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/*
* Copyright 2013-present Facebook, Inc.
*
* 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 <glog/logging.h>
#include <atomic>
#include <cassert>
#include <cinttypes>
#include <cstddef>
#include <cstring>
#include <iterator>
#include <limits>
#include <memory>
#include <type_traits>
#include <folly/FBString.h>
#include <folly/FBVector.h>
#include <folly/Portability.h>
#include <folly/Range.h>
#include <folly/detail/Iterators.h>
#include <folly/lang/Ordering.h>
#include <folly/portability/SysUio.h>
// Ignore shadowing warnings within this file, so includers can use -Wshadow.
FOLLY_PUSH_WARNING
FOLLY_GNU_DISABLE_WARNING("-Wshadow")
namespace folly {
/**
* An IOBuf is a pointer to a buffer of data.
*
* IOBuf objects are intended to be used primarily for networking code, and are
* modelled somewhat after FreeBSD's mbuf data structure, and Linux's sk_buff
* structure.
*
* IOBuf objects facilitate zero-copy network programming, by allowing multiple
* IOBuf objects to point to the same underlying buffer of data, using a
* reference count to track when the buffer is no longer needed and can be
* freed.
*
*
* Data Layout
* -----------
*
* The IOBuf itself is a small object containing a pointer to the buffer and
* information about which segment of the buffer contains valid data.
*
* The data layout looks like this:
*
* +-------+
* | IOBuf |
* +-------+
* /
* |
* v
* +------------+--------------------+-----------+
* | headroom | data | tailroom |
* +------------+--------------------+-----------+
* ^ ^ ^ ^
* buffer() data() tail() bufferEnd()
*
* The length() method returns the length of the valid data; capacity()
* returns the entire capacity of the buffer (from buffer() to bufferEnd()).
* The headroom() and tailroom() methods return the amount of unused capacity
* available before and after the data.
*
*
* Buffer Sharing
* --------------
*
* The buffer itself is reference counted, and multiple IOBuf objects may point
* to the same buffer. Each IOBuf may point to a different section of valid
* data within the underlying buffer. For example, if multiple protocol
* requests are read from the network into a single buffer, a separate IOBuf
* may be created for each request, all sharing the same underlying buffer.
*
* In other words, when multiple IOBufs share the same underlying buffer, the
* data() and tail() methods on each IOBuf may point to a different segment of
* the data. However, the buffer() and bufferEnd() methods will point to the
* same location for all IOBufs sharing the same underlying buffer.
*
* +-----------+ +---------+
* | IOBuf 1 | | IOBuf 2 |
* +-----------+ +---------+
* | | _____/ |
* data | tail |/ data | tail
* v v v
* +-------------------------------------+
* | | | | |
* +-------------------------------------+
*
* If you only read data from an IOBuf, you don't need to worry about other
* IOBuf objects possibly sharing the same underlying buffer. However, if you
* ever write to the buffer you need to first ensure that no other IOBufs point
* to the same buffer. The unshare() method may be used to ensure that you
* have an unshared buffer.
*
*
* IOBuf Chains
* ------------
*
* IOBuf objects also contain pointers to next and previous IOBuf objects.
* This can be used to represent a single logical piece of data that its stored
* in non-contiguous chunks in separate buffers.
*
* A single IOBuf object can only belong to one chain at a time.
*
* IOBuf chains are always circular. The "prev" pointer in the head of the
* chain points to the tail of the chain. However, it is up to the user to
* decide which IOBuf is the head. Internally the IOBuf code does not care
* which element is the head.
*
* The lifetime of all IOBufs in the chain are linked: when one element in the
* chain is deleted, all other chained elements are also deleted. Conceptually
* it is simplest to treat this as if the head of the chain owns all other
* IOBufs in the chain. When you delete the head of the chain, it will delete
* the other elements as well. For this reason, prependChain() and
* appendChain() take ownership of of the new elements being added to this
* chain.
*
* When the coalesce() method is used to coalesce an entire IOBuf chain into a
* single IOBuf, all other IOBufs in the chain are eliminated and automatically
* deleted. The unshare() method may coalesce the chain; if it does it will
* similarly delete all IOBufs eliminated from the chain.
*
* As discussed in the following section, it is up to the user to maintain a
* lock around the entire IOBuf chain if multiple threads need to access the
* chain. IOBuf does not provide any internal locking.
*
*
* Synchronization
* ---------------
*
* When used in multithread programs, a single IOBuf object should only be used
* in a single thread at a time. If a caller uses a single IOBuf across
* multiple threads the caller is responsible for using an external lock to
* synchronize access to the IOBuf.
*
* Two separate IOBuf objects may be accessed concurrently in separate threads
* without locking, even if they point to the same underlying buffer. The
* buffer reference count is always accessed atomically, and no other
* operations should affect other IOBufs that point to the same data segment.
* The caller is responsible for using unshare() to ensure that the data buffer
* is not shared by other IOBufs before writing to it, and this ensures that
* the data itself is not modified in one thread while also being accessed from
* another thread.
*
* For IOBuf chains, no two IOBufs in the same chain should be accessed
* simultaneously in separate threads. The caller must maintain a lock around
* the entire chain if the chain, or individual IOBufs in the chain, may be
* accessed by multiple threads.
*
*
* IOBuf Object Allocation
* -----------------------
*
* IOBuf objects themselves exist separately from the data buffer they point
* to. Therefore one must also consider how to allocate and manage the IOBuf
* objects.
*
* It is more common to allocate IOBuf objects on the heap, using the create(),
* takeOwnership(), or wrapBuffer() factory functions. The clone()/cloneOne()
* functions also return new heap-allocated IOBufs. The createCombined()
* function allocates the IOBuf object and data storage space together, in a
* single memory allocation. This can improve performance, particularly if you
* know that the data buffer and the IOBuf itself will have similar lifetimes.
*
* That said, it is also possible to allocate IOBufs on the stack or inline
* inside another object as well. This is useful for cases where the IOBuf is
* short-lived, or when the overhead of allocating the IOBuf on the heap is
* undesirable.
*
* However, note that stack-allocated IOBufs may only be used as the head of a
* chain (or standalone as the only IOBuf in a chain). All non-head members of
* an IOBuf chain must be heap allocated. (All functions to add nodes to a
* chain require a std::unique_ptr<IOBuf>, which enforces this requrement.)
*
* Copying IOBufs is only meaningful for the head of a chain. The entire chain
* is cloned; the IOBufs will become shared, and the old and new IOBufs will
* refer to the same underlying memory.
*
* IOBuf Sharing
* -------------
*
* The IOBuf class manages sharing of the underlying buffer that it points to,
* maintaining a reference count if multiple IOBufs are pointing at the same
* buffer.
*
* However, it is the callers responsibility to manage sharing and ownership of
* IOBuf objects themselves. The IOBuf structure does not provide room for an
* intrusive refcount on the IOBuf object itself, only the underlying data
* buffer is reference counted. If users want to share the same IOBuf object
* between multiple parts of the code, they are responsible for managing this
* sharing on their own. (For example, by using a shared_ptr. Alternatively,
* users always have the option of using clone() to create a second IOBuf that
* points to the same underlying buffer.)
*/
namespace detail {
// Is T a unique_ptr<> to a standard-layout type?
template <typename T>
struct IsUniquePtrToSL : std::false_type {};
template <typename T, typename D>
struct IsUniquePtrToSL<std::unique_ptr<T, D>> : std::is_standard_layout<T> {};
} // namespace detail
class IOBuf {
public:
class Iterator;
enum CreateOp { CREATE };
enum WrapBufferOp { WRAP_BUFFER };
enum TakeOwnershipOp { TAKE_OWNERSHIP };
enum CopyBufferOp { COPY_BUFFER };
typedef ByteRange value_type;
typedef Iterator iterator;
typedef Iterator const_iterator;
typedef void (*FreeFunction)(void* buf, void* userData);
/**
* Allocate a new IOBuf object with the requested capacity.
*
* Returns a new IOBuf object that must be (eventually) deleted by the
* caller. The returned IOBuf may actually have slightly more capacity than
* requested.
*
* The data pointer will initially point to the start of the newly allocated
* buffer, and will have a data length of 0.
*
* Throws std::bad_alloc on error.
*/
static std::unique_ptr<IOBuf> create(std::size_t capacity);
IOBuf(CreateOp, std::size_t capacity);
/**
* Create a new IOBuf, using a single memory allocation to allocate space
* for both the IOBuf object and the data storage space.
*
* This saves one memory allocation. However, it can be wasteful if you
* later need to grow the buffer using reserve(). If the buffer needs to be
* reallocated, the space originally allocated will not be freed() until the
* IOBuf object itself is also freed. (It can also be slightly wasteful in
* some cases where you clone this IOBuf and then free the original IOBuf.)
*/
static std::unique_ptr<IOBuf> createCombined(std::size_t capacity);
/**
* Create a new IOBuf, using separate memory allocations for the IOBuf object
* for the IOBuf and the data storage space.
*
* This requires two memory allocations, but saves space in the long run
* if you know that you will need to reallocate the data buffer later.
*/
static std::unique_ptr<IOBuf> createSeparate(std::size_t capacity);
/**
* Allocate a new IOBuf chain with the requested total capacity, allocating
* no more than maxBufCapacity to each buffer.
*/
static std::unique_ptr<IOBuf> createChain(
size_t totalCapacity,
std::size_t maxBufCapacity);
/**
* Create a new IOBuf pointing to an existing data buffer.
*
* The new IOBuffer will assume ownership of the buffer, and free it by
* calling the specified FreeFunction when the last IOBuf pointing to this
* buffer is destroyed. The function will be called with a pointer to the
* buffer as the first argument, and the supplied userData value as the
* second argument. The free function must never throw exceptions.
*
* If no FreeFunction is specified, the buffer will be freed using free()
* which will result in undefined behavior if the memory was allocated
* using 'new'.
*
* The IOBuf data pointer will initially point to the start of the buffer,
*
* In the first version of this function, the length of data is unspecified
* and is initialized to the capacity of the buffer
*
* In the second version, the user specifies the valid length of data
* in the buffer
*
* On error, std::bad_alloc will be thrown. If freeOnError is true (the
* default) the buffer will be freed before throwing the error.
*/
static std::unique_ptr<IOBuf> takeOwnership(
void* buf,
std::size_t capacity,
FreeFunction freeFn = nullptr,
void* userData = nullptr,
bool freeOnError = true) {
return takeOwnership(
buf, capacity, capacity, freeFn, userData, freeOnError);
}
IOBuf(
TakeOwnershipOp op,
void* buf,
std::size_t capacity,
FreeFunction freeFn = nullptr,
void* userData = nullptr,
bool freeOnError = true)
: IOBuf(op, buf, capacity, capacity, freeFn, userData, freeOnError) {}
static std::unique_ptr<IOBuf> takeOwnership(
void* buf,
std::size_t capacity,
std::size_t length,
FreeFunction freeFn = nullptr,
void* userData = nullptr,
bool freeOnError = true);
IOBuf(
TakeOwnershipOp,
void* buf,
std::size_t capacity,
std::size_t length,
FreeFunction freeFn = nullptr,
void* userData = nullptr,
bool freeOnError = true);
/**
* Create a new IOBuf pointing to an existing data buffer made up of
* count objects of a given standard-layout type.
*
* This is dangerous -- it is essentially equivalent to doing
* reinterpret_cast<unsigned char*> on your data -- but it's often useful
* for serialization / deserialization.
*
* The new IOBuffer will assume ownership of the buffer, and free it
* appropriately (by calling the UniquePtr's custom deleter, or by calling
* delete or delete[] appropriately if there is no custom deleter)
* when the buffer is destroyed. The custom deleter, if any, must never
* throw exceptions.
*
* The IOBuf data pointer will initially point to the start of the buffer,
* and the length will be the full capacity of the buffer (count *
* sizeof(T)).
*
* On error, std::bad_alloc will be thrown, and the buffer will be freed
* before throwing the error.
*/
template <class UniquePtr>
static typename std::enable_if<
detail::IsUniquePtrToSL<UniquePtr>::value,
std::unique_ptr<IOBuf>>::type
takeOwnership(UniquePtr&& buf, size_t count = 1);
/**
* Create a new IOBuf object that points to an existing user-owned buffer.
*
* This should only be used when the caller knows the lifetime of the IOBuf
* object ahead of time and can ensure that all IOBuf objects that will point
* to this buffer will be destroyed before the buffer itself is destroyed.
*
* This buffer will not be freed automatically when the last IOBuf
* referencing it is destroyed. It is the caller's responsibility to free
* the buffer after the last IOBuf has been destroyed.
*
* The IOBuf data pointer will initially point to the start of the buffer,
* and the length will be the full capacity of the buffer.
*
* An IOBuf created using wrapBuffer() will always be reported as shared.
* unshare() may be used to create a writable copy of the buffer.
*
* On error, std::bad_alloc will be thrown.
*/
static std::unique_ptr<IOBuf> wrapBuffer(
const void* buf,
std::size_t capacity);
static std::unique_ptr<IOBuf> wrapBuffer(ByteRange br) {
return wrapBuffer(br.data(), br.size());
}
/**
* Similar to wrapBuffer(), but returns IOBuf by value rather than
* heap-allocating it.
*/
static IOBuf wrapBufferAsValue(
const void* buf,
std::size_t capacity) noexcept;
static IOBuf wrapBufferAsValue(ByteRange br) noexcept {
return wrapBufferAsValue(br.data(), br.size());
}
IOBuf(WrapBufferOp op, const void* buf, std::size_t capacity) noexcept;
IOBuf(WrapBufferOp op, ByteRange br) noexcept;
/**
* Convenience function to create a new IOBuf object that copies data from a
* user-supplied buffer, optionally allocating a given amount of
* headroom and tailroom.
*/
static std::unique_ptr<IOBuf> copyBuffer(
const void* buf,
std::size_t size,
std::size_t headroom = 0,
std::size_t minTailroom = 0);
static std::unique_ptr<IOBuf> copyBuffer(
ByteRange br,
std::size_t headroom = 0,
std::size_t minTailroom = 0) {
return copyBuffer(br.data(), br.size(), headroom, minTailroom);
}
IOBuf(
CopyBufferOp op,
const void* buf,
std::size_t size,
std::size_t headroom = 0,
std::size_t minTailroom = 0);
IOBuf(
CopyBufferOp op,
ByteRange br,
std::size_t headroom = 0,
std::size_t minTailroom = 0);
/**
* Convenience function to create a new IOBuf object that copies data from a
* user-supplied string, optionally allocating a given amount of
* headroom and tailroom.
*
* Beware when attempting to invoke this function with a constant string
* literal and a headroom argument: you will likely end up invoking the
* version of copyBuffer() above. IOBuf::copyBuffer("hello", 3) will treat
* the first argument as a const void*, and will invoke the version of
* copyBuffer() above, with the size argument of 3.
*/
static std::unique_ptr<IOBuf> copyBuffer(
const std::string& buf,
std::size_t headroom = 0,
std::size_t minTailroom = 0);
IOBuf(
CopyBufferOp op,
const std::string& buf,
std::size_t headroom = 0,
std::size_t minTailroom = 0)
: IOBuf(op, buf.data(), buf.size(), headroom, minTailroom) {}
/**
* A version of copyBuffer() that returns a null pointer if the input string
* is empty.
*/
static std::unique_ptr<IOBuf> maybeCopyBuffer(
const std::string& buf,
std::size_t headroom = 0,
std::size_t minTailroom = 0);
/**
* Convenience function to free a chain of IOBufs held by a unique_ptr.
*/
static void destroy(std::unique_ptr<IOBuf>&& data) {
auto destroyer = std::move(data);
}
/**
* Destroy this IOBuf.
*
* Deleting an IOBuf will automatically destroy all IOBufs in the chain.
* (See the comments above regarding the ownership model of IOBuf chains.
* All subsequent IOBufs in the chain are considered to be owned by the head
* of the chain. Users should only explicitly delete the head of a chain.)
*
* When each individual IOBuf is destroyed, it will release its reference
* count on the underlying buffer. If it was the last user of the buffer,
* the buffer will be freed.
*/
~IOBuf();
/**
* Check whether the chain is empty (i.e., whether the IOBufs in the
* chain have a total data length of zero).
*
* This method is semantically equivalent to
* i->computeChainDataLength()==0
* but may run faster because it can short-circuit as soon as it
* encounters a buffer with length()!=0
*/
bool empty() const;
/**
* Get the pointer to the start of the data.
*/
const uint8_t* data() const {
return data_;
}
/**
* Get a writable pointer to the start of the data.
*
* The caller is responsible for calling unshare() first to ensure that it is
* actually safe to write to the buffer.
*/
uint8_t* writableData() {
return data_;
}
/**
* Get the pointer to the end of the data.
*/
const uint8_t* tail() const {
return data_ + length_;
}
/**
* Get a writable pointer to the end of the data.
*
* The caller is responsible for calling unshare() first to ensure that it is
* actually safe to write to the buffer.
*/
uint8_t* writableTail() {
return data_ + length_;
}
/**
* Get the data length.
*/
std::size_t length() const {
return length_;
}
/**
* Get the amount of head room.
*
* Returns the number of bytes in the buffer before the start of the data.
*/
std::size_t headroom() const {
return std::size_t(data_ - buffer());
}
/**
* Get the amount of tail room.
*
* Returns the number of bytes in the buffer after the end of the data.
*/
std::size_t tailroom() const {
return std::size_t(bufferEnd() - tail());
}
/**
* Get the pointer to the start of the buffer.
*
* Note that this is the pointer to the very beginning of the usable buffer,
* not the start of valid data within the buffer. Use the data() method to
* get a pointer to the start of the data within the buffer.
*/
const uint8_t* buffer() const {
return buf_;
}
/**
* Get a writable pointer to the start of the buffer.
*
* The caller is responsible for calling unshare() first to ensure that it is
* actually safe to write to the buffer.
*/
uint8_t* writableBuffer() {
return buf_;
}
/**
* Get the pointer to the end of the buffer.
*
* Note that this is the pointer to the very end of the usable buffer,
* not the end of valid data within the buffer. Use the tail() method to
* get a pointer to the end of the data within the buffer.
*/
const uint8_t* bufferEnd() const {
return buf_ + capacity_;
}
/**
* Get the total size of the buffer.
*
* This returns the total usable length of the buffer. Use the length()
* method to get the length of the actual valid data in this IOBuf.
*/
std::size_t capacity() const {
return capacity_;
}
/**
* Get a pointer to the next IOBuf in this chain.
*/
IOBuf* next() {
return next_;
}
const IOBuf* next() const {
return next_;
}
/**
* Get a pointer to the previous IOBuf in this chain.
*/
IOBuf* prev() {
return prev_;
}
const IOBuf* prev() const {
return prev_;
}
/**
* Shift the data forwards in the buffer.
*
* This shifts the data pointer forwards in the buffer to increase the
* headroom. This is commonly used to increase the headroom in a newly
* allocated buffer.
*
* The caller is responsible for ensuring that there is sufficient
* tailroom in the buffer before calling advance().
*
* If there is a non-zero data length, advance() will use memmove() to shift
* the data forwards in the buffer. In this case, the caller is responsible
* for making sure the buffer is unshared, so it will not affect other IOBufs
* that may be sharing the same underlying buffer.
*/
void advance(std::size_t amount) {
// In debug builds, assert if there is a problem.
assert(amount <= tailroom());
if (length_ > 0) {
memmove(data_ + amount, data_, length_);
}
data_ += amount;
}
/**
* Shift the data backwards in the buffer.
*
* The caller is responsible for ensuring that there is sufficient headroom
* in the buffer before calling retreat().
*
* If there is a non-zero data length, retreat() will use memmove() to shift
* the data backwards in the buffer. In this case, the caller is responsible
* for making sure the buffer is unshared, so it will not affect other IOBufs
* that may be sharing the same underlying buffer.
*/
void retreat(std::size_t amount) {
// In debug builds, assert if there is a problem.
assert(amount <= headroom());
if (length_ > 0) {
memmove(data_ - amount, data_, length_);
}
data_ -= amount;
}
/**
* Adjust the data pointer to include more valid data at the beginning.
*
* This moves the data pointer backwards to include more of the available
* buffer. The caller is responsible for ensuring that there is sufficient
* headroom for the new data. The caller is also responsible for populating
* this section with valid data.
*
* This does not modify any actual data in the buffer.
*/
void prepend(std::size_t amount) {
DCHECK_LE(amount, headroom());
data_ -= amount;
length_ += amount;
}
/**
* Adjust the tail pointer to include more valid data at the end.
*
* This moves the tail pointer forwards to include more of the available
* buffer. The caller is responsible for ensuring that there is sufficient
* tailroom for the new data. The caller is also responsible for populating
* this section with valid data.
*
* This does not modify any actual data in the buffer.
*/
void append(std::size_t amount) {
DCHECK_LE(amount, tailroom());
length_ += amount;
}
/**
* Adjust the data pointer forwards to include less valid data.
*
* This moves the data pointer forwards so that the first amount bytes are no
* longer considered valid data. The caller is responsible for ensuring that
* amount is less than or equal to the actual data length.
*
* This does not modify any actual data in the buffer.
*/
void trimStart(std::size_t amount) {
DCHECK_LE(amount, length_);
data_ += amount;
length_ -= amount;
}
/**
* Adjust the tail pointer backwards to include less valid data.
*
* This moves the tail pointer backwards so that the last amount bytes are no
* longer considered valid data. The caller is responsible for ensuring that
* amount is less than or equal to the actual data length.
*
* This does not modify any actual data in the buffer.
*/
void trimEnd(std::size_t amount) {
DCHECK_LE(amount, length_);
length_ -= amount;
}
/**
* Clear the buffer.
*
* Postcondition: headroom() == 0, length() == 0, tailroom() == capacity()
*/
void clear() {
data_ = writableBuffer();
length_ = 0;
}
/**
* Ensure that this buffer has at least minHeadroom headroom bytes and at
* least minTailroom tailroom bytes. The buffer must be writable
* (you must call unshare() before this, if necessary).
*
* Postcondition: headroom() >= minHeadroom, tailroom() >= minTailroom,
* the data (between data() and data() + length()) is preserved.
*/
void reserve(std::size_t minHeadroom, std::size_t minTailroom) {
// Maybe we don't need to do anything.
if (headroom() >= minHeadroom && tailroom() >= minTailroom) {
return;
}
// If the buffer is empty but we have enough total room (head + tail),
// move the data_ pointer around.
if (length() == 0 && headroom() + tailroom() >= minHeadroom + minTailroom) {
data_ = writableBuffer() + minHeadroom;
return;
}
// Bah, we have to do actual work.
reserveSlow(minHeadroom, minTailroom);
}
/**
* Return true if this IOBuf is part of a chain of multiple IOBufs, or false
* if this is the only IOBuf in its chain.
*/
bool isChained() const {
assert((next_ == this) == (prev_ == this));
return next_ != this;
}
/**
* Get the number of IOBufs in this chain.
*
* Beware that this method has to walk the entire chain.
* Use isChained() if you just want to check if this IOBuf is part of a chain
* or not.
*/
size_t countChainElements() const;
/**
* Get the length of all the data in this IOBuf chain.
*
* Beware that this method has to walk the entire chain.
*/
std::size_t computeChainDataLength() const;
/**
* Insert another IOBuf chain immediately before this IOBuf.
*
* For example, if there are two IOBuf chains (A, B, C) and (D, E, F),
* and B->prependChain(D) is called, the (D, E, F) chain will be subsumed
* and become part of the chain starting at A, which will now look like
* (A, D, E, F, B, C)
*
* Note that since IOBuf chains are circular, head->prependChain(other) can
* be used to append the other chain at the very end of the chain pointed to
* by head. For example, if there are two IOBuf chains (A, B, C) and
* (D, E, F), and A->prependChain(D) is called, the chain starting at A will
* now consist of (A, B, C, D, E, F)
*
* The elements in the specified IOBuf chain will become part of this chain,
* and will be owned by the head of this chain. When this chain is
* destroyed, all elements in the supplied chain will also be destroyed.
*
* For this reason, appendChain() only accepts an rvalue-reference to a
* unique_ptr(), to make it clear that it is taking ownership of the supplied
* chain. If you have a raw pointer, you can pass in a new temporary
* unique_ptr around the raw pointer. If you have an existing,
* non-temporary unique_ptr, you must call std::move(ptr) to make it clear
* that you are destroying the original pointer.
*/
void prependChain(std::unique_ptr<IOBuf>&& iobuf);
/**
* Append another IOBuf chain immediately after this IOBuf.
*
* For example, if there are two IOBuf chains (A, B, C) and (D, E, F),
* and B->appendChain(D) is called, the (D, E, F) chain will be subsumed
* and become part of the chain starting at A, which will now look like
* (A, B, D, E, F, C)
*
* The elements in the specified IOBuf chain will become part of this chain,
* and will be owned by the head of this chain. When this chain is
* destroyed, all elements in the supplied chain will also be destroyed.
*
* For this reason, appendChain() only accepts an rvalue-reference to a
* unique_ptr(), to make it clear that it is taking ownership of the supplied
* chain. If you have a raw pointer, you can pass in a new temporary
* unique_ptr around the raw pointer. If you have an existing,
* non-temporary unique_ptr, you must call std::move(ptr) to make it clear
* that you are destroying the original pointer.
*/
void appendChain(std::unique_ptr<IOBuf>&& iobuf) {
// Just use prependChain() on the next element in our chain
next_->prependChain(std::move(iobuf));
}
/**
* Remove this IOBuf from its current chain.
*
* Since ownership of all elements an IOBuf chain is normally maintained by
* the head of the chain, unlink() transfers ownership of this IOBuf from the
* chain and gives it to the caller. A new unique_ptr to the IOBuf is
* returned to the caller. The caller must store the returned unique_ptr (or
* call release() on it) to take ownership, otherwise the IOBuf will be
* immediately destroyed.
*
* Since unlink transfers ownership of the IOBuf to the caller, be careful
* not to call unlink() on the head of a chain if you already maintain
* ownership on the head of the chain via other means. The pop() method
* is a better choice for that situation.
*/
std::unique_ptr<IOBuf> unlink() {
next_->prev_ = prev_;
prev_->next_ = next_;
prev_ = this;
next_ = this;
return std::unique_ptr<IOBuf>(this);
}
/**
* Remove this IOBuf from its current chain and return a unique_ptr to
* the IOBuf that formerly followed it in the chain.
*/
std::unique_ptr<IOBuf> pop() {
IOBuf* next = next_;
next_->prev_ = prev_;
prev_->next_ = next_;
prev_ = this;
next_ = this;
return std::unique_ptr<IOBuf>((next == this) ? nullptr : next);
}
/**
* Remove a subchain from this chain.
*
* Remove the subchain starting at head and ending at tail from this chain.
*
* Returns a unique_ptr pointing to head. (In other words, ownership of the
* head of the subchain is transferred to the caller.) If the caller ignores
* the return value and lets the unique_ptr be destroyed, the subchain will
* be immediately destroyed.
*
* The subchain referenced by the specified head and tail must be part of the
* same chain as the current IOBuf, but must not contain the current IOBuf.
* However, the specified head and tail may be equal to each other (i.e.,
* they may be a subchain of length 1).
*/
std::unique_ptr<IOBuf> separateChain(IOBuf* head, IOBuf* tail) {
assert(head != this);
assert(tail != this);
head->prev_->next_ = tail->next_;
tail->next_->prev_ = head->prev_;
head->prev_ = tail;
tail->next_ = head;
return std::unique_ptr<IOBuf>(head);
}
/**
* Return true if at least one of the IOBufs in this chain are shared,
* or false if all of the IOBufs point to unique buffers.
*
* Use isSharedOne() to only check this IOBuf rather than the entire chain.
*/
bool isShared() const {
const IOBuf* current = this;
while (true) {
if (current->isSharedOne()) {
return true;
}
current = current->next_;
if (current == this) {
return false;
}
}
}
/**
* Return true if all IOBufs in this chain are managed by the usual
* refcounting mechanism (and so the lifetime of the underlying memory
* can be extended by clone()).
*/
bool isManaged() const {
const IOBuf* current = this;
while (true) {
if (!current->isManagedOne()) {
return false;
}
current = current->next_;
if (current == this) {
return true;
}
}
}
/**
* Return true if this IOBuf is managed by the usual refcounting mechanism
* (and so the lifetime of the underlying memory can be extended by
* cloneOne()).
*/
bool isManagedOne() const {
return sharedInfo();
}
/**
* Return true if other IOBufs are also pointing to the buffer used by this
* IOBuf, and false otherwise.
*
* If this IOBuf points at a buffer owned by another (non-IOBuf) part of the
* code (i.e., if the IOBuf was created using wrapBuffer(), or was cloned
* from such an IOBuf), it is always considered shared.
*
* This only checks the current IOBuf, and not other IOBufs in the chain.
*/
bool isSharedOne() const {
// If this is a user-owned buffer, it is always considered shared
if (UNLIKELY(!sharedInfo())) {
return true;
}
if (UNLIKELY(sharedInfo()->externallyShared)) {
return true;
}
if (LIKELY(!(flags() & kFlagMaybeShared))) {
return false;
}
// kFlagMaybeShared is set, so we need to check the reference count.
// (Checking the reference count requires an atomic operation, which is why
// we prefer to only check kFlagMaybeShared if possible.)
bool shared = sharedInfo()->refcount.load(std::memory_order_acquire) > 1;
if (!shared) {
// we're the last one left
clearFlags(kFlagMaybeShared);
}
return shared;
}
/**
* Ensure that this IOBuf has a unique buffer that is not shared by other
* IOBufs.
*
* unshare() operates on an entire chain of IOBuf objects. If the chain is
* shared, it may also coalesce the chain when making it unique. If the
* chain is coalesced, subsequent IOBuf objects in the current chain will be
* automatically deleted.
*
* Note that buffers owned by other (non-IOBuf) users are automatically
* considered shared.
*
* Throws std::bad_alloc on error. On error the IOBuf chain will be
* unmodified.
*
* Currently unshare may also throw std::overflow_error if it tries to
* coalesce. (TODO: In the future it would be nice if unshare() were smart
* enough not to coalesce the entire buffer if the data is too large.
* However, in practice this seems unlikely to become an issue.)
*/
void unshare() {
if (isChained()) {
unshareChained();
} else {
unshareOne();
}
}
/**
* Ensure that this IOBuf has a unique buffer that is not shared by other
* IOBufs.
*
* unshareOne() operates on a single IOBuf object. This IOBuf will have a
* unique buffer after unshareOne() returns, but other IOBufs in the chain
* may still be shared after unshareOne() returns.
*
* Throws std::bad_alloc on error. On error the IOBuf will be unmodified.
*/
void unshareOne() {
if (isSharedOne()) {
unshareOneSlow();
}
}
/**
* Mark the underlying buffers in this chain as shared with external memory
* management mechanism. This will make isShared() always returns true.
*
* This function is not thread-safe, and only safe to call immediately after
* creating an IOBuf, before it has been shared with other threads.
*/
void markExternallyShared();
/**
* Mark the underlying buffer that this IOBuf refers to as shared with
* external memory management mechanism. This will make isSharedOne() always
* returns true.
*
* This function is not thread-safe, and only safe to call immediately after
* creating an IOBuf, before it has been shared with other threads.
*/
void markExternallySharedOne() {
SharedInfo* info = sharedInfo();
if (info) {
info->externallyShared = true;
}
}
/**
* Ensure that the memory that IOBufs in this chain refer to will continue to
* be allocated for as long as the IOBufs of the chain (or any clone()s
* created from this point onwards) is alive.
*
* This only has an effect for user-owned buffers (created with the
* WRAP_BUFFER constructor or wrapBuffer factory function), in which case
* those buffers are unshared.
*/
void makeManaged() {
if (isChained()) {
makeManagedChained();
} else {
makeManagedOne();
}
}
/**
* Ensure that the memory that this IOBuf refers to will continue to be
* allocated for as long as this IOBuf (or any clone()s created from this
* point onwards) is alive.
*
* This only has an effect for user-owned buffers (created with the
* WRAP_BUFFER constructor or wrapBuffer factory function), in which case
* those buffers are unshared.
*/
void makeManagedOne() {
if (!isManagedOne()) {
// We can call the internal function directly; unmanaged implies shared.
unshareOneSlow();
}
}
/**
* Coalesce this IOBuf chain into a single buffer.
*
* This method moves all of the data in this IOBuf chain into a single
* contiguous buffer, if it is not already in one buffer. After coalesce()
* returns, this IOBuf will be a chain of length one. Other IOBufs in the
* chain will be automatically deleted.
*
* After coalescing, the IOBuf will have at least as much headroom as the
* first IOBuf in the chain, and at least as much tailroom as the last IOBuf
* in the chain.
*
* Throws std::bad_alloc on error. On error the IOBuf chain will be
* unmodified.
*
* Returns ByteRange that points to the data IOBuf stores.
*/
ByteRange coalesce() {
const std::size_t newHeadroom = headroom();
const std::size_t newTailroom = prev()->tailroom();
return coalesceWithHeadroomTailroom(newHeadroom, newTailroom);
}
/**
* This is similar to the coalesce() method, except this allows to set a
* headroom and tailroom after coalescing.
*
* Returns ByteRange that points to the data IOBuf stores.
*/
ByteRange coalesceWithHeadroomTailroom(
std::size_t newHeadroom,
std::size_t newTailroom) {
if (isChained()) {
coalesceAndReallocate(
newHeadroom, computeChainDataLength(), this, newTailroom);
}
return ByteRange(data_, length_);
}
/**
* Ensure that this chain has at least maxLength bytes available as a
* contiguous memory range.
*
* This method coalesces whole buffers in the chain into this buffer as
* necessary until this buffer's length() is at least maxLength.
*
* After coalescing, the IOBuf will have at least as much headroom as the
* first IOBuf in the chain, and at least as much tailroom as the last IOBuf
* that was coalesced.
*
* Throws std::bad_alloc or std::overflow_error on error. On error the IOBuf
* chain will be unmodified. Throws std::overflow_error if maxLength is
* longer than the total chain length.
*
* Upon return, either enough of the chain was coalesced into a contiguous
* region, or the entire chain was coalesced. That is,
* length() >= maxLength || !isChained() is true.
*/
void gather(std::size_t maxLength) {
if (!isChained() || length_ >= maxLength) {
return;
}
coalesceSlow(maxLength);
}
/**
* Return a new IOBuf chain sharing the same data as this chain.
*
* The new IOBuf chain will normally point to the same underlying data
* buffers as the original chain. (The one exception to this is if some of
* the IOBufs in this chain contain small internal data buffers which cannot
* be shared.)
*/
std::unique_ptr<IOBuf> clone() const;
/**
* Similar to clone(). But returns IOBuf by value rather than heap-allocating
* it.
*/
IOBuf cloneAsValue() const;
/**
* Return a new IOBuf with the same data as this IOBuf.
*
* The new IOBuf returned will not be part of a chain (even if this IOBuf is
* part of a larger chain).
*/
std::unique_ptr<IOBuf> cloneOne() const;
/**
* Similar to cloneOne(). But returns IOBuf by value rather than
* heap-allocating it.
*/
IOBuf cloneOneAsValue() const;
/**
* Return a new unchained IOBuf that may share the same data as this chain.
*
* If the IOBuf chain is not chained then the new IOBuf will point to the same
* underlying data buffer as the original chain. Otherwise, it will clone and
* coalesce the IOBuf chain.
*
* The new IOBuf will have at least as much headroom as the first IOBuf in the
* chain, and at least as much tailroom as the last IOBuf in the chain.
*
* Throws std::bad_alloc on error.
*/
std::unique_ptr<IOBuf> cloneCoalesced() const;
/**
* This is similar to the cloneCoalesced() method, except this allows to set a
* headroom and tailroom for the new IOBuf.
*/
std::unique_ptr<IOBuf> cloneCoalescedWithHeadroomTailroom(
std::size_t newHeadroom,
std::size_t newTailroom) const;
/**
* Similar to cloneCoalesced(). But returns IOBuf by value rather than
* heap-allocating it.
*/
IOBuf cloneCoalescedAsValue() const;
/**
* This is similar to the cloneCoalescedAsValue() method, except this allows
* to set a headroom and tailroom for the new IOBuf.
*/
IOBuf cloneCoalescedAsValueWithHeadroomTailroom(
std::size_t newHeadroom,
std::size_t newTailroom) const;
/**
* Similar to Clone(). But use other as the head node. Other nodes in the
* chain (if any) will be allocted on heap.
*/
void cloneInto(IOBuf& other) const {
other = cloneAsValue();
}
/**
* Similar to CloneOne(). But to fill an existing IOBuf instead of a new
* IOBuf.
*/
void cloneOneInto(IOBuf& other) const {
other = cloneOneAsValue();
}
/**
* Return an iovector suitable for e.g. writev()
*
* auto iov = buf->getIov();
* auto xfer = writev(fd, iov.data(), iov.size());
*
* Naturally, the returned iovector is invalid if you modify the buffer
* chain.
*/
folly::fbvector<struct iovec> getIov() const;
/**
* Update an existing iovec array with the IOBuf data.
*
* New iovecs will be appended to the existing vector; anything already
* present in the vector will be left unchanged.
*
* Naturally, the returned iovec data will be invalid if you modify the
* buffer chain.
*/
void appendToIov(folly::fbvector<struct iovec>* iov) const;
struct FillIovResult {
// How many iovecs were filled (or 0 on error).
size_t numIovecs;
// The total length of filled iovecs (or 0 on error).
size_t totalLength;
};
/**
* Fill an iovec array with the IOBuf data.
*
* Returns a struct with two fields: the number of iovec filled, and total
* size of the iovecs filled. If there are more buffer than iovec, returns 0
* in both fields.
* This version is suitable to use with stack iovec arrays.
*
* Naturally, the filled iovec data will be invalid if you modify the
* buffer chain.
*/
FillIovResult fillIov(struct iovec* iov, size_t len) const;
/**
* A helper that wraps a number of iovecs into an IOBuf chain. If count == 0,
* then a zero length buf is returned. This function never returns nullptr.
*/
static std::unique_ptr<IOBuf> wrapIov(const iovec* vec, size_t count);
/**
* A helper that takes ownerships a number of iovecs into an IOBuf chain. If
* count == 0, then a zero length buf is returned. This function never
* returns nullptr.
*/
static std::unique_ptr<IOBuf> takeOwnershipIov(
const iovec* vec,
size_t count,
FreeFunction freeFn = nullptr,
void* userData = nullptr,
bool freeOnError = true);
/*
* Overridden operator new and delete.
* These perform specialized memory management to help support
* createCombined(), which allocates IOBuf objects together with the buffer
* data.
*/
void* operator new(size_t size);
void* operator new(size_t size, void* ptr);
void operator delete(void* ptr);
void operator delete(void* ptr, void* placement);
/**
* Destructively convert this IOBuf to a fbstring efficiently.
* We rely on fbstring's AcquireMallocatedString constructor to
* transfer memory.
*/
fbstring moveToFbString();
/**
* Iteration support: a chain of IOBufs may be iterated through using
* STL-style iterators over const ByteRanges. Iterators are only invalidated
* if the IOBuf that they currently point to is removed.
*/
Iterator cbegin() const;
Iterator cend() const;
Iterator begin() const;
Iterator end() const;
/**
* Allocate a new null buffer.
*
* This can be used to allocate an empty IOBuf on the stack. It will have no
* space allocated for it. This is generally useful only to later use move
* assignment to fill out the IOBuf.
*/
IOBuf() noexcept;
/**
* Move constructor and assignment operator.
*
* In general, you should only ever move the head of an IOBuf chain.
* Internal nodes in an IOBuf chain are owned by the head of the chain, and
* should not be moved from. (Technically, nothing prevents you from moving
* a non-head node, but the moved-to node will replace the moved-from node in
* the chain. This has implications for ownership, since non-head nodes are
* owned by the chain head. You are then responsible for relinquishing
* ownership of the moved-to node, and manually deleting the moved-from
* node.)
*
* With the move assignment operator, the destination of the move should be
* the head of an IOBuf chain or a solitary IOBuf not part of a chain. If
* the move destination is part of a chain, all other IOBufs in the chain
* will be deleted.
*/
IOBuf(IOBuf&& other) noexcept;
IOBuf& operator=(IOBuf&& other) noexcept;
IOBuf(const IOBuf& other);
IOBuf& operator=(const IOBuf& other);
private:
enum FlagsEnum : uintptr_t {
// Adding any more flags would not work on 32-bit architectures,
// as these flags are stashed in the least significant 2 bits of a
// max-align-aligned pointer.
kFlagFreeSharedInfo = 0x1,
kFlagMaybeShared = 0x2,
kFlagMask = kFlagFreeSharedInfo | kFlagMaybeShared
};
struct SharedInfo {
SharedInfo();
SharedInfo(FreeFunction fn, void* arg);
// A pointer to a function to call to free the buffer when the refcount
// hits 0. If this is null, free() will be used instead.
FreeFunction freeFn;
void* userData;
std::atomic<uint32_t> refcount;
bool externallyShared{false};
};
// Helper structs for use by operator new and delete
struct HeapPrefix;
struct HeapStorage;
struct HeapFullStorage;
/**
* Create a new IOBuf pointing to an external buffer.
*
* The caller is responsible for holding a reference count for this new
* IOBuf. The IOBuf constructor does not automatically increment the
* reference count.
*/
struct InternalConstructor {}; // avoid conflicts
IOBuf(
InternalConstructor,
uintptr_t flagsAndSharedInfo,
uint8_t* buf,
std::size_t capacity,
uint8_t* data,
std::size_t length) noexcept;
void unshareOneSlow();
void unshareChained();
void makeManagedChained();
void coalesceSlow();
void coalesceSlow(size_t maxLength);
// newLength must be the entire length of the buffers between this and
// end (no truncation)
void coalesceAndReallocate(
size_t newHeadroom,
size_t newLength,
IOBuf* end,
size_t newTailroom);
void coalesceAndReallocate(size_t newLength, IOBuf* end) {
coalesceAndReallocate(headroom(), newLength, end, end->prev_->tailroom());
}
void decrementRefcount();
void reserveSlow(std::size_t minHeadroom, std::size_t minTailroom);
void freeExtBuffer();
static size_t goodExtBufferSize(std::size_t minCapacity);
static void initExtBuffer(
uint8_t* buf,
size_t mallocSize,
SharedInfo** infoReturn,
std::size_t* capacityReturn);
static void allocExtBuffer(
std::size_t minCapacity,
uint8_t** bufReturn,
SharedInfo** infoReturn,
std::size_t* capacityReturn);
static void releaseStorage(HeapStorage* storage, uint16_t freeFlags);
static void freeInternalBuf(void* buf, void* userData);
/*
* Member variables
*/
/*
* Links to the next and the previous IOBuf in this chain.
*
* The chain is circularly linked (the last element in the chain points back
* at the head), and next_ and prev_ can never be null. If this IOBuf is the
* only element in the chain, next_ and prev_ will both point to this.
*/
IOBuf* next_{this};
IOBuf* prev_{this};
/*
* A pointer to the start of the data referenced by this IOBuf, and the
* length of the data.
*
* This may refer to any subsection of the actual buffer capacity.
*/
uint8_t* data_{nullptr};
uint8_t* buf_{nullptr};
std::size_t length_{0};
std::size_t capacity_{0};
// Pack flags in least significant 2 bits, sharedInfo in the rest
mutable uintptr_t flagsAndSharedInfo_{0};
static inline uintptr_t packFlagsAndSharedInfo(
uintptr_t flags,
SharedInfo* info) {
uintptr_t uinfo = reinterpret_cast<uintptr_t>(info);
DCHECK_EQ(flags & ~kFlagMask, 0u);
DCHECK_EQ(uinfo & kFlagMask, 0u);
return flags | uinfo;
}
inline SharedInfo* sharedInfo() const {
return reinterpret_cast<SharedInfo*>(flagsAndSharedInfo_ & ~kFlagMask);
}
inline void setSharedInfo(SharedInfo* info) {
uintptr_t uinfo = reinterpret_cast<uintptr_t>(info);
DCHECK_EQ(uinfo & kFlagMask, 0u);
flagsAndSharedInfo_ = (flagsAndSharedInfo_ & kFlagMask) | uinfo;
}
inline uintptr_t flags() const {
return flagsAndSharedInfo_ & kFlagMask;
}
// flags_ are changed from const methods
inline void setFlags(uintptr_t flags) const {
DCHECK_EQ(flags & ~kFlagMask, 0u);
flagsAndSharedInfo_ |= flags;
}
inline void clearFlags(uintptr_t flags) const {
DCHECK_EQ(flags & ~kFlagMask, 0u);
flagsAndSharedInfo_ &= ~flags;
}
inline void setFlagsAndSharedInfo(uintptr_t flags, SharedInfo* info) {
flagsAndSharedInfo_ = packFlagsAndSharedInfo(flags, info);
}
struct DeleterBase {
virtual ~DeleterBase() {}
virtual void dispose(void* p) = 0;
};
template <class UniquePtr>
struct UniquePtrDeleter : public DeleterBase {
typedef typename UniquePtr::pointer Pointer;
typedef typename UniquePtr::deleter_type Deleter;
explicit UniquePtrDeleter(Deleter deleter) : deleter_(std::move(deleter)) {}
void dispose(void* p) override {
try {
deleter_(static_cast<Pointer>(p));
delete this;
} catch (...) {
abort();
}
}
private:
Deleter deleter_;
};
static void freeUniquePtrBuffer(void* ptr, void* userData) {
static_cast<DeleterBase*>(userData)->dispose(ptr);
}
};
/**
* Hasher for IOBuf objects. Hashes the entire chain using SpookyHashV2.
*/
struct IOBufHash {
size_t operator()(const IOBuf& buf) const noexcept;
size_t operator()(const std::unique_ptr<IOBuf>& buf) const noexcept {
return operator()(buf.get());
}
size_t operator()(const IOBuf* buf) const noexcept {
return buf ? (*this)(*buf) : 0;
}
};
/**
* Ordering for IOBuf objects. Compares data in the entire chain.
*/
struct IOBufCompare {
ordering operator()(const IOBuf& a, const IOBuf& b) const {
return &a == &b ? ordering::eq : impl(a, b);
}
ordering operator()(
const std::unique_ptr<IOBuf>& a,
const std::unique_ptr<IOBuf>& b) const {
return operator()(a.get(), b.get());
}
ordering operator()(const IOBuf* a, const IOBuf* b) const {
// clang-format off
return
!a && !b ? ordering::eq :
!a && b ? ordering::lt :
a && !b ? ordering::gt :
operator()(*a, *b);
// clang-format on
}
private:
ordering impl(IOBuf const& a, IOBuf const& b) const noexcept;
};
/**
* Equality predicate for IOBuf objects. Compares data in the entire chain.
*/
struct IOBufEqualTo : compare_equal_to<IOBufCompare> {};
/**
* Inequality predicate for IOBuf objects. Compares data in the entire chain.
*/
struct IOBufNotEqualTo : compare_not_equal_to<IOBufCompare> {};
/**
* Less predicate for IOBuf objects. Compares data in the entire chain.
*/
struct IOBufLess : compare_less<IOBufCompare> {};
/**
* At-most predicate for IOBuf objects. Compares data in the entire chain.
*/
struct IOBufLessEqual : compare_less_equal<IOBufCompare> {};
/**
* Greater predicate for IOBuf objects. Compares data in the entire chain.
*/
struct IOBufGreater : compare_greater<IOBufCompare> {};
/**
* At-least predicate for IOBuf objects. Compares data in the entire chain.
*/
struct IOBufGreaterEqual : compare_greater_equal<IOBufCompare> {};
template <class UniquePtr>
typename std::enable_if<
detail::IsUniquePtrToSL<UniquePtr>::value,
std::unique_ptr<IOBuf>>::type
IOBuf::takeOwnership(UniquePtr&& buf, size_t count) {
size_t size = count * sizeof(typename UniquePtr::element_type);
auto deleter = new UniquePtrDeleter<UniquePtr>(buf.get_deleter());
return takeOwnership(
buf.release(), size, &IOBuf::freeUniquePtrBuffer, deleter);
}
inline std::unique_ptr<IOBuf> IOBuf::copyBuffer(
const void* data,
std::size_t size,
std::size_t headroom,
std::size_t minTailroom) {
std::size_t capacity = headroom + size + minTailroom;
std::unique_ptr<IOBuf> buf = create(capacity);
buf->advance(headroom);
if (size != 0) {
memcpy(buf->writableData(), data, size);
}
buf->append(size);
return buf;
}
inline std::unique_ptr<IOBuf> IOBuf::copyBuffer(
const std::string& buf,
std::size_t headroom,
std::size_t minTailroom) {
return copyBuffer(buf.data(), buf.size(), headroom, minTailroom);
}
inline std::unique_ptr<IOBuf> IOBuf::maybeCopyBuffer(
const std::string& buf,
std::size_t headroom,
std::size_t minTailroom) {
if (buf.empty()) {
return nullptr;
}
return copyBuffer(buf.data(), buf.size(), headroom, minTailroom);
}
class IOBuf::Iterator : public detail::IteratorFacade<
IOBuf::Iterator,
ByteRange const,
std::forward_iterator_tag> {
public:
// Note that IOBufs are stored as a circular list without a guard node,
// so pos == end is ambiguous (it may mean "begin" or "end"). To solve
// the ambiguity (at the cost of one extra comparison in the "increment"
// code path), we define end iterators as having pos_ == end_ == nullptr
// and we only allow forward iteration.
explicit Iterator(const IOBuf* pos, const IOBuf* end) : pos_(pos), end_(end) {
// Sadly, we must return by const reference, not by value.
if (pos_) {
setVal();
}
}
Iterator() {}
Iterator(Iterator const& rhs) : Iterator(rhs.pos_, rhs.end_) {}
Iterator& operator=(Iterator const& rhs) {
pos_ = rhs.pos_;
end_ = rhs.end_;
if (pos_) {
setVal();
}
return *this;
}
const ByteRange& dereference() const {
return val_;
}
bool equal(const Iterator& other) const {
// We must compare end_ in addition to pos_, because forward traversal
// requires that if two iterators are equal (a == b) and dereferenceable,
// then ++a == ++b.
return pos_ == other.pos_ && end_ == other.end_;
}
void increment() {
pos_ = pos_->next();
adjustForEnd();
}
private:
void setVal() {
val_ = ByteRange(pos_->data(), pos_->tail());
}
void adjustForEnd() {
if (pos_ == end_) {
pos_ = end_ = nullptr;
val_ = ByteRange();
} else {
setVal();
}
}
const IOBuf* pos_{nullptr};
const IOBuf* end_{nullptr};
ByteRange val_;
};
inline IOBuf::Iterator IOBuf::begin() const {
return cbegin();
}
inline IOBuf::Iterator IOBuf::end() const {
return cend();
}
} // namespace folly
FOLLY_POP_WARNING