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1 // Copyright 2013 The Chromium Authors. All rights reserved. | |
2 // Use of this source code is governed by a BSD-style license that can be | |
3 // found in the LICENSE file. | |
4 | |
5 #ifndef NET_QUIC_IOVECTOR_H_ | |
6 #define NET_QUIC_IOVECTOR_H_ | |
7 | |
8 #include <stddef.h> | |
9 #include <algorithm> | |
10 #include <vector> | |
11 | |
12 #include "base/basictypes.h" | |
13 #include "base/logging.h" | |
14 #include "net/base/iovec.h" | |
15 #include "net/base/net_export.h" | |
16 | |
17 namespace net { | |
18 | |
19 // Calculate the total number of bytes in an array of iovec structures. | |
20 inline size_t TotalIovecLength(const struct iovec* iov, size_t iovcnt) { | |
21 size_t length = 0; | |
22 if (iov != NULL) { | |
23 for (size_t i = 0; i < iovcnt; ++i) { | |
24 length += iov[i].iov_len; | |
25 } | |
26 } | |
27 return length; | |
28 } | |
29 | |
30 // IOVector is a helper class that makes it easier to work with POSIX vector I/O | |
31 // struct. It is a thin wrapper by design and thus has no virtual functions and | |
32 // all inlined methods. This class makes no assumptions about the ordering of | |
33 // the pointer values of the blocks appended, it simply counts bytes when asked | |
34 // to consume bytes. | |
35 // | |
36 // IOVector is a bookkeeping object that collects a description of buffers to | |
37 // be read or written together and in order. It does not take ownership of the | |
38 // blocks appended. | |
39 // | |
40 // Because it is used for scatter-gather operations, the order in which the | |
41 // buffer blocks are added to the IOVector is important to the client. The | |
42 // intended usage pattern is: | |
43 // | |
44 // iovector.Append(p0, len0); | |
45 // ... | |
46 // iovector.Append(pn, lenn); | |
47 // int bytes_written = writev(fd, iovector.iovec(), iovector.Size()); | |
48 // if (bytes_written > 0) | |
49 // iovector.Consume(bytes_written); | |
50 // | |
51 // The sequence is the same for readv, except that Consume() in this case is | |
52 // used to change the IOVector to only keep track of description of blocks of | |
53 // memory not yet written to. | |
54 // | |
55 // IOVector does not have any method to change the iovec entries that it | |
56 // accumulates. This is due to the block merging nature of Append(): we'd like | |
57 // to avoid accidentally change an entry that is assembled by two or more | |
58 // Append()'s by simply an index access. | |
59 // | |
60 class NET_EXPORT_PRIVATE IOVector { | |
61 public: | |
62 // Provide a default constructor so it'll never be inhibited by adding other | |
63 // constructors. | |
64 IOVector(); | |
65 ~IOVector(); | |
66 | |
67 // Provides a way to convert system call-like iovec representation to | |
68 // IOVector. | |
69 void AppendIovec(const struct iovec* iov, size_t iovcnt) { | |
70 for (size_t i = 0; i < iovcnt; ++i) | |
71 Append(static_cast<char*>(iov[i].iov_base), iov[i].iov_len); | |
72 } | |
73 | |
74 // Appends at most max_bytes from iovec to the IOVector. | |
75 size_t AppendIovecAtMostBytes(const struct iovec* iov, | |
76 size_t iovcnt, | |
77 size_t max_bytes) { | |
78 size_t bytes_appended = 0; | |
79 for (size_t i = 0; i < iovcnt && max_bytes > 0; ++i) { | |
80 const size_t length = std::min(max_bytes, iov[i].iov_len); | |
81 Append(static_cast<char*>(iov[i].iov_base), length); | |
82 max_bytes -= length; | |
83 bytes_appended += length; | |
84 } | |
85 return bytes_appended; | |
86 } | |
87 | |
88 // Append another block to the IOVector. Since IOVector can be used for read | |
89 // and write, it always takes char*. Clients that writes will need to cast | |
90 // away the constant of the pointer before appending a block. | |
91 void Append(char* buffer, size_t length) { | |
92 if (buffer != NULL && length > 0) { | |
93 if (iovec_.size() > 0) { | |
94 struct iovec& last = iovec_.back(); | |
95 // If the new block is contiguous with the last block, just extend. | |
96 if (static_cast<char*>(last.iov_base) + last.iov_len == buffer) { | |
97 last.iov_len += length; | |
98 return; | |
99 } | |
100 } | |
101 struct iovec tmp = {buffer, length}; | |
102 iovec_.push_back(tmp); | |
103 } | |
104 } | |
105 | |
106 // Same as Append, but doesn't do the tail merge optimization. | |
107 // Intended for testing. | |
108 void AppendNoCoalesce(char* buffer, size_t length) { | |
109 if (buffer != NULL && length > 0) { | |
110 struct iovec tmp = {buffer, length}; | |
111 iovec_.push_back(tmp); | |
112 } | |
113 } | |
114 | |
115 // Remove a number of bytes from the beginning of the IOVector. Since vector | |
116 // I/O operations always occur at the beginning of the block list, a method | |
117 // to remove bytes at the end is not provided. | |
118 // It returns the number of bytes actually consumed (it'll only be smaller | |
119 // than the requested number if the IOVector contains less data). | |
120 size_t Consume(size_t length) { | |
121 if (length == 0) return 0; | |
122 | |
123 size_t bytes_to_consume = length; | |
124 std::vector<struct iovec>::iterator iter = iovec_.begin(); | |
125 std::vector<struct iovec>::iterator end = iovec_.end(); | |
126 for (; iter < end && bytes_to_consume >= iter->iov_len; ++iter) { | |
127 bytes_to_consume -= iter->iov_len; | |
128 } | |
129 iovec_.erase(iovec_.begin(), iter); | |
130 if (iovec_.size() > 0 && bytes_to_consume != 0) { | |
131 iovec_[0].iov_base = | |
132 static_cast<char*>(iovec_[0].iov_base) + bytes_to_consume; | |
133 iovec_[0].iov_len -= bytes_to_consume; | |
134 return length; | |
135 } | |
136 if (iovec_.size() == 0 && bytes_to_consume > 0) { | |
137 LOG(DFATAL) << "Attempting to consume " << bytes_to_consume | |
138 << " non-existent bytes."; | |
139 } | |
140 // At this point bytes_to_consume is the number of wanted bytes left over | |
141 // after walking through all the iovec entries. | |
142 return length - bytes_to_consume; | |
143 } | |
144 | |
145 // TODO(joechan): If capacity is large, swap out for a blank one. | |
146 // Clears the IOVector object to contain no blocks. | |
147 void Clear() { iovec_.clear(); } | |
148 | |
149 // Swap the guts of two IOVector. | |
150 void Swap(IOVector* other) { iovec_.swap(other->iovec_); } | |
151 | |
152 // Returns the number of valid blocks in the IOVector (not the number of | |
153 // bytes). | |
154 size_t Size() const { return iovec_.size(); } | |
155 | |
156 // Returns the total storage used by the IOVector in number of blocks (not | |
157 // the number of bytes). | |
158 size_t Capacity() const { return iovec_.capacity(); } | |
159 | |
160 // Returns true if there are no blocks in the IOVector. | |
161 bool Empty() const { return iovec_.empty(); } | |
162 | |
163 // Returns the pointer to the beginning of the iovec to be used for vector | |
164 // I/O operations. If the IOVector has no blocks appened, this function | |
165 // returns NULL. | |
166 struct iovec* iovec() { return !Empty() ? &iovec_[0] : NULL; } | |
167 | |
168 // Const version. | |
169 const struct iovec* iovec() const { return !Empty() ? &iovec_[0] : NULL; } | |
170 | |
171 // Returns a pointer to one past the last byte of the last block. If the | |
172 // IOVector is empty, NULL is returned. | |
173 const char* LastBlockEnd() const { | |
174 return iovec_.size() > 0 ? | |
175 static_cast<char *>(iovec_.back().iov_base) + iovec_.back().iov_len : | |
176 NULL; | |
177 } | |
178 | |
179 // Returns the total number of bytes in the IOVector. | |
180 size_t TotalBufferSize() const { return TotalIovecLength(iovec(), Size()); } | |
181 | |
182 void Resize(size_t count) { | |
183 iovec_.resize(count); | |
184 } | |
185 | |
186 private: | |
187 std::vector<struct iovec> iovec_; | |
188 | |
189 // IOVector has value-semantics; copy and assignment are allowed. | |
190 // This class does not explicitly define copy/move constructors or the | |
191 // assignment operator to preserve compiler-generated copy/move constructors | |
192 // and assignment operators. Note that since IOVector does not own the | |
193 // actual buffers that the struct iovecs point to, copies and assignments | |
194 // result in a shallow copy of the buffers; resulting IOVectors will point | |
195 // to the same copy of the underlying data. | |
196 }; | |
197 | |
198 } // namespace net | |
199 | |
200 #endif // NET_QUIC_IOVECTOR_H_ | |
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