GCS FUSE在Windows环境下的解决方案

public Google.Apis.Storage.v1.Data.Object CreateEmptyBlob(string bucketName, string blobName)         {            var content = Encoding.UTF8.GetBytes("");            string contentType = MimeMapping.GetMimeMapping(Path.GetFileName(blobName));            Google.Apis.Storage.v1.Data.Object blob = this.storage.UploadObject(bucketName, blobName, contentType, new MemoryStream(content));            return blob;        }

 public Google.Apis.Storage.v1.Data.Object CreateSubDir(string bucketName, string blobName)        {            string subDir = blobName.EndsWith("/") ? blobName : blobName + "/";            Google.Apis.Storage.v1.Data.Object blob = CreateEmptyBlob(bucketName, subDir);            return blob;        }

GCS对如下一下操作也支持强一致性，比如：Read-after-delete，Bucket listing，Object listing。这样可以确保系统能够遍历到最新的文件。另外对于子文件夹，如果子文件夹是空的，没有任何文件，那么遍历其父文件夹时是是可遍历到这个名如”abc/”的Object的。但是一旦该文件加下有了文件，那么在遍历其父文件夹时这个名如”abc/“将不再是Object Instance的类型，而是prefix类型。

WinFsp会在多个场景下调用Read API的操作，对于一个文件的Read操作通常不是一次性完成的，而是需要调用多次，每次调用要通过计算offset和length来定位内容。但是由于Windows的内核设定, read-ahead的长度一般是8K，如果每次Read都调用一次GCS的分段下载的API的话，网络消耗会比较大。所以GcsFuse-Win在Read这个环节增加一个了Buffer，GcsFuse-Win会以根据用户设定的Buffer大小和文件的大小计算出一个最小的Buffer Size,然后根据这个Buffer Size来预先缓存数据。比如设定Buffer Size 是4MB, 文件的大小是1.2MB，则GcsFuse-Win在在系统调用Read操作是，将该文件全部下载并缓存，这样后续的Read将会直接读取缓存中的内容。通过Buffer机制可以极大的降低网络的请求数量。

public byte[] DownloadByteRange(string bucketName, string blobName,            long firstByte, long lastByte)        {            byte[] content;            // Create an HTTP request for the media, for a limited byte range.            StorageService storage = this.storage.Service;            var uri = new Uri(                $"{storage.BaseUri}b/{bucketName}/o/{HttpUtility.UrlEncode(blobName, System.Text.Encoding.UTF8)}?alt=media");            var request = new HttpRequestMessage() { RequestUri = uri };            request.Headers.Range =                new System.Net.Http.Headers.RangeHeaderValue(firstByte,                lastByte);            var response = storage.HttpClient.SendAsync(request).Result;            if ((int)response.StatusCode == 200 | (int)response.StatusCode == 206)            {                content = response.Content.ReadAsByteArrayAsync().Result;                return content;            }            else            {                string errMsg = string.Format("Failed to download the blob:{0}" , bucketName + "/" + blobName);                throw new DownloadException(errMsg);            }                   }

public Uri InitializeResumableUploader(string bucketName, string blobName)        {            StorageService storageService = this.storage.Service;            var uri = new Uri(                $"https://storage.googleapis.com/upload/storage/v1/b/{bucketName}/o?uploadType=resumable");            var initRequest = new HttpRequestMessage() { RequestUri = uri };            string body = "{\"name\":\"" + blobName + "\"}";            initRequest.Content = new StringContent(body, Encoding.UTF8, "application/json");            string contentType = MimeMapping.GetMimeMapping(Path.GetFileName(blobName));            initRequest.Headers.Add("X-Upload-Content-Type", contentType);            initRequest.Method = new HttpMethod("POST");            var initResponse = storageService.HttpClient.SendAsync(initRequest).Result;            Uri uploadUri = null;            if ((int)initResponse.StatusCode == 200)            {                uploadUri = initResponse.Headers.Location;            }            else            {                string errMsg = string.Format("Failed to initialize the upload session :{}" + bucketName + "/" + blobName);                throw new UploadException(errMsg);            }            return uploadUri;        }

public long UploadBlobChunk(Uri uploadUri, byte[] rawData, long byteSent, long length)         {            bool isEof = false;            StorageService storageService = this.storage.Service;            var uploadRequest = new HttpRequestMessage() { RequestUri = uploadUri };            uploadRequest.Method = new HttpMethod("PUT");            uploadRequest.Content = new ByteArrayContent(rawData);            if (length % (256 * 1024) != 0)            {                long totalLength = byteSent + length;                uploadRequest.Content.Headers.ContentRange = new System.Net.Http.Headers.ContentRangeHeaderValue(byteSent, byteSent + length - 1, totalLength);                isEof = true;            }            else {                uploadRequest.Content.Headers.ContentRange = new System.Net.Http.Headers.ContentRangeHeaderValue(byteSent, byteSent + length - 1);            }            var uploadResponse = storageService.HttpClient.SendAsync(uploadRequest).Result;            if (isEof)            {                if ((int)uploadResponse.StatusCode != 200)                {                    string errMsg = string.Format("Failed to the upload :{0}", uploadUri.ToString());                    throw new UploadException(errMsg);                }            }            else {                if ((int)uploadResponse.StatusCode != 308)                {                    string errMsg = string.Format("Failed to the upload :{0}", uploadUri.ToString());                    throw new UploadException(errMsg);                }            }            return length;        }