Unity 之 加密Assetbundle不占内存 (转)

原文链接： https://www.xuanyusong.com/archives/4607

AssetBundle.LoadFromMemory基本上是无法在手机上用的，因为要多占一份内存，所以大多Unity项目都不进行资源加密。

Unity2017.2提供了一个新的API AssetBundle.LoadFromStream，通过名字就可以知道它是流加载，那么就不会像AssetBundle.LoadFromMemory那样多占一份很大的内存了。

打包Assetbundle的同时生成加密文件的两个文件分别加载它。

myab.unity3d
encypt_myab.unity3d

    [MenuItem("Tools/BuildAB")]
    static void BuildAB() 
    {
        FileUtil.DeleteFileOrDirectory(Application.streamingAssetsPath);
        Directory.CreateDirectory(Application.streamingAssetsPath);
        var manifest  = BuildPipeline.BuildAssetBundles(Application.streamingAssetsPath, BuildAssetBundleOptions.ChunkBasedCompression | BuildAssetBundleOptions.ForceRebuildAssetBundle, BuildTarget.iOS);
        foreach (var name in manifest.GetAllAssetBundles())
        {
            var uniqueSalt = Encoding.UTF8.GetBytes(name);
            var data = File.ReadAllBytes(Path.Combine(Application.streamingAssetsPath, name));
            using (var myStream = new MyStream(Path.Combine(Application.streamingAssetsPath, "encypt_" + name),FileMode.Create))
            {
                myStream.Write(data, 0, data.Length);
            }
        }
        AssetDatabase.Refresh();
    }

这里测试的Assetbundle一共有20M， 使用LZ4压缩格式。

加密和解密我这里随便写个简单的异或 ^ 。后面也可以用一些更好的算法，总之加密可以慢，但是解密一定要快。

using System.IO;
 
public class MyStream : FileStream
{
 
    const byte KEY = 64;
    public MyStream(string path, FileMode mode, FileAccess access, FileShare share, int bufferSize, bool useAsync) : base(path, mode, access, share, bufferSize, useAsync)
    {
    }
    public MyStream(string path, FileMode mode) : base(path, mode)
    {
    }
    public override int Read(byte[] array, int offset, int count)
    {
        var index =  base.Read(array, offset, count);
        for (int i = 0 ; i < array.Length; i++)
        {
            array[i] ^= KEY;
        }
        return index;
    }
    public override void Write(byte[] array, int offset, int count)
    {
        for (int i = 0; i < array.Length; i ++)
        {
            array[i] ^= KEY;
        }
        base.Write(array, offset, count);
    }
}

界面上放两个Image 分别加载它。

using System.IO;
using UnityEngine;
using UnityEngine.UI;
 
public class TestStream : MonoBehaviour
{
    [Header("是否启用Stream加载")]
    public bool isStream = true;
    float m_LoadTime ;
    void Start()
    {
        if (isStream)
        {
            float t = Time.realtimeSinceStartup;
            using (var fileStream = new MyStream(Application.streamingAssetsPath + "/encypt_myab.unity3d", FileMode.Open, FileAccess.Read, FileShare.None, 1024 * 4, false))
            {
                var myLoadedAssetBundle = AssetBundle.LoadFromStream(fileStream);
                m_LoadTime = Time.realtimeSinceStartup - t;
                GetComponent<Image>().sprite = myLoadedAssetBundle.LoadAsset<Sprite>("1");
                myLoadedAssetBundle.Unload(false);
            }
        }
        else
        {
            float t = Time.realtimeSinceStartup;
            var myLoadedAssetBundle = AssetBundle.LoadFromFile(Application.streamingAssetsPath + "/myab.unity3d");
            m_LoadTime = Time.realtimeSinceStartup - t;
            GetComponent<Image>().sprite = myLoadedAssetBundle.LoadAsset<Sprite>("1");
            myLoadedAssetBundle.Unload(false);
        }
    }
 
    private void OnGUI()
    {
        if (isStream)
        {
            GUILayout.Label(string.Format("<size=50>\nAssetBundle.LoadFromStream :{0} </size>", m_LoadTime));
        }
        else
        {
            GUILayout.Label(string.Format("<size=50>AssetBundle.LoadFromFile :{0} </size>", m_LoadTime));
        }
 
    }
}

如下图所示，在iPhone7上，基本上加载时间差不多。

注意：Android下的streamingAssets目录不能使用，因为android下是放在jar里并不是文件系统。一定要用的话需要拷贝到 Application.persistentDataPath下。

本文固定链接: https://www.xuanyusong.com/archives/4607

转载请注明: 雨松MOMO 2019年07月02日 于 雨松MOMO程序研究院 发表