DNS Channel Management

class Channel:
    def __init__(
        self,
        flags=None,                          # Optional[int]: Channel behavior flags
        timeout=None,                        # Optional[float]: Query timeout in seconds
        tries=None,                         # Optional[int]: Number of query attempts
        ndots=None,                         # Optional[int]: Number of dots for domain search
        tcp_port=None,                      # Optional[int]: TCP port for DNS queries
        udp_port=None,                      # Optional[int]: UDP port for DNS queries
        servers=None,                       # Optional[Iterable[Union[str, bytes]]]: DNS servers list
        domains=None,                       # Optional[Iterable[Union[str, bytes]]]: Search domains
        lookups=None,                       # Union[str, bytes, None]: Lookup order
        sock_state_cb=None,                 # Optional[Callable[[int, bool, bool], None]]: Socket state callback
        socket_send_buffer_size=None,       # Optional[int]: Send buffer size
        socket_receive_buffer_size=None,    # Optional[int]: Receive buffer size
        rotate=False,                       # bool: Rotate server list
        local_ip=None,                      # Union[str, bytes, None]: Local IP binding
        local_dev=None,                     # Optional[str]: Local device binding
        resolvconf_path=None,               # Union[str, bytes, None]: Custom resolv.conf path
        event_thread=False                  # bool: Use event thread mode
    ):
        """
        Create a new DNS resolution channel.
        
        Args:
            flags: Bitwise OR of ARES_FLAG_* constants for channel behavior
            timeout: Query timeout in seconds (default uses system settings)
            tries: Number of times to try each query (default: 4)
            ndots: Number of dots needed in name for initial absolute query
            tcp_port: TCP port number for DNS queries (default: 53)
            udp_port: UDP port number for DNS queries (default: 53)
            servers: List of DNS server IP addresses as strings
            domains: List of search domains for unqualified names
            lookups: String specifying lookup order (e.g., "bf" for bind then file)
            sock_state_cb: Callback for socket state changes (fd, readable, writable)
            socket_send_buffer_size: SO_SNDBUF socket option value
            socket_receive_buffer_size: SO_RCVBUF socket option value
            rotate: Whether to rotate through servers for load balancing
            local_ip: Local IP address to bind outgoing queries to
            local_dev: Local network device to bind to
            resolvconf_path: Path to custom resolv.conf file
            event_thread: Enable built-in event thread (requires thread-safe c-ares)
        
        Raises:
            AresError: If channel initialization fails
            RuntimeError: If event_thread=True but c-ares not thread-safe
        """

import pycares

# Basic channel with custom servers
channel = pycares.Channel(
    servers=['8.8.8.8', '8.8.4.4'],
    timeout=5.0,
    tries=2
)

# Advanced channel configuration
channel = pycares.Channel(
    flags=pycares.ARES_FLAG_USEVC | pycares.ARES_FLAG_IGNTC,
    servers=['1.1.1.1', '1.0.0.1'],
    domains=['example.com', 'test.org'],
    timeout=3.0,
    tries=3,
    rotate=True
)

def getsock(self):
    """
    Get socket file descriptors for I/O monitoring.
    
    Returns:
        tuple[list[int], list[int]]: (read_fds, write_fds) - Lists of socket 
        file descriptors ready for reading and writing
    """

def process_fd(self, read_fd: int, write_fd: int) -> None:
    """
    Process I/O events on specific file descriptors.
    
    Args:
        read_fd: File descriptor ready for reading (or ARES_SOCKET_BAD if none)
        write_fd: File descriptor ready for writing (or ARES_SOCKET_BAD if none)
    """

def process_read_fd(self, read_fd: int) -> None:
    """
    Process read events on a file descriptor.
    
    Args:
        read_fd: File descriptor ready for reading
    """

def process_write_fd(self, write_fd: int) -> None:
    """
    Process write events on a file descriptor.
    
    Args:
        write_fd: File descriptor ready for writing
    """

def timeout(self, t=None):
    """
    Get or set timeout for next I/O operation.
    
    Args:
        t: Optional[float] - Maximum timeout in seconds, or None for no limit
        
    Returns:
        float: Actual timeout value for next operation in seconds
        
    Raises:
        ValueError: If timeout is negative
    """

import select
import pycares

def wait_channel(channel):
    """Process all pending DNS operations until completion."""
    while True:
        read_fds, write_fds = channel.getsock()
        if not read_fds and not write_fds:
            break
            
        timeout = channel.timeout()
        if timeout == 0.0:
            # No timeout needed, process immediately
            channel.process_fd(pycares.ARES_SOCKET_BAD, pycares.ARES_SOCKET_BAD)
            continue
            
        # Wait for I/O events
        rlist, wlist, xlist = select.select(read_fds, write_fds, [], timeout)
        
        # Process ready file descriptors
        for fd in rlist:
            channel.process_read_fd(fd)
        for fd in wlist:
            channel.process_write_fd(fd)

@property
def servers(self) -> list[str]:
    """
    Get the current list of DNS servers.
    
    Returns:
        list[str]: List of DNS server IP addresses
        
    Raises:
        AresError: If unable to retrieve server list
    """

@servers.setter
def servers(self, servers) -> None:
    """
    Set the list of DNS servers for the channel.
    
    Args:
        servers: Iterable[Union[str, bytes]] - IP addresses of DNS servers
        
    Raises:
        ValueError: If any IP address is invalid
        AresError: If unable to set servers
    """

channel = pycares.Channel()

# Get current servers
current_servers = channel.servers
print(f"Current servers: {current_servers}")

# Set new servers
channel.servers = ['8.8.8.8', '8.8.4.4', '1.1.1.1']

# Add IPv6 servers
channel.servers = ['2001:4860:4860::8888', '2001:4860:4860::8844']

def cancel(self) -> None:
    """
    Cancel all pending queries on this channel.
    
    All pending query callbacks will be called with ARES_ECANCELLED error.
    """

def reinit(self) -> None:
    """
    Reinitialize the channel with current system DNS configuration.
    
    Rereads system DNS settings (resolv.conf, registry, etc.) and applies
    them to the channel.
    
    Raises:
        AresError: If reinitialization fails
    """

def close(self) -> None:
    """
    Close the channel and clean up resources.
    
    This method schedules safe channel destruction in a background thread.
    Once called, no new queries can be started. Pending queries will be
    cancelled and their callbacks will receive ARES_ECANCELLED.
    
    This method is thread-safe and can be called multiple times.
    """

def set_local_ip(self, ip) -> None:
    """
    Set the local IP address to bind outgoing queries to.
    
    Args:
        ip: Union[str, bytes] - IPv4 or IPv6 address to bind to
        
    Raises:
        ValueError: If IP address is invalid
    """

def set_local_dev(self, dev) -> None:
    """
    Set the local network device to bind outgoing queries to.
    
    Args:
        dev: str - Network device name (e.g., 'eth0', 'wlan0')
    """

channel = pycares.Channel()

# Bind to specific IP address
channel.set_local_ip('192.168.1.100')

# Bind to specific network interface
channel.set_local_dev('eth0')

# Perform queries - they will use the bound interface
channel.query('google.com', pycares.QUERY_TYPE_A, callback)

# Use TCP instead of UDP for queries
ARES_FLAG_USEVC = 1

# Only query primary DNS servers
ARES_FLAG_PRIMARY = 2

# Ignore truncated responses
ARES_FLAG_IGNTC = 4

# Don't perform recursive queries
ARES_FLAG_NORECURSE = 8

# Keep TCP connections open for multiple queries
ARES_FLAG_STAYOPEN = 16

# Don't use search domains for single-label names
ARES_FLAG_NOSEARCH = 32

# Don't look up aliases
ARES_FLAG_NOALIASES = 64

# Don't check response against query
ARES_FLAG_NOCHECKRESP = 128

# Enable EDNS (Extension Mechanisms for DNS)
ARES_FLAG_EDNS = 256

# Don't add default servers if none specified
ARES_FLAG_NO_DFLT_SVR = 512

def socket_callback(fd, readable, writable):
    """
    Socket state change callback.
    
    Args:
        fd: int - Socket file descriptor
        readable: bool - Whether socket is ready for reading
        writable: bool - Whether socket is ready for writing
    """
    if readable:
        # Add fd to read monitoring
        loop.add_reader(fd, process_read, fd)
    if writable:
        # Add fd to write monitoring  
        loop.add_writer(fd, process_write, fd)
    if not readable and not writable:
        # Socket closed, remove from monitoring
        loop.remove_reader(fd)
        loop.remove_writer(fd)

channel = pycares.Channel(sock_state_cb=socket_callback)

def ares_threadsafety() -> bool:
    """
    Check if c-ares was compiled with thread safety support.
    
    Returns:
        bool: True if thread-safe, False otherwise
    """