Serialization issues while sending struct over socket

Question

I am developing a Client/Server based on UDP I want to send different messages to the client from the server. There are different C structures defined for each message.

I would like to understand what is wrong in the way I am serializing the data.

struct Task
{
    int mType;
    int tType;
    int cCnt;
    int* cId;
    char data[128];
};

Serialization/Deserialization functions

unsigned char * serialize_int(unsigned char *buffer, int value)
{
    buffer[0] = value >> 24;
    buffer[1] = value >> 16;
    buffer[2] = value >> 8;
    buffer[3] = value;
    return buffer + 4;
}

unsigned char * serialize_char(unsigned char *buffer, char value)
{
    buffer[0] = value;
    return buffer + 1;
}

int deserialize_int(unsigned char *buffer)
{
    int value = 0;

    value |= buffer[0] << 24;
    value |= buffer[1] << 16;
    value |= buffer[2] << 8;
    value |= buffer[3];
    return value;

}

char deserialize_char(unsigned char *buffer)
{
    return buffer[0];
}

Sender side code to serialize the structure

unsigned char* serializeTask(unsigned char* msg, const Task* t)
{
    msg = serialize_int(msg,t->mType);
    msg = serialize_int(msg,t->tkType);
    msg = serialize_int(msg,t->cCnt);
    for(int i=0; i<t->cCnt; i++)
            msg = serialize_int(msg,t->cId[i*4]);

for(int i=0; i<strlen(data); i++)
    msg = serialize_char(msg,t->data[i]);

    return msg;
}

Receiver side code to de-serialize data

printf("Msg type:%d\n", deserialize_int(message) );
printf("Task Type:%d\n", deserialize_int(message+4) );
printf("Task Count:%d\n", deserialize_int(message+8));

Output 
Msg type:50364598         //Expected value is 3
Task Type:-2013036362     //Expected value is 1
Task Count:1745191094     //Expected value is 3

Question 1:
Why is the de-serialized value not same as expected?

Question 2:
How is serialization/de-serialization method different from memcpy?

Task t;
memcpy(&t, msg, sizeof(t));  //msg is unsigned char* holding the struct data

EDIT

Code which invokes serializeTask

void addToDatabase(unsigned char* message, int msgSize, Task* task)
{
    message = new unsigned char[2*msgSize+1];
    unsigned char* msg = message;  //To preserve start address of message
    message = serializeTask(message, task); //Now message points to end of the array

//Insert serialized data to DB
//msg is inserted to DB 
}

Serialized data stored in DB

Message:
00 
03 70 B6 88 03 70 B6 68 05 70 B6 68 05 70 B6 00 
00 00 00 00 00 00 00 A8 05 70 B6 AC 05 70 B6 B4 
05 70 B6 C9 05 70 B6 DE 05 70 B6 E6 05 70 B6 EE 
05 70 B6 FB 05 70 B6 64 65 66 00 63 6F 68 6F 72 
74 73 00 70 65 6E 64 69 6E 67 5F 61 73 73 69 67 
6E 5F 74 61 73 6B 73 00 70 65 6E 64 69 6E 67 5F 
61 73 73 69 67 6E 5F 74 61 73 6B 73 00 6D 65 73 
73 61 67 65 00 6D 65 73 73 61 67 65 00 3F 00 FF 
FF 00 00 FC 90 00 00 00 00 00 00 00 C9 2D B7 00 
00 00 00 10 06 70 B6 00 00 00 00 00 00 00 00 30 
06 70 B6 34 06 70 B6 3C 06 70 B6

Inspect the buffer in the debugger before you send it and after it's received. — Guy Sirton
It might be a good idea to output the message as hex pairs on both sender and receiver to make sure that it's getting through correctly, before turning to the serialization functions. — paddy
@paddy In the server side itself, I am storing the serialized data into DB and trying to retrieve it and de-serialize. Still the data is different. I will post the hex data. — cppcoder

chux - Reinstate Monica chux - Reinstate Monica · Accepted Answer · 2013-09-09T18:49:15

OP has 2 problems in serializeTask()

for(int i=0; i<t->cCnt; i++)
  msg = serialize_int(msg,t->cId[i*4]); [i*4]
...
for(int i=0; i<strlen(data); i++)
  msg = serialize_char(msg,t->data[i]); strlen(data)

Should be (assuming i<strlen(data) should have been i<strlen(t->data)

for(int i=0; i<t->cCnt; i++)
  msg = serialize_int(msg,t->cId[i]);  // [i]
...
for(int i=0; i<strlen(t->data); i++)   // strlen(data) + 1
  msg = serialize_char(msg,t->data[i]);

The first for loop serialize every 4th cId[]. OP certainly wanted to serialize consecutive cId[].
Only the length of the data string was serialized. OP certainly wanted to serialize all that and a NUL terminating byte.

The data in the posted buffer is more likely the below, which does not match the serialization code. This implies the higher level code populating Task* t is wrong. I am confident that the values seen in fields mType and tkType are either pointers or float, again Task* t is likely amiss before the serialization.

0xb6700300 or -3.576453e-06
0xb6700388 or -3.576484e-06
0xb6700568 or -3.576593e-06
0xb6700568 or -3.576593e-06
0x000000 or 0.000000e+00
0x000000 or 0.000000e+00
0xb67005a8 or -3.576608e-06
0xb67005ac or -3.576609e-06
0xb67005b4 or -3.576611e-06
0xb67005c9 or -3.576615e-06
0xb67005de or -3.576620e-06
0xb67005e6 or -3.576622e-06
0xb67005ee or -3.576624e-06
0xb67005fb or -3.576627e-06
def\0cohorts\0pending_assign_tasks\0pending_assign_tasks\0message\0message\0?\0
...

Serialization issues while sending struct over socket

1 Answers