Allow configuring SFTP max packet size

[gbaso]

Expected Behavior

Provide a property on the DefaultSftpSessionFactory that allows to configure the max packet size:

DefaultSftpSessionFactory factory = new DefaultSftpSessionFactory()
factory.setMaxPacketSize(maxPacketSize);

Current Behavior

Max packet size is not configurable via DefaultSftpSessionFactory. It defaults to 32KB according to org.apache.sshd.core.CoreModuleProperties#DEFAULT_MAX_PACKET_SIZE. To change it, you must create your own SshClient and update the property:

SshClient sshClient = SshClient.setUpDefaultClient();
PropertyResolverUtils.updateProperty(sshClient, "packet-size", <value>);

however this prevents the DefaultSftpSessionFactory to initialize the client via doInitInnerClient(), therefore the ServerKeyVerifier, PasswordIdentityProvider, KeyIdentityProvider and UserInteraction must also be configured on the client instead of relying on the cleaner API from the DefaultSftpSessionFactory.

Context

I need to change the max packet size in order to reduce the amount of remote calls for more data in my Sftp.inboundStreamingAdapter integration flow, due to complaints from our SFTP server maintainer. Alternatively, we could reduce the rate at which we read from the remote InputStream, but that would slow down and add complexity to the integration flow

[artembilan]

Well, that's exactly why we have introduced that ctor:

	/**
	 * Instantiate based on the provided {@link SshClient}, e.g. some extension for HTTP/SOCKS.
	 * @param sshClient the {@link SshClient} instance.
	 * @param isSharedSession true if the session is to be shared.
	 */
	public DefaultSftpSessionFactory(SshClient sshClient, boolean isSharedSession) {

So, you can provide any custom SshClient.

However I see you pain for the ServerKeyVerifier, PasswordIdentityProvider, KeyIdentityProvider and UserInteraction.
I think we will go ahead and introduce something like:

setSshClientConfigurer(Consumer<SshClient> sshClientConfigurer)

So, you can continue to use that default internal behavior, but will be able to customize it with required properties or so.
New feature for the current in-progress 6.4 version.
For those previous versions a workaround via mentioned ctor should be enough.

Thanks