Implement proxy jump using libssh

Gauravsingh Sisodiarequested to merge
xaerru/libssh-mirror:proxyjump into master

Implement #178 (closed)

Recursively jump jump hosts till the first jump, which is to be made by client.

This has been tested with linux containers locally. Currently the torture_config test is failing because it checks ProxyCommand after doing a proxy jump, we don't set it now.

Need some advice on the following things:

  1. Error handling of the intermediate connection.
  2. Better/Another way of verifying host, instead of using verify_knownhost from examples. I used it for testing.
  3. Cleanly exiting the IO forwarding. And the condition for the loop.

Checklist

  • Commits have Signed-off-by: with name/author being identical to the commit author
  • Code modified for feature
  • Test suite updated with functionality tests
  • Test suite updated with negative tests
  • Documentation updated

Reviewer's checklist:

  • Any issues marked for closing are addressed
  • There is a test suite reasonably covering new functionality or modifications
  • Function naming, parameters, return values, types, etc., are consistent and according to CONTRIBUTING.md
  • This feature/change has adequate documentation added
  • No obvious mistakes in the code

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