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2.9.0.md

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Introduced in 2.9.0

Major code re-factoring

Asynchronous API for making SSH global requests

A new API in Session is introduced for making SSH global requests and handling the reply asynchronously.

public GlobalRequestFuture request(Buffer buffer, String request, ReplyHandler replyHandler) throws IOException;

The Buffer is supposed to contain the full request, including the request name (for instance, "tcpip-forward"), the want-reply flag, and any additional data needed. There are several possible ways to use it.

  • want-reply == true and replyHandler != null: the methods sends the request and returns a future that is fulfilled when the request was actually sent. The future is fulfilled with an exception if sending the request failed, or with null if it was sent successfully. Once the reply is received, the handler is invoked with the SSH command (SSH_MSG_REQUEST_SUCCESS, SSH_MSG_REQUEST_FAILURE, or SSH_MSG_UNIMPLEMENTED) and the buffer received.
  • want-reply == true and replyHandler == null: the method sends the request and returns a future that is fulfilled with an exception if sending it failed, or if a SSH_MSG_REQUEST_FAILURE or SSH_MSG_UNIMPLEMENTED reply was received. Otherwise the future is fulfilled with the received Buffer once the reply has been received.
  • want-reply == false: the method sends the request and returns a future that is fulfilled when the request was actually sent. The future is fulfilled with an exception if sending the request failed, or with an empty buffer if it was sent successfully. If replyHandler != null, it is invoked with an empty buffer once the request was sent.

If the method throws an IOException, the request was not sent, and the handler will not be invoked.

Potential compatibility issues

Changes that may affect existing code

A new SFTP configuration property has been introduced that limits the maximum amount of data that can be sent in a single SSH_FXP_WRITE packet - default=256KB

    /**
     * Force the use of a max. packet length for {@link AbstractSftpSubsystemHelper#doWrite(Buffer, int)} protection
     * against malicious packets
     */
    public static final Property<Integer> MAX_WRITE_DATA_PACKET_LENGTH
            = Property.integer("sftp-max-writedata-packet-length", 256 * 1024);

This might cause SFTP write failures for clients that might have sent larger buffers and they have been accepted so far. If this happens, simply increase this value (though the choice of 256KB should be compatible with the vast majority of clients).

SSH channel identifiers have been changed to use long instead of int in order to align them with the standard that required them to be UINT32 values.

The relevant API(s) have been modified accordingly - which may cause a few incompatibility issues with code that extends/implements existing Channel classes and interfaces. In this context, the Channel interface now extends ChannelIdentifier where getId() has been renamed to getChannelId()

long used instead of int in most encoded/decoded packets that are specified as being UINT32

There are several exceptions to this rule:

  • The SFTP packet id field - an "opaque" value anyway, not used for allocation or indexing anyway

  • Various flags and mask field - there is no reason to encapsulate them into a long value since they do not represent a cardinal number of 32 bits

  • Various status code fields - ditto.

  • Cases where the value serves as argument for allocation of other data structures based on its value - e.g., arrays, lists. This was done for convenience reasons since Java does not support unsigned array/list sizes. In such cases, special validation code was applied to make sure the requested value does not exceed Integer#MAX_VALUE (sometimes even less) in order to protect the code from malicious or malformed packets. It is important to bear in mind that in the vast majority of the cases we do not want to be able to allocate arrays or lists having billions of elements as it would almost definitely cause out-of-memory issues.

User HOME directory resolution and usage have been moved to PathUtils

Was originally in HostConfigEntry.

Behavioral changes and enhancements

  • SSHD-966 Deadlock on disconnection at the end of key-exchange
  • SSHD-1055 Shut down output on port-forwarded socket on EOF in tunnel
  • SSHD-1231 Public key authentication: wrong signature algorithm used (ed25519 key with ssh-rsa signature)
  • SSHD-1233 Added support for "[email protected]" SFTP extension
  • SSHD-1244 Fixed channel window adjustment handling of large UINT32 values
  • SSHD-1244 Re-defined channel identifiers as long rather than int to align with protocol UINT32 definition
  • SSHD-1246 Added SshKeyDumpMain utility
  • SSHD-1247 Added support for Argon2id encrypted PUTTY keys
  • SSHD-1254 Support host-based pubkey authentication in the client ("[email protected]" KEX extension)
  • SSHD-1253 Class loader fails to load org.apache.sshd.common.cipher.BaseGCMCipher
  • SSHD-1256 PortForwardingTest.testRemoteForwardingSecondTimeInSameSession always fails in Github CI
  • SSHD-1257 ChannelSession: don't flush out stream if already closed
  • SSHD-1261 - Sometimes async write listener is not called
  • SSHD-1262 TCP/IP port forwarding: don't buffer, and don't read from port before channel is open
  • SSHD-1264 Create KEX negotiation proposal only once per session, not on every re-KEX
  • SSHD-1266 Fix encoding/decoding critical options in OpenSSH certificates
  • SSHD-1269 Fix TCP/IP remote port forwarding with wildcard addresses
  • SSHD-1272 Use correct signature for RSA keys from SSH agent, and by default ignore keys for which there is no signature algorithm
  • SSHD-1273 Add support to use env vars together with subsystem channels
  • SSHD-1276 Added capability to redirect command/shell STDERR stream to STDOUT one