cli-logger.ts

/**
 * @license
 * Copyright Google LLC All Rights Reserved.
 *
 * Use of this source code is governed by an MIT-style license that can be
 * found in the LICENSE file at https://angular.io/license
 */

import { filter } from 'rxjs/operators';
import { logging } from '../src';

export interface ProcessOutput {
  write(buffer: string | Buffer): boolean;
}

/**
 * A Logger that sends information to STDOUT and STDERR.
 */
export function createConsoleLogger(
  verbose = false,
  stdout: ProcessOutput = process.stdout,
  stderr: ProcessOutput = process.stderr,
  colors?: Partial<Record<logging.LogLevel, (s: string) => string>>,
): logging.Logger {
  const logger = new logging.IndentLogger('cling');

  logger.pipe(filter((entry) => entry.level !== 'debug' || verbose)).subscribe((entry) => {
    const color = colors && colors[entry.level];
    let output = stdout;

    switch (entry.level) {
      case 'warn':
      case 'fatal':
      case 'error':
        output = stderr;
        break;
    }

    // If we do console.log(message) or process.stdout.write(message + '\n'), the process might
    // stop before the whole message is written and the stream is flushed. This happens when
    // streams are asynchronous.
    //
    // NodeJS IO streams are different depending on platform and usage. In POSIX environment,
    // for example, they're asynchronous when writing to a pipe, but synchronous when writing
    // to a TTY. In windows, it's the other way around. You can verify which is which with
    // stream.isTTY and platform, but this is not good enough.
    // In the async case, one should wait for the callback before sending more data or
    // continuing the process. In our case it would be rather hard to do (but not impossible).
    //
    // Instead we take the easy way out and simply chunk the message and call the write
    // function while the buffer drain itself asynchronously. With a smaller chunk size than
    // the buffer, we are mostly certain that it works. In this case, the chunk has been picked
    // as half a page size (4096/2 = 2048), minus some bytes for the color formatting.
    // On POSIX it seems the buffer is 2 pages (8192), but just to be sure (could be different
    // by platform).
    //
    // For more details, see https://nodejs.org/api/process.html#process_a_note_on_process_i_o
    const chunkSize = 2000; // Small chunk.
    let message = entry.message;
    while (message) {
      const chunk = message.slice(0, chunkSize);
      message = message.slice(chunkSize);
      output.write(color ? color(chunk) : chunk);
    }
    output.write('\n');
  });

  return logger;
}