fix(sniffer): handle disconnected interfaces (and periodically attempt to re-connect) (#191)

* Panic on non-Timeout errors in packet Sniffer

* Attempt to Re-establish interface channels after disconnect

Sniffer::next() now returns an io::Result so the thread in main can determine between no packets & a sniffing error
- Matching on EtherType to remove duplicate code determining IP Version

Added Sniffer::reset_channel to allow main to poll a previously connected interface

* Error handling & timeout delay performed in Sniffer::next

* Removing no longer needed Ether layer in test packet builder

3 files changed, 27 insertions, 3 deletions

diff --git a/src/network/sniffer.rs b/src/network/sniffer.rs
index 52014b8..de587be 100644
--- a/src/network/sniffer.rs
+++ b/src/network/sniffer.rs
@@ -10,9 +10,15 @@ use ::pnet::packet::udp::UdpPacket;
 use ::pnet::packet::Packet;
 
 use ::ipnetwork::IpNetwork;
+use ::std::io::{self, Result};
 use ::std::net::{IpAddr, SocketAddr};
+use ::std::thread::park_timeout;
 
 use crate::network::{Connection, Protocol};
+use crate::os::shared::get_datalink_channel;
+
+const PACKET_WAIT_TIMEOUT: std::time::Duration = std::time::Duration::from_millis(10);
+const CHANNEL_RESET_DELAY: std::time::Duration = std::time::Duration::from_millis(1000);
 
 #[derive(Debug)]
 pub struct Segment {
@@ -96,7 +102,20 @@ impl Sniffer {
         }
     }
     pub fn next(&mut self) -> Option<Segment> {
-        let bytes = self.network_frames.next().ok()?;
+        let bytes = match self.network_frames.next() {
+            Ok(bytes) => bytes,
+            Err(err) => match err.kind() {
+                std::io::ErrorKind::TimedOut => {
+                    park_timeout(PACKET_WAIT_TIMEOUT);
+                    return None;
+                }
+                _ => {
+                    park_timeout(CHANNEL_RESET_DELAY);
+                    self.reset_channel().ok();
+                    return None;
+                }
+            },
+        };
         // See https://github.com/libpnet/libpnet/blob/master/examples/packetdump.rs
         // VPN interfaces (such as utun0, utun1, etc) have POINT_TO_POINT bit set to 1
         let payload_offset = if (self.network_interface.is_loopback()
@@ -133,6 +152,11 @@ impl Sniffer {
             }
         }
     }
+    pub fn reset_channel(&mut self) -> Result<()> {
+        self.network_frames = get_datalink_channel(&self.network_interface)
+            .map_err(|_| io::Error::new(io::ErrorKind::Other, "Interface not available"))?;
+        Ok(())
+    }
     fn handle_v6(ip_packet: Ipv6Packet, network_interface: &NetworkInterface) -> Option<Segment> {
         let (protocol, source_port, destination_port, data_length) =
             extract_transport_protocol!(ip_packet);
diff --git a/src/os/mod.rs b/src/os/mod.rs
index ec04ecd..4db5b0a 100644
--- a/src/os/mod.rs
+++ b/src/os/mod.rs
@@ -11,6 +11,6 @@ mod lsof_utils;
 pub(self) mod windows;
 
 mod errors;
-mod shared;
+pub(crate) mod shared;
 
 pub use shared::*;
diff --git a/src/os/shared.rs b/src/os/shared.rs
index 6731531..3c0fe74 100644
--- a/src/os/shared.rs
+++ b/src/os/shared.rs
@@ -31,7 +31,7 @@ impl Iterator for TerminalEvents {
     }
 }
 
-fn get_datalink_channel(
+pub(crate) fn get_datalink_channel(
     interface: &NetworkInterface,
 ) -> Result<Box<dyn DataLinkReceiver>, GetInterfaceErrorKind> {
     let mut config = Config::default();