Implement SFTP Phase 11: File hash extensions

- Add md5-hash@openssh.com extension (MD5 hash calculation)
- Add sha256-hash@openssh.com extension (SHA256 hash calculation)
- Server-side hash computation using md5 and sha2 crates
- Support offset and length parameters for partial file hashing
- SFTP now 100% complete with 6 extensions (2 new hash extensions)
- Total SFTP operations: 20 core + 6 extensions = 26 operations

file1.txt

@@ -0,0 +1 @@
+/Users/accusys/markbase/data/sftp_test/symlink_to_file1.txt

markbase-core/src/ssh_server/sftp_handler.rs

@@ -852,6 +852,12 @@ impl SftpHandler {
             "posix-rename@openssh.com" => {
                 self.handle_posix_rename(&mut cursor, id)
             }
+            "md5-hash@openssh.com" => {
+                self.handle_md5_hash(&mut cursor, id)
+            }
+            "sha256-hash@openssh.com" => {
+                self.handle_sha256_hash(&mut cursor, id)
+            }
             _ => {
                 warn!("Unsupported SFTP extension: {}", extension_name);
                 self.build_status_response(id, SftpStatus::SSH_FX_FAILURE, &format!("Unsupported extension: {}", extension_name))
@@ -989,6 +995,93 @@ impl SftpHandler {
         }
     }
 
+    /// 处理md5-hash@openssh.com扩展（Phase 11：MD5哈希计算）
+    fn handle_md5_hash(&self, cursor: &mut std::io::Cursor<&[u8]>, id: u32) -> Result<Vec<u8>> {
+        let path = read_sftp_string(cursor)?;
+        let offset = cursor.read_u64::<BigEndian>()?;
+        let length = cursor.read_u64::<BigEndian>()?;
+        
+        info!("md5-hash: path={}, offset={}, length={}", path, offset, length);
+        
+        let full_path = self.resolve_path(&path)?;
+        
+        match File::open(&full_path) {
+            Ok(mut file) => {
+                file.seek(SeekFrom::Start(offset))?;
+                
+                let mut buffer = vec![0u8; length as usize];
+                file.read_exact(&mut buffer)?;
+                
+                // 计算MD5哈希
+                let hash = md5::compute(&buffer);
+                let hash_hex = format!("{:x}", hash);
+                
+                // 构建响应
+                let mut response = Vec::new();
+                response.write_u8(SftpPacketType::SSH_FXP_EXTENDED_REPLY as u8)?;
+                response.write_u32::<BigEndian>(id)?;
+                
+                // hash-algorithm (SSH string)
+                response.write_u32::<BigEndian>(4)?;
+                response.write_all("md5".as_bytes())?;
+                
+                // hash-value (SSH string)
+                response.write_u32::<BigEndian>(hash_hex.len() as u32)?;
+                response.write_all(hash_hex.as_bytes())?;
+                
+                self.wrap_sftp_packet(&response)
+            }
+            Err(e) => {
+                self.build_status_response(id, SftpStatus::SSH_FX_FAILURE, &format!("MD5 hash error: {}", e))
+            }
+        }
+    }
+
+    /// 处理sha256-hash@openssh.com扩展（Phase 11：SHA256哈希计算）
+    fn handle_sha256_hash(&self, cursor: &mut std::io::Cursor<&[u8]>, id: u32) -> Result<Vec<u8>> {
+        let path = read_sftp_string(cursor)?;
+        let offset = cursor.read_u64::<BigEndian>()?;
+        let length = cursor.read_u64::<BigEndian>()?;
+        
+        info!("sha256-hash: path={}, offset={}, length={}", path, offset, length);
+        
+        let full_path = self.resolve_path(&path)?;
+        
+        match File::open(&full_path) {
+            Ok(mut file) => {
+                file.seek(SeekFrom::Start(offset))?;
+                
+                let mut buffer = vec![0u8; length as usize];
+                file.read_exact(&mut buffer)?;
+                
+                // 计算SHA256哈希（使用sha2 crate）
+                use sha2::{Sha256, Digest};
+                let mut hasher = Sha256::new();
+                hasher.update(&buffer);
+                let hash = hasher.finalize();
+                let hash_hex = format!("{:x}", hash);
+                
+                // 构建响应
+                let mut response = Vec::new();
+                response.write_u8(SftpPacketType::SSH_FXP_EXTENDED_REPLY as u8)?;
+                response.write_u32::<BigEndian>(id)?;
+                
+                // hash-algorithm (SSH string)
+                response.write_u32::<BigEndian>(6)?;
+                response.write_all("sha256".as_bytes())?;
+                
+                // hash-value (SSH string)
+                response.write_u32::<BigEndian>(hash_hex.len() as u32)?;
+                response.write_all(hash_hex.as_bytes())?;
+                
+                self.wrap_sftp_packet(&response)
+            }
+            Err(e) => {
+                self.build_status_response(id, SftpStatus::SSH_FX_FAILURE, &format!("SHA256 hash error: {}", e))
+            }
+        }
+    }
+
     /// 解析路径（安全性检查，参考OpenSSH sftp-server.c: path_resolve())
     fn resolve_path(&self, path: &str) -> Result<PathBuf> {
         info!("resolve_path: input={}, root_dir={:?}", path, self.root_dir);