Add a binding for pcap_loop

Author: saethlin

examples/loop.rs

@@ -0,0 +1,23 @@
+fn main() {
+    // get the default Device
+    let device = pcap::Device::lookup()
+        .expect("device lookup failed")
+        .expect("no device available");
+    println!("Using device {}", device.name);
+
+    // Setup Capture
+    let mut cap = pcap::Capture::from_device(device)
+        .unwrap()
+        .immediate_mode(true)
+        .open()
+        .unwrap();
+
+    let mut count = 0;
+    cap.for_each(|packet| {
+        println!("Got {:?}", packet.header);
+        count += 1;
+        if count > 100 {
+            panic!("ow");
+        }
+    });
+}

src/lib.rs

@@ -59,6 +59,7 @@
 //! ```
 
 use bitflags::bitflags;
+use std::any::Any;
 use std::borrow::Borrow;
 use std::convert::TryFrom;
 use std::ffi::{self, CStr, CString};
@@ -69,6 +70,7 @@ use std::net::IpAddr;
 use std::ops::Deref;
 #[cfg(not(windows))]
 use std::os::unix::io::{AsRawFd, RawFd};
+use std::panic::{catch_unwind, resume_unwind, AssertUnwindSafe};
 use std::path::Path;
 use std::ptr::{self, NonNull};
 use std::slice;
@@ -835,7 +837,68 @@ impl<T: State + ?Sized> From<NonNull<raw::pcap_t>> for Capture<T> {
     }
 }
 
+// Handler and its associated function let us create an extern "C" fn which dispatches to a normal
+// Rust FnMut, which may be a closure with a captured environment. The *only* purpose of this
+// generic parameter is to ensure that in Capture::pcap_loop that we pass the right function
+// pointer and the right data pointer to pcap_loop.
+struct Handler<F> {
+    func: F,
+    panic_payload: Option<Box<dyn Any + Send>>,
+    handle: NonNull<raw::pcap_t>,
+}
+
+impl<F> Handler<F>
+where
+    F: FnMut(Packet),
+{
+    extern "C" fn callback(
+        slf: *mut libc::c_uchar,
+        header: *const raw::pcap_pkthdr,
+        packet: *const libc::c_uchar,
+    ) {
+        unsafe {
+            let packet = Packet::new(
+                &*(header as *const PacketHeader),
+                slice::from_raw_parts(packet, (*header).caplen as _),
+            );
+
+            let slf = slf as *mut Self;
+            let func = &mut (*slf).func;
+            let mut func = AssertUnwindSafe(func);
+            // If our handler function panics, we need to prevent it from unwinding across the
+            // FFI boundary. If the handler panics we catch the unwind here, break out of
+            // pcap_loop, and resume the unwind outside.
+            if let Err(e) = catch_unwind(move || func(packet)) {
+                (*slf).panic_payload = Some(e);
+                raw::pcap_breakloop((*slf).handle.as_ptr());
+            }
+        }
+    }
+}
+
 impl<T: State + ?Sized> Capture<T> {
+    pub fn for_each<F>(&mut self, handler: F)
+    where
+        F: FnMut(Packet),
+    {
+        let mut handler = Handler {
+            func: AssertUnwindSafe(handler),
+            panic_payload: None,
+            handle: self.handle,
+        };
+        unsafe {
+            raw::pcap_loop(
+                self.handle.as_ptr(),
+                -1,
+                Handler::<F>::callback,
+                ptr::addr_of_mut!(handler).cast(),
+            )
+        };
+        if let Some(e) = handler.panic_payload {
+            resume_unwind(e);
+        }
+    }
+
     fn new_raw<F>(path: Option<&str>, func: F) -> Result<Capture<T>, Error>
     where
         F: FnOnce(*const libc::c_char, *mut libc::c_char) -> *mut raw::pcap_t,

src/raw.rs

@@ -99,8 +99,9 @@ pub struct pcap_send_queue {
     pub buffer: *mut c_char,
 }
 
+// This is not Option<fn>, pcap functions do not check if the handler is null.
 pub type pcap_handler =
-    Option<extern "C" fn(arg1: *mut c_uchar, arg2: *const pcap_pkthdr, arg3: *const c_uchar) -> ()>;
+    extern "C" fn(user: *mut c_uchar, h: *const pcap_pkthdr, bytes: *const c_uchar) -> ();
 
 extern "C" {
     // [OBSOLETE] pub fn pcap_lookupdev(arg1: *mut c_char) -> *mut c_char;
@@ -119,8 +120,12 @@ extern "C" {
     pub fn pcap_open_offline(arg1: *const c_char, arg2: *mut c_char) -> *mut pcap_t;
     pub fn pcap_fopen_offline(arg1: *mut FILE, arg2: *mut c_char) -> *mut pcap_t;
     pub fn pcap_close(arg1: *mut pcap_t);
-    // pub fn pcap_loop(arg1: *mut pcap_t, arg2: c_int,
-    //                  arg3: pcap_handler, arg4: *mut c_uchar) -> c_int;
+    pub fn pcap_loop(
+        arg1: *mut pcap_t,
+        arg2: c_int,
+        arg3: pcap_handler,
+        arg4: *mut c_uchar,
+    ) -> c_int;
     // pub fn pcap_dispatch(arg1: *mut pcap_t, arg2: c_int, arg3: pcap_handler,
     //                      arg4: *mut c_uchar)-> c_int;
     // pub fn pcap_next(arg1: *mut pcap_t, arg2: *mut pcap_pkthdr) -> *const c_uchar;
@@ -129,7 +134,7 @@ extern "C" {
         arg2: *mut *mut pcap_pkthdr,
         arg3: *mut *const c_uchar,
     ) -> c_int;
-    // pub fn pcap_breakloop(arg1: *mut pcap_t);
+    pub fn pcap_breakloop(arg1: *mut pcap_t);
     pub fn pcap_stats(arg1: *mut pcap_t, arg2: *mut pcap_stat) -> c_int;
     pub fn pcap_setfilter(arg1: *mut pcap_t, arg2: *mut bpf_program) -> c_int;
     pub fn pcap_setdirection(arg1: *mut pcap_t, arg2: pcap_direction_t) -> c_int;

tests/lib.rs

@@ -31,6 +31,16 @@ fn read_packet_with_full_data() {
     assert_eq!(capture.next_packet().unwrap().len(), 98);
 }
 
+#[test]
+fn read_packet_via_pcap_loop() {
+    let mut packets = 0;
+    let mut capture = capture_from_test_file("packet_snaplen_65535.pcap");
+    capture.pcap_loop(|_| {
+        packets += 1;
+    });
+    assert_eq!(packets, 1);
+}
+
 #[test]
 fn read_packet_with_truncated_data() {
     let mut capture = capture_from_test_file("packet_snaplen_20.pcap");