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// Copyright (c) 2012 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/network-stack/disk-cache
#ifndef NET_DISK_CACHE_DISK_CACHE_H_
#define NET_DISK_CACHE_DISK_CACHE_H_
#include <stdint.h>
#include <memory>
#include <string>
#include <vector>
#include "base/memory/ref_counted.h"
#include "base/strings/string_split.h"
#include "base/time/time.h"
#include "net/base/cache_type.h"
#include "net/base/completion_callback.h"
#include "net/base/net_errors.h"
#include "net/base/net_export.h"
namespace base {
class FilePath;
namespace trace_event {
class ProcessMemoryDump;
}
} // namespace base
namespace net {
class IOBuffer;
class NetLog;
}
namespace disk_cache {
class Entry;
class Backend;
// 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 (if another one exists, and |type| is not net::DISK_CACHE or
// net::MEDIA_CACHE, this operation will not complete until the previous
// duplicate gets destroyed and finishes all I/O).
//
// 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. 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_EXPORT int CreateCacheBackend(net::CacheType type,
net::BackendType backend_type,
const base::FilePath& path,
int max_bytes,
bool force,
net::NetLog* net_log,
std::unique_ptr<Backend>* backend,
const net::CompletionCallback& callback);
// Variant of the above that calls |post_cleanup_callback| once all the I/O
// that was in flight has completed post-destruction. |post_cleanup_callback|
// will get invoked even if the creation fails. The invocation will always be
// via the event loop, and never direct.
//
// This is currently unsupported for |type| == net::DISK_CACHE or
// net::MEDIA_CACHE.
//
// Note that this will not wait for |post_cleanup_callback| of a previous
// instance for |path| to run.
NET_EXPORT int CreateCacheBackend(net::CacheType type,
net::BackendType backend_type,
const base::FilePath& path,
int max_bytes,
bool force,
net::NetLog* net_log,
std::unique_ptr<Backend>* backend,
base::OnceClosure post_cleanup_callback,
const net::CompletionCallback& callback);
// This will flush any internal threads used by backends created w/o an
// externally injected thread specified, so tests can be sure that all I/O
// has finished before inspecting the world.
NET_EXPORT void FlushCacheThreadForTesting();
// The root interface for a disk cache instance.
class NET_EXPORT Backend {
public:
typedef net::CompletionCallback CompletionCallback;
class Iterator {
public:
virtual ~Iterator() {}
// OpenNextEntry returns |net::OK| and provides |next_entry| if there is an
// entry to enumerate. It returns |net::ERR_FAILED| at the end of
// enumeration. If the function returns |net::ERR_IO_PENDING|, then the
// final result will be passed to the provided |callback|, otherwise
// |callback| will not be called. If any entry in the cache is modified
// during iteration, the result of this function is thereafter undefined.
//
// Calling OpenNextEntry after the backend which created it is destroyed
// may fail with |net::ERR_FAILED|; however it should not crash.
//
// Some cache backends make stronger guarantees about mutation during
// iteration, see top comment in simple_backend_impl.h for details.
virtual int OpenNextEntry(Entry** next_entry,
const CompletionCallback& callback) = 0;
};
// 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.
// Warning: there is some inconsistency in details between different backends
// on what will succeed and what will fail. In particular the blockfile
// backend will leak entries closed after backend deletion, while others
// handle it properly.
virtual ~Backend() {}
// Returns the type of this cache.
virtual net::CacheType GetCacheType() const = 0;
// Returns the number of entries in the cache.
virtual int32_t 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,
const 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,
const 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,
const 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(const 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.
// Entries with |initial_time| <= access time < |end_time| are deleted.
virtual int DoomEntriesBetween(base::Time initial_time,
base::Time end_time,
const 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.
// Entries with |initial_time| <= access time are deleted.
virtual int DoomEntriesSince(base::Time initial_time,
const CompletionCallback& callback) = 0;
// Calculate the total size of the cache. The return value is the size in
// bytes or a net error code. If this method returns ERR_IO_PENDING,
// the |callback| will be invoked when the operation completes.
virtual int CalculateSizeOfAllEntries(const CompletionCallback& callback) = 0;
// Calculate the size of all cache entries accessed between |initial_time| and
// |end_time|.
// The return value is the size in bytes or a net error code. The default
// implementation returns ERR_NOT_IMPLEMENTED and should only be overwritten
// if there is an efficient way for the backend to determine the size for a
// subset of the cache without reading the whole cache from disk.
// If this method returns ERR_IO_PENDING, the |callback| will be invoked when
// the operation completes.
virtual int CalculateSizeOfEntriesBetween(base::Time initial_time,
base::Time end_time,
const CompletionCallback& callback);
// Returns an iterator which will enumerate all entries of the cache in an
// undefined order.
virtual std::unique_ptr<Iterator> CreateIterator() = 0;
// Return a list of cache statistics.
virtual void GetStats(base::StringPairs* stats) = 0;
// Called whenever an external cache in the system reuses the resource
// referred to by |key|.
virtual void OnExternalCacheHit(const std::string& key) = 0;
// Returns the estimate of dynamically allocated memory in bytes.
virtual size_t DumpMemoryStats(
base::trace_event::ProcessMemoryDump* pmd,
const std::string& parent_absolute_name) const = 0;
// Backends can optionally permit one to store, probabilistically, up to a
// byte associated with a key of an existing entry in memory.
// GetEntryInMemoryData has the following behavior:
// - If the data is not available at this time for any reason, returns 0.
// - Otherwise, returns a value that was with very high probability
// given to SetEntryInMemoryData(|key|) (and with a very low probability
// to a different key that collides in the in-memory index).
//
// Due to the probability of collisions, including those that can be induced
// by hostile 3rd parties, this interface should not be used to make decisions
// that affect correctness (especially security).
virtual uint8_t GetEntryInMemoryData(const std::string& key);
virtual void SetEntryInMemoryData(const std::string& key, uint8_t data);
};
// This interface represents an entry in the disk cache.
class NET_EXPORT Entry {
public:
typedef net::CompletionCallback CompletionCallback;
typedef net::IOBuffer IOBuffer;
// 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_t GetDataSize(int index) const = 0;
// Copies cached data into the given buffer of length |buf_len|. Returns the
// number of bytes read or a network error code. If this function returns
// ERR_IO_PENDING, the completion callback will be called on the current
// thread when the operation completes, and a reference to |buf| will be
// retained until the callback is called. Note that as long as the function
// does not complete immediately, the callback will always be invoked, 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, IOBuffer* buf, int buf_len,
const CompletionCallback& callback) = 0;
// Copies data from the given buffer of length |buf_len| into the cache.
// Returns the number of bytes written or a network error code. If this
// function returns ERR_IO_PENDING, the completion callback will be called
// on the current thread when the operation completes, and a reference to
// |buf| will be retained until the callback is called. Note that as long as
// the function does not complete immediately, the callback will always be
// invoked, 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, IOBuffer* buf, int buf_len,
const CompletionCallback& 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_t offset,
IOBuffer* buf,
int buf_len,
const CompletionCallback& 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_t offset,
IOBuffer* buf,
int buf_len,
const CompletionCallback& 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_t offset,
int len,
int64_t* start,
const 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 perform a definitive test of whether 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(const CompletionCallback& callback) = 0;
// Used in tests to set the last used time. Note that backend might have
// limited precision. Also note that this call may modify the last modified
// time.
virtual void SetLastUsedTimeForTest(base::Time time) = 0;
protected:
virtual ~Entry() {}
};
struct EntryDeleter {
void operator()(Entry* entry) {
// Note that |entry| is ref-counted.
entry->Close();
}
};
// Automatically closes an entry when it goes out of scope.
typedef std::unique_ptr<Entry, EntryDeleter> ScopedEntryPtr;
} // namespace disk_cache
#endif // NET_DISK_CACHE_DISK_CACHE_H_