2 * Copyright 2012 Facebook, Inc.
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
8 * http://www.apache.org/licenses/LICENSE-2.0
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
17 #ifndef FOLLY_IO_IOBUF_QUEUE_H
18 #define FOLLY_IO_IOBUF_QUEUE_H
20 #include "folly/experimental/io/IOBuf.h"
28 * An IOBufQueue encapsulates a chain of IOBufs and provides
29 * convenience functions to append data to the back of the chain
30 * and remove data from the front.
35 Options() : cacheChainLength(false) { }
36 bool cacheChainLength;
40 * Commonly used Options, currently the only possible value other than
43 static Options cacheChainLength() {
45 options.cacheChainLength = true;
49 explicit IOBufQueue(const Options& options = Options());
52 * Add a buffer or buffer chain to the end of this queue. The
53 * queue takes ownership of buf.
55 void append(std::unique_ptr<folly::IOBuf>&& buf);
58 * Add a queue to the end of this queue. The queue takes ownership of
59 * all buffers from the other queue.
61 void append(IOBufQueue& other);
62 void append(IOBufQueue&& other) {
63 append(other); // call lvalue reference overload, above
67 * Copy len bytes, starting at buf, to the end of this queue.
68 * The caller retains ownership of the source data.
70 void append(const void* buf, size_t len);
73 * Copy a string to the end of this queue.
74 * The caller retains ownership of the source data.
76 void append(const std::string& buf) {
77 append(buf.data(), buf.length());
81 * Append a chain of IOBuf objects that point to consecutive regions
84 * Just like IOBuf::wrapBuffer, this should only be used when the caller
85 * knows ahead of time and can ensure that all IOBuf objects that will point
86 * to this buffer will be destroyed before the buffer itself is destroyed;
87 * all other caveats from wrapBuffer also apply.
89 * Every buffer except for the last will wrap exactly blockSize bytes.
90 * Importantly, this method may be used to wrap buffers larger than 4GB.
92 void wrapBuffer(const void* buf, size_t len,
93 uint32_t blockSize=(1U << 31)); // default block size: 2GB
96 * Obtain a writable block of contiguous bytes at the end of this
97 * queue, allocating more space if necessary. The amount of space
98 * reserved will be between min and max, inclusive; the IOBufQueue
99 * implementation may pick a value in that range that makes efficient
100 * use of already-allocated internal space.
102 * If the caller subsequently writes anything into the returned space,
103 * it must call the postallocate() method.
105 * @return The starting address of the block and the length in bytes.
107 * @note The point of the preallocate()/postallocate() mechanism is
108 * to support I/O APIs such as Thrift's TAsyncSocket::ReadCallback
109 * that request a buffer from the application and then, in a later
110 * callback, tell the application how much of the buffer they've
113 std::pair<void*,uint32_t> preallocate(uint32_t min, uint32_t max);
116 * Tell the queue that the caller has written data into the first n
117 * bytes provided by the previous preallocate() call.
119 * @note n should be less than or equal to the size returned by
120 * preallocate(). If n is zero, the caller may skip the call
121 * to postallocate(). If n is nonzero, the caller must not
122 * invoke any other non-const methods on this IOBufQueue between
123 * the call to preallocate and the call to postallocate().
125 void postallocate(uint32_t n);
128 * Obtain a writable block of n contiguous bytes, allocating more space
129 * if necessary, and mark it as used. The caller can fill it later.
131 void* allocate(uint32_t n) {
132 void* p = preallocate(n, n).first;
138 * Split off the first n bytes of the queue into a separate IOBuf chain,
139 * and transfer ownership of the new chain to the caller. The IOBufQueue
140 * retains ownership of everything after the split point.
142 * @warning If the split point lies in the middle of some IOBuf within
143 * the chain, this function may, as an implementation detail,
146 * @throws std::underflow_error if n exceeds the number of bytes
149 std::unique_ptr<folly::IOBuf> split(size_t n);
152 * Similar to IOBuf::trimStart, but works on the whole queue. Will
153 * pop off buffers that have been completely trimmed.
155 void trimStart(size_t amount);
158 * Similar to IOBuf::trimEnd, but works on the whole queue. Will
159 * pop off buffers that have been completely trimmed.
161 void trimEnd(size_t amount);
164 * Transfer ownership of the queue's entire IOBuf chain to the caller.
166 std::unique_ptr<folly::IOBuf>&& move() {
168 return std::move(head_);
174 const folly::IOBuf* front() const {
179 * Total chain length, only valid if cacheLength was specified in the
182 size_t chainLength() const {
183 if (!options_.cacheChainLength) {
184 throw std::invalid_argument("IOBufQueue: chain length not cached");
189 const Options& options() const {
194 IOBufQueue(IOBufQueue&&);
195 IOBufQueue& operator=(IOBufQueue&&);
198 static const size_t kChainLengthNotCached = (size_t)-1;
200 IOBufQueue(const IOBufQueue&) = delete;
201 IOBufQueue& operator=(const IOBufQueue&) = delete;
205 /** Everything that has been appended but not yet discarded or moved out */
206 std::unique_ptr<folly::IOBuf> head_;
211 #endif // FOLLY_IO_IOBUF_QUEUE_H