常用AMF解析

AMF 格式是 Adobe 推出的一个二进制数据格式

AMF0 ：http://wwwimages.adobe.com/content/dam/Adobe/en/devnet/amf/pdf/amf0-file-format-specification.pdf

AMF3 ：http://download.macromedia.com/pub/labs/amf/amf3_spec_121207.pdf

rtmp流里分析帧类型18为AMF0类型，15为AMF3类型。
rtmp流里常用的AMF0格式有：
AMF_NUMBER 0x00
AMF_BOOLEAN 0x01
AMF_STRING 0x02
AMF_NULL 0x05
AMF_LONG_STRING 0x0C
AMF_OBJECT 0x03
AMF_OBJECT_END 0x09

解析流程：
一个字节为类型 ：后面字节为数据内容
例子：
01 00
01 表示后面的值为bool , 00 为值 false

各个常用类型的解析

AMF_NUMBER ：一个类型字节 ＋ 八个数据字节(大编码)

00 41 1e 9a e4 00 00 00 00
00 表示 AMF_NUMBER
41 1e 9a e4 00 00 00 00 换算为 501433

AMF_BOOLEAN ： 一个类型字节 ＋ 一个数字字节

01 01
01 表示 AMF_BOOLEAN
01 为 true

AMF_STRING ：一个类型字节 ＋ 二个字节保存长度N (大编码) ＋ N个数据字节

02 00 04 6d 70 34 32
02 表示 AMF_STRING
00 04 表示字符串长度为4
6d 70 34 32 换算成 “mp42”

AMF_NULL ： 一个类型字节

05
05 表示 AMF_NULL 后面没有数据内容

AMF_LONG_STRING ：一个类型字节 ＋ 四个字节保存长度N(大编码) ＋ N个数据字节

类似 AMF_STRING ，只是长度由4个字节组装

AMF_OBJECT ： 一个类型字节 ＋ N个组合字节[AMF_STRING ＋ 一个类型字节 ＋ 类型字节内容] ＋ 长度为0的AMF_STRING ＋ AMF_OBJECT_END类型字节

Name： level 为一个AMF_STRING类型，不带一个字节类型标示
String ｀status` 为一个AMF_STRING类型，带一个字节类型标示，也可以是带一个字节类型标示的AMF_BOOLEAN或者AMF_NUMBER

代码：
yuAMF.h

typedef enum
{
    AMF_NUMBER = 0, AMF_BOOLEAN, AMF_STRING, AMF_OBJECT,
    AMF_MOVIECLIP,      /* reserved, not used */
    AMF_NULL,
    AMF_UNDEFINED,
    AMF_REFERENCE,
    AMF_ECMA_ARRAY,
    AMF_OBJECT_END,
    AMF_STRICT_ARRAY, AMF_DATE, AMF_LONG_STRING, AMF_UNSUPPORTED,
    AMF_RECORDSET,      /* reserved, not used */
    AMF_XML_DOC, AMF_TYPED_OBJECT,
    AMF_AVMPLUS,        /* switch to AMF3 */
    AMF_INVALID = 0xff
} AMFDataType;

typedef struct AVal
{
    char *av_val;
    int av_len;
} AVal;

class uyAMF {
public:
    uyAMF(char* data , int len);
    ~uyAMF();

    bool checkout();

    AMFDataType AMF_GetType();
    unsigned short AMF_DecodeInt16();
    unsigned int AMF_DecodeInt24();
    unsigned int AMF_DecodeInt32();
    void AMF_DecodeString( AVal& bv);
    void AMF_DecodeLongString( AVal& bv);
    int AMF_DecodeBoolean();
    double AMF_DecodeNumber();
    void AMF_DecodeObject(std::map<std::string,std::string>& paramMap);

public:
    char* amf_data;
    int amf_len;
    int decode_amf_len;
};

uyAMF.cpp

uyAMF::uyAMF(char *data, int len)
:amf_data(data)
,amf_len(len)
,decode_amf_len(0)
{

}

uyAMF::~uyAMF()
{
}

AMFDataType uyAMF::AMF_GetType()
{
    decode_amf_len ++ ;
    return (AMFDataType)*amf_data++;
}

unsigned short uyAMF::AMF_DecodeInt16()
{
    if (decode_amf_len + 2 > amf_len)
    {
        return 0;
    }

    unsigned char *c = (unsigned char *) amf_data;
    unsigned short val;
    val = (c[0] << 8) | c[1];

    amf_data += 2;
    decode_amf_len += 2;
    return val;
}

unsigned int uyAMF::AMF_DecodeInt24()
{
    if (decode_amf_len + 3 > amf_len)
    {
        return 0;
    }

    unsigned char *c = (unsigned char *) amf_data;
    unsigned int val;
    val = (c[0] << 16) | (c[1] << 8) | c[2];

    amf_data += 3;
    decode_amf_len += 3;
    return val;
}

unsigned int uyAMF::AMF_DecodeInt32()
{
    if (decode_amf_len + 4 > amf_len)
    {
        return 0;
    }

    unsigned char *c = (unsigned char *)amf_data;
    unsigned int val;
    val = (c[0] << 24) | (c[1] << 16) | (c[2] << 8) | c[3];

    amf_data += 4;
    decode_amf_len += 4;
    return val;
}

void uyAMF::AMF_DecodeString(AVal& bv)
{
    if (decode_amf_len + 1 > amf_len)
    {
        bv.av_len = 0;
        bv.av_val = NULL;
        return;
    }

    bv.av_len = AMF_DecodeInt16();

    if (decode_amf_len + bv.av_len > amf_len)
    {
        bv.av_len = 0;
        bv.av_val = NULL;
        return;
    }

    bv.av_val = (bv.av_len > 0) ? (char *)amf_data : NULL;

    amf_data += bv.av_len ;
    decode_amf_len += bv.av_len;
}

void uyAMF::AMF_DecodeLongString(AVal &bv)
{
    if (decode_amf_len + 1 > amf_len)
    {
        bv.av_len = 0;
        bv.av_val = NULL;
        return;
    }

    bv.av_len = AMF_DecodeInt32();

    if (decode_amf_len + bv.av_len > amf_len)
    {
        bv.av_len = 0;
        bv.av_val = NULL;
        return;
    }

    bv.av_val = (bv.av_len > 0) ? (char *)amf_data : NULL;

    amf_data += bv.av_len ;
    decode_amf_len += bv.av_len;
}

int uyAMF::AMF_DecodeBoolean()
{
    bool succ = *amf_data != 0;

    amf_data += 1;
    decode_amf_len += 1;
    return succ;
}

double uyAMF::AMF_DecodeNumber()
{
    if (decode_amf_len + 8 > amf_len)
    {
        return 8;
    }

    double dVal;
#if __FLOAT_WORD_ORDER == __BYTE_ORDER
#if __BYTE_ORDER == __BIG_ENDIAN
    memcpy(&dVal, amf_data, 8);
#elif __BYTE_ORDER == __LITTLE_ENDIAN
    unsigned char *ci, *co;
  ci = (unsigned char *)amf_data;
  co = (unsigned char *)&dVal;
  co[0] = ci[7];
  co[1] = ci[6];
  co[2] = ci[5];
  co[3] = ci[4];
  co[4] = ci[3];
  co[5] = ci[2];
  co[6] = ci[1];
  co[7] = ci[0];
#endif
#else
    #if __BYTE_ORDER == __LITTLE_ENDIAN /* __FLOAT_WORD_ORER == __BIG_ENDIAN */
  unsigned char *ci, *co;
  ci = (unsigned char *)amf_data;
  co = (unsigned char *)&dVal;
  co[0] = ci[3];
  co[1] = ci[2];
  co[2] = ci[1];
  co[3] = ci[0];
  co[4] = ci[7];
  co[5] = ci[6];
  co[6] = ci[5];
  co[7] = ci[4];
#else /* __BYTE_ORDER == __BIG_ENDIAN && __FLOAT_WORD_ORER == __LITTLE_ENDIAN */
  unsigned char *ci, *co;
  ci = (unsigned char *)amf_data;
  co = (unsigned char *)&dVal;
  co[0] = ci[4];
  co[1] = ci[5];
  co[2] = ci[6];
  co[3] = ci[7];
  co[4] = ci[0];
  co[5] = ci[1];
  co[6] = ci[2];
  co[7] = ci[3];
#endif
#endif

    decode_amf_len += 8;
    amf_data += 8;
    return dVal;
}

bool uyAMF::checkout()
{
    return (decode_amf_len + 1 <= amf_len);
}

void uyAMF::AMF_DecodeObject(std::map<std::string, std::string>& paramMap)
{
    AVal tmp;
    std::string val;
    std::string key;

    bool succ = true;
    while (succ)
    {
        key.clear();
        val.clear();
        AMF_DecodeString(tmp);
        printf_info("Name : %s",tmp.av_val);
        AMFDataType type = AMF_GetType();
        key.append(tmp.av_val,tmp.av_len);
        switch (type)
        {
            case AMF_STRING:
                AMF_DecodeString(tmp);
                printf_info("string : %s",tmp.av_val);
                val.append(tmp.av_val,tmp.av_len);
                break;

            case AMF_NUMBER:
            {
                double db = AMF_DecodeNumber();
                printf_info("double : %f",db);
                char data[1024] = {0};
                sprintf(data,"%f",db);
                val = data;
                break;
            }

            case AMF_BOOLEAN:
            {
                bool succ = AMF_DecodeBoolean();
                printf_info("bool : %d",succ);
                val = succ ? "true" : "false";
                break;
            }
            case AMF_OBJECT_END:
            default:
                succ = false;
                break;
        }

        paramMap[key] = val;
    }
}