clientpdf/zip.js at main · abyworkings-coder/clientpdf · GitHub

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
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
// Minimal store-mode (uncompressed) ZIP writer — no dependency, no network call.
// Good enough for bundling a handful of PDF files client-side.

const CRC_TABLE = (() => {
  const table = new Uint32Array(256);
  for (let n = 0; n < 256; n++) {
    let c = n;
    for (let k = 0; k < 8; k++) {
      c = c & 1 ? (0xedb88320 ^ (c >>> 1)) : c >>> 1;
    }
    table[n] = c >>> 0;
  }
  return table;
})();

function crc32(bytes) {
  let crc = 0xffffffff;
  for (let i = 0; i < bytes.length; i++) {
    crc = CRC_TABLE[(crc ^ bytes[i]) & 0xff] ^ (crc >>> 8);
  }
  return (crc ^ 0xffffffff) >>> 0;
}

function dosDateTime(date) {
  const time =
    ((date.getHours() & 0x1f) << 11) |
    ((date.getMinutes() & 0x3f) << 5) |
    ((date.getSeconds() >> 1) & 0x1f);
  const dosDate =
    (((date.getFullYear() - 1980) & 0x7f) << 9) |
    (((date.getMonth() + 1) & 0xf) << 5) |
    (date.getDate() & 0x1f);
  return { time, dosDate };
}

/**
 * @param {{name: string, data: Uint8Array}[]} entries
 * @returns {Blob}
 */
export function createZip(entries) {
  const { time, dosDate } = dosDateTime(new Date());
  const localParts = [];
  const centralParts = [];
  let offset = 0;

  for (const entry of entries) {
    const nameBytes = new TextEncoder().encode(entry.name);
    const data = entry.data;
    const crc = crc32(data);

    const local = new DataView(new ArrayBuffer(30));
    local.setUint32(0, 0x04034b50, true);
    local.setUint16(4, 20, true);
    local.setUint16(6, 0x0800, true); // bit 11: filename/comment are UTF-8
    local.setUint16(8, 0, true); // stored, no compression
    local.setUint16(10, time, true);
    local.setUint16(12, dosDate, true);
    local.setUint32(14, crc, true);
    local.setUint32(18, data.length, true);
    local.setUint32(22, data.length, true);
    local.setUint16(26, nameBytes.length, true);
    local.setUint16(28, 0, true);
    localParts.push(new Uint8Array(local.buffer), nameBytes, data);

    const central = new DataView(new ArrayBuffer(46));
    central.setUint32(0, 0x02014b50, true);
    central.setUint16(4, 20, true);
    central.setUint16(6, 20, true);
    central.setUint16(8, 0x0800, true); // bit 11: filename/comment are UTF-8
    central.setUint16(10, 0, true);
    central.setUint16(12, time, true);
    central.setUint16(14, dosDate, true);
    central.setUint32(16, crc, true);
    central.setUint32(20, data.length, true);
    central.setUint32(24, data.length, true);
    central.setUint16(28, nameBytes.length, true);
    central.setUint16(30, 0, true);
    central.setUint16(32, 0, true);
    central.setUint16(34, 0, true);
    central.setUint16(36, 0, true);
    central.setUint32(38, 0, true);
    central.setUint32(42, offset, true);
    centralParts.push(new Uint8Array(central.buffer), nameBytes);

    offset += local.buffer.byteLength + nameBytes.length + data.length;
  }

  const centralStart = offset;
  let centralSize = 0;
  for (const part of centralParts) centralSize += part.length;

  const end = new DataView(new ArrayBuffer(22));
  end.setUint32(0, 0x06054b50, true);
  end.setUint16(4, 0, true);
  end.setUint16(6, 0, true);
  end.setUint16(8, entries.length, true);
  end.setUint16(10, entries.length, true);
  end.setUint32(12, centralSize, true);
  end.setUint32(16, centralStart, true);
  end.setUint16(20, 0, true);

  return new Blob([...localParts, ...centralParts, new Uint8Array(end.buffer)], {
    type: "application/zip",
  });
}