mdb-reader/lib/browser/data/ole.js

JavaScript library to read data from Access databases

import { Database } from "../Database.js";
const TYPES = {
    THIS_PAGE: 0x80,
    OTHER_PAGE: 0x40,
    OTHER_PAGES: 0x00,
};
/**
 * @see https://github.com/brianb/mdbtools/blob/d6f5745d949f37db969d5f424e69b54f0da60b9b/src/libmdb/data.c#L626-L688
 * @see https://github.com/spannm/jackcess/blob/4c433a4ae4969ff5658556806a35ccb13cc35313/src/main/java/io/github/spannm/jackcess/impl/LongValueColumnImpl.java#L130-L209
 */
export function readOLE(buffer, _col, database) {
    const length = buffer.readUIntLE(0, 3);
    const type = buffer.readUInt8(3);
    switch (type) {
        case TYPES.THIS_PAGE: {
            // 0-2: Length
            // 3: Type
            // 4-7: lval_dp
            // 8-11: unknown
            // 12: data
            // inline
            return buffer.slice(12, 12 + length);
        }
        case TYPES.OTHER_PAGE: {
            // single page
            const pageRow = buffer.readUInt32LE(4);
            const rowBuffer = database.findPageRow(pageRow);
            return rowBuffer.slice(0, length);
        }
        case TYPES.OTHER_PAGES: {
            // multi page
            let pageRow = buffer.readInt32LE(4);
            const result = Buffer.alloc(length);
            let offset = 0;
            do {
                const rowBuffer = database.findPageRow(pageRow);
                if (rowBuffer.length <= 4) {
                    break;
                }
                pageRow = rowBuffer.readUInt32LE(0);
                const newChunk = rowBuffer.subarray(4);
                newChunk.copy(result, offset);
                offset += newChunk.length;
            } while (pageRow !== 0);
            return result.subarray(0, length);
        }
        default: {
            throw new Error(`Unknown OLE type ${type}`);
        }
    }
}