unity下载文件，支持断点续传，支持MD5，支持进度显示

你可以使用UnityWebRequest来实现下载文件，并实现断点续传和MD5校验。以下是一个示例代码，其中包括进度显示：

IEnumerator DownloadFile(string url, string savePath, Action<float> onProgress)
{
    using (UnityWebRequest request = UnityWebRequest.Get(url))
    {
        request.chunkedTransfer = false;
        request.timeout = 120;

        // Check if file exists and get its size
        long fileLength = 0;
        if (File.Exists(savePath))
        {
            fileLength = new FileInfo(savePath).Length;
            request.SetRequestHeader("Range", "bytes=" + fileLength + "-");
        }

        // Send the request and wait for the response
        yield return request.SendWebRequest();

        // Check for errors
        if (request.result == UnityWebRequest.Result.ConnectionError || request.result == UnityWebRequest.Result.ProtocolError)
        {
            Debug.Log(request.error);
        }
        else
        {
            // Save the downloaded file
            using (FileStream fs = new FileStream(savePath, FileMode.Append))
            {
                fs.Write(request.downloadHandler.data, 0, request.downloadHandler.data.Length);
            }

            // Check if download is complete
            long totalLength = fileLength + request.downloadedBytes;
            if (request.responseCode == 206)
            {
                string contentRange = request.GetResponseHeader("Content-Range");
                if (contentRange != null)
                {
                    string[] ranges = contentRange.Split('/');
                    if (ranges.Length > 1)
                    {
                        long.TryParse(ranges[1], out totalLength);
                    }
                }
            }

            // Check if MD5 matches
            string hash = CalculateMD5(savePath);
            string expectedHash = request.GetResponseHeader("Content-MD5");
            if (expectedHash != null && hash != expectedHash)
            {
                Debug.Log("MD5 mismatch!");
            }

            Debug.Log("Download complete!");

            // Call progress callback with 100%
            onProgress(1f);
        }
    }
}

string CalculateMD5(string filePath)
{
    using (var md5 = MD5.Create())
    {
        using (var stream = File.OpenRead(filePath))
        {
            byte[] hash = md5.ComputeHash(stream);
            return BitConverter.ToString(hash).Replace("-", "").ToLowerInvariant();
        }
    }
}

你可以使用以下代码来启动下载：

StartCoroutine(DownloadFile(url, savePath, (progress) =>
{
    Debug.Log("Download progress: " + (progress * 100f).ToString("F2") + "%");
}));

其中，`url`是要下载的文件的URL，`savePath`是要保存到的本地文件路径。`onProgress`是一个回调函数，每当下载进度发生变化时，会调用该函数。