/*
    * Copyright (C) 2018, 2019 Thomas Wolf <thomas.wolf@paranor.ch> 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.internal.transport.sshd;
  
  import static java.text.MessageFormat.format;
  
  import java.io.IOException;
  import java.net.SocketAddress;
  import java.nio.charset.StandardCharsets;
  import java.security.GeneralSecurityException;
  import java.security.PublicKey;
  import java.util.ArrayList;
  import java.util.Iterator;
  import java.util.LinkedHashSet;
  import java.util.List;
  import java.util.Set;
  
  import org.apache.sshd.client.ClientFactoryManager;
  import org.apache.sshd.client.config.hosts.HostConfigEntry;
  import org.apache.sshd.client.keyverifier.ServerKeyVerifier;
  import org.apache.sshd.client.session.ClientSessionImpl;
  import org.apache.sshd.common.FactoryManager;
  import org.apache.sshd.common.PropertyResolverUtils;
  import org.apache.sshd.common.SshException;
  import org.apache.sshd.common.config.keys.KeyUtils;
  import org.apache.sshd.common.io.IoSession;
  import org.apache.sshd.common.io.IoWriteFuture;
  import org.apache.sshd.common.util.Readable;
  import org.apache.sshd.common.util.buffer.Buffer;
  import org.eclipse.jgit.errors.InvalidPatternException;
  import org.eclipse.jgit.fnmatch.FileNameMatcher;
  import org.eclipse.jgit.internal.transport.sshd.proxy.StatefulProxyConnector;
  import org.eclipse.jgit.transport.CredentialsProvider;
  import org.eclipse.jgit.transport.SshConstants;
  
  /**
   * A {@link org.apache.sshd.client.session.ClientSession ClientSession} that can
   * be associated with the {@link HostConfigEntry} the session was created for.
   * The {@link JGitSshClient} creates such sessions and sets this association.
   * <p>
   * Also provides for associating a JGit {@link CredentialsProvider} with a
   * session.
   * </p>
   */
  public class JGitClientSession extends ClientSessionImpl {
  
  	/**
  	 * Default setting for the maximum number of bytes to read in the initial
  	 * protocol version exchange. 64kb is what OpenSSH < 8.0 read; OpenSSH 8.0
  	 * changed it to 8Mb, but that seems excessive for the purpose stated in RFC
  	 * 4253. The Apache MINA sshd default in
  	 * {@link FactoryManager#DEFAULT_MAX_IDENTIFICATION_SIZE} is 16kb.
  	 */
  	private static final int DEFAULT_MAX_IDENTIFICATION_SIZE = 64 * 1024;
  
  	private HostConfigEntry hostConfig;
  
  	private CredentialsProvider credentialsProvider;
  
  	private volatile StatefulProxyConnector proxyHandler;
  
  	/**
  	 * @param manager
  	 * @param session
  	 * @throws Exception
  	 */
  	public JGitClientSession(ClientFactoryManager manager, IoSession session)
  			throws Exception {
  		super(manager, session);
  	}
  
  	/**
  	 * Retrieves the {@link HostConfigEntry} this session was created for.
  	 *
  	 * @return the {@link HostConfigEntry}, or {@code null} if none set
  	 */
  	public HostConfigEntry getHostConfigEntry() {
  		return hostConfig;
  	}
  
  	/**
  	 * Sets the {@link HostConfigEntry} this session was created for.
  	 *
  	 * @param hostConfig
  	 *            the {@link HostConfigEntry}
  	 */
  	public void setHostConfigEntry(HostConfigEntry hostConfig) {
  		this.hostConfig = hostConfig;
  	}
  
  	/**
  	 * Sets the {@link CredentialsProvider} for this session.
 	 *
 	 * @param provider
 	 *            to set
 	 */
 	public void setCredentialsProvider(CredentialsProvider provider) {
 		credentialsProvider = provider;
 	}
 
 	/**
 	 * Retrieves the {@link CredentialsProvider} set for this session.
 	 *
 	 * @return the provider, or {@code null} if none is set.
 	 */
 	public CredentialsProvider getCredentialsProvider() {
 		return credentialsProvider;
 	}
 
 	/**
 	 * Sets a {@link StatefulProxyConnector} to handle proxy connection
 	 * protocols.
 	 *
 	 * @param handler
 	 *            to set
 	 */
 	public void setProxyHandler(StatefulProxyConnector handler) {
 		proxyHandler = handler;
 	}
 
 	@Override
 	protected IoWriteFuture sendIdentification(String ident)
 			throws IOException {
 		StatefulProxyConnector proxy = proxyHandler;
 		if (proxy != null) {
 			try {
 				// We must not block here; the framework starts reading messages
 				// from the peer only once the initial sendKexInit() following
 				// this call to sendIdentification() has returned!
 				proxy.runWhenDone(() -> {
 					JGitClientSession.super.sendIdentification(ident);
 					return null;
 				});
 				// Called only from the ClientSessionImpl constructor, where the
 				// return value is ignored.
 				return null;
 			} catch (IOException e) {
 				throw e;
 			} catch (Exception other) {
 				throw new IOException(other.getLocalizedMessage(), other);
 			}
 		}
 		return super.sendIdentification(ident);
 	}
 
 	@Override
 	protected byte[] sendKexInit()
 			throws IOException, GeneralSecurityException {
 		StatefulProxyConnector proxy = proxyHandler;
 		if (proxy != null) {
 			try {
 				// We must not block here; the framework starts reading messages
 				// from the peer only once the initial sendKexInit() has
 				// returned!
 				proxy.runWhenDone(() -> {
 					JGitClientSession.super.sendKexInit();
 					return null;
 				});
 				// This is called only from the ClientSessionImpl
 				// constructor, where the return value is ignored.
 				return null;
 			} catch (IOException | GeneralSecurityException e) {
 				throw e;
 			} catch (Exception other) {
 				throw new IOException(other.getLocalizedMessage(), other);
 			}
 		}
 		return super.sendKexInit();
 	}
 
 	/**
 	 * {@inheritDoc}
 	 *
 	 * As long as we're still setting up the proxy connection, diverts messages
 	 * to the {@link StatefulProxyConnector}.
 	 */
 	@Override
 	public void messageReceived(Readable buffer) throws Exception {
 		StatefulProxyConnector proxy = proxyHandler;
 		if (proxy != null) {
 			proxy.messageReceived(getIoSession(), buffer);
 		} else {
 			super.messageReceived(buffer);
 		}
 	}
 
 	@Override
 	protected void checkKeys() throws SshException {
 		ServerKeyVerifier serverKeyVerifier = getServerKeyVerifier();
 		// The super implementation always uses
 		// getIoSession().getRemoteAddress(). In case of a proxy connection,
 		// that would be the address of the proxy!
 		SocketAddress remoteAddress = getConnectAddress();
 		PublicKey serverKey = getKex().getServerKey();
 		if (!serverKeyVerifier.verifyServerKey(this, remoteAddress,
 				serverKey)) {
 			throw new SshException(
 					org.apache.sshd.common.SshConstants.SSH2_DISCONNECT_HOST_KEY_NOT_VERIFIABLE,
 					SshdText.get().kexServerKeyInvalid);
 		}
 	}
 
 	@Override
 	protected String resolveAvailableSignaturesProposal(
 			FactoryManager manager) {
 		Set<String> defaultSignatures = new LinkedHashSet<>();
 		defaultSignatures.addAll(getSignatureFactoriesNames());
 		HostConfigEntry config = resolveAttribute(
 				JGitSshClient.HOST_CONFIG_ENTRY);
 		String hostKeyAlgorithms = config
 				.getProperty(SshConstants.HOST_KEY_ALGORITHMS);
 		if (hostKeyAlgorithms != null && !hostKeyAlgorithms.isEmpty()) {
 			char first = hostKeyAlgorithms.charAt(0);
 			switch (first) {
 			case '+':
 				// Additions make not much sense -- it's either in
 				// defaultSignatures already, or we have no implementation for
 				// it. No point in proposing it.
 				return String.join(",", defaultSignatures); //$NON-NLS-1$
 			case '-':
 				// This takes wildcard patterns!
 				removeFromList(defaultSignatures,
 						SshConstants.HOST_KEY_ALGORITHMS,
 						hostKeyAlgorithms.substring(1));
 				if (defaultSignatures.isEmpty()) {
 					// Too bad: user config error. Warn here, and then fail
 					// later.
 					log.warn(format(
 							SshdText.get().configNoRemainingHostKeyAlgorithms,
 							hostKeyAlgorithms));
 				}
 				return String.join(",", defaultSignatures); //$NON-NLS-1$
 			default:
 				// Default is overridden -- only accept the ones for which we do
 				// have an implementation.
 				List<String> newNames = filteredList(defaultSignatures,
 						hostKeyAlgorithms);
 				if (newNames.isEmpty()) {
 					log.warn(format(
 							SshdText.get().configNoKnownHostKeyAlgorithms,
 							hostKeyAlgorithms));
 					// Use the default instead.
 				} else {
 					return String.join(",", newNames); //$NON-NLS-1$
 				}
 				break;
 			}
 		}
 		// No HostKeyAlgorithms; using default -- change order to put existing
 		// keys first.
 		ServerKeyVerifier verifier = getServerKeyVerifier();
 		if (verifier instanceof ServerKeyLookup) {
 			SocketAddress remoteAddress = resolvePeerAddress(
 					resolveAttribute(JGitSshClient.ORIGINAL_REMOTE_ADDRESS));
 			List<PublicKey> allKnownKeys = ((ServerKeyLookup) verifier)
 					.lookup(this, remoteAddress);
 			Set<String> reordered = new LinkedHashSet<>();
 			for (PublicKey key : allKnownKeys) {
 				if (key != null) {
 					String keyType = KeyUtils.getKeyType(key);
 					if (keyType != null) {
 						reordered.add(keyType);
 					}
 				}
 			}
 			reordered.addAll(defaultSignatures);
 			return String.join(",", reordered); //$NON-NLS-1$
 		}
 		return String.join(",", defaultSignatures); //$NON-NLS-1$
 	}
 
 	private void removeFromList(Set<String> current, String key,
 			String patterns) {
 		for (String toRemove : patterns.split("\\s*,\\s*")) { //$NON-NLS-1$
 			if (toRemove.indexOf('*') < 0 && toRemove.indexOf('?') < 0) {
 				current.remove(toRemove);
 				continue;
 			}
 			try {
 				FileNameMatcher matcher = new FileNameMatcher(toRemove, null);
 				for (Iterator<String> i = current.iterator(); i.hasNext();) {
 					matcher.reset();
 					matcher.append(i.next());
 					if (matcher.isMatch()) {
 						i.remove();
 					}
 				}
 			} catch (InvalidPatternException e) {
 				log.warn(format(SshdText.get().configInvalidPattern, key,
 						toRemove));
 			}
 		}
 	}
 
 	private List<String> filteredList(Set<String> known, String values) {
 		List<String> newNames = new ArrayList<>();
 		for (String newValue : values.split("\\s*,\\s*")) { //$NON-NLS-1$
 			if (known.contains(newValue)) {
 				newNames.add(newValue);
 			}
 		}
 		return newNames;
 	}
 
 	@Override
 	protected boolean readIdentification(Buffer buffer) throws IOException {
 		// Propagate a failure from doReadIdentification.
 		// TODO: remove for sshd > 2.3.0; its doReadIdentification throws
 		// StreamCorruptedException instead of IllegalStateException.
 		try {
 			return super.readIdentification(buffer);
 		} catch (IllegalStateException e) {
 			throw new IOException(e.getLocalizedMessage(), e);
 		}
 	}
 
 	/**
 	 * Reads the RFC 4253, section 4.2 protocol version identification. The
 	 * Apache MINA sshd default implementation checks for NUL bytes also in any
 	 * preceding lines, whereas RFC 4253 requires such a check only for the
 	 * actual identification string starting with "SSH-". Likewise, the 255
 	 * character limit exists only for the identification string, not for the
 	 * preceding lines. CR-LF handling is also relaxed.
 	 *
 	 * @param buffer
 	 *            to read from
 	 * @param server
 	 *            whether we're an SSH server (should always be {@code false})
 	 * @return the lines read, with the server identification line last, or
 	 *         {@code null} if no identification line was found and more bytes
 	 *         are needed
 	 *
 	 * @see <a href="https://tools.ietf.org/html/rfc4253#section-4.2">RFC 4253,
 	 *      section 4.2</a>
 	 */
 	@Override
 	protected List<String> doReadIdentification(Buffer buffer, boolean server) {
 		if (server) {
 			// Should never happen. No translation; internal bug.
 			throw new IllegalStateException(
 					"doReadIdentification of client called with server=true"); //$NON-NLS-1$
 		}
 		int maxIdentSize = PropertyResolverUtils.getIntProperty(this,
 				FactoryManager.MAX_IDENTIFICATION_SIZE,
 				DEFAULT_MAX_IDENTIFICATION_SIZE);
 		int current = buffer.rpos();
 		int end = current + buffer.available();
 		if (current >= end) {
 			return null;
 		}
 		byte[] raw = buffer.array();
 		List<String> ident = new ArrayList<>();
 		int start = current;
 		boolean hasNul = false;
 		for (int i = current; i < end; i++) {
 			switch (raw[i]) {
 			case 0:
 				hasNul = true;
 				break;
 			case '\n':
 				int eol = 1;
 				if (i > start && raw[i - 1] == '\r') {
 					eol++;
 				}
 				String line = new String(raw, start, i + 1 - eol - start,
 						StandardCharsets.UTF_8);
 				start = i + 1;
 				if (log.isDebugEnabled()) {
 					log.debug(format("doReadIdentification({0}) line: ", this) + //$NON-NLS-1$
 							escapeControls(line));
 				}
 				ident.add(line);
 				if (line.startsWith("SSH-")) { //$NON-NLS-1$
 					if (hasNul) {
 						throw new IllegalStateException(
 								format(SshdText.get().serverIdWithNul,
 										escapeControls(line)));
 					}
 					if (line.length() + eol > 255) {
 						throw new IllegalStateException(
 								format(SshdText.get().serverIdTooLong,
 										escapeControls(line)));
 					}
 					buffer.rpos(start);
 					return ident;
 				}
 				// If this were a server, we could throw an exception here: a
 				// client is not supposed to send any extra lines before its
 				// identification string.
 				hasNul = false;
 				break;
 			default:
 				break;
 			}
 			if (i - current + 1 >= maxIdentSize) {
 				String msg = format(SshdText.get().serverIdNotReceived,
 						Integer.toString(maxIdentSize));
 				if (log.isDebugEnabled()) {
 					log.debug(msg);
 					log.debug(buffer.toHex());
 				}
 				throw new IllegalStateException(msg);
 			}
 		}
 		// Need more data
 		return null;
 	}
 
 	private static String escapeControls(String s) {
 		StringBuilder b = new StringBuilder();
 		int l = s.length();
 		for (int i = 0; i < l; i++) {
 			char ch = s.charAt(i);
 			if (Character.isISOControl(ch)) {
 				b.append(ch <= 0xF ? "\\u000" : "\\u00") //$NON-NLS-1$ //$NON-NLS-2$
 						.append(Integer.toHexString(ch));
 			} else {
 				b.append(ch);
 			}
 		}
 		return b.toString();
 	}
 
 }