feat: add connect timeout option for remote connections

[fmyAgi7]

No description provided.

[gemini-code-assist]

Summary of Changes

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This pull request enhances the client's connection handling by introducing a configurable timeout for remote connection attempts. This feature prevents the client from indefinitely waiting for unresponsive hosts, improving reliability and user experience. The changes involve modifying core networking functions to track connection start times and enforce the specified timeout, along with exposing this option through the client's configuration.

Highlights

• New Connect Timeout Option: Introduced a new connect_timeout option for remote connections, allowing users to specify a maximum duration for connection attempts.
• Configurable via Extended Option: The ConnectTimeout can now be configured as an extended option, providing flexibility for users to set this value.
• Connection Function Signature Update: The connect_remote function's signature has been updated to accept a timeout parameter, integrating the new timeout functionality into the connection process.
• Timeout Management in netio.c: Added connect_start and timeout fields to the dropbear_progress_connection struct and implemented logic in set_connect_fds to monitor and enforce these timeouts for pending connections.
• Dynamic Select Timeout Adjustment: A new function update_connect_timeout was added to dynamically adjust the select() system call's timeout based on the remaining time for pending connection attempts.

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[gemini-code-assist]

Code Review

This pull request introduces a connection timeout option for remote connections, which is a valuable addition. The implementation is solid, correctly integrating with the existing event loop by adjusting the select() timeout for pending connections. The changes are well-contained and logical. I've found one potential issue regarding integer overflow when parsing the timeout value, which could lead to unexpected behavior. My specific comment addresses this.

[gemini-code-assist]

The ConnectTimeout value is parsed into an unsigned int val, but then assigned to cli_opts.connect_timeout which is a signed int. If a user provides a value larger than INT_MAX, this could wrap around and become a negative number, causing the timeout to be silently ignored due to the timeout > 0 checks. It's important to validate that the parsed value fits within a signed int.

                if (m_str_to_uint(optstr, &val) == DROPBEAR_FAILURE || val > INT_MAX) {
                        dropbear_exit("Bad ConnectTimeout '%s'", optstr);
                }