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Instrumentation of Java libraries using OpenTelemetry.

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/*
 * Copyright The OpenTelemetry Authors
 * SPDX-License-Identifier: Apache-2.0
 */

package io.opentelemetry.javaagent.tooling;

import java.io.ByteArrayInputStream;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStream;
import java.net.URL;
import java.net.URLConnection;
import java.net.URLStreamHandler;
import java.util.jar.JarEntry;
import java.util.jar.JarFile;

class RemappingUrlStreamHandler extends URLStreamHandler {
  private final JarFile delegateJarFile;

  public RemappingUrlStreamHandler(File delegateFile) {
    try {
      delegateJarFile = new JarFile(delegateFile, false);
    } catch (IOException e) {
      throw new IllegalStateException("Unable to read internal jar", e);
    }
  }

  /** {@inheritDoc} */
  @Override
  protected URLConnection openConnection(URL url) throws IOException {
    String file = url.getFile();
    if ("/".equals(file)) {
      // "/" is used as the default url of the jar
      // This is called by the SecureClassLoader trying to obtain permissions
      // nullInputStream() is not available until Java 11
      return new InputStreamUrlConnection(url, new ByteArrayInputStream(new byte[0]), 0);
    }

    if (file.startsWith("/")) {
      file = file.substring(1);
    }
    JarEntry entry = delegateJarFile.getJarEntry(file);
    if (entry == null) {
      throw new FileNotFoundException(
          "JAR entry " + file + " not found in " + delegateJarFile.getName());
    }

    // That will NOT remap the content of files under META-INF/services
    if (file.endsWith(".class")) {
      return new RemappingUrlConnection(url, delegateJarFile, entry);
    } else {
      InputStream is = delegateJarFile.getInputStream(entry);
      return new InputStreamUrlConnection(url, is, entry.getSize());
    }
  }
}