public static HttpCacheResult InitializeHttpCacheResult(
string httpCacheDirectory,
Uri sourceUri,
string cacheKey,
HttpSourceCacheContext context)
{
// When the MaxAge is TimeSpan.Zero, this means the caller is passing is using a temporary directory for
// cache files, instead of the global HTTP cache used by default. Additionally, the cleaning up of this
// directory is the responsibility of the caller.
if (context.MaxAge > TimeSpan.Zero)
{
var baseFolderName = CachingUtility.RemoveInvalidFileNameChars(CachingUtility.ComputeHash(sourceUri.OriginalString));
var baseFileName = CachingUtility.RemoveInvalidFileNameChars(cacheKey) + ".dat";
var cacheFolder = Path.Combine(httpCacheDirectory, baseFolderName);
var cacheFile = Path.Combine(cacheFolder, baseFileName);
var newCacheFile = cacheFile + "-new";
return(new HttpCacheResult(
context.MaxAge,
newCacheFile,
cacheFile));
}
else
{
var temporaryFile = Path.Combine(context.RootTempFolder, Path.GetRandomFileName());
var newTemporaryFile = Path.Combine(context.RootTempFolder, Path.GetRandomFileName());
return(new HttpCacheResult(
context.MaxAge,
newTemporaryFile,
temporaryFile));
}
}
protected virtual Stream TryReadCacheFile(string uri, TimeSpan maxAge, string cacheFile)
{
// Do not need the uri here
return(CachingUtility.ReadCacheFile(maxAge, cacheFile));
}
public static async Task CreateCacheFileAsync(
HttpCacheResult result,
HttpResponseMessage response,
Action <Stream> ensureValidContents,
CancellationToken cancellationToken)
{
// Get the cache file directories, so we can make sure they are created before writing
// files to them.
var newCacheFileDirectory = Path.GetDirectoryName(result.NewFile);
var cacheFileDirectory = Path.GetDirectoryName(result.CacheFile);
// Make sure the new cache file directory is created before writing a file to it.
DirectoryUtility.CreateSharedDirectory(newCacheFileDirectory);
// The update of a cached file is divided into two steps:
// 1) Delete the old file.
// 2) Create a new file with the same name.
using (var fileStream = new FileStream(
result.NewFile,
FileMode.Create,
FileAccess.ReadWrite,
FileShare.None,
BufferSize))
{
using (var networkStream = await response.Content.ReadAsStreamAsync())
{
await networkStream.CopyToAsync(fileStream, BufferSize, cancellationToken);
}
// Validate the content before putting it into the cache.
if (ensureValidContents != null)
{
fileStream.Seek(0, SeekOrigin.Begin);
ensureValidContents.Invoke(fileStream);
}
}
if (File.Exists(result.CacheFile))
{
// Process B can perform deletion on an opened file if the file is opened by process A
// with FileShare.Delete flag. However, the file won't be actually deleted until A close it.
// This special feature can cause race condition, so we never delete an opened file.
if (!CachingUtility.IsFileAlreadyOpen(result.CacheFile))
{
File.Delete(result.CacheFile);
}
}
// Make sure the cache file directory is created before moving or writing a file to it.
if (cacheFileDirectory != newCacheFileDirectory)
{
DirectoryUtility.CreateSharedDirectory(cacheFileDirectory);
}
// If the destination file doesn't exist, we can safely perform moving operation.
// Otherwise, moving operation will fail.
if (!File.Exists(result.CacheFile))
{
File.Move(
result.NewFile,
result.CacheFile);
}
// Even the file deletion operation above succeeds but the file is not actually deleted,
// we can still safely read it because it means that some other process just updated it
// and we don't need to update it with the same content again.
result.Stream = new FileStream(
result.CacheFile,
FileMode.Open,
FileAccess.Read,
FileShare.Read | FileShare.Delete,
BufferSize);
}
public static async Task CreateCacheFileAsync(
HttpCacheResult result,
HttpResponseMessage response,
Action <Stream> ensureValidContents,
CancellationToken cancellationToken)
{
// Get the cache file directories, so we can make sure they are created before writing
// files to them.
var newCacheFileDirectory = Path.GetDirectoryName(result.NewFile);
var cacheFileDirectory = Path.GetDirectoryName(result.CacheFile);
// Make sure the new cache file directory is created before writing a file to it.
DirectoryUtility.CreateSharedDirectory(newCacheFileDirectory);
// The update of a cached file is divided into two steps:
// 1) Delete the old file.
// 2) Create a new file with the same name.
// Some FileStream operations on Windows are synchronous even though it may not seem so.
// The HTTP stack rewrite in .NET Core 2.1 introduced circumstances whereby these
// synchronous FileStream calls will keep an IO completion thread busy and block other
// HTTP requests from completing. The immediate solution is to perform write and read
// operations on separate streams, but only on .NET Core where the problem exists.
// See https://github.com/dotnet/corefx/issues/31914 for details.
const int writeBufferSize =
#if IS_CORECLR
1; // This disables write buffering.
#else
BufferSize;
#endif
using (var fileStream = new FileStream(
result.NewFile,
FileMode.Create,
FileAccess.Write,
FileShare.None,
writeBufferSize,
useAsync: true))
{
using (var networkStream = await response.Content.ReadAsStreamAsync())
{
await networkStream.CopyToAsync(fileStream, BufferSize, cancellationToken);
}
}
using (var fileStream = new FileStream(
result.NewFile,
FileMode.Open,
FileAccess.Read,
FileShare.None,
BufferSize,
useAsync: true))
{
// Validate the content before putting it into the cache.
ensureValidContents?.Invoke(fileStream);
}
if (File.Exists(result.CacheFile))
{
// Process B can perform deletion on an opened file if the file is opened by process A
// with FileShare.Delete flag. However, the file won't be actually deleted until A close it.
// This special feature can cause race condition, so we never delete an opened file.
if (!CachingUtility.IsFileAlreadyOpen(result.CacheFile))
{
File.Delete(result.CacheFile);
}
}
// Make sure the cache file directory is created before moving or writing a file to it.
if (cacheFileDirectory != newCacheFileDirectory)
{
DirectoryUtility.CreateSharedDirectory(cacheFileDirectory);
}
// If the destination file doesn't exist, we can safely perform moving operation.
// Otherwise, moving operation will fail.
if (!File.Exists(result.CacheFile))
{
File.Move(
result.NewFile,
result.CacheFile);
}
// Even the file deletion operation above succeeds but the file is not actually deleted,
// we can still safely read it because it means that some other process just updated it
// and we don't need to update it with the same content again.
result.Stream = new FileStream(
result.CacheFile,
FileMode.Open,
FileAccess.Read,
FileShare.Read | FileShare.Delete,
BufferSize,
useAsync: true);
}
