Enhance SFTP error handling in SftpController and SftpService by introducing a method to format SftpException messages. Improve listFiles method to handle empty paths and provide clearer error messages in response to exceptions.

backend/src/main/java/com/sshmanager/controller/SftpController.java

@@ -1,5 +1,6 @@
 package com.sshmanager.controller;
 
+import com.jcraft.jsch.SftpException;
 import com.sshmanager.dto.SftpFileInfo;
 import com.sshmanager.entity.Connection;
 import com.sshmanager.entity.User;
@@ -78,13 +79,28 @@ public class SftpController {
                 .collect(Collectors.toList());
             return ResponseEntity.ok(dtos);
         } catch (Exception e) {
-            log.warn("SFTP list failed: connectionId={}, path={}", connectionId, path, e);
+            String errorMsg = toSftpErrorMessage(e, path, "list");
+            log.warn("SFTP list failed: connectionId={}, path={}, error={}", connectionId, path, errorMsg, e);
             Map<String, String> err = new HashMap<>();
-            err.put("error", e.getMessage() != null ? e.getMessage() : "List failed");
+            err.put("error", errorMsg);
             return ResponseEntity.status(500).body(err);
         }
     }
 
+    private String toSftpErrorMessage(Exception e, String path, String operation) {
+        if (e.getMessage() != null && !e.getMessage().trim().isEmpty()) {
+            return e.getMessage();
+        }
+        Throwable cause = e.getCause();
+        if (cause instanceof SftpException) {
+            return SftpService.formatSftpExceptionMessage((SftpException) cause, path, operation);
+        }
+        if (e instanceof SftpException) {
+            return SftpService.formatSftpExceptionMessage((SftpException) e, path, operation);
+        }
+        return operation + " failed";
+    }
+
     @GetMapping("/pwd")
     public ResponseEntity<Map<String, String>> pwd(
             @RequestParam Long connectionId,

backend/src/main/java/com/sshmanager/service/SftpService.java

@@ -3,6 +3,7 @@ package com.sshmanager.service;
 import com.jcraft.jsch.ChannelSftp;
 import com.jcraft.jsch.JSch;
 import com.jcraft.jsch.Session;
+import com.jcraft.jsch.SftpException;
 import com.sshmanager.entity.Connection;
 import org.springframework.stereotype.Service;
 
@@ -93,7 +94,9 @@ public class SftpService {
     }
 
     public List<FileInfo> listFiles(SftpSession sftpSession, String path) throws Exception {
-        Vector<?> entries = sftpSession.getChannel().ls(path);
+        String listPath = (path == null || path.trim().isEmpty()) ? "." : path.trim();
+        try {
+            Vector<?> entries = sftpSession.getChannel().ls(listPath);
             List<FileInfo> result = new ArrayList<>();
             for (Object obj : entries) {
                 ChannelSftp.LsEntry entry = (ChannelSftp.LsEntry) obj;
@@ -107,6 +110,43 @@ public class SftpService {
                 ));
             }
             return result;
+        } catch (SftpException e) {
+            String msg = formatSftpExceptionMessage(e, listPath, "list");
+            throw new RuntimeException(msg, e);
+        }
+    }
+
+    /**
+     * Build a user-visible message from JSch SftpException (getMessage() is often null).
+     */
+    public static String formatSftpExceptionMessage(SftpException e, String path, String operation) {
+        int id = e.getId();
+        String serverMsg = e.getMessage();
+        String reason = sftpErrorCodeToMessage(id);
+        StringBuilder sb = new StringBuilder();
+        sb.append(reason);
+        if (path != null && !path.isEmpty()) {
+            sb.append(": ").append(path);
+        }
+        if (serverMsg != null && !serverMsg.trim().isEmpty()) {
+            sb.append(" (").append(serverMsg).append(")");
+        } else {
+            sb.append(" [SFTP status ").append(id).append("]");
+        }
+        return sb.toString();
+    }
+
+    private static String sftpErrorCodeToMessage(int id) {
+        switch (id) {
+            case 2: return "No such file or directory";
+            case 3: return "Permission denied";
+            case 4: return "Operation failed";
+            case 5: return "Bad message";
+            case 6: return "No connection";
+            case 7: return "Connection lost";
+            case 8: return "Operation not supported";
+            default: return "SFTP error";
+        }
     }
 
     public byte[] download(SftpSession sftpSession, String remotePath) throws Exception {