factorio-clusterio/packages/lib/src/stream.ts

import assert from "assert";
import fs from "node:fs"; // Need the non-promise api for reverse stream
import stream from "stream";
import util from "node:util";

const fsOpen = util.promisify(fs.open);
const fsFstat = util.promisify(fs.fstat);


/**
 * Transform splitting a stream into lines
 *
 * Splits up a stream of chunks by newlines and passes on the lines one by
 * one removing the line feed and optional carriage return from the lines.
 *
 * @example
 * ```ts
 * let lineStream = new lib.LineSplitter({ readableObjectMode: true });
 * lineStream.on("data", line => { console.log(line.toString("utf8")); });
 * let fileStream = (await fs.open(path)).createReadStream();
 * fileStream.pipe(lineStream);
 * ```
 */
export class LineSplitter extends stream.Transform {
	_partial: Buffer | null = null;

	_transform(chunk: Buffer, _encoding: string, callback: stream.TransformCallback) {
		if (this._partial) {
			chunk = Buffer.concat([this._partial, chunk]);
			this._partial = null;
		}

		while (chunk.length) {
			let end = chunk.indexOf("\n");
			if (end === -1) {
				this._partial = chunk;
				break;
			}

			let next = end + 1;
			// Eat carriage return as well if present
			if (end >= 1 && chunk[end-1] === "\r".charCodeAt(0)) {
				end -= 1;
			}

			let line = chunk.subarray(0, end);
			chunk = chunk.subarray(next);
			this.push(line);
		}
		callback();
	}

	_flush(callback: stream.TransformCallback) {
		if (this._partial) {
			this.push(this._partial);
			this._partial = null;
		}
		callback();
	}
}

/**
 * Transform splitting a reverse stream into lines
 *
 * Splits up a reverse stream of chunks created by {@link
 * createReverseReadStream} by newlines and passes on the
 * lines one by one in reverse order removing the line feed and optional
 * carriage return from the lines.
 *
 * @example
 * ```ts
 * let revLineStream = new lib.ReverseLineSplitter({ readableObjectMode: true });
 * revLineStream.on("data", line => { console.log(line.toString("utf8")); });
 * let revFileStream = await lib.createReverseReadStream(path);
 * revFileStream.pipe(revLineStream);
 * ```
 */
export class ReverseLineSplitter extends stream.Transform {
	_partial: Buffer | null = null;

	_transform(chunk: Buffer, _encoding: string, callback: stream.TransformCallback) {
		if (this._partial) {
			chunk = Buffer.concat([chunk, this._partial]);
			this._partial = null;
		}

		while (chunk.length) {
			let next = chunk.lastIndexOf("\n", -2);
			if (next === -1) {
				this._partial = chunk;
				break;
			}

			let end = chunk.length - 1;
			if (chunk[end] === "\n".charCodeAt(0)) {
				end -= 1;
				// Eat carriage return as well if present
				if (end - next > 0 && chunk[end] === "\r".charCodeAt(0)) {
					end -= 1;
				}
			}

			let line = chunk.subarray(next + 1, end + 1);
			chunk = chunk.subarray(0, next + 1);
			this.push(line);
		}
		callback();
	}

	_flush(callback: stream.TransformCallback) {
		if (this._partial) {
			let end = this._partial.length - 1;
			if (this._partial[end] === "\n".charCodeAt(0)) {
				end -= 1;
				// Eat carriage return as well if present
				if (end > 0 && this._partial[end] === "\r".charCodeAt(0)) {
					end -= 1;
				}
			}
			this.push(this._partial.subarray(0, end + 1));
			this._partial = null;
		}
		callback();
	}
}


type ReadStreamOptions = Parameters<typeof fs.createReadStream>[1];

/**
 * Create a file read stream running in reverse
 *
 * Like fs.createReadStream but provides data chunks starting from the end
 * of the file and progressing towards the start of the file.  The chunks
 * are not reversed, thus the file content can be recreated by concatenating
 * the chunks together in the reverse order they are read.
 *
 * @param path -
 *     Path to file to open. May be anything accepted by fs.open.
 * @param options -
 *     Options to pass to fs.createReadStream.  Values passed for `fd` and
 *     `fs` will be ignored.
 */
export async function createReverseReadStream(path: string, options?: ReadStreamOptions) {
	if (typeof options === "string") {
		options = { encoding: options };
	}
	const fileFd = await fsOpen(path, "r");
	const fileSize = (await fsFstat(fileFd)).size;
	let filePosition = fileSize;
	const reverseFs = {
		read(
			fd: number,
			buffer: Buffer,
			offset: number,
			length: number,
			position: number | null | undefined,
			callback: () => void,
		) {
			assert(fd === fileFd);
			assert(position === undefined);
			length = Math.min(length, filePosition);
			filePosition -= length;
			return fs.read(fd, buffer, offset, length, filePosition, callback);
		},
		open() { assert(false); },
		close(fd: number, callback: () => void) { return fs.close(fd, callback); },
	};
	return fs.createReadStream("", { ...options, fd: fileFd, fs: reverseFs });
}