Add error handling

Cargo.toml

@@ -11,3 +11,4 @@ dns-parser = "0.8.0"
 etherparse = "0.9.0"
 tokio = { version = "0.2", features = ["full"] }
 futures = "0.3"
+eyre = "0.6.5"

src/main.rs

@@ -3,9 +3,10 @@ use dns_parser::Packet as DNSPacket;
 use dns_parser::{RData, ResourceRecord, ResponseCode};
 use etherparse::IpHeader;
 use etherparse::PacketHeaders;
+use eyre::{Result, WrapErr};
 use futures::StreamExt;
-use pcap::stream::PacketCodec;
-use pcap::{Capture, Error, Linktype, Packet};
+use pcap::stream::{PacketCodec, PacketStream};
+use pcap::{Active, Capture, Linktype, Packet};
 use std::collections::HashMap;
 use std::net::IpAddr;
 use std::str;
@@ -20,27 +21,36 @@ struct OrigPacket {
 }
 
 #[tokio::main]
-async fn main() {
+async fn main() -> Result<()> {
  let map = Arc::new(Mutex::new(HashMap::new()));
 
+ let stream = capture_stream(map.clone())?;
  println!(
  "{:5} {:30} {:20} {}",
  "query", "name", "server IP", "response"
  );
- tokio::join!(capture_packets(map.clone()), track_no_responses(map));
+ tokio::join!(capture_packets(stream), track_no_responses(map));
+ Ok(())
 }
 
-async fn capture_packets(map: Arc<Mutex<HashMap<u16, OrigPacket>>>) {
+fn capture_stream(
+ map: Arc<Mutex<HashMap<u16, OrigPacket>>>,
+) -> Result<PacketStream<Active, PrintCodec>> {
  let mut cap = Capture::from_device("any")
- .unwrap()
+ .wrap_err("Failed to find device 'any'")?
  .immediate_mode(true)
  .open()
- .unwrap()
+ .wrap_err("Failed to start. You need to run this as root.")?
  .setnonblock()
- .unwrap();
+ .wrap_err("Failed to set nonblocking")?;
  let linktype = cap.get_datalink();
- cap.filter("udp and port 53", true).unwrap();
- let mut stream = cap.stream(PrintCodec { map, linktype }).unwrap();
+ cap.filter("udp and port 53", true)
+ .wrap_err("Failed to create BPF filter")?;
+ cap.stream(PrintCodec { map, linktype })
+ .wrap_err("Failed to create stream")
+}
+
+async fn capture_packets(mut stream: PacketStream<Active, PrintCodec>) {
  while stream.next().await.is_some() {}
 }
 
@@ -52,14 +62,21 @@ pub struct PrintCodec {
 impl PacketCodec for PrintCodec {
  type Type = ();
 
- fn decode(&mut self, packet: Packet) -> Result<(), Error> {
+ fn decode(&mut self, packet: Packet) -> Result<(), pcap::Error> {
  let mut map = self.map.lock().unwrap();
- print(packet, self.linktype, &mut *map);
+ if let Err(e) = print_packet(packet, self.linktype, &mut *map) {
+ // Continue if there's an error, but print a warning
+ eprintln!("Error parsing DNS packet: {:#}", e);
+ }
  Ok(())
  }
 }
 
-fn print(orig_packet: Packet, linktype: Linktype, map: &mut HashMap<u16, OrigPacket>) {
+fn print_packet(
+ orig_packet: Packet,
+ linktype: Linktype,
+ map: &mut HashMap<u16, OrigPacket>,
+) -> Result<()> {
  // Strip the ethernet header
  let packet_data = match linktype {
  Linktype::ETHERNET => &orig_packet.data[14..],
@@ -71,13 +88,15 @@ fn print(orig_packet: Packet, linktype: Linktype, map: &mut HashMap<u16, OrigPac
  _ => panic!("unknown link type {:?}", linktype),
  };
  // Parse the IP header and UDP header
- let packet = PacketHeaders::from_ip_slice(packet_data).unwrap();
- let (src_ip, dest_ip): (IpAddr, IpAddr) = match packet.ip.unwrap() {
- IpHeader::Version4(x) => (x.source.into(), x.destination.into()),
- IpHeader::Version6(x) => (x.source.into(), x.destination.into()),
- };
+ let packet =
+ PacketHeaders::from_ip_slice(packet_data).wrap_err("Failed to parse Ethernet packet")?;
+ let (src_ip, dest_ip): (IpAddr, IpAddr) =
+ match packet.ip.expect("Error: failed to parse IP address") {
+ IpHeader::Version4(x) => (x.source.into(), x.destination.into()),
+ IpHeader::Version6(x) => (x.source.into(), x.destination.into()),
+ };
  // Parse DNS data
- let dns_packet = DNSPacket::parse(packet.payload).unwrap();
+ let dns_packet = DNSPacket::parse(packet.payload).wrap_err("Failed to parse DNS packet")?;
  let question = &dns_packet.questions[0];
  let id = dns_packet.header.id;
  // This map is a list of requests that haven't gotten a response yet
@@ -91,7 +110,7 @@ fn print(orig_packet: Packet, linktype: Linktype, map: &mut HashMap<u16, OrigPac
  report: false,
  },
  );
- return;
+ return Ok(());
  }
  // If it's the second time we're seeing it, it's a response, so remove it from the map
  map.remove(&id);
@@ -116,6 +135,7 @@ fn print(orig_packet: Packet, linktype: Linktype, map: &mut HashMap<u16, OrigPac
  src_ip,
  response
  );
+ Ok(())
 }
 
 fn format_answers(records: Vec<ResourceRecord>) -> String {