file-server

file-server

Secure file server with the following characteristics.

• Public key cryptography is used for authentication
• User information is stored in a PostgreSQL database
• No shell file access

⚠ This is a work in progress and not ready for production yet ⚠

Implementation Status

Working

• SSH public key authentication against keys stored in PostgreSQL; keys added through the API take effect without a restart
• SFTP access confined to each user's own directory
• SFTP operations
  • upload, download and opening files for both reading and writing
  • list directories and stat files
  • create and remove directories (non-empty directories are not removed)
  • remove files
  • rename files and directories without overwriting an existing target
  • set size (truncate), permissions, and access and modification times
• Interactive shell sessions are rejected with a message
• SSH idle timeout and a cap on concurrent SSH connections
• HTTP API to create, list and delete users and their public keys, with Swagger documentation
• Graceful shutdown of both the SSH and HTTP servers on SIGINT/SIGTERM

To be implemented

• Authentication and authorisation of the HTTP API; administrative_users is validated at startup but not used yet
• SFTP operations that currently return an error
  • symbolic and hard links (Symlink, Link, Lstat, Readlink)
  • posix-rename@openssh.com and statvfs@openssh.com extensions
  • changing file ownership
• Removal of a user's directory when the user is deleted (it is currently left on disk)

Storage

• Files of each user are stored in <path_users_directory>/<username>, which is created on the first SFTP session. SFTP clients cannot reach anything outside this directory.
• Users and their public keys are stored in PostgreSQL tables users and user_credentials. The schema is migrated automatically at startup. A user cannot be deleted while it still has credentials.

Configuration

Configuration is loaded via viper. Environment variables take precedence over the configuration file.

Command-line flags

The server accepts no command-line flags or arguments.

Configuration file

A configuration file named .file-server.<ext> in the user's home directory is loaded automatically if it exists. Supported extensions include yaml, yml, json, toml, properties, and ini. Keys are the environment variables without the FILESERVER_ prefix.

host_key: ./keys/ecdsa.key
ssh_port: 8822
api_port: 8880
path_users_directory: ./data/files
path_database_connection_string: ./keys/database_connection_string
ssh_idle_timeout: 5m
ssh_max_connections: 100
administrative_users:
  - alex

Environment variables

All environment variables are prefixed with FILESERVER_.

task run sets all of the above with development defaults, except FILESERVER_SSH_IDLE_TIMEOUT and FILESERVER_SSH_MAX_CONNECTIONS, which use their defaults.

HTTP API

The API manages users and their SSH public keys. It is currently unauthenticated; do not expose the API port publicly.

Swagger UI is served at /docs/index.html.

Development

1. Create the files under keys/ (gitignored):
   • ecdsa.key — SSH host key, generated by task gen-key
   • database_password — password of the Postgres container
   • database_connection_string — connection string for task run
   • database_connection_string_docker — connection string used by the file-server container in docker-compose.yml
2. Create data/files.
3. task run starts Postgres and the server.

Tests:

• task test runs all tests; API tests are skipped without a test database.
• task test-api creates the file_server_test database in the Postgres container and runs the API tests against it.

References

• SSH File Transfer Protocol
• Request based SFTP API - pkg/sftp