LIBMAGIC(3) Introduction to Library Functions LIBMAGIC(3)

NAME

magic_open, magic_close, magic_error, magic_errno, magic_descriptor,
magic_buffer, magic_getflags, magic_setflags, magic_check,
magic_compile, magic_list, magic_load, magic_load_buffers,
magic_setparam, magic_getparam, magic_version - Magic number
recognition library

LIBRARY

library "libmagic"

SYNOPSIS

#include <magic.h>

magic_t
magic_open(int flags);

void
magic_close(magic_t cookie);

const char *
magic_error(magic_t cookie);

int
magic_errno(magic_t cookie);

const char *
magic_descriptor(magic_t cookie, int fd);

const char *
magic_file(magic_t cookie, const char *filename);

const char *
magic_buffer(magic_t cookie, const void *buffer, size_t length);

int
magic_getflags(magic_t cookie);

int
magic_setflags(magic_t cookie, int flags);

int
magic_check(magic_t cookie, const char *filename);

int
magic_compile(magic_t cookie, const char *filename);

int
magic_list(magic_t cookie, const char *filename);

int
magic_load(magic_t cookie, const char *filename);

int
magic_load_buffers(magic_t cookie, void **buffers, size_t *sizes,
size_t nbuffers);

int
magic_getparam(magic_t cookie, int param, void *value);

int
magic_setparam(magic_t cookie, int param, const void *value);

int
magic_version(void);

const char *
magic_getpath(const char *magicfile, int action);

DESCRIPTION

These functions operate on the magic database file which is described
in magic(4).

The function magic_open() creates a magic cookie pointer and returns
it. It returns NULL if there was an error allocating the magic cookie.
The flags argument specifies how the other magic functions should
behave:

MAGIC_NONE No special handling.

MAGIC_DEBUG Print debugging messages to stderr.

MAGIC_SYMLINK If the file queried is a symlink, follow it.

MAGIC_COMPRESS If the file is compressed, unpack it and look at the
contents.

MAGIC_DEVICES If the file is a block or character special device,
then open the device and try to look in its contents.

MAGIC_MIME_TYPE
Return a MIME type string, instead of a textual
description.

MAGIC_MIME_ENCODING
Return a MIME encoding, instead of a textual
description.

MAGIC_MIME A shorthand for MAGIC_MIME_TYPE | MAGIC_MIME_ENCODING.

MAGIC_CONTINUE Return all matches, not just the first.

MAGIC_CHECK Check the magic database for consistency and print
warnings to stderr.

MAGIC_PRESERVE_ATIME
On systems that support utime(3) or utimes(2), attempt
to preserve the access time of files analysed.

MAGIC_RAW Don't translate unprintable characters to a \ooo octal
representation.

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.

MAGIC_APPLE Return the Apple creator and type.

MAGIC_EXTENSION
Return a slash-separated list of extensions for this
file type.

MAGIC_COMPRESS_TRANSP
Don't report on compression, only report about the
uncompressed data.

MAGIC_NO_CHECK_APPTYPE
Don't check for EMX application type (only on EMX).

MAGIC_NO_COMPRESS_FORK
Don't allow decompressors that use fork.

MAGIC_NO_CHECK_CDF
Don't get extra information on MS Composite Document
Files.

MAGIC_NO_CHECK_COMPRESS
Don't look inside compressed files.

MAGIC_NO_CHECK_ELF
Don't print ELF details.

MAGIC_NO_CHECK_ENCODING
Don't check text encodings.

MAGIC_NO_CHECK_SOFT
Don't consult magic files.

MAGIC_NO_CHECK_TAR
Don't examine tar files.

MAGIC_NO_CHECK_TEXT
Don't check for various types of text files.

MAGIC_NO_CHECK_TOKENS
Don't look for known tokens inside ascii files.

MAGIC_NO_CHECK_JSON
Don't examine JSON files.

MAGIC_NO_CHECK_CSV
Don't examine CSV files.

MAGIC_NO_CHECK_SIMH
Don't examine SIMH tape files.

The magic_close() function closes the magic(4) database and deallocates
any resources used.

The magic_error() function returns a textual explanation of the last
error, or NULL if there was no error.

The magic_errno() function returns the last operating system error
number (errno(2)) that was encountered by a system call.

The magic_file() function returns a textual description of the contents
of the filename argument, or NULL if an error occurred. If the
filename is NULL, then stdin is used.

The magic_descriptor() function returns a textual description of the
contents of the fd argument, or NULL if an error occurred.

The magic_buffer() function returns a textual description of the
contents of the buffer argument with length bytes size.

The magic_getflags() functions returns a value representing current
flags set.

The magic_setflags() function sets the flags described above. Note
that using both MIME flags together can also return extra information
on the charset.

The magic_check() function can be used to check the validity of entries
in the colon separated database files passed in as filename, or NULL
for the default database. It returns 0 on success and -1 on failure.

The magic_compile() function can be used to compile the colon separated
list of database files passed in as filename, or NULL for the default
database. It returns 0 on success and -1 on failure. The compiled
files created are named from the basename(1) of each file argument with
".mgc" appended to it.

The 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
filename argument which is a colon separated list of database files, or
NULL for the default database.

The magic_load() function must be used to load the colon separated list
of database files passed in as filename, or NULL for the default
database file before any magic queries can performed.

The default database file is named by the MAGIC environment variable.
If that variable is not set, the default database file name is
/usr/share/misc/magic. magic_load() adds ".mgc" to the database
filename as appropriate.

The magic_load_buffers() function takes an array of size nbuffers of
buffers with a respective size for each in the array of 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.

The magic_getparam() and magic_setparam() allow getting and setting
various limits related to the magic library.

Parameter Type Default
MAGIC_PARAM_INDIR_MAX size_t 15
MAGIC_PARAM_NAME_MAX size_t 30
MAGIC_PARAM_ELF_NOTES_MAX size_t 256
MAGIC_PARAM_ELF_PHNUM_MAX size_t 128
MAGIC_PARAM_ELF_SHNUM_MAX size_t 32768
MAGIC_PARAM_REGEX_MAX size_t 8192
MAGIC_PARAM_BYTES_MAX size_t 1048576

The MAGIC_PARAM_INDIR_RECURSION parameter controls how many levels of
recursion will be followed for indirect magic entries.

The MAGIC_PARAM_NAME_RECURSION parameter controls how many levels of
recursion will be followed for for name/use calls.

The MAGIC_PARAM_NAME_MAX parameter controls the maximum number of calls
for name/use.

The MAGIC_PARAM_NOTES_MAX parameter controls how many ELF notes will be
processed.

The MAGIC_PARAM_PHNUM_MAX parameter controls how many ELF program
sections will be processed.

The MAGIC_PARAM_SHNUM_MAX parameter controls how many ELF sections will
be processed.

The magic_version() command returns the version number of this library
which is compiled into the shared library using the constant
MAGIC_VERSION from <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.

The magic_getpath() command returns the colon separated list of magic
database locations. If the filename is non-NULL, then it is returned.
Otherwise, if the MAGIC environment variable is defined, then it is
returned. Otherwise, if 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.

RETURN VALUES

The function magic_open() returns a magic cookie on success and NULL on
failure setting errno to an appropriate value. It will set errno to
EINVAL if an unsupported value for flags was given. The magic_list(),
magic_load(), magic_compile(), and magic_check() functions return 0 on
success and -1 on failure. The magic_buffer(), magic_getpath(), and
magic_file(), functions return a string on success and NULL on failure.
The magic_error() function returns a textual description of the errors
of the above functions, or NULL if there was no error. The
magic_version() always returns the version number of the library.
Finally, magic_setflags() returns -1 on systems that don't support
utime(3), or utimes(2) when MAGIC_PRESERVE_ATIME is set.

FILES

/usr/share/misc/magic The non-compiled default magic database.
/usr/share/misc/magic.mgc The compiled default magic database.

SEE ALSO

file(1), magic(4)

BUGS

The results from magic_buffer() and magic_file() where the buffer and
the file contain the same data can produce different results, because
in the magic_file() case, the program can lseek(2) and stat(2) the file
descriptor.

AUTHORS

Moans Rullgoard Initial libmagic implementation, and configuration.
Christos Zoulas API cleanup, error code and allocation handling.

illumos June 16, 2023 illumos