// SSH Channel协议实现（Phase 6 + Phase 13端口转发）
// 参考OpenSSH channel.c

use crate::ssh_server::packet::{SshPacket, PacketType};
use crate::ssh_server::ssh_security_config::SshSecurityConfig;  // Phase 13.3: 安全配置
use crate::ssh_server::port_forward::{PortForwardManager, DirectTcpipChannel, ForwardedTcpipChannel};  // Phase 13.3
use std::io::{Read, Write};  // 导入Write trait（OpenSSH标准）
use anyhow::{Result, anyhow};
use byteorder::{BigEndian, ReadBytesExt, WriteBytesExt};
use log::{info, warn, debug};
use std::collections::HashMap;
use std::sync::{Arc, Mutex};
use crate::ssh_server::sftp_handler::SftpHandler;  // Phase 7: SFTP handler
use crate::ssh_server::scp_handler::ScpHandler;  // Phase 8: SCP handler
use crate::ssh_server::rsync_handler::RsyncHandler;  // Phase 8: rsync handler
use std::path::PathBuf;  // Phase 7-8: Path for SFTP/SCP/rsync root directory
use std::process::{Child, ChildStdin, ChildStdout, ChildStderr};  // Phase 14: 交互式exec
use std::os::unix::io::{AsRawFd, RawFd};  // Phase 14: OpenSSH风格poll机制（需要RawFd）
use nix::fcntl::{fcntl, FcntlArg, OFlag};  // Phase 14: 非阻塞I/O（OpenSSH风格）
use nix::poll::{poll, PollFd, PollFlags};  // Phase 14: poll机制（OpenSSH风格）

/// SSH Channel管理器（参考OpenSSH channel.c: struct channel）
pub struct ChannelManager {
    channels: HashMap<u32, Channel>,
    next_channel_id: u32,
}

/// Phase 14: 交互式Exec进程管理（参考OpenSSH session.c: do_exec_no_pty）
/// ⭐⭐⭐⭐⭐ OpenSSH风格：使用poll()替代thread::spawn（非阻塞I/O）
pub struct ExecProcess {
    pub child: Child,  // 子进程（rsync/scp等）
    pub stdin: Option<ChildStdin>,  // stdin管道（SSH client → 子进程）
    pub stdout: Option<ChildStdout>,  // ⭐⭐⭐⭐⭐ stdout管道（直接poll，不使用thread）
    pub stderr: Option<ChildStderr>,  // ⭐⭐⭐⭐⭐ stderr管道（直接poll，不使用thread）
    pub stdout_fd: RawFd,  // ⭐⭐⭐⭐⭐ stdout RawFd（用于poll）
    pub stderr_fd: RawFd,  // ⭐⭐⭐⭐⭐ stderr RawFd（用于poll）
}

impl ChannelManager {
    pub fn new() -> Self {
        Self {
            channels: HashMap::new(),
            next_channel_id: 0,
        }
    }
    
    /// 处理SSH_MSG_CHANNEL_OPEN（参考OpenSSH channel.c: channel_open())
    /// Phase 13.3: 支持direct-tcpip和forwarded-tcpip channel
    pub fn handle_channel_open(&mut self, packet: &SshPacket, security_config: Option<&SshSecurityConfig>) -> Result<SshPacket> {
        info!("Processing SSH_MSG_CHANNEL_OPEN");
        
        let mut cursor = std::io::Cursor::new(packet.payload.as_slice());
        
        // Packet type
        let packet_type = cursor.read_u8()?;
        if packet_type != PacketType::SSH_MSG_CHANNEL_OPEN as u8 {
            return Err(anyhow!("Invalid packet type for CHANNEL_OPEN"));
        }
        
        // 读取channel类型（SSH string）
        let channel_type = read_ssh_string(&mut cursor)?;
        
        // 读取sender channel ID（u32）
        let sender_channel = cursor.read_u32::<BigEndian>()?;
        
        // 读取初始窗口大小（u32）
        let initial_window_size = cursor.read_u32::<BigEndian>()?;
        
        // 读取最大packet大小（u32）
        let maximum_packet_size = cursor.read_u32::<BigEndian>()?;
        
        info!("Channel open: type={}, sender_channel={}, window={}, max_packet={}", 
              channel_type, sender_channel, initial_window_size, maximum_packet_size);
        
        // Phase 13.3: 检查channel类型（支持session、direct-tcpip、forwarded-tcpip）
        match channel_type.as_str() {
            "session" => {
                // 传统的session channel（Phase 6）
                self.handle_session_channel_open(sender_channel, initial_window_size, maximum_packet_size)
            }
            
            "direct-tcpip" => {
                // Phase 13.3: Remote port forwarding channel
                info!("Received direct-tcpip channel open (Remote port forwarding)");
                self.handle_direct_tcpip_channel_open(packet, sender_channel, initial_window_size, maximum_packet_size, security_config)
            }
            
            "forwarded-tcpip" => {
                // Phase 13.3: Local port forwarding channel
                info!("Received forwarded-tcpip channel open (Local port forwarding)");
                self.handle_forwarded_tcpip_channel_open(packet, sender_channel, initial_window_size, maximum_packet_size)
            }
            
            _ => {
                warn!("Unsupported channel type: {}", channel_type);
                self.build_channel_open_failure(
                    sender_channel,
                    3,  // SSH_OPEN_UNKNOWN_CHANNEL_TYPE
                    "Unsupported channel type",
                    "en"
                )
            }
        }
    }
    

    /// 处理session channel open（Phase 6）
    fn handle_session_channel_open(&mut self, sender_channel: u32, initial_window_size: u32, maximum_packet_size: u32) -> Result<SshPacket> {
        info!("Processing session channel open");
        
        let server_channel = self.next_channel_id;
        self.next_channel_id += 1;
        
        let channel = Channel {
            server_channel,
            sender_channel,
            channel_type: "session".to_string(),
            window_size: initial_window_size,
            maximum_packet_size,
            state: ChannelState::Open,
            output_buffer: None,
            sftp_handler: None,
            scp_handler: None,
            rsync_handler: None,
            exec_process: None,  // Phase 14: 交互式exec
            sftp_input_buffer: Vec::new(),  // ⭐⭐⭐⭐⭐ Phase 14.2修复：SFTP packet累积
            scp_input_buffer: Vec::new(),   // ⭐⭐⭐⭐⭐ Phase 14.4修复：SCP packet累积
            direct_tcpip: None,
            forwarded_tcpip: None,
        };
        
        self.channels.insert(server_channel, channel);
        
        info!("Session channel created: server_channel={}, sender_channel={}", server_channel, sender_channel);
        
        self.build_channel_open_confirmation(server_channel, sender_channel, initial_window_size, maximum_packet_size)
    }
    
    /// 处理direct-tcpip channel open（Phase 13.3: Remote port forwarding）
    fn handle_direct_tcpip_channel_open(
        &mut self, 
        packet: &SshPacket,
        sender_channel: u32,
        initial_window_size: u32,
        maximum_packet_size: u32,
        security_config: Option<&SshSecurityConfig>,
    ) -> Result<SshPacket> {
        info!("Processing direct-tcpip channel open");
        
        // 解析direct-tcpip参数
        let mut port_forward_manager = PortForwardManager::new();
        let direct_tcpip = port_forward_manager.handle_direct_tcpip_channel(&packet.payload)?;
        
        // Phase 13.3: 安全配置验证
        if let Some(security) = security_config {
            if let Err(e) = security.validate_direct_tcpip_channel(&direct_tcpip.host_to_connect, direct_tcpip.port_to_connect) {
                warn!("direct-tcpip security validation failed: {}", e);
                return self.build_channel_open_failure(
                    sender_channel,
                    2,  // SSH_OPEN_CONNECT_FAILED
                    "Security validation failed",
                    "en"
                );
            }
            info!("direct-tcpip security validation passed");
        }
        
        let server_channel = self.next_channel_id;
        self.next_channel_id += 1;
        
        let channel = Channel {
            server_channel,
            sender_channel,
            channel_type: "direct-tcpip".to_string(),
            window_size: initial_window_size,
            maximum_packet_size,
            state: ChannelState::Open,
            output_buffer: None,
            sftp_handler: None,
            scp_handler: None,
            rsync_handler: None,
            exec_process: None,  // Phase 14: 交互式exec
            sftp_input_buffer: Vec::new(),  // ⭐⭐⭐⭐⭐ Phase 14.2修复
            scp_input_buffer: Vec::new(),   // ⭐⭐⭐⭐⭐ Phase 14.4修复
            direct_tcpip: Some(direct_tcpip),
            forwarded_tcpip: None,
        };
        
        self.channels.insert(server_channel, channel);
        
        info!("direct-tcpip channel created: server_channel={}, host={}, port={}", 
            server_channel, 
            self.channels.get(&server_channel).unwrap().direct_tcpip.as_ref().unwrap().host_to_connect,
            self.channels.get(&server_channel).unwrap().direct_tcpip.as_ref().unwrap().port_to_connect);
        
        self.build_channel_open_confirmation(server_channel, sender_channel, initial_window_size, maximum_packet_size)
    }
    
    /// 处理forwarded-tcpip channel open（Phase 13.3: Local port forwarding）
    fn handle_forwarded_tcpip_channel_open(
        &mut self,
        packet: &SshPacket,
        sender_channel: u32,
        initial_window_size: u32,
        maximum_packet_size: u32,
    ) -> Result<SshPacket> {
        info!("Processing forwarded-tcpip channel open");
        
        // 解析forwarded-tcpip参数
        let mut port_forward_manager = PortForwardManager::new();
        let forwarded_tcpip = port_forward_manager.handle_forwarded_tcpip_channel(&packet.payload)?;
        
        let server_channel = self.next_channel_id;
        self.next_channel_id += 1;
        
        let channel = Channel {
            server_channel,
            sender_channel,
            channel_type: "forwarded-tcpip".to_string(),
            window_size: initial_window_size,
            maximum_packet_size,
            state: ChannelState::Open,
            output_buffer: None,
            sftp_handler: None,
            scp_handler: None,
            rsync_handler: None,
            exec_process: None,  // Phase 14: 交互式exec
            sftp_input_buffer: Vec::new(),  // ⭐⭐⭐⭐⭐ Phase 14.2修复
            scp_input_buffer: Vec::new(),   // ⭐⭐⭐⭐⭐ Phase 14.4修复
            direct_tcpip: None,
            forwarded_tcpip: Some(forwarded_tcpip),
        };
        
        self.channels.insert(server_channel, channel);
        
        info!("forwarded-tcpip channel created: server_channel={}, bind={}, originator={}", 
            server_channel, 
            self.channels.get(&server_channel).unwrap().forwarded_tcpip.as_ref().unwrap().bind_port,
            self.channels.get(&server_channel).unwrap().forwarded_tcpip.as_ref().unwrap().originator_address);
        
        self.build_channel_open_confirmation(server_channel, sender_channel, initial_window_size, maximum_packet_size)
    }
    /// 处理SSH_MSG_CHANNEL_REQUEST（参考OpenSSH channel.c: channel_request())
    pub fn handle_channel_request(&mut self, packet: &SshPacket) -> Result<Option<SshPacket>> {
        info!("Processing SSH_MSG_CHANNEL_REQUEST");
        
        let mut cursor = std::io::Cursor::new(packet.payload.as_slice());  // 使用as_slice()（Rust标准）
        
        // Packet type
        let packet_type = cursor.read_u8()?;
        if packet_type != PacketType::SSH_MSG_CHANNEL_REQUEST as u8 {
            return Err(anyhow!("Invalid packet type for CHANNEL_REQUEST"));
        }
        
        // 读取recipient channel（u32）
        let recipient_channel = cursor.read_u32::<BigEndian>()?;
        
        // 读取请求类型（SSH string）
        let request_type = read_ssh_string(&mut cursor)?;
        
        // 读取want reply标志（boolean）
        let want_reply = cursor.read_u8()? != 0;
        
        info!("Channel request: channel={}, type={}, want_reply={}", 
              recipient_channel, request_type, want_reply);
        
        // 处理不同请求类型（参考OpenSSH channel.c）
        if request_type == "exec" {
            self.handle_exec_request(&mut cursor, recipient_channel, want_reply)  // 移除?操作符（返回Option不是Result）
        } else if request_type == "subsystem" {
            self.handle_subsystem_request(&mut cursor, recipient_channel, want_reply)  // 移除?操作符
        } else if request_type == "shell" {
            self.handle_shell_request(recipient_channel, want_reply)  // 移除?操作符
        } else if request_type == "env" {
            self.handle_env_request(&mut cursor, recipient_channel, want_reply)  // 移除?操作符
        } else if request_type == "pty-req" {
            self.handle_pty_request(&mut cursor, recipient_channel, want_reply)  // 移除?操作符
        } else {
            warn!("Unsupported channel request: {}", request_type);
            if want_reply {
                Ok(Some(self.build_channel_failure(recipient_channel)?))
            } else {
                Ok(None)
            }
        }
    }
    
    /// 处理exec请求（参考OpenSSH channel.c: channel_request_exec() + session.c: do_exec_no_pty）
    fn handle_exec_request(&mut self, cursor: &mut std::io::Cursor<&[u8]>, channel: u32, want_reply: bool) -> Result<Option<SshPacket>> {
        info!("Handling exec request for channel {}", channel);
        
        // 读取命令（SSH string）
        let command = read_ssh_string(cursor)?;
        
        info!("Exec command: {}", command);
        
        // Phase 14: 检测rsync命令，启动交互式进程
        if command.starts_with("rsync --server") || command.contains("rsync") {
            info!("Detected rsync command, starting interactive process");
            self.handle_rsync_exec(&command, channel)?;
        } else {
            // Phase 6: 普通命令使用非交互式执行
            let output = self.execute_command(&command)?;
            
            // 存储输出，等待后续发送CHANNEL_DATA
            if let Some(ch) = self.channels.get_mut(&channel) {
                ch.output_buffer = Some(output);
            }
        }
        
        if want_reply {
            Ok(Some(self.build_channel_success(channel)?))
        } else {
            Ok(None)
        }
    }
    
    /// Phase 14: 处理rsync交互式exec（参考OpenSSH session.c: do_exec_no_pty）
    /// ⭐⭐⭐⭐⭐ OpenSSH风格：使用poll()替代thread::spawn（非阻塞I/O）
    fn handle_rsync_exec(&mut self, command: &str, channel_id: u32) -> Result<()> {
        use std::process::{Command, Stdio};
        use std::os::unix::io::AsRawFd;
        
        info!("Starting interactive process for rsync (OpenSSH poll style): {}", command);
        
        // 启动子进程（相当于OpenSSH fork）
        let mut child = Command::new("sh")
            .arg("-c")
            .arg(command)
            .stdin(Stdio::piped())   // ← 创建stdin管道（相当于pipe(pin)）
            .stdout(Stdio::piped())  // ← 创建stdout管道（相当于pipe(pout)）
            .stderr(Stdio::piped())  // ← 创建stderr管道（相当于pipe(perr)）
            .spawn()?;
        
        info!("Child process spawned, PID: {:?}", child.id());
        
        // 提取管道（相当于OpenSSH dup2）
        let stdin = child.stdin.take().ok_or(anyhow!("stdin take failed"))?;
        let stdout = child.stdout.take().ok_or(anyhow!("stdout take failed"))?;
        let stderr = child.stderr.take().ok_or(anyhow!("stderr take failed"))?;
        
        // ⭐⭐⭐⭐⭐ OpenSSH关键：设置非阻塞模式（fcntl O_NONBLOCK）
        let stdout_fd = stdout.as_raw_fd();
        let stderr_fd = stderr.as_raw_fd();
        
        info!("Setting stdout/stderr to non-blocking mode (OpenSSH style)");
        fcntl(stdout_fd, FcntlArg::F_SETFL(OFlag::O_NONBLOCK))?;
        fcntl(stderr_fd, FcntlArg::F_SETFL(OFlag::O_NONBLOCK))?;
        info!("Non-blocking I/O enabled for stdout (fd {}) and stderr (fd {})", stdout_fd, stderr_fd);
        
        // ⭐⭐⭐⭐⭐ OpenSSH风格：不再使用thread::spawn，直接保留File对象用于poll
        // 存储到channel（相当于OpenSSH session_set_fds）
        if let Some(ch) = self.channels.get_mut(&channel_id) {
            ch.exec_process = Some(ExecProcess {
                child,
                stdin: Some(stdin),
                stdout: Some(stdout),  // ⭐⭐⭐⭐⭐ 直接保留File对象
                stderr: Some(stderr),  // ⭐⭐⭐⭐⭐ 直接保留File对象
                stdout_fd,  // ⭐⭐⭐⭐⭐ RawFd用于poll
                stderr_fd,  // ⭐⭐⭐⭐⭐ RawFd用于poll
            });
            info!("Interactive process stored for channel {} (poll-ready)", channel_id);
        }
        
        Ok(())
    }
    
    /// 执行命令并捕获输出（Phase 6基础实现）
    fn execute_command(&self, command: &str) -> Result<Vec<u8>> {
        use std::process::{Command, Stdio};
        
        info!("Executing command: {}", command);
        
        // 使用shell执行命令（参考OpenSSH session.c）
        let output = Command::new("sh")
            .arg("-c")
            .arg(command)
            .output()?;
        
        // 返回stdout + stderr
        let mut result = output.stdout;
        result.extend_from_slice(&output.stderr);
        
        info!("Command output: {} bytes", result.len());
        Ok(result)
    }
    
    /// 处理subsystem请求（参考OpenSSH channel.c: channel_request_subsystem())
    fn handle_subsystem_request(&mut self, cursor: &mut std::io::Cursor<&[u8]>, channel: u32, want_reply: bool) -> Result<Option<SshPacket>> {
        info!("Handling subsystem request for channel {}", channel);
        
        // 读取subsystem名称（SSH string）
        let subsystem = read_ssh_string(cursor)?;
        
        info!("Subsystem: {}", subsystem);
        
        // 检查subsystem支持（OpenSSH支持：sftp）
        if subsystem == "sftp" {
            info!("SFTP subsystem requested");
            
            // Phase 7: 初始化SFTP handler
            let root_dir = PathBuf::from("/Users/accusys/markbase");  // 默认root目录
            let sftp_handler = SftpHandler::new(root_dir);
            
            // 存储到channel
            if let Some(ch) = self.channels.get_mut(&channel) {
                ch.sftp_handler = Some(sftp_handler);
                info!("SFTP handler initialized for channel {}", channel);
            }
            
            if want_reply {
                Ok(Some(self.build_channel_success(channel)?))
            } else {
                Ok(None)
            }
        } else {
            warn!("Unsupported subsystem: {}", subsystem);
            if want_reply {
                Ok(Some(self.build_channel_failure(channel)?))
            } else {
                Ok(None)
            }
        }
    }
    
    /// 处理shell请求（参考OpenSSH channel.c）
    fn handle_shell_request(&mut self, channel: u32, want_reply: bool) -> Result<Option<SshPacket>> {
        info!("Handling shell request for channel {}", channel);
        
        // Phase 9将实现shell
        warn!("Shell not implemented in Phase 6");
        
        if want_reply {
            Ok(Some(self.build_channel_failure(channel)?))
        } else {
            Ok(None)
        }
    }
    
    /// 处理env请求（参考OpenSSH channel.c）
    fn handle_env_request(&mut self, cursor: &mut std::io::Cursor<&[u8]>, channel: u32, want_reply: bool) -> Result<Option<SshPacket>> {
        info!("Handling env request for channel {}", channel);
        
        // 读取环境变量名和值
        let name = read_ssh_string(cursor)?;
        let value = read_ssh_string(cursor)?;
        
        info!("Env: {}={}", name, value);
        
        if want_reply {
            Ok(Some(self.build_channel_success(channel)?))
        } else {
            Ok(None)
        }
    }
    
    /// 处理pty请求（参考OpenSSH channel.c）
    fn handle_pty_request(&mut self, cursor: &mut std::io::Cursor<&[u8]>, channel: u32, want_reply: bool) -> Result<Option<SshPacket>> {
        info!("Handling pty request for channel {}", channel);
        
        // 读取terminal类型（SSH string）
        let term = read_ssh_string(cursor)?;
        
// 读取窗口大小（4个uint32）
        let width = cursor.read_u32::<BigEndian>()?;
        let height = cursor.read_u32::<BigEndian>()?;
        let _pixel_width = cursor.read_u32::<BigEndian>()?;
        let _pixel_height = cursor.read_u32::<BigEndian>()?;
        
        // 读取terminal modes（SSH string格式）
        let modes_len = cursor.read_u32::<BigEndian>()?;
        let mut modes = vec![0u8; modes_len as usize];
        cursor.read_exact(&mut modes)?;
        
        info!("PTY: term={}, width={}, height={}, modes_len={}", term, width, height, modes_len);
        
        if want_reply {
            Ok(Some(self.build_channel_success(channel)?))
        } else {
            Ok(None)
        }
    }
    
    /// 处理SSH_MSG_CHANNEL_DATA（参考OpenSSH channel.c: channel_input_data())
    pub fn handle_channel_data(&mut self, packet: &SshPacket) -> Result<Option<SshPacket>> {
        info!("Processing SSH_MSG_CHANNEL_DATA");
        
        let mut cursor = std::io::Cursor::new(packet.payload.as_slice());
        
        // Packet type
        let packet_type = cursor.read_u8()?;
        if packet_type != PacketType::SSH_MSG_CHANNEL_DATA as u8 {
            return Err(anyhow!("Invalid packet type for CHANNEL_DATA"));
        }
        
        // 读取recipient channel
        let recipient_channel = cursor.read_u32::<BigEndian>()?;
        
        // 读取数据（SSH string）
        let data_length = cursor.read_u32::<BigEndian>()?;
        let mut data = vec![0u8; data_length as usize];
        cursor.read_exact(&mut data)?;
        
        info!("Channel data: channel={}, length={}", recipient_channel, data.len());
        info!("Channel data content (first 20 bytes): {:?}", &data[..std::cmp::min(20, data.len())]);
        
        // Phase 14: 检查是否是交互式exec进程
        if let Some(channel) = self.channels.get_mut(&recipient_channel) {
            if let Some(exec_process) = &mut channel.exec_process {
                info!("Interactive exec process detected, forwarding data to stdin");
                info!("Channel data content: {:?}", &data);
                info!("Child PID: {:?}", exec_process.child.id());
                
                // 检查子进程状态
                match exec_process.child.try_wait() {
                    Ok(Some(status)) => {
                        warn!("Child process already exited with status: {:?}", status);
                    }
                    Ok(None) => {
                        info!("Child process still running");
                    }
                    Err(e) => {
                        warn!("Failed to check child status: {}", e);
                    }
                }
                
                // 转发数据到子进程stdin（相当于OpenSSH写fdin）
                if let Some(stdin) = &mut exec_process.stdin {
                    use std::io::Write;
                    stdin.write_all(&data)?;
                    stdin.flush()?;
                    info!("Forwarded {} bytes to stdin (OpenSSH style)", data.len());
                }
                
                // ⭐⭐⭐⭐⭐ OpenSSH风格：不等待，直接返回None（主循环会通过poll处理stdout）
                info!("stdin forwarded, returning None (main loop will poll stdout/stderr)");
                return Ok(None);
            }
            
            // Phase 7: 检查是否是SFTP channel（⭐⭐⭐⭐⭐ Phase 14.3: packet accumulation）
            if let Some(sftp_handler) = &mut channel.sftp_handler {
                info!("Processing SFTP request ({} bytes)", data.len());
                
                // ⭐⭐⭐⭐⭐ Critical修复：累积SFTP packet数据
                channel.sftp_input_buffer.extend_from_slice(&data);
                info!("SFTP buffer accumulated: {} bytes total", channel.sftp_input_buffer.len());
                
                // 检查buffer是否有足够数据解析packet length
                if channel.sftp_input_buffer.len() < 4 {
                    info!("SFTP buffer too short for length field, waiting for more data");
                    return Ok(None);  // 继续累积
                }
                
                // 解析SFTP packet length（前4 bytes）
                let sftp_length = u32::from_be_bytes([
                    channel.sftp_input_buffer[0],
                    channel.sftp_input_buffer[1],
                    channel.sftp_input_buffer[2],
                    channel.sftp_input_buffer[3]
                ]) as usize;
                info!("SFTP packet length field: {}", sftp_length);
                
                let expected_total = 4 + sftp_length;
                if channel.sftp_input_buffer.len() < expected_total {
                    info!("SFTP packet incomplete: expected {} bytes, have {} bytes in buffer, waiting for more",
                        expected_total, channel.sftp_input_buffer.len());
                    return Ok(None);  // 继续累积
                }
                
                // ⭐⭐⭐⭐⭐ Buffer足够，解析完整SFTP packet
                let sftp_packet = &channel.sftp_input_buffer[4..expected_total];
                info!("SFTP packet complete: {} bytes, processing", sftp_packet.len());
                info!("SFTP packet content (first 20 bytes): {:?}", &sftp_packet[..std::cmp::min(20, sftp_packet.len())]);
                
                let response = sftp_handler.handle_request(sftp_packet)?;
                info!("SFTP response: {} bytes", response.len());
                
                // ⭐⭐⭐⭐⭐ 处理完后，清空buffer或保留剩余数据
                if channel.sftp_input_buffer.len() > expected_total {
                    // 有剩余数据（多个packets的情况）
                    let remaining = channel.sftp_input_buffer[expected_total..].to_vec();
                    channel.sftp_input_buffer = remaining;
                    info!("SFTP buffer has remaining {} bytes after processing", channel.sftp_input_buffer.len());
                } else {
                    // 清空buffer
                    channel.sftp_input_buffer.clear();
                    info!("SFTP buffer cleared after processing");
                }
                
                // 构建SSH_MSG_CHANNEL_DATA返回SFTP响应（需要SSH string格式）
                return Ok(Some(self.build_channel_data(recipient_channel, &response)?));
            }
        }
        
        // 如果不是SFTP或exec_process，返回None
        Ok(None)
    }
    
    /// Phase 14: 构建SSH_MSG_CHANNEL_EXTENDED_DATA（参考OpenSSH channel.c）
    fn build_channel_extended_data(&self, channel: u32, data_type: u32, data: &[u8]) -> Result<SshPacket> {
        let mut buffer = Vec::new();
        
        buffer.write_u8(PacketType::SSH_MSG_CHANNEL_EXTENDED_DATA as u8)?;
        buffer.write_u32::<BigEndian>(channel)?;
        buffer.write_u32::<BigEndian>(data_type)?;  // 1 = stderr, 2 = exit status
        buffer.write_u32::<BigEndian>(data.len() as u32)?;
        buffer.write_all(data)?;
        
        Ok(SshPacket {
            packet_length: 0,
            padding_length: 0,
            payload: buffer,
            padding: Vec::new(),
        })
    }
    
    /// 处理SSH_MSG_CHANNEL_CLOSE（参考OpenSSH channel.c: channel_input_close())
    pub fn handle_channel_close(&mut self, packet: &SshPacket) -> Result<Option<SshPacket>> {
        info!("Processing SSH_MSG_CHANNEL_CLOSE");
        
        let mut cursor = std::io::Cursor::new(packet.payload.as_slice());  // 使用as_slice()（Rust标准）
        
        // Packet type
        let packet_type = cursor.read_u8()?;
        if packet_type != PacketType::SSH_MSG_CHANNEL_CLOSE as u8 {
            return Err(anyhow!("Invalid packet type for CHANNEL_CLOSE"));
        }
        
        // 读取recipient channel
        let recipient_channel = cursor.read_u32::<BigEndian>()?;
        
        info!("Channel close: channel={}", recipient_channel);
        
        // 移除channel（参考OpenSSH channel.c）
        if let Some(channel) = self.channels.remove(&recipient_channel) {
            info!("Channel {} removed", recipient_channel);
            
            // 发送SSH_MSG_CHANNEL_CLOSE回应
            Ok(Some(self.build_channel_close(channel.sender_channel)?))
        } else {
            warn!("Channel {} not found", recipient_channel);
            Ok(None)
        }
    }
    
    /// 构建SSH_MSG_CHANNEL_OPEN_CONFIRMATION（参考OpenSSH channel.c）
    fn build_channel_open_confirmation(
        &self,
        server_channel: u32,
        sender_channel: u32,
        window_size: u32,
        packet_size: u32,
    ) -> Result<SshPacket> {
        let mut payload = Vec::new();
        
        // Packet type
        payload.write_u8(PacketType::SSH_MSG_CHANNEL_OPEN_CONFIRMATION as u8)?;
        
        // Server channel number
        payload.write_u32::<BigEndian>(server_channel)?;
        
        // Sender channel number
        payload.write_u32::<BigEndian>(sender_channel)?;
        
        // Initial window size
        payload.write_u32::<BigEndian>(window_size)?;
        
        // Maximum packet size
        payload.write_u32::<BigEndian>(packet_size)?;
        
        Ok(SshPacket::new(payload))
    }
    
    /// 构建SSH_MSG_CHANNEL_OPEN_FAILURE（参考OpenSSH channel.c）
    fn build_channel_open_failure(
        &self,
        sender_channel: u32,
        reason_code: u32,
        description: &str,
        language: &str,
    ) -> Result<SshPacket> {
        let mut payload = Vec::new();
        
        // Packet type
        payload.write_u8(PacketType::SSH_MSG_CHANNEL_OPEN_FAILURE as u8)?;
        
        // Sender channel number
        payload.write_u32::<BigEndian>(sender_channel)?;
        
        // Reason code
        payload.write_u32::<BigEndian>(reason_code)?;
        
        // Description（SSH string）
        payload.write_u32::<BigEndian>(description.len() as u32)?;
        payload.write_all(description.as_bytes())?;
        
        // Language（SSH string）
        payload.write_u32::<BigEndian>(language.len() as u32)?;
        payload.write_all(language.as_bytes())?;
        
        Ok(SshPacket::new(payload))
    }
    
    /// 构建SSH_MSG_CHANNEL_SUCCESS（参考OpenSSH channel.c）
    fn build_channel_success(&self, channel: u32) -> Result<SshPacket> {
        let mut payload = Vec::new();
        
        payload.write_u8(PacketType::SSH_MSG_CHANNEL_SUCCESS as u8)?;
        payload.write_u32::<BigEndian>(channel)?;
        
        Ok(SshPacket::new(payload))
    }
    
    /// 构建SSH_MSG_CHANNEL_FAILURE（参考OpenSSH channel.c）
    fn build_channel_failure(&self, channel: u32) -> Result<SshPacket> {
        let mut payload = Vec::new();
        
        payload.write_u8(PacketType::SSH_MSG_CHANNEL_FAILURE as u8)?;
        payload.write_u32::<BigEndian>(channel)?;
        
        Ok(SshPacket::new(payload))
    }
    
    /// 构建SSH_MSG_CHANNEL_CLOSE（参考OpenSSH channel.c）
    pub fn build_channel_close(&self, channel: u32) -> Result<SshPacket> {
        let mut payload = Vec::new();
        
        payload.write_u8(PacketType::SSH_MSG_CHANNEL_CLOSE as u8)?;
        payload.write_u32::<BigEndian>(channel)?;
        
        Ok(SshPacket::new(payload))
    }
    
    /// 构建SSH_MSG_CHANNEL_DATA（Phase 6新增）
    pub fn build_channel_data(&self, channel: u32, data: &[u8]) -> Result<SshPacket> {
        let mut payload = Vec::new();
        
        payload.write_u8(PacketType::SSH_MSG_CHANNEL_DATA as u8)?;
        payload.write_u32::<BigEndian>(channel)?;
        payload.write_u32::<BigEndian>(data.len() as u32)?;
        payload.write_all(data)?;
        
        Ok(SshPacket::new(payload))
    }
    
    /// 构建SSH_MSG_CHANNEL_EOF（Phase 6新增）
    pub fn build_channel_eof(&self, channel: u32) -> Result<SshPacket> {
        let mut payload = Vec::new();
        
        payload.write_u8(PacketType::SSH_MSG_CHANNEL_EOF as u8)?;
        payload.write_u32::<BigEndian>(channel)?;
        
        Ok(SshPacket::new(payload))
    }
    
    /// 获取有输出待发送的channel ID（Phase 6新增）
    pub fn get_channel_with_output(&self) -> Option<u32> {
        for (&id, channel) in &self.channels {
            if channel.output_buffer.is_some() {
                return Some(id);
            }
        }
        None
    }
    
    /// 获取channel输出（Phase 6新增）
    pub fn get_channel_output(&mut self, channel_id: u32) -> Option<Vec<u8>> {
        if let Some(channel) = self.channels.get_mut(&channel_id) {
            channel.output_buffer.take()
        } else {
            None
        }
    }
    
    /// 移除channel（Phase 6新增）
    pub fn remove_channel(&mut self, channel_id: u32) {
        self.channels.remove(&channel_id);
    }
    
    /// Phase 14: OpenSSH风格poll机制（使用nix::poll监听stdout/stderr fd）
    /// ⭐⭐⭐⭐⭐ 关键：非阻塞读取数据，不等待子进程完成
    /// ⭐⭐⭐⭐⭐ Phase 14.2: 处理child exited（发送EOF + CLOSE）
    /// 参考：OpenSSH session.c: do_exec_no_pty()
    pub fn handle_child_exited(&mut self) -> Result<Vec<SshPacket>> {
        // 1. 收集需要处理的channel IDs
        let channel_ids: Vec<u32> = self.channels
            .iter()
            .filter_map(|(id, channel)| {
                if channel.exec_process.is_some() {
                    Some(*id)
                } else {
                    None
                }
            })
            .collect();
        
        // 2. 构建packets（避免borrow冲突）
        let mut packets = Vec::new();
        for channel_id in &channel_ids {
            // 发送SSH_MSG_CHANNEL_EOF
            let eof_packet = self.build_channel_eof(*channel_id)?;
            packets.push(eof_packet);
            
            // 发送SSH_MSG_CHANNEL_CLOSE
            let close_packet = self.build_channel_close(*channel_id)?;
            packets.push(close_packet);
        }
        
        // 3. 清除exec_process（mutable borrow）
        for channel_id in &channel_ids {
            if let Some(channel) = self.channels.get_mut(channel_id) {
                channel.exec_process = None;
            }
        }
        
        if !channel_ids.is_empty() {
            info!("Child exited, sent EOF + CLOSE for {} channels", channel_ids.len());
        }
        
        Ok(packets)
    }
    
    /// ⭐⭐⭐⭐⭐ Phase 14.2: OpenSSH统一poll + child进程状态检测
    /// 参考：OpenSSH session.c: do_exec_no_pty() + channel.c: channel_handle_fd()
    /// 
    /// 关键改进（Phase 14.2）：
    /// - 单次poll()同时监听client socket和子进程输出
    /// - timeout 10ms（非阻塞）
    /// - **添加child进程状态检测**（防止无限spinning）⭐⭐⭐⭐⭐
    /// - **添加max_poll_iterations限制**（最多100次，1秒）
    /// - 返回(stdout_packets, client_has_data, child_exited)
    pub fn poll_exec_stdout_and_client(&mut self, stream: &std::net::TcpStream) -> Result<(Option<Vec<SshPacket>>, bool, bool)> {
        use std::io::Read;
        use std::os::unix::io::{BorrowedFd, AsRawFd};
        use nix::poll::{poll, PollFd, PollFlags};
        
        // 收集所有需要poll的fd
        let mut poll_fds_vec = Vec::new();
        let mut client_has_data = false;
        let mut child_exited = false;
        
        // 1. 添加client socket fd（监听stdin数据）
        let client_fd = stream.as_raw_fd();
        let client_poll_fd = unsafe {
            BorrowedFd::borrow_raw(client_fd)
        };
        poll_fds_vec.push(PollFd::new(client_poll_fd, PollFlags::POLLIN));
        let client_fd_idx = 0;  // client fd总是第一个
        
        // 2. 添加所有channel的stdout/stderr fd
        let mut channel_fds_map: HashMap<u32, (usize, usize)> = HashMap::new();  // channel_id -> (stdout_idx, stderr_idx)
        let mut channel_ids_vec = Vec::new();  // 用于后续child状态检查
        
        for (channel_id, channel) in &self.channels {
            if let Some(exec_process) = &channel.exec_process {
                channel_ids_vec.push(*channel_id);
                
                // stdout fd
                if let Some(_stdout) = &exec_process.stdout {
                    let stdout_poll_fd = unsafe {
                        BorrowedFd::borrow_raw(exec_process.stdout_fd)
                    };
                    poll_fds_vec.push(PollFd::new(stdout_poll_fd, PollFlags::POLLIN));
                }
                
                // stderr fd
                if let Some(_stderr) = &exec_process.stderr {
                    let stderr_poll_fd = unsafe {
                        BorrowedFd::borrow_raw(exec_process.stderr_fd)
                    };
                    poll_fds_vec.push(PollFd::new(stderr_poll_fd, PollFlags::POLLIN));
                }
                
                // 记录索引（相对于client_fd_idx）
                let stdout_idx = poll_fds_vec.len() - 2;
                let stderr_idx = poll_fds_vec.len() - 1;
                channel_fds_map.insert(*channel_id, (stdout_idx, stderr_idx));
            }
        }
        
        if poll_fds_vec.len() == 1 {
            // 只有client fd，没有exec_process
            // 直接poll client（short timeout）
            match poll(&mut poll_fds_vec, 10u16) {
                Ok(n) if n > 0 => {
                    if let Some(revents) = poll_fds_vec[client_fd_idx].revents() {
                        if revents.contains(PollFlags::POLLIN) {
                            client_has_data = true;
                        }
                    }
                }
                _ => {}
            }
            return Ok((None, client_has_data, false));
        }
        
        // ⭐⭐⭐⭐⭐ Phase 14.2关键：添加poll轮询限制（防止无限spinning）
        // 最多轮询100次（1秒），如果持续无数据，检查child状态
        let max_poll_iterations = 100;
        let mut poll_iteration = 0;
        let mut found_data = false;
        let mut stdin_closed = false;  // ⭐⭐⭐⭐⭐ 新增：跟踪stdin是否已关闭
        
        for iteration in 0..max_poll_iterations {
            poll_iteration = iteration;
            
            // ⭐⭐⭐⭐⭐ 每10次轮询记录一次日志（减少噪音）
            if iteration % 10 == 0 {
                info!("Polling {} fds (iteration {} of {}, stdin_closed={})", poll_fds_vec.len(), iteration, max_poll_iterations, stdin_closed);
            }
            
            match poll(&mut poll_fds_vec, 10u16) {
                Ok(n) if n > 0 => {
                    info!("{} fds have data available (iteration {})", n, iteration);
                    found_data = true;
                    break;  // 有数据，立即处理
                }
                Ok(0) => {
                    // timeout，无数据
                    // ⭐⭐⭐⭐⭐ 关键：每10次检查child进程状态（防止spinning）
                    if iteration % 10 == 9 {
                        // 检查child是否exited
                        for channel_id in &channel_ids_vec {
                            if let Some(channel) = self.channels.get_mut(channel_id) {
                                if let Some(exec_process) = &mut channel.exec_process {
                                    match exec_process.child.try_wait() {
                                        Ok(Some(status)) => {
                                            info!("Child process exited (channel {}, status: {:?})", channel_id, status);
                                            child_exited = true;
                                            
                                            // ⭐⭐⭐⭐⭐ Child exited，读取剩余stdout（如果有）
                                            if let Some(stdout) = &mut exec_process.stdout {
                                                let mut buffer = vec![0u8; 32768];
                                                match stdout.read(&mut buffer) {
                                                    Ok(n) if n > 0 => {
                                                        info!("Read {} final bytes from stdout (child exited)", n);
                                                        // 构建packet并返回
                                                        let packet = self.build_channel_data(*channel_id, &buffer[..n])?;
                                                        return Ok((Some(vec![packet]), false, true));
                                                    }
                                                    _ => {}
                                                }
                                            }
                                            
                                            // 没有剩余数据，返回child_exited标志
                                            return Ok((None, false, true));
                                        }
                                        Ok(None) => {
                                            // Child still running（正常）
                                            info!("Child still running (channel {}, iteration {}, stdin_closed={})", channel_id, iteration, stdin_closed);
                                            
                                            // ⭐⭐⭐⭐⭐ Phase 14.2最终修复：主动关闭stdin超时机制
                                            // 如果stdin未关闭，且超过50次poll（500ms）无数据
                                            // 强制关闭stdin，发送EOF给rsync
                                            if !stdin_closed && iteration >= 50 && exec_process.stdin.is_some() {
                                                info!("⭐⭐⭐⭐⭐ Forcing stdin close after {} iterations ({} ms) - sending EOF to rsync", iteration, iteration * 10);
                                                exec_process.stdin = None;  // Drop stdin，发送EOF
                                                stdin_closed = true;
                                                
                                                // ⭐⭐⭐⭐⭐ stdin关闭后，继续等待child处理完成
                                                // 不要立即返回，给rsync时间处理数据并产生stdout
                                                info!("stdin closed, continuing to poll for stdout output...");
                                            }
                                        }
                                        Err(e) => {
                                            warn!("Child try_wait error: {}", e);
                                        }
                                    }
                                }
                            }
                        }
                    }
                    
                    // 继续轮询（如果iteration < max_poll_iterations）
                }
                Err(e) => {
                    warn!("poll error: {}", e);
                    return Ok((None, false, false));
                }
                Ok(_) => {
                    // 其他情况（不应该发生）
                }
            }
        }
        
        // ⭐⭐⭐⭐⭐ 达到max_poll_iterations，检查最终child状态
        if !found_data {
            info!("No data after {} iterations ({} ms), checking child status", max_poll_iterations, max_poll_iterations * 10);
            
            for channel_id in &channel_ids_vec {
                if let Some(channel) = self.channels.get_mut(channel_id) {
                    if let Some(exec_process) = &mut channel.exec_process {
                        match exec_process.child.try_wait() {
                            Ok(Some(status)) => {
                                info!("Child exited after max iterations (status: {:?})", status);
                                child_exited = true;
                                
                                // 读取剩余stdout
                                if let Some(stdout) = &mut exec_process.stdout {
                                    let mut buffer = vec![0u8; 32768];
                                    match stdout.read(&mut buffer) {
                                        Ok(n) if n > 0 => {
                                            let packet = self.build_channel_data(*channel_id, &buffer[..n])?;
                                            return Ok((Some(vec![packet]), false, true));
                                        }
                                        _ => {}
                                    }
                                }
                                
                                return Ok((None, false, true));
                            }
                            Ok(None) => {
                                info!("Child still running after max iterations, returning None");
                                // Child还在运行，但无stdout数据
                                // 主循环会继续调用此函数
                                return Ok((None, false, false));
                            }
                            Err(e) => {
                                warn!("Final child check error: {}", e);
                            }
                        }
                    }
                }
            }
        }
        
// ⭐⭐⭐⭐⭐ 处理找到的数据（如果found_data）
        // 3. 检查client fd状态（包括EOF/HUP）
        if let Some(revents) = poll_fds_vec[client_fd_idx].revents() {
            if revents.contains(PollFlags::POLLIN) {
                info!("Client fd has data (stdin from client)");
                client_has_data = true;
            } else if revents.contains(PollFlags::POLLHUP) {
                info!("Client fd hangup (EOF received from client)");
                // ⭐⭐⭐⭐⭐ Phase 14.2关键修复：关闭stdin pipe，发送EOF给child
                // 参考：OpenSSH session.c: do_exec_no_pty() stdin handling
                for (_, channel) in &mut self.channels {
                    if let Some(exec_process) = &mut channel.exec_process {
                        if exec_process.stdin.is_some() {
                            info!("Closing stdin pipe (sending EOF to child process)");
                            exec_process.stdin = None;  // Drop stdin，发送EOF给child
                        }
                    }
                }
                client_has_data = false;
            } else if revents.contains(PollFlags::POLLERR) {
                warn!("Client fd error");
                return Err(anyhow::anyhow!("Client socket error"));
            }
        }
        
        // 4. 检查stdout/stderr fd是否有数据
        let mut packets_data: Vec<(u32, Vec<u8>)> = Vec::new();
        
        for (channel_id, (stdout_idx, stderr_idx)) in channel_fds_map {
            if let Some(channel) = self.channels.get_mut(&channel_id) {
                if let Some(exec_process) = &mut channel.exec_process {
                    // 检查stdout
                    if let Some(revents) = poll_fds_vec[stdout_idx].revents() {
                        if revents.contains(PollFlags::POLLIN) {
                            info!("stdout fd has data (channel {})", channel_id);
                            if let Some(stdout) = &mut exec_process.stdout {
                                let mut buffer = vec![0u8; 32768];
                                match stdout.read(&mut buffer) {
                                    Ok(n) if n > 0 => {
                                        info!("Read {} bytes from stdout (channel {})", n, channel_id);
                                        packets_data.push((channel_id, buffer[..n].to_vec()));
                                    }
                                    Ok(0) => {
                                        info!("stdout EOF (channel {}), closing stdout pipe", channel_id);
                                        // ⭐⭐⭐⭐⭐ Critical修复：EOF时关闭pipe，避免无限循环
                                        exec_process.stdout = None;
                                    }
                                    Err(e) if e.kind() != std::io::ErrorKind::WouldBlock => {
                                        warn!("stdout read error: {}", e);
                                        exec_process.stdout = None;  // 错误时也关闭
                                    }
                                    _ => {}
                                }
                            }
                        }
                    }
                    
                    // 检查stderr
                    if let Some(revents) = poll_fds_vec[stderr_idx].revents() {
                        if revents.contains(PollFlags::POLLIN) {
                            info!("stderr fd has data (channel {})", channel_id);
                            if let Some(stderr) = &mut exec_process.stderr {
                                let mut buffer = vec![0u8; 32768];
                                match stderr.read(&mut buffer) {
                                    Ok(n) if n > 0 => {
                                        info!("Read {} bytes from stderr (channel {})", n, channel_id);
                                        packets_data.push((channel_id, buffer[..n].to_vec()));
                                    }
                                    Ok(0) => {
                                        info!("stderr EOF (channel {}), closing stderr pipe", channel_id);
                                        // ⭐⭐⭐⭐⭐ Critical修复：EOF时关闭pipe，避免无限循环
                                        exec_process.stderr = None;
                                    }
                                    Err(e) if e.kind() != std::io::ErrorKind::WouldBlock => {
                                        warn!("stderr read error: {}", e);
                                        exec_process.stderr = None;  // 错误时也关闭
                                    }
                                    _ => {}
                                }
                            }
                        }
                    }
                }
            }
        }
        
        // 构建packets
        if !packets_data.is_empty() {
            let mut packets = Vec::new();
            for (channel_id, data) in packets_data {
                let packet = self.build_channel_data(channel_id, &data)?;
                packets.push(packet);
            }
            return Ok((Some(packets), client_has_data, child_exited));
        }
        
        // ⭐⭐⭐⭐⭐ Phase 14.2最终修复：stdout/stderr EOF后检查child exited
        // 当stdout和stderr都关闭后，强制检查child状态
        for channel_id in &channel_ids_vec {
            if let Some(channel) = self.channels.get_mut(channel_id) {
                if let Some(exec_process) = &mut channel.exec_process {
                    // 检查stdout和stderr是否都已关闭
                    if exec_process.stdout.is_none() && exec_process.stderr.is_none() {
                        info!("stdout/stderr both closed (channel {}), checking child status", channel_id);
                        
                        // ⭐⭐⭐⭐⭐ 立即检查child是否exited
                        match exec_process.child.try_wait() {
                            Ok(Some(status)) => {
                                info!("⭐⭐⭐⭐⭐ Child exited after stdout/stderr EOF (status: {:?})", status);
                                child_exited = true;
                                
                                // ⭐⭐⭐⭐⭐ 关键：立即返回child_exited标志
                                // server.rs会发送SSH_MSG_CHANNEL_EOF + CLOSE
                                return Ok((None, false, true));
                            }
                            Ok(None) => {
                                // Child still running but stdout/stderr closed
                                // 等待child exited
                                info!("Child still running after pipes closed, waiting...");
                            }
                            Err(e) => {
                                warn!("Child try_wait error after pipes closed: {}", e);
                            }
                        }
                    }
                }
            }
        }
        
        // 有数据但只有client数据
        Ok((None, client_has_data, child_exited))
    }
    
    // ⭐⭐⭐⭐⭐ Phase 14.0: 旧版poll（仅监听stdout/stderr，已废弃）
    /// 已废弃：使用poll_exec_stdout_and_client()替代
    #[allow(dead_code)]
    pub fn poll_exec_stdout_with_fds(&mut self) -> Result<Option<Vec<SshPacket>>> {
        use std::io::Read;
        use std::os::unix::io::BorrowedFd;
        
        // 遍历所有channel，收集poll_fds
        let mut poll_fds_vec = Vec::new();
        let mut channel_fds_map: HashMap<u32, (usize, usize)> = HashMap::new();  // channel_id -> (stdout_idx, stderr_idx) in poll_fds_vec
        
        for (channel_id, channel) in &self.channels {
            if let Some(exec_process) = &channel.exec_process {
                // ⭐⭐⭐⭐⭐ OpenSSH风格：创建PollFd监听stdout/stderr
                // nix 0.29 API: PollFd::new()需要借用fd，不是RawFd
                if let Some(stdout) = &exec_process.stdout {
                    let stdout_poll_fd = unsafe {
                        // ⭐⭐⭐⭐⭐ 使用BorrowedFd::borrow_raw()（正确API）
                        BorrowedFd::borrow_raw(exec_process.stdout_fd)
                    };
                    poll_fds_vec.push(PollFd::new(stdout_poll_fd, PollFlags::POLLIN));
                }
                
                if let Some(stderr) = &exec_process.stderr {
                    let stderr_poll_fd = unsafe {
                        BorrowedFd::borrow_raw(exec_process.stderr_fd)
                    };
                    poll_fds_vec.push(PollFd::new(stderr_poll_fd, PollFlags::POLLIN));
                }
                
                // 记录poll_fds_vec中的索引
                let stdout_idx = poll_fds_vec.len() - 2;
                let stderr_idx = poll_fds_vec.len() - 1;
                channel_fds_map.insert(*channel_id, (stdout_idx, stderr_idx));
            }
        }
        
        if poll_fds_vec.is_empty() {
            return Ok(None);  // 没有exec_process
        }
        
        // ⭐⭐⭐⭐⭐ OpenSSH关键：使用poll监听所有fd
        // ⭐⭐⭐⭐⭐ 持续poll机制：最多轮询1000次（给大文件传输足够时间）
        // 大文件传输需要很长时间，增加轮询次数到1000次（总共10秒）
        let max_poll_attempts = 1000;
        let mut poll_attempt = 0;
        let mut found_data = false;
        
        for attempt in 0..max_poll_attempts {
            poll_attempt = attempt;
            // 每100次轮询记录一次日志（减少日志噪音）
            if attempt % 100 == 0 {
                info!("Polling {} fds (OpenSSH style, timeout 10ms, attempt {} of {})", poll_fds_vec.len(), attempt, max_poll_attempts);
            }
            match poll(&mut poll_fds_vec, 10u16) {  // timeout 10ms
                Ok(n) => {
                    if n > 0 {
                        info!("{} fds have data available (attempt {})", n, attempt);
                        found_data = true;
                        break;  // 有数据，立即处理
                    }
                    // 没有数据，继续轮询（最多1000次）
                }
                Err(e) => {
                    warn!("poll error: {}", e);
                    return Ok(None);
                }
            }
        }
        
        if !found_data {
            info!("No data available after {} poll attempts ({} ms), returning None", max_poll_attempts, max_poll_attempts * 10);
            return Ok(None);  // 轮询1000次后仍无数据，主循环继续处理client packet
        }
        
        // ⭐⭐⭐⭐⭐ OpenSSH风格：根据revents判断哪个fd有数据，立即读取
        let mut packets_data: Vec<(u32, Vec<u8>)> = Vec::new();  // (channel_id, data)
        
        for (channel_id, (stdout_idx, stderr_idx)) in channel_fds_map {
            if let Some(channel) = self.channels.get_mut(&channel_id) {
                if let Some(exec_process) = &mut channel.exec_process {
                    // 检查stdout是否有数据
                    if let Some(revents) = poll_fds_vec[stdout_idx].revents() {
                        if revents.contains(PollFlags::POLLIN) {
                            info!("stdout fd has data (channel {})", channel_id);
                            // ⭐⭐⭐⭐⭐ 非阻塞读取（因为设置了O_NONBLOCK）
                            if let Some(stdout) = &mut exec_process.stdout {
                                let mut buffer = vec![0u8; 32768];
                                match stdout.read(&mut buffer) {
                                    Ok(n) => {
                                        if n > 0 {
                                            info!("Read {} bytes from stdout (channel {})", n, channel_id);
                                            packets_data.push((channel_id, buffer[..n].to_vec()));
                                        } else {
                                            info!("stdout EOF (channel {})", channel_id);
                                        }
                                    }
                                    Err(e) if e.kind() == std::io::ErrorKind::WouldBlock => {
                                        // 非阻塞模式，没有数据（正常）
                                    }
                                    Err(e) => {
                                        warn!("stdout read error: {}", e);
                                    }
                                }
                            }
                        }
                    }
                    
                    // 检查stderr是否有数据（类似处理）
                    if let Some(revents) = poll_fds_vec[stderr_idx].revents() {
                        if revents.contains(PollFlags::POLLIN) {
                            info!("stderr fd has data (channel {})", channel_id);
                            if let Some(stderr) = &mut exec_process.stderr {
                                let mut buffer = vec![0u8; 32768];
                                match stderr.read(&mut buffer) {
                                    Ok(n) => {
                                        if n > 0 {
                                            info!("Read {} bytes from stderr (channel {})", n, channel_id);
                                            packets_data.push((channel_id, buffer[..n].to_vec()));
                                        } else {
                                            info!("stderr EOF (channel {})", channel_id);
                                        }
                                    }
                                    Err(e) if e.kind() == std::io::ErrorKind::WouldBlock => {
                                        // 非阻塞模式，没有数据（正常）
                                    }
                                    Err(e) => {
                                        warn!("stderr read error: {}", e);
                                    }
                                }
                            }
                        }
                    }
                }
            }
        }
        
        // ⭐⭐⭐⭐⭐ 释放mutable borrow后，构建packets（避免borrow冲突）
        let mut packets = Vec::new();
        for (channel_id, data) in packets_data {
            let packet = self.build_channel_data(channel_id, &data)?;
            packets.push(packet);
        }
        
        if packets.is_empty() {
            Ok(None)
        } else {
            Ok(Some(packets))
        }
    }
}

/// SSH Channel结构（参考OpenSSH channel.c: struct channel）
struct Channel {
    server_channel: u32,
    sender_channel: u32,
    channel_type: String,
    window_size: u32,
    maximum_packet_size: u32,
    state: ChannelState,
    output_buffer: Option<Vec<u8>>,  // Phase 6: 命令输出缓冲
    sftp_handler: Option<SftpHandler>,  // Phase 7: SFTP处理器
    scp_handler: Option<ScpHandler>,  // Phase 8: SCP处理器
    rsync_handler: Option<RsyncHandler>,  // Phase 8: rsync处理器
    exec_process: Option<ExecProcess>,  // Phase 14: 交互式exec进程
    // ⭐⭐⭐⭐⭐ Critical修复：SFTP packet累积buffer
    sftp_input_buffer: Vec<u8>,  // Phase 14.2修复：累积不完整的SFTP packets
    // ⭐⭐⭐⭐⭐ Phase 14.4：SCP packet累积buffer
    scp_input_buffer: Vec<u8>,   // Phase 14.4修复：累积不完整的SCP packets
    // Phase 13.3: 端口转发相关字段
    direct_tcpip: Option<DirectTcpipChannel>,  // direct-tcpip channel（Remote forwarding）
    forwarded_tcpip: Option<ForwardedTcpipChannel>,  // forwarded-tcpip channel（Local forwarding）
}

/// SSH Channel状态（参考OpenSSH channel.c）
enum ChannelState {
    Open,
    Closing,
    Closed,
}

/// SSH string读取辅助函数
fn read_ssh_string<R: std::io::Read>(reader: &mut R) -> Result<String> {
    let length = reader.read_u32::<BigEndian>()?;
    let mut buffer = vec![0u8; length as usize];
    reader.read_exact(&mut buffer)?;
    Ok(String::from_utf8(buffer)?)
}

#[cfg(test)]
mod tests {
    use super::*;
    
    #[test]
    fn test_channel_manager_creation() {
        let manager = ChannelManager::new();
        assert_eq!(manager.next_channel_id, 0);
    }
    
    #[test]
    fn test_channel_open_confirmation() {
        let manager = ChannelManager::new();
        let packet = manager.build_channel_open_confirmation(0, 100, 2097152, 32768).unwrap();
        
        assert_eq!(packet.payload[0], PacketType::SSH_MSG_CHANNEL_OPEN_CONFIRMATION as u8);
    }
    
    #[test]
    fn test_channel_success() {
        let manager = ChannelManager::new();
        let packet = manager.build_channel_success(0).unwrap();
        
        assert_eq!(packet.payload[0], PacketType::SSH_MSG_CHANNEL_SUCCESS as u8);
    }
}