Initial commit

backend/src/utils/zip.js

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+/**
+ * zip.js — Minimal pure-Node.js ZIP builder / reader.
+ * No external dependencies — uses only Node's built-in zlib.
+ */
+import zlib from 'zlib';
+
+// ── CRC-32 ────────────────────────────────────────────────────────────────
+const _crcTable = (() => {
+  const t = new Uint32Array(256);
+  for (let i = 0; i < 256; i++) {
+    let c = i;
+    for (let j = 0; j < 8; j++) c = (c & 1) ? (0xEDB88320 ^ (c >>> 1)) : (c >>> 1);
+    t[i] = c;
+  }
+  return t;
+})();
+
+function crc32(buf) {
+  let crc = 0xFFFFFFFF;
+  for (let i = 0; i < buf.length; i++) crc = (crc >>> 8) ^ _crcTable[(crc ^ buf[i]) & 0xFF];
+  return (crc ^ 0xFFFFFFFF) >>> 0;
+}
+
+// ── DOS date/time ─────────────────────────────────────────────────────────
+function dosDateTime(d = new Date()) {
+  const time = ((d.getHours() << 11) | (d.getMinutes() << 5) | (d.getSeconds() >> 1)) & 0xFFFF;
+  const date = (((d.getFullYear() - 1980) << 9) | ((d.getMonth() + 1) << 5) | d.getDate()) & 0xFFFF;
+  return { time, date };
+}
+
+/**
+ * createZip(entries) → Buffer
+ * entries: [{ name: string, data: Buffer|string }]
+ */
+export function createZip(entries) {
+  const chunks = [];
+  const centralHeaders = [];
+  let offset = 0;
+  const { time: modTime, date: modDate } = dosDateTime();
+
+  for (let { name, data } of entries) {
+    if (typeof data === 'string') data = Buffer.from(data, 'utf8');
+    const nameBuf = Buffer.from(name, 'utf8');
+    const crc = crc32(data);
+    const uncompSize = data.length;
+
+    // Try deflate; use stored if compressed is larger
+    const deflated = zlib.deflateRawSync(data);
+    const useDeflate = deflated.length < uncompSize;
+    const compData = useDeflate ? deflated : data;
+    const method = useDeflate ? 8 : 0;
+
+    // Local file header
+    const lh = Buffer.alloc(30 + nameBuf.length);
+    lh.writeUInt32LE(0x04034b50, 0);
+    lh.writeUInt16LE(20, 4);
+    lh.writeUInt16LE(0, 6);
+    lh.writeUInt16LE(method, 8);
+    lh.writeUInt16LE(modTime, 10);
+    lh.writeUInt16LE(modDate, 12);
+    lh.writeUInt32LE(crc, 14);
+    lh.writeUInt32LE(compData.length, 18);
+    lh.writeUInt32LE(uncompSize, 22);
+    lh.writeUInt16LE(nameBuf.length, 26);
+    lh.writeUInt16LE(0, 28);
+    nameBuf.copy(lh, 30);
+
+    chunks.push(lh, compData);
+    centralHeaders.push({ name: nameBuf, crc, method, modTime, modDate, compSize: compData.length, uncompSize, offset });
+    offset += lh.length + compData.length;
+  }
+
+  // Central directory
+  const cdStart = offset;
+  for (const h of centralHeaders) {
+    const cd = Buffer.alloc(46 + h.name.length);
+    cd.writeUInt32LE(0x02014b50, 0);
+    cd.writeUInt16LE(20, 4);
+    cd.writeUInt16LE(20, 6);
+    cd.writeUInt16LE(0, 8);
+    cd.writeUInt16LE(h.method, 10);
+    cd.writeUInt16LE(h.modTime, 12);
+    cd.writeUInt16LE(h.modDate, 14);
+    cd.writeUInt32LE(h.crc, 16);
+    cd.writeUInt32LE(h.compSize, 20);
+    cd.writeUInt32LE(h.uncompSize, 24);
+    cd.writeUInt16LE(h.name.length, 28);
+    cd.writeUInt16LE(0, 30);
+    cd.writeUInt16LE(0, 32);
+    cd.writeUInt16LE(0, 34);
+    cd.writeUInt16LE(0, 36);
+    cd.writeUInt32LE(0, 38);
+    cd.writeUInt32LE(h.offset, 42);
+    h.name.copy(cd, 46);
+    chunks.push(cd);
+    offset += cd.length;
+  }
+
+  const cdSize = offset - cdStart;
+
+  // End of central directory
+  const eocd = Buffer.alloc(22);
+  eocd.writeUInt32LE(0x06054b50, 0);
+  eocd.writeUInt16LE(0, 4);
+  eocd.writeUInt16LE(0, 6);
+  eocd.writeUInt16LE(centralHeaders.length, 8);
+  eocd.writeUInt16LE(centralHeaders.length, 10);
+  eocd.writeUInt32LE(cdSize, 12);
+  eocd.writeUInt32LE(cdStart, 16);
+  eocd.writeUInt16LE(0, 20);
+  chunks.push(eocd);
+
+  return Buffer.concat(chunks);
+}
+
+/**
+ * readZip(buffer) → [{ name: string, data: Buffer }]
+ */
+export function readZip(buffer) {
+  // Scan backwards for EOCD signature
+  let eocdOffset = -1;
+  for (let i = buffer.length - 22; i >= Math.max(0, buffer.length - 65558); i--) {
+    if (buffer.readUInt32LE(i) === 0x06054b50) { eocdOffset = i; break; }
+  }
+  if (eocdOffset === -1) throw new Error('ZIP invalide : signature EOCD introuvable');
+
+  const entryCount = buffer.readUInt16LE(eocdOffset + 8);
+  const cdOffset   = buffer.readUInt32LE(eocdOffset + 16);
+
+  const entries = [];
+  let pos = cdOffset;
+
+  for (let i = 0; i < entryCount; i++) {
+    if (buffer.readUInt32LE(pos) !== 0x02014b50) throw new Error('ZIP invalide : signature Central Directory incorrecte');
+    const method      = buffer.readUInt16LE(pos + 10);
+    const compSize    = buffer.readUInt32LE(pos + 20);
+    const uncompSize  = buffer.readUInt32LE(pos + 24);
+    const nameLen     = buffer.readUInt16LE(pos + 28);
+    const extraLen    = buffer.readUInt16LE(pos + 30);
+    const commentLen  = buffer.readUInt16LE(pos + 32);
+    const localOffset = buffer.readUInt32LE(pos + 42);
+    const name        = buffer.toString('utf8', pos + 46, pos + 46 + nameLen);
+
+    // Read local file header to get actual extra field length
+    const localNameLen  = buffer.readUInt16LE(localOffset + 26);
+    const localExtraLen = buffer.readUInt16LE(localOffset + 28);
+    const dataStart     = localOffset + 30 + localNameLen + localExtraLen;
+
+    const compData = buffer.subarray(dataStart, dataStart + compSize);
+    const data = method === 0 ? compData : zlib.inflateRawSync(compData);
+
+    entries.push({ name, data: Buffer.from(data) });
+    pos += 46 + nameLen + extraLen + commentLen;
+  }
+
+  return entries;
+}