SFTP API in C++: libssh vs. Boost.Asio

Published {$created} by Carsten Blum

When it comes to creating a storage API using SFTP in C++, you have a few options. Two popular choices are using the libssh library and leveraging Boost.Asio directly. Both approaches have their strengths and weaknesses, so let's dive into a comparison.

libssh: The Established SFTP Library

libssh is a well-established C library for SSH2. It provides a comprehensive API for SFTP functionality, including file transfers, directory manipulation, and authentication. It's a battle-tested solution widely used in various projects.

Pros:

• Complete SFTP Implementation: libssh handles all the complexities of the SFTP protocol, freeing you from having to implement those details yourself.
• Established and Mature: Large community support and extensive documentation.
• Authentication Flexibility: Supports various authentication methods, including password, SSH keys (RSA, ECDSA-SHA2-NISTP256, and SSH-ED25519 - the latter being recommended for its security advantages - see [tutorials/advanced-ssh-key-authentication-for-sftp/]), as covered in our tutorials on key-based authentication.
• Ease of Use: The API is relatively straightforward, with clear functions for common operations.

Cons:

• Dependency: Introduces a dependency on an external library. While libssh is widely available, it's another thing to manage.
• Less Control: You're somewhat constrained by libssh's API. Fine-grained control over low-level details can be limited.
• Potential for Bloat: If you only need basic SFTP functionality, libssh might bring in more code than necessary.

Boost.Asio: Building Your Own SFTP Layer

Boost.Asio is a powerful C++ library for network and timing I/O. You can use it to implement your own SFTP client, essentially building your own SFTP layer on top of the underlying TCP connection. This is significantly more work.

Pros:

• Maximum Control: You have complete control over every aspect of the SFTP client. This allows for optimization and customization beyond what’s possible with a library like libssh.
• No External Dependency (Potentially): If you only use Asio for SFTP and not other networking tasks, you can potentially minimize the impact of adding a dependency.
• Learning Experience: Implementing SFTP yourself is a fantastic learning opportunity to understand the protocol's inner workings.

Cons:

• Significant Development Effort: Implementing SFTP from scratch is a substantial undertaking, requiring deep protocol knowledge. You're responsible for handling all the error conditions, security considerations, and potential vulnerabilities.
• Increased Complexity: Your code becomes more complex, making it harder to maintain and debug.
• Time Consuming: Building and testing a reliable SFTP client takes considerable time.

Which to Choose?

For most projects, libssh is the clear winner. The development time saved and the reliability of a well-tested library outweigh the minor downsides of an external dependency. You can easily integrate it into your C++ project. If you’re looking for a way to backup Reolink camera footage, or Axis camera recordings, libssh is your friend. Our tutorials/quick-storage-api-cpp-sftp-ftp/ showcases how easy it is.

Only consider building your own SFTP layer using Boost.Asio if you have very specific requirements that cannot be met by existing libraries and you have the resources to dedicate to the effort. Consider the implications and benefits of managed FTP hosting as a viable alternative as covered in tutorials/managed-ftp-hosting-vs-sftp-cloud-hosting/

At ftpGrid, we handle the complexities of SFTP for you. Our tutorials/quick-storage-api-series-sftp-ftp/ shows you how to leverage our API. You can use our service via SFTP.