s2-tools/dist/util/gzip.js

A collection of geospatial tools primarily designed for WGS84, Web Mercator, and S2.

import { concatUint8Arrays } from '.';
/**
 * A Browser compatible Gzip compression function
 * @param bytes - the data to decompress
 * @param format - the format of the data. Defaults to 'gzip'
 * @returns - the decompressed data
 */
export async function compressStream(bytes, format) {
    // Convert the string to a byte stream.
    const stream = new Blob([bytes]).stream();
    // Create a compressed stream.
    const compressedStream = stream.pipeThrough(new CompressionStream(format ?? 'gzip'));
    // Read all the bytes from this stream.
    const chunks = [];
    for await (const chunk of compressedStream)
        chunks.push(chunk);
    return await concatUint8Arrays(chunks);
}
/**
 * A Browser compatible Gzip decompression function
 * @param bytes - the data to decompress
 * @param format - the format of the data. Defaults to 'gzip'
 * @returns - the decompressed data
 */
export async function decompressStream(bytes, format) {
    if (format === undefined)
        format = bytes[0] === 0x1f && bytes[1] === 0x8b ? 'gzip' : 'deflate';
    // Convert the bytes to a stream.
    const stream = new Blob([bytes]).stream();
    // Create a decompressed stream.
    const decompressedStream = stream.pipeThrough(new DecompressionStream(format));
    // Read all the bytes from this stream.
    const chunks = [];
    for await (const chunk of decompressedStream)
        chunks.push(chunk);
    return await concatUint8Arrays(chunks);
}
/**
 * Find the end of the central directory
 * @param raw - the raw data
 * @returns - the end of the central directory
 */
function findEndCentralDirectory(raw) {
    let search = raw.length - 20;
    const bounds = Math.max(search - 65516, 2); // sub 2**256 - 20 (max comment length)
    while ((search = raw.lastIndexOf(0x50, search - 1)) !== -1 &&
        !(raw[search + 1] === 0x4b && raw[search + 2] === 0x05 && raw[search + 3] === 0x06) &&
        search > bounds) {
        // no-op
    }
    return search;
}
/**
 * Iterate over the items in a zip file
 * @param raw - the raw data to read
 * @yields - {@link ZipItem}
 */
export function* iterItems(raw) {
    const d = new TextDecoder();
    let at = findEndCentralDirectory(raw);
    if (at === -1) {
        throwCode(2); // bad zip format
    }
    /**
     * @param startBy - starting index
     * @param endBy - ending index
     * @returns - the subarray
     */
    const subarrayMove = (startBy, endBy) => raw.subarray((at += startBy), (at += endBy));
    const dataView = new DataView(raw.buffer, raw.byteOffset); // we don't need byteLength, could be a longer buffer :shrug:
    /**
     * @param offset - the offset to read from
     * @returns - the u16 value
     */
    const u16 = (offset) => dataView.getUint16(offset + at, true);
    /**
     * @param offset - the offset to read from
     * @returns - the u32 value
     */
    const u32 = (offset) => dataView.getUint32(offset + at, true);
    // read end central directory
    let fileCount = u16(10);
    if (fileCount !== u16(8)) {
        throwCode(3); // no multi-disk support
    }
    const centralDirectoryStart = u32(16);
    at = centralDirectoryStart;
    // read central directory
    while (fileCount-- > 0) {
        const compressionMethod = u16(10);
        const filenameLength = u16(28);
        const extraFieldsLength = u16(30);
        const commentLength = u16(32);
        const compressedSize = u32(20);
        // find local entry location
        const localEntryAt = u32(42);
        // read buffers, move at to after entry, and store where we were
        const filename = d.decode(subarrayMove(46, filenameLength));
        // we skip extraFields here
        const comment = d.decode(subarrayMove(extraFieldsLength, commentLength));
        const nextCentralDirectoryEntry = at;
        // >> start reading entry
        at = localEntryAt;
        // this is the local entry (filename + extra fields) length, which we skip
        const bytes = subarrayMove(30 + u16(26) + u16(28), compressedSize);
        yield {
            filename,
            comment,
            /**
             * @returns - the decompressed bytes
             */
            read: async () => {
                return (compressionMethod & 8) > 0
                    ? await decompressStream(bytes, 'deflate-raw')
                    : compressionMethod > 0
                        ? throwCode(1)
                        : bytes;
            },
        };
        at = nextCentralDirectoryEntry;
    }
}
/**
 * @param code - error code
 * @throws - an error
 */
function throwCode(code) {
    throw new Error(`Error code: ${code}`);
}
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