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Closure Compiler is a JavaScript optimizing compiler. It parses your JavaScript, analyzes it, removes dead code and rewrites and minimizes what's left. It also checks syntax, variable references, and types, and warns about common JavaScript pitfalls. It is used in many of Google's JavaScript apps, including Gmail, Google Web Search, Google Maps, and Google Docs. This binary checks for style issues such as incorrect or missing JSDoc usage, and missing goog.require() statements. It does not do more advanced checks such as typechecking.

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/*
 * Copyright 2018 The Closure Compiler Authors.
 *
 * 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.
 */
package com.google.javascript.jscomp;

import com.google.common.annotations.GwtIncompatible;
import com.google.common.cache.CacheBuilder;
import com.google.common.cache.CacheLoader;
import com.google.common.cache.LoadingCache;
import com.google.common.cache.RemovalNotification;
import com.google.common.io.CharStreams;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.Reader;
import java.io.Serializable;
import java.nio.charset.Charset;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.nio.file.attribute.FileTime;
import java.util.zip.ZipFile;

/**
 * A class that abstract entries from zip files via managed caching.
 *
 * Normally zip files created via URL connection cache indefinite by JDK. That's not good since a
 * zip file contents might change over time (e.g. compiler running as a worker). This class provides
 * a timestamp controlled caching which ensures we always read up-to-date zip while avoiding wasting
 * time by re-reading the zip for each entry.
 */
@GwtIncompatible("java.util.zip.ZipFile")
final class ZipEntryReader implements Serializable {

  private static final long serialVersionUID = 1L;

  private static final int ZIP_CACHE_SIZE =
      Integer.parseInt(System.getProperty("jscomp.zipfile.cachesize", "1000"));

  private static final LoadingCache zipFileCache =
      CacheBuilder.newBuilder()
          .maximumSize(ZIP_CACHE_SIZE)
          .removalListener(
              (RemovalNotification notification) -> {
                try {
                  notification.getValue().maybeClose();
                } catch (IOException e) {
                  throw new RuntimeException(e);
                }
              })
          .build(
              new CacheLoader() {
                @Override
                public CachedZipFile load(String key) throws IOException {
                  return new CachedZipFile(key);
                }
              });

  private static class CachedZipFile {
    private final Path path;
    private ZipFile zipFile;
    private volatile FileTime lastModified;

    private CachedZipFile(String zipName) {
      this.path = Paths.get(zipName);
    }

    private Reader getReader(String entryName, Charset charset) throws IOException {
      refreshIfNeeded();
      return new InputStreamReader(zipFile.getInputStream(zipFile.getEntry(entryName)), charset);
    }

    private void refreshIfNeeded() throws IOException {
      FileTime newLastModified = Files.getLastModifiedTime(path);
      if (newLastModified.equals(lastModified)) {
        return;
      }

      synchronized (this) {
        // Since we do double checked locking (newLastModified is checked out of synchronized), we
        // should test the stamp again.
        if (newLastModified.equals(lastModified)) {
          return;
        }

        maybeClose();
        zipFile = new ZipFile(path.toFile());
        lastModified = newLastModified;
      }
    }

    private void maybeClose() throws IOException {
      if (zipFile != null) {
        zipFile.close();
      }
    }
  }

  private final String zipPath;
  private final String entryName;

  public ZipEntryReader(String zipPath, String entryName) {
    this.zipPath = zipPath;
    this.entryName = entryName;
  }

  public Reader getReader(Charset charset) throws IOException {
    CachedZipFile zipFile = zipFileCache.getUnchecked(zipPath);
    return new BufferedReader(zipFile.getReader(entryName, charset));
  }

  public String read(Charset charset) throws IOException {
    CachedZipFile zipFile = zipFileCache.getUnchecked(zipPath);
    return CharStreams.toString(zipFile.getReader(entryName, charset));
  }
}