reading.ts

/**
 * @license
 * Copyright 2019 Palantir Technologies, Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import * as fs from "fs";

import { FatalError } from "../error";
import { Logger } from "../runner";

/** Read a file, but return undefined if it is an MPEG '.ts' file. */
export async function tryReadFile(filename: string, logger: Logger): Promise<string | undefined> {
    if (!fs.existsSync(filename)) {
        throw new FatalError(`Unable to open file: ${filename}`);
    }
    const buffer = Buffer.allocUnsafe(256);
    const fd = fs.openSync(filename, "r");
    try {
        fs.readSync(fd, buffer, 0, 256, 0);
        if (buffer.readInt8(0) === 0x47 && buffer.readInt8(188) === 0x47) {
            // MPEG transport streams use the '.ts' file extension. They use 0x47 as the frame
            // separator, repeating every 188 bytes. It is unlikely to find that pattern in
            // TypeScript source, so tslint ignores files with the specific pattern.
            logger.error(`${filename}: ignoring MPEG transport stream\n`);
            return undefined;
        }
    } finally {
        fs.closeSync(fd);
    }

    return fs.readFileSync(filename, "utf8");
}