问MD5在F#中的应用

EN

open System.IO
open System.Security.Cryptography

/// Given a sequence of filenames, looks for duplicate files by comparing file lengths
/// and, if necessary, hash values calculated using the specified hash algorithm.
/// Returns a sequence of tuples; the first item in the tuple is a hash value and the
/// second item is a sequence containing the names of two or more files which have
/// the same length and hash value.
let findDuplicateFiles (algorithm : HashAlgorithm) (filenames : seq<string>) =
    filenames
    |> Seq.groupBy (fun filename ->
        (FileInfo filename).Length)
    |> Seq.collect (fun (_, sameLengthFilenames) ->
        // If there's only one file with this length, there's no duplication so don't return it.
        if Seq.length sameLengthFilenames = 1 then Seq.empty
        else
            // Possible duplication. Resolve by hashing the files and comparing the hashes.
            sameLengthFilenames
            |> Seq.groupBy (fun filename ->
                using (File.OpenRead filename) algorithm.ComputeHash)
            // Check for multiple files with the same hash value.
            // Return any such filenames so outside code can determine how to handle them.
            |> Seq.filter (fun (_, sameLengthFilenames) ->
                // Collision when two or more files have the same hash.
                Seq.length sameLengthFilenames > 2))

/// Given a sequence of filenames, looks for duplicate files by comparing file lengths
/// and, if necessary, hash values calculated using the SHA256 algorithm.
/// Returns a sequence of tuples; the first item in the tuple is a hash value and the
/// second item is a sequence containing the names of two or more files which have
/// the same length and hash value.
let findDuplicateFilesSHA256 filenames =
    // NOTE: The algorithm should be bound with 'use' or 'using' here so it can be disposed,
    //       but the F# 3.1 compiler appears to dispose the object too early.
    findDuplicateFiles (SHA256.Create()) filenames

//
let printDuplicateEntry (hash : byte[], filenames : seq<string>) =
    stdout.WriteLine ""
    stdout.Write "Hash: "
    stdout.WriteLine (System.BitConverter.ToString(hash).Replace("-", ""))
    for filename in filenames do
        printfn "    %s (Length: %i)" filename ((FileInfo filename).Length)

//
let findDuplicateFilesInDirectory path =
    Directory.EnumerateFiles (path)
    |> findDuplicateFilesSHA256
    |> Seq.iter printDuplicateEntry
;;

// Example usage:
findDuplicateFilesInDirectory @"C:\Users\Jack\Desktop";;