chore: fix building pcap option

Author: nagisa

README.md

@@ -47,14 +47,14 @@ Contributions and PRs are welcome.
 
 #### Install PCAP dev libraries
 
- * Ensure you have install the libpcap-dev package
+ * Optionally, you may want to have libpcap-dev package installed (if building with `-tags pcap`.)
 
 #### Download, extract, and compile phev2mqtt
 
  * Download the phev2mqtt archive
  * Extract it
- * Go into its the top level directory and run *go build*
- * Verify it runs with *./phev2mqtt -h*
+ * Go into its the top level directory and run `go build`
+ * Verify it runs with `./phev2mqtt -h`
 
 ### Connecting to the vehicle.
 
@@ -238,10 +238,9 @@ then extract off the phone.
 *PCAP Remote* is a little more involved, but allows for live sniffing of the traffic.
 
 Once you have downloaded the PCAP file(s) from the phone, you can analyse them with
-the command *phev2mqtt decode pcap <filename>*. Adjust the verbosity level (-v)
-between 'info', 'debug' and 'trace' for more details.
+the command *phev2mqtt decode pcap <filename>*. First build a `phev2mqtt` with pcap features:
+`go build -tags pcap`; you will need libpcap for this. Adjust the verbosity level (`-v`) between
+`info`, `debug` and `trace` for more details.
 
-Additionally, the flag '--latency' will use the PCAP packet timestamps to decode
+Additionally, the flag `--latency` will use the PCAP packet timestamps to decode
 the packets with original timings which can help pinpoint app events.
-
-

cmd/pcap.go

@@ -125,8 +125,6 @@ func processPayload(cmd *cobra.Command, data []byte, dir string) {
 	}
 }
 
-var securityKey *protocol.SecurityKey
-
 var regs = map[byte]string{}
 
 var pings bool