我正在尝试编写一个C++应用程序（Linux），可以捕获无线数据包以及相关的信号强度（以dBm为单位）。捕获部分很容易，但问题在于我找不到任何关于如何获取每个数据包的信号强度的文档。
它是头部的一部分吗？
这是我目前所拥有的：
printf("Device: %s\n", dev);
printf("Number of packets: %d\n", num_packets);
printf("Filter expression: %s\n", filter_exp);
/* open capture device */
pcap_t *handler = pcap_create("wlan0", errbuf);
if (handler == NULL)
{
exit(-1);
}
if(pcap_set_rfmon(handler,1)==0 )
{
printf("monitor mode enabled\n");
}
pcap_set_snaplen(handler, 2048); // Set the snapshot length to 2048
pcap_set_promisc(handler, 0); // Turn promiscuous mode off
pcap_set_timeout(handler, 512); // Set the timeout to 512 milliseconds
int status = pcap_activate(handler);
/* now we can set our callback function */
pcap_loop(handle, num_packets, got_packet, NULL);
以下是got_packet代码：
/* define ethernet header */
ethernet = (struct sniff_ethernet*)(packet);
/* define/compute ip header offset */
ip = (struct sniff_ip*)(packet + SIZE_ETHERNET);
size_ip = IP_HL(ip)*4;
if (size_ip < 20) {
printf(" * Invalid IP header length: %u bytes\n", size_ip);
return;
}
/* print source and destination IP addresses */
printf(" From: %s\n", inet_ntoa(ip->ip_src));
printf(" To: %s\n", inet_ntoa(ip->ip_dst));
/* determine protocol */
switch(ip->ip_p) {
case IPPROTO_TCP:
printf(" Protocol: TCP\n");
break;
case IPPROTO_UDP:
printf(" Protocol: UDP\n");
return;
case IPPROTO_ICMP:
printf(" Protocol: ICMP\n");
return;
case IPPROTO_IP:
printf(" Protocol: IP\n");
return;
default:
printf(" Protocol: unknown\n");
return;
}
/* define/compute tcp header offset */
tcp = (struct sniff_tcp*)(packet + SIZE_ETHERNET + size_ip);
size_tcp = TH_OFF(tcp)*4;
if (size_tcp < 20) {
printf(" * Invalid TCP header length: %u bytes\n", size_tcp);
return;
}
printf(" Src port: %d\n", ntohs(tcp->th_sport));
printf(" Dst port: %d\n", ntohs(tcp->th_dport));
/* define/compute tcp payload (segment) offset */
payload = (char *)(packet + SIZE_ETHERNET + size_ip + size_tcp);
/* compute tcp payload (segment) size */
size_payload = ntohs(ip->ip_len) - (size_ip + size_tcp);
/*
* Print payload data; it might be binary, so don't just
* treat it as a string.
*/
if (size_payload > 0) {
printf(" Payload (%d bytes):\n", size_payload);
//print_payload(payload, size_payload);
}
非常感谢您的帮助。
更新：
这是最新情况：
根据我的研究和Guy Scott提到的，我正在寻找错误信息。我需要查看无线数据包，而不是以太网数据包。因此，以下是更新后的代码：
pcap_set_snaplen(handle, 2048); // Set the snapshot length to 2048
pcap_set_promisc(handle, 1); // Turn promiscuous mode off
pcap_set_timeout(handle, 512); // Set the timeout to 512 milliseconds
int status = pcap_activate(handle);
if(pcap_set_datalink(handle, DLT_IEEE802_11_RADIO) == -1) {
printf("Couldn't set datalink type %s: %s\n", device, pcap_geterr(handle));
}
所以现在的问题是解析数据包，这似乎是一个相当困难的问题。我对源地址、目标地址和相关信号等感兴趣。我不知道如何匹配并加载数据从数据包匹配到radiotap结构体。
struct ieee80211_radiotap_header {
u_int8_t it_version; /* set to 0 */
u_int8_t it_pad;
u_int16_t it_len; /* entire length */
u_int32_t it_present; /* fields present */
} __attribute__((__packed__));
/* Presence bits */
#define RADIOTAP_TSFT 0
#define RADIOTAP_FLAGS 1
#define RADIOTAP_RATE 2
#define RADIOTAP_CHANNEL 3
#define RADIOTAP_FHSS 4
#define RADIOTAP_ANTENNA_SIGNAL 5
#define RADIOTAP_ANTENNA_NOISE 6
#define RADIOTAP_LOCK_QUALITY 7
#define RADIOTAP_TX_ATTENUATION 8
#define RADIOTAP_DB_TX_ATTENUATION 9
#define RADIOTAP_DBM_TX_POWER 10
#define RADIOTAP_ANTENNA 11
#define RADIOTAP_DB_ANTENNA_SIGNAL 12
void process_packet (u_char * args, const struct pcap_pkthdr *header, const u_char * packet)
{
struct ieee80211_radiotap_header *packet_header = (struct ieee80211_radiotap_header *) header;
// This is where I am stuck
有人能告诉我，一旦我捕获了数据包，我如何从其中提取上述值吗？
谢谢。