public static bool VerifyHash(byte[] array, ref int offset)
{
ulong expected = SipHash.ComputeHash(array, 0, offset);
ulong actual = UInt64LE.Read(array, ref offset);
return(expected == actual);
}
public void WriteTo(byte[] array)
{
Debug.Assert(array.Length >= Size);
Debug.Assert(Format.IsValidPosition(ChunkBeginPosition));
int offset = 0;
UInt64LE.Write(array, ref offset, (ulong)ChunkBeginPosition);
UInt64LE.Write(array, ref offset, SipHash.ComputeHash(array, 0, offset));
}
public void WriteTo(byte[] array)
{
Debug.Assert(array.Length >= Size);
Debug.Assert(Format.IsValidContentLength(ContentLength));
int offset = 0;
UserData.WriteTo(array, ref offset);
UInt64LE.Write(array, ref offset, (ulong)ContentLength);
UInt64LE.Write(array, ref offset, ContentHash);
UInt64LE.Write(array, ref offset, SipHash.ComputeHash(array, 0, offset));
}
public bool ReadFrom(byte[] array)
{
Debug.Assert(array.Length >= Size);
int offset = 0;
ulong pos = UInt64LE.Read(array, ref offset);
if (!Format.IsValidPosition(pos))
{
return(false);
}
ChunkBeginPosition = (long)pos;
return(Format.VerifyHash(array, ref offset));
}
public bool ReadFrom(byte[] array)
{
Debug.Assert(array.Length >= Size);
int offset = 0;
UserData = UserData.ReadFrom(array, ref offset);
ulong len = UInt64LE.Read(array, ref offset);
if (!Format.IsValidContentLength(len))
{
return(false);
}
ContentLength = (int)len;
ContentHash = UInt64LE.Read(array, ref offset);
return(Format.VerifyHash(array, ref offset));
}
public Listener(IReadOnlyCollection <byte> fileId, Func <bool, Task <long> > flush)
{
// This mutex serves as a marker of the existence of flush listener. RemoteFLush.FlushAsync() looks at it.
// We allow all authenticated users to access the mutex.
var security = new MutexSecurity();
security.AddAccessRule(
new MutexAccessRule(
new SecurityIdentifier(WellKnownSidType.AuthenticatedUserSid, null),
MutexRights.Synchronize,
AccessControlType.Allow));
_mutex = new Mutex(true, MutexName(fileId), out bool createdNew, security);
try {
_srv = new PipeServer(PipeName(fileId), 2, async(Stream strm, CancellationToken cancel) => {
var buf = new byte[UInt64LE.Size];
if (await strm.ReadAsync(buf, 0, 1, cancel) != 1)
{
throw new Exception("Empty Flush request");
}
if (buf[0] != 0 && buf[0] != 1)
{
throw new Exception("Invalid Flush request");
}
bool flushToDisk = buf[0] == 1;
try {
long len = await flush.Invoke(flushToDisk);
Debug.Assert(len >= 0);
int offset = 0;
UInt64LE.Write(buf, ref offset, (ulong)len);
} catch {
int offset = 0;
UInt64LE.Write(buf, ref offset, ulong.MaxValue);
}
await strm.WriteAsync(buf, 0, UInt64LE.Size, cancel);
await strm.FlushAsync(cancel);
});
} catch {
_mutex.Dispose();
throw;
}
}
// Returns:
//
// * null if there is no listener associated with the file.
// * file length immediately after flushing (the flushing and the grabbing of the file length are
// done atomically) if there is a listener and the file was successfully flushed.
//
// Throws in all other cases. For example:
//
// * The remote writer failed to flush because disk is full.
// * The remote writer sent invalid response to our request.
// * Pipe permission error.
public static async Task <long?> FlushAsync(IReadOnlyCollection <byte> fileId, bool flushToDisk)
{
if (fileId == null)
{
throw new ArgumentNullException(nameof(fileId));
}
while (true)
{
using (var pipe = new NamedPipeClientStream(".", PipeName(fileId), PipeDirection.InOut,
PipeOptions.Asynchronous | PipeOptions.WriteThrough)) {
await s_connect.LockAsync();
try {
// NamedPipeClientStream has an awful API. It doesn't allow us to bail early if there is no pipe and
// to wait indefinitely if there is (this can be done with Win32 API). So we do it manually with
// a mutex existence check and a loop. We create this mutex together with the pipe to serve as
// a marker of the pipe's existence. It's difficult to use the pipe itself as such marker because
// server pipes disappear after accepting and serving a request and there may be a short gap before
// we create new server connections.
if (Mutex.TryOpenExisting(MutexName(fileId), MutexRights.Synchronize, out Mutex mutex))
{
mutex.Dispose();
}
else
{
return(null);
}
// The timeout is meant to avoid waiting forever if the pipe disappears between the moment
// we have verified its existence and our attempt to connect to it. We use a mutex to
// restrict the number of simultaneous ConnectAsync() because ConnectAsync() blocks a task
// thread for the whole duration of its execution. Without the mutex, WaitAsync() calls
// could block all task threads.
await pipe.ConnectAsync(100);
} catch (TimeoutException) {
continue;
} catch (IOException) {
continue;
} finally {
s_connect.Unlock(runNextSynchronously: false);
}
var buf = new byte[UInt64LE.Size];
if (flushToDisk)
{
buf[0] = 1;
}
try {
await pipe.WriteAsync(buf, 0, 1);
await pipe.FlushAsync();
if (await pipe.ReadAsync(buf, 0, UInt64LE.Size) != UInt64LE.Size)
{
continue;
}
} catch {
continue;
}
int offset = 0;
ulong res = UInt64LE.Read(buf, ref offset);
if (res < long.MaxValue)
{
return((long)res);
}
if (res == ulong.MaxValue)
{
throw new IOException("Remote writer failed to flush");
}
throw new Exception($"Invalid Flush response: {res}");
}
}
}
