/*
* Copyright (c) Facebook, Inc. and its affiliates.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#pragma once
#include <cassert>
#include <cstdarg>
#include <cstring>
#include <memory>
#include <stdexcept>
#include <type_traits>
#include <folly/Likely.h>
#include <folly/Memory.h>
#include <folly/Portability.h>
#include <folly/Range.h>
#include <folly/io/IOBuf.h>
#include <folly/io/IOBufQueue.h>
#include <folly/lang/Bits.h>
#include <folly/lang/Exception.h>
/**
* Cursor class for fast iteration over IOBuf chains.
*
* Cursor - Read-only access
*
* RWPrivateCursor - Read-write access, assumes private access to IOBuf chain
* RWUnshareCursor - Read-write access, calls unshare on write (COW)
* Appender - Write access, assumes private access to IOBuf chain
*
* Note that RW cursors write in the preallocated part of buffers (that is,
* between the buffer's data() and tail()), while Appenders append to the end
* of the buffer (between the buffer's tail() and bufferEnd()). Appenders
* automatically adjust the buffer pointers, so you may only use one
* Appender with a buffer chain; for this reason, Appenders assume private
* access to the buffer (you need to call unshare() yourself if necessary).
**/
namespace folly {
namespace io {
namespace detail {
template <class Derived, class BufType>
class CursorBase {
// Make all the templated classes friends for copy constructor.
template <class D, typename B>
friend class CursorBase;
public:
explicit CursorBase(BufType* buf) : crtBuf_(buf), buffer_(buf) {
if (crtBuf_) {
crtPos_ = crtBegin_ = crtBuf_->data();
crtEnd_ = crtBuf_->tail();
}
}
CursorBase(BufType* buf, size_t len) : crtBuf_(buf), buffer_(buf) {
if (crtBuf_) {
crtPos_ = crtBegin_ = crtBuf_->data();
crtEnd_ = crtBuf_->tail();
if (crtPos_ + len < crtEnd_) {
crtEnd_ = crtPos_ + len;
}
remainingLen_ = len - (crtEnd_ - crtPos_);
}
}
/**
* Copy constructor.
*
* This also allows constructing a CursorBase from other derived types.
* For instance, this allows constructing a Cursor from an RWPrivateCursor.
*/
template <class OtherDerived, class OtherBuf>
explicit CursorBase(const CursorBase<OtherDerived, OtherBuf>& cursor)
: crtBuf_(cursor.crtBuf_),
buffer_(cursor.buffer_),
crtBegin_(cursor.crtBegin_),
crtEnd_(cursor.crtEnd_),
crtPos_(cursor.crtPos_),
absolutePos_(cursor.absolutePos_),
remainingLen_(cursor.remainingLen_) {}
template <class OtherDerived, class OtherBuf>
explicit CursorBase(
const CursorBase<OtherDerived, OtherBuf>& cursor, size_t len)
: crtBuf_(cursor.crtBuf_),
buffer_(cursor.buffer_),
crtBegin_(cursor.crtBegin_),
crtEnd_(cursor.crtEnd_),
crtPos_(cursor.crtPos_),
absolutePos_(cursor.absolutePos_) {
if (cursor.isBounded() && len > cursor.remainingLen_ + cursor.length()) {
throw_exception<std::out_of_range>("underflow");
}
if (crtPos_ + len < crtEnd_) {
crtEnd_ = crtPos_ + len;
}
remainingLen_ = len - (crtEnd_ - crtPos_);
}
/**
* Reset cursor to point to a new buffer.
*/
void reset(BufType* buf) {
crtBuf_ = buf;
buffer_ = buf;
absolutePos_ = 0;
remainingLen_ = std::numeric_limits<size_t>::max();
if (crtBuf_) {
crtPos_ = crtBegin_ = crtBuf_->data();
crtEnd_ = crtBuf_->tail();
}
}
/**
* Get the current Cursor position relative to the head of IOBuf chain.
*/
size_t getCurrentPosition() const {
dcheckIntegrity();
return (crtPos_ - crtBegin_) + absolutePos_;
}
const uint8_t* data() const {
dcheckIntegrity();
return crtPos_;
}
/**
* Return the remaining space available in the current IOBuf.
*
* May return 0 if the cursor is at the end of an IOBuf. Use peekBytes()
* instead if you want to avoid this. peekBytes() will advance to the next
* non-empty IOBuf (up to the end of the chain) if the cursor is currently
* pointing at the end of a buffer.
*/
size_t length() const {
dcheckIntegrity();
return crtEnd_ - crtPos_;
}
/**
* Return the space available until the end of the entire IOBuf chain.
* For bounded Cursors, return the available space until the boundary.
*/
size_t totalLength() const {
size_t len = 0;
const IOBuf* buf = crtBuf_->next();
while (buf != buffer_ && len < remainingLen_) {
len += buf->length();
buf = buf->next();
}
return std::min(len, remainingLen_) + length();
}
/**
* Return true if the cursor could advance the specified number of bytes
* from its current position.
* This is useful for applications that want to do checked reads instead of
* catching exceptions and is more efficient than using totalLength as it
* walks the minimal set of buffers in the chain to determine the result.
*/
bool canAdvance(size_t amount) const {
if (isBounded() && amount > remainingLen_ + length()) {
return false;
}
const IOBuf* nextBuf = crtBuf_;
size_t available = length();
do {
if (available >= amount) {
return true;
}
amount -= available;
nextBuf = nextBuf->next();
available = nextBuf->length();
} while (nextBuf != buffer_);
return false;
}
/*
* Return true if the cursor is at the end of the entire IOBuf chain.
*/
bool isAtEnd() const {
dcheckIntegrity();
// Check for the simple cases first.
if (crtPos_ != crtEnd_) {
return false;
}
if (crtBuf_ == buffer_->prev()) {
return true;
}
if (isBounded() && remainingLen_ == 0) {
return true;
}
// We are at the end of a buffer, but it isn't the last buffer.
// We might still be at the end if the remaining buffers in the chain are
// empty.
const IOBuf* buf = crtBuf_->next();
while (buf != buffer_) {
if (buf->length() > 0) {
return false;
}
buf = buf->next();
}
return true;
}
/**
* Advances the cursor to the end of the entire IOBuf chain.
*/
void advanceToEnd() {
// Simple case, we're already in the last IOBuf.
if (crtBuf_ == buffer_->prev()) {
crtPos_ = crtEnd_;
return;
}
auto* nextBuf = crtBuf_->next();
while (nextBuf != buffer_) {
if (isBounded() && remainingLen_ == 0) {
crtPos_ = crtEnd_;
return;
}
absolutePos_ += crtEnd_ - crtBegin_;
crtBuf_ = nextBuf;
nextBuf = crtBuf_->next();
crtBegin_ = crtBuf_->data();
crtEnd_ = crtBuf_->tail();
if (isBounded()) {
if (crtBegin_ + remainingLen_ < crtEnd_) {
crtEnd_ = crtBegin_ + remainingLen_;
}
remainingLen_ -= crtEnd_ - crtBegin_;
}
crtPos_ = crtEnd_;
derived().advanceDone();
}
}
Derived& operator+=(size_t offset) {
Derived* p = static_cast<Derived*>(this);
p->skip(offset);
return *p;
}
Derived operator+(size_t offset) const {
Derived other(*this);
other.skip(offset);
return other;
}
Derived& operator-=(size_t offset) {
Derived* p = static_cast<Derived*>(this);
p->retreat(offset);
return *p;
}
Derived operator-(size_t offset) const {
Derived other(*this);
other.retreat(offset);
return other;
}
/**
* Compare cursors for equality/inequality.
*
* Two cursors are equal if they are pointing to the same location in the
* same IOBuf chain.
*/
bool operator==(const Derived& other) const {
const IOBuf* crtBuf = crtBuf_;
auto crtPos = crtPos_;
// We can be pointing to the end of a buffer chunk, find first non-empty.
while (crtPos == crtBuf->tail() && crtBuf != buffer_->prev()) {
crtBuf = crtBuf->next();
crtPos = crtBuf->data();
}
const IOBuf* crtBufOther = other.crtBuf_;
auto crtPosOther = other.crtPos_;
// We can be pointing to the end of a buffer chunk, find first non-empty.
while (crtPosOther == crtBufOther->tail() &&
crtBufOther != other.buffer_->prev()) {
crtBufOther = crtBufOther->next();
crtPosOther = crtBufOther->data();
}
return (crtPos == crtPosOther) && (crtBuf == crtBufOther);
}
bool operator!=(const Derived& other) const { return !operator==(other); }
template <class T>
typename std::enable_if<std::is_arithmetic<T>::value, bool>::type tryRead(
T& val) {
if (LIKELY(crtPos_ + sizeof(T) <= crtEnd_)) {
val = loadUnaligned<T>(data());
crtPos_ += sizeof(T);
return true;
}
return pullAtMostSlow(&val, sizeof(T)) == sizeof(T);
}
template <class T>
bool tryReadBE(T& val) {
const bool result = tryRead(val);
val = Endian::big(val);
return result;
}
template <class T>
bool tryReadLE(T& val) {
const bool result = tryRead(val);
val = Endian::little(val);
return result;
}
template <class T>
T read() {
if (LIKELY(crtPos_ + sizeof(T) <= crtEnd_)) {
T val = loadUnaligned<T>(data());
crtPos_ += sizeof(T);
return val;
} else {
return readSlow<T>();
}
}
template <class T>
T readBE() {
return Endian::big(read<T>());
}
template <class T>
T readLE() {
return Endian::little(read<T>());
}
/**
* Read a fixed-length string.
*
* The std::string-based APIs should probably be avoided unless you
* ultimately want the data to live in an std::string. You're better off
* using the pull() APIs to copy into a raw buffer otherwise.
*/
std::string readFixedString(size_t len) {
std::string str;
str.reserve(len);
if (LIKELY(length() >= len)) {
str.append(reinterpret_cast<const char*>(data()), len);
crtPos_ += len;
} else {
readFixedStringSlow(&str, len);
}
return str;
}
/**
* Read a string consisting of bytes until the given terminator character is
* seen. Raises an std::length_error if maxLength bytes have been processed
* before the terminator is seen.
*
* See comments in readFixedString() about when it's appropriate to use this
* vs. using pull().
*/
std::string readTerminatedString(
char termChar = '\0',
size_t maxLength = std::numeric_limits<size_t>::max());
/*
* Read all bytes until the specified predicate returns true.
*
* The predicate will be called on each byte in turn, until it returns false
* or until the end of the IOBuf chain is reached.
*
* Returns the result as a string.
*/
template <typename Predicate>
std::string readWhile(const Predicate& predicate);
/*
* Read all bytes until the specified predicate returns true.
*
* This is a more generic version of readWhile() takes an arbitrary Output
* object, and calls Output::append() with each chunk of matching data.
*/
template <typename Predicate, typename Output>
void readWhile(const Predicate& predicate, Output& out);
/*
* Skip all bytes until the specified predicate returns true.
*
* The predicate will be called on each byte in turn, until it returns false
* or until the end of the IOBuf chain is reached.
*/
template <typename Predicate>
void skipWhile(const Predicate& predicate);
size_t skipAtMost(size_t len) {
dcheckIntegrity();
if (LIKELY(crtPos_ + len < crtEnd_)) {
crtPos_ += len;
return len;
}
return skipAtMostSlow(len);
}
void skip(size_t len) {
dcheckIntegrity();
if (LIKELY(crtPos_ + len < crtEnd_)) {
crtPos_ += len;
} else {
skipSlow(len);
}
}
/**
* Skip bytes in the current IOBuf without advancing to the next one.
* Precondition: length() >= len
*/
void skipNoAdvance(size_t len) {
DCHECK_LE(len, length());
crtPos_ += len;
}
size_t retreatAtMost(size_t len) {
dcheckIntegrity();
if (len <= static_cast<size_t>(crtPos_ - crtBegin_)) {
crtPos_ -= len;
return len;
}
return retreatAtMostSlow(len);
}
void retreat(size_t len) {
dcheckIntegrity();
if (len <= static_cast<size_t>(crtPos_ - crtBegin_)) {
crtPos_ -= len;
} else {
retreatSlow(len);
}
}
size_t pullAtMost(void* buf, size_t len) {
dcheckIntegrity();
// Fast path: it all fits in one buffer.
if (LIKELY(crtPos_ + len <= crtEnd_)) {
memcpy(buf, data(), len);
crtPos_ += len;
return len;
}
return pullAtMostSlow(buf, len);
}
void pull(void* buf, size_t len) {
if (UNLIKELY(len == 0)) {
return;
}
dcheckIntegrity();
if (LIKELY(crtPos_ + len <= crtEnd_)) {
memcpy(buf, data(), len);
crtPos_ += len;
} else {
pullSlow(buf, len);
}
}
/**
* Return the available data in the current buffer.
* If you want to gather more data from the chain into a contiguous region
* (for hopefully zero-copy access), use gather() before peekBytes().
*/
ByteRange peekBytes() {
// Ensure that we're pointing to valid data
size_t available = length();
while (UNLIKELY(available == 0 && tryAdvanceBuffer())) {
available = length();
}
return ByteRange{data(), available};
}
/**
* Alternate version of peekBytes() that returns a std::pair
* instead of a ByteRange. (This method pre-dates ByteRange.)
*
* This function will eventually be deprecated.
*/
std::pair<const uint8_t*, size_t> peek() {
auto bytes = peekBytes();
return std::make_pair(bytes.data(), bytes.size());
}
void clone(std::unique_ptr<folly::IOBuf>& buf, size_t len) {
if (UNLIKELY(cloneAtMost(buf, len) != len)) {
throw_exception<std::out_of_range>("underflow");
}
}
void clone(folly::IOBuf& buf, size_t len) {
if (UNLIKELY(cloneAtMost(buf, len) != len)) {
throw_exception<std::out_of_range>("underflow");
}
}
size_t cloneAtMost(folly::IOBuf& buf, size_t len) {
// We might be at the end of buffer.
advanceBufferIfEmpty();
std::unique_ptr<folly::IOBuf> tmp;
size_t copied = 0;
for (int loopCount = 0; true; ++loopCount) {
// Fast path: it all fits in one buffer.
size_t available = length();
if (LIKELY(available >= len)) {
if (loopCount == 0) {
crtBuf_->cloneOneInto(buf);
buf.trimStart(crtPos_ - crtBegin_);
buf.trimEnd(buf.length() - len);
} else {
tmp = crtBuf_->cloneOne();
tmp->trimStart(crtPos_ - crtBegin_);
tmp->trimEnd(tmp->length() - len);
buf.prependChain(std::move(tmp));
}
crtPos_ += len;
advanceBufferIfEmpty();
return copied + len;
}
if (loopCount == 0) {
crtBuf_->cloneOneInto(buf);
buf.trimStart(crtPos_ - crtBegin_);
} else {
tmp = crtBuf_->cloneOne();
tmp->trimStart(crtPos_ - crtBegin_);
buf.prependChain(std::move(tmp));
}
copied += available;
if (UNLIKELY(!tryAdvanceBuffer())) {
return copied;
}
len -= available;
}
}
size_t cloneAtMost(std::unique_ptr<folly::IOBuf>& buf, size_t len) {
if (!buf) {
buf = std::make_unique<folly::IOBuf>();
}
return cloneAtMost(*buf, len);
}
/**
* Return the distance between two cursors.
*/
size_t operator-(const CursorBase& other) const {
BufType* otherBuf = other.crtBuf_;
size_t len = 0;
if (otherBuf != crtBuf_) {
if (other.remainingLen_ == 0) {
len += otherBuf->tail() - other.crtPos_;
} else {
len += other.crtEnd_ - other.crtPos_;
}
for (otherBuf = otherBuf->next();
otherBuf != crtBuf_ && otherBuf != other.buffer_;
otherBuf = otherBuf->next()) {
len += otherBuf->length();
}
if (otherBuf == other.buffer_) {
throw_exception<std::out_of_range>("wrap-around");
}
len += crtPos_ - crtBegin_;
} else {
if (crtPos_ < other.crtPos_) {
throw_exception<std::out_of_range>("underflow");
}
len += crtPos_ - other.crtPos_;
}
return len;
}
/**
* Return the distance from the given IOBuf to the this cursor.
*/
size_t operator-(const BufType* buf) const {
size_t len = 0;
const BufType* curBuf = buf;
while (curBuf != crtBuf_) {
len += curBuf->length();
curBuf = curBuf->next();
if (curBuf == buf || curBuf == buffer_) {
throw_exception<std::out_of_range>("wrap-around");
}
}
len += crtPos_ - crtBegin_;
return len;
}
bool isBounded() const {
return remainingLen_ != std::numeric_limits<size_t>::max();
}
protected:
void dcheckIntegrity() const {
DCHECK(crtBegin_ <= crtPos_ && crtPos_ <= crtEnd_);
DCHECK(crtBuf_ == nullptr || crtBegin_ == crtBuf_->data());
DCHECK(
crtBuf_ == nullptr ||
(std::size_t)(crtEnd_ - crtBegin_) <= crtBuf_->length());
}
~CursorBase() {}
BufType* head() { return buffer_; }
bool tryAdvanceBuffer() {
BufType* nextBuf = crtBuf_->next();
if (UNLIKELY(nextBuf == buffer_) || remainingLen_ == 0) {
crtPos_ = crtEnd_;
return false;
}
absolutePos_ += crtEnd_ - crtBegin_;
crtBuf_ = nextBuf;
crtPos_ = crtBegin_ = crtBuf_->data();
crtEnd_ = crtBuf_->tail();
if (isBounded()) {
if (crtPos_ + remainingLen_ < crtEnd_) {
crtEnd_ = crtPos_ + remainingLen_;
}
remainingLen_ -= crtEnd_ - crtPos_;
}
derived().advanceDone();
return true;
}
bool tryRetreatBuffer() {
if (UNLIKELY(crtBuf_ == buffer_)) {
crtPos_ = crtBegin_;
return false;
}
if (isBounded()) {
remainingLen_ += crtEnd_ - crtBegin_;
}
crtBuf_ = crtBuf_->prev();
crtBegin_ = crtBuf_->data();
crtPos_ = crtEnd_ = crtBuf_->tail();
absolutePos_ -= crtEnd_ - crtBegin_;
derived().advanceDone();
return true;
}
void advanceBufferIfEmpty() {
dcheckIntegrity();
if (crtPos_ == crtEnd_) {
tryAdvanceBuffer();
}
}
BufType* crtBuf_;
BufType* buffer_;
const uint8_t* crtBegin_{nullptr};
const uint8_t* crtEnd_{nullptr};
const uint8_t* crtPos_{nullptr};
size_t absolutePos_{0};
// For bounded Cursor, remainingLen_ is the remaining number of data bytes
// in subsequent IOBufs in the chain. For unbounded Cursor, remainingLen_
// is set to the max of size_t
size_t remainingLen_{std::numeric_limits<size_t>::max()};
private:
Derived& derived() { return static_cast<Derived&>(*this); }
Derived const& derived() const { return static_cast<const Derived&>(*this); }
template <class T>
FOLLY_NOINLINE T readSlow() {
T val;
pullSlow(&val, sizeof(T));
return val;
}
FOLLY_NOINLINE void readFixedStringSlow(std::string* str, size_t len) {
for (size_t available; (available = length()) < len;) {
str->append(reinterpret_cast<const char*>(data()), available);
if (UNLIKELY(!tryAdvanceBuffer())) {
throw_exception<std::out_of_range>("string underflow");
}
len -= available;
}
str->append(reinterpret_cast<const char*>(data()), len);
crtPos_ += len;
advanceBufferIfEmpty();
}
FOLLY_NOINLINE size_t pullAtMostSlow(void* buf, size_t len) {
// If the length of this buffer is 0 try advancing it.
// Otherwise on the first iteration of the following loop memcpy is called
// with a null source pointer.
if (UNLIKELY(length() == 0 && !tryAdvanceBuffer())) {
return 0;
}
uint8_t* p = reinterpret_cast<uint8_t*>(buf);
size_t copied = 0;
for (size_t available; (available = length()) < len;) {
memcpy(p, data(), available);
copied += available;
if (UNLIKELY(!tryAdvanceBuffer())) {
return copied;
}
p += available;
len -= available;
}
memcpy(p, data(), len);
crtPos_ += len;
advanceBufferIfEmpty();
return copied + len;
}
FOLLY_NOINLINE void pullSlow(void* buf, size_t len) {
if (UNLIKELY(pullAtMostSlow(buf, len) != len)) {
throw_exception<std::out_of_range>("underflow");
}
}
FOLLY_NOINLINE size_t skipAtMostSlow(size_t len) {
size_t skipped = 0;
for (size_t available; (available = length()) < len;) {
skipped += available;
if (UNLIKELY(!tryAdvanceBuffer())) {
return skipped;
}
len -= available;
}
crtPos_ += len;
advanceBufferIfEmpty();
return skipped + len;
}
FOLLY_NOINLINE void skipSlow(size_t len) {
if (UNLIKELY(skipAtMostSlow(len) != len)) {
throw_exception<std::out_of_range>("underflow");
}
}
FOLLY_NOINLINE size_t retreatAtMostSlow(size_t len) {
size_t retreated = 0;
for (size_t available; (available = crtPos_ - crtBegin_) < len;) {
retreated += available;
if (UNLIKELY(!tryRetreatBuffer())) {
return retreated;
}
len -= available;
}
crtPos_ -= len;
return retreated + len;
}
FOLLY_NOINLINE void retreatSlow(size_t len) {
if (UNLIKELY(retreatAtMostSlow(len) != len)) {
throw_exception<std::out_of_range>("underflow");
}
}
void advanceDone() {}
};
} // namespace detail
class Cursor : public detail::CursorBase<Cursor, const IOBuf> {
public:
explicit Cursor(const IOBuf* buf)
: detail::CursorBase<Cursor, const IOBuf>(buf) {}
explicit Cursor(const IOBuf* buf, size_t len)
: detail::CursorBase<Cursor, const IOBuf>(buf, len) {}
template <class OtherDerived, class OtherBuf>
explicit Cursor(const detail::CursorBase<OtherDerived, OtherBuf>& cursor)
: detail::CursorBase<Cursor, const IOBuf>(cursor) {}
template <class OtherDerived, class OtherBuf>
Cursor(const detail::CursorBase<OtherDerived, OtherBuf>& cursor, size_t len)
: detail::CursorBase<Cursor, const IOBuf>(cursor, len) {}
};
namespace detail {
template <class Derived>
class Writable {
public:
template <class T>
typename std::enable_if<std::is_arithmetic<T>::value>::type write(T value) {
const uint8_t* u8 = reinterpret_cast<const uint8_t*>(&value);
Derived* d = static_cast<Derived*>(this);
d->push(u8, sizeof(T));
}
template <class T>
void writeBE(T value) {
Derived* d = static_cast<Derived*>(this);
d->write(Endian::big(value));
}
template <class T>
void writeLE(T value) {
Derived* d = static_cast<Derived*>(this);
d->write(Endian::little(value));
}
void push(const uint8_t* buf, size_t len) {
Derived* d = static_cast<Derived*>(this);
if (d->pushAtMost(buf, len) != len) {
throw_exception<std::out_of_range>("overflow");
}
}
void push(ByteRange buf) {
if (this->pushAtMost(buf) != buf.size()) {
throw_exception<std::out_of_range>("overflow");
}
}
size_t pushAtMost(ByteRange buf) {
Derived* d = static_cast<Derived*>(this);
return d->pushAtMost(buf.data(), buf.size());
}
/**
* push len bytes of data from input cursor, data could be in an IOBuf chain.
* If input cursor contains less than len bytes, or this cursor has less than
* len bytes writable space, an out_of_range exception will be thrown.
*/
void push(Cursor cursor, size_t len) {
if (this->pushAtMost(cursor, len) != len) {
throw_exception<std::out_of_range>("overflow");
}
}
size_t pushAtMost(Cursor cursor, size_t len) {
size_t written = 0;
for (;;) {
auto currentBuffer = cursor.peekBytes();
const uint8_t* crtData = currentBuffer.data();
size_t available = currentBuffer.size();
if (available == 0) {
// end of buffer chain
return written;
}
// all data is in current buffer
if (available >= len) {
this->push(crtData, len);
cursor.skip(len);
return written + len;
}
// write the whole current IOBuf
this->push(crtData, available);
cursor.skip(available);
written += available;
len -= available;
}
}
};
} // namespace detail
enum class CursorAccess { PRIVATE, UNSHARE };
template <CursorAccess access>
class RWCursor : public detail::CursorBase<RWCursor<access>, IOBuf>,
public detail::Writable<RWCursor<access>> {
friend class detail::CursorBase<RWCursor<access>, IOBuf>;
public:
explicit RWCursor(IOBuf* buf)
: detail::CursorBase<RWCursor<access>, IOBuf>(buf), maybeShared_(true) {}
explicit RWCursor(IOBufQueue& queue)
: RWCursor((queue.flushCache(), queue.head_.get())) {}
template <class OtherDerived, class OtherBuf>
explicit RWCursor(const detail::CursorBase<OtherDerived, OtherBuf>& cursor)
: detail::CursorBase<RWCursor<access>, IOBuf>(cursor),
maybeShared_(true) {
CHECK(!cursor.isBounded())
<< "Creating RWCursor from bounded Cursor is not allowed";
}
/**
* Gather at least n bytes contiguously into the current buffer,
* by coalescing subsequent buffers from the chain as necessary.
*/
void gather(size_t n) {
// Forbid attempts to gather beyond the end of this IOBuf chain.
// Otherwise we could try to coalesce the head of the chain and end up
// accidentally freeing it, invalidating the pointer owned by external
// code.
//
// If crtBuf_ == head() then IOBuf::gather() will perform all necessary
// checking. We only have to perform an explicit check here when calling
// gather() on a non-head element.
if (this->crtBuf_ != this->head() && this->totalLength() < n) {
throw std::overflow_error("cannot gather() past the end of the chain");
}
size_t offset = this->crtPos_ - this->crtBegin_;
this->crtBuf_->gather(offset + n);
this->crtBegin_ = this->crtBuf_->data();
this->crtEnd_ = this->crtBuf_->tail();
this->crtPos_ = this->crtBegin_ + offset;
}
void gatherAtMost(size_t n) {
this->dcheckIntegrity();
size_t size = std::min(n, this->totalLength());
size_t offset = this->crtPos_ - this->crtBegin_;
this->crtBuf_->gather(offset + size);
this->crtBegin_ = this->crtBuf_->data();
this->crtEnd_ = this->crtBuf_->tail();
this->crtPos_ = this->crtBegin_ + offset;
}
using detail::Writable<RWCursor<access>>::pushAtMost;
size_t pushAtMost(const uint8_t* buf, size_t len) {
// We have to explicitly check for an input length of 0.
// We support buf being nullptr in this case, but we need to avoid calling
// memcpy() with a null source pointer, since that is undefined behavior
// even if the length is 0.
if (len == 0) {
return 0;
}
size_t copied = 0;
for (;;) {
// Fast path: the current buffer is big enough.
size_t available = this->length();
if (LIKELY(available >= len)) {
if (access == CursorAccess::UNSHARE) {
maybeUnshare();
}
memcpy(writableData(), buf, len);
this->crtPos_ += len;
return copied + len;
}
if (access == CursorAccess::UNSHARE) {
maybeUnshare();
}
memcpy(writableData(), buf, available);
copied += available;
if (UNLIKELY(!this->tryAdvanceBuffer())) {
return copied;
}
buf += available;
len -= available;
}
}
void insert(std::unique_ptr<folly::IOBuf> buf) {
this->dcheckIntegrity();
this->absolutePos_ += buf->computeChainDataLength();
if (this->crtPos_ == this->crtBegin_ && this->crtBuf_ != this->buffer_) {
// Can just prepend
this->crtBuf_->prependChain(std::move(buf));
} else {
IOBuf* nextBuf;
std::unique_ptr<folly::IOBuf> remaining;
if (this->crtPos_ != this->crtEnd_) {
// Need to split current IOBuf in two.
remaining = this->crtBuf_->cloneOne();
remaining->trimStart(this->crtPos_ - this->crtBegin_);
nextBuf = remaining.get();
buf->prependChain(std::move(remaining));
} else {
// Can just append
nextBuf = this->crtBuf_->next();
}
this->crtBuf_->trimEnd(this->length());
this->absolutePos_ += this->crtPos_ - this->crtBegin_;
this->crtBuf_->appendChain(std::move(buf));
if (nextBuf == this->buffer_) {
// We've just appended to the end of the buffer, so advance to the end.
this->crtBuf_ = this->buffer_->prev();
this->crtBegin_ = this->crtBuf_->data();
this->crtPos_ = this->crtEnd_ = this->crtBuf_->tail();
// This has already been accounted for, so remove it.
this->absolutePos_ -= this->crtEnd_ - this->crtBegin_;
} else {
// Jump past the new links
this->crtBuf_ = nextBuf;
this->crtPos_ = this->crtBegin_ = this->crtBuf_->data();
this->crtEnd_ = this->crtBuf_->tail();
}
}
}
uint8_t* writableData() {
this->dcheckIntegrity();
return this->crtBuf_->writableData() + (this->crtPos_ - this->crtBegin_);
}
private:
void maybeUnshare() {
if (UNLIKELY(maybeShared_)) {
size_t offset = this->crtPos_ - this->crtBegin_;
this->crtBuf_->unshareOne();
this->crtBegin_ = this->crtBuf_->data();
this->crtEnd_ = this->crtBuf_->tail();
this->crtPos_ = this->crtBegin_ + offset;
maybeShared_ = false;
}
}
void advanceDone() { maybeShared_ = true; }
bool maybeShared_;
};
typedef RWCursor<CursorAccess::PRIVATE> RWPrivateCursor;
typedef RWCursor<CursorAccess::UNSHARE> RWUnshareCursor;
/**
* Append to the end of a buffer chain, growing the chain (by allocating new
* buffers) in increments of at least growth bytes every time. Won't grow
* (and push() and ensure() will throw) if growth == 0.
*
* TODO(tudorb): add a flavor of Appender that reallocates one IOBuf instead
* of chaining.
*/
class Appender : public detail::Writable<Appender> {
public:
Appender(IOBuf* buf, std::size_t growth)
: buffer_(buf), crtBuf_(buf->prev()), growth_(growth) {}
uint8_t* writableData() { return crtBuf_->writableTail(); }
size_t length() const { return crtBuf_->tailroom(); }
/**
* Mark n bytes (must be <= length()) as appended, as per the
* IOBuf::append() method.
*/
void append(size_t n) { crtBuf_->append(n); }
/**
* Ensure at least n contiguous bytes available to write.
* Postcondition: length() >= n.
*/
void ensure(std::size_t n) {
if (LIKELY(length() >= n)) {
return;
}
// Waste the rest of the current buffer and allocate a new one.
// Don't make it too small, either.
if (growth_ == 0) {
throw_exception<std::out_of_range>("can't grow buffer chain");
}
n = std::max(n, growth_);
buffer_->prependChain(IOBuf::create(n));
crtBuf_ = buffer_->prev();
}
using detail::Writable<Appender>::pushAtMost;
size_t pushAtMost(const uint8_t* buf, size_t len) {
// We have to explicitly check for an input length of 0.
// We support buf being nullptr in this case, but we need to avoid calling
// memcpy() with a null source pointer, since that is undefined behavior
// even if the length is 0.
if (len == 0) {
return 0;
}
// If the length of this buffer is 0 try growing it.
// Otherwise on the first iteration of the following loop memcpy is called
// with a null source pointer.
if (UNLIKELY(length() == 0 && !tryGrowChain())) {
return 0;
}
size_t copied = 0;
for (;;) {
// Fast path: it all fits in one buffer.
size_t available = length();
if (LIKELY(available >= len)) {
memcpy(writableData(), buf, len);
append(len);
return copied + len;
}
memcpy(writableData(), buf, available);
append(available);
copied += available;
if (UNLIKELY(!tryGrowChain())) {
return copied;
}
buf += available;
len -= available;
}
}
/*
* Append to the end of this buffer, using a printf() style
* format specifier.
*
* Note that folly/Format.h provides nicer and more type-safe mechanisms
* for formatting strings, which should generally be preferred over
* printf-style formatting. Appender objects can be used directly as an
* output argument for Formatter objects. For example:
*
* Appender app(&iobuf);
* format("{} {}", "hello", "world")(app);
*
* However, printf-style strings are still needed when dealing with existing
* third-party code in some cases.
*
* This will always add a nul-terminating character after the end
* of the output. However, the buffer data length will only be updated to
* include the data itself. The nul terminator will be the first byte in the
* buffer tailroom.
*
* This method may throw exceptions on error.
*/
void printf(FOLLY_PRINTF_FORMAT const char* fmt, ...)
FOLLY_PRINTF_FORMAT_ATTR(2, 3);
void vprintf(const char* fmt, va_list ap);
/*
* Calling an Appender object with a StringPiece will append the string
* piece. This allows Appender objects to be used directly with
* Formatter.
*/
void operator()(StringPiece sp) { push(ByteRange(sp)); }
private:
bool tryGrowChain() {
assert(crtBuf_->next() == buffer_);
if (growth_ == 0) {
return false;
}
buffer_->prependChain(IOBuf::create(growth_));
crtBuf_ = buffer_->prev();
return true;
}
IOBuf* buffer_;
IOBuf* crtBuf_;
std::size_t growth_;
};
class QueueAppender : public detail::Writable<QueueAppender> {
public:
/**
* Create an Appender that writes to a IOBufQueue. When we allocate
* space in the queue, we grow no more than growth bytes at once
* (unless you call ensure() with a bigger value yourself).
*/
QueueAppender(IOBufQueue* queue, std::size_t growth)
: queueCache_(queue), growth_(growth) {}
void reset(IOBufQueue* queue, std::size_t growth) {
queueCache_.reset(queue);
growth_ = growth;
}
uint8_t* writableData() { return queueCache_.writableData(); }
size_t length() { return queueCache_.length(); }
void append(size_t n) { queueCache_.append(n); }
// Ensure at least n contiguous; can go above growth_, throws if
// not enough room.
void ensure(size_t n) {
if (length() < n) {
ensureSlow(n);
}
}
template <class T>
typename std::enable_if<std::is_arithmetic<T>::value>::type write(T value) {
// We can't fail.
if (length() >= sizeof(T)) {
storeUnaligned(queueCache_.writableData(), value);
queueCache_.appendUnsafe(sizeof(T));
} else {
writeSlow<T>(value);
}
}
using detail::Writable<QueueAppender>::pushAtMost;
size_t pushAtMost(const uint8_t* buf, size_t len) {
// Fill the current buffer
const size_t copyLength = std::min(len, length());
if (copyLength != 0) {
memcpy(writableData(), buf, copyLength);
queueCache_.appendUnsafe(copyLength);
buf += copyLength;
}
size_t remaining = len - copyLength;
// Allocate more buffers as necessary
while (remaining != 0) {
auto p = queueCache_.queue()->preallocate(
std::min(remaining, growth_), growth_, remaining);
memcpy(p.first, buf, p.second);
queueCache_.queue()->postallocate(p.second);
buf += p.second;
remaining -= p.second;
}
return len;
}
void insert(std::unique_ptr<folly::IOBuf> buf) {
if (buf) {
queueCache_.queue()->append(std::move(buf), true);
}
}
void insert(const folly::IOBuf& buf) {
queueCache_.queue()->append(buf, true);
}
template <CursorAccess access>
explicit operator RWCursor<access>() {
return RWCursor<access>(*queueCache_.queue());
}
private:
folly::IOBufQueue::WritableRangeCache queueCache_{nullptr};
size_t growth_{0};
FOLLY_NOINLINE void ensureSlow(size_t n) {
queueCache_.queue()->preallocate(n, growth_);
queueCache_.fillCache();
}
template <class T>
typename std::enable_if<std::is_arithmetic<T>::value>::type FOLLY_NOINLINE
writeSlow(T value) {
queueCache_.queue()->preallocate(sizeof(T), growth_);
queueCache_.fillCache();
storeUnaligned(queueCache_.writableData(), value);
queueCache_.appendUnsafe(sizeof(T));
}
};
} // namespace io
} // namespace folly
#include <folly/io/Cursor-inl.h>