feat: add SSH support for remote Docker connections

[dmonroy]

What do these changes do?

This PR adds comprehensive SSH support to aiodocker, enabling secure connections to remote Docker hosts using the ssh:// URL scheme. The implementation includes:

Core Features

• SSH Connector: New SSHConnector class built on asyncssh for secure tunneling
• URL Integration: Seamless integration with existing Docker URL patterns (ssh://user@host:port)
• Configuration Support: Automatic SSH config parsing via paramiko for seamless integration with existing SSH setups
• Security First: Mandatory host key verification with secure defaults

Security Features

• Enforced host key verification (no bypass options in production code)
• Automatic detection and use of ~/.ssh/known_hosts
• SSH config file integration for host-specific settings
• Credential sanitization in error messages
• Environment variable filtering for security
• Secure temporary socket file creation with restricted permissions
• Password clearing from memory after connection

Developer Experience

• Comprehensive documentation with security best practices
• Basic and advanced usage examples
• Helpful error messages with actionable solutions
• Complete test coverage for all functionality

Are there changes in behavior for the user?

New functionality only - no breaking changes:

• New URL scheme: Users can now connect using ssh://user@host:port URLs
• New optional dependency: Install with pip install aiodocker[ssh] for SSH support
• New import: from aiodocker.ssh import SSHConnector for advanced usage
• Existing functionality: All current Docker connection methods remain unchanged

Usage examples:

# Basic SSH connection
async with aiodocker.Docker(url="ssh://ubuntu@docker-host:22") as docker:
    containers = await docker.containers.list()

# Custom SSH connector
from aiodocker.ssh import SSHConnector
connector = SSHConnector("ssh://ubuntu@host:22", client_keys=["~/.ssh/my_key"])
async with aiodocker.Docker(connector=connector) as docker:
    version = await docker.version()

Related issue number

This implements a new feature request for SSH connectivity. No specific issue number - this is a proactive enhancement to support remote Docker management use cases.

Checklist

• I think the code is well written
• Unit tests for the changes exist
• Documentation reflects the changes
• If you provide code modification, please add yourself to CONTRIBUTORS.txt
  • The format is <Name> <Surname>.
  • Please keep alphabetical order, the file is sorted by names.
• Add a new news fragment into the changes folder
  • name it <issue_id>.<type> for example (588.bug)
  • if you don't have an issue_id change it to the pr id after creating the pr
  • ensure type is one of the following:
    • .feature: Signifying a new feature.
    • .bugfix: Signifying a bug fix.
    • .doc: Signifying a documentation improvement.
    • .removal: Signifying a deprecation or removal of public API.
    • .misc: A ticket has been closed, but it is not of interest to users.
  • Make sure to use full sentences with correct case and punctuation, for example: "Fix issue with non-ascii contents in doctest text files."

Implementation Details

Files Added:

• aiodocker/ssh.py - Core SSH connector implementation (300+ lines)
• docs/ssh.rst - Comprehensive SSH documentation
• examples/ssh_example.py - Basic usage example
• examples/ssh_example_advanced.py - Advanced CLI example with comprehensive operations
• tests/test_ssh.py - Complete test suite for SSH functionality

Files Modified:

• aiodocker/docker.py - Added SSH URL scheme support in Docker class constructor
• docs/index.rst - Added SSH documentation to navigation
• pyproject.toml - Added optional SSH dependencies (asyncssh>=2.14.0, paramiko>=2.9.0)
• CONTRIBUTORS.txt - Added Darwin Monroy

Security Considerations:

• Follows security best practices from docker-py
• No environment variable bypasses for security settings
• Comprehensive error handling with security-aware messaging
• Secure defaults with educational warnings for security implications

Testing:

• 9 unit tests covering URL parsing, validation, error conditions
• Manual testing against live remote Docker hosts
• Integration with existing aiodocker test patterns

News Fragment:

• Created changes/982.feature
• Content: "Add comprehensive SSH support for secure connections to remote Docker hosts via ssh:// URLs with mandatory host key verification and complete documentation."

[codecov]

Codecov Report

❌ Patch coverage is 32.67974% with 103 lines in your changes missing coverage. Please review.
✅ Project coverage is 76.82%. Comparing base (ce86470) to head (825e44c).

Files with missing lines	Patch %	Lines
aiodocker/ssh.py	33.33%	98 Missing ⚠️
aiodocker/docker.py	16.66%	5 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #982      +/-   ##
==========================================
- Coverage   81.57%   76.82%   -4.75%     
==========================================
  Files          24       25       +1     
  Lines        1422     1575     +153     
  Branches      190      214      +24     
==========================================
+ Hits         1160     1210      +50     
- Misses        186      289     +103     
  Partials       76       76              

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[Harry-Lees]

My opinion holds no weight in this project. I added some comments below since I also think this feature is useful and would be interested in having something like this in the project.

I tested this on my Macbook SSH'ing into an external Linux device and this worked with no issues, I also tried changing a few options like removing the known_hosts etc and found the logging output helpful for showing issues.

I assume this PR was written assisted by AI, looking over the code, there are a few instances which feel slightly unnatural. IMO some of the error handling that re-raises a bare Exception could be reworked and this PR does a lot of logging compared to the other areas of the library (not necessarily a bad thing).

As I say, my opinion holds no weight in this project and my views may not align with your personal or the coding styles of the rest of the project, but you may find something useful in the comments :).

[Harry-Lees]

Can some of these comments be removed, they're clearly AI written and don't really provide much value, I don't think anybody looking at

if not (1 <= self._ssh_port <= 65535):
    raise ValueError(f"Invalid SSH port: {self._ssh_port}")

would be confused unless they read a comment that says # Validate port range.

There are also a bunch of comments which say things along the lines of ... (like docker-py) which are again pretty clearly left from an AI responding to prompting.

[dmonroy]

While the comment itself is AI assisted, the motivation was not.
Using password in SSH url is supported, but discouraged for security reasons, and documented as is. I thought we could warn users about it when a password in url is detected.

docker-py references, well, this implementation was inspired in docker-py's ssh implementation. Thought it'll justify why these code blocks were there. I'm ok with removing it if it is irrelevant.

[dmonroy]

Re validating port range, I had a second thought motivated by your comment and it is indeed not the responsibility of this library to validate the port. Removed the block.