SourceFile: archive.zip
FileSize: 104857600
PartCount: 10
ChunkSize: 1048576
MD5: a1b2c3d4e5f6...

using System;
using System.IO;
using System.Security.Cryptography;
using System.Text;
public class FileSplitter
{
    /// <summary>
    /// 分割文件為多個(gè)子文件
    /// </summary>
    /// <param name="sourcePath">源文件路徑</param>
    /// <param name="outputDir">輸出目錄（默認(rèn)源文件所在目錄）</param>
    /// <param name="chunkSizeBytes">子文件大?。ㄗ止?jié)，默認(rèn) 1MB）</param>
    /// <param name="generateInfoFile">是否生成 .info 元數(shù)據(jù)文件</param>
    /// <returns>分割后的子文件數(shù)量</returns>
    public static int SplitFile(string sourcePath, string outputDir = null, 
        long chunkSizeBytes = 1024 * 1024, bool generateInfoFile = true)
    {
        // 參數(shù)校驗(yàn)
        if (!File.Exists(sourcePath))
            throw new FileNotFoundException($"源文件不存在: {sourcePath}");
        if (chunkSizeBytes <= 0)
            throw new ArgumentException("分塊大小必須大于 0", nameof(chunkSizeBytes));
        // 確定輸出目錄
        outputDir ??= Path.GetDirectoryName(sourcePath);
        Directory.CreateDirectory(outputDir);
        string fileName = Path.GetFileName(sourcePath);
        string baseName = Path.GetFileNameWithoutExtension(sourcePath);
        string extension = Path.GetExtension(sourcePath);
        string fullBaseName = baseName + extension;
        // 計(jì)算 MD5（需要在讀取流之前計(jì)算，或重新打開流）
        string md5Hash = string.Empty;
        if (generateInfoFile)
            md5Hash = CalculateFileMD5(sourcePath);
        using (FileStream sourceStream = new FileStream(sourcePath, FileMode.Open, FileAccess.Read))
        {
            long fileSize = sourceStream.Length;
            int partCount = (int)Math.Ceiling((double)fileSize / chunkSizeBytes);
            byte[] buffer = new byte[chunkSizeBytes];
            // 生成元數(shù)據(jù)文件
            if (generateInfoFile)
            {
                string infoPath = Path.Combine(outputDir, $"{fullBaseName}.info");
                using (StreamWriter infoWriter = new StreamWriter(infoPath, false, Encoding.UTF8))
                {
                    infoWriter.WriteLine($"SourceFile: {fileName}");
                    infoWriter.WriteLine($"FileSize: {fileSize}");
                    infoWriter.WriteLine($"PartCount: {partCount}");
                    infoWriter.WriteLine($"ChunkSize: {chunkSizeBytes}");
                    infoWriter.WriteLine($"MD5: {md5Hash}");
                    infoWriter.WriteLine($"CreatedAt: {DateTime.Now:yyyy-MM-dd HH:mm:ss}");
                }
            }
            // 執(zhí)行分割
            for (int i = 0; i < partCount; i++)
            {
                long position = i * chunkSizeBytes;
                int bytesToRead = (int)Math.Min(chunkSizeBytes, fileSize - position);
                sourceStream.Seek(position, SeekOrigin.Begin);
                int bytesRead = sourceStream.Read(buffer, 0, bytesToRead);
                if (bytesRead != bytesToRead)
                    Console.WriteLine($"警告: 第 {i + 1} 個(gè)分塊實(shí)際讀取 {bytesRead} 字節(jié)，預(yù)期 {bytesToRead} 字節(jié)");
                string partPath = Path.Combine(outputDir, $"{fullBaseName}.part{i + 1}");
                using (FileStream partStream = new FileStream(partPath, FileMode.Create, FileAccess.Write))
                {
                    partStream.Write(buffer, 0, bytesRead);
                }
                Console.WriteLine($"[分割] 已創(chuàng)建: {Path.GetFileName(partPath)} ({bytesRead} 字節(jié))");
            }
            Console.WriteLine($"分割完成: {partCount} 個(gè)分塊，輸出目錄: {outputDir}");
            return partCount;
        }
    }
    /// <summary>
    /// 計(jì)算文件的 MD5 校驗(yàn)值
    /// </summary>
    private static string CalculateFileMD5(string filePath)
    {
        using (var md5 = MD5.Create())
        using (var stream = File.OpenRead(filePath))
        {
            byte[] hash = md5.ComputeHash(stream);
            return BitConverter.ToString(hash).Replace("-", "").ToLowerInvariant();
        }
    }
}

public class FileMerger
{
    /// <summary>
    /// 合并子文件為完整文件
    /// </summary>
    /// <param name="partDirectory">子文件所在目錄</param>
    /// <param name="originalFileName">原文件名（如 "archive.zip"）</param>
    /// <param name="outputPath">合并后的輸出路徑</param>
    /// <param name="verifyIntegrity">是否校驗(yàn) MD5（需要 .info 文件）</param>
    /// <returns>合并后的文件大?。ㄗ止?jié)）</returns>
    public static long MergeFiles(string partDirectory, string originalFileName, 
        string outputPath, bool verifyIntegrity = true)
    {
        if (!Directory.Exists(partDirectory))
            throw new DirectoryNotFoundException($"目錄不存在: {partDirectory}");
        string extension = Path.GetExtension(originalFileName);
        string baseName = Path.GetFileNameWithoutExtension(originalFileName);
        string fullBaseName = baseName + extension;
        string pattern = $"{fullBaseName}.part*";
        // 獲取并排序分塊文件
        string[] partFiles = Directory.GetFiles(partDirectory, pattern, SearchOption.TopDirectoryOnly);
        if (partFiles.Length == 0)
            throw new FileNotFoundException($"未找到匹配的分塊文件: {pattern}");
        // 按序號(hào)排序（解析 partN 中的 N）
        Array.Sort(partFiles, (a, b) =>
        {
            int indexA = ExtractPartNumber(a, fullBaseName);
            int indexB = ExtractPartNumber(b, fullBaseName);
            return indexA.CompareTo(indexB);
        });
        // 驗(yàn)證序號(hào)連續(xù)性（可選）
        for (int i = 0; i < partFiles.Length; i++)
        {
            int expected = i + 1;
            int actual = ExtractPartNumber(partFiles[i], fullBaseName);
            if (actual != expected)
                throw new InvalidOperationException($"分塊序號(hào)不連續(xù): 期望 {expected}，實(shí)際 {actual}");
        }
        // 合并文件
        using (FileStream outputStream = new FileStream(outputPath, FileMode.Create, FileAccess.Write))
        {
            foreach (string partPath in partFiles)
            {
                using (FileStream partStream = new FileStream(partPath, FileMode.Open, FileAccess.Read))
                {
                    partStream.CopyTo(outputStream);
                }
                Console.WriteLine($"[合并] 已處理: {Path.GetFileName(partPath)}");
            }
        }
        Console.WriteLine($"合并完成: {outputPath}");
        long mergedSize = new FileInfo(outputPath).Length;
        // 完整性校驗(yàn)
        if (verifyIntegrity)
        {
            string infoPath = Path.Combine(partDirectory, $"{fullBaseName}.info");
            if (File.Exists(infoPath))
            {
                var metadata = ParseInfoFile(infoPath);
                string expectedMd5 = metadata["MD5"];
                string actualMd5 = CalculateFileMD5(outputPath);
                if (string.Equals(expectedMd5, actualMd5, StringComparison.OrdinalIgnoreCase))
                {
                    Console.WriteLine($"[校驗(yàn)] MD5 一致: {actualMd5}");
                }
                else
                {
                    Console.WriteLine($"[警告] MD5 不一致! 期望: {expectedMd5}, 實(shí)際: {actualMd5}");
                }
            }
            else
            {
                Console.WriteLine("[校驗(yàn)] 未找到 .info 文件，跳過 MD5 校驗(yàn)");
            }
        }
        return mergedSize;
    }
    /// <summary>
    /// 從文件名中提取分塊序號(hào)（如 file.zip.part3 → 3）
    /// </summary>
    private static int ExtractPartNumber(string filePath, string fullBaseName)
    {
        string fileName = Path.GetFileNameWithoutExtension(filePath);
        // 文件名格式: fullBaseName.partN
        string suffix = fileName.Substring(fullBaseName.Length + 1); // ".partN" → "partN"
        if (suffix.StartsWith("part", StringComparison.OrdinalIgnoreCase))
        {
            string numberPart = suffix.Substring(4);
            if (int.TryParse(numberPart, out int number))
                return number;
        }
        throw new InvalidOperationException($"無法解析分塊序號(hào): {filePath}");
    }
    private static Dictionary<string, string> ParseInfoFile(string infoPath)
    {
        var dict = new Dictionary<string, string>();
        foreach (var line in File.ReadAllLines(infoPath))
        {
            int colonIndex = line.IndexOf(':');
            if (colonIndex > 0)
            {
                string key = line.Substring(0, colonIndex).Trim();
                string value = line.Substring(colonIndex + 1).Trim();
                dict[key] = value;
            }
        }
        return dict;
    }
    private static string CalculateFileMD5(string filePath)
    {
        using (var md5 = MD5.Create())
        using (var stream = File.OpenRead(filePath))
        {
            byte[] hash = md5.ComputeHash(stream);
            return BitConverter.ToString(hash).Replace("-", "").ToLowerInvariant();
        }
    }
}

class Program
{
    static void Main(string[] args)
    {
        Console.WriteLine("=== 文件分割/合并工具 v2.0 ===");
        Console.WriteLine("1. 分割文件");
        Console.WriteLine("2. 合并文件");
        Console.Write("請(qǐng)選擇 (1/2): ");
        string choice = Console.ReadLine();
        try
        {
            if (choice == "1")
            {
                Console.Write("源文件路徑: ");
                string source = Console.ReadLine();
                Console.Write("分塊大小 (MB，默認(rèn) 1): ");
                string sizeInput = Console.ReadLine();
                int mb = string.IsNullOrWhiteSpace(sizeInput) ? 1 : int.Parse(sizeInput);
                Console.Write("輸出目錄 (留空則使用源文件目錄): ");
                string outputDir = Console.ReadLine();
                outputDir = string.IsNullOrWhiteSpace(outputDir) ? null : outputDir;
                FileSplitter.SplitFile(source, outputDir, mb * 1024L * 1024L);
            }
            else if (choice == "2")
            {
                Console.Write("分塊文件目錄: ");
                string partDir = Console.ReadLine();
                Console.Write("原文件名 (如 largefile.zip): ");
                string originalName = Console.ReadLine();
                Console.Write("合并后輸出路徑: ");
                string output = Console.ReadLine();
                Console.Write("是否校驗(yàn)完整性 (y/n, 默認(rèn) y): ");
                bool verify = Console.ReadLine()?.ToLower() != "n";
                FileMerger.MergeFiles(partDir, originalName, output, verify);
            }
            else
            {
                Console.WriteLine("無效輸入");
            }
        }
        catch (Exception ex)
        {
            Console.WriteLine($"錯(cuò)誤: {ex.Message}");
            if (ex.InnerException != null)
                Console.WriteLine($"詳細(xì)信息: {ex.InnerException.Message}");
        }
        Console.WriteLine("按任意鍵退出...");
        Console.ReadKey();
    }
}

using (var partStream = new FileStream(partPath, FileMode.Open, FileAccess.Read, FileShare.Read, 81920))

Parallel.For(0, partCount, i => { /* 寫入 part i */ });