Portable native Erlang raw socket interface using pcap
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Latest commit 0519839 Dec 7, 2016 @msantos makefile cleanup


ewpcap is a native Erlang interface to PCAP that can be used for reading and writing packets from the network.

ewpcap is meant to be a portable raw socket interface to all the platforms that support Erlang and libpcap.


ewpcap was written and tested under Linux. But if you are using a Unix system, you may want to use one of these projects instead:

The ewpcap interface will still go through some changes. For example, the function names may change as may the packet tuple.

ewpcap hasn't been heavily tested.


  • libpcap/winpcap

    On Ubuntu: sudo apt-get install libpcap-dev

These libraries are not required but can be used with ewpcap:

ewpcap requires beam to be running with root privileges:

* using sudo

    sudo erl -smp -pa ebin

* using capabilities

    setcap cap_net_raw=ep /path/to/beam.smp
  • SMP

SMP erlang must be enabled (erl -smp -pa ebin).


rebar3 do clean, compile, ct


open() -> {ok, Socket} | {error, Error}
open(Dev) -> {ok, Socket} | {error, Error}
open(Dev, Options) -> {ok, Socket} | {error, Error}

    Types   Dev = binary() | string()
            Error = enomem | pcap_error_string()
            Socket = resource()
            Options = [ Option ]
            Option = {promisc, boolean()}
                | {snaplen, integer()}
                | {to_ms, integer()}
                | {buffer, integer()}
                | {monitor, boolean()}
                | {filter, binary() | string()}
                | FilterOpts

    Open a network interface and begin receiving packets.

    Dev is the name of the network device. If an empty binary (<<>>)
    is passed in, pcap will select a default interface.

    If an error occurs, the PCAP string describing the error is
    returned to the caller.

    open/1 and open/2 default to:

        * promiscuous mode disabled

        * a snaplen (packet length) of 65535 bytes

        * timeout set to 500 ms

        * no filter (all packets are received)

    If ewpcap is dropping packets (see stats/1), the PCAP buffer
    size can be increased (should be some multiple of the snaplen).

    Wireless devices can be set to use monitor mode (rfmon) by
    passing in the 'monitor' option.

    For filter options, see filter/3.

    Packets are returned as messages to the caller:

        {ewpcap, Ref, DatalinkType, Time, Length, Packet}

    Ref is a reference identifying the socket handle.

    The DataLinkType is an integer representing the link layer,
    e.g., ethernet, Linux cooked socket.

    The Time is a tuple in the same format as erlang:now/0, {MegaSecs,
    Secs, MicroSecs}.

    The Length corresponds to the actual packet length on the
    wire. The captured packet may have been truncated. To get the
    captured packet length, use byte_size(Packet).

    The Packet is a binary holding the captured data.

close(Socket) -> ok

    Closes the pcap descriptor.

filter(Socket, Filter) -> ok | {error, Error}
filter(Socket, Filter, Options) -> ok | {error, Error}

    Types   Socket = resource()
            Error = enomem | pcap_error_string()
            Options = [ Option ]
            Option = {optimize, boolean()}
                | {netmask, integer()}

    Compile a PCAP filter and apply it to the PCAP descriptor.

read(Socket) -> {ok, Packet}
read(Socket, Timeout) -> {ok, Packet} | {error, eagain}

    Types   Socket = resource()
            Timeout = uint() | infinity
            Packet = binary()

    Convenience function wrapping receive, returning the packet

write(Socket) -> ok | {error, pcap_error_string()}

    Types   Socket = resource()

    Write the packet to the network. See pcap_sendpacket(3PCAP).

dev() -> {ok, string()} | {error, pcap_error_string()}

    Returns the default device used by PCAP.

getifaddrs() -> {ok, Iflist} | {error, posix()}

    Types   Iflist = [{Ifname, [Ifopt]}]
            Ifname = string()
            Ifopt = {flag, [Flag]}
                | {addr, Addr}
                | {netmask, Netmask}
                | {broadaddr, Broadaddr}
                | {dstaddr, Dstaddr}
                | {description, string()}
            Flag = loopback
            Addr = Netmask = Broadaddr = Dstaddr = ip_address()

    Returns a list of interfaces. Ifname can be used as the first
    parameter to open/1 and open/2.

    This function is modelled on inet:getifaddrs/0 but uses
    pcap_findalldevs(3PCAP) to look up the interface attributes:

        * getifaddrs/0 may return pseudo devices, such as the "any"
          device on Linux

        * getifaddrs/0 will only return the list of devices that
          can be used with open/1 and open/2. An empty list ({ok,
          []}) may be returned if the user does not have permission
          to open any of the system interfaces

stats(Socket) -> {ok, #ewpcap_stat{}} | {error, pcap_error_string()}

    Types   Socket = resource()

    To use the return value as a record, include the header:


    stats/1 returns statistics about dropped packets. See
    pcap_stats(3PCAP) for details.

    The ewpcap_stat records contains these fields:

        recv : number of packets received

        drop : number of packets dropped due to insufficient buffer

        ifdrop : number of packets dropped by the network interface

        capt : number of packets received by the application (Win32 only)



    % icmp_resend:start("eth0").
    start(Dev) ->
        {ok, Socket} = ewpcap:open(Dev, [{filter, "icmp"}]),

    resend(Socket) ->
        {ok, Packet} = ewpcap:read(Socket),
        ok = ewpcap:write(Socket, Packet),


  • ewpcap, epcap, epcap_compile ... confusing!

  • pcap_sendpacket may block

  • pcap_findalldevices blocks