How to send a SNMP-Packet via UDP

Question

The idea of my socket is receiving and sending SNMP-packets - GetRequest/GetResponse . However, the socket already receive SNMP-packets

...
unsigned char buf[8192];
...
for (;;) {
  // Receive snmp message from snmp manager
  recv_len = recvfrom(my_socket, buf, BUFSIZE, 0, (struct sockaddr
*)&remote_addr, &addr_len);
...

Now I want answer the request by a SNMP-Packet which is represents as string. Note: The response contains a GetResponse-PDU ( a2 ).

unsigned char * packet = "302902010004067075626c6963a21c...";
int r = sendto(my_socket, packet, strlen(packet), 0, (struct sockaddr *)&remote_addr, addr_len);

The return value or r is 4 and is definitely wrong because my responding SNMP-packet packet is larger than 4. Why, because it's a pointer?.

Further, the response SNMP-Packet packet is not send as SNMP-Packet, it looks different compare to packet and is not interpret as a SNMP-Packet in Wireshark. It looks like that:

How can I send a valid SNMP-Packet?

Answer 1

Your problem is the strlen(packet) value, which is 4 due to the 00 byte. strlen is meant to be used with ASCII strings, not binary strings.