/*
    * Copyright (C) 2008, Shawn O. Pearce <spearce@spearce.org> and others
    *
    * This program and the accompanying materials are made available under the
    * terms of the Eclipse Distribution License v. 1.0 which is available at
    * https://www.eclipse.org/org/documents/edl-v10.php.
    *
    * SPDX-License-Identifier: BSD-3-Clause
    */
  
  package org.eclipse.jgit.transport;
  
  import static java.nio.charset.StandardCharsets.UTF_8;
  
  import java.io.ByteArrayOutputStream;
  import java.io.File;
  import java.io.FileInputStream;
  import java.io.FileNotFoundException;
  import java.io.IOException;
  import java.io.InputStream;
  import java.io.OutputStream;
  import java.net.HttpURLConnection;
  import java.net.Proxy;
  import java.net.ProxySelector;
  import java.net.URL;
  import java.net.URLConnection;
  import java.security.DigestOutputStream;
  import java.security.GeneralSecurityException;
  import java.security.InvalidKeyException;
  import java.security.MessageDigest;
  import java.security.NoSuchAlgorithmException;
  import java.text.MessageFormat;
  import java.text.SimpleDateFormat;
  import java.time.Instant;
  import java.util.ArrayList;
  import java.util.Collections;
  import java.util.Comparator;
  import java.util.Date;
  import java.util.HashSet;
  import java.util.Iterator;
  import java.util.List;
  import java.util.Locale;
  import java.util.Map;
  import java.util.Properties;
  import java.util.Set;
  import java.util.SortedMap;
  import java.util.TimeZone;
  import java.util.TreeMap;
  import java.util.stream.Collectors;
  
  import javax.crypto.Mac;
  import javax.crypto.spec.SecretKeySpec;
  import javax.xml.parsers.ParserConfigurationException;
  import javax.xml.parsers.SAXParserFactory;
  
  import org.eclipse.jgit.internal.JGitText;
  import org.eclipse.jgit.lib.Constants;
  import org.eclipse.jgit.lib.NullProgressMonitor;
  import org.eclipse.jgit.lib.ProgressMonitor;
  import org.eclipse.jgit.util.Base64;
  import org.eclipse.jgit.util.HttpSupport;
  import org.eclipse.jgit.util.StringUtils;
  import org.eclipse.jgit.util.TemporaryBuffer;
  import org.xml.sax.Attributes;
  import org.xml.sax.InputSource;
  import org.xml.sax.SAXException;
  import org.xml.sax.XMLReader;
  import org.xml.sax.helpers.DefaultHandler;
  
  /**
   * A simple HTTP REST client for the Amazon S3 service.
   * <p>
   * This client uses the REST API to communicate with the Amazon S3 servers and
   * read or write content through a bucket that the user has access to. It is a
   * very lightweight implementation of the S3 API and therefore does not have all
   * of the bells and whistles of popular client implementations.
   * <p>
   * Authentication is always performed using the user's AWSAccessKeyId and their
   * private AWSSecretAccessKey.
   * <p>
   * Optional client-side encryption may be enabled if requested. The format is
   * compatible with <a href="http://jets3t.s3.amazonaws.com/index.html">jets3t</a>,
   * a popular Java based Amazon S3 client library. Enabling encryption can hide
   * sensitive data from the operators of the S3 service.
   */
  public class AmazonS3 {
  	private static final Set<String> SIGNED_HEADERS;
  
  	private static final String HMAC = "HmacSHA1"; //$NON-NLS-1$
  
  	private static final String X_AMZ_ACL = "x-amz-acl"; //$NON-NLS-1$
  
  	private static final String X_AMZ_META = "x-amz-meta-"; //$NON-NLS-1$
  
  	static {
  		SIGNED_HEADERS = new HashSet<>();
  		SIGNED_HEADERS.add("content-type"); //$NON-NLS-1$
  		SIGNED_HEADERS.add("content-md5"); //$NON-NLS-1$
  		SIGNED_HEADERS.add("date"); //$NON-NLS-1$
 	}
 
 	private static boolean isSignedHeader(String name) {
 		final String nameLC = StringUtils.toLowerCase(name);
 		return SIGNED_HEADERS.contains(nameLC) || nameLC.startsWith("x-amz-"); //$NON-NLS-1$
 	}
 
 	private static String toCleanString(List<String> list) {
 		final StringBuilder s = new StringBuilder();
 		for (String v : list) {
 			if (s.length() > 0)
 				s.append(',');
 			s.append(v.replaceAll("\n", "").trim()); //$NON-NLS-1$ //$NON-NLS-2$
 		}
 		return s.toString();
 	}
 
 	private static String remove(Map<String, String> m, String k) {
 		final String r = m.remove(k);
 		return r != null ? r : ""; //$NON-NLS-1$
 	}
 
 	private static String httpNow() {
 		final String tz = "GMT"; //$NON-NLS-1$
 		final SimpleDateFormat fmt;
 		fmt = new SimpleDateFormat("EEE, dd MMM yyyy HH:mm:ss", Locale.US); //$NON-NLS-1$
 		fmt.setTimeZone(TimeZone.getTimeZone(tz));
 		return fmt.format(new Date()) + " " + tz; //$NON-NLS-1$
 	}
 
 	private static MessageDigest newMD5() {
 		try {
 			return MessageDigest.getInstance("MD5"); //$NON-NLS-1$
 		} catch (NoSuchAlgorithmException e) {
 			throw new RuntimeException(JGitText.get().JRELacksMD5Implementation, e);
 		}
 	}
 
 	/** AWSAccessKeyId, public string that identifies the user's account. */
 	private final String publicKey;
 
 	/** Decoded form of the private AWSSecretAccessKey, to sign requests. */
 	private final SecretKeySpec privateKey;
 
 	/** Our HTTP proxy support, in case we are behind a firewall. */
 	private final ProxySelector proxySelector;
 
 	/** ACL to apply to created objects. */
 	private final String acl;
 
 	/** Maximum number of times to try an operation. */
 	final int maxAttempts;
 
 	/** Encryption algorithm, may be a null instance that provides pass-through. */
 	private final WalkEncryption encryption;
 
 	/** Directory for locally buffered content. */
 	private final File tmpDir;
 
 	/** S3 Bucket Domain. */
 	private final String domain;
 
 	/** Property names used in amazon connection configuration file. */
 	interface Keys {
 		String ACCESS_KEY = "accesskey"; //$NON-NLS-1$
 		String SECRET_KEY = "secretkey"; //$NON-NLS-1$
 		String PASSWORD = "password"; //$NON-NLS-1$
 		String CRYPTO_ALG = "crypto.algorithm"; //$NON-NLS-1$
 		String CRYPTO_VER = "crypto.version"; //$NON-NLS-1$
 		String ACL = "acl"; //$NON-NLS-1$
 		String DOMAIN = "domain"; //$NON-NLS-1$
 		String HTTP_RETRY = "httpclient.retry-max"; //$NON-NLS-1$
 		String TMP_DIR = "tmpdir"; //$NON-NLS-1$
 	}
 
 	/**
 	 * Create a new S3 client for the supplied user information.
 	 * <p>
 	 * The connection properties are a subset of those supported by the popular
 	 * <a href="http://jets3t.s3.amazonaws.com/index.html">jets3t</a> library.
 	 * For example:
 	 *
 	 * <pre>
 	 * # AWS Access and Secret Keys (required)
 	 * accesskey: &lt;YourAWSAccessKey&gt;
 	 * secretkey: &lt;YourAWSSecretKey&gt;
 	 *
 	 * # Access Control List setting to apply to uploads, must be one of:
 	 * # PRIVATE, PUBLIC_READ (defaults to PRIVATE).
 	 * acl: PRIVATE
 	 *
 	 * # S3 Domain
 	 * # AWS S3 Region Domain (defaults to s3.amazonaws.com)
 	 * domain: s3.amazonaws.com
 	 *
 	 * # Number of times to retry after internal error from S3.
 	 * httpclient.retry-max: 3
 	 *
 	 * # End-to-end encryption (hides content from S3 owners)
 	 * password: &lt;encryption pass-phrase&gt;
 	 * crypto.algorithm: PBEWithMD5AndDES
 	 * </pre>
 	 *
 	 * @param props
 	 *            connection properties.
 	 */
 	public AmazonS3(final Properties props) {
 		domain = props.getProperty(Keys.DOMAIN, "s3.amazonaws.com"); //$NON-NLS-1$
 
 		publicKey = props.getProperty(Keys.ACCESS_KEY);
 		if (publicKey == null)
 			throw new IllegalArgumentException(JGitText.get().missingAccesskey);
 
 		final String secret = props.getProperty(Keys.SECRET_KEY);
 		if (secret == null)
 			throw new IllegalArgumentException(JGitText.get().missingSecretkey);
 		privateKey = new SecretKeySpec(Constants.encodeASCII(secret), HMAC);
 
 		final String pacl = props.getProperty(Keys.ACL, "PRIVATE"); //$NON-NLS-1$
 		if (StringUtils.equalsIgnoreCase("PRIVATE", pacl)) //$NON-NLS-1$
 			acl = "private"; //$NON-NLS-1$
 		else if (StringUtils.equalsIgnoreCase("PUBLIC", pacl)) //$NON-NLS-1$
 			acl = "public-read"; //$NON-NLS-1$
 		else if (StringUtils.equalsIgnoreCase("PUBLIC-READ", pacl)) //$NON-NLS-1$
 			acl = "public-read"; //$NON-NLS-1$
 		else if (StringUtils.equalsIgnoreCase("PUBLIC_READ", pacl)) //$NON-NLS-1$
 			acl = "public-read"; //$NON-NLS-1$
 		else
 			throw new IllegalArgumentException("Invalid acl: " + pacl); //$NON-NLS-1$
 
 		try {
 			encryption = WalkEncryption.instance(props);
 		} catch (GeneralSecurityException e) {
 			throw new IllegalArgumentException(JGitText.get().invalidEncryption, e);
 		}
 
 		maxAttempts = Integer
 				.parseInt(props.getProperty(Keys.HTTP_RETRY, "3")); //$NON-NLS-1$
 		proxySelector = ProxySelector.getDefault();
 
 		String tmp = props.getProperty(Keys.TMP_DIR);
 		tmpDir = tmp != null && tmp.length() > 0 ? new File(tmp) : null;
 	}
 
 	/**
 	 * Get the content of a bucket object.
 	 *
 	 * @param bucket
 	 *            name of the bucket storing the object.
 	 * @param key
 	 *            key of the object within its bucket.
 	 * @return connection to stream the content of the object. The request
 	 *         properties of the connection may not be modified by the caller as
 	 *         the request parameters have already been signed.
 	 * @throws java.io.IOException
 	 *             sending the request was not possible.
 	 */
 	public URLConnection get(String bucket, String key)
 			throws IOException {
 		for (int curAttempt = 0; curAttempt < maxAttempts; curAttempt++) {
 			final HttpURLConnection c = open("GET", bucket, key); //$NON-NLS-1$
 			authorize(c);
 			switch (HttpSupport.response(c)) {
 			case HttpURLConnection.HTTP_OK:
 				encryption.validate(c, X_AMZ_META);
 				return c;
 			case HttpURLConnection.HTTP_NOT_FOUND:
 				throw new FileNotFoundException(key);
 			case HttpURLConnection.HTTP_INTERNAL_ERROR:
 				continue;
 			default:
 				throw error(JGitText.get().s3ActionReading, key, c);
 			}
 		}
 		throw maxAttempts(JGitText.get().s3ActionReading, key);
 	}
 
 	/**
 	 * Decrypt an input stream from {@link #get(String, String)}.
 	 *
 	 * @param u
 	 *            connection previously created by {@link #get(String, String)}}.
 	 * @return stream to read plain text from.
 	 * @throws java.io.IOException
 	 *             decryption could not be configured.
 	 */
 	public InputStream decrypt(URLConnection u) throws IOException {
 		return encryption.decrypt(u.getInputStream());
 	}
 
 	/**
 	 * List the names of keys available within a bucket.
 	 * <p>
 	 * This method is primarily meant for obtaining a "recursive directory
 	 * listing" rooted under the specified bucket and prefix location.
 	 * It returns the keys sorted in reverse order of LastModified time
 	 * (freshest keys first).
 	 *
 	 * @param bucket
 	 *            name of the bucket whose objects should be listed.
 	 * @param prefix
 	 *            common prefix to filter the results by. Must not be null.
 	 *            Supplying the empty string will list all keys in the bucket.
 	 *            Supplying a non-empty string will act as though a trailing '/'
 	 *            appears in prefix, even if it does not.
 	 * @return list of keys starting with <code>prefix</code>, after removing
 	 *         <code>prefix</code> (or <code>prefix + "/"</code>)from all
 	 *         of them.
 	 * @throws java.io.IOException
 	 *             sending the request was not possible, or the response XML
 	 *             document could not be parsed properly.
 	 */
 	public List<String> list(String bucket, String prefix)
 			throws IOException {
 		if (prefix.length() > 0 && !prefix.endsWith("/")) //$NON-NLS-1$
 			prefix += "/"; //$NON-NLS-1$
 		final ListParser lp = new ListParser(bucket, prefix);
 		do {
 			lp.list();
 		} while (lp.truncated);
 
 		Comparator<KeyInfo> comparator = Comparator.comparingLong(KeyInfo::getLastModifiedSecs);
 		return lp.entries.stream().sorted(comparator.reversed())
 			.map(KeyInfo::getName).collect(Collectors.toList());
 	}
 
 	/**
 	 * Delete a single object.
 	 * <p>
 	 * Deletion always succeeds, even if the object does not exist.
 	 *
 	 * @param bucket
 	 *            name of the bucket storing the object.
 	 * @param key
 	 *            key of the object within its bucket.
 	 * @throws java.io.IOException
 	 *             deletion failed due to communications error.
 	 */
 	public void delete(String bucket, String key)
 			throws IOException {
 		for (int curAttempt = 0; curAttempt < maxAttempts; curAttempt++) {
 			final HttpURLConnection c = open("DELETE", bucket, key); //$NON-NLS-1$
 			authorize(c);
 			switch (HttpSupport.response(c)) {
 			case HttpURLConnection.HTTP_NO_CONTENT:
 				return;
 			case HttpURLConnection.HTTP_INTERNAL_ERROR:
 				continue;
 			default:
 				throw error(JGitText.get().s3ActionDeletion, key, c);
 			}
 		}
 		throw maxAttempts(JGitText.get().s3ActionDeletion, key);
 	}
 
 	/**
 	 * Atomically create or replace a single small object.
 	 * <p>
 	 * This form is only suitable for smaller contents, where the caller can
 	 * reasonable fit the entire thing into memory.
 	 * <p>
 	 * End-to-end data integrity is assured by internally computing the MD5
 	 * checksum of the supplied data and transmitting the checksum along with
 	 * the data itself.
 	 *
 	 * @param bucket
 	 *            name of the bucket storing the object.
 	 * @param key
 	 *            key of the object within its bucket.
 	 * @param data
 	 *            new data content for the object. Must not be null. Zero length
 	 *            array will create a zero length object.
 	 * @throws java.io.IOException
 	 *             creation/updating failed due to communications error.
 	 */
 	public void put(String bucket, String key, byte[] data)
 			throws IOException {
 		if (encryption != WalkEncryption.NONE) {
 			// We have to copy to produce the cipher text anyway so use
 			// the large object code path as it supports that behavior.
 			//
 			try (OutputStream os = beginPut(bucket, key, null, null)) {
 				os.write(data);
 			}
 			return;
 		}
 
 		final String md5str = Base64.encodeBytes(newMD5().digest(data));
 		final String lenstr = String.valueOf(data.length);
 		for (int curAttempt = 0; curAttempt < maxAttempts; curAttempt++) {
 			final HttpURLConnection c = open("PUT", bucket, key); //$NON-NLS-1$
 			c.setRequestProperty("Content-Length", lenstr); //$NON-NLS-1$
 			c.setRequestProperty("Content-MD5", md5str); //$NON-NLS-1$
 			c.setRequestProperty(X_AMZ_ACL, acl);
 			authorize(c);
 			c.setDoOutput(true);
 			c.setFixedLengthStreamingMode(data.length);
 			try (OutputStream os = c.getOutputStream()) {
 				os.write(data);
 			}
 
 			switch (HttpSupport.response(c)) {
 			case HttpURLConnection.HTTP_OK:
 				return;
 			case HttpURLConnection.HTTP_INTERNAL_ERROR:
 				continue;
 			default:
 				throw error(JGitText.get().s3ActionWriting, key, c);
 			}
 		}
 		throw maxAttempts(JGitText.get().s3ActionWriting, key);
 	}
 
 	/**
 	 * Atomically create or replace a single large object.
 	 * <p>
 	 * Initially the returned output stream buffers data into memory, but if the
 	 * total number of written bytes starts to exceed an internal limit the data
 	 * is spooled to a temporary file on the local drive.
 	 * <p>
 	 * Network transmission is attempted only when <code>close()</code> gets
 	 * called at the end of output. Closing the returned stream can therefore
 	 * take significant time, especially if the written content is very large.
 	 * <p>
 	 * End-to-end data integrity is assured by internally computing the MD5
 	 * checksum of the supplied data and transmitting the checksum along with
 	 * the data itself.
 	 *
 	 * @param bucket
 	 *            name of the bucket storing the object.
 	 * @param key
 	 *            key of the object within its bucket.
 	 * @param monitor
 	 *            (optional) progress monitor to post upload completion to
 	 *            during the stream's close method.
 	 * @param monitorTask
 	 *            (optional) task name to display during the close method.
 	 * @return a stream which accepts the new data, and transmits once closed.
 	 * @throws java.io.IOException
 	 *             if encryption was enabled it could not be configured.
 	 */
 	public OutputStream beginPut(final String bucket, final String key,
 			final ProgressMonitor monitor, final String monitorTask)
 			throws IOException {
 		final MessageDigest md5 = newMD5();
 		final TemporaryBuffer buffer = new TemporaryBuffer.LocalFile(tmpDir) {
 			@Override
 			public void close() throws IOException {
 				super.close();
 				try {
 					putImpl(bucket, key, md5.digest(), this, monitor,
 							monitorTask);
 				} finally {
 					destroy();
 				}
 			}
 		};
 		return encryption.encrypt(new DigestOutputStream(buffer, md5));
 	}
 
 	void putImpl(final String bucket, final String key,
 			final byte[] csum, final TemporaryBuffer buf,
 			ProgressMonitor monitor, String monitorTask) throws IOException {
 		if (monitor == null)
 			monitor = NullProgressMonitor.INSTANCE;
 		if (monitorTask == null)
 			monitorTask = MessageFormat.format(JGitText.get().progressMonUploading, key);
 
 		final String md5str = Base64.encodeBytes(csum);
 		final long len = buf.length();
 		for (int curAttempt = 0; curAttempt < maxAttempts; curAttempt++) {
 			final HttpURLConnection c = open("PUT", bucket, key); //$NON-NLS-1$
 			c.setFixedLengthStreamingMode(len);
 			c.setRequestProperty("Content-MD5", md5str); //$NON-NLS-1$
 			c.setRequestProperty(X_AMZ_ACL, acl);
 			encryption.request(c, X_AMZ_META);
 			authorize(c);
 			c.setDoOutput(true);
 			monitor.beginTask(monitorTask, (int) (len / 1024));
 			try (OutputStream os = c.getOutputStream()) {
 				buf.writeTo(os, monitor);
 			} finally {
 				monitor.endTask();
 			}
 
 			switch (HttpSupport.response(c)) {
 			case HttpURLConnection.HTTP_OK:
 				return;
 			case HttpURLConnection.HTTP_INTERNAL_ERROR:
 				continue;
 			default:
 				throw error(JGitText.get().s3ActionWriting, key, c);
 			}
 		}
 		throw maxAttempts(JGitText.get().s3ActionWriting, key);
 	}
 
 	IOException error(final String action, final String key,
 			final HttpURLConnection c) throws IOException {
 		final IOException err = new IOException(MessageFormat.format(
 				JGitText.get().amazonS3ActionFailed, action, key,
 				Integer.valueOf(HttpSupport.response(c)),
 				c.getResponseMessage()));
 		if (c.getErrorStream() == null) {
 			return err;
 		}
 
 		try (InputStream errorStream = c.getErrorStream()) {
 			final ByteArrayOutputStream b = new ByteArrayOutputStream();
 			byte[] buf = new byte[2048];
 			for (;;) {
 				final int n = errorStream.read(buf);
 				if (n < 0) {
 					break;
 				}
 				if (n > 0) {
 					b.write(buf, 0, n);
 				}
 			}
 			buf = b.toByteArray();
 			if (buf.length > 0) {
 				err.initCause(new IOException("\n" + new String(buf, UTF_8))); //$NON-NLS-1$
 			}
 		}
 		return err;
 	}
 
 	IOException maxAttempts(String action, String key) {
 		return new IOException(MessageFormat.format(
 				JGitText.get().amazonS3ActionFailedGivingUp, action, key,
 				Integer.valueOf(maxAttempts)));
 	}
 
 	private HttpURLConnection open(final String method, final String bucket,
 			final String key) throws IOException {
 		final Map<String, String> noArgs = Collections.emptyMap();
 		return open(method, bucket, key, noArgs);
 	}
 
 	HttpURLConnection open(final String method, final String bucket,
 			final String key, final Map<String, String> args)
 			throws IOException {
 		final StringBuilder urlstr = new StringBuilder();
 		urlstr.append("http://"); //$NON-NLS-1$
 		urlstr.append(bucket);
 		urlstr.append('.');
 		urlstr.append(domain);
 		urlstr.append('/');
 		if (key.length() > 0)
 			HttpSupport.encode(urlstr, key);
 		if (!args.isEmpty()) {
 			final Iterator<Map.Entry<String, String>> i;
 
 			urlstr.append('?');
 			i = args.entrySet().iterator();
 			while (i.hasNext()) {
 				final Map.Entry<String, String> e = i.next();
 				urlstr.append(e.getKey());
 				urlstr.append('=');
 				HttpSupport.encode(urlstr, e.getValue());
 				if (i.hasNext())
 					urlstr.append('&');
 			}
 		}
 
 		final URL url = new URL(urlstr.toString());
 		final Proxy proxy = HttpSupport.proxyFor(proxySelector, url);
 		final HttpURLConnection c;
 
 		c = (HttpURLConnection) url.openConnection(proxy);
 		c.setRequestMethod(method);
 		c.setRequestProperty("User-Agent", "jgit/1.0"); //$NON-NLS-1$ //$NON-NLS-2$
 		c.setRequestProperty("Date", httpNow()); //$NON-NLS-1$
 		return c;
 	}
 
 	void authorize(HttpURLConnection c) throws IOException {
 		final Map<String, List<String>> reqHdr = c.getRequestProperties();
 		final SortedMap<String, String> sigHdr = new TreeMap<>();
 		for (Map.Entry<String, List<String>> entry : reqHdr.entrySet()) {
 			final String hdr = entry.getKey();
 			if (isSignedHeader(hdr))
 				sigHdr.put(StringUtils.toLowerCase(hdr), toCleanString(entry.getValue()));
 		}
 
 		final StringBuilder s = new StringBuilder();
 		s.append(c.getRequestMethod());
 		s.append('\n');
 
 		s.append(remove(sigHdr, "content-md5")); //$NON-NLS-1$
 		s.append('\n');
 
 		s.append(remove(sigHdr, "content-type")); //$NON-NLS-1$
 		s.append('\n');
 
 		s.append(remove(sigHdr, "date")); //$NON-NLS-1$
 		s.append('\n');
 
 		for (Map.Entry<String, String> e : sigHdr.entrySet()) {
 			s.append(e.getKey());
 			s.append(':');
 			s.append(e.getValue());
 			s.append('\n');
 		}
 
 		final String host = c.getURL().getHost();
 		s.append('/');
 		s.append(host.substring(0, host.length() - domain.length() - 1));
 		s.append(c.getURL().getPath());
 
 		final String sec;
 		try {
 			final Mac m = Mac.getInstance(HMAC);
 			m.init(privateKey);
 			sec = Base64.encodeBytes(m.doFinal(s.toString().getBytes(UTF_8)));
 		} catch (NoSuchAlgorithmException e) {
 			throw new IOException(MessageFormat.format(JGitText.get().noHMACsupport, HMAC, e.getMessage()));
 		} catch (InvalidKeyException e) {
 			throw new IOException(MessageFormat.format(JGitText.get().invalidKey, e.getMessage()));
 		}
 		c.setRequestProperty("Authorization", "AWS " + publicKey + ":" + sec); //$NON-NLS-1$ //$NON-NLS-2$ //$NON-NLS-3$
 	}
 
 	static Properties properties(File authFile)
 			throws FileNotFoundException, IOException {
 		final Properties p = new Properties();
 		try (FileInputStream in = new FileInputStream(authFile)) {
 			p.load(in);
 		}
 		return p;
 	}
 
 	/**
 	 * KeyInfo enables sorting of keys by lastModified time
 	 */
 	private static final class KeyInfo {
 		private final String name;
 		private final long lastModifiedSecs;
 		public KeyInfo(String aname, long lsecs) {
 			name = aname;
 			lastModifiedSecs = lsecs;
 		}
 		public String getName() {
 			return name;
 		}
 		public long getLastModifiedSecs() {
 			return lastModifiedSecs;
 		}
 	}
 
 	private final class ListParser extends DefaultHandler {
 		final List<KeyInfo> entries = new ArrayList<>();
 
 		private final String bucket;
 
 		private final String prefix;
 
 		boolean truncated;
 
 		private StringBuilder data;
 		private String keyName;
 		private Instant keyLastModified;
 
 		ListParser(String bn, String p) {
 			bucket = bn;
 			prefix = p;
 		}
 
 		void list() throws IOException {
 			final Map<String, String> args = new TreeMap<>();
 			if (prefix.length() > 0)
 				args.put("prefix", prefix); //$NON-NLS-1$
 			if (!entries.isEmpty())
 				args.put("marker", prefix + entries.get(entries.size() - 1).getName()); //$NON-NLS-1$
 
 			for (int curAttempt = 0; curAttempt < maxAttempts; curAttempt++) {
 				final HttpURLConnection c = open("GET", bucket, "", args); //$NON-NLS-1$ //$NON-NLS-2$
 				authorize(c);
 				switch (HttpSupport.response(c)) {
 				case HttpURLConnection.HTTP_OK:
 					truncated = false;
 					data = null;
 					keyName = null;
 					keyLastModified = null;
 
 					final XMLReader xr;
 					try {
 						xr = SAXParserFactory.newInstance().newSAXParser()
 								.getXMLReader();
 					} catch (SAXException | ParserConfigurationException e) {
 						throw new IOException(
 								JGitText.get().noXMLParserAvailable, e);
 					}
 					xr.setContentHandler(this);
 					try (InputStream in = c.getInputStream()) {
 						xr.parse(new InputSource(in));
 					} catch (SAXException parsingError) {
 						throw new IOException(
 								MessageFormat.format(
 										JGitText.get().errorListing, prefix),
 								parsingError);
 					}
 					return;
 
 				case HttpURLConnection.HTTP_INTERNAL_ERROR:
 					continue;
 
 				default:
 					throw AmazonS3.this.error("Listing", prefix, c); //$NON-NLS-1$
 				}
 			}
 			throw maxAttempts("Listing", prefix); //$NON-NLS-1$
 		}
 
 		@Override
 		public void startElement(final String uri, final String name,
 				final String qName, final Attributes attributes)
 				throws SAXException {
 			if ("Key".equals(name) || "IsTruncated".equals(name) || "LastModified".equals(name)) { //$NON-NLS-1$ //$NON-NLS-2$ //$NON-NLS-3$
 				data = new StringBuilder();
 			}
 			if ("Contents".equals(name)) { //$NON-NLS-1$
 				keyName = null;
 				keyLastModified = null;
 			}
 		}
 
 		@Override
 		public void ignorableWhitespace(final char[] ch, final int s,
 				final int n) throws SAXException {
 			if (data != null)
 				data.append(ch, s, n);
 		}
 
 		@Override
 		public void characters(char[] ch, int s, int n)
 				throws SAXException {
 			if (data != null)
 				data.append(ch, s, n);
 		}
 
 		@Override
 		public void endElement(final String uri, final String name,
 				final String qName) throws SAXException {
 			if ("Key".equals(name))  { //$NON-NLS-1$
 				keyName = data.toString().substring(prefix.length());
 			} else if ("IsTruncated".equals(name)) { //$NON-NLS-1$
 				truncated = StringUtils.equalsIgnoreCase("true", data.toString()); //$NON-NLS-1$
 			} else if ("LastModified".equals(name)) { //$NON-NLS-1$
 				keyLastModified = Instant.parse(data.toString());
 			} else if ("Contents".equals(name)) { //$NON-NLS-1$
 				entries.add(new KeyInfo(keyName, keyLastModified.getEpochSecond()));
 			}
 
 			data = null;
 		}
 	}
 }