Merge pull request #191 from rtobar/pcap-user-filter

Add support for user-provided libpcap filter

doc/py-recv.rst

@@ -226,11 +226,15 @@ it, or repeatedly call :py:meth:`~spead2.recv.Stream.get`.
       :param socket.socket acceptor: Listening socket
       :param int max_size: Largest packet size that will be accepted.
 
-   .. py:method:: add_udp_pcap_file_reader(filename)
+   .. py:method:: add_udp_pcap_file_reader(filename, filter='')
 
       Feed data from a pcap file (for example, captured with :program:`tcpdump`
-      or :ref:`mcdump`). This is only available if libpcap development files
-      were found at compile time.
+      or :ref:`mcdump`). An optional filter selects a subset of the packets from
+      the capture file. This is only available if libpcap development files were
+      found at compile time.
+
+      :param str filename: Filename of the capture file
+      :param str filter: Filter to apply to packets from the capture file
 
    .. py:method:: add_inproc_reader(queue)
 

include/spead2/recv_udp_pcap.h

@@ -39,6 +39,8 @@ namespace recv
 
 /**
  * Reader class that feeds data from a pcap file to a stream.
+ *
+ * An optional filter selects a subset of the packets in the capture file.
  */
 class udp_pcap_file_reader : public udp_reader_base
 {
@@ -55,10 +57,11 @@ class udp_pcap_file_reader : public udp_reader_base
      *
      * @param owner Owning stream
      * @param filename Filename of the capture file
+     * @param filter Filter to apply to packets from the capture file
      *
      * @throws std::runtime_error if @a filename could not read
      */
-    udp_pcap_file_reader(stream &owner, const std::string &filename);
+    udp_pcap_file_reader(stream &owner, const std::string &filename, const std::string &filter = "");
     virtual ~udp_pcap_file_reader();
 
     virtual void stop() override;

src/py_recv.cpp

@@ -276,10 +276,10 @@ static void add_udp_ibv_reader_new(stream &s, const udp_ibv_config_wrapper &conf
 #endif  // SPEAD2_USE_IBV
 
 #if SPEAD2_USE_PCAP
-static void add_udp_pcap_file_reader(stream &s, const std::string &filename)
+static void add_udp_pcap_file_reader(stream &s, const std::string &filename, const std::string &filter)
 {
     py::gil_scoped_release gil;
-    s.emplace_reader<udp_pcap_file_reader>(filename);
+    s.emplace_reader<udp_pcap_file_reader>(filename, filter);
 }
 #endif
 
@@ -773,7 +773,7 @@ py::module register_module(py::module &parent)
 #endif
 #if SPEAD2_USE_PCAP
         .def("add_udp_pcap_file_reader", add_udp_pcap_file_reader,
-             "filename"_a)
+             "filename"_a, "filter"_a = "")
 #endif
         .def("add_inproc_reader", add_inproc_reader,
              "queue"_a)

src/recv_udp_pcap.cpp

@@ -98,7 +98,7 @@ void udp_pcap_file_reader::run()
         stopped();
 }
 
-udp_pcap_file_reader::udp_pcap_file_reader(stream &owner, const std::string &filename)
+udp_pcap_file_reader::udp_pcap_file_reader(stream &owner, const std::string &filename, const std::string &user_filter)
     : udp_reader_base(owner)
 {
     // Open the file
@@ -108,8 +108,11 @@ udp_pcap_file_reader::udp_pcap_file_reader(stream &owner, const std::string &fil
         throw std::runtime_error(errbuf);
     // Set a filter to ensure that we only get UDP4 packets with no fragmentation
     bpf_program filter;
+    std::string filter_expression = "ip proto \\udp and ip[6:2] & 0x3fff = 0";
+    if (!user_filter.empty())
+        filter_expression += " and (" + user_filter + ')';
     if (pcap_compile(handle, &filter,
-                     "ip proto \\udp and ip[6:2] & 0x3fff = 0",
+                     filter_expression.c_str(),
                      1, PCAP_NETMASK_UNKNOWN) != 0)
         throw std::runtime_error(pcap_geterr(handle));
     if (pcap_setfilter(handle, &filter) != 0)

src/spead2/recv/__init__.pyi

@@ -179,7 +179,7 @@ class _Stream:
                            comp_vector: int = ..., max_poll: int = ...) -> None: ...
     @overload
     def add_udp_ibv_reader(self, config: UdpIbvConfig) -> None: ...
-    def add_udp_pcap_file_reader(self, filename: str) -> None: ...
+    def add_udp_pcap_file_reader(self, filename: str, filter: str = ...) -> None: ...
     def add_inproc_reader(self, queue: spead2.InprocQueue) -> None: ...
     def stop(self) -> None: ...
     @property