file' event we care about forwards straight
  // to a hashing + write pipeline; any extra fields are ignored.
  const busboy = Busboy({
    headers: req.headers,
    limits: { fileSize: MAX_FILE_BYTES, files: 1 },
  });

  const hasher = createHash('sha256');
  let byteCount = 0;

  // We'd like to pipe the busboy file into TWO sinks: the temp file and the
  // hasher. PassThrough splits a stream in one line: one upstream, two
  // downstreams, no buffering we have to manage ourselves.
  const toHash = new PassThrough();
  const toDisk = new PassThrough();
  toHash.on('data', (chunk) => {
    hasher.update(chunk);
    byteCount += chunk.length;
  });

  const writeToDisk = pipeline(toDisk, createWriteStream(tempPath));

  const fileDone = new Promise((resolveFile, rejectFile) => {
    busboy.on('file', (fieldname, file, info) => {
      gotFile = true;
      originalName = sanitize(info.filename || 'upload');
      mimeType = info.mimeType || mimeType;

      file.on('limit', () => { truncated = true; });

      file.on('data', (chunk) => {
        toHash.write(chunk);
        toDisk.write(chunk);
      });

      file.on('end', () => {
        toHash.end();
        toDisk.end();
      });

      file.on('error', rejectFile);
    });

    busboy.on('finish', resolveFile);
    busboy.on('error', rejectFile);
  });

  // Pump the request through busboy. If anything throws here we clean up and
  // reply with 400 — we never leave a half-written temp file behind.
  try {
    req.pipe(busboy);
    await fileDone;
    await writeToDisk;
  } catch (err) {
    await safeUnlink(tempPath);
    return respond(res, 400, { ok: false, error: String(err?.message || err) });
  }

  if (!gotFile) {
    await safeUnlink(tempPath);
    return respond(res, 400, { ok: false, error: 'no `file` field in request' });
  }

  if (truncated) {
    await safeUnlink(tempPath);
    return respond(res, 413, {
      ok: false,
      error: `file exceeded the ${MAX_FILE_BYTES}-byte cap`,
    });
  }

  const sha256 = hasher.digest('hex');

  // Scan from the on-disk copy. Scanning in parallel with receive would
  // save latency on huge files, but doubles the error surface — we would
  // need to coordinate two independent failure modes. On-disk-then-scan is
  // what every mature scanning service does; we can revisit once we have
  // a reason.
  const scan = await scanStream(createReadStream(tempPath), { sha256 });

  const now = new Date().toISOString();
  const upload = {
    hash: sha256,
    size: byteCount,
    name: originalName,
    mime: mimeType,
    received_at: now,
  };

  let stored = false;
  let finalPath = null;

  if (scan.verdict === 'clean') {
    finalPath = resolve(UPLOAD_DIR, `${sha256}.bin`);
    try {
      await rename(tempPath, finalPath);
      stored = true;
      await writeFile(
        resolve(UPLOAD_DIR, `${sha256}.json`),
        JSON.stringify({ upload, scan }, null, 2),
        'utf8',
      );
    } catch (err) {
      // Rare: another concurrent upload of the same bytes won the race.
      // The existing file is already correct; drop ours and move on.
      await safeUnlink(tempPath);
      stored = true;
      finalPath = resolve(UPLOAD_DIR, `${sha256}.bin`);
    }
  } else {
    // Infected or error — the bytes do not stay on our disk.
    await safeUnlink(tempPath);
  }

  // The signed report is what callers persist. It carries the upload metadata
  // AND the scan outcome, so a downstream verifier can confirm this exact
  // (hash, size, verdict) tuple came from this service and was not edited.
  const reportPayload = {
    v: 1,
    kind: 'prometheus.scan-report',
    service: 'prometheus',
    issued_at: now,
    upload: {
      hash: upload.hash,
      size: upload.size,
      name: upload.name,
      mime: upload.mime,
    },
    scan: {
      verdict: scan.verdict,
      engine: scan.engine,
      signatures: scan.signatures,
      duration_ms: scan.duration_ms,
      ...(scan.virustotal ? { virustotal: scan.virustotal } : {}),
    },
    stored,
  };
  const report = signReport(reportPayload);

  return respond(res, scan.verdict === 'error' ? 502 : 200, {
    ok: scan.verdict !== 'error',
    upload,
    scan: {
      verdict: scan.verdict,
      engine: scan.engine,
      signatures: scan.signatures,
      duration_ms: scan.duration_ms,
      ...(scan.error ? { error: scan.error } : {}),
      ...(scan.virustotal ? { virustotal: scan.virustotal } : {}),
    },
    stored,
    report,
  });
}

/* ----------------------- helpers ----------------------- */

function respond(res, status, body) {
  const json = JSON.stringify(body);
  res.writeHead(status, {
    'content-type': 'application/json; charset=utf-8',
    'content-length': Buffer.byteLength(json),
    'cache-control': 'no-store',
  });
  res.end(json);
}

function sanitize(name) {
  // Keep the publisher's filename for display, but strip path separators and
  // control characters — nothing we write to disk is derived from this; it is
  // just metadata for the UI.
  return String(name)
    .replace(/[\\/\x00-\x1f]/g, '_')
    .slice(0, 200);
}

async function safeUnlink(path) {
  try { await unlink(path); } catch { /* already gone */ }
}