通过PHP的解包函数读取Struct中的Struct

Question

我想知道如何通过php的unpack函数读取结构中的结构.当我得到一个IS_MCI数据包时,我检查它的类型以确保它等于ISP_MCI,然后检查NumC以找出该数据包中有多少个CompCar结构.问题是尝试通过单个函数将这些内容解压缩到一个数组中.我总是得到一个未定义的偏移量.所以,我正在寻找一些新的眼睛.

你会如何处理这个数据包？

有问题的结构是这样的:

struct IS_MCI // Multi Car Info - if more than 8 in race then more than one of these is sent
{
    byte    Size;       // 4 + NumC * 28
    byte    Type;       // ISP_MCI
    byte    ReqI;       // 0 unless this is a reply to an TINY_MCI request
    byte    NumC;       // number of valid CompCar structs in this packet

    CompCar Info[8];    // car info for each player, 1 to 8 of these (NumC)
};

struct CompCar // Car info in 28 bytes - there is an array of these in the MCI (below)
{
    word    Node;       // current path node
    word    Lap;        // current lap
    byte    PLID;       // player's unique id
    byte    Position;   // current race position : 0 = unknown, 1 = leader, etc...
    byte    Info;       // flags and other info - see below
    byte    Sp3;
    int     X;          // X map (65536 = 1 metre)
    int     Y;          // Y map (65536 = 1 metre)
    int     Z;          // Z alt (65536 = 1 metre)
    word    Speed;      // speed (32768 = 100 m/s)
    word    Direction;  // direction of car's motion : 0 = world y direction, 32768 = 180 deg
    word    Heading;    // direction of forward axis : 0 = world y direction, 32768 = 180 deg
    short   AngVel;     // signed, rate of change of heading : (16384 = 360 deg/s)
};

Answer 1

$msg = 
   chr(0x20) // Size = 32 (4+1*28)
  . chr(0x1) // Type = 1
  . chr(0x0) // ReqI=0
  . chr(0x1) // NumC=1
    . chr(0x1) . chr(0x0) // node=1
    . chr(0x2) . chr(0x0)  // lap=2
    . chr(0x3) // puid=3
    . chr(0x5) // pos=5
    . chr(0x10) // info=16
    . chr(0x0) //sp3=0
    . chr(0x0) . chr(0x0) . chr(0x1) . chr(0x0) // x=65536
    . chr(0x0) . chr(0x0) . chr(0x2) . chr(0x0) // y=65536*2
    . chr(0x0) . chr(0x0) . chr(0x3) . chr(0x0)  // z=65536*3
    . chr(0x0) . chr(0x20) // speed=8192
    . chr(0x0) . chr(0x10) // dir=4096
    . chr(0x0) . chr(0x8) // heading=2048
    . chr(0x0) . chr(0x4) // AngVel=1024
;

$IS_MCI = unpack('CSize', $msg);
if ( strlen($msg) < $IS_MCI['Size'] ) {
  die("not enough data");
}
$IS_MCI += unpack('CType/CReqI/CNumC', substr($msg, 1));
$IS_MCI['Info'] = array();

for($i=0; $i<$IS_MCI['NumC']; $i++) {
  $data = substr($msg, 4+($i*28), 28);
  $IS_MCI['Info'][] = unpack('vNode/vLap/CPLID/CPosition/CInfo/CSp3/lX/lY/lZ/vSpeed/vDirection/vHeading/sAngVel', $data);
}
print_r($IS_MCI);

印刷

Array
(
    [Size] => 32
    [Type] => 1
    [ReqI] => 0
    [NumC] => 1
    [Info] => Array
        (
            [0] => Array
                (
                    [Node] => 1
                    [Lap] => 2
                    [PLID] => 3
                    [Position] => 5
                    [Info] => 16
                    [Sp3] => 0
                    [X] => 65536
                    [Y] => 131072
                    [Z] => 196608
                    [Speed] => 8192
                    [Direction] => 4096
                    [Heading] => 2048
                    [AngVel] => 1024
                )

        )

)

现在，该代码做出了一些您可能不希望认为是理所当然的假设（即添加更多的错误/读取数据处理）。

• 它假设数据包 ($msg) 在代码运行之前已被完全读取。您可能只想读取当前需要的部分（则不需要 substr()）。或者至少要做好消息可能以多个块的形式到达的准备。
• 它还认为 size/num 参数是理所当然的，即它不检查这些值是否可行以及是否有足够的数据可用。这绝对是你必须改变的事情。Size必须介于 0...228 之间，NumC 必须介于 0...8 之间，并且两个值必须匹配在一起，依此类推。
• 还要仔细看看我在 unpack() 中使用的格式标识符。对于word我使用过的v，它代表“无符号短（始终为16位，小端字节顺序）。但是对于int我使用过l：“有符号长（始终为32位，机器字节顺序）”。这在我的机器上没问题。但是搜索协议文档以了解数据的字节顺序。

$msg 中的测试数据取自以下结果

__declspec(align(1)) struct CompCar // Car info in 28 bytes - there is an array of these in the MCI (below)
{
    word    Node;       // current path node
    word    Lap;        // current lap
    byte    PLID;       // player's unique id
    byte    Position;   // current race position : 0 = unknown, 1 = leader, etc...
    byte    Info;       // flags and other info - see below
    byte    Sp3;
    int     X;          // X map (65536 = 1 metre)
    int     Y;          // Y map (65536 = 1 metre)
    int     Z;          // Z alt (65536 = 1 metre)
    word    Speed;      // speed (32768 = 100 m/s)
    word    Direction;  // direction of car's motion : 0 = world y direction, 32768 = 180 deg
    word    Heading;    // direction of forward axis : 0 = world y direction, 32768 = 180 deg
    short   AngVel;     // signed, rate of change of heading : (16384 = 360 deg/s)
};

__declspec(align(1)) struct IS_MCI // Multi Car Info - if more than 8 in race then more than one of these is sent
{
    byte    Size;       // 4 + NumC * 28
    byte    Type;       // ISP_MCI
    byte    ReqI;       // 0 unless this is a reply to an TINY_MCI request
    byte    NumC;       // number of valid CompCar structs in this packet

    CompCar Info[1];    // example: one element, fixed
};

int _tmain(int argc, _TCHAR* argv[])
{
  struct IS_MCI mci = {
    32, 1, 0, 1,
    { 1, 2, 3, 5, 16, 0, 65536, 65536*2, 65536*3, 8192, 4096, 2048, 1024 }
  };

  WSADATA wsaData;
  WORD wVersionRequested = MAKEWORD( 2, 2 );
   int err = WSAStartup( wVersionRequested, &wsaData );
  if ( err != 0 ) {
      /* Tell the user that we could not find a usable */
      /* WinSock DLL.                                  */
      return 1;
  }

  SOCKET s = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
  sockaddr_in addr; 
  addr.sin_family = AF_INET;
  addr.sin_addr.s_addr = inet_addr( "127.0.0.1" );
  addr.sin_port = htons( 8081 );
  if ( 0!=connect( s, (SOCKADDR*) &addr, sizeof(addr) ) ) {
    printf("%X ", WSAGetLastError());
    return 0;
  }
  send(s, (const char*)&mci, sizeof(mci), 0);
  shutdown(s, SD_BOTH);
  closesocket(s);
  return 0;
}