front_end/panels/timeline/SaveFileFormatter.ts

// Copyright 2023 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

import type * as Trace from '../../models/trace/trace.js';
/**
 * Generates a JSON representation of an array of objects with the objects
 * printed one per line for improved readability (but not *too* verbose).
 */
export function*
    arrayOfObjectsJsonGenerator(arrayOfObjects: readonly Trace.Types.Events.Event[]): IterableIterator<string> {
  const ITEMS_PER_ITERATION = 10_000;

  // Stringify and emit items separately to avoid a giant string in memory.
  yield '[\n';
  if (arrayOfObjects.length > 0) {
    const itemsIterator = arrayOfObjects[Symbol.iterator]();
    // Emit first item manually to avoid a trailing comma.
    const firstItem = itemsIterator.next().value;
    yield `  ${JSON.stringify(firstItem)}`;

    let itemsRemaining = ITEMS_PER_ITERATION;
    let itemsJSON = '';
    for (const item of itemsIterator) {
      itemsJSON += `,\n  ${JSON.stringify(item)}`;
      itemsRemaining--;
      if (itemsRemaining === 0) {
        yield itemsJSON;
        itemsRemaining = ITEMS_PER_ITERATION;
        itemsJSON = '';
      }
    }
    yield itemsJSON;
  }
  yield '\n]';
}
/**
 * Generates a JSON representation of the TraceObject file line-by-line for a nicer printed
 * version with one trace event per line.
 */
export function*
    traceJsonGenerator(
        traceEvents: readonly Trace.Types.Events.Event[],
        metadata: Readonly<Trace.Types.File.MetaData>|null,
        ): IterableIterator<string> {
  // Ensure that enhancedTraceVersion is placed at the top of metadata. See `maximumTraceFileLengthToDetermineEnhancedTraces`
  if (metadata?.enhancedTraceVersion) {
    metadata = {
      enhancedTraceVersion: metadata.enhancedTraceVersion,
      ...metadata,
    };
  }

  yield `{"metadata": ${JSON.stringify(metadata || {}, null, 2)}`;
  yield ',\n"traceEvents": ';
  yield* arrayOfObjectsJsonGenerator(traceEvents);
  yield '}\n';
}