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  .TH PCAP 3PCAP "20 April 2018"
  .SH NAME
  pcap \- Packet Capture library
  .SH SYNOPSIS
  .nf
  .ft B
  #include <pcap/pcap.h>
  .LP
  .ft B
  .ft
  .fi
  .SH DESCRIPTION
  The Packet Capture library
  provides a high level interface to packet capture systems. All packets
  on the network, even those destined for other hosts, are accessible
  through this mechanism.
  It also supports saving captured packets to a ``savefile'', and reading
  packets from a ``savefile''.
  .SS Opening a capture handle for reading
  To open a handle for a live capture, given the name of the network or
  other interface on which the capture should be done, call
  .BR pcap_create (),
  set the appropriate options on the handle, and then activate it with
  .BR pcap_activate ().
  .PP
  To obtain a list of devices that can be opened for a live capture, call
  .BR pcap_findalldevs ();
  to free the list returned by
  .BR pcap_findalldevs (),
  call
  .BR pcap_freealldevs ().
  .BR pcap_lookupdev ()
  will return the first device on that list that is not a ``loopback``
  network interface.
  .PP
  To open a handle for a ``savefile'' from which to read packets, given the
  pathname of the ``savefile'', call
  .BR pcap_open_offline ();
  to set up a handle for a ``savefile'', given a
  .B "FILE\ *"
  referring to a file already opened for reading, call
  .BR pcap_fopen_offline ().
  .PP
  In order to get a ``fake''
  .B pcap_t
  for use in routines that require a
  .B pcap_t
  as an argument, such as routines to open a ``savefile'' for writing and
  to compile a filter expression, call
  .BR pcap_open_dead ().
  .PP
  .BR pcap_create (),
  .BR pcap_open_offline (),
  .BR pcap_fopen_offline (),
  and
  .BR pcap_open_dead ()
  return a pointer to a
  .BR pcap_t ,
  which is the handle used for reading packets from the capture stream or
  the ``savefile'', and for finding out information about the capture
  stream or ``savefile''.
  To close a handle, use
  .BR pcap_close ().
  .PP
  The options that can be set on a capture handle include
  .IP "snapshot length"
  If, when capturing, you capture the entire contents of the packet, that
  requires more CPU time to copy the packet to your application, more disk
  and possibly network bandwidth to write the packet data to a file, and
  more disk space to save the packet.  If you don't need the entire
  contents of the packet - for example, if you are only interested in the
  TCP headers of packets - you can set the "snapshot length" for the
  capture to an appropriate value.  If the snapshot length is set to
  .IR snaplen ,
  and
  .I snaplen
  is less
  than the size of a packet that is captured, only the first
  .I snaplen
  bytes of that packet will be captured and provided as packet data.
  .IP
  A snapshot length of 65535 should be sufficient, on most if not all
  networks, to capture all the data available from the packet.
  .IP
  The snapshot length is set with
  .BR pcap_set_snaplen ().
  .IP "promiscuous mode"
  On broadcast LANs such as Ethernet, if the network isn't switched, or if
  the adapter is connected to a "mirror port" on a switch to which all
  packets passing through the switch are sent, a network adapter receives
  all packets on the LAN, including unicast or multicast packets not sent
  to a network address that the network adapter isn't configured to
  recognize.
  .IP
  Normally, the adapter will discard those packets; however, many network
  adapters support "promiscuous mode", which is a mode in which all
  packets, even if they are not sent to an address that the adapter
  recognizes, are provided to the host.  This is useful for passively
  capturing traffic between two or more other hosts for analysis.
  .IP
  Note that even if an application does not set promiscuous mode, the
  adapter could well be in promiscuous mode for some other reason.
  .IP
  For now, this doesn't work on the "any" device; if an argument of "any"
  or NULL is supplied, the setting of promiscuous mode is ignored.
  .IP
  Promiscuous mode is set with
  .BR pcap_set_promisc ().
  .IP "monitor mode"
  On IEEE 802.11 wireless LANs, even if an adapter is in promiscuous mode,
  it will supply to the host only frames for the network with which it's
  associated.  It might also supply only data frames, not management or
  control frames, and might not provide the 802.11 header or radio
  information pseudo-header for those frames.
  .IP
  In "monitor mode", sometimes also called "rfmon mode" (for "Radio
  Frequency MONitor"), the adapter will supply all frames that it
  receives, with 802.11 headers, and might supply a pseudo-header with
  radio information about the frame as well.
  .IP
  Note that in monitor mode the adapter might disassociate from the
  network with which it's associated, so that you will not be able to use
  any wireless networks with that adapter.  This could prevent accessing
  files on a network server, or resolving host names or network addresses,
  if you are capturing in monitor mode and are not connected to another
  network with another adapter.
  .IP
  Monitor mode is set with
  .BR pcap_set_rfmon (),
  and
  .BR pcap_can_set_rfmon ()
  can be used to determine whether an adapter can be put into monitor
  mode.
  .IP "packet buffer timeout"
  If, when capturing, packets are delivered as soon as they arrive, the
  application capturing the packets will be woken up for each packet as it
  arrives, and might have to make one or more calls to the operating
  system to fetch each packet.
  .IP
  If, instead, packets are not delivered as soon as they arrive, but are
  delivered after a short delay (called a "packet buffer timeout"), more
  than one packet can be accumulated before the packets are delivered, so
  that a single wakeup would be done for multiple packets, and each set of
  calls made to the operating system would supply multiple packets, rather
  than a single packet.  This reduces the per-packet CPU overhead if
  packets are arriving at a high rate, increasing the number of packets
  per second that can be captured.
  .IP
  The packet buffer timeout is required so that an application won't wait
  for the operating system's capture buffer to fill up before packets are
  delivered; if packets are arriving slowly, that wait could take an
  arbitrarily long period of time.
  .IP
  Not all platforms support a packet buffer timeout; on platforms that
  don't, the packet buffer timeout is ignored.  A zero value for the
  timeout, on platforms that support a packet buffer timeout, will cause a
  read to wait forever to allow enough packets to arrive, with no timeout.
  A negative value is invalid; the result of setting the timeout to a
  negative value is unpredictable.
  .IP
  .BR NOTE :
  the packet buffer timeout cannot be used to cause calls that read
  packets to return within a limited period of time, because, on some
  platforms, the packet buffer timeout isn't supported, and, on other
  platforms, the timer doesn't start until at least one packet arrives.
  This means that the packet buffer timeout should
  .B NOT
  be used, for example, in an interactive application to allow the packet
  capture loop to ``poll'' for user input periodically, as there's no
  guarantee that a call reading packets will return after the timeout
  expires even if no packets have arrived.
  .IP
  The packet buffer timeout is set with
  .BR pcap_set_timeout ().
  .IP "buffer size"
  Packets that arrive for a capture are stored in a buffer, so that they
  do not have to be read by the application as soon as they arrive.  On
  some platforms, the buffer's size can be set; a size that's too small
  could mean that, if too many packets are being captured and the snapshot
  length doesn't limit the amount of data that's buffered, packets could
  be dropped if the buffer fills up before the application can read
  packets from it, while a size that's too large could use more
  non-pageable operating system memory than is necessary to prevent
  packets from being dropped.
  .IP
  The buffer size is set with
  .BR pcap_set_buffer_size ().
  .IP "timestamp type"
  On some platforms, the time stamp given to packets on live captures can
  come from different sources that can have different resolutions or that
  can have different relationships to the time values for the current time
  supplied by routines on the native operating system.  See
  .BR pcap-tstamp (@MAN_MISC_INFO@)
  for a list of time stamp types.
  .IP
  The time stamp type is set with
  .BR pcap_set_tstamp_type ().
  .PP
  Reading packets from a network interface may require that you have
  special privileges:
  .TP
  .B Under SunOS 3.x or 4.x with NIT or BPF:
  You must have read access to
  .I /dev/nit
  or
  .IR /dev/bpf* .
  .TP
  .B Under Solaris with DLPI:
  You must have read/write access to the network pseudo device, e.g.
  .IR /dev/le .
  On at least some versions of Solaris, however, this is not sufficient to
  allow
  .I tcpdump
  to capture in promiscuous mode; on those versions of Solaris, you must
  be root, or the application capturing packets
  must be installed setuid to root, in order to capture in promiscuous
  mode.  Note that, on many (perhaps all) interfaces, if you don't capture
  in promiscuous mode, you will not see any outgoing packets, so a capture
  not done in promiscuous mode may not be very useful.
  .IP
  In newer versions of Solaris, you must have been given the
  .B net_rawaccess
  privilege; this is both necessary and sufficient to give you access to the
  network pseudo-device - there is no need to change the privileges on
  that device.  A user can be given that privilege by, for example, adding
  that privilege to the user's
  .B defaultpriv
  key with the
  .B usermod (@MAN_ADMIN_COMMANDS@)
  command.
  .TP
  .B Under HP-UX with DLPI:
  You must be root or the application capturing packets must be installed
  setuid to root.
  .TP
  .B Under IRIX with snoop:
  You must be root or the application capturing packets must be installed
  setuid to root.
  .TP
  .B Under Linux:
  You must be root or the application capturing packets must be installed
  setuid to root (unless your distribution has a kernel
  that supports capability bits such as CAP_NET_RAW and code to allow
  those capability bits to be given to particular accounts and to cause
  those bits to be set on a user's initial processes when they log in, in
  which case you  must have CAP_NET_RAW in order to capture and
  CAP_NET_ADMIN to enumerate network devices with, for example, the
  .B \-D
  flag).
  .TP
  .B Under ULTRIX and Digital UNIX/Tru64 UNIX:
  Any user may capture network traffic.
  However, no user (not even the super-user) can capture in promiscuous
  mode on an interface unless the super-user has enabled promiscuous-mode
  operation on that interface using
  .IR pfconfig (8),
  and no user (not even the super-user) can capture unicast traffic
  received by or sent by the machine on an interface unless the super-user
  has enabled copy-all-mode operation on that interface using
  .IR pfconfig ,
  so
  .I useful
  packet capture on an interface probably requires that either
  promiscuous-mode or copy-all-mode operation, or both modes of
  operation, be enabled on that interface.
  .TP
  .B Under BSD (this includes macOS):
  You must have read access to
  .I /dev/bpf*
  on systems that don't have a cloning BPF device, or to
  .I /dev/bpf
  on systems that do.
  On BSDs with a devfs (this includes macOS), this might involve more
  than just having somebody with super-user access setting the ownership
  or permissions on the BPF devices - it might involve configuring devfs
  to set the ownership or permissions every time the system is booted,
  if the system even supports that; if it doesn't support that, you might
  have to find some other way to make that happen at boot time.
  .PP
  Reading a saved packet file doesn't require special privileges.
  .PP
  The packets read from the handle may include a ``pseudo-header''
  containing various forms of packet meta-data, and probably includes a
  link-layer header whose contents can differ for different network
  interfaces.  To determine the format of the packets supplied by the
  handle, call
  .BR pcap_datalink ();
  .I https://www.tcpdump.org/linktypes.html
  lists the values it returns and describes the packet formats that
  correspond to those values.
  .PP
  Do
  .B NOT
  assume that the packets for a given capture or ``savefile`` will have
  any given link-layer header type, such as
  .B DLT_EN10MB
  for Ethernet.  For example, the "any" device on Linux will have a
  link-layer header type of
  .B DLT_LINUX_SLL
  even if all devices on the system at the time the "any" device is opened
  have some other data link type, such as
  .B DLT_EN10MB
  for Ethernet.
  .PP
  To obtain the
  .B "FILE\ *"
  corresponding to a
  .B pcap_t
  opened for a ``savefile'', call
  .BR pcap_file ().
  .TP
  .B Routines
  .RS
  .TP
  .BR pcap_create (3PCAP)
  get a
  .B pcap_t
  for live capture
  .TP
  .BR pcap_activate (3PCAP)
  activate a
  .B pcap_t
  for live capture
  .TP
  .BR pcap_findalldevs (3PCAP)
  get a list of devices that can be opened for a live capture
  .TP
  .BR pcap_freealldevs (3PCAP)
  free list of devices
  .TP
  .BR pcap_lookupdev (3PCAP)
  get first non-loopback device on that list
  .TP
  .BR pcap_open_offline (3PCAP)
  open a
  .B pcap_t
  for a ``savefile'', given a pathname
  .TP
  .BR pcap_open_offline_with_tstamp_precision (3PCAP)
  open a
  .B pcap_t
  for a ``savefile'', given a pathname, and specify the precision to
  provide for packet time stamps
  .TP
  .BR pcap_fopen_offline (3PCAP)
  open a
  .B pcap_t
  for a ``savefile'', given a
  .B "FILE\ *"
  .TP
  .BR pcap_fopen_offline_with_tstamp_precision (3PCAP)
  open a
  .B pcap_t
  for a ``savefile'', given a
  .BR "FILE\ *" ,
  and specify the precision to provide for packet time stamps
  .TP
  .BR pcap_open_dead (3PCAP)
  create a ``fake''
  .B pcap_t
  .TP
  .BR pcap_close (3PCAP)
  close a
  .B pcap_t
  .TP
  .BR pcap_set_snaplen (3PCAP)
  set the snapshot length for a not-yet-activated
  .B pcap_t
  for live capture
  .TP
  .BR pcap_snapshot (3PCAP)
  get the snapshot length for a
  .B pcap_t
  .TP
  .BR pcap_set_promisc (3PCAP)
  set promiscuous mode for a not-yet-activated
  .B pcap_t
  for live capture
  .TP
  .BR pcap_set_protocol_linux (3PCAP)
  set capture protocol for a not-yet-activated
  .B pcap_t
  for live capture (Linux only)
  .TP
  .BR pcap_set_rfmon (3PCAP)
  set monitor mode for a not-yet-activated
  .B pcap_t
  for live capture
  .TP
  .BR pcap_can_set_rfmon (3PCAP)
  determine whether monitor mode can be set for a
  .B pcap_t
  for live capture
  .TP
  .BR pcap_set_timeout (3PCAP)
  set packet buffer timeout for a not-yet-activated
  .B pcap_t
  for live capture
  .TP
  .BR pcap_set_buffer_size (3PCAP)
  set buffer size for a not-yet-activated
  .B pcap_t
  for live capture
  .TP
  .BR pcap_set_tstamp_type (3PCAP)
  set time stamp type for a not-yet-activated
  .B pcap_t
  for live capture
  .TP
  .BR pcap_list_tstamp_types (3PCAP)
  get list of available time stamp types for a not-yet-activated
  .B pcap_t
  for live capture
  .TP
  .BR pcap_free_tstamp_types (3PCAP)
  free list of available time stamp types
  .TP
  .BR pcap_tstamp_type_val_to_name (3PCAP)
  get name for a time stamp type
  .TP
  .BR pcap_tstamp_type_val_to_description (3PCAP)
  get description for a time stamp type
  .TP
  .BR pcap_tstamp_type_name_to_val (3PCAP)
  get time stamp type corresponding to a name
  .TP
  .BR pcap_set_tstamp_precision (3PCAP)
  set time stamp precision for a not-yet-activated
  .B pcap_t
  for live capture
  .TP
  .BR pcap_get_tstamp_precision (3PCAP)
  get the time stamp precision of a
  .B pcap_t
  for live capture
  .TP
  .BR pcap_datalink (3PCAP)
  get link-layer header type for a
  .B pcap_t
  .TP
  .BR pcap_file (3PCAP)
  get the
  .B "FILE\ *"
  for a
  .B pcap_t
  opened for a ``savefile''
  .TP
  .BR pcap_is_swapped (3PCAP)
  determine whether a ``savefile'' being read came from a machine with the
  opposite byte order
  .TP
  .BR pcap_major_version (3PCAP)
  .PD 0
  .TP
  .BR pcap_minor_version (3PCAP)
  get the major and minor version of the file format version for a
  ``savefile''
  .PD
  .RE
  .SS Selecting a link-layer header type for a live capture
  Some devices may provide more than one link-layer header type.  To
  obtain a list of all link-layer header types provided by a device, call
  .BR pcap_list_datalinks ()
  on an activated
  .B pcap_t
  for the device.
  To free a list of link-layer header types, call
  .BR pcap_free_datalinks ().
  To set the link-layer header type for a device, call
  .BR pcap_set_datalink ().
  This should be done after the device has been activated but before any
  packets are read and before any filters are compiled or installed.
  .TP
  .B Routines
  .RS
  .TP
  .BR pcap_list_datalinks (3PCAP)
  get a list of link-layer header types for a device
  .TP
  .BR pcap_free_datalinks (3PCAP)
  free list of link-layer header types
  .TP
  .BR pcap_set_datalink (3PCAP)
  set link-layer header type for a device
  .TP
  .BR pcap_datalink_val_to_name (3PCAP)
  get name for a link-layer header type
  .TP
  .BR pcap_datalink_val_to_description (3PCAP)
  get description for a link-layer header type
  .TP
  .BR pcap_datalink_name_to_val (3PCAP)
  get link-layer header type corresponding to a name
  .RE
  .SS Reading packets
  Packets are read with
  .BR pcap_dispatch ()
  or
  .BR pcap_loop (),
  which process one or more packets, calling a callback routine for each
  packet, or with
  .BR pcap_next ()
  or
  .BR pcap_next_ex (),
  which return the next packet.
  The callback for
  .BR pcap_dispatch ()
  and
  .BR pcap_loop ()
  is supplied a pointer to a
  .IR "struct pcap_pkthdr" ,
  which includes the following members:
  .RS
  .TP
  .B ts
  a
  .I struct timeval
  containing the time when the packet was captured
  .TP
  .B caplen
  a
  .I bpf_u_int32
  giving the number of bytes of the packet that are available from the
  capture
  .TP
  .B len
  a
  .I bpf_u_int32
  giving the length of the packet, in bytes (which might be more than the
  number of bytes available from the capture, if the length of the packet
  is larger than the maximum number of bytes to capture).
  .RE
  .PP
  The callback is also supplied a
  .I const u_char
  pointer to the first
  .B caplen
  (as given in the
  .I struct pcap_pkthdr
  mentioned above)
  bytes of data from the packet.  This won't necessarily be the entire
  packet; to capture the entire packet, you will have to provide a value
  for
  .I snaplen
  in your call to
  .BR pcap_set_snaplen ()
  that is sufficiently large to get all of the packet's data - a value of
  65535 should be sufficient on most if not all networks).  When reading
  from a ``savefile'', the snapshot length specified when the capture was
  performed will limit the amount of packet data available.
  .PP
  .BR pcap_next ()
  is passed an argument that points to a
  .I struct pcap_pkthdr
  structure, and fills it in with the time stamp and length values for the
  packet.  It returns a
  .I const u_char
  to the first
  .B caplen
  bytes of the packet on success, and NULL on error.
  .PP
  .BR pcap_next_ex ()
  is passed two pointer arguments, one of which points to a
  .IR struct pcap_pkthdr *
  and one of which points to a
  .IR "const u_char" *.
  It sets the first pointer to point to a
  .I struct pcap_pkthdr
  structure with the time stamp and length values for the packet, and sets
  the second pointer to point to the first
  .B caplen
  bytes of the packet.
  .PP
  To force the loop in
  .BR pcap_dispatch ()
  or
  .BR pcap_loop ()
  to terminate, call
  .BR pcap_breakloop ().
  .PP
  By default, when reading packets from an interface opened for a live
  capture,
  .BR pcap_dispatch (),
  .BR pcap_next (),
  and
  .BR pcap_next_ex ()
  will, if no packets are currently available to be read, block waiting
  for packets to become available.  On some, but
  .I not
  all, platforms, if a packet buffer timeout was specified, the wait will
  terminate after the packet buffer timeout expires; applications should
  be prepared for this, as it happens on some platforms, but should not
  rely on it, as it does not happen on other platforms.  Note that the
  wait might, or might not, terminate even if no packets are available;
  applications should be prepared for this to happen, but must not rely on
  it happening.
  .PP
  A handle can be put into ``non-blocking mode'', so that those routines
  will, rather than blocking, return an indication that no packets are
  available to read.  Call
  .BR pcap_setnonblock ()
  to put a handle into non-blocking mode or to take it out of non-blocking
  mode; call
  .BR pcap_getnonblock ()
  to determine whether a handle is in non-blocking mode.  Note that
  non-blocking mode does not work correctly in Mac OS X 10.6.
  .PP
  Non-blocking mode is often combined with routines such as
  .BR select (2)
  or
  .BR poll (2)
  or other routines a platform offers to wait for any of a set of
  descriptors to be ready to read.  To obtain, for a handle, a descriptor
  that can be used in those routines, call
  .BR pcap_get_selectable_fd ().
  Not all handles have such a descriptor available;
  .BR pcap_get_selectable_fd ()
  will return \-1 if no such descriptor exists.  In addition, for various
  reasons, one or more of those routines will not work properly with the
  descriptor; the documentation for
  .BR pcap_get_selectable_fd ()
  gives details.  Note that, just as an attempt to read packets from a
  .B pcap_t
  may not return any packets if the packet buffer timeout expires, a
  .BR select (),
  .BR poll (),
  or other such call may, if the packet buffer timeout expires, indicate
  that a descriptor is ready to read even if there are no packets
  available to read.
  .TP
  .B Routines
  .RS
  .TP
  .BR pcap_dispatch (3PCAP)
  read a bufferful of packets from a
  .B pcap_t
  open for a live capture or the full set of packets from a
  .B pcap_t
  open for a ``savefile''
  .TP
  .BR pcap_loop (3PCAP)
  read packets from a
  .B pcap_t
  until an interrupt or error occurs
  .TP
  .BR pcap_next (3PCAP)
  read the next packet from a
  .B pcap_t
  without an indication whether an error occurred
  .TP
  .BR pcap_next_ex (3PCAP)
  read the next packet from a
  .B pcap_t
  with an error indication on an error
  .TP
  .BR pcap_breakloop (3PCAP)
  prematurely terminate the loop in
  .BR pcap_dispatch ()
  or
  .BR pcap_loop ()
  .TP
  .BR pcap_setnonblock (3PCAP)
  set or clear non-blocking mode on a
  .B pcap_t
  .TP
  .BR pcap_getnonblock (3PCAP)
  get the state of non-blocking mode for a
  .B pcap_t
  .TP
  .BR pcap_get_selectable_fd (3PCAP)
  attempt to get a descriptor for a
  .B pcap_t
  that can be used in calls such as
  .BR select (2)
  and
  .BR poll (2)
  .RE
  .SS Filters
  In order to cause only certain packets to be returned when reading
  packets, a filter can be set on a handle.  For a live capture, the
  filtering will be performed in kernel mode, if possible, to avoid
  copying ``uninteresting'' packets from the kernel to user mode.
  .PP
  A filter can be specified as a text string; the syntax and semantics of
  the string are as described by
  .BR pcap-filter (@MAN_MISC_INFO@).
  A filter string is compiled into a program in a pseudo-machine-language
  by
  .BR pcap_compile ()
  and the resulting program can be made a filter for a handle with
  .BR pcap_setfilter ().
  The result of
  .BR pcap_compile ()
  can be freed with a call to
  .BR pcap_freecode ().
  .BR pcap_compile ()
  may require a network mask for certain expressions in the filter string;
  .BR pcap_lookupnet ()
  can be used to find the network address and network mask for a given
  capture device.
  .PP
  A compiled filter can also be applied directly to a packet that has been
  read using
  .BR pcap_offline_filter ().
  .TP
  .B Routines
  .RS
  .TP
  .BR pcap_compile (3PCAP)
  compile filter expression to a pseudo-machine-language code program
  .TP
  .BR pcap_freecode (3PCAP)
  free a filter program
  .TP
  .BR pcap_setfilter (3PCAP)
  set filter for a
  .B pcap_t
  .TP
  .BR pcap_lookupnet (3PCAP)
  get network address and network mask for a capture device
  .TP
  .BR pcap_offline_filter (3PCAP)
  apply a filter program to a packet
  .RE
  .SS Incoming and outgoing packets
  By default, libpcap will attempt to capture both packets sent by the
  machine and packets received by the machine.  To limit it to capturing
  only packets received by the machine or, if possible, only packets sent
  by the machine, call
  .BR pcap_setdirection ().
  .TP
  .BR Routines
  .RS
  .TP
  .BR pcap_setdirection (3PCAP)
  specify whether to capture incoming packets, outgoing packets, or both
  .RE
  .SS Capture statistics
  To get statistics about packets received and dropped in a live capture,
  call
  .BR pcap_stats ().
  .TP
  .B Routines
  .RS
  .TP
  .BR pcap_stats (3PCAP)
  get capture statistics
  .RE
  .SS Opening a handle for writing captured packets
  To open a ``savefile`` to which to write packets, given the pathname the
  ``savefile'' should have, call
  .BR pcap_dump_open ().
  To open a ``savefile`` to which to write packets, given the pathname the
  ``savefile'' should have, call
  .BR pcap_dump_open ();
  to set up a handle for a ``savefile'', given a
  .B "FILE\ *"
  referring to a file already opened for writing, call
  .BR pcap_dump_fopen ().
  They each return pointers to a
  .BR pcap_dumper_t ,
  which is the handle used for writing packets to the ``savefile''.  If it
  succeeds, it will have created the file if it doesn't exist and
  truncated the file if it does exist.
  To close a
  .BR pcap_dumper_t ,
  call
  .BR pcap_dump_close ().
  .TP
  .B Routines
  .RS
  .TP
  .BR pcap_dump_open (3PCAP)
  open a
  .B pcap_dumper_t
  for a ``savefile``, given a pathname
  .TP
  .BR pcap_dump_fopen (3PCAP)
  open a
  .B pcap_dumper_t
  for a ``savefile``, given a
  .B "FILE\ *"
  .TP
  .BR pcap_dump_close (3PCAP)
  close a
  .B pcap_dumper_t
  .TP
  .BR pcap_dump_file (3PCAP)
  get the
  .B "FILE\ *"
  for a
  .B pcap_dumper_t
  opened for a ``savefile''
  .RE
  .SS Writing packets
  To write a packet to a
  .BR pcap_dumper_t ,
  call
  .BR pcap_dump ().
  Packets written with
  .BR pcap_dump ()
  may be buffered, rather than being immediately written to the
  ``savefile''.  Closing the
  .B pcap_dumper_t
  will cause all buffered-but-not-yet-written packets to be written to the
  ``savefile''.
  To force all packets written to the
  .BR pcap_dumper_t ,
  and not yet written to the ``savefile'' because they're buffered by the
  .BR pcap_dumper_t ,
  to be written to the ``savefile'', without closing the
  .BR pcap_dumper_t ,
  call
  .BR pcap_dump_flush ().
  .TP
  .B Routines
  .RS
  .TP
  .BR pcap_dump (3PCAP)
  write packet to a
  .B pcap_dumper_t
  .TP
  .BR pcap_dump_flush (3PCAP)
  flush buffered packets written to a
  .B pcap_dumper_t
  to the ``savefile''
  .TP
  .BR pcap_dump_ftell (3PCAP)
  get current file position for a
  .B pcap_dumper_t
  .RE
  .SS Injecting packets
  If you have the required privileges, you can inject packets onto a
  network with a
  .B pcap_t
  for a live capture, using
  .BR pcap_inject ()
  or
  .BR pcap_sendpacket ().
  (The two routines exist for compatibility with both OpenBSD and WinPcap;
  they perform the same function, but have different return values.)
  .TP
  .B Routines
  .RS
  .TP
  .BR pcap_inject (3PCAP)
  .PD 0
  .TP
  .BR pcap_sendpacket (3PCAP)
  transmit a packet
  .PD
  .RE
  .SS Reporting errors
  Some routines return error or warning status codes; to convert them to a
  string, use
  .BR pcap_statustostr ().
  .TP
  .B Routines
  .RS
  .TP
  .BR pcap_statustostr (3PCAP)
  get a string for an error or warning status code
  .RE
  .SS Getting library version information
  To get a string giving version information about libpcap, call
  .BR pcap_lib_version ().
  .TP
  .B Routines
  .RS
  .TP
  .BR pcap_lib_version (3PCAP)
  get library version string
  .RE
  .SH BACKWARDS COMPATIBILITY
  .PP
  In versions of libpcap prior to 1.0, the
  .B pcap.h
  header file was not in a
  .B pcap
  directory on most platforms; if you are writing an application that must
  work on versions of libpcap prior to 1.0, include
  .BR <pcap.h> ,
  which will include
  .B <pcap/pcap.h>
  for you, rather than including
  .BR <pcap/pcap.h> .
  .PP
  .BR pcap_create ()
  and
  .BR pcap_activate ()
  were not available in versions of libpcap prior to 1.0; if you are
  writing an application that must work on versions of libpcap prior to
  1.0, either use
  .BR pcap_open_live ()
  to get a handle for a live capture or, if you want to be able to use the
  additional capabilities offered by using
  .BR pcap_create ()
  and
  .BR pcap_activate (),
  use an
  .BR autoconf (1)
  script or some other configuration script to check whether the libpcap
  1.0 APIs are available and use them only if they are.
  .SH SEE ALSO
  autoconf(1), tcpdump(1), tcpslice(1), pcap-filter(@MAN_MISC_INFO@), pfconfig(8),
  usermod(@MAN_ADMIN_COMMANDS@)
  .SH AUTHORS
  The original authors of libpcap are:
  .LP
  Van Jacobson,
  Craig Leres and
  Steven McCanne, all of the
  Lawrence Berkeley National Laboratory, University of California, Berkeley, CA.
  .LP
  The current version is available from "The Tcpdump Group"'s Web site at
  .LP
  .RS
  .I https://www.tcpdump.org/
  .RE
  .SH BUGS
  To report a security issue please send an e-mail to security@tcpdump.org.
  .LP
  To report bugs and other problems, contribute patches, request a
  feature, provide generic feedback etc please see the file
  .I CONTRIBUTING
  in the libpcap source tree root.