简介
Buffer封装了一个可变长的buffer，支持廉价的前插操作，以及内部挪腾操作避免额外申请空间
使用vector作为缓冲区(可自动调整扩容)
设计图
源码剖析
已经编写好注释
buffer.h
// Copyright 2010, Shuo Chen. All rights reserved.
// http://code.google.com/p/muduo/
//
// Use of this source code is governed by a BSD-style license
// that can be found in the License file.// Author: Shuo Chen (chenshuo at chenshuo dot com)
//
// This is a public header file, it must only include public header files.#ifndef MUDUO_NET_BUFFER_H
#define MUDUO_NET_BUFFER_H#include "muduo/base/copyable.h"
#include "muduo/base/StringPiece.h"
#include "muduo/base/Types.h"#include "muduo/net/Endian.h"#include <algorithm>
#include <vector>#include <assert.h>
#include <string.h>
//#include <unistd.h> // ssize_tnamespace muduo
{
namespace net
{/// A buffer class modeled after org.jboss.netty.buffer.ChannelBuffer
///
/// @code
/// +-------------------+------------------+------------------+
/// | prependable bytes | readable bytes | writable bytes |
/// | | (CONTENT) | |
/// +-------------------+------------------+------------------+
/// | | | |
/// 0 <= readerIndex <= writerIndex <= size
/// @endcode
class Buffer : public muduo::copyable
{public:static const size_t kCheapPrepend = 8;//预留8字节static const size_t kInitialSize = 1024;//缓冲区初始化大小explicit Buffer(size_t initialSize = kInitialSize): buffer_(kCheapPrepend + initialSize),readerIndex_(kCheapPrepend),writerIndex_(kCheapPrepend){assert(readableBytes() == 0);assert(writableBytes() == initialSize);assert(prependableBytes() == kCheapPrepend);}// implicit copy-ctor, move-ctor, dtor and assignment are fine// NOTE: implicit move-ctor is added in g++ 4.6void swap(Buffer& rhs)//交换缓冲区{buffer_.swap(rhs.buffer_);std::swap(readerIndex_, rhs.readerIndex_);std::swap(writerIndex_, rhs.writerIndex_);}size_t readableBytes() const//剩余可读字节大小{ return writerIndex_ - readerIndex_; }size_t writableBytes() const//剩余可写字节大小{ return buffer_.size() - writerIndex_; }size_t prependableBytes() const//已读字节大小{ return readerIndex_; }const char* peek() const//readIndex{ return begin() + readerIndex_; }const char* findCRLF() const{// FIXME: replace with memmem()?const char* crlf = std::search(peek(), beginWrite(), kCRLF, kCRLF+2);return crlf == beginWrite() ? NULL : crlf;}const char* findCRLF(const char* start) const//在start~writeIndex区间寻找kCRLF{assert(peek() <= start);assert(start <= beginWrite());// FIXME: replace with memmem()?const char* crlf = std::search(start, beginWrite(), kCRLF, kCRLF+2);return crlf == beginWrite() ? NULL : crlf;}const char* findEOL() const//在readIndex~writeIndex区间寻找'\n'{const void* eol = memchr(peek(), '\n', readableBytes());return static_cast<const char*>(eol);}const char* findEOL(const char* start) const{assert(peek() <= start);assert(start <= beginWrite());const void* eol = memchr(start, '\n', beginWrite() - start);return static_cast<const char*>(eol);}// retrieve returns void, to prevent// string str(retrieve(readableBytes()), readableBytes());// the evaluation of two functions are unspecifiedvoid retrieve(size_t len)//回收len个字节的数据(可读数据){assert(len <= readableBytes());if (len < readableBytes()){readerIndex_ += len;}else{retrieveAll();}}void retrieveUntil(const char* end)//回收readINdex~len区间的数据{assert(peek() <= end);assert(end <= beginWrite());retrieve(end - peek());}//回收相应类型大小的数据void retrieveInt64(){retrieve(sizeof(int64_t));}void retrieveInt32(){retrieve(sizeof(int32_t));}void retrieveInt16(){retrieve(sizeof(int16_t));}void retrieveInt8(){retrieve(sizeof(int8_t));}void retrieveAll()//回收所有空间{readerIndex_ = kCheapPrepend;writerIndex_ = kCheapPrepend;}string retrieveAllAsString()//返回缓冲区所有剩余的数据{return retrieveAsString(readableBytes());}string retrieveAsString(size_t len)//回收len大小的数据,并将这段数据返回{assert(len <= readableBytes());string result(peek(), len);retrieve(len);return result;}//返回StringPiece类型,该类保存一个char*指针,并保存len长度,并提供一些基础方法(可以理解为低配版std::string)//保存StringPiece toStringPiece() const{return StringPiece(peek(), static_cast<int>(readableBytes()));}void append(const StringPiece& str){append(str.data(), str.size());}void append(const char* /*restrict*/ data, size_t len){ensureWritableBytes(len);//确保有可写字节大小的空间std::copy(data, data+len, beginWrite());//将追加数据加入缓冲区hasWritten(len);//更新writerIndex_}void append(const void* /*restrict*/ data, size_t len){append(static_cast<const char*>(data), len);}void ensureWritableBytes(size_t len)//确保有可写字节大小的空间{//如果可写空间大于len则什么也不干,小于则调整bufferif (writableBytes() < len){makeSpace(len);}assert(writableBytes() >= len);}char* beginWrite()//writeIndex{ return begin() + writerIndex_; }const char* beginWrite() const//writeIndex{ return begin() + writerIndex_; }void hasWritten(size_t len)//writerIndex_追加移动len个字节{assert(len <= writableBytes());writerIndex_ += len;}void unwrite(size_t len)//writerIndex_减少移动len个字节{assert(len <= readableBytes());writerIndex_ -= len;}////// Append int64_t using network endian/////将类型大小的数据转成网络字节数(大端)后放入缓冲区void appendInt64(int64_t x){int64_t be64 = sockets::hostToNetwork64(x);append(&be64, sizeof be64);}////// Append int32_t using network endian///void appendInt32(int32_t x){int32_t be32 = sockets::hostToNetwork32(x);append(&be32, sizeof be32);}void appendInt16(int16_t x){int16_t be16 = sockets::hostToNetwork16(x);append(&be16, sizeof be16);}void appendInt8(int8_t x){append(&x, sizeof x);}////// Read int64_t from network endian////// Require: buf->readableBytes() >= sizeof(int32_t)//在缓冲区中读Intxx类型大小的数据,转换为主机字节序,并调整缓冲区的下标,然后返回数据int64_t readInt64(){int64_t result = peekInt64();retrieveInt64();return result;}////// Read int32_t from network endian////// Require: buf->readableBytes() >= sizeof(int32_t)int32_t readInt32(){int32_t result = peekInt32();retrieveInt32();return result;}int16_t readInt16(){int16_t result = peekInt16();retrieveInt16();return result;}int8_t readInt8(){int8_t result = peekInt8();retrieveInt8();return result;}////// Peek int64_t from network endian////// Require: buf->readableBytes() >= sizeof(int64_t)//在缓冲区中读Intxx类型大小的数据,转换为主机字节序,然后返回数据int64_t peekInt64() const{assert(readableBytes() >= sizeof(int64_t));int64_t be64 = 0;::memcpy(&be64, peek(), sizeof be64);return sockets::networkToHost64(be64);}////// Peek int32_t from network endian////// Require: buf->readableBytes() >= sizeof(int32_t)int32_t peekInt32() const{assert(readableBytes() >= sizeof(int32_t));int32_t be32 = 0;::memcpy(&be32, peek(), sizeof be32);return sockets::networkToHost32(be32);}int16_t peekInt16() const{assert(readableBytes() >= sizeof(int16_t));int16_t be16 = 0;::memcpy(&be16, peek(), sizeof be16);return sockets::networkToHost16(be16);}int8_t peekInt8() const{assert(readableBytes() >= sizeof(int8_t));int8_t x = *peek();return x;}////// Prepend int64_t using network endian/////转换为网络字节序,在缓冲区中读Intxx类型大小的数据,并调整缓冲区的下标,然后返回数据//将Intxx类型大小的数据转换为网络字节序,然后以前插的方式加入缓冲区void prependInt64(int64_t x){int64_t be64 = sockets::hostToNetwork64(x);prepend(&be64, sizeof be64);}////// Prepend int32_t using network endian///void prependInt32(int32_t x){int32_t be32 = sockets::hostToNetwork32(x);prepend(&be32, sizeof be32);}void prependInt16(int16_t x){int16_t be16 = sockets::hostToNetwork16(x);prepend(&be16, sizeof be16);}void prependInt8(int8_t x){prepend(&x, sizeof x);}void prepend(const void* /*restrict*/ data, size_t len)//以前插的方式加入缓冲区,并调整下标{assert(len <= prependableBytes());readerIndex_ -= len;const char* d = static_cast<const char*>(data);std::copy(d, d+len, begin()+readerIndex_);}//可以抽象理解为将buffer_修改为std::max(kInitialSize(1024),readableBytes()+reserve)大小的空间void shrink(size_t reserve){// FIXME: use vector::shrink_to_fit() in C++ 11 if possible.Buffer other;other.ensureWritableBytes(readableBytes()+reserve);//保证other拥有buffer_未读取数据的大小加上reserve预留空间大小的容量other.append(toStringPiece());//将buffer_的数据追加到otherswap(other);//调用swap与buffer_交换}size_t internalCapacity() const//返回vector实际占用的容量{return buffer_.capacity();}/// Read data directly into buffer.////// It may implement with readv(2)/// @return result of read(2), @c errno is savedssize_t readFd(int fd, int* savedErrno);private:char* begin(){ return &*buffer_.begin(); }const char* begin() const{ return &*buffer_.begin(); }void makeSpace(size_t len){// 可写空间 + 已读空间 ==除去缓冲区未读数据外的空间大小//len(需要的空间大小)+kCheapPrepend(8字节预留内存)//小于则直接resize,大于则将数据移到前端if (writableBytes() + prependableBytes() < len + kCheapPrepend)//{// FIXME: move readable databuffer_.resize(writerIndex_+len);}else{// move readable data to the front, make space inside bufferassert(kCheapPrepend < readerIndex_);size_t readable = readableBytes();std::copy(begin()+readerIndex_,//将可读数据移动到前端，在缓冲区内部腾出空间begin()+writerIndex_,begin()+kCheapPrepend);readerIndex_ = kCheapPrepend;writerIndex_ = readerIndex_ + readable;assert(readable == readableBytes());}}private:std::vector<char> buffer_;size_t readerIndex_;size_t writerIndex_;static const char kCRLF[];
};} // namespace net
} // namespace muduo#endif // MUDUO_NET_BUFFER_Hbuffer.cc
// Copyright 2010, Shuo Chen. All rights reserved.
// http://code.google.com/p/muduo/
//
// Use of this source code is governed by a BSD-style license
// that can be found in the License file.// Author: Shuo Chen (chenshuo at chenshuo dot com)
//#include "muduo/net/Buffer.h"#include "muduo/net/SocketsOps.h"#include <errno.h>
#include <sys/uio.h>using namespace muduo;
using namespace muduo::net;const char Buffer::kCRLF[] = "\r\n";const size_t Buffer::kCheapPrepend;
const size_t Buffer::kInitialSize;ssize_t Buffer::readFd(int fd, int* savedErrno)
{// saved an ioctl()/FIONREAD call to tell how much to readchar extrabuf[65536];struct iovec vec[2];const size_t writable = writableBytes();vec[0].iov_base = begin()+writerIndex_;vec[0].iov_len = writable;vec[1].iov_base = extrabuf;vec[1].iov_len = sizeof extrabuf;// when there is enough space in this buffer, don't read into extrabuf.// when extrabuf is used, we read 128k-1 bytes at most.//1.如果buffer_::size大于extrabuf::size,那我们则只用buffer_存取数据//2.如果小于,则两块内存都使用,根据下标顺序先将数据写入buffer_,再将数据写入writable//在这个表达式下,一次性最多能读取的数据大小为writable==65535,65535+65536=131071,也就是128k-1的大小,而一次性最少的空间为extrabuf(64k)+buffer_(初始化最少空间为1k+8byte)const int iovcnt = (writable < sizeof extrabuf) ? 2 : 1;const ssize_t n = sockets::readv(fd, vec, iovcnt);if (n < 0){*savedErrno = errno;}//如果读取的数据小于writable,则直接更新buffer_下标就行了,//因为上述无论是第一种情况还是第二种情况,数据都是先写入buffer_else if (implicit_cast<size_t>(n) <= writable){writerIndex_ += n;}//如果是第二种情况则直接把下标设置在末尾,然后调用append函数并将extrabuf的数据写入buffer_(内部会调整buffer_大小并追加数据)else{writerIndex_ = buffer_.size();append(extrabuf, n - writable);}// if (n == writable + sizeof extrabuf)// {// goto line_30;// }return n;
}
