1This folder provides an example implementation of how to add custom tcp header 2options and custom socket options. 3 4It does this by implementing the (seldom used) tcp md5 signature. 5 6To enable it, add an LWIP_HOOK_FILENAME hook file, include tcp_md5.h in it and 7define these hooks: 8 9 #define LWIP_HOOK_TCP_INPACKET_PCB(pcb, hdr, optlen, opt1len, opt2, p) tcp_md5_check_inpacket(pcb, hdr, optlen, opt1len, opt2, p) 10 #define LWIP_HOOK_TCP_OPT_LENGTH_SEGMENT(pcb, internal_len) tcp_md5_get_additional_option_length(pcb, internal_len) 11 #define LWIP_HOOK_TCP_ADD_TX_OPTIONS(p, hdr, pcb, opts) tcp_md5_add_tx_options(p, hdr, pcb, opts) 12 #define LWIP_HOOK_SOCKETS_SETSOCKOPT(s, sock, level, optname, optval, optlen, err) tcp_md5_setsockopt_hook(sock, level, optname, optval, optlen, err) 13 14Then, in your sockets application, enable md5 signature on a socket like this: 15 16 struct tcp_md5sig md5; 17 struct sockaddr_storage addr_remote; /* Initialize this to remote address and port */ 18 memcpy(&md5.tcpm_addr, &addr_remote, sizeof(addr_remote)); 19 strcpy(md5.tcpm_key, key); /* this is the md5 key per connection */ 20 md5.tcpm_keylen = strlen(key); 21 if ((ret = setsockopt(sockfd, IPPROTO_TCP, TCP_MD5SIG, &md5, sizeof(md5))) < 0) { 22 perror("setsockopt TCP_MD5SIG"); 23 return; 24 } 25 26After that, your connection (client) or all incoming connections (server) require 27tcp md5 signatures. 28