netcdf4-wasm/dist/lazy/blob-reader.js

NetCDF4 library compiled to WebAssembly with TypeScript bindings

"use strict";
// Lazy file reading - browser Blob/File backend
//
// Reads byte ranges out of a Blob/File with FileReaderSync. Because the read must
// be synchronous (libc read() is), this only works inside a Web Worker, where
// FileReaderSync exists. On the main thread there is no synchronous way to read a
// Blob, so construction throws with a clear message.
Object.defineProperty(exports, "__esModule", { value: true });
exports.BlobReader = void 0;
function getFileReaderSync() {
    return globalThis.FileReaderSync;
}
class BlobReader {
    constructor(blob) {
        this.blob = blob;
        const ctor = getFileReaderSync();
        if (!ctor) {
            throw new Error("BlobReader requires FileReaderSync, which is only available inside a Web Worker. " +
                "Run lazy Blob reading in a worker, or load the file with the default (eager) path.");
        }
        this.readerCtor = ctor;
    }
    get size() {
        return this.blob.size;
    }
    read(offset, length) {
        const end = Math.min(offset + length, this.blob.size);
        if (offset < 0 || offset >= this.blob.size || end <= offset) {
            return new Uint8Array(0);
        }
        const slice = this.blob.slice(offset, end);
        const buffer = new this.readerCtor().readAsArrayBuffer(slice);
        return new Uint8Array(buffer);
    }
    close() {
        // Nothing to release.
    }
}
exports.BlobReader = BlobReader;
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