1+ #pragma once
2+
3+ #include < vector>
4+ #include < string>
5+ #include < algorithm>
6+ #include < stddef.h>
7+
8+ // 网络库底层的缓冲区类型定义
9+ class Buffer
10+ {
11+ public:
12+ static const size_t kCheapPrepend = 8 ;
13+ static const size_t kInitialSize = 1024 ;
14+
15+ explicit Buffer (size_t initalSize = kInitialSize )
16+ : buffer_(kCheapPrepend + initalSize)
17+ , readerIndex_(kCheapPrepend )
18+ , writerIndex_(kCheapPrepend )
19+ {
20+ }
21+
22+ size_t readableBytes () const { return writerIndex_ - readerIndex_; }
23+ size_t writableBytes () const { return buffer_.size () - writerIndex_; }
24+ size_t prependableBytes () const { return readerIndex_; }
25+
26+ // 返回缓冲区中可读数据的起始地址
27+ const char *peek () const { return begin () + readerIndex_; }
28+ void retrieve (size_t len)
29+ {
30+ if (len < readableBytes ())
31+ {
32+ readerIndex_ += len; // 说明应用只读取了可读缓冲区数据的一部分，就是len长度 还剩下readerIndex+=len到writerIndex_的数据未读
33+ }
34+ else // len == readableBytes()
35+ {
36+ retrieveAll ();
37+ }
38+ }
39+ void retrieveAll ()
40+ {
41+ readerIndex_ = kCheapPrepend ;
42+ writerIndex_ = kCheapPrepend ;
43+ }
44+
45+ // 把onMessage函数上报的Buffer数据 转成string类型的数据返回
46+ std::string retrieveAllAsString () { return retrieveAsString (readableBytes ()); }
47+ std::string retrieveAsString (size_t len)
48+ {
49+ std::string result (peek (), len);
50+ retrieve (len); // 上面一句把缓冲区中可读的数据已经读取出来 这里肯定要对缓冲区进行复位操作
51+ return result;
52+ }
53+
54+ // buffer_.size - writerIndex_
55+ void ensureWritableBytes (size_t len)
56+ {
57+ if (writableBytes () < len)
58+ {
59+ makeSpace (len); // 扩容
60+ }
61+ }
62+
63+ // 把[data, data+len]内存上的数据添加到writable缓冲区当中
64+ void append (const char *data, size_t len)
65+ {
66+ ensureWritableBytes (len);
67+ std::copy (data, data+len, beginWrite ());
68+ writerIndex_ += len;
69+ }
70+ char *beginWrite () { return begin () + writerIndex_; }
71+ const char *beginWrite () const { return begin () + writerIndex_; }
72+
73+ // 从fd上读取数据
74+ ssize_t readFd (int fd, int *saveErrno);
75+ // 通过fd发送数据
76+ ssize_t writeFd (int fd, int *saveErrno);
77+
78+ private:
79+ // vector底层数组首元素的地址 也就是数组的起始地址
80+ char *begin () { return &*buffer_.begin (); }
81+ const char *begin () const { return &*buffer_.begin (); }
82+
83+ void makeSpace (size_t len)
84+ {
85+ /* *
86+ * | kCheapPrepend |xxx|reader | writer | // xxx标示reader中已读的部分
87+ * | kCheapPrepend | len |
88+ **/
89+ if (writableBytes () + prependableBytes () < len + kCheapPrepend ) // 也就是说 len > xxx + writer的部分
90+ {
91+ buffer_.resize (writerIndex_ + len);
92+ }
93+ else // 这里说明 len <= xxx + writer 把reader搬到从xxx开始 使得xxx后面是一段连续空间
94+ {
95+ size_t readable = readableBytes (); // readable = reader的长度
96+ std::copy (begin ()+readerIndex_, begin ()+writerIndex_, // 把这一部分数据拷贝到begin+kCheapPrepend起始处
97+ begin ()+kCheapPrepend );
98+ readerIndex_ = kCheapPrepend ;
99+ writerIndex_ = readerIndex_+readable;
100+ }
101+ }
102+
103+ std::vector<char > buffer_;
104+ size_t readerIndex_;
105+ size_t writerIndex_;
106+ };
0 commit comments