php passing c struct data throught socket programming

Question

Dear All, How to make a php socket client that needs to perform socket_sendto to linux C socket server which has following struct

typedef struct
{
  UI2             todo;   
  char            rz[LNG_RZ + 1]; 
  char            saId[LNG_SAT_ID + 1]; 
  char            user[LNG_USER + 1]; 
  char            lang[LANGLEN + 1]; 
  SI4             result;       
  UI4             socket;  
  char            text[LNG_ALLG + 1]; 
  char            filename[MAX_PATHLEN];
}  dmsAuf_Head;        

Obviously, PHP is known not to support struct how can I pass the c data to socket using php

I know there is a trick to make c struct object using the method below:

class dmsAuf_Head {
  public            todo;            
  public            rz    
  public            saId    
  public            user    
  public            lang    
  public            result;                         
  public            socket;        
  public            text   
  public            filename 
}

$obj = new dmsAuf_Head();

but this would not take care of the size of the attribute? Any recommnedation?

Answer 1

IT would be best if you serialized your data into a textual format like JSON (or maybe using the pack function) before you send it over the line. Upon receipt, you can deserialize it into the appropriate data structure.

Answer 2

You'll need to fwrite the data in the proper order. The pack function will be useful.

http://us2.php.net/pack

fwrite($sock, pack('v', 0x1234)); // send a 16 bit integer

Of course you have to be careful regarding how the C structure is built (padding, etc), the endianness the target machine is expecting, and so on.

Because of all that, it is usually better for both systems to simply read/write the data needed sequentially and fill in the structures manually (field by field), as opposed to trying to fread/fwrite the structure itself as one big block. On the PHP side, it may look like:

class dmsAuf_Head {
  public            $todo;            
  public            $rz;    
  public            $saId;    
  public            $user;    
  public            $lang;    
  public            $result;                         
  public            $socket;        
  public            $text;   
  public            $filename; 

  public function send($sock)
  {
    fwrite($sock, pack('v', $this->todo));
    // .. fwrite the rest
  }
}

$foo = new dmsAuf_Head();
$foo->send($sock);

(Note that you can build a single packed string and send it all in one go if you use multiple arguments.)

Answer 3

How to serialzied everything before sending???

As proposed by the developer of the c socket server, they are using the following c code to send value to the c socket server:

 rval = send(dms_aufHead->socket, (char *) dms_aufHead, sizeof(dmsAuf_Head), 0);

So how can I send dms_aufHead data using php instead?

Answer 4

There is no such data protocol / format as a "c struct" it's up to the C compiler how it stores this data - and up to the programmer of the C program to decide how to populate/retrieve values from the struct. Even if you were writing a client in C using the same struct you'd need to convert it to a different representation to transfer it to the server. The same is true of PHP - although 'serialize' provides a built-in mechanism for creating a portable representation of a PHP data structure.

You need to write PHP code to create a respresentation of the data which the server can process - which has very little to do with how the server stores/manipulates the data internally. For the server to exist, then it must have capability to parse data in some format - go find out what that format is and write your PHP accordingly.

OTOH if the server does not yet exist, then there are C/C++ libs available which will parse a PHP serialized data structure (see this SO topic) or if there is a requirement to support a more formal protocol, then have a look at soap.

Answer 5

As proposed by the developer of the c socket server, they are using the following c code to send value to the c socket server:

rval = send(dms_aufHead->socket, (char *) dms_aufHead, sizeof(dmsAuf_Head), 0);

So how can I send dms_aufHead data using php instead?

What if (for example) $rz is only 3 char(for this case) instead of 13 char as desired length? what should I output for PHP?