file/doc/libmagic.man

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.Dd June 16, 2023
.Dt LIBMAGIC 3
.Os
.Sh NAME
.Nm magic_open ,
.Nm magic_close ,
.Nm magic_error ,
.Nm magic_errno ,
.Nm magic_descriptor ,
.Nm magic_buffer ,
.Nm magic_getflags ,
.Nm magic_setflags ,
.Nm magic_check ,
.Nm magic_compile ,
.Nm magic_list ,
.Nm magic_load ,
.Nm magic_load_buffers ,
.Nm magic_setparam ,
.Nm magic_getparam ,
.Nm magic_version
.Nd Magic number recognition library
.Sh LIBRARY
.Lb libmagic
.Sh SYNOPSIS
.In magic.h
.Ft magic_t
.Fn magic_open "int flags"
.Ft void
.Fn magic_close "magic_t cookie"
.Ft const char *
.Fn magic_error "magic_t cookie"
.Ft int
.Fn magic_errno "magic_t cookie"
.Ft const char *
.Fn magic_descriptor "magic_t cookie" "int fd"
.Ft const char *
.Fn magic_file "magic_t cookie" "const char *filename"
.Ft const char *
.Fn magic_buffer "magic_t cookie" "const void *buffer" "size_t length"
.Ft int
.Fn magic_getflags "magic_t cookie"
.Ft int
.Fn magic_setflags "magic_t cookie" "int flags"
.Ft int
.Fn magic_check "magic_t cookie" "const char *filename"
.Ft int
.Fn magic_compile "magic_t cookie" "const char *filename"
.Ft int
.Fn magic_list "magic_t cookie" "const char *filename"
.Ft int
.Fn magic_load "magic_t cookie" "const char *filename"
.Ft int
.Fn magic_load_buffers "magic_t cookie" "void **buffers" "size_t *sizes" "size_t nbuffers"
.Ft int
.Fn magic_getparam "magic_t cookie" "int param" "void *value"
.Ft int
.Fn magic_setparam "magic_t cookie" "int param" "const void *value"
.Ft int
.Fn magic_version "void"
.Ft const char *
.Fn magic_getpath "const char *magicfile" "int action"
.Sh DESCRIPTION
These functions
operate on the magic database file
which is described
in
.Xr magic __FSECTION__ .
.Pp
The function
.Fn magic_open
creates a magic cookie pointer and returns it.
It returns
.Dv NULL
if there was an error allocating the magic cookie.
The
.Ar flags
argument specifies how the other magic functions should behave:
.Bl -tag -width MAGIC_COMPRESS
.It Dv MAGIC_NONE
No special handling.
.It Dv MAGIC_DEBUG
Print debugging messages to stderr.
.It Dv MAGIC_SYMLINK
If the file queried is a symlink, follow it.
.It Dv MAGIC_COMPRESS
If the file is compressed, unpack it and look at the contents.
.It Dv MAGIC_DEVICES
If the file is a block or character special device, then open the device
and try to look in its contents.
.It Dv MAGIC_MIME_TYPE
Return a MIME type string, instead of a textual description.
.It Dv MAGIC_MIME_ENCODING
Return a MIME encoding, instead of a textual description.
.It Dv MAGIC_MIME
A shorthand for MAGIC_MIME_TYPE | MAGIC_MIME_ENCODING.
.It Dv MAGIC_CONTINUE
Return all matches, not just the first.
.It Dv MAGIC_CHECK
Check the magic database for consistency and print warnings to stderr.
.It Dv MAGIC_PRESERVE_ATIME
On systems that support
.Xr utime 3
or
.Xr utimes 2 ,
attempt to preserve the access time of files analysed.
.It Dv MAGIC_RAW
Don't translate unprintable characters to a \eooo octal representation.
.It Dv MAGIC_ERROR
Treat operating system errors while trying to open files and follow symlinks
as real errors, instead of printing them in the magic buffer.
.It Dv MAGIC_APPLE
Return the Apple creator and type.
.It Dv MAGIC_EXTENSION
Return a slash-separated list of extensions for this file type.
.It Dv MAGIC_COMPRESS_TRANSP
Don't report on compression, only report about the uncompressed data.
.It Dv MAGIC_NO_CHECK_APPTYPE
Don't check for
.Dv EMX
application type (only on EMX).
.It Dv MAGIC_NO_COMPRESS_FORK
Don't allow decompressors that use fork.
.It Dv MAGIC_NO_CHECK_CDF
Don't get extra information on MS Composite Document Files.
.It Dv MAGIC_NO_CHECK_COMPRESS
Don't look inside compressed files.
.It Dv MAGIC_NO_CHECK_ELF
Don't print ELF details.
.It Dv MAGIC_NO_CHECK_ENCODING
Don't check text encodings.
.It Dv MAGIC_NO_CHECK_SOFT
Don't consult magic files.
.It Dv MAGIC_NO_CHECK_TAR
Don't examine tar files.
.It Dv MAGIC_NO_CHECK_TEXT
Don't check for various types of text files.
.It Dv MAGIC_NO_CHECK_TOKENS
Don't look for known tokens inside ascii files.
.It Dv MAGIC_NO_CHECK_JSON
Don't examine JSON files.
.It Dv MAGIC_NO_CHECK_CSV
Don't examine CSV files.
.It Dv MAGIC_NO_CHECK_SIMH
Don't examine SIMH tape files.
.El
.Pp
The
.Fn magic_close
function closes the
.Xr magic __FSECTION__
database and deallocates any resources used.
.Pp
The
.Fn magic_error
function returns a textual explanation of the last error, or
.Dv NULL
if there was no error.
.Pp
The
.Fn magic_errno
function returns the last operating system error number
.Pq Xr errno 2
that was encountered by a system call.
.Pp
The
.Fn magic_file
function returns a textual description of the contents of the
.Ar filename
argument, or
.Dv NULL
if an error occurred.
If the
.Ar filename
is
.Dv NULL ,
then stdin is used.
.Pp
The
.Fn magic_descriptor
function returns a textual description of the contents of the
.Ar fd
argument, or
.Dv NULL
if an error occurred.
.Pp
The
.Fn magic_buffer
function returns a textual description of the contents of the
.Ar buffer
argument with
.Ar length
bytes size.
.Pp
The
.Fn magic_getflags
functions returns a value representing current
.Ar flags
set.
.Pp
The
.Fn magic_setflags
function sets the
.Ar flags
described above.
Note that using both MIME flags together can also
return extra information on the charset.
.Pp
The
.Fn magic_check
function can be used to check the validity of entries in the colon
separated database files passed in as
.Ar filename ,
or
.Dv NULL
for the default database.
It returns 0 on success and \-1 on failure.
.Pp
The
.Fn magic_compile
function can be used to compile the colon
separated list of database files passed in as
.Ar filename ,
or
.Dv NULL
for the default database.
It returns 0 on success and \-1 on failure.
The compiled files created are named from the
.Xr basename 1
of each file argument with
.Dq .mgc
appended to it.
.Pp
The
.Fn magic_list
function dumps all magic entries in a human readable format,
dumping first the entries that are matched against binary files and then the
ones that match text files.
It takes and optional
.Fa filename
argument which is a colon separated list of database files, or
.Dv NULL
for the default database.
.Pp
The
.Fn magic_load
function must be used to load the colon
separated list of database files passed in as
.Ar filename ,
or
.Dv NULL
for the default database file before any magic queries can performed.
.Pp
The default database file is named by the MAGIC environment variable.
If that variable is not set, the default database file name is __MAGIC__.
.Fn magic_load
adds
.Dq .mgc
to the database filename as appropriate.
.Pp
The
.Fn magic_load_buffers
function takes an array of size
.Fa nbuffers
of
.Fa buffers
with a respective size for each in the array of
.Fa sizes
loaded with the contents of the magic databases from the filesystem.
This function can be used in environment where the magic library does
not have direct access to the filesystem, but can access the magic
database via shared memory or other IPC means.
.Pp
The
.Fn magic_getparam
and
.Fn magic_setparam
allow getting and setting various limits related to the magic
library.
.Bl -column "MAGIC_PARAM_ELF_PHNUM_MAX" "size_t" "Default" -offset indent
.It Sy "Parameter" Ta Sy "Type" Ta Sy "Default"
.It Li MAGIC_PARAM_INDIR_MAX Ta size_t Ta 15
.It Li MAGIC_PARAM_NAME_MAX Ta size_t Ta 30
.It Li MAGIC_PARAM_ELF_NOTES_MAX Ta size_t Ta 256
.It Li MAGIC_PARAM_ELF_PHNUM_MAX Ta size_t Ta 128
.It Li MAGIC_PARAM_ELF_SHNUM_MAX Ta size_t Ta 32768
.It Li MAGIC_PARAM_REGEX_MAX Ta size_t Ta 8192
.It Li MAGIC_PARAM_BYTES_MAX Ta size_t Ta 1048576
.El
.Pp
The
.Dv MAGIC_PARAM_INDIR_RECURSION
parameter controls how many levels of recursion will be followed for
indirect magic entries.
.Pp
The
.Dv MAGIC_PARAM_NAME_RECURSION
parameter controls how many levels of recursion will be followed for
for name/use calls.
.Pp
The
.Dv MAGIC_PARAM_NAME_MAX
parameter controls the maximum number of calls for name/use.
.Pp
The
.Dv MAGIC_PARAM_NOTES_MAX
parameter controls how many ELF notes will be processed.
.Pp
The
.Dv MAGIC_PARAM_PHNUM_MAX
parameter controls how many ELF program sections will be processed.
.Pp
The
.Dv MAGIC_PARAM_SHNUM_MAX
parameter controls how many ELF sections will be processed.
.Pp
The
.Fn magic_version
command returns the version number of this library which is compiled into
the shared library using the constant
.Dv MAGIC_VERSION
from
.In magic.h .
This can be used by client programs to verify that the version they compile
against is the same as the version that they run against.
.Pp
The
.Fn magic_getpath
command returns the colon separated list of magic database locations.
If the
.Fa filename
is non-NULL, then it is returned.
Otherwise, if the
.Dv MAGIC
environment variable is defined, then it is returned.
Otherwise, if
.Fa action
is 0 (meaning "file load"), then any user-specific magic database file is included.
Otherwise, only the system default magic database path is included.
.Sh RETURN VALUES
The function
.Fn magic_open
returns a magic cookie on success and
.Dv NULL
on failure setting errno to an appropriate value.
It will set errno to
.Er EINVAL
if an unsupported value for flags was given.
The
.Fn magic_list ,
.Fn magic_load ,
.Fn magic_compile ,
and
.Fn magic_check
functions return 0 on success and \-1 on failure.
The
.Fn magic_buffer ,
.Fn magic_getpath ,
and
.Fn magic_file ,
functions return a string on success and
.Dv NULL
on failure.
The
.Fn magic_error
function returns a textual description of the errors of the above
functions, or
.Dv NULL
if there was no error.
The
.Fn magic_version
always returns the version number of the library.
Finally,
.Fn magic_setflags
returns \-1 on systems that don't support
.Xr utime 3 ,
or
.Xr utimes 2
when
.Dv MAGIC_PRESERVE_ATIME
is set.
.Sh FILES
.Bl -tag -width __MAGIC__.mgc -compact
.It Pa __MAGIC__
The non-compiled default magic database.
.It Pa __MAGIC__.mgc
The compiled default magic database.
.El
.Sh SEE ALSO
.Xr file __CSECTION__ ,
.Xr magic __FSECTION__
.Sh BUGS
The results from
.Fn magic_buffer
and
.Fn magic_file
where the buffer and the file contain the same data
can produce different results, because in the
.Fn magic_file
case, the program can
.Xr lseek 2
and
.Xr stat 2
the file descriptor.
.Sh AUTHORS
.An M\(oans Rullg\(oard
Initial libmagic implementation, and configuration.
.An Christos Zoulas
API cleanup, error code and allocation handling.