File Hashing

API

(Note: The high-level file transfer API supports automatic hashing after upload/download).

Standard commands supported by most servers

• HashAlgorithms - Get the hash types supported by the server, if any (represented by flags).

• GetHash() - Gets the hash of an object on the server using the currently selected hash algorithm. Supported algorithms are available in the HashAlgorithms property. You should confirm that it's not equal to FtpHashAlgorithm.NONE (which means the server does not support the HASH command).

• GetHashAlgorithm() - Query the server for the currently selected hash algorithm for the HASH command.

• SetHashAlgorithm() - Selects a hash algorithm for the HASH command, and stores this selection on the server.

Non-standard commands supported by certain servers only. Learn more

• GetChecksum() - Retrieves a checksum of the given file using a checksumming method that the server supports, if any. The algorithm used goes in this order : HASH, MD5, XMD5, XSHA1, XSHA256, XSHA512, XCRC.

• GetMD5() - Retrieves the MD5 checksum of the given file, if the server supports it.

• GetXMD5() - Retrieves the MD5 checksum of the given file, if the server supports it.

• GetXSHA1() - Retrieves the SHA1 checksum of the given file, if the server supports it.

• GetXSHA256() - Retrieves the SHA256 checksum of the given file, if the server supports it.

• GetXSHA512() - Retrieves the SHA512 checksum of the given file, if the server supports it.

• GetXCRC() - Retrieves the CRC32 checksum of the given file, if the server supports it.

FAQs

What kind of hashing commands are supported?

We support XCRC, XMD5, and XSHA which are non-standard commands and contain no kind of formal specification. They are not guaranteed to work and you are strongly encouraged to check the FtpClient.Capabilities flags for the respective flag (XCRC, XMD5, XSHA1, XSHA256, XSHA512) before calling these methods.

Support for the MD5 command as described here has also been added. Again, check for FtpFeature.MD5 before executing the command.

Support for the HASH command has been added to FluentFTP. It supports retrieving SHA-1, SHA-256, SHA-512, and MD5 hashes from servers that support this feature. The returned object, FtpHash, has a method to check the result against a given stream or local file. You can read more about HASH in this draft.

How do I verify the hash/checksum of a file and retry if the checksum mismatches?

Add the FtpVerify options to UploadFile() or DownloadFile() to enable automatic checksum verification.

// retry 3 times when uploading a file
client.RetryAttempts = 3;

// upload a file and retry 3 times before giving up
client.UploadFile(@"C:\MyVideo.mp4", "/htdocs/MyVideo.mp4", FtpExists.Overwrite, false, FtpVerify.Retry);

All the possible configurations are:

• FtpVerify.OnlyChecksum - Verify checksum, return true/false based on success.

• FtpVerify.Delete - Verify checksum, delete target file if mismatch.

• FtpVerify.Retry - Verify checksum, retry copying X times and then give up.

• FtpVerify.Retry | FtpVerify.Throw - Verify checksum, retry copying X times, then throw an error if still mismatching.

• FtpVerify.Retry | FtpVerify.Delete - Verify checksum, retry copying X times, then delete target file if still mismatching.

• FtpVerify.Retry | FtpVerify.Delete | FtpVerify.Throw - Verify checksum, retry copying X times, delete target file if still mismatching, then throw an error