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This is a very quick and very dirty guide to adding support for new
capture file formats. If you see any errors or have any improvements,
submit patches - free software is a community effort....
To add the ability to read a new capture file format, you have to:
write an "open" routine that can read the beginning of the
capture file and figure out if it's in that format or not,
either by looking at a magic number at the beginning or by using
some form of heuristic to determine if it's a file of that type
(if the file format has a magic number, that's what should be
used);
write a "read" routine that can read a packet from the file and
supply the packet length, captured data length, time stamp, and
packet pseudo-header (if any) and data, and have the "open"
routine set the "subtype_read" member of the "wtap" structure
supplied to it to point to that routine;
write a "seek and read" routine that can seek to a specified
location in the file for a packet and supply the packet
pseudo-header (if any) and data, and have the "open" routine set
the "subtype_seek_read" member of the "wtap" structure to point
to that routine;
write a "close" routine, if necessary (if, for example, the
"open" routine allocates any memory), and set the
"subtype_close" member of the "wtap" structure to point to it,
otherwise leave it set to NULL;
add an entry for that file type in the "open_info_base[]" table
in "wiretap/file_access.c", giving a pointer to the "open" routine,
a name to use in file open dialogs, whether the file type uses a
magic number or a heuristic, and if it uses a heuristic, file
extensions for which the heuristic should be tried first. More
discriminating and faster heuristics should be put before less
accurate and slower heuristics;
add a registration routine passing a "file_type_subtype_info" struct
to wtap_register_file_type_subtypes(), giving a descriptive name, a
short name that's convenient to type on a command line (no blanks or
capital letters, please), common file extensions to open and save,
any block types supported, and pointers to the "can_write_encap" and
"dump_open" routines if writing that file is supported (see below),
otherwise just null pointers.
Wiretap applications typically first perform sequential reads through
the capture file and may later do "seek and read" for individual frames.
The "read" routine should set the variable data_offset to the byte
offset within the capture file from which the "seek and read" routine
will read. If the capture records consist of:
capture record header
pseudo-header (e.g., for ATM)
frame data
then data_offset should point to the pseudo-header. The first
sequential read pass will process and store the capture record header
data, but it will not store the pseudo-header. Note that the
seek_and_read routine should work with the "random_fh" file handle
of the passed in wtap struct, instead of the "fh" file handle used
in the normal read routine.
To add the ability to write a new capture file format, you have to:
add a "can_write_encap" routine that returns an indication of
whether a given packet encapsulation format is supported by the
new capture file format;
add a "dump_open" routine that starts writing a file (writing
headers, allocating data structures, etc.);
add a "dump" routine to write a packet to a file, and have the
"dump_open" routine set the "subtype_write" member of the
"wtap_dumper" structure passed to it to point to it;
add a "dump_close" routine, if necessary (if, for example, the
"dump_open" routine allocates any memory, or if some of the file
header can be written only after all the packets have been
written), and have the "dump_open" routine set the
"subtype_close" member of the "wtap_dumper" structure to point
to it;
put pointers to the "can_write_encap" and "dump_open" routines
in the "file_type_subtype_info" struct passed to
wtap_register_file_type_subtypes().
In the wiretap directory, add your source file to CMakelists.txt.
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