Serialization issues while sending struct over socket - c

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

Answer 1

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
...