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// Copyright (c) 2011 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
// Defines the public interface of the disk cache. For more details see
// http://dev.chromium.org/developers/design-documents/disk-cache
#ifndef NET_DISK_CACHE_DISK_CACHE_H_
#define NET_DISK_CACHE_DISK_CACHE_H_
#pragma once
#include <string>
#include <vector>
#include "base/basictypes.h"
#include "base/time.h"
#include "net/base/net_api.h"
#include "net/base/cache_type.h"
#include "net/base/completion_callback.h"
class FilePath;
namespace base {
class MessageLoopProxy;
}
namespace net {
class IOBuffer;
class NetLog;
}
namespace disk_cache {
class Entry;
class Backend;
typedef net::CompletionCallback CompletionCallback;
// Returns an instance of a Backend of the given |type|. |path| points to a
// folder where the cached data will be stored (if appropriate). This cache
// instance must be the only object that will be reading or writing files to
// that folder. The returned object should be deleted when not needed anymore.
// If |force| is true, and there is a problem with the cache initialization, the
// files will be deleted and a new set will be created. |max_bytes| is the
// maximum size the cache can grow to. If zero is passed in as |max_bytes|, the
// cache will determine the value to use. |thread| can be used to perform IO
// operations if a dedicated thread is required; a valid value is expected for
// any backend that performs operations on a disk. The returned pointer can be
// NULL if a fatal error is found. The actual return value of the function is a
// net error code. If this function returns ERR_IO_PENDING, the |callback| will
// be invoked when a backend is available or a fatal error condition is reached.
// The pointer to receive the |backend| must remain valid until the operation
// completes (the callback is notified).
NET_API int CreateCacheBackend(net::CacheType type, const FilePath& path,
int max_bytes, bool force,
base::MessageLoopProxy* thread,
net::NetLog* net_log, Backend** backend,
CompletionCallback* callback);
// The root interface for a disk cache instance.
class NET_API Backend {
public:
// If the backend is destroyed when there are operations in progress (any
// callback that has not been invoked yet), this method cancels said
// operations so the callbacks are not invoked, possibly leaving the work
// half way (for instance, dooming just a few entries). Note that pending IO
// for a given Entry (as opposed to the Backend) will still generate a
// callback from within this method.
virtual ~Backend() {}
// Returns the number of entries in the cache.
virtual int32 GetEntryCount() const = 0;
// Opens an existing entry. Upon success, |entry| holds a pointer to an Entry
// object representing the specified disk cache entry. When the entry pointer
// is no longer needed, its Close method should be called. The return value is
// a net error code. If this method returns ERR_IO_PENDING, the |callback|
// will be invoked when the entry is available. The pointer to receive the
// |entry| must remain valid until the operation completes.
virtual int OpenEntry(const std::string& key, Entry** entry,
CompletionCallback* callback) = 0;
// Creates a new entry. Upon success, the out param holds a pointer to an
// Entry object representing the newly created disk cache entry. When the
// entry pointer is no longer needed, its Close method should be called. The
// return value is a net error code. If this method returns ERR_IO_PENDING,
// the |callback| will be invoked when the entry is available. The pointer to
// receive the |entry| must remain valid until the operation completes.
virtual int CreateEntry(const std::string& key, Entry** entry,
CompletionCallback* callback) = 0;
// Marks the entry, specified by the given key, for deletion. The return value
// is a net error code. If this method returns ERR_IO_PENDING, the |callback|
// will be invoked after the entry is doomed.
virtual int DoomEntry(const std::string& key,
CompletionCallback* callback) = 0;
// Marks all entries for deletion. The return value is a net error code. If
// this method returns ERR_IO_PENDING, the |callback| will be invoked when the
// operation completes.
virtual int DoomAllEntries(CompletionCallback* callback) = 0;
// Marks a range of entries for deletion. This supports unbounded deletes in
// either direction by using null Time values for either argument. The return
// value is a net error code. If this method returns ERR_IO_PENDING, the
// |callback| will be invoked when the operation completes.
virtual int DoomEntriesBetween(const base::Time initial_time,
const base::Time end_time,
CompletionCallback* callback) = 0;
// Marks all entries accessed since |initial_time| for deletion. The return
// value is a net error code. If this method returns ERR_IO_PENDING, the
// |callback| will be invoked when the operation completes.
virtual int DoomEntriesSince(const base::Time initial_time,
CompletionCallback* callback) = 0;
// Enumerates the cache. Initialize |iter| to NULL before calling this method
// the first time. That will cause the enumeration to start at the head of
// the cache. For subsequent calls, pass the same |iter| pointer again without
// changing its value. This method returns ERR_FAILED when there are no more
// entries to enumerate. When the entry pointer is no longer needed, its
// Close method should be called. The return value is a net error code. If
// this method returns ERR_IO_PENDING, the |callback| will be invoked when the
// |next_entry| is available. The pointer to receive the |next_entry| must
// remain valid until the operation completes.
//
// NOTE: This method does not modify the last_used field of the entry, and
// therefore it does not impact the eviction ranking of the entry.
virtual int OpenNextEntry(void** iter, Entry** next_entry,
CompletionCallback* callback) = 0;
// Releases iter without returning the next entry. Whenever OpenNextEntry()
// returns true, but the caller is not interested in continuing the
// enumeration by calling OpenNextEntry() again, the enumeration must be
// ended by calling this method with iter returned by OpenNextEntry().
virtual void EndEnumeration(void** iter) = 0;
// Return a list of cache statistics.
virtual void GetStats(
std::vector<std::pair<std::string, std::string> >* stats) = 0;
};
// This interface represents an entry in the disk cache.
class NET_TEST Entry {
public:
// Marks this cache entry for deletion.
virtual void Doom() = 0;
// Releases this entry. Calling this method does not cancel pending IO
// operations on this entry. Even after the last reference to this object has
// been released, pending completion callbacks may be invoked.
virtual void Close() = 0;
// Returns the key associated with this cache entry.
virtual std::string GetKey() const = 0;
// Returns the time when this cache entry was last used.
virtual base::Time GetLastUsed() const = 0;
// Returns the time when this cache entry was last modified.
virtual base::Time GetLastModified() const = 0;
// Returns the size of the cache data with the given index.
virtual int32 GetDataSize(int index) const = 0;
// Copies cache data into the given buffer of length |buf_len|. If
// completion_callback is null, then this call blocks until the read
// operation is complete. Otherwise, completion_callback will be
// called on the current thread once the read completes. Returns the
// number of bytes read or a network error code. If a completion callback is
// provided then it will be called if this function returns ERR_IO_PENDING,
// and a reference to |buf| will be retained until the callback is called.
// Note that the callback will be invoked in any case, even after Close has
// been called; in other words, the caller may close this entry without
// having to wait for all the callbacks, and still rely on the cleanup
// performed from the callback code.
virtual int ReadData(int index, int offset, net::IOBuffer* buf, int buf_len,
CompletionCallback* completion_callback) = 0;
// Copies cache data from the given buffer of length |buf_len|. If
// completion_callback is null, then this call blocks until the write
// operation is complete. Otherwise, completion_callback will be
// called on the current thread once the write completes. Returns the
// number of bytes written or a network error code. If a completion callback
// is provided then it will be called if this function returns ERR_IO_PENDING,
// and a reference to |buf| will be retained until the callback is called.
// Note that the callback will be invoked in any case, even after Close has
// been called; in other words, the caller may close this entry without
// having to wait for all the callbacks, and still rely on the cleanup
// performed from the callback code.
// If truncate is true, this call will truncate the stored data at the end of
// what we are writing here.
virtual int WriteData(int index, int offset, net::IOBuffer* buf, int buf_len,
CompletionCallback* completion_callback,
bool truncate) = 0;
// Sparse entries support:
//
// A Backend implementation can support sparse entries, so the cache keeps
// track of which parts of the entry have been written before. The backend
// will never return data that was not written previously, so reading from
// such region will return 0 bytes read (or actually the number of bytes read
// before reaching that region).
//
// There are only two streams for sparse entries: a regular control stream
// (index 0) that must be accessed through the regular API (ReadData and
// WriteData), and one sparse stream that must me accessed through the sparse-
// aware API that follows. Calling a non-sparse aware method with an index
// argument other than 0 is a mistake that results in implementation specific
// behavior. Using a sparse-aware method with an entry that was not stored
// using the same API, or with a backend that doesn't support sparse entries
// will return ERR_CACHE_OPERATION_NOT_SUPPORTED.
//
// The storage granularity of the implementation should be at least 1 KB. In
// other words, storing less than 1 KB may result in an implementation
// dropping the data completely, and writing at offsets not aligned with 1 KB,
// or with lengths not a multiple of 1 KB may result in the first or last part
// of the data being discarded. However, two consecutive writes should not
// result in a hole in between the two parts as long as they are sequential
// (the second one starts where the first one ended), and there is no other
// write between them.
//
// The Backend implementation is free to evict any range from the cache at any
// moment, so in practice, the previously stated granularity of 1 KB is not
// as bad as it sounds.
//
// The sparse methods don't support multiple simultaneous IO operations to the
// same physical entry, so in practice a single object should be instantiated
// for a given key at any given time. Once an operation has been issued, the
// caller should wait until it completes before starting another one. This
// requirement includes the case when an entry is closed while some operation
// is in progress and another object is instantiated; any IO operation will
// fail while the previous operation is still in-flight. In order to deal with
// this requirement, the caller could either wait until the operation
// completes before closing the entry, or call CancelSparseIO() before closing
// the entry, and call ReadyForSparseIO() on the new entry and wait for the
// callback before issuing new operations.
// Behaves like ReadData() except that this method is used to access sparse
// entries.
virtual int ReadSparseData(int64 offset, net::IOBuffer* buf, int buf_len,
CompletionCallback* completion_callback) = 0;
// Behaves like WriteData() except that this method is used to access sparse
// entries. |truncate| is not part of this interface because a sparse entry
// is not expected to be reused with new data. To delete the old data and
// start again, or to reduce the total size of the stream data (which implies
// that the content has changed), the whole entry should be doomed and
// re-created.
virtual int WriteSparseData(int64 offset, net::IOBuffer* buf, int buf_len,
CompletionCallback* completion_callback) = 0;
// Returns information about the currently stored portion of a sparse entry.
// |offset| and |len| describe a particular range that should be scanned to
// find out if it is stored or not. |start| will contain the offset of the
// first byte that is stored within this range, and the return value is the
// minimum number of consecutive stored bytes. Note that it is possible that
// this entry has stored more than the returned value. This method returns a
// net error code whenever the request cannot be completed successfully. If
// this method returns ERR_IO_PENDING, the |callback| will be invoked when the
// operation completes, and |start| must remain valid until that point.
virtual int GetAvailableRange(int64 offset, int len, int64* start,
CompletionCallback* callback) = 0;
// Returns true if this entry could be a sparse entry or false otherwise. This
// is a quick test that may return true even if the entry is not really
// sparse. This method doesn't modify the state of this entry (it will not
// create sparse tracking data). GetAvailableRange or ReadSparseData can be
// used to perfom a definitive test of wether an existing entry is sparse or
// not, but that method may modify the current state of the entry (making it
// sparse, for instance). The purpose of this method is to test an existing
// entry, but without generating actual IO to perform a thorough check.
virtual bool CouldBeSparse() const = 0;
// Cancels any pending sparse IO operation (if any). The completion callback
// of the operation in question will still be called when the operation
// finishes, but the operation will finish sooner when this method is used.
virtual void CancelSparseIO() = 0;
// Returns OK if this entry can be used immediately. If that is not the
// case, returns ERR_IO_PENDING and invokes the provided callback when this
// entry is ready to use. This method always returns OK for non-sparse
// entries, and returns ERR_IO_PENDING when a previous operation was cancelled
// (by calling CancelSparseIO), but the cache is still busy with it. If there
// is a pending operation that has not been cancelled, this method will return
// OK although another IO operation cannot be issued at this time; in this
// case the caller should just wait for the regular callback to be invoked
// instead of using this method to provide another callback.
//
// Note that CancelSparseIO may have been called on another instance of this
// object that refers to the same physical disk entry.
// Note: This method is deprecated.
virtual int ReadyForSparseIO(CompletionCallback* completion_callback) = 0;
protected:
virtual ~Entry() {}
};
} // namespace disk_cache
#endif // NET_DISK_CACHE_DISK_CACHE_H_