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// Copyright 2016 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.
#ifndef NET_HTTP2_DECODER_DECODE_BUFFER_H_
#define NET_HTTP2_DECODER_DECODE_BUFFER_H_
// DecodeBuffer provides primitives for decoding various integer types found in
// HTTP/2 frames. It wraps a byte array from which we can read and decode
// serialized HTTP/2 frames, or parts thereof. DecodeBuffer is intended only for
// stack allocation, where the caller is typically going to use the DecodeBuffer
// instance as part of decoding the entire buffer before returning to its own
// caller.
#include <stddef.h>
#include <stdint.h>
#include <algorithm>
#include "base/logging.h"
#include "base/macros.h"
#include "base/strings/string_piece.h"
#include "net/base/net_export.h"
namespace net {
class DecodeBufferSubset;
class NET_EXPORT_PRIVATE DecodeBuffer {
public:
DecodeBuffer(const char* buffer, size_t len)
: buffer_(buffer), cursor_(buffer), beyond_(buffer + len) {
DCHECK(buffer != nullptr);
DCHECK_LE(len, MaxDecodeBufferLength());
}
explicit DecodeBuffer(base::StringPiece s)
: DecodeBuffer(s.data(), s.size()) {}
// Constructor for character arrays, typically in tests. For example:
// const char input[] = { 0x11 };
// DecodeBuffer b(input);
template <size_t N>
explicit DecodeBuffer(const char (&buf)[N]) : DecodeBuffer(buf, N) {}
bool Empty() const { return cursor_ >= beyond_; }
bool HasData() const { return cursor_ < beyond_; }
size_t Remaining() const {
DCHECK_LE(cursor_, beyond_);
return beyond_ - cursor_;
}
size_t Offset() const { return cursor_ - buffer_; }
size_t FullSize() const { return beyond_ - buffer_; }
// Returns the minimum of the number of bytes remaining in this DecodeBuffer
// and |length|, in support of determining how much of some structure/payload
// is in this DecodeBuffer.
size_t MinLengthRemaining(size_t length) const {
return std::min(length, Remaining());
}
// For string decoding, returns a pointer to the next byte/char to be decoded.
const char* cursor() const { return cursor_; }
// Advances the cursor (pointer to the next byte/char to be decoded).
void AdvanceCursor(size_t amount) {
DCHECK_LE(amount, Remaining()); // Need at least that much remaining.
DCHECK_EQ(subset_, nullptr) << "Access via subset only when present.";
cursor_ += amount;
}
// Only call methods starting "Decode" when there is enough input remaining.
char DecodeChar() {
DCHECK_LE(1u, Remaining()); // Need at least one byte remaining.
DCHECK_EQ(subset_, nullptr) << "Access via subset only when present.";
return *cursor_++;
}
uint8_t DecodeUInt8() { return static_cast<uint8_t>(DecodeChar()); }
uint16_t DecodeUInt16() {
DCHECK_LE(2u, Remaining());
const uint8_t b1 = DecodeUInt8();
const uint8_t b2 = DecodeUInt8();
// Note that chars are automatically promoted to ints during arithmetic,
// so the b1 << 8 doesn't end up as zero before being or-ed with b2.
// And the left-shift operator has higher precedence than the or operator.
return b1 << 8 | b2;
}
uint32_t DecodeUInt24() {
DCHECK_LE(3u, Remaining());
const uint8_t b1 = DecodeUInt8();
const uint8_t b2 = DecodeUInt8();
const uint8_t b3 = DecodeUInt8();
return b1 << 16 | b2 << 8 | b3;
}
// For 31-bit unsigned integers, where the 32nd bit is reserved for future
// use (i.e. the high-bit of the first byte of the encoding); examples:
// the Stream Id in a frame header or the Window Size Increment in a
// WINDOW_UPDATE frame.
uint32_t DecodeUInt31() {
DCHECK_LE(4u, Remaining());
const uint8_t b1 = DecodeUInt8() & 0x7f; // Mask out the high order bit.
const uint8_t b2 = DecodeUInt8();
const uint8_t b3 = DecodeUInt8();
const uint8_t b4 = DecodeUInt8();
return b1 << 24 | b2 << 16 | b3 << 8 | b4;
}
uint32_t DecodeUInt32() {
DCHECK_LE(4u, Remaining());
const uint8_t b1 = DecodeUInt8();
const uint8_t b2 = DecodeUInt8();
const uint8_t b3 = DecodeUInt8();
const uint8_t b4 = DecodeUInt8();
return b1 << 24 | b2 << 16 | b3 << 8 | b4;
}
// We assume the decode buffers will typically be modest in size (i.e. often a
// few KB, perhaps as high as 100KB). Let's make sure during testing that we
// don't go very high, with 32MB selected rather arbitrarily.
static constexpr size_t MaxDecodeBufferLength() { return 1 << 25; }
protected:
#ifndef NDEBUG
// These are part of validating during tests that there is at most one
// DecodeBufferSubset instance at a time for any DecodeBuffer instance.
void set_subset_of_base(DecodeBuffer* base, const DecodeBufferSubset* subset);
void clear_subset_of_base(DecodeBuffer* base,
const DecodeBufferSubset* subset);
#endif
private:
#ifndef NDEBUG
void set_subset(const DecodeBufferSubset* subset);
void clear_subset(const DecodeBufferSubset* subset);
#endif
// Prevent heap allocation of DecodeBuffer.
static void* operator new(size_t s);
static void* operator new[](size_t s);
static void operator delete(void* p);
static void operator delete[](void* p);
const char* const buffer_;
const char* cursor_;
const char* const beyond_;
const DecodeBufferSubset* subset_ = nullptr; // Used for DCHECKs.
DISALLOW_COPY_AND_ASSIGN(DecodeBuffer);
};
// DecodeBufferSubset is used when decoding a known sized chunk of data, which
// starts at base->cursor(), and continues for subset_len, which may be
// entirely in |base|, or may extend beyond it (hence the MinLengthRemaining
// in the constructor).
// There are two benefits to using DecodeBufferSubset: it ensures that the
// cursor of |base| is advanced when the subset's destructor runs, and it
// ensures that the consumer of the subset can't go beyond the subset which
// it is intended to decode.
// There must be only a single DecodeBufferSubset at a time for a base
// DecodeBuffer, though they can be nested (i.e. a DecodeBufferSubset's
// base may itself be a DecodeBufferSubset). This avoids the AdvanceCursor
// being called erroneously.
class NET_EXPORT_PRIVATE DecodeBufferSubset : public DecodeBuffer {
public:
DecodeBufferSubset(DecodeBuffer* base, size_t subset_len)
: DecodeBuffer(base->cursor(), base->MinLengthRemaining(subset_len)),
base_buffer_(base) {
#ifndef NDEBUG
DebugSetup();
#endif
}
~DecodeBufferSubset() {
size_t offset = Offset();
#ifndef NDEBUG
DebugTearDown();
#endif
base_buffer_->AdvanceCursor(offset);
}
private:
DecodeBuffer* const base_buffer_;
#ifndef NDEBUG
size_t start_base_offset_; // Used for DCHECKs.
size_t max_base_offset_; // Used for DCHECKs.
void DebugSetup();
void DebugTearDown();
#endif
DISALLOW_COPY_AND_ASSIGN(DecodeBufferSubset);
};
} // namespace net
#endif // NET_HTTP2_DECODER_DECODE_BUFFER_H_
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