@phi-ag/rvt/dist/cfb/header.js

Parse Revit file format

import { assertEqual, assertZero } from "./utils.js";
export const maxFatSectorsHeader = 109;
export const parseHeader = (chunk) => {
    const signature = [0xd0, 0xcf, 0x11, 0xe0, 0xa1, 0xb1, 0x1a, 0xe1];
    assertEqual(chunk, 0, signature, "signature");
    assertEqual(chunk, 24, [0x3e, 0x00], "minor version");
    const view = new DataView(chunk.buffer, chunk.byteOffset);
    const version = view.getUint16(26, true);
    if (version !== 3 && version !== 4)
        throw Error(`Unexpected compound file major version (${version})`);
    assertEqual(chunk, 28, [0xfe, 0xff], "byte order");
    const sectorSizeBits = view.getUint16(30, true);
    const sectorSize = 1 << sectorSizeBits;
    const maxSectorEntries = 1 << (sectorSizeBits - 2);
    const miniSectorSizeBits = view.getUint16(32, true);
    const miniSectorSize = 1 << miniSectorSizeBits;
    assertZero(chunk, 34, 6, "reserved");
    const directorySectorCount = view.getUint32(40, true);
    if (version === 3 && directorySectorCount !== 0)
        throw Error(`Unexpected compound file sector count (${directorySectorCount})`);
    const fatSectorCount = view.getUint32(44, true);
    const directoryStart = view.getUint32(48, true);
    assertZero(chunk, 52, 4, "transaction signature");
    const miniFatCutoff = view.getUint32(56, true);
    const miniFatStart = view.getUint32(60, true);
    const miniFatSectorCount = view.getUint32(64, true);
    const diFatStart = view.getUint32(68, true);
    const diFatCount = view.getUint32(72, true);
    const fatSectors = new Uint32Array(fatSectorCount);
    const fatSectorsHeaderCount = Math.min(fatSectorCount, maxFatSectorsHeader);
    for (let i = 0; i < fatSectorsHeaderCount; ++i) {
        fatSectors[i] = view.getUint32(76 + i * 4, true);
    }
    const header = {
        version,
        sectorSize,
        sectorSizeBits,
        maxSectorEntries,
        miniSectorSize,
        miniSectorSizeBits,
        directorySectorCount,
        fatSectorCount,
        directoryStart,
        miniFatCutoff,
        miniFatStart,
        miniFatSectorCount,
        diFatStart,
        diFatCount
    };
    return [header, fatSectors];
};