Update Phase 6: Fix SFTP subsystem initialization and data handling

Phase 6 updates:
- Add SftpHandler integration in Channel structure
- Initialize SFTP handler on subsystem request
- Handle SFTP packets via CHANNEL_DATA
- Fix CHANNEL_DATA response handling in server loop

Phase 7 progress:
- SFTP subsystem initialization working
- SSH_FXP_INIT/VERSION handshake working
- SFTP packet format partially implemented
- Need further debugging for complete SFTP functionality

Current status:
- SSH command execution fully working (Phase 6 ✓)
- SFTP connection initialization working
- File transfer operations pending debug

markbase-core/src/ssh_server/channel.rs

@@ -8,6 +8,8 @@ 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 std::path::PathBuf;  // Phase 7: Path for SFTP root directory
 
 /// SSH Channel管理器（参考OpenSSH channel.c: struct channel）
 pub struct ChannelManager {
@@ -73,6 +75,7 @@ impl ChannelManager {
             maximum_packet_size,
             state: ChannelState::Open,
             output_buffer: None,  // Phase 6: 初始化为空
+            sftp_handler: None,  // Phase 7: 初始化为空
         };
         
         self.channels.insert(server_channel, channel);
@@ -184,7 +187,17 @@ impl ChannelManager {
         // 检查subsystem支持（OpenSSH支持：sftp）
         if subsystem == "sftp" {
             info!("SFTP subsystem requested");
-            // Phase 7将实现SFTP
+            
+            // 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 {
@@ -258,10 +271,10 @@ impl ChannelManager {
     }
     
     /// 处理SSH_MSG_CHANNEL_DATA（参考OpenSSH channel.c: channel_input_data())
-    pub fn handle_channel_data(&mut self, packet: &SshPacket) -> Result<()> {
+    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());  // 使用as_slice()（Rust标准）
+        let mut cursor = std::io::Cursor::new(packet.payload.as_slice());
         
         // Packet type
         let packet_type = cursor.read_u8()?;
@@ -273,13 +286,41 @@ impl ChannelManager {
         let recipient_channel = cursor.read_u32::<BigEndian>()?;
         
         // 读取数据（SSH string）
-        let data = read_ssh_string(&mut cursor)?;
+        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())]);
         
-        // 简化实现：接受数据（实际应处理）
+        // Phase 7: 检查是否是SFTP channel
+        if let Some(channel) = self.channels.get_mut(&recipient_channel) {
+            if let Some(sftp_handler) = &mut channel.sftp_handler {
+                info!("Processing SFTP request ({} bytes)", data.len());
+                
+                // SFTP data是SSH string格式：前4 bytes是length field
+                // 真正的SFTP packet从data[4]开始（跳过length field）
+                if data.len() < 4 {
+                    warn!("SFTP data too short (less than 4 bytes)");
+                    return Ok(None);
+                }
+                
+                let sftp_packet_length = u32::from_be_bytes([data[0], data[1], data[2], data[3]]) as usize;
+                let sftp_packet = &data[4..4 + sftp_packet_length];
+                
+                info!("SFTP packet: length={}, content={:?}", sftp_packet_length, &sftp_packet[..std::cmp::min(20, sftp_packet.len())]);
+                
+                // 处理SFTP请求
+                let response = sftp_handler.handle_request(sftp_packet)?;
+                info!("SFTP response: {} bytes", response.len());
+                
+                // 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)?));
+            }
+        }
         
-        Ok(())
+        // 如果不是SFTP，返回None（Phase 6的普通channel data处理）
+        Ok(None)
     }
     
     /// 处理SSH_MSG_CHANNEL_CLOSE（参考OpenSSH channel.c: channel_input_close())
@@ -455,6 +496,7 @@ struct Channel {
     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
 }
 
 /// SSH Channel状态（参考OpenSSH channel.c）