Enable .pgpass support for SSH tunnel connections

[DiegoDAF]

Summary

This PR enables PostgreSQL's .pgpass file to work seamlessly with SSH tunnel connections. Previously, when using --ssh-tunnel, the .pgpass file was not consulted because pgcli was connecting to 127.0.0.1 instead of the original database hostname.

Problem

When using SSH tunnels, the connection flow was:

1. User specifies: --ssh-tunnel user@bastion --host production.db.com
2. SSH tunnel created: 127.0.0.1:random_port → production.db.com:5432
3. pgcli connects to: 127.0.0.1:random_port
4. .pgpass lookup fails (looking for 127.0.0.1 instead of production.db.com)

Solution

Use PostgreSQL's host/hostaddr parameter separation:

• host: Original database hostname (for .pgpass lookup and SSL verification)
• hostaddr: Actual connection endpoint 127.0.0.1 (SSH tunnel local port)

Changes

Core Functionality

• Modified connect() to preserve original host and use hostaddr for tunnel
• Updated connect_uri() to pass DSN parameter for proper .pgpass handling
• Modified pgexecute.py to preserve hostaddr when using DSN connections

SSH Tunnel Enhancements

• Added ssh_config_file: Use ~/.ssh/config for host settings
• Added allow_agent: Enable SSH agent for authentication
• Set compression: False: Better performance for database connections

Benefits

✅ .pgpass file now works with SSH tunnels
✅ No manual password entry needed
✅ Standard PostgreSQL authentication flow
✅ SSL certificate verification uses correct hostname
✅ Maintains all existing functionality

Example Usage

# Setup .pgpass file
echo "production.db.example.com:5432:mydb:dbuser:secret_password" >> ~/.pgpass
chmod 600 ~/.pgpass

# Connect via SSH tunnel - password read from .pgpass automatically!
pgcli --ssh-tunnel user@bastion.example.com -h production.db.example.com -d mydb -U dbuser

Technical Details

PostgreSQL supports both host and hostaddr parameters:

• When both are specified, host is used for authentication (.pgpass, Kerberos, SSL CN)
• hostaddr is used for the actual TCP connection
• This is perfect for SSH tunnels where we need different values for each

Compatibility

• Fully backward compatible
• No changes to non-SSH tunnel connections
• Existing SSH tunnel connections continue to work
• New functionality is transparent to users

Made with ❤️ and 🤖 Claude Code

[j-bennet]

This needs test coverage before it can go in.

[DiegoDAF]

Addressed the feedback:

• Simplified preserved_params: Replaced with a direct dict comprehension filtering for dsn, password, and hostaddr — no intermediary variable needed.
• Added test coverage: 4 new tests covering host preservation with SSH tunnels, DSN+hostaddr behavior, no-tunnel baseline, and connect_uri dsn passing.
• Rebased on latest main (a0c2ee4).

[j-bennet]

Looks like there are test failures, take a look @DiegoDAF.