OpenRTMFP/Cumulus Primer(9)AMF解析之BinaryReader/Writer
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OpenRTMFP/Cumulus Primer(9)AMF解析之BinaryReader/Writer
- Author: 柳大·Poechant(钟超)
- Email: zhongchao.ustc#gmail.com (#->@)
- Blog: Blog.CSDN.net/Poechant
- Date: April 24th, 2012
本文介绍 CumulusServer 中如何对 AMF 数据格式进行序列化与反序列化。
1 AMF3 数据格式基础
首先介绍一下变长整数(Variable Length Integer),比如 UInt32 如下。
上图摘自 Adobe AMF3 官方文档,这是一种压缩方式的整数存储,且每一字节都对后面的数据具有预知作用。那么字符串如何处理呢?下面是字符串的处理方式,AMF0 和 AMF3 都才用 UTF-8 编码方式,并做如下压缩处理:
上图摘自 Adobe AMF3 官方文档。
2 序列化
序列化包括 8 位、16 位、32 位,以及 UTF-8 和 UTF-16(I guess)编码的 String,还有原生数据(Raw Data)、变长无符号整数(Variable Length Unsigned Integer)以及 IP 地址。所谓序列化就是按照指定格式编写各种对象、基础数据类型值。
class BinaryWriter : public Poco::BinaryWriter {public: BinaryWriter(std::ostream& ostr); virtual ~BinaryWriter(); void writeRaw(const Poco::UInt8* value,Poco::UInt32 size); void writeRaw(const char* value,Poco::UInt32 size); void writeRaw(const std::string& value); void write8(Poco::UInt8 value); void write16(Poco::UInt16 value); void write32(Poco::UInt32 value); void writeString8(const std::string& value); void writeString8(const char* value,Poco::UInt8 size); void writeString16(const std::string& value); void writeString16(const char* value,Poco::UInt16 size); void write7BitValue(Poco::UInt32 value); void write7BitLongValue(Poco::UInt64 value); void writeAddress(const Address& address,bool publicFlag); void writeAddress(const Poco::Net::SocketAddress& address,bool publicFlag); static BinaryWriter BinaryWriterNull;};
请注意其中名为 BinaryWriterNull 的成员。构造函数定义为:
BinaryWriter::BinaryWriter(ostream& ostr): Poco::BinaryWriter(ostr,BinaryWriter::NETWORK_BYTE_ORDER) {}BinaryWriter::~BinaryWriter() { flush();}
其中 writeRaw 是简单地封装 Poco::BinaryWriter::writeRaw(),如下:
inline void BinaryWriter::writeRaw(const Poco::UInt8* value,Poco::UInt32 size) { Poco::BinaryWriter::writeRaw((char*)value,size);}inline void BinaryWriter::writeRaw(const char* value,Poco::UInt32 size) { Poco::BinaryWriter::writeRaw(value,size);}inline void BinaryWriter::writeRaw(const std::string& value) { Poco::BinaryWriter::writeRaw(value);}
写入整数实现如下,用的是从 Poco::BinaryReader 继承来的重载运算符操作:
inline void BinaryWriter::write8(Poco::UInt8 value) { (*this) << value;} inline void BinaryWriter::write16(Poco::UInt16 value) { (*this) << value;}inline void BinaryWriter::write32(Poco::UInt32 value) { (*this) << value;}
写入字符串:
void BinaryWriter::writeString8(const char* value,UInt8 size) { write8(size); writeRaw(value,size);}void BinaryWriter::writeString8(const string& value) { write8(value.size()); writeRaw(value);}void BinaryWriter::writeString16(const char* value,UInt16 size) { write16(size); writeRaw(value,size);}void BinaryWriter::writeString16(const string& value) { write16(value.size()); writeRaw(value);}
写入变长整数,这段代码含义也一目了然,就是读取变长无符号 32 位整数、64 位整数。
void BinaryWriter::write7BitValue(UInt32 value) { UInt8 shift = (Util::Get7BitValueSize(value)-1)*7; bool max = false; if(shift>=21) { // 4 bytes maximum shift = 22; max = true; } while(shift>=7) { write8(0x80 | ((value>>shift)&0x7F)); shift -= 7; } write8(max ? value&0xFF : value&0x7F);}void BinaryWriter::write7BitLongValue(UInt64 value) { UInt8 shift = (Util::Get7BitValueSize(value)-1)*7; bool max = shift>=63; // Can give 10 bytes! if(max) ++shift; while(shift>=7) { write8(0x80 | ((value>>shift)&0x7F)); shift -= 7; } write8(max ? value&0xFF : value&0x7F);}
写入 IP 地址的两个函数暂略。
3 反序列化
反序列化就是从指定格式的数据中读出各类型的数据值。
class BinaryReader : public Poco::BinaryReader {public: BinaryReader(std::istream& istr); virtual ~BinaryReader(); Poco::UInt32 read7BitValue(); Poco::UInt64 read7BitLongValue(); Poco::UInt32 read7BitEncoded(); void readString(std::string& value); void readRaw(Poco::UInt8* value,Poco::UInt32 size); void readRaw(char* value,Poco::UInt32 size); void readRaw(Poco::UInt32 size,std::string& value); void readString8(std::string& value); void readString16(std::string& value); Poco::UInt8 read8(); Poco::UInt16 read16(); Poco::UInt32 read32(); bool readAddress(Address& address); static BinaryReader BinaryReaderNull;};
构造与析构函数都很简单:
BinaryReader::BinaryReader(istream& istr) : Poco::BinaryReader(istr,BinaryReader::NETWORK_BYTE_ORDER) {}BinaryReader::~BinaryReader() {}
读取原生数据(Raw Data):
inline void BinaryReader::readRaw(Poco::UInt8* value,Poco::UInt32 size) { Poco::BinaryReader::readRaw((char*)value,size);}inline void BinaryReader::readRaw(char* value,Poco::UInt32 size) { Poco::BinaryReader::readRaw(value,size);}inline void BinaryReader::readRaw(Poco::UInt32 size,std::string& value) { Poco::BinaryReader::readRaw(size,value);}
写整数,用的是 Poco::BinaryWriter 的重载运算符:
inline void BinaryWriter::write8(Poco::UInt8 value) { (*this) << value;}inline void BinaryWriter::write16(Poco::UInt16 value) { (*this) << value;}inline void BinaryWriter::write32(Poco::UInt32 value) { (*this) << value;}
读写整数依旧使用从 Poco::BinaryReader 继承来的运算符操作:
UInt8 BinaryReader::read8() { UInt8 c; (*this) >> c; return c;}UInt16 BinaryReader::read16() { UInt16 c; (*this) >> c; return c;}UInt32 BinaryReader::read32() { UInt32 c; (*this) >> c; return c;}
写字符串:
void BinaryWriter::writeString8(const char* value,UInt8 size) { write8(size); writeRaw(value,size);}void BinaryWriter::writeString8(const string& value) { write8(value.size()); writeRaw(value);}void BinaryWriter::writeString16(const char* value,UInt16 size) { write16(size); writeRaw(value,size);}void BinaryWriter::writeString16(const string& value) { write16(value.size()); writeRaw(value);}
读取变长整数,分别针对 UInt32 和 UInt64,要理解 AMF3 的变长整数才能理解这个:
UInt32 BinaryReader::read7BitValue() { UInt8 n = 0; UInt8 b = read8(); UInt32 result = 0; while ((b&0x80) && n < 3) { result <<= 7; result |= (b&0x7F); b = read8(); ++n; } result <<= ((n<3) ? 7 : 8); // Use all 8 bits from the 4th byte result |= b; return result;}UInt64 BinaryReader::read7BitLongValue() { UInt8 n = 0; UInt8 b = read8(); UInt64 result = 0; while ((b&0x80) && n < 8) { result <<= 7; result |= (b&0x7F); b = read8(); ++n; } result <<= ((n<8) ? 7 : 8); // Use all 8 bits from the 4th byte result |= b; return result;}
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转载请注明来自柳大的CSDN博客:Blog.CSDN.net/Poechant
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