/// <summary>
/// Returns true if the remote storage ETag and user file system ETags are equal. False - otherwise.
/// </summary>
/// <param name="userFileSystemPath">User file system item.</param>
/// <param name="remoteStorageItem">Remote storage item info.</param>
/// <remarks>
/// ETag is updated on the server during every document update and is sent to client with a file.
/// During client->server update it is sent back to the remote storage together with a modified content.
/// This ensures the changes on the server are not overwritten if the document on the server is modified.
/// </remarks>
internal static async Task <bool> ETagEqualsAsync(string userFileSystemPath, FileSystemItemBasicInfo remoteStorageItem)
{
string remoteStorageETag = remoteStorageItem.ETag;
string userFileSystemETag = await ETag.GetETagAsync(userFileSystemPath);
if (string.IsNullOrEmpty(remoteStorageETag) && string.IsNullOrEmpty(userFileSystemETag))
{
// We assume the remote storage is not using ETags or no ETag is ssociated with this file/folder.
return(true);
}
return(remoteStorageETag == userFileSystemETag);
}
/// <summary>
/// Creates or updates folder in the remote storage.
/// </summary>
/// <param name="remoteStoragePath">Path of the folder to be created or updated in the remote storage.</param>
/// <param name="newInfo">New information about the folder, such as modification date, attributes, custom data, etc.</param>
/// <param name="mode">Specifies if a new folder should be created or existing folder should be updated.</param>
/// <returns>New ETag returned from the remote storage.</returns>
protected async Task <string> CreateOrUpdateFolderAsync(string remoteStoragePath, IFolderBasicInfo newInfo, FileMode mode)
{
// Get ETag and lock-token here and send it to the remote storage with the new item content/info if needed.
if (mode == FileMode.Open)
{
// Get ETag.
string eTag = await ETag.GetETagAsync(UserFileSystemPath);
// Get lock-token.
string lockToken = Lock?.LockToken;
}
DirectoryInfo remoteStorageItem = new DirectoryInfo(remoteStoragePath);
try
{
Program.RemoteStorageMonitorInstance.Enabled = false; // Disable RemoteStorageMonitor to avoid circular calls.
remoteStorageItem.Create();
string userFileSystemPath = Mapping.ReverseMapPath(remoteStoragePath);
if (mode == FileMode.Open)
{
// Verify that the item in the remote storage is not modified since it was downloaded to the user file system.
// In your real-life application you will send the ETag to the server as part of the update request.
FileSystemItemBasicInfo itemInfo = Mapping.GetUserFileSysteItemBasicInfo(remoteStorageItem);
if (!(await ETag.ETagEqualsAsync(userFileSystemPath, itemInfo)))
{
throw new ConflictException(Modified.Server, "Item is modified in the remote storage, ETags not equal.");
}
}
// Update ETag/LastWriteTime in user file system, so the synchronyzation or remote storage monitor would not start the new update.
// This is only required to avoid circular updates because of the simplicity of this sample.
// In your real-life application you will receive a new ETag from server in the update response.
string eTag = newInfo.LastWriteTime.ToBinary().ToString();
await ETag.SetETagAsync(userFileSystemPath, eTag);
remoteStorageItem.Attributes = newInfo.Attributes;
remoteStorageItem.CreationTimeUtc = newInfo.CreationTime;
remoteStorageItem.LastWriteTimeUtc = newInfo.LastWriteTime;
remoteStorageItem.LastAccessTimeUtc = newInfo.LastAccessTime;
remoteStorageItem.LastWriteTimeUtc = newInfo.LastWriteTime;
return(eTag);
}
finally
{
Program.RemoteStorageMonitorInstance.Enabled = true;
}
}
/// <summary>
/// Returns true if the remote storage ETag and user file system ETags are equal. False - otherwise.
/// </summary>
/// <param name="userFileSystemPath">User file system item.</param>
/// <param name="remoteStorageItem">Remote storage item info.</param>
/// <remarks>
/// ETag is updated on the server during every document update and is sent to client with a file.
/// During client->server update it is sent back to the remote storage together with a modified content.
/// This ensures the changes on the server are not overwritten if the document on the server is modified.
/// </remarks>
internal static async Task <bool> ETagEqualsAsync(string userFileSystemPath, FileSystemItemBasicInfo remoteStorageItem)
{
string remoteStorageETag = remoteStorageItem.ETag;
// Intstead of the real ETag we store remote storage LastWriteTime when
// creating and updating files/folders.
string userFileSystemETag = await ETag.GetETagAsync(userFileSystemPath);
if (string.IsNullOrEmpty(userFileSystemETag))
{
// No ETag associated with the file. This is a new file created in user file system.
return(false);
}
return(remoteStorageETag == userFileSystemETag);
}
/// <summary>
/// Creates or updates file in the remote storage.
/// </summary>
/// <param name="remoteStoragePath">Path of the file to be created or updated in the remote storage.</param>
/// <param name="newInfo">New information about the file, such as modification date, attributes, custom data, etc.</param>
/// <param name="mode">Specifies if a new file should be created or existing file should be updated.</param>
/// <param name="newContentStream">New file content or null if the file content is not modified.</param>
/// <returns>New ETag returned from the remote storage.</returns>
protected async Task <string> CreateOrUpdateFileAsync(string remoteStoragePath, IFileBasicInfo newInfo, FileMode mode, Stream newContentStream = null)
{
// Get ETag and lock-token here and send it to the remote storage with the new item content/info if needed.
if (mode == FileMode.Open)
{
// Get ETag.
string eTag = await ETag.GetETagAsync(UserFileSystemPath);
// Get lock-token.
string lockToken = Lock?.LockToken;
}
FileInfo remoteStorageItem = new FileInfo(remoteStoragePath);
try
{
Program.RemoteStorageMonitorInstance.Enabled = false; // Disable RemoteStorageMonitor to avoid circular calls.
// If another thread is trying to sync the same file, this call will fail in other threads.
// In your implementation you must lock your remote storage file, or block it for reading and writing by other means.
await using (FileStream remoteStorageStream = remoteStorageItem.Open(mode, FileAccess.Write, FileShare.None))
{
string userFileSystemPath = Mapping.ReverseMapPath(remoteStoragePath);
if (mode == FileMode.Open)
{
// Verify that the item in the remote storage is not modified since it was downloaded to the user file system.
// In your real-life application you will send the ETag to the server as part of the update request.
FileSystemItemBasicInfo itemInfo = Mapping.GetUserFileSysteItemBasicInfo(remoteStorageItem);
if (!(await ETag.ETagEqualsAsync(userFileSystemPath, itemInfo)))
{
throw new ConflictException(Modified.Server, "Item is modified in the remote storage, ETags not equal.");
}
}
// Update ETag/LastWriteTime in user file system, so the synchronyzation or remote storage monitor would not start the new update.
// This is only required to avoid circular updates because of the simplicity of this sample.
// In your real-life application you will receive a new ETag from the server in the update response
// and return it from this method.
string eTag = newInfo.LastWriteTime.ToBinary().ToString();
await ETag.SetETagAsync(userFileSystemPath, eTag);
// Update remote storage file content.
if (newContentStream != null)
{
await newContentStream.CopyToAsync(remoteStorageStream);
remoteStorageStream.SetLength(newContentStream.Length);
}
// Update remote storage file basic info.
WindowsFileSystemItem.SetFileInformation(
remoteStorageStream.SafeFileHandle,
newInfo.Attributes,
newInfo.CreationTime,
newInfo.LastWriteTime,
newInfo.LastAccessTime,
newInfo.LastWriteTime);
return(eTag);
}
}
finally
{
Program.RemoteStorageMonitorInstance.Enabled = true;
}
}
