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// Copyright (C) 2019 The Qt Company Ltd.
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR LGPL-3.0-only OR GPL-2.0-only OR GPL-3.0-only
#ifndef HPACKTABLE_P_H
#define HPACKTABLE_P_H
//
// W A R N I N G
// -------------
//
// This file is not part of the Qt API. It exists for the convenience
// of other Qt classes. This header file may change from version to
// version without notice, or even be removed.
//
// We mean it.
//
#include <QtCore/qbytearray.h>
#include <QtCore/private/qglobal_p.h>
#include <QtCore/qpair.h>
#include <vector>
#include <memory>
#include <deque>
#include <set>
QT_BEGIN_NAMESPACE
namespace HPack
{
struct Q_AUTOTEST_EXPORT HeaderField
{
HeaderField()
{
}
HeaderField(const QByteArray &n, const QByteArray &v)
: name(n),
value(v)
{
}
bool operator == (const HeaderField &rhs) const
{
return name == rhs.name && value == rhs.value;
}
QByteArray name;
QByteArray value;
};
using HeaderSize = QPair<bool, quint32>;
HeaderSize entry_size(QByteArrayView name, QByteArrayView value);
inline HeaderSize entry_size(const HeaderField &entry)
{
return entry_size(entry.name, entry.value);
}
/*
Lookup table consists of two parts (HPACK, 2.3):
the immutable static table (pre-defined by HPACK's specs)
and dynamic table which is updated while
compressing/decompressing headers.
Table must provide/implement:
1. Fast random access - we read fields' indices from
HPACK's bit stream.
2. FIFO for dynamic part - to push new items to the front
and evict them from the back (HPACK, 2.3.2).
3. Fast lookup - encoder receives pairs of strings
(name|value) and it has to find an index for a pair
as the whole or for a name at least (if it's already
in either static or dynamic table).
Static table is an immutable vector.
Dynamic part is implemented in a way similar to std::deque -
it's a vector of pointers to chunks. Each chunk is a vector of
(name|value) pairs. Once allocated with a fixed size, chunk
never re-allocates its data, so entries' addresses do not change.
We add new chunks prepending them to the front of a vector,
in each chunk we fill (name|value) pairs starting from the back
of the chunk (this simplifies item eviction/FIFO).
Given a 'linear' index we can find a chunk number and
offset in this chunk - random access.
Lookup in a static part is straightforward:
it's an (immutable) vector, data is sorted,
contains no duplicates, we use binary search comparing string values.
To provide a lookup in dynamic table faster than a linear search,
we have an std::set of 'SearchEntries', where each entry contains:
- a pointer to a (name|value) pair (to compare
name|value strings).
- a pointer to a chunk containing this pair and
- an offset within this chunk - to calculate a
'linear' index.
Entries in a table can be duplicated (HPACK, 2.3.2),
if we evict an entry, we must update our index removing
the exactly right key, thus keys in this set are sorted
by name|value pairs first, and then by chunk index/offset
(so that NewSearchEntryKey < OldSearchEntry even if strings
are equal).
*/
class Q_AUTOTEST_EXPORT FieldLookupTable
{
public:
enum
{
ChunkSize = 16,
DefaultSize = 4096 // Recommended by HTTP2.
};
FieldLookupTable(quint32 maxTableSize, bool useIndex);
bool prependField(const QByteArray &name, const QByteArray &value);
void evictEntry();
quint32 numberOfEntries() const;
quint32 numberOfStaticEntries() const;
quint32 numberOfDynamicEntries() const;
quint32 dynamicDataSize() const;
void clearDynamicTable();
bool indexIsValid(quint32 index) const;
quint32 indexOf(const QByteArray &name, const QByteArray &value) const;
quint32 indexOf(const QByteArray &name) const;
bool field(quint32 index, QByteArray *name, QByteArray *value) const;
bool fieldName(quint32 index, QByteArray *dst) const;
bool fieldValue(quint32 index, QByteArray *dst) const;
bool updateDynamicTableSize(quint32 size);
void setMaxDynamicTableSize(quint32 size);
static const std::vector<HeaderField> &staticPart();
private:
// Table's maximum size is controlled
// by SETTINGS_HEADER_TABLE_SIZE (HTTP/2, 6.5.2).
quint32 maxTableSize;
// The tableCapacity is how many bytes the table
// can currently hold. It cannot exceed maxTableSize.
// It can be modified by a special message in
// the HPACK bit stream (HPACK, 6.3).
quint32 tableCapacity;
using Chunk = std::vector<HeaderField>;
using ChunkPtr = std::unique_ptr<Chunk>;
std::deque<ChunkPtr> chunks;
using size_type = std::deque<ChunkPtr>::size_type;
struct SearchEntry;
friend struct SearchEntry;
struct SearchEntry
{
SearchEntry();
SearchEntry(const HeaderField *f, const Chunk *c,
quint32 o, const FieldLookupTable *t);
const HeaderField *field;
const Chunk *chunk;
const quint32 offset;
const FieldLookupTable *table;
bool operator < (const SearchEntry &rhs) const;
};
bool useIndex;
std::set<SearchEntry> searchIndex;
SearchEntry frontKey() const;
SearchEntry backKey() const;
bool fieldAt(quint32 index, HeaderField *field) const;
const HeaderField &front() const;
HeaderField &front();
const HeaderField &back() const;
quint32 nDynamic;
quint32 begin;
quint32 end;
quint32 dataSize;
quint32 indexOfChunk(const Chunk *chunk) const;
quint32 keyToIndex(const SearchEntry &key) const;
enum class CompareMode {
nameOnly,
nameAndValue
};
static std::vector<HeaderField>::const_iterator findInStaticPart(const HeaderField &field, CompareMode mode);
mutable QByteArray dummyDst;
Q_DISABLE_COPY_MOVE(FieldLookupTable)
};
}
QT_END_NAMESPACE
#endif
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