the-algorithm/ann/src/main/java/com/twitter/ann/faiss/NativeUtils.java

package com.twitter.ann.faiss;

import java.io.File;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStream;
import java.nio.file.Files;
import java.nio.file.StandardCopyOption;
import java.util.Locale;

public final class NativeUtils {

  private static final int MIN_PREFIX_LENGTH = 3;
  public static final String NATIVE_FOLDER_PATH_PREFIX = "nativeutils";

  public static File temporaryDir;

  private NativeUtils() {
  }

  private static File unpackLibraryFromJarInternal(String path) throws IOException {
    if (null == path || !path.startsWith("/")) {
      throw new IllegalArgumentException("The path has to be absolute (start with '/').");
    }

    String[] parts = path.split("/");
    String filename = (parts.length > 1) ? parts[parts.length - 1] : null;

    if (filename == null || filename.length() < MIN_PREFIX_LENGTH) {
      throw new IllegalArgumentException("The filename has to be at least 3 characters long.");
    }

    if (temporaryDir == null) {
      temporaryDir = createTempDirectory(NATIVE_FOLDER_PATH_PREFIX);
      temporaryDir.deleteOnExit();
    }

    File temp = new File(temporaryDir, filename);

    try (InputStream is = NativeUtils.class.getResourceAsStream(path)) {
      Files.copy(is, temp.toPath(), StandardCopyOption.REPLACE_EXISTING);
    } catch (IOException e) {
      temp.delete();
      throw e;
    } catch (NullPointerException e) {
      temp.delete();
      throw new FileNotFoundException("File " + path + " was not found inside JAR.");
    }

    return temp;
  }

  /**
   * Unpack library from JAR into temporary path
   *
   * @param path The path of file inside JAR as absolute path (beginning with
   *             '/'), e.g. /package/File.ext
   * @throws IOException              If temporary file creation or read/write
   *                                  operation fails
   * @throws IllegalArgumentException If source file (param path) does not exist
   * @throws IllegalArgumentException If the path is not absolute or if the
   *                                  filename is shorter than three characters
   *                                  (restriction of
   *                                  {@link File#createTempFile(java.lang.String, java.lang.String)}).
   * @throws FileNotFoundException    If the file could not be found inside the
   *                                  JAR.
   */
  public static void unpackLibraryFromJar(String path) throws IOException {
    unpackLibraryFromJarInternal(path);
  }

  /**
   * Loads library from current JAR archive
   * <p>
   * The file from JAR is copied into system temporary directory and then loaded.
   * The temporary file is deleted after
   * exiting.
   * Method uses String as filename because the pathname is "abstract", not
   * system-dependent.
   *
   * @param path The path of file inside JAR as absolute path (beginning with
   *             '/'), e.g. /package/File.ext
   * @throws IOException              If temporary file creation or read/write
   *                                  operation fails
   * @throws IllegalArgumentException If source file (param path) does not exist
   * @throws IllegalArgumentException If the path is not absolute or if the
   *                                  filename is shorter than three characters
   *                                  (restriction of
   *                                  {@link File#createTempFile(java.lang.String, java.lang.String)}).
   * @throws FileNotFoundException    If the file could not be found inside the
   *                                  JAR.
   */
  public static void loadLibraryFromJar(String path) throws IOException {
    File temp = unpackLibraryFromJarInternal(path);

    try (InputStream is = NativeUtils.class.getResourceAsStream(path)) {
      Files.copy(is, temp.toPath(), StandardCopyOption.REPLACE_EXISTING);
    } catch (IOException e) {
      temp.delete();
      throw e;
    } catch (NullPointerException e) {
      temp.delete();
      throw new FileNotFoundException("File " + path + " was not found inside JAR.");
    }

    try {
      System.load(temp.getAbsolutePath());
    } finally {
      temp.deleteOnExit();
    }
  }

  private static File createTempDirectory(String prefix) throws IOException {
    String tempDir = System.getProperty("java.io.tmpdir");
    File generatedDir = new File(tempDir, prefix + System.nanoTime());

    if (!generatedDir.mkdir()) {
      throw new IOException("Failed to create temp directory " + generatedDir.getName());
    }

    return generatedDir;
  }

  public enum OSType {
    Windows, MacOS, Linux, Other
  }

  protected static OSType detectedOS;

  /**
   * detect the operating system from the os.name System property and cache
   * the result
   *
   * @returns - the operating system detected
   */
  public static OSType getOperatingSystemType() {
    if (detectedOS == null) {
      String osname = System.getProperty("os.name", "generic").toLowerCase(Locale.ENGLISH);
      if ((osname.contains("mac")) || (osname.contains("darwin"))) {
        detectedOS = OSType.MacOS;
      } else if (osname.contains("win")) {
        detectedOS = OSType.Windows;
      } else if (osname.contains("nux")) {
        detectedOS = OSType.Linux;
      } else {
        detectedOS = OSType.Other;
      }
    }
    return detectedOS;
  }
}